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The oxidation of oleic acid by permanganate in oil in water emulsion
Cofloids and Surfaces. 4 (1982) 33-41 Ekevier Scientific PrMishing Company,
Amsterdam -
Printed in The Netherlands
THE OXIDATION OF OLEIC ACID BY PEBMANGANATE WATER EMUISKON NISSIM GARTI
33
IN OIL iN
and EJLTAN AVNl
Cusalikstilute of Apptr’ed Chemistry. School of Applied The Hebrew Uniuersify of Jerusalem. Jerusatem (Ismel)
Science and Technology.
(Received November 14th. 1980; accepted in final form April 29th. 1981) ABSTRACT The oxfdatton OPoleic acid and the cleavage of the carbon-carbon double bond was achieved using potassium permanganate added to oil in water emulsion, The best emuMPier to enable the oxldatton and cleavage of the doublet bond was
polyoxyethytanelauryl ether (HLD 16.3) which formed the best emulsion wrlh the
smaller droplets, The oxtdatlon ts controlled hy parameters afFecting emulsion stability. Increasing the concentrations of emulsifier or oxidizing agent improves the otetc acZd conversion
and axeIaakacid formation,
emulsion
Poor stirring, low HLB’s, high oil phase content and poor
preparation decrease the yteelds_
INTRODUCTION OIeic acid can be oxidized by any of a wide variety of common oxidants including percbloric acid, chramk acid, potassium permanganate, performic acid, peracetic acid, alkaline hydrogen peroxide, osmfum tetra oxide and others [l]. Movt miId oxidizing agents wir1yield dihydroxystearic together with ketohydroxy- and dikatosi%ric acids when the reaction is carried out in aqueous diIute solutions, When cleavage of the carbon-carbon doubIe bond to form azaleic (HOOC
(CHt),COOH)
or pekugonic (CHa (CH&COOH)
acids is required, more drastic
conditions are needed and oxidation is achieved with nitric acid, ozone or the above mentioned oxidants in a combination with other oxidizing reagents
and cosoIvents [2]. The oxidation
of oleic acid with
permanganate
has been studied
by several
investigators [3-G] and was found to yieId mainly dihydroxy-, ketohydroxyand diketostearic acids as a function of the applied pH [6 3. Many attempts to improve the permanganate oxidation have been made including the use of crown ethers [7J and phase-transfer-catalysis[S-11]. For example, it has heen reported that a-oIefins are quantitatively oxidized by neutral aqueous potassium permanganate to carboxylic acids containing
0166-6622f82~0U0~600~$02.76~
1982
Etsevier Scientific
Publishing Company
34
one less carbon atom than the starting olefin, when the reactions aze carried out with either a crown ether [I] or quaternary ammonium salts [8, lo]. The hydroxyIation of cyclic olefins to cfss-diofswith basic potassium permanganate and quaternary mmonium phese-transfer-catalystshas been also investigated [9]. RecentIy an oxidation of methyl oleate to methyl pelargonate and monomethyl azalate in the presence of aqueous permanganate solution was obtained using a combination of phase-transfer-catalystand RuOl [12]. Surfactante and macromotecules are increasingly utilized as reaction media for some orgarlic reactions Tusuallycarried out in two phases with vigorous stirring. The r&es of reaction, products distribution, yields and in some cases stereochemistzyare affected 1131. The only oxidation reaction in micelIar system that wae studied in connection to the function of the emulsifier and its concentxation is the auto-oxidation of ]inoIeic acid [14]. The reaction site was postulated to be the hydrocarbon pIaced in the interior of the micel]. An interesting short report shows possible emulsion oxidation of cyctoolefins using aqueous alkaline hydrogen peroxide to give at,o -alkanedicarboxyhc acids in a one-s&p process, generally in good yields CM]. Yet, the study does not give any details concerning the emulsion formation and stability or other parameters affecting the reaction. In the couxse of our search for possible organic reactions to be carried out in emuMona, ming as reaction medium, we wish to report the oxidation of oleic acid by permanganate in emufsion; facilitating cleavage of the carboncarbon double bond and the formation of the dibasic azaleic acid. The parameters affecting the emuIsian skbility are studied in connection with product yields; rates of reaction and products distribution. EXPERIMENTAL
ilfatetiws Technical grade obic acid (99% fatty acids) containing 80% okk and 20% of stearic and palmitic a&s (as anaXyzedby gas-liquid chromatography) tram bferck was us44 for all oxidation processes. Potassium permanganate analar pure from BDH was used without any further puriWation. Pure azaleic and pelargonic acids were used ax atarnfardsfor identification and quantitative evaIuation of the product obtained in each reaction. 9,10Dihydroxystearic, 9,10-diketostearic and 9,lMcetohydroxystearic acids were identified in the product mixture using standard analytical methods as d&bed in the early literature [6]. Non-ionic emulsifiers, commer&lIy available from Atlas Euopel S.p.A were used. Three main groups of emulsifiers served for emulsifying ofeic acid in water (o/w emulsion); poSyoxyethylene ethers of long-chain fatty alcohols (“Brijs”), polyoxyetbylene esters of long-chain fatty acids (“My@“), longchain carboxylic acid esters of polyoxyethylenated &&Gol, sorbitan, or isosorbides (Yweens”)r
36
Emulsion formation Prior to any oxidation reaction an e.nuIsion between the oleic acid and the water was formed using variws amounts of t;everaI combinations of emulsifiers with stirring at elevated temperatures (for details see Table 1). The em&ion was cooled to room temperature and passed through a Silverson homogenizer to reduce the particle size of the em&ion dropbts. The emuIsion stability was tested using standard methods such as centtifugation, incubation at 3fi”C and estimation of the particle size distribution by counting the dropIets under m optical CarI-Zeiss microscope (magn_ 800-1000).
