- Email: [email protected]
Chromatography of monomers
Jownal of Chromatography, 325 (1985) 367-378 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands CHROM. 17 610
CHROMATOGRAPHY
OF MONOMERS
II*. GLASS CAPILLARY GAS CHROMATOGRAPHY ESTERS OF ACRYLIC AND METHACRYLIC ACIDS
OF Cr-C1s
ALKYL
ALES HORNA* and JAN TABORSKq Department of Analytical Chemistry, University of Chemical Technology, 532 10 Pardubice (Czechoslovakia) OLDRICH DUFKA and PAVEL MATOUSEK Research Institute for Synthetic Resins and Luquers, 532 07 Pardubice (Czechoslovakia) and JAROSLAV CHUtiCEK Department of Analytical Chemistry, University of Chemical Technology, 532 10 Pardubice (Czechoslovakia) (Received January 25th, 1985)
SUMMARY
Retention indices of 38 acrylate and methacrylate monomers at different column temperatures are reported. The temperature dependences of the retention indices and the incremental effects of the methylene group were determined on non-polar (OV-101, SE-54) and a polar (SP-1000) capillary column, operated isothermally between 80 and 200°C.
INTRODUCTION
Acrylic and methacrylic acid esters are produced on a large scale for a number of technological applications. However, these compounds have associated health hazards and environmental effects. The importance of chromatography, especially gas chromatography (GC), in the analysis of acrylates and methacrylates has grown considerably since the 1970’s. Thus, GC is now the most frequently used method for the analysis of such monomers. More than 100 papers have been published on the GC of individual aliphatic alkyl esters of acrylic and methacrylic acids. However, there are few reports dealing with the GC of long-chain alkyl acrylates and methacrylates’. Gas chromatographic studies of homologous series of C1-C6 alkyl esters of acrylic and methacrylic acids on packed columns have been published only by Haken and co-workers2p3. The present study concerns the effects on retention behaviour of both the coll
For Part I, see ref. 4.
0021-9673/85/SO3.30
0
1985 Elsevier Science Publishers B.V.
368
A. HORNA et al.
umn temperature and the number of carbon atoms in the alkyl chain for Cr-Cis alkyl esters of acrylic and methacrylic acids on non-polar (OV-101, SE-54) and polar (SP-1000) capillary columns at temperatures between 80 and 200°C. EXPERIMENTAL
The esters, either prepared in the laboratory or of commercial origin, were characterized as previously reported4.GC analyses were carried out on a Varian Model 3700 instrument equipped with a flame ionization detector. The injector and detector temperatures were 200 and 25o”C, respectively, for the higher alkyl esters. The glass capillary columns used were a laboratory-made OV-101 (19 m x 0.28 mm I.D.), SE-54 (30 m x 0.24 mm I.D.) supplied by Supelco (Bellefonte, PA, U.S.A.) and SP-1000 (46 m x 0.23 mm I.D.) supplied by SGE (North Melbourne, Australia). Nitrogen was used as carrier gas with a splitting ratio of cu. 1:lOO. The column temperatures used were 80 and 12o’C with both injector and flame ionization detector operated at 2OO“C,and 170 and 200°C with injector and detector temperatures of 25o”C, respectively, for analysis of higher alkyl esters. Retention times were measured from the time of sample injection by a reporting integrator Autolab System IV (Spectra-Physics). The retention indices were calculated off-line using a TI-58C calculator, the dead time being first determined using the retention of methane. The average values of the retention indices presented were calculated from five to ten measurements. RESULTS AND DISCUSSION
The retention indices of all 38 Ci-Cis alkyl esters of acrylic and methacrylic acids examined are summarized in Tables I-III. The retention indices were determined on non-polar OV-101 and SE-54 phases (Tables I and II) and on polar SP1000 (Table III) at the following column temperatures: 80 and 12o’C for C1-C6 nalkyl and CJ-Cs isoalkyl esters; 170 and 2Oo’C for C&Cl0 n-alkyl and 2-ethylhexyl esters and at 200°C for Ci2, Ci4, Cl6 and C1s n-alkyl esters. In addition to the retention indices (I) of the studied monomers, standard deviations are shown and the increments per methylene group, dZ(CH2), and temperature dependence of the retention indices expressed by lO(dZ/dT) were calculated. Generally, considering the data determined on all phases used, it can be stated that the retention indices of the studied acrylates and methacrylates are temperature dependent. However, it is evident that the magnitude of the shifts, due to a change in column temperature, strongly varies both with the individual ester and the polarity of the stationary phase. On non-polar OV-101 (Table I) within the temperature range considered, the retention indices of C1-Cs alkyl esters of acrylic and methacrylic acids slightly decrease with increasing temperature. However, in the case of higher (C,-CiO) alkyl acrylates and methacrylates, the temperature dependence of the retention indices can be considered to be insignificant within the precision of the measurements. On SE-54 (Table II) the retention indices of Cl-C4 n-alkyl acrylates increase strongly with increasing column temperature, although the retention indices of the other lower esters, with the exceptions of isohexyl acrylate and methacrylate, slightly
. CHROMATOGRAPHY
OF MONOMERS.
369
II.
