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Electrochemical polymerization of dicarboxylic acids—II. Oligomers and side products in the polymerization of adipic acid
Fur. Polvm. J. Vol. 20, No. 12, pp. 1199-1208, 1984
0014-3057~84 $3.00+(/.00 Copyright :~ 1984 Pergamon Press Ltd
Printed in Great Britain. All rights reserved
ELECTROCHEMICAL POLYMERIZATION OF DICARBOXYLIC ACIDS--II OLIGOMERS
AND
SIDE
PRODUCTS OF
IN
ADIPIC
THE
POLYMERIZATION
ACID
A. GOZLAN a n d A. Z1LKHA Department of Organic Chemistry, The Hebrew University of Jerusalem. Jerusalem 91904, Israel
(Received 13 April 1984) A b s t r a c t - - T h e electrochemical polymerization of adipic acid in methanol and in methanol pyridine ( 1 : 1) via the Kolbe reaction nHOOC(CH04COOH
2he
, n'(CH2)" 4 + 2nCO 2 + nH~
was investigated as regards the oligomeric and side products. GC MS, i.r. and N M R were used to identify the m a n y products. Gaseous and volatile c o m p o u n d s were identified as C 4 and C s hydrocarbons besides 7- and 6-valerolactones. The less volatile c o m p o u n d s were separated on silica gel columns to fractions, viz. that eluted by heptane which contained hydrocarbons, that eluted by benzene which contained ether and ester groups and that eluted by methanol which contained higher oligomeric products containing oxygen. Four types of hydrocarbons were formed, viz. n-alkanes, n-alkenes, x-alkenes (the place of the double bond is not known) and cycloalkanes. Saturated and unsaturated oligomeric mono- and di-carboxylic acids were also formed.
a variac to adjust the current strength. The polarity of the current was changed every 90 sec.
INTRODUCTION In p r e v i o u s w o r k [1] we h a v e s h o w n , d u r i n g s t u d y o f t h e e l e c t r o c h e m i c a l p o l y m e r i z a t i o n o f a d i p i c acid, that besides the formation of insoluble polymer, n HOOC(CH2)4COOH
E~. . . . . lyric oxidation
~ _[_(CH2)4_]_" + 2nCO2
t h e r e were o t h e r low m o l e c u l a r w e i g h t f r a c t i o n s f o r m e d in relatively h i g h yields. W e n o w r e p o r t o n the separation, identification and characterization of these products.
Determination ~[ carboxylic acids' hy methylation An aliquot portion of solution to be analysed was methylated by diazomethane generated by the addition of 60°~i aqueous K O H to "Diazald'" (N-methyl-N-nitroso-ptoluene sulphonamide) as described before [I]. GC was used to determine the methyl esters formed.
TLC T L C was carried out on precoated plastic sheets, (I.2 m m silica gel (polygram Sil N-HR/UV254: Macherey-Nogel, Germany).
EXPERIMENTAL
Column chromatography
Materials Adipic acid, triethylamine (BDH), methanol, pyridine (Mallinckrodt, analytical grade) and "Diazald" (Aldrich) were used.
Electrolysis cell The cell was equipped with a magnetic stirrer, a thermometer and a reflux condenser to the top of which were connected pre-weighed U-tubes containing drierite and ascarite to measure quantitatively the evolved CO 2. It had a double jacket for circulating a cooling liquid (acetone cooled to the required temperature). Two Pt electrodes (2 x 3 cm) soldered in glass tubes were inserted into the cell through a ground joint, and the distance between them was kept constant by Teflon bars. A chopped power supply, 300 V/3 A, with the possibility of reversing the polarity of the current every 10 sec up to 3 min was used.
Electrolysis of adipic acid The required a m o u n t of adipic acid was introduced into the electrolysis cell and dissolved in the required solvent. Triethylamine was added, and the current was passed using
A column packed with silica gel (Woelhm) was used to separate the oily fraction obtained in the electrolysis. The column was washed with 250 ml of each of methanol. benzene and heptane before use for the separation. The oil was dissolved in a small volume of benzene, passed through the column and eluted by heptane then benzene followed by methanol.
Gas chromatograph)' (GC) Gas chromatography was carried out either on a Packard 7400 or on a Packard-Becker 417 instrument. For the separation of~'- and 6-valerolactone, a glass G C column ]in was used containing 5°,0 butanediolsuccinate (BDS) on c.w./h.m.d.s. 60/80. The injector and detector (f.i.d.) temperatures were 2 4 0 . The starting column temperature was 80'; after 4rain, it was heated to 4'/min up to a final temperature of 2 0 0 . The N 2 flow was regulated at 20 ml/min. Biphenyl was used as an internal standard. For the separation of the C 4 hydrocarbon fraction, a stainless steel column of ~4india. packed with 40°~, cinnamaldehyde on c.p. 60/80 was used. The temperature of the column was 30 ~, and that of the injector and detector 50 .
1199
1200
A. GOZLANand A. ZILKHA
The C8hydrocarbon fraction was separated on a lin glass column packed with 20~ squalane on c.p. 60/80. The temperature of the column was programmed for 13 min at 60° and then was raised to 3°/min to 120°, the final temperature. The N 2 flow was 10 ml/min. The hydrocarbons in the heptane fraction were determined using either a column of BDS as described before for separation of ,/- and &-valerolactone or a column packed with 3~ SE 30 on c.w./h.m.d.s. 60/80 under the following conditions: starting column temperature 80°, rate of heating 4°/min, final temperature 270°, held there for 60 min.
benzene each were collected. The last was free from any material. The first two fractions were mixtures as seen from GC. They contained, as seen from i.r. and NMR, short or long hydrocarbon chains, to which were connected such groups as O
II
CH30 C - - , --O--CH3, --CH3, - - C H = C H 2 and
--CH=CH--.
They did not contain RESULTS AND DISCUSSION To determine the soluble low molecular weight products formed in the electrochemical polymerization of adipic acid, an experiment was carried out under the conditions previously developed [1] for the polymerization of adipic acid. The electrolysis was carried in methanol-pyridine (1:1) starting with 10 g adipic acid and using triethylamine (10Yo) as a base. To prevent coating of the electrodes with polymer, the polarity of the current was reversed every 90 sec. The reaction was stopped after 7 hr, before complete consumption of the adipic acid, because towards the end of the electrolysis the concentration of the acid is small allowing other materials such as methanol to be oxidized and give undesirable side products, not connected with the oxidation of adipic acid. The insoluble polymer (1 g) was separated and the filtrate was diluted with benzene, extracted with cold 5Yo KOH to remove unreacted adipic acid and acidic material. The benzene solution was evaporated after washing with 1~ HCI to yield 1.46 g of a yellow oil. Gas chromatography (GC) of this oil on a column packed with 3YooSE 30 at temperatures from 80 to 250 ° showed the presence of various products having different molecular weights. In order to separate the oil into various fractions, we carried out TLC experiments. With heptane as eluent, the oil separated, part of it moved to the front, and part of it remained at the starting point. Using benzene as eluent and using the same plate of TLC, a new material appeared which moved close to the front of the benzene. Material still remained at the starting point. Using methanol, all the material moved towards the front. The TLC experiment showed that the oil was composed of three groups of material, the first of which was eluted with heptane, the second with benzene and the third with methanol. These results were utilized to separate the oil on a column of silica gel. The amount of silica gel taken was 100 times that of the oil. It was eluted with heptane (5 x 50 ml) until no more material passed, followed by benzene (6 x 50 ml), and then the yellow material remaining in the column was fully eluted by methanol (5 x 50 ml). The fraction eluted by heptane was investigated by i.r. and NMR. The i.r. spectrum did not show the presence of functional groups and was similar to that of unsaturated hydrocarbons (absorption at 1640cm-t). The N M R spectrum showed the same results; besides the hydrocarbon chains, there were olefinic hydrogens of C H = C H and CH=CH2 groups. GC of this fraction (heating from 80 to 250 °) showed that it was composed of many compounds. In the elution with benzene, 6 fractions of 50 ml
COOH or - - C H ~ - - 0 - - C - -
II
0 Fractions 3-5 contained the same groups as before, as well as methylene ~- to ester groups. They did not contain carboxyl groups. GC showed peaks from fraction 3 but not from fractions 4-5, which presumably contained material of higher molecular weight. Fractions 4 and 5 were combined; their average molecular weight was 410, determined cryoscopically using CBr 4 [2]. By N M R it is difficult to give a structural formula, especially since the fractions are composed of a mixture of oligomers. Elemental analysis was: C, 69.82; H, 10.91; O, 19.27; N, 0.0Yoo,corresponding to an average formula C24H450 5. NOW if the oxygens belong to CH30 ether, CH3OCO ester and to --C--OIl O internal ester groups and we subtract the sum of these groups (C4H605) from the average formula, then the formula of the hydrocarbon chain will be C20H39 , i.e. approx. (CH2)20. Noting that adipic acid has 4CH 2 groups in the chain, the following tentative structural formula may be written, giving an idea of the sort of products formed. CH3OC "-[(CH2)4]~ 2 C--O--[(CH2)4]~3OCH3
II
11
O C The fraction eluted by methanol had the same functional groups found in the benzene fractions, as seen from i.r. and NMR. It also contained COOH groups, but it was difficult to identify the presence of C = C double bonds due to their low concentration. GC of the fraction using a column at 250 ° did not show the presence of any volatile material. Elemental analysis was: C, 66.41; H, 10.23; O, 22.5; N, 0.86Yo, corresponding to the formula C24HnsO6N0.3 . Note that the oxygen content in this fraction was higher than that in the benzene fraction meaning that the methanol fraction contained compounds having a shorter hydrocarbon chain with more functional groups. All these results indicate that the oily product obtained in the electrolysis is composed of a complex mixture of saturated and unsaturated hydrocarbons up to compounds (oligomers) having an increasing percentage of oxygen, due to ester and methoxy groups. In addition the oil contained nitrogen from participation of the pyridine or Et3N in the reaction. The oil consists of low molecular weight compounds, having a relatively low boiling point that pass out in
Polymerization of dicarboxylic acids II GC, and of higher oligomers having molecular weights above 400. These results indicate that the polymerization is much more complex than a Kolbe reaction. If we add the weight of the various products isolated from the reaction, namely 4.01 g (CO2; measured by being trapped in U-tubes containing Ascarite and Drierite as in microanalysis), 1.0 g (insoluble polymer), 1.46g (oil) and 1.5 (acidic material), we obtain 7.97 g which is less than the weight of adipic acid used (10 g) in the electrolysis. This means that volatile products are also formed and are lost in the work-up of the reaction mixture, where the solvents are evaporated at 6 0 in vacuo (25 mm Hg). To try to trap these products, we performed an experiment using 14.6 g adipic acid. At the end of the electrolysis, the insoluble polymer was filtered, and the filtrate was investigated by GC using a column containing 5% butane diol succinate (BDS). The temperature was raised from 80 to 200 ° . Two relatively strong peaks and several smaller peaks were obtained (Fig. 1). The two peaks were investigated by GC MS. The molecular peak obtained in the mass spectrum of the first peak was m/e 100 and, there were strong peaks at m/e 85 (M-15) and 56 (M-44) which are characteristic of ?-lactones; the product was identified as 7-valerolactone and verified by comparison with G C - M S spectrum of 7-valerolactone under the same conditions. The second peak in the GC had in its mass spectrum a molecular peak at role 100 and a base peak at m/e 42; it was identified as 6-valerolactone. The amounts of 7-valerolactone and 6-valerolactone obtained based on GC were 0.49 and 0.26 g respectively.