TABLE
1
Pmducts distribution obtained fram oteic acid oxidatbn with permanganate carried out tn oil in water emuMon, using Etij XI (HLB 16.9) as emuhifier Reaction conditions: 10-C. mechanitial rtirring at 1200 rpm, H h. __-_ Prepa- WC% Wt.% Mare %= Yietd of products (mob %) KEInOJ ration oteIc b OkiC emuMconversion method acid Aaate fc DIot-, ketot-, UnidentiCier diketofied stearb products respectively
:II II II
11
S-7
2
S.7 8-S 15.0
2
6.7
2
a.5 0-S
8.7
79
3: S9 g-1
2.0 3.0
2 16 60 79 8s 80 56
0.5
37
2: 1:o
II
;x
1
11
:s
;2 28
3” 11 37 S8 42 45
3”
z
3: 56
s”
::
53
23,17,
11
14,20,13 12,18,10 12.18. 10 :fX; (: 2) :3’:; (49) 123) (31) (10) (21) 12,18,10 (1S) i 9) ( 8)
9 0
2 1x 8 0 a 9 1 8 7 1 10 : f
‘(I) Qfetc acid. water and emulsifier mired bogether; (II) oleic acid was added dropwise to aqueous emulsifier sotutbn; (III) aqueous emubifier sotutian was added dmpw&e to the ateb acid_ blKotar ratio. ‘WaIctition based on 100% oteic acid.
Reaction procedure The homogenized emulsion was transferred into a three-neck reactbl;r ves& which was placed in a thermostatic bath keeping the reaction mixture temperature betow ZO”C. The reaction vessel was equipped with a mec!,anical stirrer, pH electrode (EL-Hama, pH meter), and CD1 Inlet (to control the pH of the reaction during the oxidation). The reaction started rsdSzen the powdered potassium permanganate was added in one portion to the vigorously stirred emulsion. Samples were withdraw m from the reaction vessel at constant intervti and were quenched by bubblng SO2 to reduce the MnOl to soIuble MnSOJ salt and stop the oxidati
RESULTS In a control reaction frea oIeic acid was treated with aqueous potassium permanganate in the absence of the emulsifiers, in stirred two-phase r;aIution. There was no sig&icant oxidation, and the oleic acid remained unaffected. The emulsifiers used for the em&ion formation were based on mturated fatty acids and in a separate control test reaction they were found to be resistant to permanganate. A model em&ion based on 6.7 wt.% of oleic acid in water, 0.6 wt.% ethoxylated Iauryl ether {Stij 35) was prepared by adding the oleic acti to the aqueaus emulsifier sotution. Addition of the pulverized yennanganate (2:l to oleic acid) caused almost immediate disappearance of the permanganate r;oIor. The product was shown to contain large amounts of azaieic and pelargonic acids together with dihydroxy-, ketohydroxy- and diketo-stearic acids. The possibfity that the reaction is a regular alkahn~permanganate oxidation that occurs between the sduble portion of the fatty acid saIt (formed due to the perman ganate reduction Iiberating potassium hydroxide base) and the permanganate was ru!ed out in an experiment In which the pII of the reaction was maintained neutral by continuous simuItaneous bubbling of CO1 gas during the reaction and measun ‘ng of the pH during that procesS+ Figure 1 illustrates a typical pH behavior of the reaction without the CO* addition and in the presence of the bubbling gas. The drop In the gas consumption indicated that the reaction is terminated after 4-5 min- Figure 2
37
loo
50
0
0
246 tlmin)
. L 1
2
itminI
3
4%
Fig- 1, A typical pH behavior and CO, consumption during oxidation of oleic acid with permanganate in oil in water emulsion. Reaction conditions: 6.7% oleic acid in water. KBInO,lofr?ic acid molar ratio of 2,0-S% emuhifiet Brij 36, lO’C, vigorous stirring. pH or the reactionsystem without CO, IO), in the presence of bubbling CO, (~1 and the CO, flow rate during the reaction (a).
