HYDROCYANIC ACID 20% solution

Explain what happens to (a) the pH of a solution of phosphoric acid after the addition of solid sodium dihydrogen phosphate (b) the percentage deprotonation of HCN in a hydrocyanic acid solution after the addition of hydrobromic acid (c) the concentration of H ions when pyridinium chloride is added to an aqueous solution of the base pyridine. 

TLV equals that of hydrogen cyanide. 10% hydrocyanic acid solution has flash point of 2° C and a vapor pressure of 226mm Hg at 20 C. Log P octanot/water is estimated, cial first aid required in the event of poisoning antidotes must be available (with instructions). Unbreakable packaging preferred if breakable, keep in unbreakable container. 

Hydrocyanic acid may be approximately estimated by dissolving 1 gram of oil in 5 c.c. of alcohol, and adding 50 c.c. of water. Then add ammonio-silver nitrate solution and shake well. Acidify slightly with nitric acid, and collect, wash, and dry the silver cyanide precipitated. Ignite and weigh the silver, 4 parts of which correspond to practically 1 of 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. 

Method B A solution of (/ )-oxynitrilase (150 pL, sec Method A) is dropped onto 2 g of Avicel cellulose [soaked in 20 mL of 0.01 M acetate buffer (pH 5.4) for 1 2 h, filtered off and pressed]. 20 mL of ethyl acetate (saturated with 0.01 M acetate buffer, pi I 5.4) are added, followed by 5 mmol of aldehyde and 250 pL (6.5 mmol) of hydrocyanic acid. After stirring at r.t. (Tabic 1) the mixture is filtered, and the filter cake pressed and washed with ethyl acetate. The combined solutions are dried and concentrated. 

A solution of (R)-oxynilrilase (F.C 4.1.2.10, 100 pi., 1000 unils/ml.) is dropped onto 1.5 g of Avicel cellulose (soaked in 0.02 M sodium acetate buffer. pH 4.5). 20 mL of diisopropyl ether are added, followed by 5 mmol of ketone and 200 pL of hydrocyanic acid, and the mixture is stirred (Table 3). The catalyst is filtered off. washed with diisopropyl ether, and the combined filtrates are concentrated. 

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 ... 

If the solution becomes too alkaline, the nitrile formed will add to a second molecule of unsaturated ketone so readily that the product will consist almost entirely of a high-melting (284-286°) substance. For this reason it is essential to measure the acetic acid accurately if too much is used, addition of hydrocyanic acid will not take place. 

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. 

The rate of reaction between hydrocyanic acid (HCN) and acetaldehyde (CH3CHO) to give acetaldehyde cyanohydrin has been studied in a constant-volume batch reactor at 25°C in dilute aqueous solution, buffered to keep the pH constant (Svirbely and Roth, 1953). The reaction is... 

For the reaction between hydrocyanic acid (HCN) and acetaldehyde (CH3CHO) in aqueous solution,... 

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. 

Liquid hydrogen cyanide, hydrogen cyanide in aqueous solution (hydrocyanic acid), and concentrated vapor are absorbed rapidly through the intact skin and may cause poisoning with little or no irritant effect on the skin itself. The liquid in the eye may cause some local irritation the attendant absorption may be hazardous. ... 

The free D-glucononitrile was also degraded to D-arabinose by Wohl and Wollenberg by simple heating of its solution and elimination of hydrocyanic acid with carbon dioxide gas. 

Ethylene cyanohydrin has been prepared by the action of ethylene oxide upon anhydrous hydrocyanic acid 1 but the majority of methods described in the literature have involved the interaction of ethylene chlorohydrin and alkali cyanide. This has been effected in the absence of a solvent by heating to ioo° in a closed vessel,2 by boiling the reagents in 50 per cent aqueous-alcoholic solution,3 by adding a concentrated aqueous solution of potassium or sodium cyanide to a boiling solution of ethylene chlorohydrin in absolute alcohol,4 and in aqueous solution at 45 °.5... 

Most of the insoluble single (yanides dissolve in solutions of the alkaline cyanides, forming double cyanides. Some of these double compounds, when acted upon by hydrochloric acid, evolve hydrocyanic acid, producing chlorides of both metals, as in the case of dipotassio zincio tetraoyauide. These ore called easily deootigmdble cyanides, and are indicated in the above Tabic by the comma being placed between the cyanogen and the metals. 

This is a white crystalline solid made by treating polonium(IV) hydroxide or chloride with aqueous hydrocyanic acid. It blackens rapidly on standing owing to radiation decomposition. Its solubility in aqueous potassium cyanide is low, increasing from 0.089 mg (of Po210)/liter in 0.05 M solution to 1.19 mg/liter in 1.5 M solution, so that cyanide complex ions may be formed (11). 

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