Besides these two lactones which are lost during the evaporation in vacuo, there must be other volatile products, since the balance of all the products isolated is still less than the starting weight of adipic acid. We considered the formation of C4 gaseous products, which can be formed if the adipic acid is decarboxylated from both ends during the electrolysis. To trap such products, the gases evolved during the electrolysis after passing through the reflux condenser were passed into a tube cooled in acetone-solid CO2 mixture. About 2 ml liquid were trapped at the end of the electrolysis. The solution was diluted by CCI 4 and investigated by NMR. The peaks obtained were at: 6 (ppm) (the numbers inside the brackets are the integration values): 5.7, 4.98, 4.88 (m, 42) ( - - C H i C H i ) : 5.28 ( m ) ( C H ~ C H ) ; 4.2 (s, 64); 3.5 (s, 190): 2.12 (q), 1.95 (d, integ, for both 52); 1.32 (t, 69); 0.88 (t, 6). From these peaks it is possible to conclude that the following groups are present: CH~---CH~, C H = C H , CH3CH=CH2, CH2=CH--CH2CH3, CH2CH3 and CH3OH. These volatile C4 compounds were separated by GC using a column packed with 40% cinnamaldehyde on c.p. 60/80 at a column temperature of 30. Five peaks were obtained (Fig. 2) and were analysed by GC-MS. From the mass spectra and by comparison with the literature, it was concluded that peak 1 (mol. peak 58, base peak 41) was n-butane and peak 4 was 1,3-butadiene (tool. peak
1
2 3
I
2
I 0
I 2
I 4
1201
[ 6
I 8
Retention
1 10
time
I 12
I 14
I 16
I 18
(min)
Fig. 1. GC separation of 7- (I) and 6- (2) valerolactone on 5% BDS.
I 0
I 2
4
Retention
i 6
8
time
1 10
(min)
Fig. 2. GC separation of C4 hydrocarbons on 40°, cinnamaldehyde at 30~. (1) n-Butane, (2) l-butene, (3) trans-2butene, (4) 1,3-butadiene, (5) cis-2-butene.
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A. GOZLANand A. ZILKHA
56, base peak 39). Peaks 2, 3, 5 all have a mol. peak of 56 and a base peak 41. From their mass spectrum, the N M R spectrum, retention time in GC, and the literature, it was concluded that peak 2 (which is the biggest) belongs to l-butene, and peaks 3 and 5 are trans-2-butene and cis-2-butene respectively. It seemed plausible that, after finding C4 hydrocarbons, there must be also higher oligomers such as C s compounds. To look for these hydrocarbons, the electrolysis solution after separation from the insoluble polymer was neutralized by conc. HCI to remove the pyridine and then analysed by GC on a column packed by 20~ squalane on c.p. 60/80 heated to 70 ° . Eight peaks were obtained and were analysed by GC MS. The structures were deduced by comparison with MS in the literature [3] as well as with authentic samples where available. Peak 1 was 1,7-octadiene (mol. peak at m/e 110) and peak 2 (mol. peak at role 112) was 1-octene. Peak 3 was a linear chain octene (tool. peak at m/e 112) but it was not possible from the data available to indicate the exact place of the C = C double bond, so it will be denoted as x-octene. Peak 4 (m/e 114) was n-octane. Peak 5 (m/e 114) had fragments at m/e = 82 (M-32) and 83 (M-31) besides peaks at m/e 59 and 31 indicating the presence of ions containing oxygen. Based on the literature [4] this compound is probably CH2=CHCHzCH2COOCH 3. Peak 6 had a weak tool. peak at 116, a base peak at m/e 74, in addition to peaks at m/e 85 (M-31), 59 (COOCH3) "+ and 87 (CH2CH2COOCH3) "+. Further, the pattern of the fragmentation of the hydrocarbon chain was that of a saturated one, and the product was identified as CH3(CH2)3COOCH 3. Peak 7 was 7-valerolactone. Peak 8 was obtained in small amount and was identified as cyclooctane (relatively strong mol. peak at m/e 112). To confirm the compositions of the side products and oligomers formed, we carried out another electrolysis of adipic acid (30 mmol) in methanol (30 ml) in the presence of triethylamine (3 mmol). The current strength was 1.3A, and its polarity was changed every 90 sec. The electrolysis solution, after removal of polymer, was analysed by GC for derivatives higher than the octenes by being passed over a column of 5% BDS. Besides, 7- and cS-valerolactone (the quantity of the former was double that of the latter), the solution contained C~2 hydrocarbons which were identified by G C - M S as 1-dodecene and x-dodecene (the place of the double bond is not known exactly) which comprised 80~ of the C~2 hydrocarbons, n-Dodecane and cyclododecane were also present. Two other peaks were identified as the methyl esters of two C9 acids, namely CH3(CHz)vCOOH
and
CHz~CH
(CH2)6COOH
(formed from dimerization of 2 molecules of adipic acid, one of which has undergone decarboxylation of its two COOH groups and the other of only one; Table 1).
Table 1. Valerolactones and other products obtained in the electrolytes of adipic acid in methanol* Product 1. 2. 3. 4. 5. 6. 7. 8.
(mmol)
n-Dodecane 1-Dodecene x-Dodecene Cyclododecane CH3(CH2)7COOMe CH2zCH(CHz)6COOMe 7-Valerolactone 6-Valerolactone
(0.03) (0.13) (0.18) (0.05) (0.08) (0.16) (I.87) (1.10)
*Adipic acid (30mmol) was electrolysed in methanol (30ml) in the presence of triethylamine (3 retool), current strength 1,3 A. The electrolysis solution was filtered from polymer and analysed for derivatives higher than the octenes by GC using a 5% BDS column. The compounds are given in the order of their appearance in GC.
methylated by diazomethane and the methyl esters were analysed by GC on two columns, 5~o BDS, which gives good separation between esters of saturated and unsaturated carboxylic acids having the same number of carbon atoms but is not suitable for the separation of high molecular weight products, and 3~o SE 30 which gives a good separation of the esters of acids having different molecular weights. The gas chromatogram of the separation on 5 ~ BDS is given in Fig. 3. Nine peaks were obtained and were analysed by GC-MS. Peak 1 had a molecular peak at m/e 172 and peaks at m/e (M-29), (M-31), (M-43), 87, 101, 115 and 74 which was the base peak belonging to the product of the MacLafferty rearrangement OH
I
[CH3--O--C=CH2] +• . The results, compared with those for an authentic sample, showed the product to be the methyl ester of n-octoic acid. Peak 2 had a molecular peak at m/e 170 and fragmentations at m/e (M-31), (M-32) and (M-74) typical of methyl esters of unsaturated carboxylic acids having the double bond after the fourth carbon atom. The base peak was the rearrangement peak at m/e 74. There were also peaks at m/e 41, 55, 59, 69, 87 and 10l. The indications are of a terminal double bond and this was further checked by carrying out an i.r. on all the solid acid mixtures, where only peaks for e-olefins (CH2=CH) were found. All these results indicate that the product is a methyl ester of
CH2=CH(CH2)6COOH. Peak 3 is a very large peak corresponding to dimethyl adipate [5]. It had the same retention time as an authentic sample. Peak 4 was identified as the methyl ester of C H 3 ( C H 2 ) l t COOH. Peak 5 showed fragmentations at m/e 226 (weak molecular peak), (M-31), (M-32), (M-74), 143 ([CH30 C (CH2)6] + ),
Analysis of carboxylic acidfraction The fraction extracted from the reaction mixture by 5~ KOH was acidified by conc. HC1, concentrated and extracted by ether (500 ml). The ether was dried and evaporated yielding 1.13 g solid yellowish material that was dissolved in THF. An aliquot was
LI
O 87, 74 (base peak from rearrangement), 59, 55 and 41 +
(CH2:CH--CH2). The indications are of a methyl ester of an un-
1203
Polymerization of dicarboxylic acids--lI
r"-~
3 6
2 9
I 10
I 20
I 30
Retention t i m e (min)
Fig. 3. GC separation on 5~o BDS of carboxylic acids from the electrolysis of adipic acid in methanol after conversion to the methyl esters. (1) CH3(CH2)TCOOMe, (2) CH2---CH(CH2)o--COOMe, (3) MeOCO(CH2)4COOMe, (4) CH3(CH2)uCOOMe, (5) CH~zCH(CH2)IoCOOMe, (6) MeOCO(CH2)sCOOMe, (7) CH3(CH2)Is--COOMe, (8) CH:=CH--(CH2)u--COOMe, (9) MeOCO(CH2)I2COOMe. saturated acid, having a terminal double bond. This view is supported by i.r. of all the fractions where only a vinyl double bond was found. So the structure is CH2=CH (CH2),)COOMe. Peak 6. The highest peak observed in the mass spectrum was at m/e = 199, which is not a molecular peak. There were peaks at m/e (M-64), 87, 101, 74 (rearrangement peak) besides strong peaks at m/e 84 and 98 which are characteristic of dimethyl esters of dicarboxylic acids having a long aliphatic chain. Such esters are known [6] usually not to show a molecular peak, and a peak at M-31 is the highest peak observed. So if the molecular weight is 199 + 31 = 230, then the compound is dimethyl sebacate. The structure was confirmed by comparison with an authentic MS and comparison of GC retention time. Peak 7showed a very weak molecular peak at m/e 284 and peaks at m/e 255 (m-29), 253 (M-31) and 241 (M-43). The spectrum closely resembles that given for CH3(CH2)~6--COOCH 3 [7] which is characteristic of fragmentations of methyl esters of long chain paraffinic fatty acids. According to its molecular weight, the product is CH3(CH2)IsCOOCH 3. Peak 8 showed a weak molecular peak at m/e 282 besides peaks at m/e 251 (M-31), 250 (M-32), 208 (M-74L 74 (basic peak from MacLafferty rearrangement) 41 [CH2~CH--CH2] +, 43, 55, 69, 83 and 97. The spectrum is that of a methyl ester of an unsaturated acid and, since from i.r. we have only a vinyl unsaturation, the product is the methyl ester of CH2=CH(CH2)I4COOH. Peak 9. The highest peak observed was at 255 which is not a molecular peak. There were also the regular fragmentation peaks for methyl esters, peaks at m/e 84, 98 and 112 which are characteristic of dimethyl esters of dicarboxylic acids. It is known [6] that dimethyl esters give a relatively strong peak at M-31, so that the molecular weight may be 255 + 31 = 286 which is in accordance with the structure CH~OOC(CH2)~2COOCH 3. This is supported by
the presence of peaks at m/e (M-64), (M-73), (M-92), (M-105) and (M-123). No other esters were found on injection of the mixture on an SE 30 column, where higher column temperature (270) was employed. The reaction mixture after extraction by KOH for removing acidic material was separated on a chromatography column as before to heptane, benzene and methanol fractions.
