Hydrocyanic Acid Production

The third large-scale use of methane is in hydrocyanic acid production (1,2.3), and there are two known methods for HCN synthesis (Equations (7) and (S))  

The Andrussow process (7) uses Pt(-f Rh or Ir) in the form of gauze (as in the Nila oxidation process) and its yield is 60-65% for complete conversion per pass. 

The second method is the pyrolysis of a methane-ammonia mixture (8) in the presence of Pt deposited inside a-alumina tubes. The yield is 80-85% based on Nllj and 90 - 91% based on CH4. Alumina participates in the formation of the actual catalyst (a Pt Al alloy). This method is also applied in industry (the Degussa process). 

Tlie awinigan process uses higher alkanes, as well as methane, in a fluidized bed of coke at 1300 I600 C. A high consumption of electrical energy is required, however, and this limits practical interest to locations where cheap electricity is avaUabIc. 

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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. 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

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. ... 

Hydrocyanic acid, HCN, also known as prussic acid, or formo-nitrile, is the product of decomposition of numerous glucosides found in a very large number of plants, usually together with some other volatile compound, so that essential oils containing hydrocyanic acid do not, for practical purposes, exist in the first instance as such in the plant, but are only developed on the decomposition of the glucoside. 

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. 

Hormann, A.L., Coffer, M.T. and Shaw, C.F. Ill (1988) Reversibly and irreversibly formed products from the reactions of mercaptalbumin (AlbSH) with Et3PAuCN and of AlbSAuPEts with hydrocyanic acid. Journal of the American Chemical Society, 110, 3278-3284. 

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. 

Casadei, E., P. Jansen, A. Rodrigues, A. Molin, and H. Rosling. 1984. Mantakassa an epidemic of spastic paraparesis associated with chronic cyanide intoxication in a cassava staple area of Mozambique. 2. Nutritional factors and hydrocyanic acid content of cassava products. Bull. World Health Org. 62 485-492. 

Further evidence for the formation of intermediate compounds in catalytic reactions is afforded by the observation (a) that optically active camphor is formed from optically inactive (racemic) camphor carboxylic acid in the presence of the d- or /-forms of quinine, quinidine or nicotine and (6) that optically active bases, e.g., quinidine, catalyze the synthesis of optically active mandelonitrile from benzaldehyde and hydrocyanic acid.10 These results hardly admit of any other interpretation than the intermittent production of a catalyst-reactant compound. 

In his later papers on degradation reactions, Zempl4n employed sodium methoxide and used chloroform as the solvent for the sugar derivative. When the acyl groups are removed, the cyanohydrin can be considered an intermediate product which loses hydrocyanic acid to yield an aldose. It is possible that the acetyl and nitrile groups are eliminated simultaneously by concurrent reactions. 

The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudocyanogen sulphide, (CNS)3 (cf. p. 236). The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts ... 

Cyanogen Diselenide or Selenocyanogen, Sea(CN)2.-—By heating together selenious anhydride, anhydrous hydrocyanic acid and acetic anhydride to 100° C. under pressure in a sealed tube until solution is complete, there are formed on evaporation of the product, yellowish crystals which have been regarded as impure cyanogen diselenide, Se2(CN)2. On examination under the microscope these yellowish crystals appear as a mixture of browmish plates and needle-shaped crystals.4... 

Vanadyl Cyanide.—Berzelius5 obtained vanadyl cyanide by the action of hydrocyanic acid on hydrated hypovanadic oxide in the absence of air. The product was not, however, analysed. 

The tests to be made on spirits and liqueurs include a certain number which are common to all these products, such as determinations of the alcoholic strength, extract and ash, and tests for impurities and denaturing agents other investigations are made only with certain products, examples of these being the examination of kirschwasser for hydrocyanic acid, the determination of sugars in liqueurs, etc. The former are treated under General Methods and the latter in the Special Part. 

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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