decrease. The retention indices of higher (C&&J alkyl esters of acrylic acid seem to be more sensitive to temperature on SE-54 than those of the corresponding methacrylates. On polar SP-1000 (Table III) the retention indices of all acrylates and methacrylates studied increase with increasing column temperature. The shifts in the retention indices of acrylates and methacrylates are more pronounced than those on the non-polar phases OV-101 and SE-54. Considering the retention index contribution per methylene group (Tables IIII) in the alkyl chain of the esters, the correlation between retention and structure was examined. With higher (C&is) alkyl esters of acrylic and methacrylic acids the dZ(CH2) values, calculated as the difference between the retention indices of two successive members of the homologous series (Fig. l), vary only slightly from the value of 100 on the non-polar phases OV-101 and SE-54 as well as on the polar SP-1000. These values are also comparable to the values of the slope of linear plots (Table IV) obtained by linear regression analysis of the dependence of the retention index on the number of carbon atoms in the alkyl chain. The above patterns in retention behaviour are in agreement with the statement that “in any homologous series, the retention index of the higher members increases by 100 index units per methylene group introduced”5. However, considering the dZ(CH2) values for the short chain alkyl esters of acrylic and methacrylic acids (Tables I-III), the first members of the homologous series of both n-alkyl and isoalkyl esters exhibit considerably different values to the other higher members. The increments per methylene group calculated as the difference between the retention indices of the ethyl and methyl esters do not exceed 80 retention index units. On the other hand, when calculated as the difference in retention indices between the isobutyl and isopropyl esters the dZ(CH2) values vary from 111.l on OV-101 to 130.7 retention index units on polar SP-1000. Table IV lists the equations Z = m + pC determined by linear regression analysis of plots of retention index vs. the number of carbon atoms in the alkyl chain, C, for the esters studied. The correlation coefficients of the individual data points in relation to the line fitted to these points are also shown. The positive deviation of the methyl esters and the negative deviation of the isopropyl esters from the plot for higher members of the homologous series is apparent (Fig. 2) on the non-polar phases as well as on the polar one. Similar behaviour occurs with homologous series of aliphatic esters of halogenated and/or unhalogenated acid&‘. It should be explained in terms of the electronic interactions and the steric hindrances. However, trivial interpretations of the deviations of the methyl and isopropyl esters can be suggested by considering the number of C-H linkages of the a-carbon atom in the alkyl chain of the aliphatic esters. The methyl (l), ethyl and higher n-alkyl(2), isopropyl (3), isobutyl and higher isoalkyl (4) esters are conveniently represented as 0
0
0
II
II
R-C-O-CH2-H
(1)
CHJ
RKLO--C-H
R&H&H
(2)
0
CH3 I
I
R&-(CH,)+H
I CH,
CH3
(3)
(4)
OctYl Nonyl Dacyl Dodecyl Tetradecyl Hexadecyl cktad=yl 2-Ethylhexyl
PrOPYl Butyl Pentyl Hexyl Isopropyl Isobutyl 1sopenty1 Isohexyl Heptyl
Ethyl
Methyl
Acrylate
602.3 680.7 779.3 878.4 978.3 1077.1 726.1 838.5 941.3 1036.2
f f f f f f f f f f
0.8 0.6 0.7 0.1 0.8 0.6 0.5 0.4 0.3 0.3
78.4 98.6 99.1 99.9 98.8
112.4 102.8 94.9
-
598.4 677.8 776.6 876.2 975.7 1075.2 725.2 836.3 939.5 1036.1
f f f f f f f f f f
1.0 1.2 0.4 0.7 0.5 0.3 0.4 0.5 0.4 0.7
I f S.D.
I f S.D.
AI(CH2)
T = 120°C
T=81PC
79.4 98.8 99.6 99.5 99.5 111.1 103.2 96.6
-
AI(CHd -1.0 -0.7 -0.2 -0.6 -0.7 -0.5 -0.2 -0.6 -0.5 0.0
lO(AI/AT) (80 vs. 120-C)
f f l f
0.5 0.3 0.2 0.2
1214.3 f 0.2
1173.4 1273.3 1373.3 1473.5
1073.0 f 0.5
-
100.4 99.9 100.0 100.2
-
100.6 100.6 100.5 100.5
1674.7 1875.8 ff 0.8 0.2 2076.8 f 0.6 2277.7 f 0.5
-
100.0 100.8 99.6
1215.7 f 0.2
100.6 1273.2 f 0.4 1374.0 f 0.4 1473.6 f 0.2
-
AI
1173.2 f 0.5
1072.6 f 0.6
I f S.D.
I f S.D. AI
T=2OO=C
T = 170°C
DE-
0.5
-
--
0.0 0.2 0.0
-0.1
-0.1
.
lO(AI/dT) (170 vs. 200-C)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 2oo’C ON OV-101
TABLE I
:
Y
;‘
z
8
?
0
13.2 95.4 98.8 98.3 99.0
116.8 100.8 94.3
-
696.2 767.5 864.5 963.8 1062.3 1161.3 805.7 925.1 1026.7 1122.1
f f f f f f f f f f
1.1 1.1 0.4 0.4 0.4 0.5 0.5 0.5 0.7 0.6 71.3 97.0 99.3 98.5 99.0 119.4 101.6 95.4
-
-0.8 -1.3 -0.9 -0.8 -0.1 -0.7 -1.4 -0.8 -0.6 -0.3 1257.2 1356.5 1456.5 1556.0
f f f f
0.5 0.3 0.2 0.2
1158.0 f 0.3
1295.4 f 0.2
0.8 0.5 0.6 0.7 0.7 1.0 0.5 0.5 0.7 0.5
-
f f f f f f f f f f
OCtadeJJyl 2-Ethylhexyl
699.5 712.1 868.1 966.9 1065.2 1164.2 811.3 928.1 1028.9 1123.2
Dccyl Dodecyl Tetradeql Hexadecyl
my1 Nonyl
Heptyl
ROPYl Butyl penty1 Hexyl Isopropyl Isobutyl 1sopenty1 Isohexyl
Methyl Ethyl
Methacrylate
-
99.2 99.3 100.0 99.5
-
1257.3 1357.1 1457.3 1556.6 1756.5 1957.6 2158.2 2358.6 1296.8
f f f f f f f f f
0.5 0.2 0.3 0.1 0.1 0.3 0.3 0.5 0.3
1157.9 f 0.4
99.4 99.8 100.2 99.3 100.0 100.6 100.3 100.2 -
-
0.0 0.2 0.3 0.2 0.5
0.0
P
F
g
g
g
4
$
3
F
iz
2.
.
Decyl Dodecyl Tetradecyl Hexackcyl Gctadecyl ZEthylbexyl
OctYl Nonyl
Heptyl
I=penty1 Isohexyl
PrOPYl Butyl penty1 Hexyl Isopropyl Isobutyl
Meibyl Ethyl
112.6 101.8 94.4
1.1 857.5 f 0.4 959.3 f 0.2 1053.7 f 0.2
0.1 0.1 0.2 0.2 0.2 0.1 0.7 0.3 0.1 0.1 116.5 105.0 96.7
-
74.2 92.5 90.9 90.2 99.4
-
f f f f f f f f f f
647.4 721.6 814.1 905.0 995.2 1094.6 731.2 853.7 958.7 1055.4
-
79.8 97.6 98.7 97.7 99.7
0.1
0.8 0.1 0.7 0.4 0.6
622.2 f 702.0 f 799.6 f 898.3 f 996.0 f 1095.7 f 744.9 f
AI(CHz)
I f S.D.
I f S.D.
