Organic 2 Review Problem 154

Organic 2 Review Problem 154 - 138 P RACTICAL ORGANIC...

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138 PRACTICAL ORGANIC CHEMISTRY p. 229) the free phenylhydrazine base may be used directly. Condensation occurs more readily and a cleaner product is obtained, however, if the reaction is carried out in weakly acidic solution—preferably at about pH 5 (see foot- note, p. 509). The phenylhydrazine base should therefore always be dissolved in acetic acid for this purpose. Phenylhydrazine is, however, frequently supplied in the form of its hydro- chloride or sulphate, since these salts on exposure to light darken less rapidly than the free base. If these salts are used, however, osazone formation is unsatisfactory, partly because the mineral acid formed by hydrolysis of C,H 6 NHNH,,HC1 ^ C 6 H 6 NHNH 1 + HCl the salt hydrolyse8 the glucosazone to glucosone, CHO-CO-(CHOH) 8 CH 1 OH. Therefore if these salts are used, they should be mixed in solution with a small excess of sodium acetate, whereby the pH of the solution is raised to approxi- mately the required value. On the other hand, care should be taken not to
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