Organic 2 Review Problem 165

Organic 2 Review Problem 165 - PREPARATIONS 149 Two methods...

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PREPARATIONS 149 Two methods of preparing pinacol from acteone are given below. In Method (A) sodium is added to acetone which is floating on 30% aqueous potas- sium hydroxide and which therefore contains a strictly limited amount of water. The method is simple and reasonably rapid but gives a low yield of pinacol. In Method (B), a modified method due to R. Adams, magnesium is treated with mercuric chloride and thus activated by the formation, of a film of magnesium amalgam. It therefore reacts with acetone to give the magnesium derivative of pinacol, which on hydrolysis furnishes the free pinacol. The scale 2(CHJ 1 CO + Mg -> (CH,) 2 C - C(CH 8 ), -> (CHJ 2 C - C(CH 3 ), OH OH Mg of this preparation can readily be increased above that given below. METHOD (A) Required: Acetone, 60 ml.; 30% aqueous potassium hydroxide, 90 ml.; sodium, 17 g. Fit a 250 ml. round-bottomed flask with a refhix water- condenser down which pieces of sodium may be dropped: alternatively, use a flask having a short straight stoppered side-
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