A 1-l. round-bottomed flask is fitted with a three-bulbed Glinsky fractionating column connected to a water-cooled condenser set for distillation. The crude diacetone alcohol (p. 199) which will usually weigh about 1100 g. (9.5 moles) and will have a specific gravity of about 0.91 is placed in the flask together with 0.1 g. of iodine. The mixture is now distilled steadily but not too rapidly (Note 1) with a small free flame, and three portions are collected as follows: I, 56–80°; II, 80–126°; III, 126–131° (Note 2). The first portion is acetone containing a small amount of mesityl oxide and water (Note 3). The second portion separates into two layers—water and crude mesityl oxide. The third portion is pure mesityl oxide.

While the third fraction is distilling, the aqueous layer in fraction II is separated in a separatory funnel and the crude mesityl oxide is dried with anhydrous calcium chloride and distilled through a Glinsky column; by this means a further amount of acetone and a small intermediate fraction (85-126°), which is best discarded, are separated. The pure mesityl oxide itself then distils between 126° and 130° and is added to the pure product already obtained as the third portion of the first distillation. The first complete distillation will require about five hours; the redistillation of portion III will take about one hour. The yield is 650 g. (65 per cent of the theoretical amount based on the total acetone employed) (Note 4). About 300 g. of acetone is recovered (Note 3).