Halogenation of Imidoyl Chlorides

The yields are good, especially when the aromatic ring is deactivated by the presence of substituents, such as chloro, nitro, and carboxyl groups. However, 2,5-dichloro-4-nitrophenylformamide (XLVII) reacts with elimination of cyanogen chloride, as evidenced by the isolation of substantial amounts of 1,2,4,5-tetrachlorobenzene (XLVIII) ( ). 

4-Chlorophenylcarbonimidoyl dichloride ( ). To a solution of 67.5 g (0.5 mole) of sulfuryl chloride in 150 ml of thionyl chloride, 77.5 g (0.5 mole) of N-(4-chlorophenyl)formamide is added portionwise at 15-20°C. After stirring for several hours at room temperature the reaction mixture is heated slowly to 80°C, and the thionyl chloride is removed by distillation. Vacuum distillation of the residue yields 89 g (86%) of 4-chlorophenyl-carbonimidoyl dichloride, b.p. 110-113V10 mm. 

Aliphatic formamides, such as cyclohexylformamide, react likewise. However, the reaction has to be conducted stepwise, i.e., the initial conversion to XLVI has to be complete, otherwise chlorination of the formamide occurs faster, giving rise to the formation of isocyanates XLIX ( ). 

The reaction of phenylthioformamide (L) with bromine yields 4-bromo-phenylcarbonimidoyl dibromide (LI), most likely by a similar mechanism ( ). 

In the absence of the chlorinating agent reaction of the imidoyl chloride XLVI (R = aryl) with unreacted arylformamide occurs with formation of formamidines ( 3,57,58,86,134,152 Chapter 3). 

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The halogenation of imidoyl chlorides and iminium chlorides occurs readily, provided that an a-hydrogen is present. Thus, a simple method of dihalogenation of aliphatic carboxylic acid amides is provided by the addition of halogen to imidoyl chlorides and iminium chlorides. 

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