Organic 2 Review Problem 251

Organic 2 Review Problem 251 - PREPARATIONS 235 Required:...

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PREPARATIONS 235 Required: Benzoin, i g.; acetic acid, 15 ml.; phenylhydrazine, 2 ml. (a) Dissolve i g. of powdered benzoin in 15 ml. of hot glacial acetic acid contained in a boiling-tube, and add 2 ml. of phenylhydra- zine. Heat the tube in a boiling water-bath for 20 minutes. The osazone crystallises out either during the heating or when the tube is removed from the bath and the contents stirred. Cool the tube thoroughly in water, filter off the yellow crystals at the pump through a small Buchner funnel, drain, and then wash thoroughly first with glacial acetic acid and then with ethanol, in order to remove all traces of the original mother-liquor. The benzil osazone is thus obtained as fine yellow crystals, which when dry are pure. M.p. 225°. Yield, i g. The osazone can be recrystallised from acetic acid, or (better) from benzene, although the benzene solution may require seeding or scratch- ing before crystallisation starts. ( b
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