Hydrazines radical formation from

Hydrazine-derived drugs (e.g. phenylhydrazine) are metabolized to thiol-reactive intermediate radicals which form thiyl radicals on haemoglobin, detectable in vivo [72, 73]. Reduction of quinones by thiols can generate, not only quinone radical anions [74—76], but also thiyl radicals [77, 78]. Other examples of thiyl radical formation resulting from drug metabolism eire discussed by De Gray and Mason [28]. 

Removal of an electron from a hydrazine unit changes the lone pair orbital occupancy from four to three, which has a large effect on the preferred geometry with respect to the nitrogens. The formation of a three-electron bond has also been demonstrated in the cation radical of octamethyl-l,2,4,5-tetra-aza-3,6-disilacyclohexane. In this cation radical, the spin density is distributed between only two of the four nitrogen atoms. There is a pronounced interaction of the unpaired electron with protons of the methyl groups joined to these two nitrogen atoms. 

The regioselectivity of pyrazole 55 formation is completely the reverse of that of pyrazoline 57 in the reaction of ketones 54 with hydrazines without DPPH. In addition, heterocycles 56 cannot be obtained from 57 by the action of DPPH. These facts show that the radical-initiated treatment of a, 3-unsaturated ketones with hydrazines does not occur via the initial pyrazoline 57 formation. 

The one-electron oxidation of a secondary amine results in the formation of a secondary aminium ion which on deprotonation gives an aminyl radical (Scheme 1). The nature of the final products derived from these intermediates dqiends very much on the structure of the substrate and the reaction conditions. If the amine has a hydrogen atom on the a-carbon atom the major products usually result from deprotonation at this a-position. With aromatic secondary amines, products can result from coupling of the delocalized radicals at a ring carbon atom. The formal dimerization of aminyl radicals shown in Scheme 21 is therefore not often a useful method of preparation of hydrazines. Nickel peroxide has been used to oxidize diphenylamine to tetraphenylhydrazine in moderate yield, and other secondary arylamines also give... 

The heat of formation of the NH2 radical, and hence i)(NH2 -H) from the heat of formation of ammonia and Z)(H2), has been derived from the kinetics of the pyrolysis of benzylamine and hydrazine. These results lead to Z)(NH2 - H) = 100 kcal and 104 2 kcal respectively9... 

Thermochemical data for alkyl amino radicals show for alkylhydrazines a trend in D (N-N) for these compounds in which the N-N bond was strengthened by increasing the degree of substitution by methyl in NH2 NH2 . From these values it was possible to determine values for the enthalpies of formation of the alkylamino radicals , and to confirm these by electron impact studies. The latter values were found to be in agreement with those obtained from pyrolysis studies. Hydrazine has often been used as a source of amino radicals by pyrolysis flame decomposition shock tube decomposition , electrodeless discharge and microwave discharge , viz. 

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