Patent GB-317342-A (GB)
Title: Improvements in or relating to the manufacture of alkoxy aliphatic anhydrides
IPC: C07C51/56
Filed: 1928-04-14
Abstract: 317,342. Dreyfus, H. April 14, 1928. Alkoxy aliphatic anhydrides are prepared by the thermal decomposition, of the vapours of the corresponding acids. The reaction may be performed in the presence or absence of contact materials, such as pumice, fireclay, kieselguhr, graphite, and corundum, and/or of catalysts; suitable catalysts, which may be used singly or in combination, are salts of phosphoric acids, water binding agents (such as phosphoric acids, bisulphates, pyrosulphates, and zinc chloride), tungstic acid, alkaline, earth tungstates, sugar charcoal, lamp black and like amorphous carbons, alkali chlorides and sulphates, boric acid, alkali borates, and copper. The reaction may be performed by rapidly passing the acid vapours, admixed or not with indifferent gases such as nitrogen and under ordinary or reduced pressure or increased pressure of the order of 3-5 atmospheres, through tubes of copper, fireclay or silica, which may contain contact materials and/or cata.lysts and are heated to any suitable temperature, preferably to 500-800‹ C. When the reaction is conducted in the presence of copper, nickel, or other metal forming an easily reducible oxide, for instance in apparatus made of or lined with such metals, it is advantageous to pass hydrogen or other reducing gas through the reaction zone during and/or prior to the re action, and preferably also after the reaction. It is preferred also, whether metals such as copper &c. are present or not, to mix carbon dioxide or mixtures thereof with carbon monoxide with the acid vapours to be decomposed. The reaction zone should be thoroughly cleaned before starting or re-starting the apparatus, suitably by washing it in turn with dilute nitric acid and water and then scouring with steam; this treatment may be followed by preliminary treatment with hydrogen &c. as described above. An alternative method of conducting the reaction consists in mixing the acid vapour with nitrogen, hydrogen, steam or other inert gas preheated to a temperature above that at which the reaction is to proceed. The separation of the anhydride from the reaction products may be effected by any of the methods described in Specification 305,147 in connection with acetic and other aliphatic anhydrides. A further method of separation consists in causing the reaction products to impinge upon a cold stream of benzene or other water-insoluble solvent for the anhydride. In one example, methoxyacetic acid vapour is passed through a fireclay or silica tube heated to 500-700‹ C. and containing pumice or silica coated with sodium bisulphate or pyrosulphate. The reaction products are separated by fractional condensation. In another example, the conditions of the first example are modified by using a copper tube filled with pumice or kieselguhr coated with calcium chloride and by passing hydrogen through the tube while it is being heated up and preferably also during the reaction. In a further example, methoxyacetic acid vapour is mixed with steam superheated to 800‹ C., the mixture having a temperature between 500 and 700‹ C. The anhydride, is recovered by passing the reaction products over calcium chloride at 250-300‹ C. and condensing the remaining vapours.