SYNTHESIS OF DICHLOROMETHYL METHYL ETHER (1,1-dichloro-dimethyl ether)

• In a fume cupboard equip a 500-ml three-necked flask with a dropping funnel, a mechanical stirrer, a thermometer and a reflux condenser, using a double-neck adapter to accommodate the last two items. 

• Protect the condenser and dropping funnel with calcium chloride guard-tubes. 

• Place 50 ml of phosphorus oxychloride and 156 g (0.75 mol) of phosphorus pentachloride in the flask and 48 g (49 ml, 0.8 mol) of methyl formate in the dropping funnel. 

• Cool the mixture to 10 °C and add the methyl formate dropwise at such a rate that the reaction temperature does not rise above 20 °C (about 1 hour). 

• When the addition is complete, remove the ice-bath, stir the mixture until all the phosphorus pentachloride has dissolved, keeping the temperature below 30 °C by occasional cooling. 

• Remove the stirrer, condenser, thermometer and dropping funnel, stopper the two side-necks and insert a simple distillation head into the central neck. Introduce a pine splint to serve as an anti-bumping device (1) and attach a condenser leading to a receiver flask via a receiver adapter for vacuum distillation. 

• Distil the reaction mixture under reduced pressure (water pump) on a water bath at about 60 °C and collect the distillate in a flask cooled to —25 to — 30 °C in a cooling bath (acetone-Car-dice or ice-salt). 

• The distillate weighs 209 g and consists of a mixture of dich-loromethyl methyl ether (b.p. 85 °C) and phosphorus oxychloride (b.p. 105 °C). 

• Fractionally distil the mixture at atmospheric pressure through a 50-cm column filled with glass helices and surrounded by a heating jacket at 60 °C, using a reflux ratio of about 1:8. 

• Collect the fraction which boils between 82 and 95 °C and refractionate to give 70 g (76%) pure dichloromethyl methyl ether, b.p. 85 °C. Protect the product from moisture.

Notes to keep in mind:

1.  A conventional capillary air leak, inserted into a side-neck, should only be used in this case if the air supply is pre-dried since the product is susceptible to de-composition by moisture.