Quantitative Hydrolysis-Gas Chromatographic Methods for the Determination of Selected Acids and Glycols in Polyesters B. J. Allen," G. M. Elsea, K. P. Keller, and H. D. Klnder Research Laboratories, Tennessee Eastman Company, Division of Eastman Kodak Company, Kingsport, Tennessee 37662
The objective of this work was to develop precise quantltative methods of analysis for determining repeat units of polyesters. These methods have In common an alkaline hydrolysis of polyesters followed by gas chromatographic determination of the glycols and acids produced from the hydrolyses. I n order to obtain rapid chromatographic analyses, trimethylsiiyl derivatives of the glycols and acids were formed by a reaction with N,O-bis(trimethyisiiyi)trifluoracetamide. The relative standard devlation varies from 0.8 % for the determination of 1,Cbutanedioi to approximately 2 % for 1,Ccyclohexanedlmethanol. For the determination of different concentrations of isophthaiic acid, the standard deviation varies from 0.7 to 2.4 % . These methods provide rapid and precise determinations for selected acids and glycols in polyesters.
Several methods have been described for determining the diethylene glycol content of poly(ethy1ene terephthalate) (PET) (1-3). These methods have in common the decomposition of the polyester through alkaline hydrolysis or hydrazinolysis followed by the determination of the diethylene glycol content by titration or gas chromatographic methods (4-8). However, none of these methods describe the quantitative determination of other glycol or acid content of polyesters. The objective of this work was to develop a precise, accurate method to determine the glycols and methyl ester end groups in PET and to develop a method for general use in determining glycols and acids in polyesters.
EXPERIMENTAL Apparatus. Hewlett-Packard Model 5711A gas chromatograph equipped with a flame ionization detector and a Hewlett-Packard Model 3352B laboratory data system were used. Reagents. Redistilled Eastman Kodak 2-ethoxyethanol (Practical Grade) was used. The internal standard solutions were (1)dodecane, 1g diluted to 100 mL with 2-ethoxyethanol; (2) nonyl alcohol, 5 g diluted to 100 mL with 2-ethoxyethanol; (3) propyl alcohol, 0.4 g diluted to 100 mL with 2-ethoxyethanol; (4) heptadecane, 1 g diluted to 100 mL with 2-ethoxyethanol. Procedure. The amount of sample used for the alkaline hydrolysis is controlled by the type of determination. For example, a 1-g sample is sufficient for the determination of the glycols and acids comprising the major portion of the repeat units. A 4-g sample is used when determining trace components such as the methyl ester end groups. The sample is weighed into a 100-mL flask, and 50 mL of 1 N potassium hydroxide (KOH) in 2-ethoxyethanol is added to the flask. A condenser cooled by chilled water is attached to the flask, and the reaction mixture is protected from carbon dioxide by means of a tube packed with Ascarite absorbant and Drierite desiccant. The contents of the flask are heated and maintained at reflux temperature for 10 min with constant stirring. The flask is allowed to cool to room temperature, and the hydrolysate is adjusted to a pH of 1using concentrated hydrochloric acid (5 mL). An internal standard is added to the flask. Pyridine (25 mL) is added to dissolve the acids present, and an aliquot sample is centrifuged to remove the potassium chloride. Approximately 50 p L of hydrolyzed sample is allowed to react at room temperature for 5 to 10 min with 500 pL of N,O-bis(trimethy1-
