Epoxides reaction with, phosgene

Primary cycloaUphatic amines react with phosgene to form isocyanates. Reaction of isocyanates with primary and secondary amines forms ureas. Dehydration of ureas or dehydrosulfuri2ation of thioureas results in carhodiimides. The nucleophilicity that deterrnines rapid amine reactivity with acid chlorides and isocyanates also promotes epoxide ring opening to form hydroxyalkyl- and dihydroxyalkylaniines. Michael addition to acrylonitrile yields stable cyanoethylcycloalkylarnines. 

We introduced these guanidinium salts in a 1985 patent (Ref. 6) on the conversion of carboxylic acids to acid chlorides with phosgene. In this process, only 0.02 mol. % of HBGCI was required, two orders of magnitude less than the quantities of other catalysts typically used. Many new other applications including phosgene reactions with phenols, thiols, aldehydes, epoxides or O-demethyla-tion methods have been developed later and are discussed in this book. 

Scheme 54 General reaction of epoxides with phosgene.

The reaction of phosgene with an epoxide catalyzed by pyridine to afford (3-chloro chloroformates is well known (Ref. 55). Unfortunately, this reaction often leads to non regio-specific ring opening of the epoxides and produces bis-p-chlorocarbonates as side products in yield up to 20-30% [Scheme 54]. 

There is thus considerable scope for further examination of the reactions of phosgene with a wide variety of alcohols, diols, aldehydes, hydroxy-aldehydes, epoxides, esters, acids and anhydrides to produce the desired range of chlorinated organic materials. The analogous reactions of COFj and of COCIF will be described in Chapters 13 and 16, respectively. 

Processes for the continuous production of chloro-substituted chloroformates, CHjClCHROCOCl (R = H, Me, CH OCH 2CH=CH or CHjOPh) from the reaction of phosgene with 1,2-epoxides have been disciosed, in which activated carbon is used as a catalyst, and the reaction is conducted at an operating temperature of 75-115 C in a circulating stream of pre-formed chloroformate [229]. 

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