Hydrolysis base-promoted

On the other hand, " C-labeling studies have shown that the base-promoted hydrolysis of chlorobenzene (second entry in Table 24.3) proceeds by the elimination-addition mechanism and involves benzyne as an intermediate. 

Write the mechanism of the last step in the Gabriel amine synthesis, the base-promoted hydrolysis of a phthalimi.de to yield an amine plus phthalale ion. 

Both acid- and base-promoted reactions may be affected by acidic surfaces and, hence, by the factors which influence the surface acidity. Kinetic evidence for increased Br nsted acidity at clay surfaces has been presented by McAuliffe and Coleman (80) who studied the hydrolysis of ethylacetate and the inversion of sucrose. They noted that potentionmetrie pH measurements did not explain the catalytically effective H+-concentration at the clay surface. 

Rate data for hydrolysis reactions in homogeneous aqueous solutions have been reviewed (79), but application of these data to environmental conditions involving mineral surfaces remains difficult due to the unknown effects sorption may have. Several studies have demonstrated that acid-catalyzed reactions are promoted if the substrate is sorbed at clay surfaces (70-74 and other works reviewed by Theng, 8), but inhibition may also occur if substrate hydrolysis is base-promoted (74). 

For N-methyl-p-toluyl carbamate, a chemical susceptible to neutral and base-promoted decomposition, the rates of hydrolysis on Na-montmorillonite and kaolinite were slower than in aqueous solution of the same bulk pH. A possible explanation is the lower pH at the clay surface (74). The following hydrolysis mechanism in aqueous solution was proposed ... 

The acid-catalysed hydrolysis of the acylal, 1-phenoxyethyl propionate (13), has been studied using the PM3 method in the gas phase. The kinetics and mechanism of the hydrolysis of tetrahydro-2-furyl and tetrahydropyran-2-yl alkanoates (14) in water and water-20% ethanol have been reported. In acidic and neutral media, kinetics, activation parameters, isotope-exchange studies, substituent effects, solvent effects and the lack of buffer catalysis pointed clearly to an Aai-1 mechanism with formation of the tetrahydro-2-furyl or tetrahydropyran-2-yl carbocation as the rate-limiting step (Scheme 1). There is no evidence of a base-promoted Bac2 mechanism up to pH 12. ... 

Alternative to the acid hydrolysis of the p-lactam amide system is the base promoted saponification reaction. Robinson and Pluschke [64] have employed the LiOH-promoted hydrolysis of the bicyclic p-lactam 17 as a means to the synthesis of key diamino acid residue 18, employed in the preparation of a malaria-vaccine candidate, Scheme 6. 

Smith exploited a Lewis-acid-mediated asymmetric Diels-Alder reaction34 between 1,3-butadiene and the Oppolzer acryloyl camphorsultam 78 to set the remote C(29) stereocentre in phenylsulfone 57 (Scheme 17.17). This tactic procured acid 8 in 93% enantiomeric excess (ee), after base-promoted hydrolysis of the chiral auxiliary. Utilising a procedure published by Martin and co-workers,35 Smith iodolactonised acid 8, and... 

The reaction typically gives 60% to 70% of the maximum yield. The reaction is a reversible process. An ester reacting with water, giving the carboxylic acid and alcohol, is called hydrolysis it is acid catalyzed. The base-promoted decomposition of esters yields an alcohol and a salt of the carboxylic acid this process is called saponification. 

Propose a mechanism for the base-promoted hydrolysis of y-butyrolactone ... 

The mechanism for basic hydrolysis begins with attack by hydroxide on the electrophilic carbon of the cyano group. Protonation gives the unstable enol tautomer of an amide. Removal of a proton from oxygen and reprotonation on nitrogen gives the amide. Further hydrolysis of the amide to the carboxylate salt involves the same base-promoted mechanism as that already discussed. 

Saponification is the base-promoted hydrolysis of the ester linkages in fats and oils (review Section 21-7B). One of the products is soap, and the word saponification is derived from the Latin word saponis, meaning soap. Saponification was discovered before 500 b.c., when people found that a curdy material resulted when animal fat was heated with wood ashes. Alkaline substances in the ashes promote hydrolysis of the ester linkages of the fat. Soap is currently made by boiling animal fat or vegetable oil with a solution of sodium hydroxide. The following reaction shows formation of soap from tristearin, a component of beef fat. 

Base-promoted hydrolysis of an ester. Originally used to describe the hydrolysis of fats to make soap. (p. 1206)... 

For GC analysis, the salts of the lowest molecular weight acids present in ozonation products subjected to base-promoted hydrolysis have been converted to their benzyl esters by reaction with benzyl bromide (Bonnet et al. 1989). The salts of all acids produced have commonly been converted to the free acids, usually with the aid of a cation exchange resin. The acids have then been converted to methyl esters by reaction with diazomethane (Bonnet et al. 1989) or, more often, have been converted to trimethylsilyl (TMS) esters (Matsumoto et al. 1986, Taneda et al. 1989, Habu et al. 1990). Trimethylsilylation has the major advantage that alcoholic and phenolic hydroxyl groups are simultaneously converted to TMS ethers, thus greatly facilitating GC analysis. 

Corey and Wollenberg have found it possible to introduce a THP-blocked trans allylic alcohol unit via reaction of 2-cyclopentenone and other cyclic enones with the highly reactive mixed cuprate 28.58 Through hydrolysis, mesylation, and base-promoted cyclization of adduct 29, the vinylcyclopropane 30 was obtained (Scheme 8). Thermolysis at 600 °C caused ring expansion to 31. 

Q I Mechanism 22.9 Base-Promoted Hydrolysis of an Ester to a Carboxylic Acid... 

Hydrolysis is base promoted, not base catalyzed, because the base ( OH) is the nucleophile that adds to the ester and forms part of the product. It participates in the reaction and is not regenerated later. 

Example 2.14. A rationale for the involvement of different leaving groups in the acid- and base-promoted hydrolysis of amides. 

Analysis of the starting material indicates an acidic phenolic hydroxyl, a thioester susceptible to base-promoted hydrolysis, and an a,j8-doubly unsaturated ketone that could undergo 1,4-addition followed by subsequent reaction. From the structure of the product, it is clear that both the thioester and the a,/3-unsaturated ketone undergo reaction. Because hydroxide is the base, a proton will be removed readily from the phenolic hydroxyl group, forming 3-9-1. 

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