sily1)trifluoroacetamide (BSTFA) to form the silyl ethers and esters of the glycols and acids, respectively. The silylated hydrolysate is chromatographed by injecting 0.1 r L of sample into the gas chromatograph. The silyl derivative of diethylene glycol is separated from the silyl derivative of ethylene glycol using a 10-ft x '/8-in. stainless steel column packed with 100/200-mesh Chromosorb G-HP solid support containing 3% by weight of Versilube F-50 liquid phase. Versilube F-50 is the trademark for a mixture of trichlorophenyl silicone (10%) and methyl silicone manufactured by General Electric. Figure 1 is a chromatogram obtained for the silyl derivatives of the hydrolysate of an experimental PET. Dodecane is used as an internal standard, and the column is operated isothermally at 127 "C with a nitrogen carrier gas flow rate of 10 mL/min. Figure 2 is a chromatogram of the silyl derivatives of ethylene glycol, 1,4-butanediol, and the cis and trans isomers of 1,4cyclohexanedimethanol from the hydrolysate of an experimental polyester. A 6-ftX '/&. glass column packed with 100/200-mesh Chromosorb W-HP solid support containing 10% by weight of Versilube F-50 liquid phase was used for this separation. Nonyl alcohol was used as an internal standard, and the column was operated at 120 "C for 8 min and programmed to 210 "C at 4 "C/min with a nitrogen carrier gas flow rate of 20 mL/min. High-boiling acids, such as terephthalic and isophthalic acids, were separated using a 6-ft X '/&. stainless steel column packed with 100/120-mesh Chromosorb W-HPsolid support containing 10% by weight Versilube F-50 liquid phase. Figure 3 is the chromatogram obtained for the separation of the silyl derivatives of isophthalic and terephthalic acid from an experimental polyester. The column was operated isothermally at 183 "C with a nitrogen carrier gas flow rate of 33 mL/min. Figure 4 is the same separation, but heptadecane has been added as an internal standard to permit the calculations of the weight percent acids. Another important use of the alkaline hydrolysis/gas chromatographic procedure is the determination of methyl ester end groups. If the polyester is terminated with methyl ester end groups, then methyl alcohol is produced when the polyester is hydrolyzed. By determining the concentration of methyl alcohol, one can calculate the number of methyl ester end groups in PET. The hydrolysis procedure for determining methyl ester end groups is the same as that discussed for the glycols and acids. The gas chromatographic procedure is different in that no silylation reagent is used. The hydrolyzed sample is separated using a 6-ft X '/&. glass column containing 60/80-mesh Chromosorb 102 column packing. Propyl alcohol is used as the internal standard, and the column is operated isothermally at 145 "C with a nitrogen carrier gas flow rate of 10 mL/min. Figure 5 is a chromatogram obtained from the hydrolysis of PET for the determination of methyl alcohol.
DISCUSSION Saponification of polyesters with alcoholic KOH is one of the most widely used techniques for decomposing polyesters into their respective glycols and acids. Potassium hydroxide in boiling 2-ethoxyethanol rapidly attacks polyesters. It is important that complete hydrolysis be obtained, and a study of the reaction indicated that a 10-min reflux period in 50 mL of 1N KOH (in 2-ethoxyethanol) was sufficient for saponifying 1 to 4 g of most polyesters. The one exception to these conditions was in the hydrolysis of highly crystalline PET. A hydrolysis time of 15 to 20 min was required for this type of polyester. A plot of hydrolysis time vs. the ratio of diANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
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+====--
24r I 1>
DIETHYLENE GLYCOL,TMS ETHER INTERNA L STANDARD
2o LIQUID PHASE: "VERSI LUBE" F-50 COLUMN TEMP: 127'C N, FLOW RATE: 10 MLlMlN
-
I
IF
ETHYLENE GLYCOL, TMS ETHER
I
INTERNAL STANDARD
COLUMN: "CHRCMOSORB" 102 PACKING COLUMN TEMP: 146'C N z FLOW RATE: 1 O M U M l N
12
ETHYL ALCOHOL
-
t
I
