Can. J. Chem. 57. 240 (1979). From the heats of hydrolysis of en01 ethers, the heats of formation of the en01 ethers, and thence the free energies of formation of the en01 ethers in aqueous solution can be calculated. For this calculation it was necessary to determine the free energies of transfer from the gas phase to aqueous solution. By methods previously published it was possible to estimate the free energy change for the hypothetical hydrolysis reaction leading from the en01 ether to the enol, which in turn made possible calculation of the free energy of formation of the enol. Finally the free energy change for enolization in aqueous solution could be calculated using the known free energy of formation of the corresponding keto tautonler. In this way the following were determined: carbonyl compound, pKenOl = -log ([enol]/[keto]):

Can. J. Chem. 58, 1281 (1980). Heats of hydrolysis have been measured for the trimethyl orthoesters of isobutyric, propionic, benzoic, methoxyacetic, chloroacetic, and cyanoacetic acids using aqueous acid with an organic cosolvent where necessary, and of the corresponding esters in alkaline solution. Solubilities or free energies of transfer from gas to aqueous solution have been measured. permitting calculation of the free energies of formation of the aqueous orthoesters, and by methods which we have published previously, calculation of the free energies of formation of the covalent hydrates of the esters, and the free energy changes for hydration of these esters.Using estimated pKa values equilibrium constants were calculated for the addition of hydroxide to the esters. The data are ingood agreement with the appropriate Marcus equation relating rate and equilibrium constants with a value forb of 8.99 f 0.17. This line was used to estimate the equilibrium constant for addition of hydroxide, and thence of water, to some additional esters where only the rate constant was available. Rate constants for hydrolysis of methyl esters in aqueous solution at 25°C were calculated from literature data, correcting for the effect of other conditions as necessary. From the equilibrium constants for addition of water we could estimate the rate constants for uncatalyzed hydrolysis; for the cases where this rate constant has been measured, the agreement was satisfactory. For acid catalyzed hydrolysis the data permit a test of the two alternative mechanisms considered previously, namely specific acid catalysis and general acid catalysis with hydronium ion acting as a general acid. For esters the mechanism is clearly specific acid catalysis, but for aldehydes and ketones it appears very likely that the mechanism is general acid catalysis.J. PETER GUTHRIE et PATRICIA A. CULLIMORE. Can. J. Chem. 58, 1281 (1980). On a mesure les chaleurs d'hydrolyse des orthoesters trimethyliques des acides isobutyrique, propionique, benzoique, methoxyacetique, chloroacetique et cyanacttique en utilisant une solution aqueuse acide avec un cosolvant organique lorsque cela s'avkre necessaire; on a aussi mesure les chaleurs d'hydrolyse des esters correspondants en solution basique. On a mesure les solubilites ou les energies libresde transfertde la phase gazeuse a la solution aqueuse ce qui a permisde calculerles energies libres de formation des orthoesters aqueux et de calculer, au moyen de methodes publiees anterieurement, les energies libres de formation des hydrates covalents des esters et les changements d'energie libre d'hydratation de ces esters.On a calcule les constantes d'equilibre de la reaction d'addition de I'hydroxyde sur les esters en utilisant les valeurs approximatives du pKa. Les donnees sont en parfait accord avec I'equation appropriee de Marcus reliant la vitesse et les constantes d'equilibre avec une valeur de b = 8.99 f 0.17. Cette donnee est utiliste pour evaluer la constante d'equilibre de la reaction d'addition d'hydroxyde et pa...

All four rate constants required to describe the hydration and aldolization/dealdolization reactions.of chalcone ( 1,3-diphenyl-2-propen-I-one) have been determined in aqueous sodium hydroxide solutions. Kinetics were studied starting with chalcone, with its hydrate, 1.3-diphenyl-3-hydroxy-I-propanone, and with benzaldehyde in the presence of excess acetophenone. The rate constants for hydroxide catalyzed reactions, defined in terms of eq.

. Can. J. Chem. 71, 2109Chem. 71, (1993.Heats of hydrolysis of N-methylformanilide dimethyl acetal have been measured in basic solution. The heat of formation of N-methylformanilide was obtained by determining the equilibrium constant in aqueous solution for its formation from formic acid and N-methylaniline as a function of temperature: m : (~) = -33.78 * 1.85 kcal/mol. These data permit the calculation of the heat of formation of N-methylfonnanilide dimethyl acetal, AH;(l) = -72.95 * 1.85 kcal/mol. The free energy of formation of the tetrahedral intermediate in the hydrolysis of N-methylformanilide was calculated by methods we have previously reported. Consideration of the energetics of the intermediates and the known rates of reaction leads to the conclusion that the rate-determining step for alkaline hydrolysis is cleavage of the C-N bond. Operant en solution basique, on a mesurC les chaleurs d'hydrolyse l'acktal dimkthylique de la N-mCthylformanilide. On a obtenu la chaleur de formation de la N-mCthylformanilide en determinant la constante d'kquilibre en fonction de la temperature (en solution aqueuse) pour sa formation 2 partir de l'acide formique et la N-methylaniline: m;(1) = -33,78 * 1,85 kcal/mol. Ces donnCes permettent de calculer la chaleur de formation de I'acCtal dimkthylique de la N-mCthylformanilide, mY(1) = -72,95 * 1,85 kcal/mol. Utilisant des methodes dkcrites anterieurement, on a calculC 1'Cnergie libre de formation de I'intermCdiaire tCtraCdrique implique dans l'hydrolyse de la N-mCthylformanilide. Une considCration des energies des intermediaires et des constantes de vitesse connues mkne i la conclusion que 1'Ctape qui dktermine la vitesse de la reaction de l'hydrolyse alcaline est le clivage de la liaison C-N.[Traduit par la redaction]

. Can. J . Chem. 60,747 (1982). The steroid dimer a,a'-bis(17~-(4'-imidazolyl)-ll-keto-5a-androstan-3~-amino)-p-xylene, 3. has been synthesized by reductive amination o f 17P-(4'-imidazolyl)-5a-androstane-3,11-dione by p-xylenediamine in the presence o f sodium cyanoborohydride, and by reductive amination o f terephthalaldehyde by 3P-amino-I7P-(4'-imidazolyl)-5a-androstan-lI-one. Introduction We have previously (1) reported studies of the imidazolyl steroid, 1, which can act as a catalyst, in aqueous solution, for active esters %a-d, and which shows a marked specificity for esters with a hydrophobic acyf group, such as 2b-d, with 2d being the best substrate found so far. Careful analysis of the kinetic behavior of these reactions showed that there was a potential rate enhancement, due to favorable hydrophobic interactions between steroid and ester, of as much as 156-fold for a phenanthrene ring interacting with the steroid, but that much of this was masked by unavoidable rate-retarding steric effects in the vicinity of the reaction center, so that only a 3.6-fold rate enhancement was observable. In related studies of enolization catalyzed by 1 (2) it was found that the same hydrophobic effect was present and the steric retardation was less, so that more of the potential effect became apparent; in fact a 118fold rate enhancement relative to imidazole was directly observable.A clear conclusion from these experiments was that in order to get a large rate enhancement for ester hydrolysis, a greater area of hydrophobic contact between substrate and catalyst was essential. A conceptually simple way to achieve such an increased area of contact would be to use dimeric