PREPARATIONS 231 Dibenzal-acetone. C 6 H 5 CHrCHCOCHiCHC 6 H 5 (Claisen Reaction). (Semi-micro Scale.) When an ethanolic solution containing both acetone and two equivalents of benzaldehyde is made alkaline with sodium hydroxide, rapid condensation occurs with the formation of dibenzal-acetone, or dibenzylidene-acetone. This 2C 6 H 6 CHO + CH 3 COCH 3 = C 6 H 5 CH:CHCOCH:CHC 6 H 6 + 2 H 8 O Dibenzal-acetone. is a particular example of the Claisen Reaction,* for Claisen showed that alde-hydes under the influence of sodium hydroxide will condense with (i) another aldehyde, or (ii) a ketone, with the elimination of water. Thus benzal-dehyde will condense with (i) acetaldehyde to give cinnamic aldehyde, and with (ii) one equivalent of acetone to give (mono) benzal-acetone. In these (i) C 6 H 5 CHO + HCH 2 CHO = C 6 H 6 CHiCH CHO + H 2 O Cinnamic aldehyde, (ii) C 6 H 5 CHO 4- HCH 2 COCH 3 = C 8 H 6 CHtCHCOCH 3 + H 2 O Benzylidene-acetone. reactions it is probable that an intermediate hydroxy-compound is formed
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