GB443151A - Manufacture of organic acid anhydrides - Google Patents

Abstract

Organic acid anhydrides are made by the oxidation of the aldehyde with air, oxygen or ozone and taking steps during or after the reaction to prevent the hydrolysis of the anhydride. The hydrolysis may be prevented by adding a water-binding agent such as anhydrous copper or calcium sulphate or silica gel or by means of a solvent for the anhydride in which water is insoluble such as benzene, toluene or xylene; the product is rapidly cooled and the oxidation is effected rapidly by adding a catalyst which may be a metal or compound thereof having more than one valency or mixtures thereof. The oxidation may occur at or below ordinary temperature or at raised temperature, and ordinary or raised pressure, and the process may be continuous. The removal of water from the reaction product may be effected by spraying the product into the hot or superheated vapour of the corresponding acid or on to heated stationary or moving surfaces in such vapour, and in this stage reduced pressure may be employed. In examples: (1) oxygen is introduced into a mixture of glacial acetic acid and acetaldehyde containing manganese acetate in a vessel provided with a stirrer and cooling means and maintained at 42 DEG C. at 2 atmospheres pressure, the product being cooled to - 10 DEG C. and then treated for separating out the water; (3) anhydrous copper sulphate is added and the temperature is 25 DEG C.; (4) manganese and cobalt acetates are employed as catalyst at 30--50 DEG C.; (5) manganese, cobalt and nickel acetates are used; (6) manganese cobalt, mercury and sodium acetates are used; (7) finely-divided copper and cobalt are used; (11) oxygen containing ozone is supplied, without a catalyst; (12) propionic anhydride is made from a mixture of propionic acid, propionaldehyde and manganese cobalt and copper acetates at 45 DEG C. and 2 atmospheres pressure; butyric anhydride is made similarly, using copper acetate as catalyst; (14) benzoic anhydride is made from a mixture of acetic acid, acetaldehyde, cobalt and nickel acetates and benzaldehyde at 42--46 DEG C. and 1,7 atmospheres pressure; (15) the reaction product of example 7 is sprayed into the middle of a column containing acetic acid vapour, acetic acid and water passing off through a dephlegmator, while the acetic acid and anhydride collected in the still are separated by fractional distillation; (16) the operation is effected as in example 15, but the mixture is sprayed on to a solid body in the column at 300 DEG C.; (17) the operation is effected as in example 15, but acetic acid vapour at 300 DEG C. is also admitted to the column; (18) butyric anhydride is separated as in example 15; (19) reduced pressure is employed in the separation.