Ch_322b_20.12 - Coupling Reactions of Aryldiazonium Salts...

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Coupling Reactions of Aryldiazonium Salts Aryldiazonium ions are weak electrophiles that react with electron-rich aromatics such as phenols and N,N-disubstituted aryl amines to give azo compounds . G : G = R 2 N-, HO- + N N: : + N N + electrophile G : H : N N + : electrophilic aromatic substitution stabilization by substituent (-H + ) G : : N N : an azo compound
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N=N SO 3 - Na + OH orange II synthesized from OH 2-naphthol SO 3 - Na + H 2 N p-aminobenzenesulfonic acid Azo compounds are typically intensely colored because of their extended ! -electron systems that absorb radiation in the visible region. They are used commercially as dyes. Substituent groups such as -SO 3 - Na + are introduced to make them water soluble to promote their binding to polar fibers (wool, cotton, nylon). Azo Dyes
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Azo Dyes as pH Indicators Azo dyes are used as pH indicators because their ! -electron systems change dramatically between the free base and conjugate acid forms, leading to different colors for the two forms.
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