Phosgene equivalent, trichloromethyl chloroformate

TRICHLOROMETHYL CHLOROFORMATE AS A PHOSGENE EQUIVALENT 3-ISOCYANATOPROPANOYL CHLORIDE... 

Trichloromethyl chloroformate (diphosgene) is used as a safe substitute for highly toxic phosgene gas. The latter is generated in situ by addition of catalytic amounts of tertiary amines or amides, or active carbon. Diphosgene also disproportionates to 2 equivalents of phosgene on heating above 250°C. 

Solid bis(trichloromethyl) carbonate as phosgene equivalent) added under Nj to a stirred soln. of cyclohexanecarboxaldehyde and a little pyridine in carbon tetrachloride at —20 at such a rate that the temp, remained at —10° to —20°, the viscous slurry allowed to warm to room temp, over 90 min, heated to 40° for 1 h, cooled to room temp., and stirred overnight cyclohexyl(chloro)methyl chloroformate. Y 89%. The method is mild, high-yielding, and avoids the use of hazardous phosgene. F.e.s. M.J. Coghlan, B.A. Caley, Tetrahedron Letters 30, 2033-6 (1989). 

Therefore, diphosgene can be regarded as being equivalent to two molecules of phosgene, into which it is slowly decomposed when pure [58]. One of the internal trichloromethyl chlorine atoms probably plays the Nu role in a four-membered cyclic transition state. A continuous stream of phosgene is also emitted when trichloromethyl chloroformate is simply heated under reflux [55]. 

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