Figure 1. Chromatogram of TMS derivatives of the glycols from the hydrolysis of poly(ethy1ene terephthalate) 36
r
Figure 5. Chromatogram of methanol from the hydrolysis of poly(ethylene terephthalate)
trans 1.4 CYCLOHEXANEDIMETHANOL, TMS ETHER
28
LIQUID PHASE COLUMN TEMP
"VERSILUBE" F-SO 120°C HOLD 8 M I N PROGRAM TO 1 W C AT 8'ClMIN
INTERNAL STANDARD
1.20
Y
0
I 20
I
I I I 60 80 100 HYDROLYSIS TIME, M I N
40
1
132
1 140
Figure 6. Determination of optimum hydrolysis time
ETHYLENE GLYCOL,TMS ETHER
Table I. Recovery of Methyl Alcohol from Hydrolysis Procedure Flgure 2. Chromatogram of silylated glycols
Methyl alcohol Added, mg Found, mg Added, mg Found, mg 0.47 0.79 1.50 3.56
TEREPHTHALIC ACID,TMS ESTER 20
ISOPHTHALIC ACID, TMS ESTER
I
t
Flgure 3. Chromatogram of TMS derivatives of isophthalic acid/ terephthalic acid
i TEREPHTHALIC ACID, TMS ESTER
INTERNAL STANDARD
? 1 82 t
\
LlOUlD PHASE: "VERSILUBE" F-50 COLUMN TEMP: 183°C N, FLOW RATE: 33 MLlMIN
Figure 4. Chromatogram of weight percent isophthalic acid ethylene glycol to internal standard is shown in Figure 6. When determining methyl ester end groups, it was desirable to know if any methyl alcohol was lost during the alkaline hydrolysis procedure. Selected amounts of methyl alcohol were added to the hydrolysis mixture and taken through the hydrolysis procedure, and the amount of methyl alcohol was determined by gas chromatography. The data obtained, as 742
3.71 4.19 5.92
3.65 4.06
'
5.97
Table 11. Precision of Hydrolysis-Gas Chromatographic Methods
LIOUID PHASE: "VERSILUEE" F-50 COLUMN TEMP: 183'C N1 FLOW RATE: 3 3 M L I M I N
"r
0.45 0.86 1.51 3.38
ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
Component Diethylene glycol, TMS ether 1,4-Butanediol, TMS ether 1,4-Cyclohexanedimethanol TMS ether Isophthalic acid, TMS ester Isophthalic acid, TMS ester Methyl alcohol
Concn, %
1.781 6.59
20.45 5.00 60.00 0.088
SD
No.
0.019 0.050 0.40
40
0.12
20 20 20
0.44 0.002
20 20
shown in Table I, indicate that no methyl alcohol is lost during hydrolysis. Silylation as an aid to chromatographic analysis is widely used. Silylation lowers the boiling point, reduces the polarity of a compound, and decreases the possibilities of hydrogen bonding. Silyl derivatives of compounds are usually more volatile and sometimes more stable because the number of reactive sites with active hydrogen are reduced. Glycols and acids from the hydrolyzed polyesters react rapidly with BSTFA at room temperature to form the silyl ethers and silyl esters, respectively. However, to ensure complete silylation, the samples are allowed to react from 5 to 10 min. The data given in Table I1 show that the precision of the overall method is good. These data were collected over a period of 7 months. This method is relatively simple and fast. The method has been used to analyze experimental polyesters for the amount of monomers present in the repeat units and for determining the composition of copolymers and polymer blends. The relative standard deviation varies from 0.8% for
the determination of IP-butanediol to approximately 2 % for 1,4-cyclohexanedimethanol.For the determination of different concentrations of isophthalic acid, the standard deviation varies from 0.7 to 2.4%.
(5) G. Heiemann, P. Kwch, and H. J. Nettelbeck, Fresenlu’ 2.Anal. Chem., 211-212, 401-409 (1965). (6) D. R. Gaskilc, A. G. Chaser,and C. A. Lucchesi, Anal. Chem., 39, 106-108 (1967). (7) H. D. ’Dinse and E. Tucek, Faserforsch. Textiltech., 21, 205 (1970). (8) H. Glamann and J. Woitrik, Faserforsch. Textilt.ech., 25, 86 (1974).
LITERATURE CITED (1) . . J. R. Kirby. .. A. J. Baldwin. and R. H. Heldner. Anal. Chem... 37.. 1308 (1965). (2) 0. G. Esposito and M. H. Swann, Anal. Chem., 33, 1854 (1961). (3) L. H. Ponder, Anal. Chem., 40, 229 (1968). (4) G. Stein and S. Dugal, Melliand Textilber. Int., 55, 585 (1974).