AI(CH2)
T = 12O’C
T=WC
6.3 4.9 3.6 1.7 -0.2 -0.3 -1.9 -1.0 -0.2 0.4
IO(AI/AT) (80 vs. 120°C)
f f f f
0.6 0.5 0.3 0.3
1232.7 f 0.1
1196.4 1296.8 1396.7 1495.6
1095.3 f 0.2
I f S.D.
T = 17o’C
-
101.1 100.4 99.9 98.9 -
-
AI(CHz)
1201.4 1302.2 1400.9 1498.3 1695.7 1898.5 2099.0 2299.6 1233.2
f f f f f f f f f
1098.5 f
I f S.D.
0.7 0.8 0.7 1.0 0.4 1.0 0.9 0.7 0.9
1.4
T=ZOO’C
102.9 100.8 98.7 97.4 98.7 101.4 100.3 100.3
-
AI(CH2)
DE-
1.7 1.8 1.4 0.9 0.2
1.1
lO(AI/AT) (I 70 vs. 200-C)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 200°C ON SE-54
TABLE II
Decrl DodecYl Tetrad-1 Hexadecyl Octadecyl 2-Ethylbexyl
WY1 Nonyl
Methyl Ethyl ROPYl Butyl Penty1 Hexyl IwrOPYl Isobutyl 1Rqlenty1 Isohexyl Heptyl
Mefhacrylate
714.0 786.3 883.1 981.5 1079.7 1178.8 822.2 940.4 1042.5 1135.6
f f f f f f f f f f
0.2 0.1 0.3 0.2 0.2 0.2 0.2 0.1 0.2 0.2
72.3 96.8 98.4 98.2 99.1
118.2 102.1 93.1
-
712.0 783.2 880.7 919.9 1078.7 1178.1 818.5 939.6 1042.5 1137.7
f f f f f f f f f f
1.0 0.6 0.3 0.1 0.1 0.2 0.1 0.2 0.3 0.1 71.2 97.5 99.2 98.8 99.4 121.1 102.9 95.2
-0.5 -0.8 -0.6 -0.4 -0.3 -0.2 -0.9 -0.2 0.0 0.5 f f f rt
0.3 0.2 0.2 0.2
1311.7 f 0.0
1277.0 1376.6 1476.4 1575.8
1177.6 zk 0.2
-
-
-
-
99.4 99.6 99.8 99.4
1.0
f f f f
0.2 0.3 0.7 0.2
2318.3 f 0.1 1313.0 f 0.2
1576.4 1775.4 1976.7 2178.9
0.2 1377.5 1477.5 ff 0.4
1277.0 f 0.4
1179.8 f
97.2
-
99.7
98.9 99.5 100.7 101.1
100.5 100.0
-
z
E
3 3
0.4
5 0.2 -
%
2 0
0.3 0.4
0.0
0.7
Hexadejl octadecyl 2-Ethylhexyl
Dacyl DOdCCYl
Nonyl
mtYl
H-1
iz$’
Wvyl Isobutyl
pentyl Hay1
bPY1 Butyl
Methyl Ethyl
Acrylate
1169.1 1265.2 1361.6 993.7 1109.3 1217.3 1304.3
f f f f f f f
0.6 0.7 0.5 0.2 0.1 0.1 0.1
936.8 f 0.6 989.0 f 0.3 1073.9 f 0.6
95.2 96.1 96.4
52.2 84.9
115.6 108.0 87.0
-
940.9 993.3 1080.2 1177.6 1275.7 1373.9 995.1 1115.2 1226.3 1317.3
* f i f i f f f i f
I f S.D.
AI(CH,)
I f S.D.
1.1 1.1 1.0 1.2 1.4 0.7 0.0 0.1 0.5 0.3
12o’C
T=
T=MC
52.4 86.9 97.4 98.1 98.2 120.1 111.1 91.0
-
AI 1.0 1.1 1.6 2.1 2.6 3.1 0.4 1.5 2.3 3.3
lO(AI/AT) (80 vs. INTC)
f f f f
0.7 0.6 0.8
0.4
1494.6 f 0.3
1488.9 1589.9 1689.3 1788.9
1387.8 f 0.5
-
101.1 101.0 99.4 99.6 -
-
1494.9 1595.4 1695.4 1794.7 1996.1 2200.6 2401.5 2601.9 1500.1
f f f f l f f f f
0.9 0.8 0.6 0.5 0.5 0.7 0.7 0.8 0.7
1392.2 f 0.8
I f S.D.
I f S.D. Al(CH2)
T-2WC
T = 17OY
100.5 100.2
100.0 99.3 100.7 102.3
102.7 100.5
-
AI(CHd
DE-
1.8
2.0 1.9 -
2.0 1.8
1.5
10 (AI/AT) (170 vs. 2WC)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 200% ON SP-1000
TABLE III
..
9’
$ p !k
g
9
.
octadecyl ZEthylhexyl
Decyl WY1 Tetradecyl Hexadecyl
Heptyl %Yl Nonyl
ROPYl Butyl Penty1 Hexyl Isopropyl Isobutyl 1sopcllty1 Isohexyl
Methyl Ethyl
Methacrylate
1002.0 1043.4 1127.1 1219.8 1313.8 1408.9 1039.1 1162.4 1266.3 1351.8
f f f f f f l f f f
0.5 0.7 0.5 0.5 0.4 0.4 0.4 1.0 1.1 1.3
41.4 83.7 92.7 94.0 95.1
123.3 103.9 85.5
-
1010.1 1046.2 1136.9 1232.2 1327.7 1424.1 1042.6 1173.3 1280.8 1369.6
f f f f f f f f f f
0.3 0.5 0.7 0.8 0.8 0.8 0.9 0.9 0.6 0.8 36.1 90.7 95.3 95.5 96.4 130.7 107.5 88.8
-
2.0 0.7 2.5 3.1 3.5 3.8 0.9 2.7 3.6 4.5 f f f f
0.5 0.6 0.4 0.4
1540.5 f 0.1
-
1534.0 1632.2 1732.1 1832.7
1434.8 f 0.1
-
99.2 98.2 99.9 100.6
-
1538.2 1639.1 1739.7 1841.2 2042.3 2244.8 2446.5 2645.3 1546.2
f f f f f f f f l
0.6 0.6 0.7 0.4 0.8 0.7 0.8 0.4 0.4
1439.3 l 1.0
98.9 100.9 100.6 101.5 100.6 101.3 loo.9 99.4 -
-
1.9
2.3 2.5 2.8
a
F
g
8
’ .
376
A. HORNA
et al.
