Rhodanines

Rhodanines.—The 2,4-oxothiones and 2,4-dithiones of thiazolidine, generally known by their trivial names rhodanine (361), isorhodanine (362), and thiorhodanine (363), have been the subject of continued studies, particularly by Russian research workers, with the ultimate aim of their incorporation into cyanine and other dye structures. They resemble one another in their general properties and are here dealt with together. 

Isorhodanines (364) are readily accessible from thiazolidine-2,4-diones (371) by the action of phosphorus pentasulphide in dioxan. Aminolysis by aniline, phenylhydrazine, or isonicotinoyl hydrazide produces the corresponding 4-imino-derivatives (372 X = PhN, PhNHN, or NC H -CONHN).  

Hydrazinolysis of (364) using thiosemicarbazide produces thiazolidine-2,4-dione 4-thiosemicarbazone (372 R = H, X = NHjCSNHN), which is converted, on condensation with chloroacetic acid, into the asymmetric 2,4 -azine (373),2  

The alkylation of rhodanine and its 5-benzylidene derivatives by di azomethane in a variety of solvents, or by alcohols containing three moles of sodium methoxide (i.e. under conditions in which rhodanine is ionized) produces a mixture of the iS- and A -methyl derivatives. In contrast, un-ionized rhodanine e.g. in ethanol acidified to pH 3—4.5) resists alkylation entirely.  

Isorhodanine (362) is convertible, by way of 5-anilinomethylene-isorhodanine, into a variety of quinomerocyanine dyes, e.g. (380) and (381). 4-Phenyliminothiazolidin-2-one, obtainable from isorhodanine by the action of aniline, gives rise to a comparable series of dyes. Their electronic spectra and solvatochromic properties were recorded and discussed.  

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A-2-Thiazoline-4-ones are usually obtained by the heterocydization method (38b-388). 2 Alkylthio-4(5)-thiazolones (162) are obtained by alkylation at sulfur of rhodanine (160) in nonpolar solvent (Scheme 85). 

Arylthio-5-ethyl-4(5)-thiazolone derivatives (164, 165. and 166) have been prepared by treatment of rhodanine (163) with the appropriate aryldiazonium salts (Scheme 86) (395). 

Merocyanines belong to the class of nonionic methine dyes combining two nuclei, one of which is a ketomethylene of acidic nature such as pyrazolone, rhodanine, oxazolone, thiohydantoin,. 

The linking methine cheiin includes an even number of methine groups (0,2,4). They are commonly named as derivatives of the ketomethylene ring, for example. 3-ethyl-5-(3-ethyl-4,5-diphenylthiazolin-2-ylidene)-rhodanine (5) and 4-[4- 3-methyl-4,5-diphenylthiazolin-2-ylidene)-2-butenylidene]-3-methyl-l-p-sulfophenyl-2-pvrazolin-5-one (6) (Scheme 4). 

The choice of the intermediate depends on the reactivity of the ring. For a pyrazolone (34) rather than 35 is used it is the reverse for rhodanine (Schemes 52 and 53). 

Among the thiazole derivatives known for a long time, but whose structure was not at once acknowledged as such, leading to some controversies, are so-called thiocyanoacetic acid, thiohydantoine, rhodanine, mercaptothiazole, and sulfuvinuric acid. 

To the rhodaninic acid of Nencki (22), for which he proposed formula 39. 

In 1877, Nencki (22) condensing ammonium thiocyanate with chloroacetic acid, attributed the name rhodaninic acid (Rhodaninsaure) to the compound he obtained. He noted the ability of rhodaninic acid to give colored derivatives with ferric salts. 

In 1879, Liebermann and Lange (20) demonstrated the formula of rhodaninic acid to be 39. 

In 1884, Nencki (70), studying the properties of rhodaninic acid, confirmed the formula proposed by Libermann and Lange (39) and noted its ability to condense with aldehydes. 

In 1886, Ginsburg and Bondzynski (71) and Berlinerblau (72) developed the reaction of rhodanine with aldehydes, but proposed a chain formula for the condensation product. 

In 1887 (57) and 1889 (73) Andreasch confirmed the cyclic formula proposed by Liebermann and Lange (20). Freydl (74) obtained rhodaninic acid by condensing thioglycolic acid with thiocyanic acid. 

In 1902, Wheeler and Johnson (63) obtained 5-substituted rhodanines (54) by condensing substituted bromornalonic esters with postassium thiocyanate, then thiolacetic acid, the cydization resulting from an alkaline treatment. 

In 1908, Korner (77) developed the synthesis of N-substituted rhodanines (55) from dithiocarbaminacetic acid ... 

During a relatively long period, the condensation of rhodanines with aldehydes was developed, especially by Andreasch s group (78-87). Finally, Holmberg (88, 89) described the best method to obtain rhodanines the condensation of ammonium dithiocarbamate with a sodium or potassium salt of an a-chloro acid. 

C3NS S — N — — Thiamine hydrochloride monohydrate rhodanine 2-imino-5-phenyl-4-thiazolidinone ... 

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