Quinizarin sulphonate

Aluminium salt of quinizarin sulphonic acid — — Binsbergen, de Lange, 1968... 

An interesting observation in the two-electron reduction of quinones [37] has been the loss of sulphonate (-SO3 ) group fi om the fiilly reduced quinizarin-2-sulphonate when reduction takes place at pH < 7 and the solution is made alkaline. Such -SOs" loss was not observed when reduction took place in the alkaline solutions or when quinizarin-6-sulphonate was used. On re-oxidation, quinizarin (and not its 2-sulphonate) was generated. Alkali was ruled out as cause of the -SOs loss. Two alternative mechanisms involving tautomerisation and/or base-induced P-elimination of -SO3 were proposed for this very interesting and rare observation. 

As in the case of the reduced quinones, the difference and absolute absorption spectra of the one-electron oxidised species have been studied in most of the above-named quinones. Two such typical difference and corrected spectra are shown m Figures 9 and 10, respectively, representing the neutral and anionic forms of one-electron oxidised quinizarin 2-sulphonate. 

S Intermediates derived from anthraquinone. The principal primary intermediates are a- and jS- (1- and 2-) aminoanthraquinones and quinizarin-(1,4-dihydroxyanthraquinone), parent substances for more complex intermediates and dyes. a-Aminoanthraquinone is easily prepared by pressure amination of the a-sulphonic acid, itself obtained from a Hg-catalysed sulphonation from which ecological problems arise (section 2.7.7). jS-Aminoanthraquinone is made by amination of the 2-chloro compound (Figure 2.23). 

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