A comparative study of the linear solvation energy relationship for the reactivity of pyridine carboxylic acids with diazodiphenylmethane in protic and aprotic solvents

Abstract

The effects of protic and aprotic solvents on the reactivity of picolinic, nicotinic and isonicotinic acid, as well as of some substituted nicotinic acids, with diazodiphenylmethane (DDM) were investigated. In order to explain the kinetic results through solvent effects, the second-order rate constants for the reaction of the examined acids with DDM were correlated using the Camlet-Taft Solvatochromic Equation. The correlations of the kinetic data were realized by means of multiple linear regression analysis and the solvent effects on the reaction rates were analyzed in terms of the contributions of the initial and the transition state. The signs of the coefficients of the Equation support the already known reaction mechanism. Solvation models for all the investigated acids are suggested and related to their specific structure.

U ovom radu analiziran je uticaj protičnih i aprotičnih rastvarača na reaktivnost pikolinske, nikotinske i izonikotinske kiseline, kao i nekoliko supstituisanih nikotinskih kiselina sa diazodifenilmetanom (DDM). Da bi se dobijeni kinetički podaci mogli objasniti pomoću efekata rastvarača, konstante drugog reda za reakciju ispitivanih kiselina i DDM-a su korelisane Kamlet-Taftovom totalnom solvatohromnom jednačinom. Korelacija kinetičkih podataka urađena je višestrukom linearnom regresionom analizom i efekat rastvarača je posmatran sa strane osnovnog stanja, odnosno reaktanata, i prelaznog stanja u reakciji. Aritmetički znaci ispred koeficijenata u jednačini su u skladu sa poznatim mehanizmom ispitivane reakcije. Solvatacioni modeli za sve ispitivane kiseline su predloženi i povezani sa specifičnostima njihovih struktura.