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REVISTA DE CHIMIE
https://doi.org/10.37358/Rev.Chim.1949

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Revista de Chimie, Volume 57, Issue 1, pp. (2006)




Azocoupling in orto-position, a linear-relationship approach to mechanism

Abstract:

The kinetic data for the azocoupling in orto position of substituted benzenediazonium cations to 1-naphthol-4-sulphonic acid (series A) <4,5>, 4-chloro-1-naphthol (series B) and 1-amino-naphthalene-4-sulfonic acid (series C) <6,7> is aqueous solution(series B in H2O: CH3OH, 1:1 solution) are analized in a linear relationship rate constant -s-Hammett constant, approach. Good correlations with s-Hammett for the benzene-substituent are obtained for all 3 series (N=11, 9, 9; r2> 0,97) indicating a common reaction mechanism. The values of the reaction constants in the range r:3.2-3.9 indicates a rather weak conjugation from the substituent to the reaction centre, favouring the hypothesis of Zollinger, a transition state near to the sigma aduct of figure 1. The hypothesis of a H2O molecule binding to the transition state is also favoured by the differences in activation entropies ÄS#, large and positive for series A and B, but negative for series C, where H2O molecule binding to the transition complex (as in fig.1) is not possible. Keywords: Azocoupling mechanism, orto-position azocoupling, linear-relatioship

Issue: 2006 Volume 57, Number 1
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