33884-43-4

A 2-L, three-necked flask has a mechanical stirrer, thermometer, and gas inlet tube. In the flask, 750 mL of dichloromethane, 112 g (2.00 mol) of acrolein (Note 1), and 0.10 g of dicinnamalacetone indicator are placed under nitrogen. The yellow solution is cooled to 0–5°C with an ice bath. Gaseous hydrogen bromide is bubbled into the solution with stirring until the indicator becomes deep red. The ice bath is removed, and 1.0 g of p-toluenesulfonic acid monohydrate and 152.2 g (2.00 mol, 144 mL) of 1,3-propanediol are added. The yellow solution is stirred at room temperature for 8 hr and then concentrated with a rotary evaporator. The residual oil is washed with two 250-mL portions of saturated aqueous sodium bicarbonate and dried over anhydrous potassium carbonate. Vacuum distillation through a 30-cm Vigreux column yields 252 g (65%) of 2-(2-Bromoethyl)-1,3-dioxane as a colourless liquid.

This bromide is recognized to possess irritant properties and should therefore invariably be handled with gloved hands inside an efficient hood. It is also advisable that these reagents be refrigerated for long-term storage in order to minimize the potential for acid liberation.