Quantitative Gas Liquid Chromatography of Thiocresols and Thioxylenols as Acetate Esters PETER
P. CROITORU
Consolidation Coal
W. FREEDMAN
and ROBERT
Co., library,
Pa.
b A rapid quantitative procedure is
I
EXPERIMENTAL
Reagents and Apparatus. The column was prepared by packing 157, by weight polypropylene sebacate on Chromosorb W, 60- to 80-mesh, into a 3.5 meter X 0.6 cm. i.d. aluminum tube. Polypropylene sebacate was purchased from Griffin and George, Ltd., 285 Ealing Rd., Alperton, Wembley, Middlesex, England. Celanese KO, 9 ester was obtained from the Celanese Corp. 0-, m-, and p-thiocresols were obtained pure from the Consolidation Coal Co. Triethylamine (boiling point 80" to 90" C.) was obtained from Matheson Coleman and Bell. 2,&Thioxylenol was obtained pure from the Consolidation Coal Co. Its purity was confirmed by infrared analysis by observation of the presence of the 13.07-micron band, the absence of the 12.43-micron band (2,5), and the absence of the 12.42-micron band (2,4). A mixture of 10% 2,5-thioxylenol in 2,4-thioxylenol was obtained from the Consolidation Coal Co. The 2,6-thioxylenol had been removed by fractionation and its absence proved by the absence
thiocresols or thioxylenols are very difficult to separate by fractionation. Similarity of boiling points and the reduced degree of hydrogen bonding (as compared to oxygen analogs) also render separation on gas liquid chromatographic columns impractical even with the use of capillary columns. The reactivity of these thiols toward metal may also be a significant factor. TT'e found that the silyl ethers (3)gave only partial separation and were highly unstable. The acetates, however, were readily prepared and gave quantitative separation. Thiocresol has been acetylated by acetyl chloride (1, 4) in nonaqueous media. The acetate has also been prepared by the action of acetic anhydride in the presence of aqueous base (4). A preparation of thiol acetates is described, using acetic anhydride as the acylating agent in the presence of an escess of triethylamine. The latter speeds up the reaction by combining with the liberated acetic acid. Reaction is almost instantaneous a t room temperature. sOmRIc
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- Thiocresol
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of the 13.07-micron band. Because of the proximity of the 2,4 and 2,s bands it was necessary to establish the composition of this mixture by gas chromatography of the acetates. Procedure. Thiocresols or thioxylenols (1 ml.), triethylamine (1 ml.), and acetic anhydride (1.5 ml.) are placed in a 60-ml. separatory funnel and shaken gently for 30 seconds. Distilled water (40 ml.) and benzene (0.5 to 2 ml.) are added. The benzene is added 0.5 ml. a t a time until the organic phase separates cleanly on top of the aqueous phase after gentle equilibration. The lower layer is withdrawn and rejected. Two more water washes are applied and the product is dried over a small amount of calcium sulfate in a vial. For gas chromatographic analysis, a 2- to 5-pl. sample is injected a t a column temperature of 180" C. with a helium flow rate of 60 to 70 ml. per minute. In the Perkin-Elmer 154C chromatograph used, this requires an inlet pressure of about 25 p.s.i.g. Peak areas were recorded. Response factors of individual thiol acetate isomers were close to 1.00 on a weight basis. This was determined by chromatographing known mixtures of pure thiol acetates.
The water-washed and dried product is readily separated chromatographically by using polypropylene sebacate on acid-washed Chromosorb IT.
described for the preparation and gas liquid separation of the acetates of thiocresols and thioxylenols. The esters are prepared by reaction of the thiols with acetic anhydride in the presence of an organic base at room temperature under anhydrous conditions.
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Acetate
RESULTS AND DISCUSSION
Before giving examples of actual analytical separations in graphical and
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0
LlLJLI
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a
0 V
W K
V I
U T
m-Thiocresol Acetote
a
30
29 28
27
26
25 24
RETENTION
Figure
1536
1.
TIME
23
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22 21
20
19
MINUTES
Separation of thiocresol acetates
ANALYTICAL CHEMISTRY
18
Acetote
l A J , 39 38
37
36
35
34 33 32 31
RETENTION TIME Fiugre 2.
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I
30 29 28 27
MINUTES
Separation of thioxylenol acetates
6
Table I.
Recovery of Thiocresols
Compounds o-Thiocresol acetate m-Thiocresol acetate p-Thiocresol acetate
Added, Found, wt. yo wt. 70 47 3 47.5 8.5 8.3 44 4 44.3
tabular form, it sermcd desirable to show that the reaction was quantitative on a