Analysis of the heptane .[kaction The heptane fraction contained only hydrocarbons as seen from i.r., and was analysed by GC using two different columns, viz. 5% BDS and 31!~iSE 30. The latter gives better separation for high molecular weight compounds. GC-MS was utilized for analysing the products. Figure 4 shows the chromatogram on 5°o BDS with 16 peaks. The peaks can be divided into 3 groups according to their retention time (molecular weights). The first group had 4 peaks. Their analysis and structure assignment were based on their fragmentation patterns and on comparison with an authentic sample, where available. Thus peaks 1-4 were n-dodecane, 1-dodecene. x-dodecene and cyclododecane, respectively. The second group comprising peaks 5 8 was similar to the first differing only in molecular weight. Thus these peaks were identified as n-hexadecane. 1-hexadecene, x-hexadecene and cyclohexadecene, respectively. The third group comprising peaks 9 12 were identified as the higher homologues n-eicosane (CH3--(CH2)Is--CH3), l-eicosene, x-eicosene and cycloeicosene, respectively. The fourth group comprising peaks 13 16 were identified as n-tetracosane (CH3--(CH2)22--CH3), l-tetracosene, x-tetracosene and cyclotetracosane. The heptane fraction thus contains 4 groups of hydrocarbons from C~2, C16, C20 and C24, i.e. C4,, hydrocarbons where n = 3 6. In every group, four different hydrocarbons were present ciz. n-alkane, 1-alkene, x-alkene and cycloalkane. Since there is a limit to the working temperature of
1204
A. GOZLANand A. ZILKHA 6
5
'°t
2
14 1.5
[ 10
0
1 ZO
30
Retention time (min)
Fig. 4. GC separation of the hydrocarbons in the heptane fraction on 5% BDS (electrolysis in methanol). (1) n-Dodecane, (2) 1-dodecene, (3) x-dodecene, (4) cyclododecane, (5) n-hexadecane, (6) l-hexadecene, (7) x-hexadecene, (8) cyclohexadecane, (9) eicosane (CH3(CH2)]sCH3), (10) l-eicosene, (11) x-eicosene, (12) cycloeicosane, (13) tetracosane (CH3(CHz)22CH3), (14) 1-tetracosene, (15) x-tetracosene, (16) cyclotetracosane. the 5% BDS column, we checked the presence of higher molecular weight hydrocarbons on a 3% SE 30 column. Another two series of hydrocarbons of C28 and C32 were found. The first series but not the
F
i 0
L 1 10
8
second could be separated clearly between the saturated, unsaturated, and cyclohydrocarbon. It seemed that there are no higher molecular weight hydrocarbons present in any significant amount, since no
9 11
I
I
I
20
30
40
Retention time (min)
Fig. 5. GC separation of the front benzene fraction on 5% BDS (electrolysis in methanol). (1) CH3(CH2)TCOOMe, (2) CH2~CH(CH2)6COOMe, (3) MeOCH(CH2)sCH=CH2 I
CH 3 (4) MeO(CH2)II--CH 3, (5) MeOCH2--(CH2)3CH=CHCH2(CHz)4CH 3, (6) CH3--(CHz)IICOOMe, (7) CH2=CH(CH2)t0COOMe, (8) MeOCH2(CH2)3CH=CHCH2(CH2)8--CH3, (9) CH3(CH2)]sCOOMe, (10) CH2=CH(CH2)]4COOMe, (11) MeOCH2(CH2)3CH=CH(CH2)Lz--CH 3, (12) CH3--(CH2)Ig--COOMe, (13) CH2~-CH(CHz)]s--COOMe.
Polymerization of dicarboxylic acids
peak appeared on injection at a column temperature of 270 even 1 hr after the C32 hydrocarbons have passed.
Analysis of the jront benzene ,fraction This fraction was analysed on two GC columns~ 5% BDS (Fig. 5) and 3% SE 30 (Fig. 6). Four groups of peaks can be seen, the separation of the higher molecular weight fractions not being sharp. Figure 5 shows that peaks 1-5 of the first group become peaks 6 8 of the second homologous series with peaks 3, 4 becoming shoulders of peak 7. In the third group, we find the homologues of peaks 1, 2 and 5 in peaks 9, 10 and 11. Peak 10 is broad and may contain the homologues of peaks 3 and 4 also. Comparison of the GC on SE 30 (Fig. 6) with that on BDS (Fig. 5) shows that, in the first group of peaks, peak 1 of Fig. 6 is a mixture of peaks 1 and 2 of Fig. 5. Similarly peak 2 is a mixture of peaks 3 and 4 and peak 3 is peak 5 (Fig. 5). Nevertheless, there is still good separation between the various products and use of the two chromatograms can help evaluate quantitatively the products.
II
1205
The peaks in the GC carried on BDS (Fig. 5) were identified as follows: all peaks without figure number belong to Fig. 5. Peak 1 was CH3(CH2)TCOOCH~, methyl-noctoate. Peak 2 was CH2~---CH(CH2)6COOCH.~. Peak 3 showed a molecular weight peak at m/e 198. The base peak was at m/e = 59 which together with peaks at m/e 45 +
(CH:=O--CH~) and 73 are characteristic of ions containing oxygen. Other peaks present include (M-15) and (M-32). It is known [8] that long chain saturated aliphatic ethers have fragmentations similar to alkenes. Besides the fragmentations at m/e 41, 55 and 69 (C,,H,,, ions), there are fragments at masses of C,,H2,, , as in dienes. All these results indicate an unsaturated methyl ether. The presence of peak m/e 41 +
(CH==CH--CH2) indicates that the double bond is at the end of the
11 9
2
12
T 0
10
[
I
1
I
I
2o
30
40
50
60
Retention
time
(min)
Fig. 6. GC separation of front-benzene fraction on 31,~oSE 30 (electrolysis in methanol). (1) Mixture of peaks 1 and 2 (Fig. 5), (2) mixture of peaks 3 and 4 (Fig. 5), (3) peak 5 (Fig. 5), (6)
M e O C H ( C H 2 h 2 C H = C H 2 and MeOCH2(CH2h4CH 3,
I
CH3 (9)
MeOCH(CH2)I6CH=CH 2 and CH30(CH2)I9--CH 3.
I
CH3 (10) MeOCH2(CH 2)3CH=-CHCH2(CHDI2-CH3, (11)
MeOC(CH2)]9CH 3 and MeOC(CH=llsCH~--CH 2,
II 0
II 0
(12) MeOCH(CH2h0CH=CH 2 and MeO(CH.,)x3--CH ~, I CH 3 (13)
MeOC(CH2)23CH 3 and
I[ o
MeOC(CHx)22CH=CH>(14) MeO(CH2)27CH ~. tl o
1206
A. GOZLANand A. ZILKHA
chain. The structure of the product based on molecular weight and fragmentation is CH30--CH(CH2)sCH~---CH2.
I
CH 3 Peak 4. showed a molecular weight peak at m/e 200. The base peak was at m/e 45 which, together with a peak at m/e 59, suggests ions containing oxygen. The peak at m/e 168 (M--CH3OH) may be due to a methyl ether having a long chain. The cluster of peaks of the hydrocarbon fragmentations show the presence of a saturated chain; the smooth lowering in the strength of the peaks from C3-C4 onward points to the presence of a linear chain. The structure of the compound is CH30(CH2)II--CH 3. Peak 5. The molecular peak at m/e 198 was accompanied by peaks at m/e 166 (M--CH3OH), 45 basic peak +
(CH2=O--CH3)
CH3OCH2--(CH2)3--CH=CH--CHz--(CH2)4CH 3 82
CH2~-~-CH(CH2)I4COOCH 3.
