Anhydrides with active hydrogen

Glacial acetic acid, pure or mixed with other solvents, is one of the most attractive solvents for the titration of amines. Commercial acetic acid containing not more than 1% of water (Karl Fischer titration check) can be used in normal practice for the highest accuracy, however, the water content must be lowered to about 0.01% by addition of acetic anhydride and standing for 24 h not more than the stoichiometric amount of acetic anhydride should be used in order to avoid possible reactions with active hydrogen-containing analyte components such as primary or secondary amines or alcohols. A similar procedure is followed in the preparation of perchloric acid titrant from the commercial... 

The curing (hardening) of epoxy compounds can be produced by (a) anhydrides of carboxylic acids [poly(carboxylic acid anhydrides)], (b) compounds with active hydrogen [polyamines, polyphenols, polyalcohols, poly(carboxylic acids), polythiols], or (c) catalysts such as Lewis acids or t-amines. These compounds, which are called curing agents, are used in quantities of up to 30-40 % by weight. 

Isatin (190) is a compound with interesting chemistry. It can be iV-acetylated with acetic anhydride, iV-methylated via its sodium or potassium salt and O-methylated via its silver salt. Oxidation of isatins with hydrogen peroxide in methanolic sodium methoxide yields methyl anthranilates (81AG(E)882>. In moist air, O-methylisatin (191) forms methylisatoid (192). Isatin forms normal carbonyl derivatives (193) with ketonic reagents such as hydroxylamine and phenylhydrazine and the reactive 3-carbonyl group also undergoes aldol condensation with active methylene compounds. Isatin forms a complex derivative, isamic acid (194), with ammonia (76JCS(P1)2004). 

Attempts to prepare an anhydride from 3-carboxymethylquinucli-dine-2-carboxylic acid (40) in the presence of acetic anhydride and sodium acetate led unexpectedly to the tricyclic j8-diketone (59).133 This reacts with compounds containing active hydrogen (water, alcohols, and amines) to yield 2-acetylquinuclidine-3-acetic acid derivatives (60).133... 

The Pasteur method can also be applied to the resolution of neutral racemates, if these can be first converted into an acidic or basic derivative from which eventually a mixture of crystalline diastereoisomeric salts may be prepared by appropriate neutralisation. Thus, a racemic alcohol (e.g. ( )-octan-2-ol, Expt 5.220) may be converted into the corresponding racemic hydrogen phthalate ester by heating with phthalic anhydride, and the ester is then resolved by the Pasteur procedure using an optically active base. The resulting optically active hydrogen phthalate ester is then carefully hydrolysed with aqueous sodium hydroxide to regenerate one of the optically active forms of the alcohol. 

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