Colorants and Brightening Agents

Dye Intermedia.tes, Dye intermediates are defined as those precursors to colorants that are manufactured within the dyes industry, and they are neady always colodess. Colored precursors are conveniendy termed color bases. As distinct from primaries they are only rarely manufactured in single-product units because of the comparatively low tonnages requited. Fluorescent brightening agents (FBAs) are neither intermediates nor tme colorants. Basic manufacturing processes for FBAs are described in Reference 18 (see Fluorescent whitening agents). 

Benzofuran derivatives such as 2-cyanobenzofuran-5-sulfonic acid esters and amides have found wide application as color developers in photographic processes (44USP2350127). The substituted benzofurans (507), (508) and (509) are used as brightening agents in textiles, wool, paper, cellulose and nylon (53MI31201). 

In a completely different application, Shimoyama et al. [530] have reported a 3D fluorescence method using quartz fibre optics for the non-destructive determination of colorants on woodblock prints. Cleve et al. [531] have developed an on-line fluorescence spectroscopic method to measure sizing effects and optical brightening agents in polyamide woven fabrics. According to Allen [532] the in situ capability of fluorescence is very viable as a monitoring probe via a fibre optic technique. 

Lesser amounts of sodium thiocyanate are used in color toning photographic paper, as a stabilizer in rapid film development, and as a sensitizing agent in color negative-film emulsions. It is also used as a brightener in copper electroplating. 

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