Kinetics and mechanism of the reaction of alkoxymethylidene malonate and malononitrile with hydrazines and anilines. (26th April 2013)

• Record Type: Journal Article
• Authors: Tarabová, Denisa; Milata, Viktor; Hanusek, Jiří
• Is Part Of: Journal of physical organic chemistry. Volume 26:Number 6(2013:Jun.)
• Page Start: 503
• Page End: 509
• Publication Date: 2013-04-26
• Subjects: alkoxymethylene malonate -- alkoxymethylene malononitrile -- anilines -- hydrazines -- kinetics -- mechanism -- nucleophilic vinylic substitution; Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3115
• Languages: English
• ISSNs: 0894-3230

Abstract

Abstract : The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (alkyl: methyl, ethyl) and (ethoxymethylidene)malononitrile with substituted hydrazines and anilines R 1 –NH2 (R 1 : (CH3 )2 N, CH3 NH, NH2, C6 H5 NH, CH3 CONH, 4‐CH3 C6 H4 SO2 NH, 3‐ and 4‐X‐C6 H4 ; X: H, 4‐Br, 4‐CH3, 4‐CH3 O, 3‐Cl) 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 k obs 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 Brønsted plots are linear (without deviating N ‐methyl and N, N ‐dimethylhydrazine), and their slopes (βNuc ) 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 ± . Brønsted and Hammett plots gave βNuc = 1.08 and ρ = −3.7 which is consistent with a late transition state whose structure resembles T ± . Copyright © 2013 John Wiley & Sons, Ltd. Abstract : The kinetics and mechanism of the nucleophilic vinylic substitution of dialkyl (alkoxymethylidene)malonates (1a, b ) and (ethoxymethylidene)malononitrile (1c ) with substituted hydrazines and anilines were studied at 25 °C in methanol. The reactions showed overall second‐order and third‐order kinetics with hydrazines and anilines, respectively. Brønsted and Hammett plots obtained from the measured data reflected gradually increasing order of the C−N bond formed in the transition state with the increasing reactivity of1 1 1 and with the change from hydrazines to anilines.