TABLE IV REGRESSION EQUATIONS FOR PLOTS OF RETENTION OF n-ALKYL AND ISOALKYL TERS AGAINST THE NUMBER OF CARBON ATOMS IN THE ALKYL CHAIN, C
Ester series
Phase
COlUmn temperatye (‘C)
Regresdon eqn.
Cl+ n-alkyl acrylates
ov-101
80 120 80 120 80 120
I = 482.0 + I = 478.7 + I = 504.8 + I = 535.3 + I = 797.2 + I = 797.5 +
80 120 80 120 80 120
I I I I I I
= = = = = =
444.4 437.8 466.3 451.7 722.8 714.4
+ 98.9 C + 99.9 C + 98.1 C + 100.9 c + 97.5 C + 101.1 c
0.9997 0.9998 0.9998 0.9997 0.9981 0.9984
80 120 80 120 80 120
2 Z I I Z I
= = = = = =
575.4 569.7 589.2 585.0 855.5 854.8
+ + + + + +
98.0 98.5 98.2 98.8 91.8 94.7
C C C C C C
0.99998 0.99999 0.99999 0.99999 0.9997 0.99994
80 120 80 120 80 120
I I I z I I
= = = = = =
539.0 532.1 551.5 544.7 786.7 783.8
+ + + + + +
97.6 98.5 97.6 99.1 94.7 98.2
C C C c C C
0.9998 0.9998 0.9996 0.9997 0.9984 0.9985
SE-54 SP-1000 Cd-C6 isoalkyl acrylates
ov-101 SE-54 SP-1000
C2Cb n-alkyl methacrylates
ov-101 SE-54 SP-1000
Cd-C, isoalkyl methacrylates
ov-101 SE-54 SP-1000
99.2 99.4 98.4 92.7 93.7 95.7
Es-
Correlation coe$icien1 C C C C C c
0.999998 0.999999 0.999994 0.9999 0.9997 0.9997
C6C1s n-alkyl acrylates
ov-101 SE-54 SP-1000
200 200 200
2 = 470.0 + 100.4 c I = 501.0 + 99.9 c I = 788.2 + 100.8 C
0.9999998 0.99999 0.999997
C&-f& n-alkyl acrylates
ov-101 SE-54 SP-1000
170 170 170
Z = 472.6 + 100.1 C I = 495.4 + 100.1 c I = 786.9 + 100.3 C
0.9999997 0.99999 0.999992
C6-C18 n-alkyl methacrylates
ov-101 SE-54 SP-1000
200 200 200
I = 556.5 + 100.1 C z = 577.5 + 100.0 c I = 834.0 + 100.7 C
0.999999 0.99999 0.999998
C.&i0 n-alkyl methacrylates
ov-101 SE-54 SP-1000
170 170 170
Z = 560.6 + I = 580.0 + Z = 838.0 +
0.999999 0.9999998 0.99999
99.5 C 99.6 C 99.4 C
where R is the acid chain and n 1,2,3,-** the number of methylene groups. A comparison of structures 1 and 2 reveals that three hydrogen atoms are bonded to the a-carbon atom in methyl esters (1) but only two in the ethyl and higher n-alkyl esters (2). Similarly, one hydrogen atom is bonded to the a-carbon atom of isopropyl esters (3), but two in isobutyl and higher isoalkyl esters (4). Thus, the number of hydrogen
,‘ CHROMATOGRAPHY OF MONOMERS. II.
I 2500
2000
1500
6lx
/' 60C 1000 6
7
6910
12
14
16
c 16
l/ T
I
/' 2
3
_.__ 4
5c
6
Fig. 1. Plots of the retention index, Z, of higher alkyl esters of acrylic and methacrylic acids versus the number of carbon atoms; C, in the n-alkyl chains at a cohtmn temperature of 2WC on non-polar OV101 and polar SP-1000 phases. Ester series: 1 = C6-Cls n-alkyl acrylates on OV-101; 2 = Cs-Crs n-alkyl methacrylates on OV-101; 3 = C6-Cls n-alkyl acrylates on SP-loo0, 4 = C&r8 n-alkyl methacrylates on SP-1000. Fig. 2. Plots of retention index, Z,of lower alkyl esters of acrylic and me&acrylic acids versus the number of carbon atoms, C, in the aliphatic chain at 8o’C on non-polar OV-101 and polar SP-1000 phases. Homologous series: 1 = isoalkyl acrylates on OV-101; 2 = n-alkyl acrylates on OV-101; 3 = isoalkyl methacrylates on OV-101; 4 = n-alkyl methacrylates on OV-101; 5 = isoalkyl acrylates on SP-loo0, 6 = isoalkyl methacrylates on SP-1000; 7 = n-alkyl acrylates on SP-loo0, 8 = n-alkyl methacrylates on SP-looo.
atoms bonded to the a-carbon atom of the alkyl chain can be correlated with the deviations of the methyl and isopropyl esters from the retention behaviour exhibited by homologous series of aliphatic n-alkyl and isoalkyl esters. CONCLUSIONS
The retention data summarized in this paper are useful for identification purposes in gas chromatography of the industrially important group of acrylate and methacrylate monomers under various operating conditions. Having studied the relationship between the retention index and molecular structure in homologous series of C1-C r8 alkyl esters of acrylic and methacrylic acids, deviations were found to be exhibited by the methyl and isopropyl esters. This behaviour can be explained by the different configuration at the a-carbon atom of the alkyl chains of these esters compared to those in the higher n-alkyl and isoalkyl esters.
* 378
A. HORNA et u/.
REFERENCES 1 2 3 4 5 6 7 8
M. Linkiewin, A. Szocik and H. Smolik, Chem. Ad (Warsaw), 26 (1981) 153. R. W. Germaine and J. K. Haken, J. Chromatogr., 43 (1969) 43. J. R. Ashesand J. K. Haken, J. Chromatogr., 111 (1975) 171. A. Homa, H. Pechovi, A. T&move and J. ChurGek, J. Chromatogr., 288 (1984) 230. E. Kov&i, A&m. Chromatogr., 1 (1965) 229. K. Kou&ek, L. Homovh and J. Chur&k, J. Chromarogr., 244 (1982) 142. K. Kombek, L. Homovfi, A. Homa and J. Churitik, J. Chromatogr., 262 (1983) 316. J. K. Haken, H. N. T. Hartley (nee Dinh) and D. Srisukh, Chromatographia, !7 (1983) 589.
