Cyanines selenazole

In the first chapter, devoted to thiazole itself, specific emphasis has been given to the structure and mechanistic aspects of the reactivity of the molecule most of the theoretical methods and physical techniques available to date have been applied in the study of thiazole and its derivatives, and the results are discussed in detail The chapter devoted to methods of synthesis is especially detailed and traces the way for the preparation of any monocyclic thiazole derivative. Three chapters concern the non-tautomeric functional derivatives, and two are devoted to amino-, hydroxy- and mercaptothiazoles these chapters constitute the core of the book. All discussion of chemical properties is complemented by tables in which all the known derivatives are inventoried and characterized by their usual physical properties. This information should be of particular value to organic chemists in identifying natural or Synthetic thiazoles. Two brief chapters concern mesoionic thiazoles and selenazoles. Finally, an important chapter is devoted to cyanine dyes derived from thiazolium salts, completing some classical reviews on the subject and discussing recent developments in the studies of the reaction mechanisms involved in their synthesis. 

Selenazoles and their derivatives, that is. selenazolines and selenazo-lidines. aremainh used in cyanine-type dyes and photographic sensitizers as well as in pharmacology and chemotheraphs. 

The preparation of substituted selenazole thioethers (Scheme 22) has already been described (35. 36). These compounds are obtained by the action of a haloketothioether on. for example, selenoacetamide. selenobenzamide, and A -ethylselenourea. These selenazoles have not been characterized, but they have been used as intermediates in the preparation of cyanine dyes. 

This volume is intended to present a comprehensive description of the chemistry of thiazole and its monocyclic derivatives, based on the chemical literature up to December, 1976. It is not concerned with polycyclic thiazoles, such as benzo- or naphthothiazole, nor with hydrogenated derivatives, such as thiazolines or thiazolidines later volumes in this series are devoted to these derivatives. The chemistry of thiamine has also been excluded from the present volume because of the enormous amount of literature corresponding to the subject and is developed in another volume. On the other hand, a discussion of selenazole and its monocyclic derivatives has been included, and particular emphasis has been given to the cyanine dyes derived from thiazolium salts. 

Chapters III to VII discuss the general properties of thiazoles having hydrocarbon and functional substituents, respectively. A special chapter (Chapter VIII) is devoted to mcso-ionic thiazoles, and Chapter IX describes the thiazolium salts and their numerous cyanine dyes derivatives. The last chapter concerns the monocyclic selenazoles. 

In two patents,the preparation of thioether-substituted selena-zoles of the general formula (6) have been described. These are stated to be formed by reaction of halogenoketothioethers with selenoamide components selenoacetamide, selenobenzamide, and A -ethylseleno-urea are given as examples. The resulting selenazoles were not further characterized. They are stated to be starting materials for the preparation of cyanine dyestuffs which are useful photographically. 

Because of the basic nitrogen atom, alkyl-selenazoles form quaternary salts. 2,4-Dimethyl-3-ethylselenazolium iodide (mp 157-158 0) was prepared by Brooker et al in 87% yield as colorless crystals by heating of 2,4-dimethylselenazole in excess ethyl iodide for 2 days. By reaction with the corresponding quaternary salts, the following cyanine dyes (8) were prepared" l 3-diethyl-4-methylselenazolo-2 -... 

Dinuclear cyanines, see Thiazoiocyanines 2,2 -Dioxo-A-3,3 -biselenazol-5.5 -inylidene-bis hydrazones, from 2-hydrazino-selenazoles, by oxidation with FeCl3 and H,Oj, 252... 

Sodium nitrite, in monomethine thiazolo-cyanine synthesis, 52 Solvatochromism, of neutrocyanines, 75 of selenazole dyes. 251 Solvent, effect in resonance theory, 71 polarity of, in relation with solvatochromism. 75... 

Substituted selenazole thioethers, intermediates in preparation of cyanine dyes, 236... 

Parts 2 and 3 of the comprehensive review of the chemistry of thiazole have appearedthese include chapters on meso-ionic thiazoles and on cyanine dyes derived from thiazolium salts, and also one on selenazole and its derivatives. The chemistry of selenazole is also included in a review of selenium-nitrogen heterocycles. An account of the chemistry of thiazolidin-4-ones (which includes 2,4-diones but not rhodanine and isorhodanine) updates an earlier review. Reviews on cyclic sulphur-nitrogen compounds and on the synthesis and transformations of nitrogen- and sulphur-containing bicyclic heterocycles have appeared. More general reviews, which contain chemistry relevant to this section, cover reactions based on the onium salts of aza-aromatics, the synthesis of... 

Ch. 9 Cyanine Dyes Derived fiom Thiazolium Salts Ch. 10 Selenazole and Derivatives... 

Two relevant reviews, on meso-ionic ring systems and on selenium-nitrogen heterocycles, have been published and a three-part volume on Thiazole and Its Derivatives has appeared. Parts 1 and 2 of this volume are concerned with the chemistry of thiazole and substituted thiazoles, and the third part contains chapters on meso-ionic compounds, on cyanine dyes, and on selenazoles. 

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