Identification of Alcohols by Color Reactions SIR: The reaction between ethylenc glycol and guaiacol in the presence of concentrated sulfuric acid, has been reported to produce an intense purple color (1). I have repeated this reaction with a pure sample of ethylene glycol trapped from a gas chromatograph separation, and found it to be completely colorless. In addition, ethylene glycol obtained from five different sources gave the following results: Jefferson Chemical Co., colorless; Fisher (E-178, certified), colorless to barely perceptible purple; Fisher (E-177, reagent), colorless to barely perceptible purple; Enion Carbide (production), a very faint trace purple; and Wyandotte (practical) very faint trace purple. An investigation was carried out to determine what caused the reported purple color obtained from some samples of ethylene glycol. A sample of pure ethylene glycol was aerated a t 62" C. for 48 hours. At the end of this period, the aerated solution which originally gave a colorless reaction, now gave a light purple color. At the end of 96 hours, it gave an intense purple color. Infrared spectra, Figure 1, showed absorption a t 5.75 microns of 0.10 and 0.12, respectively, indicating formation of increasing amounts of carbonyl compounds resulting from the oxidation of ethylene glycol. The hydroperoxide numbers determined by the potassium iodide-sodium thiosulfate procedure ( 2 )
a'
t
1
~
Figure 1 . 7. 2.
Spectra of ethylene glycol Aerated for 48 hours Aerated for 96 hours
were 0.26 and 0.45, respectively, indicating intermediate stages of oxidation. To demonstrate the effect of small amounts of oxidation products in ethylene glycol, 0.1% of glycolic acid, glyoxal, and acetaldehyde were added separately to a pure sample of ethylene glycol. I n each case a purple color resulted in the presence of guaiacol. Because of the discrepancy of the color reaction reported ( I ) for ethylene
glycol, a spot check was made of the color reactions of several alcohols. The color reaction of methanol was found to be colorless, whereas a rose color was reported. As in the case of ethylene glycol, addition of small amounts of the corresponding oxidation products, produced a color reaction. Addition of 0.1% formaldehyde produced a purple color and addition of 1% formic acid produced a rose color. The reaction between propanol-2 and guaiacol was found to be pale yellow in color instead of the intense purple color that was reported. Similarly, the purple color between n-heptanol and guaiacol could not be reproduced. From the above data, it would appear that the color reactions reported have in some instances resulted from the use of impure materials containing oxidation products. The other color reactions have not been examined by this laboratory, and should be checked before acceptance. LITERATURE CITED
( I ) Christiansen, G. hl., ANAL. CHEM. 34, 1030 (1962). ( 2 ) Stansbury, M.E., IND.ENG.CHEM., ANAL.ED. 13, 627 (1941).
JULES B. COUNTS U. S. Army Coating and Chemical Laboratory Aberdeen Proving Ground, Md.
Methyl Esterification of Nonvolatile Pia nt Acids for Gas Chromatographic Analysis SIR: Complexity of plant composition has made studies of plant material difficult except by chromatographic techniques. Column and paper chromatography can be slow and yet result in incomplete separations. Qualitative and quantitative examinations by these methods are time-consuming and tedious. Use of gas liquid chromatography (GLC) has been particularly expedient for examination of complex mixtures for qualitative and quantitative evaluationf. However, the compounds to be examined must be volatile to effect gas chromatographic mobility. Volatile acids can be examined directly but nonvolatile acids are usually esterified before gas chromatographic study. Certain acids such as the hydroxy, keto, unsaturated, di- and tricarboxylic 926
ANALYTICAL CHEMISTRY
acids are difficult to esterify by the usual method with diazomethane or mineral acid-alcohol (3) because side reactions occur or the reaction is incomplete. This report will discuss the results obtained by using a mixture of thionyl chloride, methanol, and hydrogen chloride for preparation of the esters of these acids. This reagent efficiently esterified the acids derived from plant material within 10 minutes. EXPERIMENTAL
Reagents. Anhydrous methanolhydrogen chloride, 5-1Oy0 acid. Thionyl chloride (Eastman Kodak, Rochester, S . Y.). Chromosorb W, 100- to 120-mesh, H M D S (JohnsManville, X . Y.). Acids were commercial products of
reagent grade, used without further purification. Neopentyl glycol succinate was prepared at this laboratory. Apparatus. Dual hydrogen flame ionization detector gas chromatograph ( F & 11, Series 810, Avondale, Pa.) with a linear temperature programmer. Recorder, 1-mv. (Leeds & Northrup, Model H , Philadelphia, Pa.). Procedure. The nonvolatile acids were isolated from plant extracts in a manner similar to the method described by Uurchfield and Storrs ( 3 ) . Duolite A4 (anionic resin) was substituted for the Dowex 1, and the acids were eluted from the resin with 2 N ammonium hydroxide. The percolate was evaporated to dryness on a rotary evaporator a t water-aspirator pressure in a flask submerged in a water bath held a t 50" C.