Peak 9 (Fig. 6) is a homologue of peak 6 (Fig. 6) and is composed of a mixture of the following two methyl ethers: CH3OCH (CH2)I6CH=CH 2 and
I CH3
71
Peak 6 showed a weak molecular peak at m/e 228, peaks at m/e 197 (M-31), 74 (base peak from MacLafferty rearrangement of ester), 59 and 87. The fragmentation corresponds to a methyl ester of an unbranched saturated carboxylic acid CH3(CH2)II COOCH3. Peak 7 was identified as CH2=CH(CH2)t0 COOCH 3. Peak 6 o f G C on SE 30 (Fig. 6) is the two shoulders of peak 7 of GC on BDS (Fig. 5). It shows in the high mass ranges a peak at role 224 (probably M-32 where M =256) and a peak at role 222 (M-32 where M = 254), i.e. a mixture of two compounds. From the mass spectra and data for the lower homologues, the compounds are
Peak 10 (Fig. 6) is analogous to peak 8 (Fig. 5). Its highest peak is at m/e 278 which is M-32. Its structure is Peak 12 mol. peak at m/e 340 was identified as CH3OC(CH2)IgCH3.
II
O Peak I1 (Fig. 6) is a mixture of two methyl esters one saturated [m/e 311 (M-29) M-31 and M-43] and one unsaturated (m/e 338, M-31, M-32 and M-74), the structure of the latter being CH3OC(CH2)IsCH=CH2.
II
O Peak 12. The MS is similar to that of an alkane and an alkadiene and is analogous to that of peak 9 (Fig. 6). The peak corresponds to a mixture of CH3OCH--(CH 2)IOCH~--CH2
I CH3 M = 366 and
CH30--CH(CH2)I2CH=CH 2 and
CH30(CH2)23--CH3 M = 368
I CH3 CH3OCH2(CH 2)taCH 3(M = 256)
Peak 8. According to its position, this peak is a homologue of peak 5; their mass spectra resemble each other with peaks at m/e 45 and 82. Base peak at m/e 55 (instead of 45 with peak 5) and fragmentations at role 85 and role 99 for C, H2n,~ chains. The molecular peak is absent and the highest peak is at role 222 which is M-32 so that the molecular weight is 254 and the structure of the compound is: CH3OCH2--(CH2)3CH=CH--CH2--(CH2)8CH 3 45
82
127
Peak 9. Molecular peak at role 284 which is 5~o of the base peak at m/e 74, rearrangement peak of a methyl ester, / O H ] +" CH30--C. [ .
~CH2J
CH30(CH2)19--CH3.
CH3OCH2(CH2)3CH~CHCH2(CH2)12--CH3.
and 59. There were also relatively strong peaks at m/e 82 and m/e 71. The plausible structure of the product seems to be:
45
There was also a series of peaks at 59, 87, 101 up to 171 which are indicative of a methyl ester of a saturated long chain carboxylic acid [6]. The compound is CH3(CH2)IsCOOCH 3. Peak I0. Retention time and MS are the same as for peak 8 in the carboxylic acid mixture from before, weak mol. peak at 282, so the compound is
Peak 13. It was not possible to obtain the higher peaks in the MS because of the small amount of material but, according to the peaks at rn/e 55 (base), 43, 74, 87 and 101 and by analogy with peak 11 (Fig. 6), the compounds are: CH3OC(CH2)23CH3
II
O
and CH3OC(CHz)22CH=CH:
II
O Peak 14. No MS spectrum could be obtained but by analogy to lower homologues it may be CH30(CH2)27--CH 3 (Fig. 6).
Analysis of the benzene fraction There were no volatiles in this fraction and the product was analysed by i.r. and NMR. The i.r. spectrum showed strong peaks of the symmetric and assymetric C--H stretching vibrations of
1207
Polymerization of dicarboxylic acids It --CH2-groups at 2858 and 2930 cm ~, respectively, while the respective absorptions of the methyl groups appeared only as a shoulder at 2960 cm ~ indicating the preponderance of methylene groups over methyl groups. There were also the rocking vibrations of the --CH2-groups at 720 and at 730 cm L(weaker), the latter absorption indicating a certain degree of crystallinity in the (CH2),, chains [8]. These results show the presence of relatively long straight chains of methylene groups with a small amount of methyl groups. Absorptions at 1643 CA ~ together with absorptions at 910 and 990cm ] indicate the presence of vinyl - - C H = C H 2 double bonds and at 965 cm indicate the presence of trans-internal double bonds. There were absorptions for ester groups at 1740, 1780 and at 1360, 1440, 1260, 1120 (--OMe), 1170 and l l00cm ~ indicating the presence of three types of ester groups, Pi,-. methyl esters, internal ester groups between two aliphatic chains and 7-1actone. The 7-1actone is not 7-valerolactone, since this was not found in GC. NMR showed the following peaks, (integration values given in brackets): 6(ppm): 0.93 (CH3) (9); 1.27 (CH2) (70): 1.67 (CH2--/]-- to functional groups) besides 2.14 (--CH2-- ~ to C~---O or C = C ) (14): 3.23 (CH~O, - - C H 2 0 - - ) (5); 3.6
the presence of which was confirmed by anhydrous titration with KOCH~ in methanol. There were also peaks for methyl ester, methyl ether, internal ester groups and for - - C H = C H , at 1643, 910 and 990 cm ~but the latter were much weaker than in the benzene fraction, indicating their smaller amount. The NMR spectrum of the methanol fraction was analysed as for the benzene fraction: it was found to correspond to the following groups: (CH2)~4 {CHO,: X--(CH2)7--X, where X is a functional group such as C ~ O or C = C , (CH~OCH2--)3, (--Ctt~OC--)2, (CH3OC--)> O
O
( - - C H z C H 2 ) I , (COOH)2. It can be seen that, in the methanol fractiom the ratio of functional groups to the methylene groups is higher than in the benzene fraction, and the oxygen containing groups are also more pronounced. If" we join all the above partial structures, we obtain the structural formula C~tH980~ (tool. wt 950}. If we subtract from this structure the groups incorporated in the oligomers but not from adipic acid, i.e. 3CH30--, 2CH 3 - groups from CH;OC,
O
II
O
(CH3OC--) (3); 3.72 (CH2OC--)
II
/ (2); 4.6
O
/CH2--CH I\
[--CH
\
l/
X-o-co /
CH of 7-1actone) (1); 4.77, 4.99, 5.53, 6.06 ( - - C H = C H , ) besides 5.35 ( - - C H = C H - - ) (5). From the i.r. and NMR spectra, it can be concluded that the benzene fraction is composed of the following groups: (CH2)35-(CH3)3 where the CH2 groups are not attached to any functional group, (CH2)5 attached to the carbonyt group of ester or to a double bond, (CH~OCH,--)~, (CH3OC--)I, (--CU2OC-)-b
II
O
[I
O
l-7-1actone group, (CH2=CH)Ls and ( - - C H = CH-)-05 with a trans-configuration. It is difficult to give a structural formula to the oligomers, but the presence of (CH2)3s relative to the other groups is significant in indicating the extent of the straight Kolbe reaction.
Analysis of the methanol Jiaction In this fraction no volatiles were observed in GC on an SE 30 column up to 270'. The i.r. spectrum of this fraction resembles that of the benzene fraction with the following differences. There was no absorption for 7-1actone at 1780cm ~. The absorptions at 1000-1300cm ~ are not sharp and resemble those of a polyester, with maximum absorptions at 1100, 1120, 1170 and 1265cm t. There is a weak absorption from 3400 to 2500 cm ~ which, besides a shoulder at 1700 cm ~, is characteristic of COOH groups,
then the general structural formula reduces to C46Hs30~> Based on the ["act that the starting compound was adipic acid. this can be written as C40H83(CO2)6 or [(CH2)414[(CH2)4CO2]p This means that, on average, out of 10 molecules of adipic acid reacted to give the methanol fraction. 4 of them suffered decarboxylation of both COOH groups and 6 of them of only one. Therefore the percent decarboxylation is 6+(2x4) 2x10
x 100 = 70.
In summary, the separation of the non-volatiles (by chromatography} obtained in the electrolysis of adipic acid yielded 4 fractions. (1) The heptane fraction consisting of straight chain hydrocarbons, whether saturated or unsaturated, together with cyclic hydrocarbons. The extent of decarboxylation in this fraction was 100%. (2) The front-benzene fraction composed of methyl esters and methylethers of saturated and unsaturated straight aliphatic chains having structures such as CH3OC(CH?)4,, I--CH~,CH~OC{CH~),, O
,
O
- - C H = C H 2, CH30(CH2)4, , ]--CH~, etc. ~3) The benzene fraction composed of oligomers of relatively high molecular weight that were not volatile in GC. The oxygen content in this fraction is higher than in the previous fraction due to an increase in the ether, and methyl ester groups as well as to the presence of internal ester groups and ?,-lactone groups. The extent of decarboxylation in this fraction was 88.5. (4) The methanol fraction consisted of oligomers with a still higher content of oxygen, and the extent of decarboxylation was lower at 700;.
1208
A. GOZLAN and A. ZILKHA REFERENCES
1. A. Gozlan, G. Again, S. Vardi and A. Zilkha, Eur. Polym. J. 20, 759 (1984). 2. H. Keller and H. V. Halban, Heh~. chim. Acta 27, 1439 (1944). 3. Selected Mass Spectral Data, American Petroleum Research Institute, Project 44, Thermodynamics Research Center, Department of Chemistry, Univ. College Station, Texas (1966). 4. H. Budzikiewicz, C. Djerassi and D. H. Williams, Mass
Spectrometry of Organic Compounds. Holden Day, San Francisco (1967). 5. F. W. McLafferty, Mass Spectrometry of Organic Ions, p. 447. Academic Press, New York (1963). 6. Ref. 5, p. 446. 7. Ref. 5, p. 401. 8. S. R. Heller and G. W. A. Milne, EPA/NIH, Mass Spectral Data Base, Vol. 1, p. 162 (1978). 9. M. Avram and Gh. D. Mateescu, Infrared Spectroscopy, p. 136. Wiley-lnterscience, New York (1972).