CHROMATOGRAPHY
OF MONOMERS
II*. GLASS CAPILLARY GAS CHROMATOGRAPHY ESTERS OF ACRYLIC AND METHACRYLIC ACIDS
OF Cr-C1s
ALKYL
ALES HORNA* and JAN TABORSKq Department of Analytical Chemistry, University of Chemical Technology, 532 10 Pardubice (Czechoslovakia) OLDRICH DUFKA and PAVEL MATOUSEK Research Institute for Synthetic Resins and Luquers, 532 07 Pardubice (Czechoslovakia) and JAROSLAV CHUtiCEK Department of Analytical Chemistry, University of Chemical Technology, 532 10 Pardubice (Czechoslovakia) (Received January 25th, 1985)
SUMMARY
Retention indices of 38 acrylate and methacrylate monomers at different column temperatures are reported. The temperature dependences of the retention indices and the incremental effects of the methylene group were determined on non-polar (OV-101, SE-54) and a polar (SP-1000) capillary column, operated isothermally between 80 and 200°C.
INTRODUCTION
Acrylic and methacrylic acid esters are produced on a large scale for a number of technological applications. However, these compounds have associated health hazards and environmental effects. The importance of chromatography, especially gas chromatography (GC), in the analysis of acrylates and methacrylates has grown considerably since the 1970’s. Thus, GC is now the most frequently used method for the analysis of such monomers. More than 100 papers have been published on the GC of individual aliphatic alkyl esters of acrylic and methacrylic acids. However, there are few reports dealing with the GC of long-chain alkyl acrylates and methacrylates’. Gas chromatographic studies of homologous series of C1-C6 alkyl esters of acrylic and methacrylic acids on packed columns have been published only by Haken and co-workers2p3. The present study concerns the effects on retention behaviour of both the coll
For Part I, see ref. 4.
0021-9673/85/SO3.30
0
1985 Elsevier Science Publishers B.V.
368
A. HORNA et al.
umn temperature and the number of carbon atoms in the alkyl chain for Cr-Cis alkyl esters of acrylic and methacrylic acids on non-polar (OV-101, SE-54) and polar (SP-1000) capillary columns at temperatures between 80 and 200°C. EXPERIMENTAL
The esters, either prepared in the laboratory or of commercial origin, were characterized as previously reported4.GC analyses were carried out on a Varian Model 3700 instrument equipped with a flame ionization detector. The injector and detector temperatures were 200 and 25o”C, respectively, for the higher alkyl esters. The glass capillary columns used were a laboratory-made OV-101 (19 m x 0.28 mm I.D.), SE-54 (30 m x 0.24 mm I.D.) supplied by Supelco (Bellefonte, PA, U.S.A.) and SP-1000 (46 m x 0.23 mm I.D.) supplied by SGE (North Melbourne, Australia). Nitrogen was used as carrier gas with a splitting ratio of cu. 1:lOO. The column temperatures used were 80 and 12o’C with both injector and flame ionization detector operated at 2OO“C,and 170 and 200°C with injector and detector temperatures of 25o”C, respectively, for analysis of higher alkyl esters. Retention times were measured from the time of sample injection by a reporting integrator Autolab System IV (Spectra-Physics). The retention indices were calculated off-line using a TI-58C calculator, the dead time being first determined using the retention of methane. The average values of the retention indices presented were calculated from five to ten measurements. RESULTS AND DISCUSSION
The retention indices of all 38 Ci-Cis alkyl esters of acrylic and methacrylic acids examined are summarized in Tables I-III. The retention indices were determined on non-polar OV-101 and SE-54 phases (Tables I and II) and on polar SP1000 (Table III) at the following column temperatures: 80 and 12o’C for C1-C6 nalkyl and CJ-Cs isoalkyl esters; 170 and 2Oo’C for C&Cl0 n-alkyl and 2-ethylhexyl esters and at 200°C for Ci2, Ci4, Cl6 and C1s n-alkyl esters. In addition to the retention indices (I) of the studied monomers, standard deviations are shown and the increments per methylene group, dZ(CH2), and temperature dependence of the retention indices expressed by lO(dZ/dT) were calculated. Generally, considering the data determined on all phases used, it can be stated that the retention indices of the studied acrylates and methacrylates are temperature dependent. However, it is evident that the magnitude of the shifts, due to a change in column temperature, strongly varies both with the individual ester and the polarity of the stationary phase. On non-polar OV-101 (Table I) within the temperature range considered, the retention indices of C1-Cs alkyl esters of acrylic and methacrylic acids slightly decrease with increasing temperature. However, in the case of higher (C,-CiO) alkyl acrylates and methacrylates, the temperature dependence of the retention indices can be considered to be insignificant within the precision of the measurements. On SE-54 (Table II) the retention indices of Cl-C4 n-alkyl acrylates increase strongly with increasing column temperature, although the retention indices of the other lower esters, with the exceptions of isohexyl acrylate and methacrylate, slightly
. CHROMATOGRAPHY
OF MONOMERS.
369
II.
