Hydrocyanic Acid—Hydrogen Cyanide

Hydrocyanic acid or hydrogen cyanide is the simple binary acid of cyanogen, corresponding to hydrochloric acid, the binary acid of chlorine. 

The group (CN) is considered as a unit and is sometimes denoted by the symbol Cy, but this is not desirable. 

Hydrocyanic acid is most easily prepared from its potassium salt, K(CN), which is obtained principally by the decomposition of the complex double cyanides of iron as we shall soon consider. The acid is also obtained by the hydrolysis of certain glucosides, e.g., amygdalin, in bitter almonds. It is prepared synthetically by reactions to be discussed presently in connection with the constitution of it and its salts. It is a colorless liquid with a characteristic odor and burns with a violet flame. It boils at 26.1 and solidifies to crystals which melt at —14°. It is an extremely strong poison the best antidotes being chlorine and hydrogen dioxide. It is readily absorbed by metallic nickel which is thus used in gas masks for this purpose. It is stable in dry air but in presence of water is readily hydrolyzed yielding ammonia and formic acid as the chief products. 

Formic Nitrile.—It is thus known also as formic nitrile. 

The two simple salts of hydrocyanic acid which are used in the synthesis of organic cyanogen compounds are potassium cyanide, K—(CN), and silver cyanide, Ag—(CN). These are both prepared by the action of the metallic oxides or hydroxides on the acid. 

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As early as 1908, Rosenthaler found in the ferment mixture of emulsin a u-oxynitrilase , which directed the addition of hydrocyanic acid (hydrogen cyanide) to benzaldehyde asymmetrically to give x-hydroxybenzeneacetonitrilc (mandelonitrile)9. This result was confirmed1 °, however, it was not until 1963 that Pfeil ct al. first isolated and characterized the enzyme (R)-oxyni-trilase [EC 4.1.2.101 from bitter almonds (Prunus amygdalus)1 12. The yellow-colored enzyme contains a flavin-adenine dinucleotide (FAD)11 and loses its activity by splitting off this prosthet-... 

This section is devoted to the addition of acids to ethylene pxidos. To facilitate its presentation the material will be divided into two prindpd categories (I) condensation with mineral adds (2) oon-densation with mganio acids. The hrst- will include halog acidB and otb strong minend acids the second will include carboxylic acids, sulfonic acida. and hydrocyanic acid hydrogen cyanide). 

Hexanenitrile, 2-hydroxy-Hydrocyanic acid hydrogen cyanide HCN... 

Hydrocyanic acid (hydrogen cyanide) White with 1 /2-inch green stripe completely around cartridge near bottom... 

Hydrocyanic acid, hydrogen cyanide, HCN a highly poisonous compound found widely in nature. It is released from Cyanogenic glycosides (see) by the action of 3-glucosidases (e.g. emulsin) and oxini-trilases. A number of plants, especially those contain-... 

Hydrocyanic Acid Hydrogen Cyanide Prussic Acid... 

Hydrocyanic Acid (Hydrogen Cyanide) 4 4 2 N 6.1 P063 Hood >240 ... 

Because of its low acidity, hydrogen cyanide seldom adds to nonactivated multiple bonds. Catalytic processes, however, may be applied to achieve such additions. Metal catalysts, mainly nickel and palladium complexes, and [Co(CO)4]2 are used to catalyze the addition of HCN to alkenes known as hydrocyanation.l67 l74 Most studies usually apply nickel triarylphosphites with a Lewis acid promoter. The mechanism involves the insertion of the alkene into the Ni—H bond of a hydrido nickel cyanide complex to form a cr-alkylnickel complex173-176 (Scheme 6.3). The addition of DCN to deuterium-labeled compound 17 was shown to take place... 

MSS (abont 200 to 400 pg from a cigarette delivering 15 to 25 mg of FTC tar ), its toxicity (other than ciliastasis) when examined alone, and the fact that consumers would be more familiar with the toxic properties of hydrogen cyanide (also known as hydrocyanic acid or cyanide ) than with the toxic properties of MSS components such as acrolein or phenol. Most of the effort dnring this period dealt with filter-tip additives other than carbon. 

AC Hydrocyanic acid (Prussic acid), hydrogen cyanide... 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

Cyan-verbindung, /. cyanogen compound, -verg tung,/. cyanogen poisoning, -wasser-stoff, m. hydrogen cyanide hydrocyanic acid. 

Hydrogen cyanide (hydrocyanic acid) is a colorless liquid (b.p. 25.6°C) that is miscible with water, producing a weakly acidic solution. It is a highly toxic compound, but a very useful chemical intermediate with high reactivity. It is used in the synthesis of acrylonitrile and adiponitrile, which are important monomers for plastic and synthetic fiber production. 

Another example of an acid is hydrogen cyanide, HCN, which transfers its proton to water when it dissolves to form the solution known as hydrocyanic acid, HCN(aq). However, only a small fraction of the HCN molecules donate their protons, and so we classify HCN as a weak acid in water. We write the proton transfer reaction with equilibrium half-arrows ... 

Free cyanide is the primary toxic agent in the aquatic environment. Free cyanide refers to the sum of molecular HCN and the cyanide anion (CN ), regardless of origin. In aqueous solution with pH 9.2 and lower, the majority of the free cyanide is in the form of molecular HCN. The chemical names for HCN include hydrogen cyanide, hydrocyanic acid, cyanohydric acid, and prussic acid. 

Hydrogen cyanide (Table 15.1) is a colorless, flammable liquid or gas that boils at 25.7°C and freezes at minus 13.2°C. The gas rarely occurs in nature, is lighter than air, and diffuses rapidly. It is usually prepared commercially from ammonia and methane at elevated temperatures with a platinum catalyst. It is miscible with water and alcohol, but is only slightly soluble in ether. In water, HCN is a weak acid with the ratio of HCN to CN about 100 at pH 7.2, 10 at pH 8.2, and 1 at pH 9.2. HCN can dissociate into H+ and CN. Cyanide ion, or free cyanide ion, refers to the anion CN derived from hydrocyanic acid in solution, in equilibrium with simple or complexed cyanide molecules. Cyanide ions resemble halide ions in several ways and are sometimes referred to as pseudohalide ions. For example, silver cyanide is almost insoluble in water, as are silver halides. Cyanide ions also form stable complexes with many metals. 

HYDROGEN CYANIDE, LIQUEFIED ICSC 0492 HYDROGEN CYANIDE, LIQUEFIED Hydrocyanic acid Prussic acid (liquefied)... 

Remarks on Sections 6 and 7.-—The method here described for the synthesis of cyanohydrins—treatment of the bisulphite compound of the aldehyde with potassium cyanide—cannot be used in all cases. Concentrated solutions of hydrocyanic acid or anhydrous hydrogen cyanide are often used. The general method for the synthesis of a-amino-acids, the nitriles of which are formed by the union of ammonium cyanide with aldehydes or ketones (Strecker), is to be contrasted with that for the synthesis of a-hydroxy acids. For additional amino-acid syntheses see Chap. VII. 2, p. 276. 

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