Fig, 2. The rate 00 conversion OF olelc acid and Che rate of Parrnation OCaLaleIc acid with time in a typ[cal permanganate oxidation 3nemubton: (A) conversion of deic acid; (I) formation of azalcic acid,
shows the ofeic disappearance
and the azaleic acid formation
a typical oxidation reaction, Three possible methods for prepating
with time in
the emulsion, prior to the oxidation process, were tested. From Table 1 it can be seen that, by addIng the oieic acid into the aqueous emulsifier solution, the best emursion is formed, having the smallest droplet size distribution. High oIeic acid conversion and azaleic acid formation were ob,tain&. When the emuIsion wag less stibfe, having bigger particles, the ohic acid was oxidized mainly into dihydroxy-stearic acid and only a very small portion was converted into the dibasic acid. The effect of the emulsifier concentration was examined using various amounts of Brij 35 (HLB = 16,9) and keeping other emulsion formation parameters constant. Figure 3 illustrates the rate of consumption of ofeic
oY’-,
thin)
X
emulsifier
,
Brij
35
Fig. 3. The rate of cocsumption of olek acid with time as a function of the emubifier (Brij 35) concentration, 0% emulsifier (0); 0.1% emulsifier (0); 0.6% emutsifier (a); 1.0% iXXMtbifier (VI; 2.0% emulsifier (A) and 3.0% emulsifier (I). Pig- 4. Percent conversion of oleic acid as a fun&ton of the emu.kifier (Srij 3s) concentration in oxfdatkn reaction having a KMnOJofeic acid ratfo of 2 and oteic acid concentratlon of 6.7% in water.
38
acid with tie_ The increasing amounts of emuIsifier enhance the oxidation reaction up to a maximum fom which even higher concentrations of em&itier will not increae the conversion of oleic acid but will further oxidize the intermediate products to azaleic acid (see aIso Fig. 4 and Table 1). Increasing the ratio of oxidizing agent to oleic acid from 1 to 6 caused a dramatic improvement to the consumption of oleic acid, and the formation of azakic acid (Figs. S and 6), together with some dihyclroxy- and ketohydroxystearic acids (Table 1).
t(minl
t (min)
Fig_ 5. The of& acid consumption with Unte aa a funchn of the tncreaslng amounts OF oxidant. KMnOJoteIc acfd ratto of 1 (0); 2 and 3 (A,#); 4 and 6 (0~0). Pig. 6. The azaalek acid famathm as a function of the Increasing amounts of oxidant. ~h~,bhdC add ratio of L (=); 0 [A); 3 (P); 4 (0); 6 {a}.
Emubification of the oIeic acid in higher oil phase ctincentrationst# = 0.057 k 0.16) was more difficuXtand as a resuft the emulsion was Lessstable with larger droplets. only Ss% of the oIeic acid were converted when # was 0.16 in comparison to 78.7% conversion when Q = 0.067 (see Table 1). The stirring effect was found to be very trfgnificautin this reaction. Figure 7 demonstrates rates of consumption of oleic acid as a function of the rate of stirring. The highly stirred systems were significantly more effective in the raleicacid oxidation_
Pig. 7. The sliming effect on the oleic acid commptbn In 6.7%ofi add, KbfnO,loIeic ratio of 2. When 0.6% SrJj 35 was used at 1000 RPM
39
Since if was reported in the comlriercial literature that the required HLB for the oleic acid emulsification was ca. 16, the Brij 35 was chosen to serve as a single emulsifier for most of the oxidation reactions. The search for the best required HLB for such emulsification was achieved by testing a variety of emulsifier combinations at various HLB’s. When the hydrophilic portion of the emulsifier was elongated by adding more polyoxyethylene groups higher HLB values were obtained, All HLB’s higher than 15 were found suitable for this reaction as can be seen from Fig. 8 and Table 2. Emulsifiers TABLE
2
The effect of the nature of the emuhifier aad required HLB on the aleic acid oxidation in
emubkn oxMatIonby permanganate
KMnOJoCelc = 2; 5.7% oleic in water; 0.5 wt.% emulsifier; 10°C; 30 min; 1200 rpm. HLg
Emulsifier
C!hemtcal comporitton --
Mole % of olelc acfd conversion
Btij 35
X6,9
FatyoxyethyleneCwcyl ether
78.7
Myrj $2
m-9
Polyoryathylene t *karate
72.5
Tween
16.7
f’olyoxyethylene zorbitan Iauryl ester
66.2
20
l
Myrj 49
15.0
Ibtyoxyefhylene s tearate
60.0
Myrj Sl
26*0
I’atyoxyethylene qtearate
71.8
Myr) 62
10.9
Potyoxyethylene &earate
72.6
M:vj 63
17*9
Pdyoxyethylene dearate
78.0
Myrj 59
18.8
Potyowyethykns
80.1
dearate
0s 0
k_
430 t~lnin3r acid consumptkn
1
as a function of the nature of the hydrophitic part of the = 16) (0); Myxj 51 (HLB = 16.0) (0); Myrj 62 (HLB = 16.9) (0); Myzj 63 (HLB - 17.9) (0); Myrj 69 (HLB - 18.8) (A). Pig. 0. Olek emukifkr. Myrj 49 (HLB
40
having HLB’s lower than 15 were found to be less effective. Among the emulsifiers having the same required KLB, (16.9). the Brij 35 (polyoxyethylene lauryl ether) was proven to be the best (Fig. 9).
