Sulfonic acid chlorides, identification

A second reagent, 5-dimethylamino-naphthalene-l-sulfonic acid chloride (DANSyl-chloride), that allows a very sensitive identification of the N-terminal amino acid, was introduced by Gray and Heartley in 1963 [7]. It reacts with amino groups under mild conditions and yields DANSyl-peptides in which the sulfonamide bond is more resistant to acid hydrolysis than the peptide bonds are. Hence DANSyl-amino acids (Fig. 1) are released intact on hydrolysis and can be visualized, after chromatography on paper or on thin layer plates, even in minute amounts by their fluorescence under UV-light. 

Aryl arenesulfonates mostly crystallize readily and are useful for identification of phenols or sulfonic acids they are easily obtained from the acid chlorides and phenols in the presence of alkali689 or a tertiary base690 by the Schotten-Baumann procedure. 

The present volume is a revised and enlarged third edition of the book formerly titled Tables for Identification of Organic Compounds, Four new classes of compounds, i.e., sulfonyl chlorides, sulfonamides, thiols and thioethers were added, bringing the number of classes included in the book to twenty-six. The tables of alkanes, alkenes, alkynes, aromatic hydrocarbons, phenols, nitriles and sulfonic acids were all thoroughly revised and considerably enlarged. In all, the addition of 2400 compounds to the third edition, raised the total number of parent compounds in the book to over 8150. 

Among derivatives of sulfonic acid, the following are suitable for identification heavy-metal salts, chlorides, and crystalline sulfonamides (formed from chlorides and organic bases). To identify anthraquinone-... 

Dry sulfonic acid (2 g) is rapidly triturated with 5 —6 g of PCI 5 and the mixture is transferred into a 20-ml flask where it is heated with occasional stirring for 4 — 6 hr. This is carried out under reflux in an oil bath heated first to 110 °C, and then, after 2 hr, to 150 °C. After cooling, the reaction mixture is diluted with 10 ml of benzene, heated to incipient boiling, and after partial cooling, filtered through a small folded filter paper into a separatory funnel (50 ml volume). The residue in the flask is extracted once more with 10 ml of boiling benzene and the partly cooled benzene solution is filtered into the same separatory funnel. The combined benzene extracts are extracted twice with 10 ml of water, filtered, and worked up either directly to an N-substituted sulfonamide (procedure a), or the sulfonyl chloride might be isolated and purified by crystallization before it is used for identification (procedure b). It can also be further converted to sulfonamide (procedure c). 

Since the sulfone amides are hydrolyzed less readily than the amides of carboxylic acids, we have in benzene sulfonyl chloride a reagent not only for the isolation and identification of some of these substances but also a means for determining the structure of a given product. For example, glycocoll and alanine may be combined to jdeld two different products. After reaction with benzene sulfonyl chloride and hydrolysis of the resultant products, we shall obtain in one instance a glycocoll residue united to the sulfonyl radical, whereas in the second instance alanine is obtained in the form of its sulfonyl derivative. 

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