Benzenediazonium hydrogen sulphate

The student is recommended to carry out the preparation of iodo-benzene in order to gain experience in the preparation of aqueous solutions of diazonium compounds, and then to prepare a solution of benzenediazonium hydrogen sulphate with which to carry out the chief reactions that diazonium compounds undergo. 

To prepare the solid benzenediazonium chloride or sulphate, the reaction is conducted in the absence of water as far as possible. The source of nitrous acid is one of its organic esters (e.g. pentyl nitrite) and a solution of hydrogen chloride gas in absolute ethanol upon the addition of ether only the diazonium salt is precipitated as a crystalline solid. 

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