Equilibrium constants for σ-complex formation between cyanide ion and 1,3,5-trinitrobenzene in alcoholic solvents

Abstract

Equilibrium constants have been determined spectrophotometrically for the reaction of cyanide ion with 1,3,5-trinitrobenzene in methanol, ethanol, 11-and iso-propanol, and n-and t-butanol. The equilibrium constants at 25 'C vary from 39 1 mole-' for the reaction in methanol to 500 000 1 mole-' with t-butanol as solvent. Enthalpy changes, determined fromequilibriummeasurements and by direct calorimetry, vary from 0 to -15.5 kcal mole-' and the calculated entropy changes decrease from 7 to -26 cal deg-' mole-' as the solvent is changed from methanol to t-butanol. These results are interpreted on the basis that desolvation of the small cyanide ion is the primary factor influencing enthalpies and entropies of reaction. The equilibrium constant in t-butanol is comparable to the values observed for aprotic solvents such as chloroform and acetone.

Kinetic Studies of the Reactions of Cyanide Ion and 1,3,5-Trinitrobenzene in Ethanol, n-Propanol, Isopropanol, and t-Butanol at 25.0 °C

“…This is consistent with the formulation of this species as a-complex 1 (X = CN) (5). The rate of formation of this complex was followed at 580 nm since at this wavelength a-complex 1 (X = n-C3H70) has negligible absorption.…”

“…The resulting solutions possessed absorption maxima at 436 and 546 nm consistent with the formulation of the species in solution as ocomplex 1 (X = CN) (5).…”

“…Tetraphenylarsonium cyanide was prepared as described previously (5) and dried to constant weight in uacuo over phosphorus(V) pentoxide.…”

“…The visible absorption characteristics of o-complex 1 (X = CN), together with equilibrium constants and thermodynamic parameters associated with its formation, in a number of alcohols have been reported (5). The thermodynamic results were interpreted in terms of desolvation of the cyanide ion as being the primary factor affecting the enthalpies and entropies of formation (5).…”

“…The visible absorption characteristics of o-complex 1 (X = CN), together with equilibrium constants and thermodynamic parameters associated with its formation, in a number of alcohols have been reported (5). The thermodynamic results were interpreted in terms of desolvation of the cyanide ion as being the primary factor affecting the enthalpies and entropies of formation (5). As part of a series of kinetic studies of the reactions of sulfite, cyanide, and various alkoxide (X = H, CH,O, CH,, CHO, NH,, NHCH,, and N(CH,),) (6,7) and, as an extension to earlier equilibrium studies, we have investigated the kinetics of reaction of 1,3,5-trinitrobenzene and cyanide ion in several alcohols.…”