Salicylaldehydes their salts

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

Most nickel(II) complexes with the various Schiff bases derived from salicylaldehyde and different amines have usually been easily prepared by three general methods (i) the reaction of a nickel(II) salt, usually hydrated nickel(II) acetate, with the preformed Schiff base using water, EtOH, MeOH or their mixtures as reaction medium (ii) the condensation reaction of bis(salicylaldehydato)nickel(II) with the appropriate amine in refluxing EtOH or H20/EtOH mixture (iii) the template reaction of the aldehyde with the appropriate amine in the presence of a nickel salt. In Table 97 the formulas, synthetic methods and some physicochemical properties for a number of nickel(II) salicylaldiminato complexes are reported. Examples of dinuclear complexes formed with Schiff bases are specifically reported in Section 50.5.8.5. 

The Vilsmeier-Haack reaction (herein, Vilsmeier reaction ) provides an effective method for the formylation of aromatic systems. The combination of phosphoryl chloride with V-methylaniline or dimethylformamide generates an iminium phosphorus derivative or chloro-iminium cation that is the active electrophile in an electrophilic substitution reaction. The resulting substitution product is an iminium salt 1, which is hydrolyzed on workup with alkali to give the carbaldehyde product 2 (Scheme l).1,2 The method is particularly useful with activated arenes or electron-rich heterocycles, such as pyrroles, furans, thiophenes, and indoles. We had a special interest in the preparation of indole-7-carbal-dehydes, namely, their properties as isosteres of salicylaldehyde. Thus, we became involved in a wide-ranging investigation of 4,6-dimethoxy-... 

Hydroxamic acid gives a strong color with ferric chloride. This reaction is suitable for the detection of aldehydes in the presence of ketones. Aromatic / -hydroxyaldehydes, / -aminobenzaldehyde, vanillin, / -dimethyl-aminobenzaldehyde, salicylaldehyde, and aliphatic aldehydes with a hydroxy group in the y-position do not react. A positive reaction is observed with benzyl ketones in strongly alkaline media. It is necessary, therefore, to keep the mixture distinctly but not excessively alkaline. This reaction can be utilized for the separation of aldehydes from their mixture with ketones by converting the acid to its insoluble copper salt. Paper chromatography can be used for the identification of aldehydes in mixtures (41). 

The general term Salen-type is used in literature to describe the class of [O, N, N, O] tetradentate bis-Schiff base ligands. Some of the salen ligands 167,168 and 169 and their metal complexes are illustrated in Fig. 9.9. Commercial synthesis of chiral Salen complex 171, from chiral diamine salt 172 and salicylaldehyde derivative 173 is presented in Scheme 9.45 [83]. 

Carbenes belong to the most investigated reactive species in the field of organic chemistry. Besides their role as excellent ligands in metal-based catalytic reactions, organic carbene catalysis has emerged as an exceptionally fruitful research area. In 2002, Rovis reported a highly enantioselective intramolecular Stetter reaction of unsaturated esters 50 derived from salicylaldehyde by the catalysis of chiral aminoindanol-derived triazolium salt 49 (Scheme 36.14) [20a]. 

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