0014-3057~84 $3.00+(/.00 Copyright :~ 1984 Pergamon Press Ltd
Printed in Great Britain. All rights reserved
ELECTROCHEMICAL POLYMERIZATION OF DICARBOXYLIC ACIDS--II OLIGOMERS
AND
SIDE
PRODUCTS OF
IN
ADIPIC
THE
POLYMERIZATION
ACID
A. GOZLAN a n d A. Z1LKHA Department of Organic Chemistry, The Hebrew University of Jerusalem. Jerusalem 91904, Israel
(Received 13 April 1984) A b s t r a c t - - T h e electrochemical polymerization of adipic acid in methanol and in methanol pyridine ( 1 : 1) via the Kolbe reaction nHOOC(CH04COOH
2he
, n'(CH2)" 4 + 2nCO 2 + nH~
was investigated as regards the oligomeric and side products. GC MS, i.r. and N M R were used to identify the m a n y products. Gaseous and volatile c o m p o u n d s were identified as C 4 and C s hydrocarbons besides 7- and 6-valerolactones. The less volatile c o m p o u n d s were separated on silica gel columns to fractions, viz. that eluted by heptane which contained hydrocarbons, that eluted by benzene which contained ether and ester groups and that eluted by methanol which contained higher oligomeric products containing oxygen. Four types of hydrocarbons were formed, viz. n-alkanes, n-alkenes, x-alkenes (the place of the double bond is not known) and cycloalkanes. Saturated and unsaturated oligomeric mono- and di-carboxylic acids were also formed.
a variac to adjust the current strength. The polarity of the current was changed every 90 sec.
INTRODUCTION In p r e v i o u s w o r k [1] we h a v e s h o w n , d u r i n g s t u d y o f t h e e l e c t r o c h e m i c a l p o l y m e r i z a t i o n o f a d i p i c acid, that besides the formation of insoluble polymer, n HOOC(CH2)4COOH
E~. . . . . lyric oxidation
~ _[_(CH2)4_]_" + 2nCO2
t h e r e were o t h e r low m o l e c u l a r w e i g h t f r a c t i o n s f o r m e d in relatively h i g h yields. W e n o w r e p o r t o n the separation, identification and characterization of these products.
Determination ~[ carboxylic acids' hy methylation An aliquot portion of solution to be analysed was methylated by diazomethane generated by the addition of 60°~i aqueous K O H to "Diazald'" (N-methyl-N-nitroso-ptoluene sulphonamide) as described before [I]. GC was used to determine the methyl esters formed.
TLC T L C was carried out on precoated plastic sheets, (I.2 m m silica gel (polygram Sil N-HR/UV254: Macherey-Nogel, Germany).
EXPERIMENTAL
Column chromatography
Materials Adipic acid, triethylamine (BDH), methanol, pyridine (Mallinckrodt, analytical grade) and "Diazald" (Aldrich) were used.
Electrolysis cell The cell was equipped with a magnetic stirrer, a thermometer and a reflux condenser to the top of which were connected pre-weighed U-tubes containing drierite and ascarite to measure quantitatively the evolved CO 2. It had a double jacket for circulating a cooling liquid (acetone cooled to the required temperature). Two Pt electrodes (2 x 3 cm) soldered in glass tubes were inserted into the cell through a ground joint, and the distance between them was kept constant by Teflon bars. A chopped power supply, 300 V/3 A, with the possibility of reversing the polarity of the current every 10 sec up to 3 min was used.
Electrolysis of adipic acid The required a m o u n t of adipic acid was introduced into the electrolysis cell and dissolved in the required solvent. Triethylamine was added, and the current was passed using
A column packed with silica gel (Woelhm) was used to separate the oily fraction obtained in the electrolysis. The column was washed with 250 ml of each of methanol. benzene and heptane before use for the separation. The oil was dissolved in a small volume of benzene, passed through the column and eluted by heptane then benzene followed by methanol.
Gas chromatograph)' (GC) Gas chromatography was carried out either on a Packard 7400 or on a Packard-Becker 417 instrument. For the separation of~'- and 6-valerolactone, a glass G C column ]in was used containing 5°,0 butanediolsuccinate (BDS) on c.w./h.m.d.s. 60/80. The injector and detector (f.i.d.) temperatures were 2 4 0 . The starting column temperature was 80'; after 4rain, it was heated to 4'/min up to a final temperature of 2 0 0 . The N 2 flow was regulated at 20 ml/min. Biphenyl was used as an internal standard. For the separation of the C 4 hydrocarbon fraction, a stainless steel column of ~4india. packed with 40°~, cinnamaldehyde on c.p. 60/80 was used. The temperature of the column was 30 ~, and that of the injector and detector 50 .
1199
1200
A. GOZLANand A. ZILKHA
The C8hydrocarbon fraction was separated on a lin glass column packed with 20~ squalane on c.p. 60/80. The temperature of the column was programmed for 13 min at 60° and then was raised to 3°/min to 120°, the final temperature. The N 2 flow was 10 ml/min. The hydrocarbons in the heptane fraction were determined using either a column of BDS as described before for separation of ,/- and &-valerolactone or a column packed with 3~ SE 30 on c.w./h.m.d.s. 60/80 under the following conditions: starting column temperature 80°, rate of heating 4°/min, final temperature 270°, held there for 60 min.
benzene each were collected. The last was free from any material. The first two fractions were mixtures as seen from GC. They contained, as seen from i.r. and NMR, short or long hydrocarbon chains, to which were connected such groups as O
II
CH30 C - - , --O--CH3, --CH3, - - C H = C H 2 and
--CH=CH--.
They did not contain RESULTS AND DISCUSSION To determine the soluble low molecular weight products formed in the electrochemical polymerization of adipic acid, an experiment was carried out under the conditions previously developed [1] for the polymerization of adipic acid. The electrolysis was carried in methanol-pyridine (1:1) starting with 10 g adipic acid and using triethylamine (10Yo) as a base. To prevent coating of the electrodes with polymer, the polarity of the current was reversed every 90 sec. The reaction was stopped after 7 hr, before complete consumption of the adipic acid, because towards the end of the electrolysis the concentration of the acid is small allowing other materials such as methanol to be oxidized and give undesirable side products, not connected with the oxidation of adipic acid. The insoluble polymer (1 g) was separated and the filtrate was diluted with benzene, extracted with cold 5Yo KOH to remove unreacted adipic acid and acidic material. The benzene solution was evaporated after washing with 1~ HCI to yield 1.46 g of a yellow oil. Gas chromatography (GC) of this oil on a column packed with 3YooSE 30 at temperatures from 80 to 250 ° showed the presence of various products having different molecular weights. In order to separate the oil into various fractions, we carried out TLC experiments. With heptane as eluent, the oil separated, part of it moved to the front, and part of it remained at the starting point. Using benzene as eluent and using the same plate of TLC, a new material appeared which moved close to the front of the benzene. Material still remained at the starting point. Using methanol, all the material moved towards the front. The TLC experiment showed that the oil was composed of three groups of material, the first of which was eluted with heptane, the second with benzene and the third with methanol. These results were utilized to separate the oil on a column of silica gel. The amount of silica gel taken was 100 times that of the oil. It was eluted with heptane (5 x 50 ml) until no more material passed, followed by benzene (6 x 50 ml), and then the yellow material remaining in the column was fully eluted by methanol (5 x 50 ml). The fraction eluted by heptane was investigated by i.r. and NMR. The i.r. spectrum did not show the presence of functional groups and was similar to that of unsaturated hydrocarbons (absorption at 1640cm-t). The N M R spectrum showed the same results; besides the hydrocarbon chains, there were olefinic hydrogens of C H = C H and CH=CH2 groups. GC of this fraction (heating from 80 to 250 °) showed that it was composed of many compounds. In the elution with benzene, 6 fractions of 50 ml
COOH or - - C H ~ - - 0 - - C - -
II
0 Fractions 3-5 contained the same groups as before, as well as methylene ~- to ester groups. They did not contain carboxyl groups. GC showed peaks from fraction 3 but not from fractions 4-5, which presumably contained material of higher molecular weight. Fractions 4 and 5 were combined; their average molecular weight was 410, determined cryoscopically using CBr 4 [2]. By N M R it is difficult to give a structural formula, especially since the fractions are composed of a mixture of oligomers. Elemental analysis was: C, 69.82; H, 10.91; O, 19.27; N, 0.0Yoo,corresponding to an average formula C24H450 5. NOW if the oxygens belong to CH30 ether, CH3OCO ester and to --C--OIl O internal ester groups and we subtract the sum of these groups (C4H605) from the average formula, then the formula of the hydrocarbon chain will be C20H39 , i.e. approx. (CH2)20. Noting that adipic acid has 4CH 2 groups in the chain, the following tentative structural formula may be written, giving an idea of the sort of products formed. CH3OC "-[(CH2)4]~ 2 C--O--[(CH2)4]~3OCH3
II
11
O C The fraction eluted by methanol had the same functional groups found in the benzene fractions, as seen from i.r. and NMR. It also contained COOH groups, but it was difficult to identify the presence of C = C double bonds due to their low concentration. GC of the fraction using a column at 250 ° did not show the presence of any volatile material. Elemental analysis was: C, 66.41; H, 10.23; O, 22.5; N, 0.86Yo, corresponding to the formula C24HnsO6N0.3 . Note that the oxygen content in this fraction was higher than that in the benzene fraction meaning that the methanol fraction contained compounds having a shorter hydrocarbon chain with more functional groups. All these results indicate that the oily product obtained in the electrolysis is composed of a complex mixture of saturated and unsaturated hydrocarbons up to compounds (oligomers) having an increasing percentage of oxygen, due to ester and methoxy groups. In addition the oil contained nitrogen from participation of the pyridine or Et3N in the reaction. The oil consists of low molecular weight compounds, having a relatively low boiling point that pass out in
Polymerization of dicarboxylic acids II GC, and of higher oligomers having molecular weights above 400. These results indicate that the polymerization is much more complex than a Kolbe reaction. If we add the weight of the various products isolated from the reaction, namely 4.01 g (CO2; measured by being trapped in U-tubes containing Ascarite and Drierite as in microanalysis), 1.0 g (insoluble polymer), 1.46g (oil) and 1.5 (acidic material), we obtain 7.97 g which is less than the weight of adipic acid used (10 g) in the electrolysis. This means that volatile products are also formed and are lost in the work-up of the reaction mixture, where the solvents are evaporated at 6 0 in vacuo (25 mm Hg). To try to trap these products, we performed an experiment using 14.6 g adipic acid. At the end of the electrolysis, the insoluble polymer was filtered, and the filtrate was investigated by GC using a column containing 5% butane diol succinate (BDS). The temperature was raised from 80 to 200 ° . Two relatively strong peaks and several smaller peaks were obtained (Fig. 1). The two peaks were investigated by GC MS. The molecular peak obtained in the mass spectrum of the first peak was m/e 100 and, there were strong peaks at m/e 85 (M-15) and 56 (M-44) which are characteristic of ?-lactones; the product was identified as 7-valerolactone and verified by comparison with G C - M S spectrum of 7-valerolactone under the same conditions. The second peak in the GC had in its mass spectrum a molecular peak at role 100 and a base peak at m/e 42; it was identified as 6-valerolactone. The amounts of 7-valerolactone and 6-valerolactone obtained based on GC were 0.49 and 0.26 g respectively.
