Carbonyl halides, reactions phosgene

Phosgene can be used as the starting material for the preparation of other potentially useful carbonyl halides and carbonyl pseudohalides. Reaction of phosgene with fluorspar, for example, gives COCIF (see Section 9.1.1 and Chapter 16). With aluminium(III) bromide, COBrj is formed (Section 9.1.2.6). Reaction of COClj with HF gives COFj (see Section 9.10.4 and Chapter 13), reaction with silver cyanide gives carbonyl dicyanide, CO(CN)j (Section 9.1.7), whereas reaction with a mixture of sodium fluoride and HCN gives the mixed carbonyl halide pseudohalide, COFCN (Section 9.1.7 and Chapter 13). The chemistry of these... 

It is also interesting to note that the mixed carbonyl halide, COBrCl, has been prepared by the reaction of phosgene with aluminium(III) bromide (see Section 9.1.2.6) [2127] ... 

Dichlorodifluoromethane reacts with WO at 525 C mainly to give CO, WOF and WOCl. Small amounts of phosgene and carbonyl difluoride are also formed, but these compounds may arise from the reactions of the CO with the nickel halide films formed on the inside surfaces of the nickel reactor [2159]. 

Aryl cyanates and other stabilized cyanates can be acylated with various acyl halides to yield /V-acylchloroformimidatcs 15416 (cf. Houben-Weyl, Vol. E4, p 546). These compounds, which are surprisingly stable, easily react with amidincs to form 1,3,5-triazines 16.417 This reaction is believed to proceed via a nucleophilic substitution of the halide atom, followed by cyclization to the carbonyl carbon of the acyl group.417. In the case of phosgene (R2 = Cl), addition of amidines to the activated cyanates is not selective417,418 for formation of the 1,3,5-triazines. 

By analogy with the general synthesis of imidoyl chlorides it can be expected that carbamates and thiocarbamates undergo reaction with a variety of acid halides to afford 1-haloformimidates and 1-halothio-formimidates, respectively. For example, carbamates have been reacted with carbonyl chloride ( ), pyrocatecholphosphorus trichloride ( ), and phosphorus pentachloride ( ), and isocyanates were obtained. In view of the catalytic effect of N,N-dimethylformamide in the phosgenation of carbamates to isocyanates, the intermediacy of 1-chloroformimidates X is anticipated ( ). 

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