Reaction with aqueous bases

Section 15 13 Thiols are compounds of the type RSH They are more acidic than alco hols and are readily deprotonated by reaction with aqueous base Thiols can be oxidized to sulfemc acids (RSOH) sulfimc acids (RSO2H) and sulfonic acids (RSO3H) The redox relationship between thiols and disul tides IS important m certain biochemical processes... 

The reaction often works poorly unless an excess of the nucleophile is used because the product thiol can undergo a second S 2 reaction with alkyl halide to give a sulfide as a by-product. To circumvent this problem, thiourea, (NH2J2C=S, is often used as the nucleophile in the preparation of a thiol from an alkyl halide. The reaction occurs by displacement of the halide ion to yield an intermediate alkyl isothiourea salt, which is hydrolyzed by subsequent reaction with aqueous base. 

The 2H-and 3//-pyrroles and -indoles are considerably more basic than the corresponding H-isomers and they readily undergo alkylation to give the quaternary salts, which are then highly susceptible to nucleophilic attack. Thus, for example, methylation of the trialkyl-3//-indole (507), followed by reaction with aqueous base, yields the indolin-2-ol (508). A similar reaction sequence results from the acylation of (507) under Schotten-Baumann conditions to give (509 X = OH). When the benzoylation is conducted in benzene in the absence of the base, the 2-chloroindoline (509 X = C1) is formed and acylation of (507) with a carboxylic acid anhydride produces the ester (509 X = OCOR) (79HC(25-3)l). 

The dianion [Ru6C(CO)l6]2-, 18, isoelectronicwith 16, has been prepared by treatment of 17 with sodium methoxide in methanol to yield [Ru6C(C0),6C02Me] followed by reaction with aqueous base [Eq. (11)]... 

Aldol reactions between two different carbonyl compounds are called mixed or crossed aldol reactions. With aqueous bases, these reactions are of little synthetic value if both reactants have a-hydrogens because they afford mixtures of products. However, under carefully controlled conditions, it is possible to condense ketones with aldehydes in the presence of dilute sodium hydroxide to furnish P-hydroxyke-tones, provided that the aldehyde is added slowly to the ketone. 

In a basic aqueous solution, esters react with hydroxide ion to form the salt of the carboxyhc acid and the alcohol from which the ester is constituted. Name each of the following esters, and indicate the products of their reaction with aqueous base. 

Under similar reaction conditions ethyl[l- C]acetate adds to y-butyrolactone to provide /3-[l- C]acetyl-Y-butyrolactone (77) (Figure 6.28), which upon hydrolysis gave 5-chloro-2-[carbonyl- C]pentanone t781. Subsequent reaction with aqueous base converted 78 into... 

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