decrease. The retention indices of higher (C&&J alkyl esters of acrylic acid seem to be more sensitive to temperature on SE-54 than those of the corresponding methacrylates. On polar SP-1000 (Table III) the retention indices of all acrylates and methacrylates studied increase with increasing column temperature. The shifts in the retention indices of acrylates and methacrylates are more pronounced than those on the non-polar phases OV-101 and SE-54. Considering the retention index contribution per methylene group (Tables IIII) in the alkyl chain of the esters, the correlation between retention and structure was examined. With higher (C&is) alkyl esters of acrylic and methacrylic acids the dZ(CH2) values, calculated as the difference between the retention indices of two successive members of the homologous series (Fig. l), vary only slightly from the value of 100 on the non-polar phases OV-101 and SE-54 as well as on the polar SP-1000. These values are also comparable to the values of the slope of linear plots (Table IV) obtained by linear regression analysis of the dependence of the retention index on the number of carbon atoms in the alkyl chain. The above patterns in retention behaviour are in agreement with the statement that “in any homologous series, the retention index of the higher members increases by 100 index units per methylene group introduced”5. However, considering the dZ(CH2) values for the short chain alkyl esters of acrylic and methacrylic acids (Tables I-III), the first members of the homologous series of both n-alkyl and isoalkyl esters exhibit considerably different values to the other higher members. The increments per methylene group calculated as the difference between the retention indices of the ethyl and methyl esters do not exceed 80 retention index units. On the other hand, when calculated as the difference in retention indices between the isobutyl and isopropyl esters the dZ(CH2) values vary from 111.l on OV-101 to 130.7 retention index units on polar SP-1000. Table IV lists the equations Z = m + pC determined by linear regression analysis of plots of retention index vs. the number of carbon atoms in the alkyl chain, C, for the esters studied. The correlation coefficients of the individual data points in relation to the line fitted to these points are also shown. The positive deviation of the methyl esters and the negative deviation of the isopropyl esters from the plot for higher members of the homologous series is apparent (Fig. 2) on the non-polar phases as well as on the polar one. Similar behaviour occurs with homologous series of aliphatic esters of halogenated and/or unhalogenated acid&‘. It should be explained in terms of the electronic interactions and the steric hindrances. However, trivial interpretations of the deviations of the methyl and isopropyl esters can be suggested by considering the number of C-H linkages of the a-carbon atom in the alkyl chain of the aliphatic esters. The methyl (l), ethyl and higher n-alkyl(2), isopropyl (3), isobutyl and higher isoalkyl (4) esters are conveniently represented as 0
0
0
II
II
R-C-O-CH2-H
(1)
CHJ
RKLO--C-H
R&H&H
(2)
0
CH3 I
I
R&-(CH,)+H
I CH,
CH3
(3)
(4)
OctYl Nonyl Dacyl Dodecyl Tetradecyl Hexadecyl cktad=yl 2-Ethylhexyl
PrOPYl Butyl Pentyl Hexyl Isopropyl Isobutyl 1sopenty1 Isohexyl Heptyl
Ethyl
Methyl
Acrylate
602.3 680.7 779.3 878.4 978.3 1077.1 726.1 838.5 941.3 1036.2
f f f f f f f f f f
0.8 0.6 0.7 0.1 0.8 0.6 0.5 0.4 0.3 0.3
78.4 98.6 99.1 99.9 98.8
112.4 102.8 94.9
-
598.4 677.8 776.6 876.2 975.7 1075.2 725.2 836.3 939.5 1036.1
f f f f f f f f f f
1.0 1.2 0.4 0.7 0.5 0.3 0.4 0.5 0.4 0.7
I f S.D.
I f S.D.
AI(CH2)
T = 120°C
T=81PC
79.4 98.8 99.6 99.5 99.5 111.1 103.2 96.6
-
AI(CHd -1.0 -0.7 -0.2 -0.6 -0.7 -0.5 -0.2 -0.6 -0.5 0.0
lO(AI/AT) (80 vs. 120-C)
f f l f
0.5 0.3 0.2 0.2
1214.3 f 0.2
1173.4 1273.3 1373.3 1473.5
1073.0 f 0.5
-
100.4 99.9 100.0 100.2
-
100.6 100.6 100.5 100.5
1674.7 1875.8 ff 0.8 0.2 2076.8 f 0.6 2277.7 f 0.5
-
100.0 100.8 99.6
1215.7 f 0.2
100.6 1273.2 f 0.4 1374.0 f 0.4 1473.6 f 0.2
-
AI
1173.2 f 0.5
1072.6 f 0.6
I f S.D.
I f S.D. AI
T=2OO=C
T = 170°C
DE-
0.5
-
--
0.0 0.2 0.0
-0.1
-0.1
.
lO(AI/dT) (170 vs. 200-C)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 2oo’C ON OV-101
TABLE I
:
Y
;‘
z
8
?
0
13.2 95.4 98.8 98.3 99.0
116.8 100.8 94.3
-
696.2 767.5 864.5 963.8 1062.3 1161.3 805.7 925.1 1026.7 1122.1
f f f f f f f f f f
1.1 1.1 0.4 0.4 0.4 0.5 0.5 0.5 0.7 0.6 71.3 97.0 99.3 98.5 99.0 119.4 101.6 95.4
-
-0.8 -1.3 -0.9 -0.8 -0.1 -0.7 -1.4 -0.8 -0.6 -0.3 1257.2 1356.5 1456.5 1556.0
f f f f
0.5 0.3 0.2 0.2
1158.0 f 0.3
1295.4 f 0.2
0.8 0.5 0.6 0.7 0.7 1.0 0.5 0.5 0.7 0.5
-
f f f f f f f f f f
OCtadeJJyl 2-Ethylhexyl
699.5 712.1 868.1 966.9 1065.2 1164.2 811.3 928.1 1028.9 1123.2
Dccyl Dodecyl Tetradeql Hexadecyl
my1 Nonyl
Heptyl
ROPYl Butyl penty1 Hexyl Isopropyl Isobutyl 1sopenty1 Isohexyl
Methyl Ethyl
Methacrylate
-
99.2 99.3 100.0 99.5
-
1257.3 1357.1 1457.3 1556.6 1756.5 1957.6 2158.2 2358.6 1296.8
f f f f f f f f f
0.5 0.2 0.3 0.1 0.1 0.3 0.3 0.5 0.3
1157.9 f 0.4
99.4 99.8 100.2 99.3 100.0 100.6 100.3 100.2 -
-
0.0 0.2 0.3 0.2 0.5
0.0
P
F
g
g
g
4
$
3
F
iz
2.
.
Decyl Dodecyl Tetradecyl Hexackcyl Gctadecyl ZEthylbexyl
OctYl Nonyl
Heptyl
I=penty1 Isohexyl
PrOPYl Butyl penty1 Hexyl Isopropyl Isobutyl
Meibyl Ethyl
112.6 101.8 94.4
1.1 857.5 f 0.4 959.3 f 0.2 1053.7 f 0.2
0.1 0.1 0.2 0.2 0.2 0.1 0.7 0.3 0.1 0.1 116.5 105.0 96.7
-
74.2 92.5 90.9 90.2 99.4
-
f f f f f f f f f f
647.4 721.6 814.1 905.0 995.2 1094.6 731.2 853.7 958.7 1055.4
-
79.8 97.6 98.7 97.7 99.7
0.1
0.8 0.1 0.7 0.4 0.6
622.2 f 702.0 f 799.6 f 898.3 f 996.0 f 1095.7 f 744.9 f
AI(CHz)
I f S.D.
I f S.D.
AI(CH2)
T = 12O’C
T=WC
6.3 4.9 3.6 1.7 -0.2 -0.3 -1.9 -1.0 -0.2 0.4
IO(AI/AT) (80 vs. 120°C)
f f f f
0.6 0.5 0.3 0.3
1232.7 f 0.1
1196.4 1296.8 1396.7 1495.6
1095.3 f 0.2
I f S.D.