t(min) Fig. 9. Azalelc acid forntatfion with time as the fun&on of the type ofemulsifter used In 6,7% okic acid, emdsbn KMnCB,lolekratio of 2 and 0.5%emuhifier. Span 20, (A); *een 21 (0 1; Myrj 49 (0,; tieen 20 (v)+
DISCUSSLON
The oxidation
of oleic acid by permanganate is illustrated in eq. (1):
‘OIYH CH~(CH#X CH,(CH&CO&i
= CH(CHl),CO~H + KO&(CJ$)~
-+ CH,QXC,),CH COrH
qH(o) -
CH(CH&
CO,H
4
(11
In order to achieve the formation of azaleic acid, at least a ~WQ-step reaction should take place, The permangauati molecuks shoutd intcwct for a relatively long period of time with the fatty acid which is situated in the interior part of the mlcelle without Ieaving it. The tzdsifier at the proper HLB will fam a reIatively stable emulsion with small drapleb, increasingsignificantly the contact Between the
permanganate and the oleic acid and keeping the formed intermediate at the interface. Thus, the parameters affecting ~muIsioonstabilrty such as type of surfactant, emulsifier HLB, emulsifier concentration, phase concentration and stirring will defect the ratt?of conversion and the product distribution. Therefore it can be clearly seen that by adding the oil into the aqueous phase smaller particles were formed, stabiIiziug the emulsion and causing higher conversion into azaleic acid. The emuIsifk~ having higher HLB values will result in better emulsions and will improve the yields of conversion into azaleic acid. The stirring will cause better contact between the emu&ion droplets and the soiuble permangauate motecuks which wili enhance the oxidation. Higher permaugauate
couc&trations
wilJ force most of the oleic acid to
undergo further oxidation and cleavage of the double bond will be achieved.
41
Thus wheq 6:l ratio is added most of the product will be azaleic acid. T-hisreaction, also not yet completely studied,opens a new area for investi* io new routes for mild oxidations gation which might lead in the futur,, that are, so far, difficult to carry out in two-phase systems. The emulsion technique will facilitate those reactions and make them possible. REFERENCES 1 N.O.V. Sonntag, in D. Swern (Ed.), “Baileyb Industrial Oil and Fat Products”, 4th edn. John Wifey and Sons. New York 1979. pp. 133. 2 K.B. Sharpless, J. Org. Chem., 39 (1974) 2314. 3 G. King, J. Chem. Sot., (1936) 1788. 4 R.S. hforrelt and E-0. Phillips. J. Sac. Chem. Ind., 57 (1938) 245. 5T.F. Hilditch and H. Plimmer, J. Chem. Sue., (1942) 2Q4. 6 J.E. Coleman, C. Ricciuti and 0. Swem, J. Am. Chem, Sot., 78 (1956) 5342.
VoL
1,
7 S.&f. StarIF, J. Am. Chem. Sac., 93 (1971) 195. 8 D.J. Sam, and H.B. Simmarw, J. Am. Chem. Sot., 94 (1972) 4024. 9 Bf. lbfakoaja and M. Wawryniewicz. Tetrahedron L&t., (1969) 4669. ZO W.P. Weher and J.P. Shepherd, Tetrahedron Lett.. (1972) 4907. 11 AM, Hertiott and I). Picker, Tetrahedron Lett., (1974) 1611. 12T.A. Foglta, P.A. Barr and A.J. Malloy, J. Am. Oil Chem. Sot., 54 (1977) 858A. 13 J.H. Fendter and E.J. Fettdler in %%taIysis in MIcelIar and Micromotecular Systems.” Academic Pre-, New York, 197L. 14 J, SwarbrIck and C.T. Rhodes, J. Pharm. Scf., 54 (1966). lb M.L. Fremery and E.K. PieIds, J. Org. Chem., 28 (1963) 2S37.
