Patent GB-719695-A (GB)
Title: Oxidation process
IPC: C07B35/04
Filed: 1951-04-24
Abstract: A process for producing aromatic carboxylic acids, aromatic carboxylic acid amides and aromatic carboxylic acid salts, each having the carboxyl carbon atom or atoms directly attached to nuclear carbon atoms comprises oxidizing alkyl aromatic hydrocarbons and/or alkyl aromatic carboxylic acids by contacting such material with elemental sulphur and/or an inorganic sulphurous material having substantially all its sulphur atoms at a valence level below plus six and above minus two, and water, in the presence of ammonia at a temperature above about 550 DEG  F. Alkyl aromatic hydrocarbons having at least one hydrogen atom attached to the alpha carbon atom are more suitable and those having only quaternary alpha carbon atoms in the alkyl group may require longer reaction time and/or temperatures.  As oxidizing agents may be used a water-soluble polysulphide or a sulphur compound convertible to sulphur under the conditions of the reaction, e.g. a mixture of hydrogen sulphide and sulphur dioxide, or sulphur dioxide or a water-soluble sulphite with up to about 6 per cent of the total sulphur required may be used. When using such compounds a small amount of sulphur also is preferably added.  The extent to which oxidation proceeds can be controlled by varying the amount of sulphur present, e.g. xylene may be oxidized to a phthalic acid when at least 6 gm. atoms of sulphur per gm. mol. are present, or to a mixture of phthalic and toluic acids when less sulphur is used.  A large excess of water and ammonia is preferred.  Ammonium salts e.g. the carbonate, bicarbonate, sulphide or sulphite may be used as the source of ammonia under reaction conditions.  The reaction temperature may be about 550 DEG to 675 DEG  F. and the pressure about 1000 to 3000 lbs. sq. in.  The products may be freed from sulphur by dissolving them in caustic alkali, filtering and reprecipitating with sulphuric acid.  Hydrogen sulphide and ammonia produced in the working up of the product may be re-used, e.g. by adsorption in water to give ammonium sulphide, which may be converted by air-blowing to the polysulphide which is introduced into the reaction mixture.  In examples: (1) p-xylene containing as impurity m-xylene and ethylbenzene is heated with sulphur and aqueous ammonia in the mol. ratio 1 : 8 : 10 at 580 DEG F. and 2950 lbs. sq. in. to give a mixture containing ammonia, hydrogen sulphide, ammonium polysulphide ammonium phthalate, terephthalamide and ammonium terephthalamide.  After boiling off hydrogen sulphide and ammonia, the amides and ammonium salts are converted to sodium salts by boiling with sodium hydroxide (strong acid may alternatively be used in this stage).  Acidification to pH6 precipitates sulphur which is filtered off and terephthalic acid is then precipitated by acidification to pH3; using generally similar methods there are effected the oxidation of (2) mixed C8 aromatic stock (about 80 per cent mixed m- and p-xylenes, with also o-xylene, ethylbenzene and paraffinic hydrocarbons); (3) mixed toluic acids produced by air oxidation of liquid xylenes in the presence of a cobalt catalyst, mixed phthalic acids being produced; (4) ethylbenzene to benzoic acid, (in the form of benzamide and ammonium benzoate); (5) durene to give pyromellitic acid.  In example (6) p-xylene, sulphur and ammonia (1 : 7 : 6) are reacted continuously by passage through a heated stainless steel coil, to give toluic and terephthalic acids.  Similarly to (1) there are also produced (7) a mixture of mono- and dibasic acids (predominantly 5-methylisophthalic acid), and 1,3,5-benzene tricarboxylic acid, by oxidation of mesitylene.  In example (8) a -methyl-naphthalene is reacted with an aqueous ammonium polysulphideammonium bisulphide solution (prepared by suspending sulphur in ammonium hydroxide, bubbling in hydrogen sulphide, and then sulphur dioxide).  After heating with sodium hydroxide, the reaction mixture yielded a -naphthoic acid and a crystalline product of undetermined composition.