Carboxyl group,

The blocking and deblocking of carboxyl groups occurs by reactions similar to those described for hydroxyl and amino groups. The most important protected derivatives are f-butyl, benzyl, and methyl esters. These may be cleaved in this order by trifluoroacetic acid, hydrogenolysis, and strong acid or base (J.F.W. McOmie, 1973). 2,2,2-Trihaloethyl esters are cleaved electro-lytically (M.F. Semmelhack, 1972) or by zinc in acetic acid like the Tbeoc- and Tceoc-protected hydroxyl and amino groups. 

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Later findings have modified the rule, especially when the carbon atoms concerned are connected with carbonyl- or carboxyl-groups, but it still holds good for monohydric unsaturated alcohols. 

A selection of important anionic surfactants is displayed in table C2.3.1. Carboxylic acid salts or tire soaps are tire best known anionic surfactants. These materials were originally derived from animal fats by saponification. The ionized carboxyl group provides tire anionic charge. Examples witlr hydrocarbon chains of fewer tlran ten carbon atoms are too soluble and tliose witlr chains longer tlran 20 carbon atoms are too insoluble to be useful in aqueous applications. They may be prepared witlr cations otlrer tlran sodium. 

The aliphatic acids are all soluble in cold water. The aromatic acids are very sparingly soluble in cold water, but readily soluble in boiling water. Phthalic acid, having two carboxyl groups, is more soluble than the other aromatic acids in cold water. 

Heating the acids or their salts with soda lime eliminates the carboxyl group, volatile products being often detectable. 

Physical Properties. Glycine is a colourless crystalline solid soluble in water. Owing to the almost equal opposing effects of the amino and the carboxylic groups. its aqueous solution is almost neutral (actually, slightly acidic to phenolphthalein) and glycine is therefore known as a neutral ampholyte. f It exhibits both acidic and basic properties. 

Although two isomeric esters are theoretically possible, the main product is the 2-ester (formulated above) traces of the isomeric l-ester are eliminated during purification. These derivatives possess a free carboxyl group their equivalent weights may therefore be determined by titration with standard alkali and thus serve as an additional check upon the identity of the compound. 

Vigorous oxidation of a monosaccharide (e.g., with dUute nitric acid) produces carboxyl groups at both ends of the chain. Thus galactose gives the sparingly soluble mucic acid glucose affords the soluble saccharic acid, which is best isolated as the sparingly soluble acid potassium salt. 

This substance (dA, I A) contains a free carboxyl group and is treated in warm acetone solution with an equimolecular quantity of the optically active base brucine (IB) upon cooling, the brucine salt (dA, IB) separates out first in a moderately pure condition, whilst the brucine salt (lA, IB) remains in solution ... 

There are complications in applying the Hinsberg test to certain amines containing hydroxyl, nitro and carboxyl groups, e.g., p-N-methylamiiiobenzoic acid CHjNHC.HjCOOH (I 4) may behave in this test as a primary amine (soluble in alkali) so that it is essential to consider the properties of the original compound in conjunction with the results of the test. 

Salicylic acid. The preparation of salicylic acid by passing carbon dioxide into dry sodium phenoxide at 170-190° is the classical example of the Kolbe-Schmltt reaction. The latter is a method for introducing a carboxyl group directly into a phenol nucleus. 

Sigel and co-workers" investigated the interaction between the aromatic rings of phenyl carboxylates (Ph-(CFl2)n-C02) and 1,10-phenanthroline in ternary copper(II) complexes. Variation of the number of methylene units between the aromatic ring and the carboxylate group (n=0-5) revealed that the arene - arene interaction is most pronounced for n=l. This interaction is more efficient in a 60% 1,4-... 

The aldehyde or ketone needed for this reaction is not always readily available. TM 133, labelled with radioactive in one carboxyl group, was needed for a biochemical labelling experiment. How would you make it ... 

In contrast, equilibrium properties have been successfully discussed in terms of the field effect. Notable instances are those of the ionisation constants of saturated dibasic acids, - and of carboxyl groups held in... 

In readily available (see p. 22f.) cyclic imidoesters (e.g. 2-oxazolines) the ot-carbon atom, is metallated by LDA or butyllithium. The heterocycle may be regarded as a masked formyl or carboxyl group (see p. 22f.), and the alkyl substituent represents the carbon chain. The lithium ion is mainly localized on the nitrogen. Suitable chiral oxazolines form chiral chelates with the lithium ion, which are stable at —78°C (A.I. Meyers, 1976 see p. 22f.). 

In synthetic target molecules esters, lactones, amides, and lactams are the most common carboxylic acid derivatives. In order to synthesize them from carboxylic acids one has generally to produce an activated acid derivative, and an enormous variety of activating reagents is known, mostly developed for peptide syntheses (M. Bodanszky, 1976). In actual syntheses of complex esters and amides, however, only a small selection of these remedies is used, and we shall mention only generally applicable methods. The classic means of activating carboxyl groups arc the acyl azide method of Curtius and the acyl chloride method of Emil Fischer. 

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