Amsterdam -
Printed in The Netherlands
THE OXIDATION OF OLEIC ACID BY PEBMANGANATE WATER EMUISKON NISSIM GARTI
33
IN OIL iN
and EJLTAN AVNl
Cusalikstilute of Apptr’ed Chemistry. School of Applied The Hebrew Uniuersify of Jerusalem. Jerusatem (Ismel)
Science and Technology.
(Received November 14th. 1980; accepted in final form April 29th. 1981) ABSTRACT The oxfdatton OPoleic acid and the cleavage of the carbon-carbon double bond was achieved using potassium permanganate added to oil in water emulsion, The best emuMPier to enable the oxldatton and cleavage of the doublet bond was
polyoxyethytanelauryl ether (HLD 16.3) which formed the best emulsion wrlh the
smaller droplets, The oxtdatlon ts controlled hy parameters afFecting emulsion stability. Increasing the concentrations of emulsifier or oxidizing agent improves the otetc acZd conversion
and axeIaakacid formation,
emulsion
Poor stirring, low HLB’s, high oil phase content and poor
preparation decrease the yteelds_
INTRODUCTION OIeic acid can be oxidized by any of a wide variety of common oxidants including percbloric acid, chramk acid, potassium permanganate, performic acid, peracetic acid, alkaline hydrogen peroxide, osmfum tetra oxide and others [l]. Movt miId oxidizing agents wir1yield dihydroxystearic together with ketohydroxy- and dikatosi%ric acids when the reaction is carried out in aqueous diIute solutions, When cleavage of the carbon-carbon doubIe bond to form azaleic (HOOC
(CHt),COOH)
or pekugonic (CHa (CH&COOH)
acids is required, more drastic
conditions are needed and oxidation is achieved with nitric acid, ozone or the above mentioned oxidants in a combination with other oxidizing reagents
and cosoIvents [2]. The oxidation
of oleic acid with
permanganate
has been studied
by several
investigators [3-G] and was found to yieId mainly dihydroxy-, ketohydroxyand diketostearic acids as a function of the applied pH [6 3. Many attempts to improve the permanganate oxidation have been made including the use of crown ethers [7J and phase-transfer-catalysis[S-11]. For example, it has heen reported that a-oIefins are quantitatively oxidized by neutral aqueous potassium permanganate to carboxylic acids containing
0166-6622f82~0U0~600~$02.76~
1982
Etsevier Scientific
Publishing Company
34
one less carbon atom than the starting olefin, when the reactions aze carried out with either a crown ether [I] or quaternary ammonium salts [8, lo]. The hydroxyIation of cyclic olefins to cfss-diofswith basic potassium permanganate and quaternary mmonium phese-transfer-catalystshas been also investigated [9]. RecentIy an oxidation of methyl oleate to methyl pelargonate and monomethyl azalate in the presence of aqueous permanganate solution was obtained using a combination of phase-transfer-catalystand RuOl [12]. Surfactante and macromotecules are increasingly utilized as reaction media for some orgarlic reactions Tusuallycarried out in two phases with vigorous stirring. The r&es of reaction, products distribution, yields and in some cases stereochemistzyare affected 1131. The only oxidation reaction in micelIar system that wae studied in connection to the function of the emulsifier and its concentxation is the auto-oxidation of ]inoIeic acid [14]. The reaction site was postulated to be the hydrocarbon pIaced in the interior of the micel]. An interesting short report shows possible emulsion oxidation of cyctoolefins using aqueous alkaline hydrogen peroxide to give at,o -alkanedicarboxyhc acids in a one-s&p process, generally in good yields CM]. Yet, the study does not give any details concerning the emulsion formation and stability or other parameters affecting the reaction. In the couxse of our search for possible organic reactions to be carried out in emuMona, ming as reaction medium, we wish to report the oxidation of oleic acid by permanganate in emufsion; facilitating cleavage of the carboncarbon double bond and the formation of the dibasic azaleic acid. The parameters affecting the emuIsian skbility are studied in connection with product yields; rates of reaction and products distribution. EXPERIMENTAL
ilfatetiws Technical grade obic acid (99% fatty acids) containing 80% okk and 20% of stearic and palmitic a&s (as anaXyzedby gas-liquid chromatography) tram bferck was us44 for all oxidation processes. Potassium permanganate analar pure from BDH was used without any further puriWation. Pure azaleic and pelargonic acids were used ax atarnfardsfor identification and quantitative evaIuation of the product obtained in each reaction. 9,10Dihydroxystearic, 9,10-diketostearic and 9,lMcetohydroxystearic acids were identified in the product mixture using standard analytical methods as d&bed in the early literature [6]. Non-ionic emulsifiers, commer&lIy available from Atlas Euopel S.p.A were used. Three main groups of emulsifiers served for emulsifying ofeic acid in water (o/w emulsion); poSyoxyethylene ethers of long-chain fatty alcohols (“Brijs”), polyoxyetbylene esters of long-chain fatty acids (“My@“), longchain carboxylic acid esters of polyoxyethylenated &&Gol, sorbitan, or isosorbides (Yweens”)r
36
Emulsion formation Prior to any oxidation reaction an e.nuIsion between the oleic acid and the water was formed using variws amounts of t;everaI combinations of emulsifiers with stirring at elevated temperatures (for details see Table 1). The em&ion was cooled to room temperature and passed through a Silverson homogenizer to reduce the particle size of the em&ion dropbts. The emuIsion stability was tested using standard methods such as centtifugation, incubation at 3fi”C and estimation of the particle size distribution by counting the dropIets under m optical CarI-Zeiss microscope (magn_ 800-1000).
