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J Hazard Mater. 2013 Feb 15;246-247:154-62. doi: 10.1016/j.jhazmat.2012.12.003. Epub 2012 Dec 10.

Mechanisms of the thermal decay of chlorpropham.

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WestCHEM School of Chemistry, University of Glasgow, Joseph-Black-Building, University Avenue, Glasgow G12 8QQ, United Kingdom.


DFT calculations were performed on the thermal reactions of chlorpropham 1, a carbamate pesticide and plant growth regulator frequently used in the storage of potatoes. At the conditions normally used in applying 1 (injection of a methanolic solution of 1 into a hot air stream, T ≈ 500°C), both ester pyrolysis of 1 and a methanol-or water-catalysed isocyanate cleavage are expected to proceed rapidly (lifetime of 1 less than a second). In both reactions, the final reaction product will be toxic and carcinogenic m-chloroaniline 2. Matrix-isolation experiments indicate that 1 undergoes thermal decay at temperatures as low as 250°C. Up to temperatures of ca. 500°C, formation of m-chlorophenylisocyanate 4 and isopropanol was the predominant reaction observed, while formation of propene, CO(2), and m-chloroaniline 2 was the most important reaction channel at higher pyrolysis temperatures. m-Chlorophenyl carbamic acid 3 could not be observed. The results indicate that at lower temperatures, 1 decays exclusively via isocyanate cleavage of 1, provided that traces of catalytic water or other protic compounds are present. At higher temperatures, ester cleavage of 1 becomes competitive and outweighs the isocyanate cleavage by a factor of ca. 10:1.

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