Arylamines nitrosation

We learned m the preceding section that different reactions are observed when the var lous classes of alkylammes—primary secondary and tertiary—react with mtrosatmg agents Although no useful chemistry attends the nitrosation of tertiary alkylammes elec trophilic aromatic substitution by mtrosyl cation ( N=0 ) takes place with A A dialkyl arylamines... 

Diazotization (Section 22 16) The reaction by which a pn mary arylamine is converted to the corresponding diazo mum ion by nitrosation... 

Tertiary alkylamines illustrate no useful chemistry on nitrosation. Tertiary arylamines undergo nitrosation of the ring by electrophilic aromatic substitution. 

Research into the mechanism of diazotization was based on Bamberger s supposition (1894 b) that the reaction corresponds to the formation of A-nitroso-A-alkyl-arylamines. The TV-nitrosation of secondary amines finishes at the nitrosoamine stage (because protolysis is not possible), but primary nitrosoamines are quickly transformed into diazo compounds in a moderately to strongly acidic medium. The process probably takes place by a prototropic rearrangement to the diazohydroxide, which is then attacked by a hydroxonium ion to yield the diazonium salt (Scheme 3-1 see also Sec. 3.4). 

Primary arylamines, like primary alkylamines, form diazonium ion salts on nitrosation. Aryl diazonium ions are considerably more stable than their alkyl counterparts. Whereas alkyl diazonium ions decompose under the conditions of their formation, aryl diazonium salts are stable enough to be stored in aqueous solution at 0-5°C for a reasonable time. Loss of nitrogen from an aryl diazonium ion generates an unstable aryl cation and is much slower than loss of nitrogen from an alkyl diazonium ion. 

Alkyl nitrites have been used to effect nitrosation or diazotisation in aprotic solvents. Typically, arylamines react in benzene solution to give biaryls (Cadogan et al., 1966). Friedman and coworkers have examined the products from alkyl nitrites and amines in a number of solvents. No mechanistic study aimed at identifying the details of the nitrosation reaction was attempted rather the emphasis was on the intermediacy of a diazoalkane and subsequent reaction of carbocations (Friedman and Bayless, 1969 Friedman et al., 1969). 

Nitrosation. This reagent reacts with arylamines readily to furnish 1,3-diaryltriazenes. Hydrazides give acyl azides and arylamines furnish diazoaminoarenes ArN=NNHAr. 

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