Estimation of Trace Amounts of Acetaldehyde in Vinyl Chloride JOHN D. COTMAY,
GEORGE C. CLAVEH, JR.
JR., AND
Plastics Division, Monsanto Chemical Co., Springfield 2, .Mass.
IST methods for tht. t,htiniation of aldehydes in both micro
M.and macro quantities have been reported (1-7, Some of these procedures have been evaluated in terms of their 10-13).
,
usefuliiess in determining the aldehyde content, of vinyl chloride. Method3 involving the use of p-hydrosydiphenyl plus sulfuric acid ( 11 ,I, benzenesulfohydrosaiiiic acid ( 5 ) ,the silver-ammonia complex ( 8 ) , fuchsinsulfurous acid ( 6 ) , 2-n~ethylindole ( 4 ) , and the polarograph ( 7 , 9, 1 4 ) were evaluated in this investigation. Satisfactory techniques were developed for determination of trace amounk of acetaldehyde in various media using p-hydroxydiphenyl, polarographic reduction, and 2-methylindole. Of these, only the 2-methylindole procedure was applicable to the determination of acetaldehyde in vinyl chloride over the range of 1 to 50 p.p.m. 2-Methylindole condenses rapidly with acetaltlehyde in acidic media to yield a highly insoluble, colorless precipitate. The chemical reaction is probably: (*I13 C’FTOFI
”
€I
‘CH,
.ketaldehyde is extracted quantitatively from vinyl chloride as the aldehyde ammonia addition product. I n the strongly acidic reagent solution the addition product is hydrolyzed and the acetaldehyde reacts as indicated above. For very dilute solutions of aldehyde the precipitate is colloidally dispersed and the turbidity is proportional to the concentration of aldehyde. 111 the range of 1 to 20 p.p.ni., this method is accurate t o *0.27 p.p.ni. By a dilution procedure the analysis can be extended to concentrations as high as 50 p.p.ni. with errors proportional to the extent of dilution.
is rinsed several times with distilled n.at,cr. The total volume of solution a t t,his point should not exceed 50 ml. T.rt.ent,ymilliliters of 2-methylindole reagent’solution are added and the mixture is shaken. The solution is diluted to 100 nil. with distilled water and allowed to stand for 10 minutes. The turbidity is then measured with a suitable turbidimeter such as the Hellige. Aldehyde concentrations from 1 to 20 p.p.rn. are read directly from a previously prepared calibration chart. A separate calibration is required for each turbidimeter. It was observed during calibration measurements that blank runs on the reagents always give a small turbidimeter reading, even when scrupulous care has been eserted to exclude dirt during sample preparation. The origin of this blank reading is instrumental. Subtracting the reading for the blank from readings on known aldehyde sample.< resulted in a linear turbidit~-roucentrationdependence betweeii 2 and 20 p.p.ni. which extrapolated to zero for zero aldehyde conrentration. Result,s of representative determinations of acetaldehyde and accuracy are included in Table I. To estend the range of analysis from 20 to 50 p.p.m. two alternative procedures are suggested, each requiring a preliminary indication that acetaldehyde is present in excess of 20 p.p.ni. A. Extraction and precipitation are carried out m usual and, after reaction of acetaldehyde and 2-niethylindole, the solution is diluted from 100 to 200 ml. R. The cstraction of aldehyde is carried out on 50 rather than 100 grams of vinyl chloride. The rest of the procedure is as described. I n this procedure the concentration of aldehyde read from the calibration chart is multiplied by 2. Accuracy p.p.m. as a consequence of doubling by this method is about 2~0.5 the errors. Procedure €3 is preferred. Precipitate formed in solutions of widely diffei,ent acetaldehyde concentration differ in particle size distributions, and another set of calibration data k required for more concentrated solutions. The use of Procedure B avoids the necessity for additional calibration. _ ..
PROCEDURE
Onr, milliliter of filterocl concentrated ammonium hydroxide
is placed in a pressure bottle caapable of withstanding 200 pounds per square inch, and 100 grams of vinyl chloride are weighed below it,s boiling point into the bottle, which is capped with a tin-lined crown closure. The cap serves as a safety release in the event of excess pressure. The sealed bottle ie placed on a rot,ary shaker inside a sturdy nietal box and, after it has come t,o room temperature, is shaken continuously for 1 hour. The bottle is then chilled in ice water and the crown seal is cautiouslp punctured with a sharp ice pick, preferably in a well ventilated hood, When the vinyl chloride has evaporated, the content,s of the bottle are washed into a 100-nil. volumetric flask, and the bottle
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Table I. D e t e r m i n a t i o n of Acetaldehyde Sample
Aldehyde Added, P.P.hf.
.\ldehyde Found. P.P.M. 1.1 3 6 5.3 8.5
REAGENTS
2-JIethylindole was synthesized by condensing phenylhydrazine and acet,one. The crude product’ was purified by steam distillation followed by repeated crystallization from methanolwater. In this way a colorltm product melting at 59-60” was obtained. Subsequently, the rwgent has been purchased from Bios Laboratories, New Tork, N. P. Steam distillation and crystallization from methanol-water are required to free this product, from undesirable colored impurities. A test solution is prepared by dissolving 0.1 t o 0.2 gram of 2met hylindole in a solution of 60 nil. of concentrated hydrochloric arid (sperific gravity 1.19) in 30 ml. of distilled water. The reagent solution oxidizes rapidly and should not be used after 10 to 12 hours.
..
-1.2 13.3 I I ~ n i deviation i
Deviation P,P,lf, 1.n 0 4 0 0 0.1
0.0 0.1
iO.27
LITERATURE CITED (1) Chelintsev. V. V., and Niktin, E. K.. J . & ? I . Chen. (C’.S.S.R.), 7,2324 (1937). (2) Egami, H., J . Chem. SOC. J a p a n , 62,277 (1941). (3) Feigl, F., “Spot Tests,’’ p. 301. Sew Tork, Sordemann Puhlishing Co., 1937. (4) Fische, F., and Robbins. S. S..Biocheni. Z.. 271, 304 (1934). ( 5 ) Gattermann, L., and Wieland, H., “Laborakxy Methods of Organic Chemistry,” p. 192, London, Macmillan Co., 1941. (6) Hahnel, S., Svensk K e m . Tids.,46, 45 (1934). (7) Kolthoff, I., M., and Lingane, J. J . , “Polarography,” p. 353, New York, Interscience Publishers, 1941. (8) Sandell, E. B., “Colorimetric Determination of Traces of Bletals,” p. 394, New York, Interscience Publishers, 1944. (9) Semerano, G., and Polacsek, B., Gatz. chim. ital., 68, 298 (1938). (10) Smoler, I., Collection Czechoslae. Chem. Coni~nutbs.,2, 699 (1930). (11) Stotz, E., J. Biol. Chem., 148, 585 (1943). (12) VanEck, P. N., Pharm. Weekblad, 6 5 , 8 2 (1928). (13) Veibel, S., Bull. SOC. chim., 21, 1410 (1927). (14) Winkel, A., and Proske, G., Rer., 69, 693 (193tii.
RECEIVED February 13, 1931
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