TABLE
1
Pmducts distribution obtained fram oteic acid oxidatbn with permanganate carried out tn oil in water emuMon, using Etij XI (HLB 16.9) as emuhifier Reaction conditions: 10-C. mechanitial rtirring at 1200 rpm, H h. __-_ Prepa- WC% Wt.% Mare %= Yietd of products (mob %) KEInOJ ration oteIc b OkiC emuMconversion method acid Aaate fc DIot-, ketot-, UnidentiCier diketofied stearb products respectively
:II II II
11
S-7
2
S.7 8-S 15.0
2
6.7
2
a.5 0-S
8.7
79
3: S9 g-1
2.0 3.0
2 16 60 79 8s 80 56
0.5
37
2: 1:o
II
;x
1
11
:s
;2 28
3” 11 37 S8 42 45
3”
z
3: 56
s”
::
53
23,17,
11
14,20,13 12,18,10 12.18. 10 :fX; (: 2) :3’:; (49) 123) (31) (10) (21) 12,18,10 (1S) i 9) ( 8)
9 0
2 1x 8 0 a 9 1 8 7 1 10 : f
‘(I) Qfetc acid. water and emulsifier mired bogether; (II) oleic acid was added dropwise to aqueous emulsifier sotutbn; (III) aqueous emubifier sotutian was added dmpw&e to the ateb acid_ blKotar ratio. ‘WaIctition based on 100% oteic acid.
Reaction procedure The homogenized emulsion was transferred into a three-neck reactbl;r ves& which was placed in a thermostatic bath keeping the reaction mixture temperature betow ZO”C. The reaction vessel was equipped with a mec!,anical stirrer, pH electrode (EL-Hama, pH meter), and CD1 Inlet (to control the pH of the reaction during the oxidation). The reaction started rsdSzen the powdered potassium permanganate was added in one portion to the vigorously stirred emulsion. Samples were withdraw m from the reaction vessel at constant intervti and were quenched by bubblng SO2 to reduce the MnOl to soIuble MnSOJ salt and stop the oxidati
RESULTS In a control reaction frea oIeic acid was treated with aqueous potassium permanganate in the absence of the emulsifiers, in stirred two-phase r;aIution. There was no sig&icant oxidation, and the oleic acid remained unaffected. The emulsifiers used for the em&ion formation were based on mturated fatty acids and in a separate control test reaction they were found to be resistant to permanganate. A model em&ion based on 6.7 wt.% of oleic acid in water, 0.6 wt.% ethoxylated Iauryl ether {Stij 35) was prepared by adding the oleic acti to the aqueaus emulsifier sotution. Addition of the pulverized yennanganate (2:l to oleic acid) caused almost immediate disappearance of the permanganate r;oIor. The product was shown to contain large amounts of azaieic and pelargonic acids together with dihydroxy-, ketohydroxy- and diketo-stearic acids. The possibfity that the reaction is a regular alkahn~permanganate oxidation that occurs between the sduble portion of the fatty acid saIt (formed due to the perman ganate reduction Iiberating potassium hydroxide base) and the permanganate was ru!ed out in an experiment In which the pII of the reaction was maintained neutral by continuous simuItaneous bubbling of CO1 gas during the reaction and measun ‘ng of the pH during that procesS+ Figure 1 illustrates a typical pH behavior of the reaction without the CO* addition and in the presence of the bubbling gas. The drop In the gas consumption indicated that the reaction is terminated after 4-5 min- Figure 2
37
loo
50
0
0
246 tlmin)
. L 1
2
itminI
3
4%
Fig- 1, A typical pH behavior and CO, consumption during oxidation of oleic acid with permanganate in oil in water emulsion. Reaction conditions: 6.7% oleic acid in water. KBInO,lofr?ic acid molar ratio of 2,0-S% emuhifiet Brij 36, lO’C, vigorous stirring. pH or the reactionsystem without CO, IO), in the presence of bubbling CO, (~1 and the CO, flow rate during the reaction (a).
