The retroaldol reaction of cinnamaldehyde

Self Cite

). The kinetics and equilibria involved in the aldol condensation of acetone, acting as carbon acid, and acetophenone have been studied in aqueous alkaline solution. The enone isolated is the E isomer. The reactions are all first order in hydroxide, with rate and equilibrium constants (defined for E-enone as initial compound) of: k12 = (5. There is an equilibration of the two enones in base that is faster than hydration to the ketol: k14 = (3.14 f 0.8455To analyze the behavior of the enone:ketol equililbrium system in acid we simultaneously fitted analytical data for all three species (E-enone, Z-enone, and ketol) to a kinetic model, so that the rate constants were determined by the best fit to all of the data for an experiment. J . PETER GUTHRIE et XIAO-PING W A N G .Can [Traduit par la rkdaction]

Section: Introductionsupporting

confidence: 65%

The aldol condensation of acetone with acetophenone

Guthrie¹,

Wang²

1992

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“…From the boiling point data gathered to evaluate the heat of vaporization, the vapor pressure at 25°C could be calculated by a procedure that we recently reported (8). This procedure uses the available vapor pressure data and values of the heat of vaporization and heat capacity of vaporization (estimated using our atomic additivity parameters (10)). The value so obtained was P25"~ = 6.22 X Torr.…”

Section: Or' Oh Or'mentioning

confidence: 99%

Hydration of acylimidazoles: tetrahedral intermediates in acylimidazole hydrolysis and nucleophilic attack by imidazole on esters. The question of concerted mechanisms for acyl transfers

Guthrie¹,

Pike²

1987

Self Cite

. Can. J . Chem. 65, 1951Chem. 65, (1987.Heats of hydrolysis have been measured for three acylimidazole acetals. From these results free energies of formation in aqueous solution have been calculated for the acetals and the corresponding tetrahedral intermediates. Having free energies of formation for the tetrahedral intermediates allows a detailed analysis of the energetics of both the unobservable nucleophilic reaction of imidazole with ethyl acetate and also the observable reaction of imidazole with p-nitrophenyl acetate. pK, values of 1-(3-aminopropy1)-imidazole and 1-(2-aminoethy1)-imidazole have been determined to allow calculation of the a* value for the imidazolyl substituent. The dependence of imidazole pK, values on the electron-withdrawing properties of the 1-substituent was also determined. There is a linear free energy relation between the free energy change for replacement of OH in a carbonyl hydrate by imidazolyl and the sum of the a* values for the other substituents. The implications of these results for the question of concerted versus stepwise mechanisms for the reactions of imidazole with aryl acetates have been examined. An equilibrium constant has been calculated for the addition of imidazole to p-nitrophenyl acetate. A simple extension of Marcus theory allows the free energy surface for a three-dimensional reaction coordinate diagram to be calculated using the energy levels of the tetrahedral intermediate determined in this work, the energy level of the acylium ion derived from literature data, and intrinsic barriers for the edge reactions. It is shown that the reaction of imidazole with p-nitrophenyl acetate probably follows a concerted path. General conclusions from this theory of concerted reactions are discussed.

“…The agreement for the two directions was good in each case. The results of these experiments are summarized in additivity as previously proposed (18). Where a compound is solid at room temperature, the vapor pressure was calcu-"~l l at 25°C; units are kcal mol-I and cal deg-' mol-' lated at the melting point using the heat of vaporization and hEst~mated using an average value for AS, = 13 0 cal deg-I mol-' (16); Table 3.…”

Section: Heats Of Formationmentioning

confidence: 90%

Equilibrium constants and heats of formation of methyl esters and N,N-dimethyl amides of substituted benzoic acids

Guthrie¹,

Pike²,

Lee³

1992

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.Heats of methanolysis and dimethylaminolysis of substituted benzoyl chlorides (4-X-C6H4-COC1, X = H, CH,, 0CH3, C1, NO,) have been measured, as have the heats of hydrolysis of the esters, permitting the calculation of the heats of formation of the benzoyl chlorides (4-X-C6H4-COCl, X, DHf: CH30, -80. 29 of transfer from methanol to water and from gas to water were determined for the esters and amides. Free energies of formation in aqueous solution were calculated for the acids, esters and amides, making use of thermodynamic estimation procedures where necessary. Equilibrium constants were measured for ester formation in water (X, K (M-I): CH30, 0.14; CH,, 0.14; H, 0.12; C1, 0.15; NO,, 0.13) and N,N-dimethylaminolysis in methanol (X, K (M-I): CH30, 8.16; CH,, 17.5; H, 26.5; C1, 22.6; NO,, 41.0). Partition constants for esters and amides were measured for methanol/dodecane and dodecane/water, permitting calculation of the free energy of transfer from methanol to water (4-X-C6H4-COOCH,, X, DG,,: CH30, 3.12; CH,, 3.17; H, 3.01; C1, 3.43; NO,, 2.89; 4-X-C6H4-CON(CH,),, X, DG,,: CH30, 0.96; CH,, 1.48; H, 0.92; Cl, 1.77; NO2, 0.99). These data permit calculation of the equilibrium constants for dimethylaminolysis of substituted methyl benzoates in water, and for amide formation in water (4-X-C6H4-CON(CH,),, X, K(M-', reactants and products as neutral molecules): CH30, 767; CH,, 752; H, 2050; C1, 1020; NO,, 2350). In the course of our calorimetric measurements we derived an improved value for the heat of solution of HC1 in methanol.