Hydrolysis in supercritical water: identification and implications of a polar transition state

Abstract

Reaction of guaiacol (o-methoxyphenol) in supercritical water at densities of 0 < pw < 0.7 g/cm3 and with added salts at pw = 0.50 g/cm3 showed its hydrolysis to catechol (o-hydroxyphenol) and methanol to be through a polar transition state. Correlation of the reaction kinetics following a modified Herbrandson analysis provided a quantitative summary of the greater polarity of the hydrolysis transition state relative to the hydrolysis reactants as Vzmhm ~^wm^wm " VGm<5Gm = 190 ± 20 (cm^cal/mol2)1/2. Salt addition at pw = 0.5 g/cm3 further shifted the transition-state equilibrium toward the transition-state species. A sodium chloride loading of 0.71 mmol/cm3 led to an "effective water density" of pWieff =1.1 g/cm3.Supercritical fluid (SCF) solvents have attracted considerable interest in separation processes because, near Tc

Reactions at supercritical conditions: Applications and fundamentals

“…This expectation has been verified experimentally for reactions in a series of different liquid solvents (Eckert et al, 1974;Moore and Pearson, 1981) and for hydrolysis reactions in a single SC solvent (water) wherein the solubility parameter was changed by varying the density (Huppert et al, 1989).…”

“…Klein's group at the University of Delaware studied the reaction pathways, kinetics, and mechanisms of solvolysis and pyrolysis of coal model compounds in SC water and other SCFs (Lawson and Klein, 1985;Townsend and Klein, 1985;Klein, 1985, 1987;Townsend et al, 1988;Abraham et al, 1988;Huppert et al, 1989;Wu et al, 1989Wu et al, , 1991aKlein et al, 1990Torry et al, 1992;Boock et al, 1992). They examined the effects of temperature, solvent density, phase behavior, and added salts, and used transition-state theory to interpret their results.…”

Kinetics of phenol oxidation in supercritical water

“…Streit (1988, 1989) included elementary reaction steps that involved water as a reactant in their detailed kinetic models of methane oxidation in SCW. Additionally, several pyrolysis studies in SCW revealed that water was an active participant in the reaction and not merely an inert solvent (Lawson and Klein, 1985;Townsend and Klein, 1985;Townsend et al, 1988;Huppert et al, 1989;Houser et al, 1986).…”

Utilization of Sub and Supercritical Water Reactions in Resource Recovery of Biomass Wastes

“…Using guaiacol as a lignin model compound, the reaction pathway of the supercritical water reaction of guaiacol was studied [52][53][54][55][56][57][58][59][60]. Lawson and Klein 1985 [52] are among the pioneers in the study of guaiacol in supercritical water.…”