Dimethylmalonic acid anhydride

Dimethylketene Acetic anhydride (25 g), dimethylmalonic acid (6.5 g), and concentrated sulfuric acid (1 drop) are placed in a dry Claisen flask dissolution occurs when the mixture is shaken. The solution is set aside at room temperature for 2 days, then a little powdered barium carbonate is added and the acetic acid and anhydride are removed by gentle heating in a vacuum. A new receiver is then attached and this is cooled in ice. The temperature is then gradually raised to about 100°, whereupon the dimethylmalonic anhydride decomposes with evolution of carbon dioxide and distillation of the dimethylketene produced. The yield is 65% (2.3 g) and the b.p. 34°. 

Dimethylketene has beep obtained in unspecified yield by heating the monochloride of dimethylmalonic acid it is probable that the malonic anhydride was formed as an intermediate. This method failed in attempted applications to diethylketene, and carbon suboxide. Low yields of carbon suboxide have been obtained by tteating malonyl chloride with lead, silver, or zinc oxide or with silver oxalate or malonate, and by treating silver malonate with cinnamoyl chloride malonic anhydrides or mixed anhydrides may be intermediates. 

A mixed trimer of dimethylketene with carbon dioxide 41 is also obtained indirectly in the reaction of dimethylmalonic acid and acetic anhydride. 

Dimethylmalonic acid and acetic anhydride heated slowly to boiling with distillation of the resulting acetic acid, air admitted after G02-evolution has... 

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