Synthesis and Studies in the Light Fastness of Azo Dyes

The aim of the work was to prepare polycyclic systems of types (A), (B) or (c) in which two or more aromatic rings are linked via the tetrahedral carbon atom of a spiro system and to use these as intermediates for the synthesis of azo-dyestuffs in which the aromatic nuclei are further linked to suitable chromophoric groups. Such spiro-intermediates have not, to our knowledge, been previously used for this purpose. It was considered that the derived dyestuffs, in which two planar chromophores are held at right angles and insulated from one another by a tetrahedral carbon atom, might show interesting and unusual properties. In practice, it was found that the spiro-2:2'-bisindane systems of type (A) were not readily prepared and while some compounds incorporating the spiro-1:1'-bisindane system (B) could be obtained relatively easily, they were not readily converted into dyestuffs. The spiro-9:9'-bifluorene system (c) was eventually chosen as the most convenient for the present work and the derived 2,2'-diamino compound was diazotised and coupled with a variety of 2-hydroxynaphthoic acid anilides. The resulting red dyestuffs were found to have a better light fastness than the corresponding non-spiro dyes prepared from 2-aminofluorene