Hydrocyanic Acid, Diluted

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. 

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... 

In the course of treating lignin with nitric acid, especially with dilute acid, hydrocyanic acid is evolved. This is. explained by the formation of nitrosophenols that undergo a tautomeric conversion into quinone oximes, the latter then being oxidized and hydrolysed. During these reactions HCN is split off in a manner resembling that reported by Seyewetz [64] (compare Vol. I). 

Cyanide. Sodium cyanide. [CAS 143-33-9]. NaCN. white solid, soluble, very poisonous, formed (1) by reaction of sodamide and carbon at high temperature, (2) by reaction of calcium cyanamide and sodium chloride at high temperature, reacts in dilute solution in air with gold or silver to form soluble sodium gold or silver cyanide, and used for this purpose in the cyanide process for recovery of gold. The perceniage of available cyanide is greater than in potassium cyanide previously used. Used as a source of cyanide, and for hydrocyanic acid. 

The liquid is now acidified with dilute sulphuric acid the hydrocyanic acid is driven off by boiling in a fume chamber (caution ) and the sulphuric acid exactly precipitated with strong baryta-water. After boiling with animal charcoal, the solution is filtered and evaporated to a syrup on a water bath. On long standing, the lactone of oc-d-glucohep-tonic acid separates in crystals. These are macerated with a little 80% alcohol, and filtered at the pump. The substance is then dissolved in 3 times its weight of water, and treated with animal charcoal in the warm. The filtrate is concentrated and set aside to crystallise. 

The details of this preparation are practically the same as those given for p-tolu-nitrile (Preparation 82). A cuprous-potassium cyanide solution, prepared as therein described, is warmed to about 70°, and added in small portions to a solution of benzene-diazonium chloride prepared from 18-6 gms. (1 mol.) of aniline as described in Preparation 379. When the addition is complete, the liquid is warmed on a water bath for 15 minutes and distilled in steam the distillate is extracted with ether. The ethereal solution is washed repeatedly with dilute caustic soda and with dilute sulphuric acid, dried over anhydrous potassium carbonate, filtered, and the oil which remains on driving off the ether fractionated. Owing to the evolution of cyanogen and hydrocyanic acid, this preparation must be carried out in a good fume cupboard. 

Amygdalin (the glucoside of bitter almonds) is a white crystalline compound, soluble in water, readily hydrolysed on heating with dilute sulphuric acid to benzaldehyde, hydrocyanic acid and glucose. 

Heat amygdalin with dilute sulphuric acid under reflux for a short time. Remove benzaldehyde and hydrocyanic acid by steam distillation. Test for benzaldehyde (phenylhydrazone test) and hydrocyanic acid (Prussian blue test) in distillate, and for glucose (osazone test) in residue. 

The total hydrocyanic acid is determined similarly, but after the cyanohydrin of benzaldehyde has been decomposed. For this purpose, 100 c.c. of the spirit in a 300 c.c. flask are rendered strongly alkaline with ammonia and then treated with a measured excess of the silver nitrate solution. The whole is shaken, immediately acidified with dilute nitric acid and diluted to the mark, an aliquot part of the filtered liquid being then treated as in the determination of the free hydrocyanic acid. 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

Hydrocyanic acid may on the same grounds be termed formonitrile, for, on standing with dilute acid, it is converted into formic acid by assumption of the elements of water H—C=N + 2H20 - H—CO-OH + NH3 and cyanogen, for the same reasons, may be named oxaloni-... 

The union of acetylene and nitrogen to hydrocyanic acid takes place rather smoothly if the easy clecomposability of acetylene is lessened by dilution with hydrogen, as was already done by Berthelot.6 His experiments were recently again taken up by Gruszkiewicz.7 The electrodes were blackened by a deposition of carbon except with a maximum content of acetylene of 5 per cent, by volume (composition of tne gas mixture 5 per cent, acetylene, 5 per cent, nitrogen and 90 per cent, hydrogen). 

Potassium eobalti-cyanide may also be produced by the addition of dilute acetic acid or hydrogen chloride to a solution of the cobalto-cyanide in excess of potassium cyanide. The acid liberates hydrocyanic acid, which reacts as follows ... 

Dilute hydrochloric acid hydrocyanic acid, HCN, with an odour reminiscent of bitter almonds, is evolved in the cold. It should be smelled with great caution. A more satisfactory method for identifying hydrocyanic acid consists in converting it into ammonium thiocyanate by allowing the vapour to come into contact with a little ammonium polysulphide on filter paper. The paper may be conveniently placed over the test-tube or dish in which the substance is being treated with the dilute acid. Upon adding a drop of iron(III) chloride solution and a drop of dilute hydrochloric acid to the filter paper, the characteristic red colouration, due to the iron(III) thiocyanate complex, Fe(SCN)3, is obtained (see reaction 6 below). Mercury(II) cyanide is not decomposed by dilute acids. 

Alternatively, place a drop of the test solution (or a few milligrams of the test solid) in the reaction bulb of Fig. 11.56, add 2 thin pieces zinc foil and 2-3 drops dilute sulphuric acid. Place a small circle of quantitative filter paper (or drop-reaction paper) moistened with acetate-benzidine acetate reagent across the funnel. The paper is coloured blue by the hydrocyanic acid carried over with the hydrogen. 

With dilute sulphuric acid, no reaction occurs in the cold, but on boiling hydrocyanic acid (POISON) is evolved ... 

In this case, use is made of the property of very dilute, gaseous hydrochloric acid of reacting with mercuric cyanide, liberating an equivalent quantity of hydrocyanic acid, while phosgene does not do this. ... 

Until a few years ago, hydrocyanic acid was always prepared by heating potassium ferrocyanide with dilute sulphuric acid. Nowadays, it is preferred to employ the alkali cyanides, either sodium or potassium, as these are manufactured synthetically on a large scale and very cheaply. Usually 50% aqueous sulphuric acid is run on to sodium cyanide either in concentrated solution or in lumps, and then the mixture heated in order to drive off the hydrocyanic acid. As it is evolved, the acid is dried by passing through calcium chloride and then liquefied by passing it first... 

Pure anhydrous hydrocyanic acid is a clear colourless liquid with a peculiar odour which is usually compared with that of bitter almonds. It has been observed, however, that this substance has an indefinite odour which varies with the degree of its dilution with air and the period of exposure to it. ... 

Because of its high vapour tension as well as its low density it is difficult to maintain a high concentration of hydrocyanic acid in an open place. As the toxic action is considerably reduced by dilution, numerous artifices were used during the war to render this gas more persistent. Lebeau, in France, suggested mixing it with the smoke-producing chlorides, as stannic, titanium or arsenic chloride. The result was that the already low stability of the hydrocyanic acid was still further reduced. Then it was proposed to add a proportion of chloroform to the mixture, this forming the mixture termed " Vincennite by the French. It consisted of 50% hydrocyanic acid, 30% arsenic trichloride, 15% stannic chloride and 5% chloroform. 

Benzidine Acetate Reaction. If a solution of benzidine acetate is added to a dilute solution of hydrocyanic acid in presence of copper acetate, an intense blue colouration is produced. This reaction, which was suggested by Pertusi and Gastaldi, is more conveniently applied by means of papers prepared as follows ... 

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