Effects of solvent and structure on the reactivity of 2-substituted nicotinic acids with diazodiphenylmethane in aprotic solvents

Abstract

The rate constants for the reactions of diazodiphenylmethane (DDM) with 2-substituted nicotinic acids in nine aprotic solvents at 30°C were determined. The obtained second order rate constants in aprotic solvents were correlated using the Kamlet-Taft solvatochromic equation in the complete form: log k = log k0 + sπ*+ a( + bβ. The correlations of the kinetic data were realized by means of multiple linear regression analysis. The obtained results were analyzed in terms of the initial and the transition state of the reaction and compared with previously determined kinetic data for nicotinic acid. The signs of the equation coefficients (s, a and b) are in agreement with the reaction mechanism and the influence of the solvent on the reaction rate is discussed based on the correlation results. The mode of the transmission of the substituent effect is discussed in light of the contribution of solute-solvent interaction to the reactivity of the acid. The substituent effect was additionally analyzed by the Hammett equation, log k = pσ + log k0.

Konstante brzine za reakciju diazodifenilmetana (DDM) sa 2-susptituisanim nikotinskim kiselinama u devet aprotičnih rastvarača su određene na 30 °S. Dobijene konstante brzine za reakciju drugog reda su korelisane Kamlet-Taftovom totalnom solvatohromnom jednačinom u obliku: log k = log k0 + sπ*+ a( + bβ. Korelacija kinetičkih podataka izvršena je višestrukom linearnom regresionom analizom. Dobijeni rezultati su analizirani u odnosu na osnovno i prelazno stanje i upoređeni sa ranije određenim vrednostima za nesupstituisanu kiselinu. Znaci ispred koeficijenata u jednačini su u skladu sa pretpostavljenim mehanizmom reakcije. Diskutovan je prenos efekata supstituenata na reakcioni centar uzimajući u obzir doprinos efekata rastvarača na reaktivnost ispitivanih jedinjenja. Efekat supstituenata je dodatno analiziran Hametovom jednačinom: log k = pσ + log k0.