A Survey of Thermodynamic Parameters for Solvolysis in Water

Abstract

A method is suggested for determining the standard state entropies (s$) of the transition state for the neutral hydrolysis of esters in water. This has required the development of methods for approximating initial state parameters where experimental data are lacking.Characteristic linear correlations between the entropy and enthalpy of activation are observed for hydrolysis in water, as well as for the bimolecular halide exchange reaction in acetone and for acid-base equilibria. Expla~~ations are advanced to explain the observed trends.Fro111 the derived standard state entropies, a method for estimating the charge development in the transition state for the methyl and isopropyl halides is proposed. With this further detailed knowledge of the transition state in the methyl halide series, reasonable values of the activation enthalpy can be calculated from available thermochemical data.

The Influence of Solvent on the Solvolysis of Ethyl Cinnamate in Water Acetone Mixed Solvent System

“…In the light of finding of Robertson [10] and .Singh A K. [11] and from above noted trend, it is concluded that solvating power of Acetone change the mechanism of the reaction from biomolecular to unimolecular, The resent report of Singh A K [12]has been support of our finding Table-IV Variation of 3+ Log k with log[ H2O] (water -Acetone) at different temperature …”

Kinetics of the hydrolysis of acyl chlorides in pure water

“…Comparison with Table I11 shows that the discontinuity in the rate order is accompanied by a large positive change in the entropy of activation (AS*), suggesting a significant change of mechanism. Similar variations in the values of this parameter mark the differences between the SN2 and SN1 mechanisms for the hydrolyses of alkyl halides in water (11). Hence.…”

“…This was taken to indicate concurrent breaking of the alkyl-oxygen and sulfur-halogen bonds in both unimolecular and bimolecular hydrolysis, a single transition state being involved in each case. Comparison of the present data for the hydrolyses of phenyl, methyl, ethyl, and propyl chloroformates with those for bi~nolecular hydrolysis of alkyl halides in water (11) for SN2 displacements. This may reflect more ordered transition states which could arise if the reactions were to involve tetrahedral intermediates (111) , mechanism [2], rather _than direct displacements through the SN2 transition states (II).…”

“…While it must be admitted that the accessible temperature range of 20 "C for the phenyl compound is too small to yield a very accurate value for this parameter, this does not apply to the methyl compound. Comparison of (VI) with the alternative S,2 transition state (11) shows that the charge Darameters should be considered to be corn-distributions are similar in both cases. I t is.…”

A kinetics study of dipolar protic solvent in alkaline hydrolysis of ethyl Nicotinate in water-ethanol media- A Solvent effect

“…Log K= log k o + n log [H 2 O] Where 'n' is the solvent number (number of water molecule associated with activated complex) which is evaluated from the slopes of log k verses log [H 2 O] Table-6 , tells about the criteria for studying about the mechanism of reaction and is tabulated in Table-6 and their plots in Fig.-3.From the Table-6 C. The decreasing number of water molecules involved in the formation of activated complex, it is inferred that ethanol in the reaction media acts as structure reformer and in so, it shift the equilibrium of water from bulky form to its dense form and in light of Robertson 9 . So it is concluded that mechanistic pathway of reaction in presence of ethanol is change from unimoleculer to bimolecular.…”