Chloroacetaldehyde, condensation with preparation

When chloroacetaldehyde is condensed with higher thioamides prepared from amides and phosphorus pentasulfide according to Schwarz s method (222), 2-substituted thiazoles are obtained (4, 10,"22, 175). 

Thieno[2,3- >][l]benzothiophens (293), including the parent compound, were prepared from substituted 2-benzo[Z>]thiophenthiols, obtained from the corresponding lithium derivative followed by condensation with chloroacetaldehyde diethylacetal, chloroacetone, or 3-chlorobutan-2-one, and finally cyclization with hot polyphosphoric acid. For the synthesis of thieno[3,2-6][l]benzothiophens (294), the necessary thiol was... 

AminothiaZoles. In contrast to the pyrazolones, pyridones, and indoles just described, aminotliiazoles are used as diazo components. As such they provide dyes that ate more bathochromic than their benzene analogues. Thus aminothiazoles are used chiefly to provide dyes in the red-blue shade areas. The most convenient synthesis of 2-aminothiazoles is by the condensation of thiourea with an a-chlorocarbonyl compound for example, 2-aminothiazole [96-50A-] (94) is prepared by condensing thiourea [62-56-6J with a-chloroacetaldehyde [107-20-0J both readily available intermediates. 

One of the earliest diazo components of this type to be introduced was 2-amino-5-nitrothiazole (4.81), prepared by condensation of thiourea with chloroacetaldehyde and nitration of the resultant 2-aminothiazole (Scheme 4.32). This component yields bright dischargeable blues, such as Cl Disperse Blue 82 (4.82), which have outstanding build-up, very high extinction coefficients and good fastness to burnt gas fumes. Use of diazo component 4.81 with coupling component 4.83 yields a greenish blue dye. 

Thiazole itself can be obtained by condensing chloroacetaldehyde and thioformamide (Scheme 159). The reaction is explosive and proceeds in low yield because of the instability of the thioformamide under acid conditions. Higher thioamides are more stable and react under milder conditions with chloroacetaldehyde, affording 2-substituted thiazoles in moderate yields. It is possible, and often preferable, to prepare the thioamide in situ in dioxane solution by the action of phosphorus pentasulfide on the corresponding amide and in the presence of solid MgC03 (Scheme 160). With arylthioamides, except for some nitrothiobenzamides, yields are usually higher and the cyclization is carried out over several hours in boiling absolute alcohol. Chloroacetaldehyde can be replaced in these reaction by derivatives such as 1,2-dichloro- or dibromo-ethyl methyl or ethyl ether, 1,2-dichloro- or dibromo-ethyl acetate, 2-chloro- or dibromo-ethyl acetate, and 2-chloro or bromo-diethyl-acetal. 

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