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Kinetics and mechanism of the reaction of alkoxymethylidene malonate and malononitrile with hydrazines and anilines
Authors: Tarabová Denisa | Milata Viktor | Hanusek Jiří
Year: 2013
Type of publication: článek v odborném periodiku
Name of source: Journal of Physical Organic Chemistry
Publisher name: John Wiley & Sons Ltd.
Place: Chichester
Page from-to: 503-509
Titles:
Language Name Abstract Keywords
cze Kinetika a mechanismus reakce alkoxymethyliden malonátů a malononitrilu s hydraziny a aniliny Kinetika a mechanismus nukleofiliní vinylové substituce dialkyl (alkoxymethyliden)malonatů (alkyl: methyl, ethyl) a (ethoxymethyliden)malononitrilu se substituovanými hydraziny a aniliny R1NH2 (R1: (CH3)2N, CH3NH, NH2, C6H5NH, CH3CONH, 4-CH3C6H4SO2NH, 3- a 4-X-C6H4; X: H, 4-Br, 4-CH3, 4-CH3O, 3-Cl) byly studovány při 25 C v methanolu. Bylo zjištěno, že reakce se všemi hydraziny (s výjimkou reakce (ethoxymethyliden)malononitrilu a N,N-dimethylhydrazinu) se řídí kinetikou druhého řádu a k(obs) je lineárně závislá na koncentraci hydrazinu, což je v souladu s rychlost určujícím atakem hydrazinu na dvojnou vazbu substrátu. Odpovídající Bronstedovy závislosti jsou lineární (kromě vybočujících N-methyl a N,N-dimethylhydrazinu), a jejich směrnice (beta-Nuc) postupně rostou z 0.59 na 0.71, což odráží postupně rostoucí řád vznikající vazby C-N v transitiním stavu. Odchylky obou methyl hydrazinů jsou pravděpodobně způsobeny různým místem nukleofility/bazicity těchto sloučenin (tertciárníy/sekundární vs. primární dusík). Poněkud odlišná situace byla pozorována u anilinů (a jednou u N,N-dimethylhydrazinu), kde byly pozorovány parabolické závislosti. Kinetika; mechanismus; alkoxymethyliden malonát; alkoxymethyliden malononitril; hydraziny; aniliny
eng Kinetics and mechanism of the reaction of alkoxymethylidene malonate and malononitrile 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 R1NH2 (R1: (CH3)2N, CH3NH, NH2, C6H5NH, CH3CONH, 4-CH3C6H4SO2NH, 3- and 4-X-C6H4; X: H, 4-Br, 4-CH3, 4-CH3O, 3-Cl) were studied at 25 degrees 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 (Nuc) gradually increase from 0.59 to 0.71 which reflects gradually increasing order of the CN 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 +/-. BrOnsted and Hammett plots gave Nuc=1.08 and =3.7 which is consistent with a late transition state whose structure resembles T +/-. alkoxymethylene malonate; alkoxymethylene malononitrile; anilines; hydrazines; kinetics; mechanism; nucleophilic vinylic substitution

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