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A series of 2-thiazolylazo dyes for cellulose acetate was prepared. Substituents in the 4-position have little effect on the color of 2-thiazolylazo dyes. The color of the dyes containing various groups in the 5-position deepens in the order of increasing negativity of the substituent. Thus, dyes containing the nitro group in the 5-thiazolyl position are blue to greenish blue; these dyes have superior dyeing and fastness properties. The bathochromism of the 2-thiazolylazo dyes is illustrated by comparison of the blue dyes from 2-amino-5-nitrothiazole with dyes from the benzene analog, p-nitroaniline; dyes from the latter are red.The bathochromism of the 2-thiazolylazo dyes is discussed in terms of the influence of the 2-thiazolylazo structure and of substitution on the coupler and diazonium constituents.The preparation and properties of new 2-aminothiazole intermediates are described. Certain problems encountered in nitration and oxidation reactions are discussed.

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This paper concerns the effects of the position and the nature of substituents on the colour of azo dyes derived from 2‐arainothiophens. Of primary interest is the colour shift from the red of phenylazo dyes to the greenish blue of the analogous 5‐substituted 3‐nitro‐2‐thienylazo dyes. The greenish blue of 2‐amino‐3‐nitro‐5‐aeyl(or aroyl)thiophen dyes is in striking contrast with the violet—red of 2‐amino‐5‐acylthiophen dyes and the violet of dyes from 2‐amino‐3:5‐bismethylsulphonylthiophen. Even simple aniline coupling components afford blues to blue‐greens with the 5‐substituted 2‐amino‐3‐nitrothiophens. However, progressively increased bathoehromic shifts to bluish green are obtained with the following coupler types— tetrahydroquinoline, benzomorpholine, and 2‐alkoxy‐5‐acetamidoaniline. Dyes from 2‐amino‐3‐nitro‐5‐acylthiophens, particularly, have excellent affinity for secondary cellulose acetate and give good exhaustion and level dyeing. They colour cellulose acetate deep, bright blues to greens. Dyed fabrics have superior gas‐fume fastness, moderate light fastness, and good dischargeability.