ANALYTICAL CHEMISTRY
1312 sulfate or manganese sulfate is heated to 200" C. Nitrous vapors are evolved because the following reaction takes place. When these sulfates are heated to 150" to 200' C. and 154' to 300" C. respectively, they are changed into the anhydrous sulfates ( 2 ) . Superheated steam results %hen the water is lost. The steam reacts, a t the place of its release, n i t h the nitrosamine with which i t is in contact, and hydrolysis of the latter occurs. Nitrous acid can also be produced without the addition of any water-releasing material, if nitrosamines are heated t o incipient charring with access of air. I n this case, the superheated steam resulting from the decomposition of the organic compound brings about the hydrolysis of the nitrosamine. These instances are additional evidence of the analytical value of hydrolyses occasioned by superheated steam, a matter that has been discussed elsewhere ( 4 ) . This pyrolytic splitting off of nitrous acid when a dry mixture of a nitrosamine and hydrated zinc sulfate or manganese sulfate is heated can also be utilized as a test for these organic compounds. S o nitrous acid is J ielded when C-nitroso compounds are subjected t o the pyrolytic procedure. DETECTION BY HEATING WITH HYDRATED 3IANGANESE (ZINC) SULFATE
Reagents. Hydrated manganese sulfate or hydrated zinc sulfate and Griess reagent (prepared as described previously).
Procedure. The test is made in a micro test tube. One drop of the test solution or a tiny bit of the solid is mixed with several centigrams of hydrated manganese or zinc sulfate, and taken t o dryness if need be. The mouth of the test tube is covered with a disk of filter paper that has been moistened with a drop of Griess reagent, and the tube is heated in the flame of a microburner. A red-violet stain appears on the colorless paper if N-nitroso compounds are present. A positive response F a s given by 10 y of S-nitrosodicyclohesylamine, 5 y of N-nitrosodiphenylamine, and 1.5 y of iY-dinitrosopiperazine. ACKNOWLEDGMENT
This study x a s kindly supported by the Conselho Sacional dr Pesquisas. LITERATURE CITED
Baumgarten, P., llarggraff, J., Ber. 63, 1019 (1930). (2) Duval, C., "Inorganic Thermogravimetric .halysis," pp. 190, 277, Elsevier, Xew York, 1955. (3) Feigl, F., ANAL.CHEM.27, 1316 (1955). (4) Feigl, F., lIoscovici, R., Analyst 80, 803 (1955). ( 5 ) Rosenthaler, L., Pharm. Acta Helc. 25, 365 (1950). (6) Sommer, F., Pincus, H., Ber. 48, 1963 (1915). (1)
RECEIVED for review February 13, 1956. Accepted April 18, 1956.
Rapid Determination of Carbonyl Content in Acrylonitrile ROBERT L. MAUTE and M. L. OWENS, JR. Monsanto Chemical Co., Texas City, r e x .
Low concentrations (0 to 0.2$%)of aldehydes and ketones in acrylonitrile can be rapidly determined by a modified hydroxylamine hydrochloride method employing a unique nonaqueous system. -4ccurate acetaldehyde content is found by allowing the sample to react with an alcoholic solution of the reagent for 1 minute before titration of the liberated acid with methanolic caustic to the thymol blue end point; total carbonyls are determined by increasing the reaction time to 5 minutes. The precision of the method for acetaldehyde is within A0.003y0 in the range from 0 to 0.1%. For the higher molecular weight ketones which react more slowly, or for mixtures of carbonyls, the precision is within =k0.005%.
hydes was modified in an attempt to apply it to low concentrations, but it was also found to be unsatisfactory. A widely used method for total carbonyl determination is the hydroxylamine hydrochloride method, which was used for fornialdehyde as early as 1895 ( 8 ) and has been improved by using pyridine as the osimation catalyst for quantitative determination of pure compounds ( 3 ) . A hydroxylamine hydrochloride procedure has been employed using mised aqueous-alcoholic reagents (1, 10, 14), with the end point detected by p H determination or by use of indicators (3, 14).
Table I.
Determination of -4cetaldehyde Weight %
Taken
ARIOUS carbonyl impurities are produced in the manufacture of acrylonitrile from acetylene and hydrogen cyanide. Among these are acetaldehyde (6, 8, 16), methyl vinyl ketone (6, 16), and paraldehyde (8). Because of their chemical and physical properties some of these carbonyl compounds may not be completely removed during purification of crude acrylonitrile; hence, rapid methods for the determination of aldehydes and ketones in product acrylonitrile became necessary. Many methods are available for the determination of carbonyl compounds, but few can be applied for trace amounts. One widely used method for the detection and determination of aldehydes (11, 16)is the fuchsin procedure. However, for quantitative results the reagent must be freshly prepared and kept in an inert atmosphere (11); a calibration curve must also be prepared for each batch of reagent for best results. Different aldehydes give varying color intensities and hence, the method is poor for mistures of aldehydes. The silver oside method (It)for alde-
0.135 0.170 0.123 ?.235
Found 0 . 14.5 0.176 0.125
1.LU
