Quantitative Determination of Small Amounts of Hydrocyanic Acid NATH.4N
GALESAND ANDREWJ.
PENSA
Chemical Laboratory of the Bureau of Food and Drugs, Department of Health, New York, N. Y.
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H E most commonly used methods ( I ) for the determination of hydrocyanic acid have the objection that they are not quantitative for very small amounts. The method outlined below affords a means by simple technic of determining hydrocyanic acid quantitatively in exceedingly small amounts, the delicacy being measured by the amount of ammonia which can be determined by Nessler's reagent-namely, one part in one hundred million. Hydrocyanic acid, known also as formonitrile, is subject to the general characteristic reactions of alkyl nitrilesnamely, hydrolysis with either alkali or acid to form the alkyl acids or their salts and ammonia or its salts. These reactions, where R is the alkyl group, are: RCN RCN
HCL + 2Hz0 +RCOOH + NH4Cl ++ KOH + 2Hz0 +RCOOK + NH40H
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EXPERIMENTAL DATA Solutions containing 1, 2, 3, 4, and 5 cc. of concentrated hydrochloric acid, 5 cc. of standard potassium cyanide solution (1 cc. equivalent to 0.1 mg. of hydrocyanic acid), and 20 cc. of distilled water were autoclaved for 30 minutes between 140' and 150" C. Hydrolysis was not complete when 1, 2, and 3 cc. of acid were used, whereas 4 and 5 cc. of acid showed complete hydrolysis and the ammonia evolved checked quantitatively with equivalent standard ammonium chloride solutions. Autoclaving 5 cc. of standard potassium cyanide solutions with 5 cc. of concentrated c. P. hydrochloric acid and 20 cc. of water a t 100' and 105" C. for 30 minutes showed that the liberation of ammonia was not quantitative, although more was formed a t the higher temperature. Complete hydrolysis was obtained between 140" and 150' C. when autoclaved for 30 minutes. Solutions containing 5 cc. of standard potassium cyanide, 5 cc. of concentrated c. P. hydrochloric acid, and 10 cc. of 0.1 N sodium hydroxide were autoclaved for 30 minutes between 140' and 150" C. Some of these solutions were Nesslerized directly with 5 cc. of Nesshr's reagent, but the acidity was too great for the development of the characteristic brownish yellow color. In the others, the excess acid was neutralized with sodium hydroxide before Nesslerization. In these cases a turbidity formed due to impurities in the alkali, such as magnesium, calcium, and aluminum. However, when the excess acid was evaporated and the solution then diluted and Nesslerized, the resulting color was clear and checked quantitatively with ammonium chloride standards. For 5 cc. of the Nessler's reagent, the acid content of the solution must not exceed 0.4 cc. of concentrated hydrochloric acid. Samples containing 5, 10, 15, 20, and 25 cc. of the standard potassium cyanide solutions were autoclaved in the usual manner with 5 cc. of concentrated c. P. hydrochloric acid and 10 cc. of 0.1 N sodium hydroxide. Upon subsequent removal of excess acid and Nesslerization, the characteristic brownish yellow color developed and ranged from a clear light comparable color to the brownish yellow precipitate of the iodide of Millon base, NH2 HgO HgI. It is necessary, therefore, when the solution to be Nesslerized contains ammonia derived from more than 0.5 mg. of hydrocyanic acid, to take an aliquot portion for colorimetric comparison. C. P.
and for hydrocyanic acid: HCN HC1 2Hz0 +HCOOH NH&1 HCN KOH 2Hz0 +HCOOK ",OH
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and maintain the temperature between 140' and 150' C, for 30 minutes. After cooling, empty and rinse with distilled water into a 50-cc. beaker. Evaporate slowly on a hot plate almost to dryness to get rid of the excess acid. Dilute with distilled water, transfer to a Nessler tube, and add 5 cc. of Nessler's reagent ( 2 ) . Compare the resulting color with a series of standard ammonium chloride solutions and calculate the parts per million of the cyanide or hydrocyanic acid present in the sample. When the ampoule is used as the autoclave, cool in an ice bath before the addition of the hydrochloric acid and then immediately seal the ampoule.
