Alkyldiazonium ions

The a-carbons of nitrosamines undergo enzymatic hydroxylation followed by oxidative cleavage leading to the formation of alkyldiazo hydroxides, alkyldiazonium ions and alkyl cations [34]. These cations are postulated to initiate the process of carcinogenesis in some cases by alkylating the base units of DNA [35, 36]. 

The main drawback to this reaction is the toxicity of diazomethane and some of its precursors. One possible alternative is the use of alkyltriazenes as reactive alkylating agents.52 Alkyltriazenes are readily prepared from primary amines and aryldiazonium salts.53 The triazenes, on being protonated by the carboxylic acid, generate a reactive alkylating agent that is equivalent, if not identical, to the alkyldiazonium ions generated from diazoalkanes. 

Alkyldiazonium Ions. The intermediacy of alkyldiazonium ions in a variety of organic reactions is well established.450 152 They are common intermediates in the acid-catalyzed decomposition of diazo compounds and the nitrous acid-induced deamination of aliphatic primary amines. The evidence for RN2+ (R = alkyl) intermediates come from both rate data and product analysis studies. However, direct investigation of alkyldiazonium ions has been difficult due to their instability. 

The stability of alkyldiazonium ions may be greatly increased by an appropriate molecular structure. Bott has reported the generation of a variety of stable vinyldia-zonium ions461 [Eqs. (4.135) and (4.136)]. The results are summarized in... 

Aromatic Diazonium Ions. In contrast to alkyldiazonium ions, aryldiazonium ions are well-studied.469 77 They were known as early as 1894. They are isolable as ionic salts with a variety of counterions such as BIT, PF6, SbCl6, SbF6, AsF6-, and C104. They undergo a variety of nucleophilic reactions and an excellent review is available on the subject.478... 

Taft and Cannell also determined thiocyanate isothiocyanate ratios for the deamination of benzhydrylamine and for the isobutyl fraction in the deamination of isobutylamine. The values of [RNCS] [RSCN] were 9 1 and 5-3 1, respectively. It is interesting that values for the benzhydryl- and t-butyl-amines bracket that for isobutylamine. It is most unlikely that the isobutyl cation is of intermediate selectivity, and the results may suggest that the reaction of primary alkyldiazonium ions is sufficiently near the mechanistic borderline for so strong a nucleophile as thiocyanate to force an Sif2 displacement on the isobutyldiazonium ion. 

Whereas aryldiazonium salts can usually be isolated or used as intermediates in coupling reactions (industrial production of azo dyes), alkyldiazonium ions are usually so short-lived that they cannot even be observed spectroscopically. Cyclopropyldiazonium salts stand in between due to the high energy of the cyclopropyl cation they cannot usually be isolated, but they can be used as intermediates in coupling reactions. 

There is evidence that carbocations do play a role in the reaction of some diazonium ions. For example, the products of nucleophilic addition to f-butyl carbocations are essentially the same whether the carbocations are produced from aliphatic amines or from solvolysis of the corresponding alkyl halide. The decomposition of the diazonium ion to form a carbocation should become less favorable as the stability of the carbocation decreases, and the formation of an ethyl cation from ethyldiazonium ion in the gas phase has been calculated to be endothermic by 13.9kcal/mol. The decomposition of a 1° alkyldiazonium ion to N2 and a 1° carbocation in solution may be energetically more favorable, perhaps even exothermic, but it is questionable... 

A similar conclusion was reached by Monera, O. D. Chang, M.-K. Means, G. E. /. Org. Chem. 1989,54,5424, who investigated the deamination of 1-octanamine in a series of solutions ranging horn pH 2 to pH 10. The relative distribution of products—1-octanol, 2-octanol, 1-octene, and 2-octenes (80% trans, 20% cis)—did not vary significantly asa function of pH. The authors interpreted the results in terms of conformationally determined reactions of the alkyldiazonium ion. 

Primary aliphatic amines (RNH2) react with nitrous acid in the same way that primary arylamines (ArNH2) do, to form diazonium ions. But alkyldiazonium ions RN2 are much less stable than aryldiazonium ions ArN2 and readily lose nitrogen even at 0°C. Explain the difference. 

The alkyldiazonium ion is expected to have an exceedingly short lifetime and a single-step process may more accurately describe the elimination step ... 

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