Diazonium ions dimerization

Xu and Li (1989) investigated H — CIDNP spectra of fifteen substituted benzene-diazonium ions during reduction with NaBH4. The spectra are consistent with a mechanism in which the first step is the addition of a hydride ion to the diazonium ion. The diazene formed (Ar - N2 - H) is assumed to dimerize and disproportionate into a radical pair [Ar-N-NH2 N = N — Ar] which loses one equivalent of N2 yielding [Ar—N —NH2 Ar] and recombines to give the diarylhydrazine. A proportion of the aryl radicals escape and form the hydro-de-diazoniation product. 

Zollinger (1971) calculated the actual rate constant referring to the monomeric diazo component from the (overall) measured rates and the dimerization equilibrium constant. The ratio of rates of the first to the second azo coupling reaction of the biphenyl-4,4 -bis-diazonium ion with the trianion of 2-naphthol-3,6-disulfonic acid at 15 °C, k /k2 9 is 80. 

Substituted 2-naphthols, as azo coupling components 356ff., 362 Sulfanilic acid 14, 71 Sulfidomolybdenum dimer anion, complex with diazonium ions 117 Surface-enhanced Raman spectroscopy 280... 

In aqueous solution, instead of undergoing reaction (c), the aryl radicals can dimerize to give biaryls (d) or react with diazonium ions to give azo compounds (e), copper(i) chloride... 

Diazotization of a-aminonitriles has been reported to generate free radicals, presumably from the diazonium ion. The cyanide group is clearly important, as this reaction is usually observed only with cyano diazonium ions. Diazotization of 2-amino-2-methylpropanenitrile (179) yields 2-nitrosopropanenitrile (180) which can be trapped to give 181, presumably by reaction of the radical 182 with NO. Further evidence of the existance of 182 is provided by observation of its dimerization product. 

The most favorable dimer of frans-triazene was predicted to form by simultaneous approach of the hydrogen of N, to N of the second molecule dissociation of the dimer can lead to the tautomeric triazenes [12]. The tautomerization of triazenes by a [1.3]-H shift probably has a high energy barrier [9]. The thermodynamically favored protonation site of trans-tnazene is N , and Np is the one least favored [12, 14]. Kinetic reasons suggest a protonation at N,, because the resulting cation can be considered a complex of an ammonia molecule and a diazonium ion, products which also result from the protonation of organic triazenes [14]. 

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