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Kinetics and mechanism of the reaction of polarized ethylenes with hydrazines and anilines
Authors: Hanusek Jiří | Tarabová Denisa | Milata Viktor
Year: 2013
Type of publication: ostatní - přednáška nebo poster
Page from-to: nestránkováno
Titles:
Language Name Abstract Keywords
eng Kinetics and mechanism of the reaction of polarized ethylenes with hydrazines and anilines The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R1-NH2 (R1: (CH3)2N, CH3NH, NH2, C6H5NH, CH3CONH, 4-CH3C6H4SO2NH, 3- and 4-X-C6H4) were studied at 25 °C in methanol. It was found that the reactions with all hydrazines (the only exception was the reaction of (ethoxymethylidene)malononitrile with N,N-dimethylhydrazine) showed overall second-order kinetics and kobs were linearly dependent on the hydrazine concentration which is consistent with the rate-limiting attack of the hydrazine on the double bond of the substrate. Corresponding Bronsted plots are linear (without deviating N-methyl and N,N-dimethylhydrazine) and their slopes (beta-Nuc) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the C-N bond formed in the transition state. The deviation of both methylated hydrazines is probably caused by the different site of nucleophilicity/basicity in these compounds (tertiary/secondary vs. primary nitrogen). A somewhat different situation was observed with the anilines (and once with N,N-dimethylhydrazine) where parabolic dependences of the kinetics gradually changing to linear dependences as the concentration of nucleophile/base increases. The second-order term in the nucleophile indicates the presence of a steady-state intermediate - most probably T?. Br?nsted and Hammett plots gave ?Nuc = 1.08 and ? = ?3.7 which is consistent with a late transition state whose structure resembles T?. Kinetics; mechanism; polarized ethylenes; hydrazines; anilines

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