Disproportionation of amines

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Equation (3) can also describe the disproportionation of amines such as aniline [151,154] and diethylamine [153]. However, the related expression... 

The disproportionation of amines is visualised as a nucleophilic substitution at the a-carbon atom of an amine adsorbed on an acidic site [149,153]. The attacking species is an amine adsorbed by a hydrogen bond onto a basic site... 

All metal amination catalysts are active in the disproportionation of amines, which can lead to equilibration of primary, secondary, and tertiary amines. For example, for simple primary amines the initial step is the formation of an aldimine by dehydrogenation (Scheme 2). Subsequent addition of an amine and hydrogenation lead to a mixture of primary, secondary, and tertiary amines. The same active metal sites catalyze alcohol amination and amine disproportionation, which explains why the reactant alcohol inhibits disproportionation and selectivity for the desired amine drops considerably only after consumption of alcohol [2]. It is also evident from Scheme 2 that sufficient hydrogen present on the metal surface can reduce the concentration of imine and thus suppress disproportionation. 

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See also in sourсe #XX -- [ ]

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