T = 17o’C
-
101.1 100.4 99.9 98.9 -
-
AI(CHz)
1201.4 1302.2 1400.9 1498.3 1695.7 1898.5 2099.0 2299.6 1233.2
f f f f f f f f f
1098.5 f
I f S.D.
0.7 0.8 0.7 1.0 0.4 1.0 0.9 0.7 0.9
1.4
T=ZOO’C
102.9 100.8 98.7 97.4 98.7 101.4 100.3 100.3
-
AI(CH2)
DE-
1.7 1.8 1.4 0.9 0.2
1.1
lO(AI/AT) (I 70 vs. 200-C)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 200°C ON SE-54
TABLE II
Decrl DodecYl Tetrad-1 Hexadecyl Octadecyl 2-Ethylbexyl
WY1 Nonyl
Methyl Ethyl ROPYl Butyl Penty1 Hexyl IwrOPYl Isobutyl 1Rqlenty1 Isohexyl Heptyl
Mefhacrylate
714.0 786.3 883.1 981.5 1079.7 1178.8 822.2 940.4 1042.5 1135.6
f f f f f f f f f f
0.2 0.1 0.3 0.2 0.2 0.2 0.2 0.1 0.2 0.2
72.3 96.8 98.4 98.2 99.1
118.2 102.1 93.1
-
712.0 783.2 880.7 919.9 1078.7 1178.1 818.5 939.6 1042.5 1137.7
f f f f f f f f f f
1.0 0.6 0.3 0.1 0.1 0.2 0.1 0.2 0.3 0.1 71.2 97.5 99.2 98.8 99.4 121.1 102.9 95.2
-0.5 -0.8 -0.6 -0.4 -0.3 -0.2 -0.9 -0.2 0.0 0.5 f f f rt
0.3 0.2 0.2 0.2
1311.7 f 0.0
1277.0 1376.6 1476.4 1575.8
1177.6 zk 0.2
-
-
-
-
99.4 99.6 99.8 99.4
1.0
f f f f
0.2 0.3 0.7 0.2
2318.3 f 0.1 1313.0 f 0.2
1576.4 1775.4 1976.7 2178.9
0.2 1377.5 1477.5 ff 0.4
1277.0 f 0.4
1179.8 f
97.2
-
99.7
98.9 99.5 100.7 101.1
100.5 100.0
-
z
E
3 3
0.4
5 0.2 -
%
2 0
0.3 0.4
0.0
0.7
Hexadejl octadecyl 2-Ethylhexyl
Dacyl DOdCCYl
Nonyl
mtYl
H-1
iz$’
Wvyl Isobutyl
pentyl Hay1
bPY1 Butyl
Methyl Ethyl
Acrylate
1169.1 1265.2 1361.6 993.7 1109.3 1217.3 1304.3
f f f f f f f
0.6 0.7 0.5 0.2 0.1 0.1 0.1
936.8 f 0.6 989.0 f 0.3 1073.9 f 0.6
95.2 96.1 96.4
52.2 84.9
115.6 108.0 87.0
-
940.9 993.3 1080.2 1177.6 1275.7 1373.9 995.1 1115.2 1226.3 1317.3
* f i f i f f f i f
I f S.D.
AI(CH,)
I f S.D.
1.1 1.1 1.0 1.2 1.4 0.7 0.0 0.1 0.5 0.3
12o’C
T=
T=MC
52.4 86.9 97.4 98.1 98.2 120.1 111.1 91.0
-
AI 1.0 1.1 1.6 2.1 2.6 3.1 0.4 1.5 2.3 3.3
lO(AI/AT) (80 vs. INTC)
f f f f
0.7 0.6 0.8
0.4
1494.6 f 0.3
1488.9 1589.9 1689.3 1788.9
1387.8 f 0.5
-
101.1 101.0 99.4 99.6 -
-
1494.9 1595.4 1695.4 1794.7 1996.1 2200.6 2401.5 2601.9 1500.1
f f f f l f f f f
0.9 0.8 0.6 0.5 0.5 0.7 0.7 0.8 0.7
1392.2 f 0.8
I f S.D.
I f S.D. Al(CH2)
T-2WC
T = 17OY
100.5 100.2
100.0 99.3 100.7 102.3
102.7 100.5
-
AI(CHd
DE-
1.8
2.0 1.9 -
2.0 1.8
1.5
10 (AI/AT) (170 vs. 2WC)
RETENTION INDICES, THEIR STANDARD DEVIATIONS, RETENTION INCREMENTS PER METHYLENE GROUP AND TEMPERATURE PENDENCE FOR ACRYLATE AND METHACRYLATE ESTERS AT COLUMN TEMPERATURES FROM 80 TO 200% ON SP-1000
TABLE III
..
9’
$ p !k
g
9
.
octadecyl ZEthylhexyl
Decyl WY1 Tetradecyl Hexadecyl
Heptyl %Yl Nonyl
ROPYl Butyl Penty1 Hexyl Isopropyl Isobutyl 1sopcllty1 Isohexyl
Methyl Ethyl
Methacrylate
1002.0 1043.4 1127.1 1219.8 1313.8 1408.9 1039.1 1162.4 1266.3 1351.8
f f f f f f l f f f
0.5 0.7 0.5 0.5 0.4 0.4 0.4 1.0 1.1 1.3
41.4 83.7 92.7 94.0 95.1
123.3 103.9 85.5
-
1010.1 1046.2 1136.9 1232.2 1327.7 1424.1 1042.6 1173.3 1280.8 1369.6
f f f f f f f f f f
0.3 0.5 0.7 0.8 0.8 0.8 0.9 0.9 0.6 0.8 36.1 90.7 95.3 95.5 96.4 130.7 107.5 88.8
-
2.0 0.7 2.5 3.1 3.5 3.8 0.9 2.7 3.6 4.5 f f f f
0.5 0.6 0.4 0.4
1540.5 f 0.1
-
1534.0 1632.2 1732.1 1832.7
1434.8 f 0.1
-
99.2 98.2 99.9 100.6
-
1538.2 1639.1 1739.7 1841.2 2042.3 2244.8 2446.5 2645.3 1546.2
f f f f f f f f l
0.6 0.6 0.7 0.4 0.8 0.7 0.8 0.4 0.4
1439.3 l 1.0
98.9 100.9 100.6 101.5 100.6 101.3 loo.9 99.4 -
-
1.9
2.3 2.5 2.8
a
F
g
8
’ .
