The carbylamine reaction (also known as the Hoffmann isocyanide synthesis) is the synthesis of an isocyanide by the reaction of a primary amine, chloroform, and base. The conversion involves the intermediacy of dichlorocarbene.
Illustrative is the synthesis of tert-butyl isocyanide from tert-butylamine in the presence of catalytic amount of the phase transfer catalyst benzyltriethylammonium chloride.[1]
- Me3CNH2 + CHCl3 + 3 NaOH → Me3CNC + 3 NaCl + 3 H2O
Similar reactions have been reported for aniline. It is used to prepare secondary amines.
Test for primary amines
[edit]As it is only effective for primary amines, the carbylamine reaction can be used as a chemical test for their presence. In this context, the reaction is also known as Saytzeff's isocyanide test.[2] In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed, as indicated by a foul odour. The carbylamine test does not give a positive reaction with secondary and tertiary amines.
Mechanism
[edit]The mechanism involves the addition of amine to dichlorocarbene, a reactive intermediate generated by the dehydrohalogenation of chloroform. Two successive base-mediated dehydrochlorination steps result in formation of the isocyanide.
See also
[edit]References
[edit]- ^ G. W. Gokel; R. P. Widera; W. P. Weber (1988). "Phase-transfer Hofmann Carbylamine Reaction: tert-Butyl Isocyanide". Organic Syntheses. 55: 232. doi:10.15227/orgsyn.055.0096.
- ^ Carbylamine reaction
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