GB312733A - Improvements in or relating to the manufacture of aliphatic anhydrides - Google Patents

Abstract

312,733. Dreyfus. H. March 21, 1928. Grant of Patent opposed. Addition to 280,972. Acetic, propionic, butyric, and other aliphatic anhydrides.-The process of the parent Specification, in which acetic anhydride is produced by heating acetic acid vapour in presence of a phosphoric acid, which may be deposited upon or mixed with porous materials, is applied to the production of other aliphatic acid anhydrides: and aliphatic acid anhydrides (including acetic anhydride) are produced with particular advantage when the phosphoric acid is deposited upon or mixed with carbon, charcoal. or carborundum. A suitable catalyst may be prepared by carbonizing a mixture of ortho-phosphoric acid and an organic substance such as cane sugar, or by mixing with or spreading upon carborundum a substance such as orthophosphoric acid or ammonium phosphate and heating, whereby meta- or pyrophosphoric acid is produced. The reaction may be effected by passing the vapour of the aliphatic acid over. the catalyst in tubes made of or lined with gold, platinum or the like at 300-600‹ C. at ordinary, increased, or reduced pressure. The catalyst may be regenerated continuously, for instance by circulating it between the reaction zone and a regenerating zone in which it may be heated to remove the water absorbed. The reaction vapours may be treated in any suitable manner to separate the anhydride; for instance by leading them through a fractionation column maintained at a temperature between the boiling-points of water and the anhydride; or by passing them through one or more solvents for the anhydride of higher boiling point than water, such as chlorbenzene, p-dichlorbenzene, benzyl ether, tetrachlorethane, paraffin oil, triacetin, phenetole, anisole, one or more cresols, or p-cresyl acetate; or the vapours may be condensed in presence of the vapour of an entraining liquid which carries away the water vapour, as described in Specification 303,772 ; or the vapours may be led under the surface of an extracting liquid insoluble in water and maintained below the boiling-point of water, as described in Specification 298,667; or the vapours may be passed over one or more water-binding substances below the temperature at which the vapours are produced but preferably above the boiling-point of water, as described in Specification 289,972. When the vapours are produced under pressure, the pressure should be released before the separation of the anhydride. The anhydride may be purified by distillation over anhydrous sodium or other acetate. The initial material may be dilute or concentrated acid. Examples describe the production of acetic and propionic anhydrides at 450-500‹ C.