RECEIVED for review September
27,1976. Accepted February 4,1977. Part of this work was presented at the 27th Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1-5, 1976.
Isomer Distribution and Identification for the Chlorination Reaction of Acetylated 3-, 4-, 5-,and 6-Chloro-2-methylanilines by Gas-Liquid Chromatography Robert C. Duty’ Depatfmento de Quimica , Universidad Autonoma de Guadalajara I Guadalajara, Jalisco , Mexico
Isomer distributions were determlned for the chlorlnatlon reactlon of 3-, 4-, 5-, and 6-chloro-2-methylanlllnes and thelr ldentlflcatlons were made by hydrolyzing the acetylated compounds to the free amines and Comparing the retentlon times of their Isomers on three different chromatographlc columns. Only 4-chloro-2-methylanlllne produced all possible (three) dlchloro Isomers. The 3-chloro-, 4-chloro-, and 5chloro-methylanlllnes produced two dlchloro Isomers each. One dlchloro isomer, 3,5-dlchloro-2-methylanlllne was not produced by elther of Its posslble precursors. Dlpole moment calculations for the dlchloro lsomers agreed favorably wlth thelr retention times on the nonpolar substrate, Apleron J.
During the course of experimental work in this laboratory on the reaction of phosphorus pentachloride with o-nitrosotoluene (I),the problem of identifying dichlorinated isomers of 2-methylaniline needed to be solved. An examination of the literature revealed that only a few of these compounds had been identified and reported. Consequently, a synthesis of these isomers (there are a total of six isomers) was begun by an established procedure using potassium chlorate (2) and the commercially available 3-chloro-, 4-chloro-, 5-ChlOrO-, and 6-chloro-2-methylanilines. As was soon discovered, these dichlorinated derivatives were exceedingly difficult to purify and identify for two reasons: isomer contamination and/or low melting points. This problem is presented to provide retention time standards for the identification of five of these six dichloro-2-methylaniline isomers. This was solved by synthesizing mixtures of isomers which, because of the unique nature of the synthesis, may be used to identify all the dichloro isomers solely by their retention times without isolation of the pure components. The success of this approach is corroborated by isolating two of the isomers and spectroscopically confirming their isomeric identity, and by correlation of retention times to calculated dipole moments. ‘Present address, Illinois State University, Normal, Ill. 61761.
There have been numerous studies reported in the literature where isomer identification and distribution have been accomplished by gas chromatographic techniques. However, in the majority of these studies, product identification was made possible by comparing their retention times with known compounds, i.e., the analysis of isomeric diaminotoluenes with the N-trifluoroacetyl derivatives (3),the separation of mono and dichloroaniline isomers (4), the identification of isomeric toluidines (5) and the separation and identification of seven chlorinated derivatives of toluene (6). Classes of organic compounds can be identified by reaction chromatography where known compounds are not required. One of the earliest studies of this type was made by Rowan (7)where aromatics and olefins were absorbed in sulfuric acid and catalytically hydrogenated with hydrogen. The normal paraffins were separated by molecular sieves, the olefins were removed by mercuric perchlorate, and the C6 naphthenes were converted to aromatics by a dehydrogenation column. Consequently, with a proper selection of columns, he could assign certain peaks to a particular class of compounds. Unfortunately, the dichlorinated isomers of 2-methylaniline could not be analyzed by any of these methods. Nevertheless, one can resort to chemical reactions which could convert each of these isomers to known chemical isomers, e.g., deamination and/or diazonium reaction displacements of the amino group by a chloro group could be successfully done. This is unnecessary, however, in the context of this study which identified unknown peaks by the comparison of their isomer retention times on three different columns which proved remarkably successful. Only two gas chromatographic columns would be required to identify all six dichloro isomers if they yielded a separate peak for each isomer. Three columns were used in this study to be assured that the 3,5-dichloro-2-methylanilineis absent and not coeluting with another isomer. This idea of comparing isomers is similar to the Korner method of absolute orientation (8). Wilhelm Korner had compared the number of isomers generated from the isomeric dibromobenzenes to identify the three unknown dibromobenzenes. In this study we were starting with known isomeric ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
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