Esterification and ester hydrolysis

A review of the chemical and physical mechanisms of the storage stability of fast pyrolysis bio-oils

“…Figure 5 shows that the hydrolysis rate of ethyl acetate varied continuously over five orders of magnitude, when the pH was changed from -0.9 to 3.7 (Euranto 1969). The esterification rate (forward reaction) can be calculated from the hydrolysis rate (reverse reaction) multiplied by the thermodynamic equilibrium constant.…”

Improved delivery through biological membranes IX: Kinetics and mechanism of hydrolysis of methylsulfinylmethyl 2-acetoxybenzoate and related aspirin prodrugs

“…The relatively high enthalpies ( AHr) and small negative entropies (AS*) of activation of I11 and VI are typical for unimolecular ester hydrolysis following cleavage of the alkyl-oxygen bond (11). The values for VII and VIII fall into the range of neutral ester hydrolysis by general base catalysis (1 1) ( Table X).…”

Unanticipated Acyloxymethylation of Sumatriptan Indole Nitrogen Atom and its Implications in Prodrug Design

“…25 times faster than its pivaloyloxymethyl counterpart 4a (assuming that k 0 for 4b increases two times when temperature increases 108C). Such difference in reactivity, together with the unusually high k 0 values displayed by compounds 4 when compared with analogous esters derived from simple aliphatic alcohols (usually in the range of 10 -10 to 10 -7 s -1 at 258C; [26]), is consistent with an S N 1-type mechanism that involves departure of the carboxylate leaving group in the rate-limiting step, followed by trapping of the resulting iminium ion by water (Scheme 3, path a). According to this mechanism, which has been reported for a wide range of N-acyloxymethyl derivatives of weakly NH-acidic compounds such as amides [27 -29] and sulfonamides [9,15,20], the rates of hydrolysis increase with acidity of the carboxylic acid (the pK a s for pivalic acid and 4-methoxybenzoic acid are 5.04 and 4.51, respectively [22]).…”