Hydrogen-cyanide formation

Thermal decomposition under hydrogen of a series of pentacyanocobaltate complexes (CN-, N02-, NO- or N3-ligands) revealed that the latter complex is the most exothermic by far. Presence of iron powder suppresses hydrogen cyanide formation. 

Following a similar motivation, a schematic flow scheme of a miniplant for hydrogen cyanide formation via the Degussa route was proposed in [30],... 

Tuovinen, H., Blomqvist, P., and Saric, F. Modelling of hydrogen cyanide formation in room fires. Fire Safety Journal, 2004. 39(8), 737-755. 

Johnson, W.R. and J.C. Kang Mechanisms of hydrogen cyanide formation from the pyrolysis of amino acids and related compounds J. Org. Chem. 36 (1971) 189-192. 

Koji, T, M. Risa, F. Masahiro, and T. Hideki A pyrolysis study on hydrogen cyanide formation in tobacco smoke 56th Tobacco Science Research Conference, Program Booklet and Abstracts, Vol. 56, Paper No. 76, 2002, pp. 66-67. 

Hydrogen cyanide formation may contribute to the toxicity of snake venom, owing to the high levels of L-amino acid oxidase in some snake venoms. This enzyme is harmless on injection, but the tissue destruction caused by other venom components probably provides the required substrate and cofactor for HCN production. Cyanide inhibits ion... 

Hydrogen cyanide adds to an olefinic double bond most readily when an adjacent activating group is present in the molecule, eg, carbonyl or cyano groups. In these cases, a Michael addition proceeds readily under basic catalysis, as with acrylonitrile (qv) to yield succinonitnle [110-61-2], C4H4N2, iu high yield (13). Formation of acrylonitrile by addition across the acetylenic bond can be accompHshed under catalytic conditions (see Acetylene-DERIVED chemicals). 

Under certain conditions hydrogen cyanide can polymerize to black soHd compounds, eg, hydrogen cyanide homopolymer [26746-21-4] (1) and hydrogen cyanide tetramer [27027-02-2], C H N (2). There is usually an incubation period before rapid onset of polymer formation. Temperature has an inverse logarithmic effect on the incubation time. Acid stabilizers such as sulfuric and phosphoric acids prevent polymerization. The presence of water reduces the incubation period. 

Commercial potassium cyanide made by the neutralization or wet process contains 99% KCN the principal impurities are potassium carbonate, formate, and hydroxide. To prepare 99.5 + % KCN, high quahty hydrogen cyanide and KOH must be used. 

Table 3. Equilibrium Constants for Formation of Cyanohydrins from Hydrogen Cyanide Plus Carbonyl Compounds ...

Production of cyanohydrins is accompHshed through the base-cataly2ed combination of hydrogen cyanide and the carbonyl compound in a solvent, usually the cyanohydrin itself (17). The reaction is carried out at high dilution of the feeds, at 10—15°C, and pH 6.5—7.5. The product is continuously removed from the reaction 2one, cooled to push the equilibrium toward cyanohydrin formation, and then stabili2ed with mineral acid. Purification is usually effected by distillation. 

Cyanohydrin Synthesis. Another synthetically useful enzyme that catalyzes carbon—carbon bond formation is oxynitnlase (EC 4.1.2.10). This enzyme catalyzes the addition of cyanides to various aldehydes that may come either in the form of hydrogen cyanide or acetone cyanohydrin (152—158) (Fig. 7). The reaction constitutes a convenient route for the preparation of a-hydroxy acids and P-amino alcohols. Acetone cyanohydrin [75-86-5] can also be used as the cyanide carrier, and is considered to be superior since it does not involve hazardous gaseous HCN and also virtually eliminates the spontaneous nonenzymatic reaction. (R)-oxynitrilase accepts aromatic (97a,b), straight- (97c,e), and branched-chain aUphatic aldehydes, converting them to (R)-cyanohydrins in very good yields and high enantiomeric purity (Table 10). 

The use of fire retardants in polymers has become more complicated with the realisation that more deaths are probably caused by smoke and toxic combustion products than by fire itself. The suppression of a fire by the use of fire retardants may well result in smouldering and the production of smoke, rather than complete combustion with little smoke evolution. Furthermore, whilst complete combustion of organic materials leads to the formation of simple molecules such as CO2, H2O, N2, SO2 and hydrogen halides, incomplete combustion leads to the production of more complex and noxious materials as well as the simple structured but highly poisonous hydrogen cyanide and carbon monoxide. 

Chemical Reactivity - Reactivity with Water. When potassiiun cyanide dissolves in water, a mild reaction occurs and poisonous hydrogen cyanide gas is released. The gas readily dissipates, however if it collects in a confined space, then workers may be exposed to toxic levels. If the water is acidic, toxic amounts of the gas will form instantly Reactivity with Common Materials Contact with even weak acids will result in the formation of deadly hydrogen cyanide gas Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Cyanohydrin formation (Section 17.7) Hydrogen cyanide adds to the carbonyl group of aldehydes and ketones. 

The formation of adducts of enamines with acidic carbon compounds has been achieved with acetylenes (518) and hydrogen cyanide (509,519,520) (used as the acetone cyanohydrin). In these reactions an initial imonium salt formation can be assumed. The addition of malonic ester to an enamine furnishes the condensation product, also obtained from the parent ketone (350,521). 

Hot spot formation witliin tlie reactor can result in catalyst breakdown or physical deterioration of tlie reactor vessel." If tlie endothermic cyanide reaction has ceased (e.g., because of poor catalyst performance), the reactor is likely to overheat. Iron is a decomposition catalyst for hydrogen cyanide and ammonia under the conditions present in the cyanide reactor, and e. posed iron surfaces in the reactor or reactor feed system can result in uncontrolled decomposition, which could in turn lead to an accidaital release by overheating and overpressure. 

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