Hydrogen cyanide properties

The physical properties of hydrogen cyanide are Hsted in Table 1. 

Chemical Properties. Hydrogen cyanide is a weak acid its ionization constant is of the same magnitude as that of the natural amino acids (qv). Its stmcture is that of a linear, triply bonded molecule, HC=N. 

Cyanohydrins are usually colorless to straw yellow Hquids with an objectionable odor akin to that of hydrogen cyanide. The lower molecular-weight cyanohydrins can be distilled under reduced pressure provided the cyanohydrin is kept at a slightly acidic pH. Table 2 Hsts physical properties of some common cyanohydrins. 

Three eheinieal properties of hydrogen cyanide eontribute to tlie potential for an aeeidental release of the eheinieal. "... 

These possess the dangerous reactions of the CN ion, or cyano group. The hexacyanoferrate (III) anion also has oxidising properties. Finally, it is thought to produce an extremely unstable acid in certain conditions. These salts also produce hydrogen cyanide, which is highly toxic, in an acid medium (see p.334). 

Some properties of potassium cyanide, hydrogen cyanide, and sodium cyanide... 

Table 15.1 Some Properties of Potassium Cyanide, Hydrogen Cyanide, and Sodium Cyanide... 

Property Potassium Cyanide Hydrogen Cyanide Sodium Cyanide... 

Hydrogen cyanide (HCN) is a colorless, highly poisonous gas or liquid (below 26.7 °C) having an odor of bitter almonds (Hartung 1994 Pesce 1994). It is a weak acid. Exposures may occur in industrial situations as well as from cigarette smoke and combustion products and from naturally occurring cyanide compounds in foods. There is a potential for exposure when any acid is mixed with a cyanide salt. Intravenously administered sodium nitroprusside (Na2[Fe(CN)5N0]-2H20) has been used clinically to lower blood pressure (Schulz et al. 1982). Chemical and physical properties are listed in Table 5-2. 

Oxynitrilases are enzymes that catalyze the formation and cleavage of cyanohydrins through the stereoselective addition of hydrogen cyanide to aldehydes or methyl ketones giving enantiopure a-hydroxynitriles. The use of (R)-oxynitrilases for the preparation of chiral cyanohydrins has dramatically grown in the last decade because of their possibihties as precursors for the synthesis of many compounds with physiological properties [50]. 

By-products of this reaction are acetonitrile, CH3-C=N, and hydrogen cyanide. This is now a major source of these two materials. Interestingly, the C2 by-product acetonitrile has a bp of 81.6 °C, whereas acrylonitrile with three carbons has a lower bp of 77.3 °C, quite an unusual reversal of this physical property s dependence on molecular weight. The TWA of acrylonitrile is 2 ppm and it is on the list of Reasonably Anticipated to Be Human Carcinogens. ... 

Hydrogen cyanide is extremely toxic hy ingestion, inhalation, skin absorption, and all routes of exposure. An oral dose of 50 mg could be lethal to humans (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 2nd ed.. New York John Wiley). Symptoms from acute poisoning include labored breathing, shortness of breath, paralysis, unconsciousness, and respiratory failure. Lower doses can cause headache, nausea and vomiting. Oral LDsoin mice is 3.7 mg/kg. Amyl nitrite is an effective antidote. 

Potassium cyanide is a dangerously toxic substance. Ingestion of 100 to 150 mg can cause collapse and cessation of breathing in humans. At lower doses, the acute effects are nausea, vomiting, headache, confusion and muscle weakness (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, ed. pp. 292-294. New York John Wdey Sons). Contact with acid can liberate highly toxic vapors of hydrogen cyanide. Sodium thiosulfate and sodium sulfate have shown antidotal activity to KCN toxicity. 

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