Chloroacetaldehyde dimethyl acetal

CLEAR COLORLESS TO YELLOWISH LIQUID

Chloroacetaldehyde dimethyl acetal can be used as a reactant to synthesize:

• 2-(chloromethyl)-4,7-dethyl-1,3-dioxepane
• 2-(chloromethyl)-5,6-benzo-1,3-dioxepane
• ketene dimethyl acetal

Chloroacetaldehyde dimethyl acetal is obtained by the stoichiometric reaction of vinyl acetate and chlorine in the presence of excess methanol. The specific steps are as follows:
186 ml (172 g = 2.0 mol) of vinyl acetate and 142 g (2.0 mol) of chlorine were simultaneously introduced into 324 ml of methanol with stirring and cooling at 0 ° to 2 ° within 1 hour. Then 50 ml of low boilers were distilled off over a 50 cm Vigreux column, then 19.8 g of an intermediate run of a batch which had been carried out in the same way were added, and finally 34 g of calcium oxide were added with stirring and cooling at 40 ° -50 ° C. within 30 minutes. After neutralization was complete, the reaction mixture was in the form of two separate liquid phases. After the layers had been separated off, the upper layer obtained was fractionated, 88 g of the forerunner, which mainly comprised methyl acetate and methanol, 19.8 g of the intermediate run, which mainly contained methanol, chloroacetaldehyde, chloroacetaldehyde mono and dimethylacetal, and the main fraction was 223.1 g of chloroacetaldehyde dimethylacetal ds 89.5% d. Th. Were obtained. If the lower layer formed after the calcium oxide addition is shaken twice with 100 ml of methyl acetate each time and the combined organic phases are distilled, 92.1% of theory. Th. Chloroacetaldehyde dimethyl acetal obtained.

Chloroacetaldehyde dimethyl acetal is a clear, colorless liquid. It reacts with hydroxythiol to form hydroxy acetal.

Purify the acetal by fractional distillation. [Melhotra J Indian Chem Soc 36 4405 1959, Beilstein 1 IV 3134.]