Possible reaction mechanisms of hydrogen cyanide formation from oxime blocked isocyanates and related organic compounds during total cyanide analysis

Abstract

Frequent reports by paint manufactures of hydrogen cyanide detection in waste contaminated with oxime blocked isocyanates lead to an investigation of possible hydrogen cyanide generating reaction pathways. GC‐MS is empolyed to analyze traces of byproducts of the total cyanide analysis. A Beckmann Rearrangement of oxime blocked isocyanates has been detected. The formation of α‐ketocyanides and their hydrolysis to free hydrogen cyanide is reported as the key compound that leads to hydrogen cyanide generation. Hydrogen cyanide yields from the reaction of NO_x or hydroxylamine with ketones, alcohols, amines, peptides, EDTA, ascorbic acid and cyanides. The presence of an organic phase improves hydrogen cyanide yields. A sample pretreatment for oxime blocked isocyanate samples is described.

Key words:

• Total cyanide analysis
• hydrogen cyanide generation
• blocked isocyanates
• oximes
• ketones
• α‐ketocyanides