Cleavage of the Carbon—Sulfur Bond. Rates of Hydrolysis of Some Alkyl Acetates and the Corresponding Thiolacetates in Aqueous Acetone

Rylander, Paul N.; Tarbell, D. S.

doi:10.1021/ja01163a061

Cited by 84 publications

(53 citation statements)

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“…Clearly, plausible substituent shifts of the activation energy must be derived from the experimental data in the same kind of aqueous solution reported by the same laboratory. 36 Compared to available experimental activation energies collected in Table 1, the SVPE calculations with the previously calibrated 0.001 au contour (default) systematically underestimate the energy barriers, although the calculated energy barriers adequately reflect an important trend for the substituent shifts of the experimental activation energies. According to the experimental activation energies determined in the same laboratory 36 for the four alkyl acetates considered here, changing the leaving group OR′ from R′ ) CH 3 to R′ ) CH 2 CH 3 and to R′ ) CH(CH 3 ) 2 does not significantly change the first energy barrier.…”

Section: Resultsmentioning

confidence: 85%

Energy Barriers for Alkaline Hydrolysis of Carboxylic Acid Esters in Aqueous Solution by Reaction Field Calculations

2000

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The hydrolysis of six representative alkyl esters in aqueous solution were evaluated by performing ab initio molecular orbital calculations using five different self-consistent reaction field (SCRF) procedures. Energy barriers were obtained for hydrolysis by bimolecular base-catalyzed acyl-oxygen cleavage (B AC 2) and bimolecular base-catalyzed alkyl-oxygen cleavage (B AL 2). Despite strong solute-solvent hydrogen bonding, the calculated solvent shifts of the energy barriers are dominated by electrostatic interactions between solute and solvent, and nonelectrostatic interactions largely cancel out. SCRF calculations that ignore volume polarization or use a charge renormalization scheme usually overestimate the solvent shifts of the energy barriers. A recently developed surface and volume polarization for electrostatic interaction (SVPE) procedure yields results comparable to experimental data when the solute cavity surface is defined as the 0.002 au electron charge isodensity contour. The differences between values from the SVPE calculations with this contour and the corresponding average experimental values for the examined esters are smaller than the range of experimental values reported by different laboratories. The SVPE calculations for the B AC 2 hydrolysis predicted the lowest energy barrier for methyl formate and the highest for tert-butyl acetate, and the remaining four esters grouped closely. These results are consistent with the substituent shifts of the experimental activation energies. The energy barriers predicted for B AL 2 hydrolysis are always considerably higher than those predicted for the B AC 2, consistent with the observation that in aqueous solution B AL 2 hydrolysis is negligible compared to B AC 2 for alkyl esters.

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Section: Resultsmentioning

confidence: 85%

Energy Barriers for Alkaline Hydrolysis of Carboxylic Acid Esters in Aqueous Solution by Reaction Field Calculations

2000

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“…The calculated energy barrier, 11.4 kcal/mol, is in good agreement with the experimental determinations of activation energy, 10.45 or 12.2 kcal/mol, reported for the hydrolysis of methyl acetate in aqueous solution. 11,12 As seen in Table 1, the energy barrier, 7.6 kcal/mol, calculated for the first step of the cocaine benzoyl-ester hydrolysis through the hydroxide attack from the Re face of the carbonyl is ∼1 kcal/mol lower than that through hydroxide attack from the Si face. The energy barrier, 7.0 kcal/mol, calculated for the first step of the cocaine methyl-ester hydrolysis, is slightly lower than the lowest barrier, 7.6 kcal/mol, for the first step of the cocaine benzoyl-ester hydrolysis.…”

Section: Resultsmentioning

confidence: 99%

Theoretical Studies of Competing Reaction Pathways and Energy Barriers for Alkaline Ester Hydrolysis of Cocaine

