Ethyl benzoate saponification

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

On the basis of the general mechanism for basic ester hydrolysis shown in Figure 20.5, write an analogous sequence of steps for the saponification of ethyl benzoate. 

The presence of water results in very rapid saponification of ethyl benzoate. Dimethyl sulfoxide (Crown Zellerbach Corp.) may be dried by stirring with calcium hydride for 4-8 hours, followed by distillation under reduced pressure at 80-90° without filtration. Commercial 2-butyl alcohol and ethyl benzoate are conveniently dried by stirring for 2-4 hours with calcium hydride followed by filtration. 

The potassium should be free of oxide and/or hydroxide to avoid subsequent saponification of ethyl benzoate. 

A Bac2 mechanism is proposed for die saponification of ethyl benzoate in ethanol-water.37 The reactions of aryl benzoates in absolute ethanol with ethoxide, aryloxides and acetophenone oximates occur via a stepwise mechanism in which the formation of the tetrahedral intermediate is rate determining.38 A stepwise mechanism is also supported for the reactions of /7-nitrophenyl-substituted benzoates with hydroxide and / -chlorophcnoxidc. The evidence comes from breaks in Hammett plots as the acyl... 

What actually takes place is the alcoholysis [represented in Eqs. (8) and (9)], which was estimated by Gibby and Waters to be one thousand times as rapid as the saponification according to Eq. (7). Then the ethyl benzoate is saponified slowly. The greater rapidity of alcoholysis compared with hydrolysis may be shown qualitatively by a simple eiqieriment with tri-acetin. Some triacetin, CgHsCOCOCHt)) which is odorless, is added to a solution of sodium hydroxide in 50 per cent alcohol the odor of ethyl acetate is apparent at once and shows that the immediate reaction is the formation of ethyl acetate. On this accoimt, it is necessary to use an effi-cmnt reflux condenser when determining saponification numbers of even high-boiling acetates. ... 

Ropp and Raaen (1954) compared the molar radioactivities of product after 3% and after 100% reaction for the saponification of a series of 0-oarbonyl-labeled ring-substituted ethyl benzoates at 25°0, and for the formation of the 2,4-dinitrophenylhydrazones of a series of ring-substituted carbonyl-labeled acetophenones. In both series of reactions studied the isotope effects k jk) for the carbon-14-labeled reactants varied with the ring substituent, the greater the electron-donating ability of the substituent, the smaller k jk and thus the larger the isotope effect. 

Boil 2 cc. of ethyl benzoate in a small r.b. flask fitted with an efficient reflux condenser, with 30 cc. of 25 per cent XaOH. An ebullator tube will assist in preventing bumping. Saponification will be complete after about thirty minutc.s, as will be indicated bt the disappearance of the ester layer. 

Nair, Nanarati, Nair, Kisliuk, Gaumont, Hsiao and Kalman have prepared the 5,8-dideazapteroic acid derivative (676), a useful precursor to polyglutamate analogues, from (228) and ethyl />-(jV-propargyl)benzoate, followed by saponification. Similarly, (232q) and (232r) were obtained from (228) and (231) R = 2-butynyl or cyclopropylmethyl) (Scheme 3.148) [275]. 

N-Boc leucine was converted to an acid chloride by treatment with isobutyl chloroformate. Subsequent treatment with diazomethane gave the diazoketone (6.241), which was treated with silver benzoate. This led to a Wolff rearrange-mentl40 and formation of 6.242. I ll Reduction of the ester moiety to an aldehyde with diisobutylaluminum hydride allowed condensation with the lithium enolate of ethyl acetate to give 6.243. Saponification led to N-Boc-5-amino-3-hydroxy-7-methyloctanoic acid (6.244, given the pseudonym AHM0A).1 H Amino acid... 

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