Besides these two lactones which are lost during the evaporation in vacuo, there must be other volatile products, since the balance of all the products isolated is still less than the starting weight of adipic acid. We considered the formation of C4 gaseous products, which can be formed if the adipic acid is decarboxylated from both ends during the electrolysis. To trap such products, the gases evolved during the electrolysis after passing through the reflux condenser were passed into a tube cooled in acetone-solid CO2 mixture. About 2 ml liquid were trapped at the end of the electrolysis. The solution was diluted by CCI 4 and investigated by NMR. The peaks obtained were at: 6 (ppm) (the numbers inside the brackets are the integration values): 5.7, 4.98, 4.88 (m, 42) ( - - C H i C H i ) : 5.28 ( m ) ( C H ~ C H ) ; 4.2 (s, 64); 3.5 (s, 190): 2.12 (q), 1.95 (d, integ, for both 52); 1.32 (t, 69); 0.88 (t, 6). From these peaks it is possible to conclude that the following groups are present: CH~---CH~, C H = C H , CH3CH=CH2, CH2=CH--CH2CH3, CH2CH3 and CH3OH. These volatile C4 compounds were separated by GC using a column packed with 40% cinnamaldehyde on c.p. 60/80 at a column temperature of 30. Five peaks were obtained (Fig. 2) and were analysed by GC-MS. From the mass spectra and by comparison with the literature, it was concluded that peak 1 (mol. peak 58, base peak 41) was n-butane and peak 4 was 1,3-butadiene (tool. peak
1
2 3
I
2
I 0
I 2
I 4
1201
[ 6
I 8
Retention
1 10
time
I 12
I 14
I 16
I 18
(min)
Fig. 1. GC separation of 7- (I) and 6- (2) valerolactone on 5% BDS.
I 0
I 2
4
Retention
i 6
8
time
1 10
(min)
Fig. 2. GC separation of C4 hydrocarbons on 40°, cinnamaldehyde at 30~. (1) n-Butane, (2) l-butene, (3) trans-2butene, (4) 1,3-butadiene, (5) cis-2-butene.
1202
A. GOZLANand A. ZILKHA
56, base peak 39). Peaks 2, 3, 5 all have a mol. peak of 56 and a base peak 41. From their mass spectrum, the N M R spectrum, retention time in GC, and the literature, it was concluded that peak 2 (which is the biggest) belongs to l-butene, and peaks 3 and 5 are trans-2-butene and cis-2-butene respectively. It seemed plausible that, after finding C4 hydrocarbons, there must be also higher oligomers such as C s compounds. To look for these hydrocarbons, the electrolysis solution after separation from the insoluble polymer was neutralized by conc. HCI to remove the pyridine and then analysed by GC on a column packed by 20~ squalane on c.p. 60/80 heated to 70 ° . Eight peaks were obtained and were analysed by GC MS. The structures were deduced by comparison with MS in the literature [3] as well as with authentic samples where available. Peak 1 was 1,7-octadiene (mol. peak at m/e 110) and peak 2 (mol. peak at role 112) was 1-octene. Peak 3 was a linear chain octene (tool. peak at m/e 112) but it was not possible from the data available to indicate the exact place of the C = C double bond, so it will be denoted as x-octene. Peak 4 (m/e 114) was n-octane. Peak 5 (m/e 114) had fragments at m/e = 82 (M-32) and 83 (M-31) besides peaks at m/e 59 and 31 indicating the presence of ions containing oxygen. Based on the literature [4] this compound is probably CH2=CHCHzCH2COOCH 3. Peak 6 had a weak tool. peak at 116, a base peak at m/e 74, in addition to peaks at m/e 85 (M-31), 59 (COOCH3) "+ and 87 (CH2CH2COOCH3) "+. Further, the pattern of the fragmentation of the hydrocarbon chain was that of a saturated one, and the product was identified as CH3(CH2)3COOCH 3. Peak 7 was 7-valerolactone. Peak 8 was obtained in small amount and was identified as cyclooctane (relatively strong mol. peak at m/e 112). To confirm the compositions of the side products and oligomers formed, we carried out another electrolysis of adipic acid (30 mmol) in methanol (30 ml) in the presence of triethylamine (3 mmol). The current strength was 1.3A, and its polarity was changed every 90 sec. The electrolysis solution, after removal of polymer, was analysed by GC for derivatives higher than the octenes by being passed over a column of 5% BDS. Besides, 7- and cS-valerolactone (the quantity of the former was double that of the latter), the solution contained C~2 hydrocarbons which were identified by G C - M S as 1-dodecene and x-dodecene (the place of the double bond is not known exactly) which comprised 80~ of the C~2 hydrocarbons, n-Dodecane and cyclododecane were also present. Two other peaks were identified as the methyl esters of two C9 acids, namely CH3(CHz)vCOOH
and
CHz~CH
(CH2)6COOH
(formed from dimerization of 2 molecules of adipic acid, one of which has undergone decarboxylation of its two COOH groups and the other of only one; Table 1).
Table 1. Valerolactones and other products obtained in the electrolytes of adipic acid in methanol* Product 1. 2. 3. 4. 5. 6. 7. 8.
(mmol)
n-Dodecane 1-Dodecene x-Dodecene Cyclododecane CH3(CH2)7COOMe CH2zCH(CHz)6COOMe 7-Valerolactone 6-Valerolactone
(0.03) (0.13) (0.18) (0.05) (0.08) (0.16) (I.87) (1.10)
*Adipic acid (30mmol) was electrolysed in methanol (30ml) in the presence of triethylamine (3 retool), current strength 1,3 A. The electrolysis solution was filtered from polymer and analysed for derivatives higher than the octenes by GC using a 5% BDS column. The compounds are given in the order of their appearance in GC.
methylated by diazomethane and the methyl esters were analysed by GC on two columns, 5~o BDS, which gives good separation between esters of saturated and unsaturated carboxylic acids having the same number of carbon atoms but is not suitable for the separation of high molecular weight products, and 3~o SE 30 which gives a good separation of the esters of acids having different molecular weights. The gas chromatogram of the separation on 5 ~ BDS is given in Fig. 3. Nine peaks were obtained and were analysed by GC-MS. Peak 1 had a molecular peak at m/e 172 and peaks at m/e (M-29), (M-31), (M-43), 87, 101, 115 and 74 which was the base peak belonging to the product of the MacLafferty rearrangement OH
I
[CH3--O--C=CH2] +• . The results, compared with those for an authentic sample, showed the product to be the methyl ester of n-octoic acid. Peak 2 had a molecular peak at m/e 170 and fragmentations at m/e (M-31), (M-32) and (M-74) typical of methyl esters of unsaturated carboxylic acids having the double bond after the fourth carbon atom. The base peak was the rearrangement peak at m/e 74. There were also peaks at m/e 41, 55, 59, 69, 87 and 10l. The indications are of a terminal double bond and this was further checked by carrying out an i.r. on all the solid acid mixtures, where only peaks for e-olefins (CH2=CH) were found. All these results indicate that the product is a methyl ester of
CH2=CH(CH2)6COOH. Peak 3 is a very large peak corresponding to dimethyl adipate [5]. It had the same retention time as an authentic sample. Peak 4 was identified as the methyl ester of C H 3 ( C H 2 ) l t COOH. Peak 5 showed fragmentations at m/e 226 (weak molecular peak), (M-31), (M-32), (M-74), 143 ([CH30 C (CH2)6] + ),
Analysis of carboxylic acidfraction The fraction extracted from the reaction mixture by 5~ KOH was acidified by conc. HC1, concentrated and extracted by ether (500 ml). The ether was dried and evaporated yielding 1.13 g solid yellowish material that was dissolved in THF. An aliquot was
LI
O 87, 74 (base peak from rearrangement), 59, 55 and 41 +
(CH2:CH--CH2). The indications are of a methyl ester of an un-
1203
Polymerization of dicarboxylic acids--lI
r"-~
3 6
2 9
I 10
I 20
I 30
Retention t i m e (min)
Fig. 3. GC separation on 5~o BDS of carboxylic acids from the electrolysis of adipic acid in methanol after conversion to the methyl esters. (1) CH3(CH2)TCOOMe, (2) CH2---CH(CH2)o--COOMe, (3) MeOCO(CH2)4COOMe, (4) CH3(CH2)uCOOMe, (5) CH~zCH(CH2)IoCOOMe, (6) MeOCO(CH2)sCOOMe, (7) CH3(CH2)Is--COOMe, (8) CH:=CH--(CH2)u--COOMe, (9) MeOCO(CH2)I2COOMe. saturated acid, having a terminal double bond. This view is supported by i.r. of all the fractions where only a vinyl double bond was found. So the structure is CH2=CH (CH2),)COOMe. Peak 6. The highest peak observed in the mass spectrum was at m/e = 199, which is not a molecular peak. There were peaks at m/e (M-64), 87, 101, 74 (rearrangement peak) besides strong peaks at m/e 84 and 98 which are characteristic of dimethyl esters of dicarboxylic acids having a long aliphatic chain. Such esters are known [6] usually not to show a molecular peak, and a peak at M-31 is the highest peak observed. So if the molecular weight is 199 + 31 = 230, then the compound is dimethyl sebacate. The structure was confirmed by comparison with an authentic MS and comparison of GC retention time. Peak 7showed a very weak molecular peak at m/e 284 and peaks at m/e 255 (m-29), 253 (M-31) and 241 (M-43). The spectrum closely resembles that given for CH3(CH2)~6--COOCH 3 [7] which is characteristic of fragmentations of methyl esters of long chain paraffinic fatty acids. According to its molecular weight, the product is CH3(CH2)IsCOOCH 3. Peak 8 showed a weak molecular peak at m/e 282 besides peaks at m/e 251 (M-31), 250 (M-32), 208 (M-74L 74 (basic peak from MacLafferty rearrangement) 41 [CH2~CH--CH2] +, 43, 55, 69, 83 and 97. The spectrum is that of a methyl ester of an unsaturated acid and, since from i.r. we have only a vinyl unsaturation, the product is the methyl ester of CH2=CH(CH2)I4COOH. Peak 9. The highest peak observed was at 255 which is not a molecular peak. There were also the regular fragmentation peaks for methyl esters, peaks at m/e 84, 98 and 112 which are characteristic of dimethyl esters of dicarboxylic acids. It is known [6] that dimethyl esters give a relatively strong peak at M-31, so that the molecular weight may be 255 + 31 = 286 which is in accordance with the structure CH~OOC(CH2)~2COOCH 3. This is supported by
the presence of peaks at m/e (M-64), (M-73), (M-92), (M-105) and (M-123). No other esters were found on injection of the mixture on an SE 30 column, where higher column temperature (270) was employed. The reaction mixture after extraction by KOH for removing acidic material was separated on a chromatography column as before to heptane, benzene and methanol fractions.
