Rate and Product Studies of Solvolyses of Benzyl Fluoroformate

Abstract

Abstract:The specific rates of solvolysis of benzyl fluoroformate have been measured in several hydroxylic solvents at 25.0 °C. For methanolysis, the solvent deuterium isotope effect and activation parameters were determined and activation parameters were also determined for solvolyses in ethanol and 80% ethanol. For several of the binary hydroxylic solvents, measurement of product ratios allowed selectivity values to be determined. An extended Grunwald-Winstein treatment of the data led to sensitivities to changes in solvent nucleophilicity and ionizing power. Comparison with previously determined specific rates for solvolysis of the chloroformate gave fluorine/chlorine rate ratios greater than unity. All of the determinations made were consistent with an addition-elimination (associationdissociation) mechanism, with addition rate-determining.

Kinetic Studies of the Solvolyses of 2,2,2-Trichloro-1,1-Dimethylethyl Chloroformate

“…All of the tabulated values are in the range expected for an additionelimination mechanism and they indicate a large degree of nucleophilic assistance at the transition state of the rls. 24 The lower m values (m = 0.39) for the solvolysis of 2,2,2-trichloro-1,1-dimethylethyl chloroformate, relative to n-octyl fluoroformate, 8 phenyl chloroformate, 16 methyl chloroformate, 22 and ethyl chloroformate, 23 may reflect a reduced need for solvation of the developing negative charge on the carbonyl oxygen, (see Table 3). …”

“…24 The substrate did not react with the pure acetonitrile within the stock solution. The 2,2,2-trichloro-1,1-dimethylethyl chloroformate (Aldrich 96%) was used as received.…”

“…The monitoring of increases in conductivity with time and the calculation of the rate constants (first-order coefficients) were conducted as previously reported. 24 The multiple regression analyses were performed using commercially available packages.…”

Kinetic Studies of the Solvolyses of Isopropenyl Chloroformate

“…13 For isopropenyl chloroformate, the values for the ratio l/m of 3.09 is similar to those previously observed for the solvolyses of n-octyl fluoroformate (l/m = 2.28), 7a phenyl chloroformate (l/m = 2.98), 11 methyl chloroformate (l/m = 2.74), 12 and ethyl chloroformate (l/m = 2.84) 7b , which have been shown to solvolyze over a wide range of solvent type with the addition step of an addition-elimination pathway being rate limiting.…”

“…13 The substrate did not react with the pure acetonitrile within the stock solution. The isopropenyl chloroformate (Aldrich 97%) was used as received.…”