Fig, 2. The rate 00 conversion OF olelc acid and Che rate of Parrnation OCaLaleIc acid with time in a typ[cal permanganate oxidation 3nemubton: (A) conversion of deic acid; (I) formation of azalcic acid,
shows the ofeic disappearance
and the azaleic acid formation
a typical oxidation reaction, Three possible methods for prepating
with time in
the emulsion, prior to the oxidation process, were tested. From Table 1 it can be seen that, by addIng the oieic acid into the aqueous emulsifier solution, the best emursion is formed, having the smallest droplet size distribution. High oIeic acid conversion and azaleic acid formation were ob,tain&. When the emuIsion wag less stibfe, having bigger particles, the ohic acid was oxidized mainly into dihydroxy-stearic acid and only a very small portion was converted into the dibasic acid. The effect of the emulsifier concentration was examined using various amounts of Brij 35 (HLB = 16,9) and keeping other emulsion formation parameters constant. Figure 3 illustrates the rate of consumption of ofeic
oY’-,
thin)
X
emulsifier
,
Brij
35
Fig. 3. The rate of cocsumption of olek acid with time as a function of the emubifier (Brij 35) concentration, 0% emulsifier (0); 0.1% emulsifier (0); 0.6% emutsifier (a); 1.0% iXXMtbifier (VI; 2.0% emulsifier (A) and 3.0% emulsifier (I). Pig- 4. Percent conversion of oleic acid as a fun&ton of the emu.kifier (Srij 3s) concentration in oxfdatkn reaction having a KMnOJofeic acid ratfo of 2 and oteic acid concentratlon of 6.7% in water.
38
acid with tie_ The increasing amounts of emuIsifier enhance the oxidation reaction up to a maximum fom which even higher concentrations of em&itier will not increae the conversion of oleic acid but will further oxidize the intermediate products to azaleic acid (see aIso Fig. 4 and Table 1). Increasing the ratio of oxidizing agent to oleic acid from 1 to 6 caused a dramatic improvement to the consumption of oleic acid, and the formation of azakic acid (Figs. S and 6), together with some dihyclroxy- and ketohydroxystearic acids (Table 1).
t(minl
t (min)
Fig_ 5. The of& acid consumption with Unte aa a funchn of the tncreaslng amounts OF oxidant. KMnOJoteIc acfd ratto of 1 (0); 2 and 3 (A,#); 4 and 6 (0~0). Pig. 6. The azaalek acid famathm as a function of the Increasing amounts of oxidant. ~h~,bhdC add ratio of L (=); 0 [A); 3 (P); 4 (0); 6 {a}.
Emubification of the oIeic acid in higher oil phase ctincentrationst# = 0.057 k 0.16) was more difficuXtand as a resuft the emulsion was Lessstable with larger droplets. only Ss% of the oIeic acid were converted when # was 0.16 in comparison to 78.7% conversion when Q = 0.067 (see Table 1). The stirring effect was found to be very trfgnificautin this reaction. Figure 7 demonstrates rates of consumption of oleic acid as a function of the rate of stirring. The highly stirred systems were significantly more effective in the raleicacid oxidation_
Pig. 7. The sliming effect on the oleic acid commptbn In 6.7%ofi add, KbfnO,loIeic ratio of 2. When 0.6% SrJj 35 was used at 1000 RPM
39
Since if was reported in the comlriercial literature that the required HLB for the oleic acid emulsification was ca. 16, the Brij 35 was chosen to serve as a single emulsifier for most of the oxidation reactions. The search for the best required HLB for such emulsification was achieved by testing a variety of emulsifier combinations at various HLB’s. When the hydrophilic portion of the emulsifier was elongated by adding more polyoxyethylene groups higher HLB values were obtained, All HLB’s higher than 15 were found suitable for this reaction as can be seen from Fig. 8 and Table 2. Emulsifiers TABLE
2
The effect of the nature of the emuhifier aad required HLB on the aleic acid oxidation in
emubkn oxMatIonby permanganate
KMnOJoCelc = 2; 5.7% oleic in water; 0.5 wt.% emulsifier; 10°C; 30 min; 1200 rpm. HLg
Emulsifier
C!hemtcal comporitton --
Mole % of olelc acfd conversion
Btij 35
X6,9
FatyoxyethyleneCwcyl ether
78.7
Myrj $2
m-9
Polyoryathylene t *karate
72.5
Tween
16.7
f’olyoxyethylene zorbitan Iauryl ester
66.2
20
l
Myrj 49
15.0
Ibtyoxyefhylene s tearate
60.0
Myrj Sl
26*0
I’atyoxyethylene qtearate
71.8
Myr) 62
10.9
Potyoxyethylene &earate
72.6
M:vj 63
17*9
Pdyoxyethylene dearate
78.0
Myrj 59
18.8
Potyowyethykns
80.1
dearate
0s 0
k_
430 t~lnin3r acid consumptkn
1
as a function of the nature of the hydrophitic part of the = 16) (0); Myxj 51 (HLB = 16.0) (0); Myrj 62 (HLB = 16.9) (0); Myzj 63 (HLB - 17.9) (0); Myrj 69 (HLB - 18.8) (A). Pig. 0. Olek emukifkr. Myrj 49 (HLB
40
having HLB’s lower than 15 were found to be less effective. Among the emulsifiers having the same required KLB, (16.9). the Brij 35 (polyoxyethylene lauryl ether) was proven to be the best (Fig. 9).
