KINETIC STUDY ON COMPLEXATION OF BORIC ACID WITH 4-ISOPROPYLTROPOLONE IN NON-AQUEOUS SOLVENTS

摘要

Rates for the complexation of trigonal boric acid with bidentate 4-isopropyltropolone (Hipt) in 1,1,3,3-tetramethylurea (TMU), N,N-dimethylformamide (DMF) and acetonitrile (AN) to form the tetrahedral 1:1 complex have been followed at various temperatures and pressures by using a high-pressure stopped-flow apparatus with spectrophotometric detection. Rate constants at 25.0 degrees C and activation parameters in TMU, DMF and AN obtained at I = 0.10 mol kg(-1) (NaCF3SO3) are as follows: k = 22.8 +/- 0.9 mol(-1) kg s(-1), Delta H-not equal = 43.8 +/- 1.3 kJ mol(-1), Delta S-not equal = -72 +/- 4 J mol(-1) K-1, Delta V-not equal = -4.7 +/- 0.6 cm(3) mol(-1) for the reaction in TMU; k = 51.9 +/- 3.2 mol(-1) kg s(-1), Delta H not equal = 32.0 +/- 2.2 kT mol(-1), Delta S-not equal = -104 +/- 7 J mol(-1) K-1, Delta V-not equal = -4.6 +/- 1.3 cm(3) mol(-1) for the reaction in DMF; k = 171 +/- 2 mol(-1) kg s(-1), Delta H-not equal = 22.3 +/- 1.1 kJ mol(-1), Delta S-not equal = -128 +/- 4 J mol(-1) K-1, Delta V-not equal = -4.6 +/- 0.7 cm(3) mol(-1) for the reaction in AN. Negative values of Delta S-not equal and Delta V-not equal indicate that the activation mode in the complexation of the bidentate Hipt is associative and that the rate-determining step is the change in the coordination environment of boron from trigonal to tetrahedral. [References: 30]