376
A. HORNA
et al.
TABLE IV REGRESSION EQUATIONS FOR PLOTS OF RETENTION OF n-ALKYL AND ISOALKYL TERS AGAINST THE NUMBER OF CARBON ATOMS IN THE ALKYL CHAIN, C
Ester series
Phase
COlUmn temperatye (‘C)
Regresdon eqn.
Cl+ n-alkyl acrylates
ov-101
80 120 80 120 80 120
I = 482.0 + I = 478.7 + I = 504.8 + I = 535.3 + I = 797.2 + I = 797.5 +
80 120 80 120 80 120
I I I I I I
= = = = = =
444.4 437.8 466.3 451.7 722.8 714.4
+ 98.9 C + 99.9 C + 98.1 C + 100.9 c + 97.5 C + 101.1 c
0.9997 0.9998 0.9998 0.9997 0.9981 0.9984
80 120 80 120 80 120
2 Z I I Z I
= = = = = =
575.4 569.7 589.2 585.0 855.5 854.8
+ + + + + +
98.0 98.5 98.2 98.8 91.8 94.7
C C C C C C
0.99998 0.99999 0.99999 0.99999 0.9997 0.99994
80 120 80 120 80 120
I I I z I I
= = = = = =
539.0 532.1 551.5 544.7 786.7 783.8
+ + + + + +
97.6 98.5 97.6 99.1 94.7 98.2
C C C c C C
0.9998 0.9998 0.9996 0.9997 0.9984 0.9985
SE-54 SP-1000 Cd-C6 isoalkyl acrylates
ov-101 SE-54 SP-1000
C2Cb n-alkyl methacrylates
ov-101 SE-54 SP-1000
Cd-C, isoalkyl methacrylates
ov-101 SE-54 SP-1000
99.2 99.4 98.4 92.7 93.7 95.7
Es-
Correlation coe$icien1 C C C C C c
0.999998 0.999999 0.999994 0.9999 0.9997 0.9997
C6C1s n-alkyl acrylates
ov-101 SE-54 SP-1000
200 200 200
2 = 470.0 + 100.4 c I = 501.0 + 99.9 c I = 788.2 + 100.8 C
0.9999998 0.99999 0.999997
C&-f& n-alkyl acrylates
ov-101 SE-54 SP-1000
170 170 170
Z = 472.6 + 100.1 C I = 495.4 + 100.1 c I = 786.9 + 100.3 C
0.9999997 0.99999 0.999992
C6-C18 n-alkyl methacrylates
ov-101 SE-54 SP-1000
200 200 200
I = 556.5 + 100.1 C z = 577.5 + 100.0 c I = 834.0 + 100.7 C
0.999999 0.99999 0.999998
C.&i0 n-alkyl methacrylates
ov-101 SE-54 SP-1000
170 170 170
Z = 560.6 + I = 580.0 + Z = 838.0 +
0.999999 0.9999998 0.99999
99.5 C 99.6 C 99.4 C
where R is the acid chain and n 1,2,3,-** the number of methylene groups. A comparison of structures 1 and 2 reveals that three hydrogen atoms are bonded to the a-carbon atom in methyl esters (1) but only two in the ethyl and higher n-alkyl esters (2). Similarly, one hydrogen atom is bonded to the a-carbon atom of isopropyl esters (3), but two in isobutyl and higher isoalkyl esters (4). Thus, the number of hydrogen
,‘ CHROMATOGRAPHY OF MONOMERS. II.
I 2500
2000
1500
6lx
/' 60C 1000 6
7
6910
12
14
16
c 16
l/ T
I
/' 2
3
_.__ 4
5c
6
Fig. 1. Plots of the retention index, Z, of higher alkyl esters of acrylic and methacrylic acids versus the number of carbon atoms; C, in the n-alkyl chains at a cohtmn temperature of 2WC on non-polar OV101 and polar SP-1000 phases. Ester series: 1 = C6-Cls n-alkyl acrylates on OV-101; 2 = Cs-Crs n-alkyl methacrylates on OV-101; 3 = C6-Cls n-alkyl acrylates on SP-loo0, 4 = C&r8 n-alkyl methacrylates on SP-1000. Fig. 2. Plots of retention index, Z,of lower alkyl esters of acrylic and me&acrylic acids versus the number of carbon atoms, C, in the aliphatic chain at 8o’C on non-polar OV-101 and polar SP-1000 phases. Homologous series: 1 = isoalkyl acrylates on OV-101; 2 = n-alkyl acrylates on OV-101; 3 = isoalkyl methacrylates on OV-101; 4 = n-alkyl methacrylates on OV-101; 5 = isoalkyl acrylates on SP-loo0, 6 = isoalkyl methacrylates on SP-1000; 7 = n-alkyl acrylates on SP-loo0, 8 = n-alkyl methacrylates on SP-looo.
atoms bonded to the a-carbon atom of the alkyl chain can be correlated with the deviations of the methyl and isopropyl esters from the retention behaviour exhibited by homologous series of aliphatic n-alkyl and isoalkyl esters. CONCLUSIONS
The retention data summarized in this paper are useful for identification purposes in gas chromatography of the industrially important group of acrylate and methacrylate monomers under various operating conditions. Having studied the relationship between the retention index and molecular structure in homologous series of C1-C r8 alkyl esters of acrylic and methacrylic acids, deviations were found to be exhibited by the methyl and isopropyl esters. This behaviour can be explained by the different configuration at the a-carbon atom of the alkyl chains of these esters compared to those in the higher n-alkyl and isoalkyl esters.
* 378
A. HORNA et u/.
REFERENCES 1 2 3 4 5 6 7 8
M. Linkiewin, A. Szocik and H. Smolik, Chem. Ad (Warsaw), 26 (1981) 153. R. W. Germaine and J. K. Haken, J. Chromatogr., 43 (1969) 43. J. R. Ashesand J. K. Haken, J. Chromatogr., 111 (1975) 171. A. Homa, H. Pechovi, A. T&move and J. ChurGek, J. Chromatogr., 288 (1984) 230. E. Kov&i, A&m. Chromatogr., 1 (1965) 229. K. Kou&ek, L. Homovh and J. Chur&k, J. Chromarogr., 244 (1982) 142. K. Kombek, L. Homovfi, A. Homa and J. Churitik, J. Chromatogr., 262 (1983) 316. J. K. Haken, H. N. T. Hartley (nee Dinh) and D. Srisukh, Chromatographia, !7 (1983) 589.