Analysis of the heptane .[kaction The heptane fraction contained only hydrocarbons as seen from i.r., and was analysed by GC using two different columns, viz. 5% BDS and 31!~iSE 30. The latter gives better separation for high molecular weight compounds. GC-MS was utilized for analysing the products. Figure 4 shows the chromatogram on 5°o BDS with 16 peaks. The peaks can be divided into 3 groups according to their retention time (molecular weights). The first group had 4 peaks. Their analysis and structure assignment were based on their fragmentation patterns and on comparison with an authentic sample, where available. Thus peaks 1-4 were n-dodecane, 1-dodecene. x-dodecene and cyclododecane, respectively. The second group comprising peaks 5 8 was similar to the first differing only in molecular weight. Thus these peaks were identified as n-hexadecane. 1-hexadecene, x-hexadecene and cyclohexadecene, respectively. The third group comprising peaks 9 12 were identified as the higher homologues n-eicosane (CH3--(CH2)Is--CH3), l-eicosene, x-eicosene and cycloeicosene, respectively. The fourth group comprising peaks 13 16 were identified as n-tetracosane (CH3--(CH2)22--CH3), l-tetracosene, x-tetracosene and cyclotetracosane. The heptane fraction thus contains 4 groups of hydrocarbons from C~2, C16, C20 and C24, i.e. C4,, hydrocarbons where n = 3 6. In every group, four different hydrocarbons were present ciz. n-alkane, 1-alkene, x-alkene and cycloalkane. Since there is a limit to the working temperature of
1204
A. GOZLANand A. ZILKHA 6
5
'°t
2
14 1.5
[ 10
0
1 ZO
30
Retention time (min)
Fig. 4. GC separation of the hydrocarbons in the heptane fraction on 5% BDS (electrolysis in methanol). (1) n-Dodecane, (2) 1-dodecene, (3) x-dodecene, (4) cyclododecane, (5) n-hexadecane, (6) l-hexadecene, (7) x-hexadecene, (8) cyclohexadecane, (9) eicosane (CH3(CH2)]sCH3), (10) l-eicosene, (11) x-eicosene, (12) cycloeicosane, (13) tetracosane (CH3(CHz)22CH3), (14) 1-tetracosene, (15) x-tetracosene, (16) cyclotetracosane. the 5% BDS column, we checked the presence of higher molecular weight hydrocarbons on a 3% SE 30 column. Another two series of hydrocarbons of C28 and C32 were found. The first series but not the
F
i 0
L 1 10
8
second could be separated clearly between the saturated, unsaturated, and cyclohydrocarbon. It seemed that there are no higher molecular weight hydrocarbons present in any significant amount, since no
9 11
I
I
I
20
30
40
Retention time (min)
Fig. 5. GC separation of the front benzene fraction on 5% BDS (electrolysis in methanol). (1) CH3(CH2)TCOOMe, (2) CH2~CH(CH2)6COOMe, (3) MeOCH(CH2)sCH=CH2 I
CH 3 (4) MeO(CH2)II--CH 3, (5) MeOCH2--(CH2)3CH=CHCH2(CHz)4CH 3, (6) CH3--(CHz)IICOOMe, (7) CH2=CH(CH2)t0COOMe, (8) MeOCH2(CH2)3CH=CHCH2(CH2)8--CH3, (9) CH3(CH2)]sCOOMe, (10) CH2=CH(CH2)]4COOMe, (11) MeOCH2(CH2)3CH=CH(CH2)Lz--CH 3, (12) CH3--(CH2)Ig--COOMe, (13) CH2~-CH(CHz)]s--COOMe.
Polymerization of dicarboxylic acids
peak appeared on injection at a column temperature of 270 even 1 hr after the C32 hydrocarbons have passed.
Analysis of the jront benzene ,fraction This fraction was analysed on two GC columns~ 5% BDS (Fig. 5) and 3% SE 30 (Fig. 6). Four groups of peaks can be seen, the separation of the higher molecular weight fractions not being sharp. Figure 5 shows that peaks 1-5 of the first group become peaks 6 8 of the second homologous series with peaks 3, 4 becoming shoulders of peak 7. In the third group, we find the homologues of peaks 1, 2 and 5 in peaks 9, 10 and 11. Peak 10 is broad and may contain the homologues of peaks 3 and 4 also. Comparison of the GC on SE 30 (Fig. 6) with that on BDS (Fig. 5) shows that, in the first group of peaks, peak 1 of Fig. 6 is a mixture of peaks 1 and 2 of Fig. 5. Similarly peak 2 is a mixture of peaks 3 and 4 and peak 3 is peak 5 (Fig. 5). Nevertheless, there is still good separation between the various products and use of the two chromatograms can help evaluate quantitatively the products.
II
1205
The peaks in the GC carried on BDS (Fig. 5) were identified as follows: all peaks without figure number belong to Fig. 5. Peak 1 was CH3(CH2)TCOOCH~, methyl-noctoate. Peak 2 was CH2~---CH(CH2)6COOCH.~. Peak 3 showed a molecular weight peak at m/e 198. The base peak was at m/e = 59 which together with peaks at m/e 45 +
(CH:=O--CH~) and 73 are characteristic of ions containing oxygen. Other peaks present include (M-15) and (M-32). It is known [8] that long chain saturated aliphatic ethers have fragmentations similar to alkenes. Besides the fragmentations at m/e 41, 55 and 69 (C,,H,,, ions), there are fragments at masses of C,,H2,, , as in dienes. All these results indicate an unsaturated methyl ether. The presence of peak m/e 41 +
(CH==CH--CH2) indicates that the double bond is at the end of the
11 9
2
12
T 0
10
[
I
1
I
I
2o
30
40
50
60
Retention
time
(min)
Fig. 6. GC separation of front-benzene fraction on 31,~oSE 30 (electrolysis in methanol). (1) Mixture of peaks 1 and 2 (Fig. 5), (2) mixture of peaks 3 and 4 (Fig. 5), (3) peak 5 (Fig. 5), (6)
M e O C H ( C H 2 h 2 C H = C H 2 and MeOCH2(CH2h4CH 3,
I
CH3 (9)
MeOCH(CH2)I6CH=CH 2 and CH30(CH2)I9--CH 3.
I
CH3 (10) MeOCH2(CH 2)3CH=-CHCH2(CHDI2-CH3, (11)
MeOC(CH2)]9CH 3 and MeOC(CH=llsCH~--CH 2,
II 0
II 0
(12) MeOCH(CH2h0CH=CH 2 and MeO(CH.,)x3--CH ~, I CH 3 (13)
MeOC(CH2)23CH 3 and
I[ o
MeOC(CHx)22CH=CH>(14) MeO(CH2)27CH ~. tl o
1206
A. GOZLANand A. ZILKHA
chain. The structure of the product based on molecular weight and fragmentation is CH30--CH(CH2)sCH~---CH2.
I
CH 3 Peak 4. showed a molecular weight peak at m/e 200. The base peak was at m/e 45 which, together with a peak at m/e 59, suggests ions containing oxygen. The peak at m/e 168 (M--CH3OH) may be due to a methyl ether having a long chain. The cluster of peaks of the hydrocarbon fragmentations show the presence of a saturated chain; the smooth lowering in the strength of the peaks from C3-C4 onward points to the presence of a linear chain. The structure of the compound is CH30(CH2)II--CH 3. Peak 5. The molecular peak at m/e 198 was accompanied by peaks at m/e 166 (M--CH3OH), 45 basic peak +
(CH2=O--CH3)
CH3OCH2--(CH2)3--CH=CH--CHz--(CH2)4CH 3 82
CH2~-~-CH(CH2)I4COOCH 3.
