Jb. Ellington et al., EFFECT OF LOCAL COMPOSITION ENHANCEMENTS ON THE ESTERIFICATION OF PHTHALIC-ANHYDRIDE WITH METHANOL IN SUPERCRITICAL CARBON-DIOXIDE, Industrial & engineering chemistry research, 33(4), 1994, pp. 965-974
We report the pressure effect on the bimolecular rate constants for th
e esterification of phthalic anhydride with methano in supercritical c
arbon dioxide at 40 and 50-degrees-C. We observe as much as a 25-fold
decrease in the bimolecular rate constant based on bulk concentrations
when increasing the pressure from 97.5 to 166.5 bar. Calculations of
the anticipated pressure effect on the rate constant according to tran
sition-state theory suggest a less than 2-fold decrease for that incre
ase in pressure. Therefore, we attribute the apparently large values o
f the rate constants at lower pressures to an actual increase in the l
ocal concentration of the methanol around the phthalic anhydride at th
ose conditions. To further support this interpretation we present solv
atochromic measurements of the local composition of methanol around a
solute in supercritical fluid solutions at the temperatures and pressu
res used in the kinetic experiments. We present plausible evidence tha
t the observed kinetic measurements can be explained by the local conc
entration of the methanol around the phthalic anhydride being signific
antly higher than the bulk concentration when operating in the supercr
itical fluid mixture.