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It is evident -from the above reactions that the hydrolysis of hydrocyanic acid must be carried out in a closed system; for hydrocyanic acid would be volatilized with acid hydrolysis, and ammonia with alkali hydrolysis. In the industrial manufacture (4) of ammonia and formates NaCN) is autoclaved with a mixture of cyanides (KCX 5 to 10 parts of water for 20 to 30 minutes between 180' and 190" C. In a series of laboratory experiments samples containing standard aqueous potassium cyanide solutions equivalent to 0.01, 0.10, and 1.0 mg. of hydrocyanic acid were autoclaved for 30 minutes between 180' and 190' C. and when Nesslerized checked with equivalent ammonium chloride solutions. The hydrolysis of the potassium cyanide solution is due t o the alkaline reaction of this salt. This method has two disadvantages, the caustic action on the glass autoclave and high temperature. The optimum conditions for hydrolysis, as experimentally deduced, were obtained by autoclaving for 30 minutes between 140' and 150" C. in an acid solution. The glass autoclave is the Leiboff urea apparatus (3) for the determination of urea in blood. This apparatus is essentially a brass stand with a thermometer in the hollow of the rod and a circular brass plate containing six grooves from which are suspended the six glass autoclaves. The stand with the suspended autoclaves is set in an oil bath. The glass autoclave, of approximately 35 cc. capacity, is made gas-tight by a ground-glass rod which seals a t the neck when the rod is so suspended. Lacking the Leiboff urea apparatus, satisfactory results could be obtained with ordinary medicinal ampoules.
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PROCEDURE Distil the hydrocyanic acid in the usual manner from a solution acidified with tartaric acid and collect the distillate into 10 cc. of 0.1 ilisodium hydroxide. Transfer the distillate, approximately 25 cc., to the autoclave and add 5 cc. concentrated c. P. hydrochloric acid. Heat slowly in the oil bath 80
March 15, 1933
INDUSTRIAL AND ENGINEERING
A one-gram sample of powder collected from a copper coil of a gas heater contained, as determined by this method, a cyanide equivalent to 75 parts per million hydrocyanic acid. This sample proved to be interesting, for Nesslerization resulted in a turbid solution which proved to be due to iron carbonyl, which, present in the original sample, distilled over with the hydrocyanic acid. The iron carbonyl was precipitated as iron hydroxide by boiling the alkali solution containing the carbonyl and the cyanide. The filtrate was autoclaved in the usual manner, and when Kesslerized a clear solution resulted.
CHEMISTRY
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ACKNOWLEDGMENT The writers express their appreciation to Reginald Miller for his cooperation in this work. LITERATURE CITED (1) Autenreith, W., “Laboratory Manual for the Detection of Poisons and Powerful Drugs,’’ 6th American edition, Blakiston, 1928. (2) Folin, O., “Laboratory Manual of Biological Chemistry,” Appleton, 1923. (3) Leiboff, S. L., and Kahn, B. S., J.Bid. Chem., 83,347-52 (1929). (4) Mange, L., Industrie Chimique, 5, 286-8 (1918). RDCEIYED November 23, 1932.