Peak 9 (Fig. 6) is a homologue of peak 6 (Fig. 6) and is composed of a mixture of the following two methyl ethers: CH3OCH (CH2)I6CH=CH 2 and
I CH3
71
Peak 6 showed a weak molecular peak at m/e 228, peaks at m/e 197 (M-31), 74 (base peak from MacLafferty rearrangement of ester), 59 and 87. The fragmentation corresponds to a methyl ester of an unbranched saturated carboxylic acid CH3(CH2)II COOCH3. Peak 7 was identified as CH2=CH(CH2)t0 COOCH 3. Peak 6 o f G C on SE 30 (Fig. 6) is the two shoulders of peak 7 of GC on BDS (Fig. 5). It shows in the high mass ranges a peak at role 224 (probably M-32 where M =256) and a peak at role 222 (M-32 where M = 254), i.e. a mixture of two compounds. From the mass spectra and data for the lower homologues, the compounds are
Peak 10 (Fig. 6) is analogous to peak 8 (Fig. 5). Its highest peak is at m/e 278 which is M-32. Its structure is Peak 12 mol. peak at m/e 340 was identified as CH3OC(CH2)IgCH3.
II
O Peak I1 (Fig. 6) is a mixture of two methyl esters one saturated [m/e 311 (M-29) M-31 and M-43] and one unsaturated (m/e 338, M-31, M-32 and M-74), the structure of the latter being CH3OC(CH2)IsCH=CH2.
II
O Peak 12. The MS is similar to that of an alkane and an alkadiene and is analogous to that of peak 9 (Fig. 6). The peak corresponds to a mixture of CH3OCH--(CH 2)IOCH~--CH2
I CH3 M = 366 and
CH30--CH(CH2)I2CH=CH 2 and
CH30(CH2)23--CH3 M = 368
I CH3 CH3OCH2(CH 2)taCH 3(M = 256)
Peak 8. According to its position, this peak is a homologue of peak 5; their mass spectra resemble each other with peaks at m/e 45 and 82. Base peak at m/e 55 (instead of 45 with peak 5) and fragmentations at role 85 and role 99 for C, H2n,~ chains. The molecular peak is absent and the highest peak is at role 222 which is M-32 so that the molecular weight is 254 and the structure of the compound is: CH3OCH2--(CH2)3CH=CH--CH2--(CH2)8CH 3 45
82
127
Peak 9. Molecular peak at role 284 which is 5~o of the base peak at m/e 74, rearrangement peak of a methyl ester, / O H ] +" CH30--C. [ .
~CH2J
CH30(CH2)19--CH3.
CH3OCH2(CH2)3CH~CHCH2(CH2)12--CH3.
and 59. There were also relatively strong peaks at m/e 82 and m/e 71. The plausible structure of the product seems to be:
45
There was also a series of peaks at 59, 87, 101 up to 171 which are indicative of a methyl ester of a saturated long chain carboxylic acid [6]. The compound is CH3(CH2)IsCOOCH 3. Peak I0. Retention time and MS are the same as for peak 8 in the carboxylic acid mixture from before, weak mol. peak at 282, so the compound is
Peak 13. It was not possible to obtain the higher peaks in the MS because of the small amount of material but, according to the peaks at rn/e 55 (base), 43, 74, 87 and 101 and by analogy with peak 11 (Fig. 6), the compounds are: CH3OC(CH2)23CH3
II
O
and CH3OC(CHz)22CH=CH:
II
O Peak 14. No MS spectrum could be obtained but by analogy to lower homologues it may be CH30(CH2)27--CH 3 (Fig. 6).
Analysis of the benzene fraction There were no volatiles in this fraction and the product was analysed by i.r. and NMR. The i.r. spectrum showed strong peaks of the symmetric and assymetric C--H stretching vibrations of
1207
Polymerization of dicarboxylic acids It --CH2-groups at 2858 and 2930 cm ~, respectively, while the respective absorptions of the methyl groups appeared only as a shoulder at 2960 cm ~ indicating the preponderance of methylene groups over methyl groups. There were also the rocking vibrations of the --CH2-groups at 720 and at 730 cm L(weaker), the latter absorption indicating a certain degree of crystallinity in the (CH2),, chains [8]. These results show the presence of relatively long straight chains of methylene groups with a small amount of methyl groups. Absorptions at 1643 CA ~ together with absorptions at 910 and 990cm ] indicate the presence of vinyl - - C H = C H 2 double bonds and at 965 cm indicate the presence of trans-internal double bonds. There were absorptions for ester groups at 1740, 1780 and at 1360, 1440, 1260, 1120 (--OMe), 1170 and l l00cm ~ indicating the presence of three types of ester groups, Pi,-. methyl esters, internal ester groups between two aliphatic chains and 7-1actone. The 7-1actone is not 7-valerolactone, since this was not found in GC. NMR showed the following peaks, (integration values given in brackets): 6(ppm): 0.93 (CH3) (9); 1.27 (CH2) (70): 1.67 (CH2--/]-- to functional groups) besides 2.14 (--CH2-- ~ to C~---O or C = C ) (14): 3.23 (CH~O, - - C H 2 0 - - ) (5); 3.6
the presence of which was confirmed by anhydrous titration with KOCH~ in methanol. There were also peaks for methyl ester, methyl ether, internal ester groups and for - - C H = C H , at 1643, 910 and 990 cm ~but the latter were much weaker than in the benzene fraction, indicating their smaller amount. The NMR spectrum of the methanol fraction was analysed as for the benzene fraction: it was found to correspond to the following groups: (CH2)~4 {CHO,: X--(CH2)7--X, where X is a functional group such as C ~ O or C = C , (CH~OCH2--)3, (--Ctt~OC--)2, (CH3OC--)> O
O
( - - C H z C H 2 ) I , (COOH)2. It can be seen that, in the methanol fractiom the ratio of functional groups to the methylene groups is higher than in the benzene fraction, and the oxygen containing groups are also more pronounced. If" we join all the above partial structures, we obtain the structural formula C~tH980~ (tool. wt 950}. If we subtract from this structure the groups incorporated in the oligomers but not from adipic acid, i.e. 3CH30--, 2CH 3 - groups from CH;OC,
O
II
O
(CH3OC--) (3); 3.72 (CH2OC--)
II
/ (2); 4.6
O
/CH2--CH I\
[--CH
\
l/
X-o-co /
CH of 7-1actone) (1); 4.77, 4.99, 5.53, 6.06 ( - - C H = C H , ) besides 5.35 ( - - C H = C H - - ) (5). From the i.r. and NMR spectra, it can be concluded that the benzene fraction is composed of the following groups: (CH2)35-(CH3)3 where the CH2 groups are not attached to any functional group, (CH2)5 attached to the carbonyt group of ester or to a double bond, (CH~OCH,--)~, (CH3OC--)I, (--CU2OC-)-b
II
O
[I
O
l-7-1actone group, (CH2=CH)Ls and ( - - C H = CH-)-05 with a trans-configuration. It is difficult to give a structural formula to the oligomers, but the presence of (CH2)3s relative to the other groups is significant in indicating the extent of the straight Kolbe reaction.
Analysis of the methanol Jiaction In this fraction no volatiles were observed in GC on an SE 30 column up to 270'. The i.r. spectrum of this fraction resembles that of the benzene fraction with the following differences. There was no absorption for 7-1actone at 1780cm ~. The absorptions at 1000-1300cm ~ are not sharp and resemble those of a polyester, with maximum absorptions at 1100, 1120, 1170 and 1265cm t. There is a weak absorption from 3400 to 2500 cm ~ which, besides a shoulder at 1700 cm ~, is characteristic of COOH groups,
then the general structural formula reduces to C46Hs30~> Based on the ["act that the starting compound was adipic acid. this can be written as C40H83(CO2)6 or [(CH2)414[(CH2)4CO2]p This means that, on average, out of 10 molecules of adipic acid reacted to give the methanol fraction. 4 of them suffered decarboxylation of both COOH groups and 6 of them of only one. Therefore the percent decarboxylation is 6+(2x4) 2x10
x 100 = 70.
In summary, the separation of the non-volatiles (by chromatography} obtained in the electrolysis of adipic acid yielded 4 fractions. (1) The heptane fraction consisting of straight chain hydrocarbons, whether saturated or unsaturated, together with cyclic hydrocarbons. The extent of decarboxylation in this fraction was 100%. (2) The front-benzene fraction composed of methyl esters and methylethers of saturated and unsaturated straight aliphatic chains having structures such as CH3OC(CH?)4,, I--CH~,CH~OC{CH~),, O
,
O
- - C H = C H 2, CH30(CH2)4, , ]--CH~, etc. ~3) The benzene fraction composed of oligomers of relatively high molecular weight that were not volatile in GC. The oxygen content in this fraction is higher than in the previous fraction due to an increase in the ether, and methyl ester groups as well as to the presence of internal ester groups and ?,-lactone groups. The extent of decarboxylation in this fraction was 88.5. (4) The methanol fraction consisted of oligomers with a still higher content of oxygen, and the extent of decarboxylation was lower at 700;.
1208
A. GOZLAN and A. ZILKHA REFERENCES
1. A. Gozlan, G. Again, S. Vardi and A. Zilkha, Eur. Polym. J. 20, 759 (1984). 2. H. Keller and H. V. Halban, Heh~. chim. Acta 27, 1439 (1944). 3. Selected Mass Spectral Data, American Petroleum Research Institute, Project 44, Thermodynamics Research Center, Department of Chemistry, Univ. College Station, Texas (1966). 4. H. Budzikiewicz, C. Djerassi and D. H. Williams, Mass
Spectrometry of Organic Compounds. Holden Day, San Francisco (1967). 5. F. W. McLafferty, Mass Spectrometry of Organic Ions, p. 447. Academic Press, New York (1963). 6. Ref. 5, p. 446. 7. Ref. 5, p. 401. 8. S. R. Heller and G. W. A. Milne, EPA/NIH, Mass Spectral Data Base, Vol. 1, p. 162 (1978). 9. M. Avram and Gh. D. Mateescu, Infrared Spectroscopy, p. 136. Wiley-lnterscience, New York (1972).