Organic 2 Review Problem 311

Organic 2 Review Problem 311 - PREPARATIONS 295 acid. The...

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PREPARATIONS 295 acid. The ease of cyclisation of various hydrazones varies greatly. Indole itself cannot be prepared from acetaldehyde phenylhydrazone: on the other hand, the phenylhydrazones of some saturated cyclic ketones undergo cyclisation very readily even when boiled with acetic acid. This is illustrated in the following preparation, in which cyclohexanone is converted into its phenylhydrazone, and the latter, without isolation, is converted into 1,2,3,4-tetrahydrocarbazole by boiling with acetic acid: ,CH 2 CH 2 H 2 C CH 2 H 2 C CH 2 C 6 H 5 NH-NH 2 + I I —j, i I _ OC CH 2 C 6 H 5 NH-NiC CH 2 X CH 2 \{i 2 Required: Cyclohexanone, 9 ml.; phenylhydrazine, 8 ml. Dissolve 8-8 g. (9-0 ml.) of cyclohexanone in 50 ml. of glacial acetic acid, add 8 ml. of phenylhydrazine, and boil the solution under reflux for 5 minutes. Cool the solution, when the tetrahydrocarbazole will crystallise out. Filter at the pump, drain well, and recrystallise either from aqueous ethanol or (better) from aqueous acetic acid. The recrystallisation should be
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