Hydrocyanic acid preparation

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. 

Mandelic acid is best prepared by the hydrolysis of mandeloni-trile with hydrochloric acid. The mandelonitrile has been prepared from amygdalin, by the action of hydrocyanic acid on benzaldehyde, and by the action of sodium or potassium cyanide on the sodium bisulfite addition product of benzaldehyde. ... 

The first methacrylic esters were prepared by dehydration of hydroxyisobutyric esters, prohibitively expensive starting points for commercial synthesis. In 1932 J. W. C. Crawford discovered a new route to the monomer using cheap and readily available chemicals—acetone, hydrocyanic acid, methanol and sulphuric acid— and it is his process which has been used, with minor modifications, throughout the world. Sheet poly(methyl methacrylate) became prominent during World War II for aircraft glazing, a use predicted by Hill in his early patents, and since then has found other applications in many fields. 

A general method for preparing (/ )-cyanohydrins, derived from ketones, is the (/ )-oxyni-trilase-catalyzed addition of hydrocyanic acid to ketones in an organic solvent30. The (R)-cyanohydrins are obtained with good chemical yields and in high optical purity (Table 3)30. 

Nitriles are organic derivatives of hydrocyanic acid in which the substituting group is attached to carbon. Their formula is R.C N. Because most nitriles can be derived from corresponding acid amides, R.CO.NH2, by removal of w, they are called nitriles. For instance, the compd CH3.CN is called acetonitrile because it is derived from acetamide. It can also be called methyl cyanide. The compd C2HS.CN is called either propionitrile or ethyl cyanide, etc The first nitrile to be prepared was propionitrile which J. Pelouze obtained in 1834 by distg Ba ethyl sulfate with K cyanide... 

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. 

Free aldonic acid nitriles have been prepared in a few cases. Kiliani obtained the cyanohydrin of D-fructose by adding hydrocyanic acid to the ketose and Miksic obtained the nitriles already mentioned in a similar way. 

Barium cyanide is prepared by reacting barium hydroxide with hydrocyanic acid ... 

Mercury(ll) cyanide is prepared by the action of mercury(ll) oxide on aqueous hydrocyanic acid, followed by evaporation ... 

The discovery of bromine by A.-J. Balard and the preparation of prussic (hydrocyanic) acid, an oxygen-free acid, by Gay-Lussac made the evidence conclusive. Davy s formal announcement of the elementary... 

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... 

When an aldehyde is allowed to react with an optically active amine and hydrocyanic acid, one of the two diastereomeric amino nitriles, (124a) or (124b), may be formed in excess. To prepare the chiral amino acids (125a) or (125b), the nitriles (124a) and (124b), respectively, are hydrolyzed with mineral acids, whereupon R is split off. However, this asymmetric synthesis of amino acids has no industrial significance. 

H. Kiliani, as Fischer always emphatically acknowledged, discovered and developed the method of building up the aldose series by the cyanohydrin reaction to give nitriles from the nitrile, the next higher aldonic acid could then be prepared. In 1890, A. Wohl, working in Fischer s Berlin laboratory, elaborated the dehydration of an aldose oxime to the nitrile, from which the next lower aldose could be prepared by loss of hydrocyanic acid. Fischer exploited the possibilities of sugar extension and degradation afforded by the use of these two important methods. 

In order to avoid the preparation and handling of anhydrous hydrocyanic acid the passage of the gas direct from a generator (Am. Soc., 43, 348) and the use of zinc cyanide (Am. Soc., 45, 2373) have been tried with very satisfactory results. 

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. 

Initial preparative work with oxynitrilases in neutral aqueous solution [517, 518] was hampered by the fact that under these reaction conditions the enzymatic addition has to compete with a spontaneous chemical reaction which limits enantioselectivity. Major improvements in optical purity of cyanohydrins were achieved by conducting the addition under acidic conditions to suppress the uncatalyzed side reaction [519], or by switching to a water immiscible organic solvent as the reaction medium [520], preferably diisopropyl ether. For the latter case, the enzymes are readily immobilized by physical adsorption onto cellulose. A continuous process has been developed for chiral cyanohydrin synthesis using an enzyme membrane reactor [61]. Acetone cyanhydrin can replace the highly toxic hydrocyanic acid as the cyanide source [521], Inexpensive defatted almond meal has been found to be a convenient substitute for the purified (R)-oxynitrilase without sacrificing enantioselectivity [522-524], Similarly, lyophilized and powered Sorghum bicolor shoots have been successfully tested as an alternative source for the purified (S)-oxynitrilase [525],... 

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... 

Artificial products, obtained by addition of aromatic substances to commercial alcohol, may however be recognised, as they contain little or no hydrocyanic acid and are rich in benzaldehyde. Kirschwasser and similar spirits are prepared, although rarely, from alcohol and bitter almond or cherry laurel water and in such cases hydrocyanic acid is present. Artificial products are generally prepared from rectified alcohol and thus have a low coefficient of impurity and contain only very small amounts of higher alcohols. 

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