230 PRACTICAL ORGANIC CHEMISTRY usually give direct addition products with ammonia, although polymerisation CH 8 CHO + HNH, = CH 8 CH(OH)NH 2 > (C 2 H 7 ON) 8 may follow. Formaldehyde is an exception among the aliphatic aldehydes, since it undergoes condensation with ammonia to give hexamethylene tetramine (or 6CH 2 O + 4NH 8- (CH 2 ) 6 N 4 + 6K 2 O urotropine (p. 379), a reaction which resembles that given by benzaldehyde. Required: Benzaldehyde, 5 ml.; concentrated ammonia, 50 ml. Place 5 ml. of benzaldehyde in a wide-necked stout-walled bottle of about ioo ml capacity (a conical flask is too fragile for this purpose) and add 50 ml. of concentrated ( d , 0-880) ammonia solution. Cork the bottle securely, shake vigorously, and then allow to stand for 24 hours, by which time the layer of benzaldehyde at the bottom of the bottle will have been converted into a hard mass of hydrobenzamide. (If after 24 hours the crude hydrobenzamide is still syrupy, shake the mixture vigorously and allow to stand for another hour, when the
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