Linear and Non-linear Free Energy R elationships in Nu cleophilic Substituti on Reactio n of ۲-Bromo-۵-Nitrothioph ene with Morpholin e

Solvents ca n considerably change both the rat e and the m echanism of a chemical reaction. So lvent e ffects are closely related to the natu re and exte nt of solute- solvent interactions [۱]. In many physical a nd chemical processes taking place in solution, binary mixtures of sol vents are frequently used as a media in which solvent- solvent interactions as w ell as solut e-solvent interactions are considered . The solvent effe ct on a typical property is describ ed by a ge neral corre lation model, which gives asimultaneou s separate c alculation of the contributions of non-specific solute-sol vent intera ctions (such as pol arity and polarizability) and specific solute-sol vent interactions (such a s hydrogen bond d onor-acceptor abilities ) [۲]. In th is work, th e relation of the kinetic data of t he SNAr re action b etween ۲-bromo-۵-nitrothiophene (BNT) and morpholine (Mo) with the solvent compositio n was studied in binary mixtur es of solvent s.Experimental section The kinetic s of the rea ction was s pectrophoto meterically studied, by running th e reactions in the thermostatted cells of spectrophotometer at ۲۵ ºC. A Per kin-Elmer U V-vis ۲۵ spectrophotometer c oupled with a thermocell was used with ۱. ۰۰ cm silica cells. Absorbance was measured at wavelength ۴۳۰-۴۵۵ nm, depending on the type of solvent was used. Concentrati on of ۲-bro mo-۵-n itrothiophe ne and morp holine were ۵× ۱۰-۴ an d ۰.۲۰ mol.L-۱, respectively. Therefore, the re action was studied pseudo-first-order. On the other ha nd, the reaction rate was slow enou gh to enable us to study the kinetics of reactions b y initial rate method. Reaction w as carried out in different c omposition of aqueous solutions of methanol, ethanol, and ۲-propano l and meth anol-ethyl acetate mixtures.