Determination of Dextrin, Maltose, and Dextrose in Corn Sirup W. R. FETZER,J. W. EVANS, AND J. B. LONGENECKER, Union Starch and Refining Company, Granite City, Ill. An addition in procedure is applied to the termination. The methods may ORN sirup (glucose, or method of moisture determination by distillation be roughly grouped as follows: ‘lglue” as it is called colloquially by the candy with toluene, as proposed by Bidwell and Sterling 1. Algebraic solution from manufacturer) has become an solids, specific rotation, indispensable part of the manuand modiJied by Rice, to make it applicable to and reducing sugar equafacture of confectionery. One corn sirup. A new melhod for the direct detertions. mination of dextrin in Corn sirup is proposed. 2 . Precipitation by alcohol and of the solution dextrin by billion one hundred forty million Based on the method of direct determination of Poundswere refined in 1929, with algebraic equations. a value of 34 million dollars. It dextrin, a procedure f o r the complete analysis 3. Fermentation methods. is produced by the acid hydroyl4. Destruction of the sugars, corn sirup is presented, which allows two check followed by polariscopic starch ullder a pressis of d e t e r m i n a t i o n of the sure of approximately 40 pounds, equations-purity and speciJic rotation. Analydextrin , and then algein three different purities-low, ses of several brands of confectioners’ corn sirup braic solution. regular, and high. “Purity” is are made. defined within the industry as Algebraic solution for three carthe amount of reducing sugars exbohydrates requires three equapressed as dextrose, on a dry substance basis. The “regular” tions, and the following are easily available in the laboratory: purity of 43 to 44 forms the bulk of the commercial production. x + y + z = solids Corn sirup is a thick, colorless solution of the three carbo196x 138.5y 52.,2 = specific rotation hydrates-dextrin, maltose, and dextrose. The gravity of 1.1111~ + 1.0555~+ z = reducing sugars as dextrose after the sirup will run from 41 O to 46” BB. (1O BB. being expressed acid hydrolysis 0.606~+ z = purity or reducing sugars as dexa t 100’ F.). Sirups with a gravity of 41” and 42’ BB. are trose on original sirup more often called “mixing sirups,” and are used by manufacturers of mixed table sirups. Confectioners’ sirup runs from It would seem, since dextrin has no reducing power, as shown 43” to 46” BB., the bulk being sold a t 43” BB., as this gravity by the last equation, that the solution for the three carborepresents the high practical limit a t which this heavy, vis- hydrates would be simple, but the experience of the present cous sirup may be handled economically. authors and that of others (4) has been that small experiAlthough there are many published analyses for corn sirups mental errors are enormously multiplied, so that the final or starch hydrolytic products, few are applicable to the comresults, even in simple mixtures such as corn sirup, can be mercial product, because the sirups used for analysis have been regarded only as approximate. prepared by boiling starch in open vessels, with acids different Recognition of this difficulty has stimulated other investifrom those used in the commercial process. Further, most gators to the direct determination of dextrin by precipitation workers employ a low concentration of starch suspension, by alcohol or a similar chemical, in which dextrin is insoluble whereas in the industry it is customary to use a suspension but maltose and dextrose are soluble. Keener (5) stated that from 22” to 26” BB., the latter figure representing the practical the precipitfttion of dextrin by alcohol was a most promising limit for pumping suspended starch. It is well known in the method but that it required further study. Experience in industry that the maximum purity attainable in manufacture this laboratory has been that precipitation by alcohol is. not is affected by the concentration of the starch suspension used, a disagreeable determination from an analytical standand it is reasonable to assume that the ratio of the various only point, but that it also gives unreliable results, as shown in carbohydrate constituents might be altered by these same Table I. concentration differences of the starch. OF DEXTRIN BY ALCOHOL Many methods have been proposed for the analysis of corn TABLEI. DATAON PRECIPITATION 5.0 sirup. All make use of several algebraic equations obtained 5.0 5.0 5.0 Weight corn sirup, grams 5.0 0.9 0.9 0.9 0.9 0.9 Water in corn sirup, ml. from laboratory determinations, such as specific rotation, re41.1 5 2 . 1 31.1 20.1 9.1 Water added ml. 158 147 179 168 95% alcohol added ml. 190 ducing power before and after acid inversion, etc. Almost 75 70 90 80 85 Final alcohol (calcd.). % 4.0 1.4 all employ the solids equation obtained from the moisture de19.8 13.9 8.0 Dextrin found; %
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