Zhan

Landry

2001

J. Phys. Chem. A

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Reaction pathways, solvent effects, and energy barriers have been determined for the base-catalyzed hydrolysis of the benzoyl-ester and methyl-ester groups of neutral cocaine and three smaller alkyl esters in aqueous solution by performing a series of ab initio molecular orbital and density functional theory calculations. The reaction coordinate calculations indicate that both the benzoyl-ester hydrolysis and the methyl-ester hydrolysis occur through a two-step process known for the majority of alkyl esters, i.e., the formation of a tetrahedral intermediate by the attack of hydroxide oxygen at the carbonyl carbon (first step) followed by the decomposition of the tetrahedral intermediate to products (second step). This is the first first-principles study of the whole reaction pathway for cocaine benzoyl-and methyl-ester hydrolyses. The decomposition of the tetrahedral intermediate requires a proton transfer from the hydroxide/hydroxyl oxygen to the ester oxygen, as the C-O bond between carbonyl carbon and ester oxygen gradually breaks. We have examined two competing pathways for the second step of cocaine hydrolysis: one associated with the direct proton transfer from the hydroxide/ hydroxyl oxygen to the ester oxygen, and the other associated with a water-assisted proton transfer. The energy barriers calculated for the second step of the benzoyl-and methyl-ester hydrolyses with water-assisted proton transfer are lower than the first step, whereas with direct proton transfer the barrier for the second step is higher. The first step should be rate-determining for the hydrolysis of both esters in aqueous solution, thus providing theoretical support to the design of the analogues of the first transition state that elicited anticocaine catalytic antibodies. The energy barrier, 7.6 kcal/mol, calculated for the first step of benzoyl-ester hydrolysis through the hydroxide attack from the Re face of the carbonyl is ∼1 kcal/mol lower than that through the hydroxide attack from the Si face. The energy barrier, 7.0 kcal/mol, calculated for the first step of cocaine methyl-ester hydrolysis is slightly lower than that of the benzoyl-ester. The effect of substituents on this energy barrier suggests that the transition state is significantly stabilized by hydrogen bonding between the hydroxide oxygen and the hydrogen for the carboxylic acid or alcohol moiety.

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“…refs. [4][5][6][7][8][9][10][11][12][13][14][15][16] and a limited amount of work using thionoesters has been reported (17)(18)(19)(20). However, only three reports, none of which contain kinetic analyses, could be found concerning the base catalysed hydrolysis of dithioesters (2 1-23), According to Sakurada (21), the action of aqueous alkali on ethyl dithioacetate leads to the production of dithioacetic acid, however, two other studies (22,23) report that thiol acids are produced by dithioester hydrolysis.…”

Section: Introductionmentioning

confidence: 99%

An investigation of the biphasic kinetics observed during the hydroxide ion-catalyzed hydrolysis of alkyl dithioesters

Storer¹

1983

Can. J. Chem.

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Kinetic evidence is presented for the establishment of an equilibrium, in dilute aqueous alkaline solutions, between alkyl dithioesters and a species I. The species I is formed cither by the extraction of a proton from, or by the addition of an hydroxide ion to, the dithioester. In the former case I would be an anion (probably an enethiolate) formed by the removal of a proton from the α-carbon atom, and in the latter case I would be a stabilized tetrahedral intermediate formed by the addition of an hydroxide ion to the thiocarbonyl carbon atom. It has not been possible, using kinetic evidence alone, to distinguish conclusively between these two possibilities. However, using the available evidence, arguments are presented in favor of I being an enethiolate anion.

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Cleavage of the Carbon—Sulfur Bond. Rates of Hydrolysis of Some Alkyl Acetates and the Corresponding Thiolacetates in Aqueous Acetone

Cited by 84 publications

References 0 publications

Energy Barriers for Alkaline Hydrolysis of Carboxylic Acid Esters in Aqueous Solution by Reaction Field Calculations

Energy Barriers for Alkaline Hydrolysis of Carboxylic Acid Esters in Aqueous Solution by Reaction Field Calculations

Theoretical Studies of Competing Reaction Pathways and Energy Barriers for Alkaline Ester Hydrolysis of Cocaine

An investigation of the biphasic kinetics observed during the hydroxide ion-catalyzed hydrolysis of alkyl dithioesters

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