t(min) Fig. 9. Azalelc acid forntatfion with time as the fun&on of the type ofemulsifter used In 6,7% okic acid, emdsbn KMnCB,lolekratio of 2 and 0.5%emuhifier. Span 20, (A); *een 21 (0 1; Myrj 49 (0,; tieen 20 (v)+
DISCUSSLON
The oxidation
of oleic acid by permanganate is illustrated in eq. (1):
‘OIYH CH~(CH#X CH,(CH&CO&i
= CH(CHl),CO~H + KO&(CJ$)~
-+ CH,QXC,),CH COrH
qH(o) -
CH(CH&
CO,H
4
(11
In order to achieve the formation of azaleic acid, at least a ~WQ-step reaction should take place, The permangauati molecuks shoutd intcwct for a relatively long period of time with the fatty acid which is situated in the interior part of the mlcelle without Ieaving it. The tzdsifier at the proper HLB will fam a reIatively stable emulsion with small drapleb, increasingsignificantly the contact Between the
permanganate and the oleic acid and keeping the formed intermediate at the interface. Thus, the parameters affecting ~muIsioonstabilrty such as type of surfactant, emulsifier HLB, emulsifier concentration, phase concentration and stirring will defect the ratt?of conversion and the product distribution. Therefore it can be clearly seen that by adding the oil into the aqueous phase smaller particles were formed, stabiIiziug the emulsion and causing higher conversion into azaleic acid. The emuIsifk~ having higher HLB values will result in better emulsions and will improve the yields of conversion into azaleic acid. The stirring will cause better contact between the emu&ion droplets and the soiuble permangauate motecuks which wili enhance the oxidation. Higher permaugauate
couc&trations
wilJ force most of the oleic acid to
undergo further oxidation and cleavage of the double bond will be achieved.
41
Thus wheq 6:l ratio is added most of the product will be azaleic acid. T-hisreaction, also not yet completely studied,opens a new area for investi* io new routes for mild oxidations gation which might lead in the futur,, that are, so far, difficult to carry out in two-phase systems. The emulsion technique will facilitate those reactions and make them possible. REFERENCES 1 N.O.V. Sonntag, in D. Swern (Ed.), “Baileyb Industrial Oil and Fat Products”, 4th edn. John Wifey and Sons. New York 1979. pp. 133. 2 K.B. Sharpless, J. Org. Chem., 39 (1974) 2314. 3 G. King, J. Chem. Sot., (1936) 1788. 4 R.S. hforrelt and E-0. Phillips. J. Sac. Chem. Ind., 57 (1938) 245. 5T.F. Hilditch and H. Plimmer, J. Chem. Sue., (1942) 2Q4. 6 J.E. Coleman, C. Ricciuti and 0. Swem, J. Am. Chem, Sot., 78 (1956) 5342.
VoL
1,
7 S.&f. StarIF, J. Am. Chem. Sac., 93 (1971) 195. 8 D.J. Sam, and H.B. Simmarw, J. Am. Chem. Sot., 94 (1972) 4024. 9 Bf. lbfakoaja and M. Wawryniewicz. Tetrahedron L&t., (1969) 4669. ZO W.P. Weher and J.P. Shepherd, Tetrahedron Lett.. (1972) 4907. 11 AM, Hertiott and I). Picker, Tetrahedron Lett., (1974) 1611. 12T.A. Foglta, P.A. Barr and A.J. Malloy, J. Am. Oil Chem. Sot., 54 (1977) 858A. 13 J.H. Fendter and E.J. Fettdler in %%taIysis in MIcelIar and Micromotecular Systems.” Academic Pre-, New York, 197L. 14 J, SwarbrIck and C.T. Rhodes, J. Pharm. Scf., 54 (1966). lb M.L. Fremery and E.K. PieIds, J. Org. Chem., 28 (1963) 2S37.