314,035. Selden, Co., (Assignees of Jaeger, A. O). June 23, 1928, [Convention date]. Monocarboxylic acids; aromatic hydrocarbons ; benzaldehyde; benzoic esters; benzophenone; anthraquinone.-Monocarboxylic acids are obtained from polycarboxylic acids and their derivatives, e.g. phthalic anhydride and its nitro- or halogen substitution products, diphenic acid, adipic acid, succinic acid, maleic acid, or tartaric acids, by passage over catalysts which tend to split off carboxy groups in the presence of hydrogen or.reducing gases, such as illuminating gas or natural gas, or reducing vapours such as methyl alcohol or methyl formate. Contact masses which can be used include (1) porous or capillary substances such as kieselguhr, pumice, volcanic rocks, silica gel, etched quartz fragments, filter stones, active carbons, undiluted and diluted base-exchange substances, such as two-component or multi-component zeolites, non- silicious base-exchange bodies, and leached products of base exchange substances such as glaucosil &c. ; (2) known carboxy-splitting catalysts such as oxides of thorium, other rare earths, beryllium, aluminium, cadmium, zirconium, titanium, alkalis, and alkaline earths, which may be associated with porous substances; (3) hydrogenation catalysts, e.g. zinc, copper, silver, gold, iron, cobalt, manganese, thallium, lead, the platinum metals, tin, or their compounds. Oxidation catalysts, e.g. catalysts containing vanadium, columbium, tantalum, bismuth, manganese, chromium molybdenum, tungsten, or uranium may be included in the contact mass. Salts of the metal acids are also effective. Metal alloys can also be used, including alloys of iron, e.g. ferrochrome, ferrotungsten, ferrotitanium, ferromolybdenum, ferrovanadium, ferromanganese, silico - ferromanganese, aluminium - silico - ferromauganese ; copper alloys, e.g. brass, bronze, aluminium bronze; aluminium alloys e.g. duralumins; and alloys containing beryllium or magnesium. Many minerals are also suitable as contact masses, including titanium minerals, e.g. nitile, ilmenite and titanite; zirkite, zircon, thorite and rare earth metals, pyromorphite, cryolite, spinel, corundum, topaz, witherite, barite, calcite, magnesite, dolomite. vanadite, apatite, borax, carnallite, feldspar, and muscovite. The reaction may be carried out at reduced, normal or elevated pressure. In the vapour phase, a circulatory process is preferably used, the reaction products and unreacted substances, together with carbon monoxide and dioxide formed, being removed. The reducing gases may then be re-circulated. The surface of the converter may present a face of non-ferrous metal, e.g. aluminium or copper, to the reacting components. Inert gases such as nitrogen or steam may be present. Operating in the liquid phase, the finely-divided catalyst is suspended in the liquid, or gaseous catalysts such as iron carbonyl may be used, and the reaction is preferably carried out at increased temperatures in autoclaves. The following examples are given (1) Quartz fragments are boiled in potassium hydroxide solution, washed with water and dilute hydrochloric acid and then spraved with sodium chloride solution. Phthalic anhydride vapour and hydrogen are passed over this contact mass at 360‹-420‹ C., producing benzoic acid. The sodium chloride may be partly or wholly replaced by other salts of the alkalis and alkaline-earths, the chlorides, phosphates and borates being suitable. The quartz may be replaced by the porous substances specified above, asbestos, various minerals, silicates, metals, metal alloys, or slag wool. Steam may be added. (2) Crushed pumice is coated by spraying with a suspension of zinc hydroxide, and then treated with dilute nitric acid and dried. Phthalic anhydride and hydrogen are passed over the mass at temperatures between 350‹ and 450‹ C., preferably between 380‹ and 400‹ C. Benzoic acid is obtained, together with traces of benzaldehyde and benzene. A large execess of hydrogen is preferable, as also is the addition of steam. When methyl alcohol is used as the reducing agent, some methyl benzcate is also obtained. The zinc in the catalyst may be replaced by beryllium, cadmium, boron, aluminium, titanium, zirconium, tin, lead, thorium, cerium or other rare earths, present as oxides, salts or other compounds, with or without carriers. Other elements may also be present in the mass, and many minerals, as specified above, may be used. (3) Hot pumice fragments are coated by spraying with an aqueous solution of copper nitrate or suspension of copper hydrate, and subsequently treated with reducing gases, e.g. hydrogen, water gas, methyl alcohol or methyl formate vapour. A mixture of phthalic anhydride and hydrogen is passed over the mass in a suitable converter at 360‹-400‹ C., yielding benzoic acid with some benzaldehyde and benzene. If steam is added, benzoic acid of high purity is obtained, which may be used directly for the production of esters, such as methyl, ethyl, butyl, benzyl, amyl or cyclohexyl benzoates. The copper may be wholly or partly replaced by iron, cobalt, lead, silver or gold, as oxides or salts. These contact mases partially decompose the benzoic acid, and small amounts of benzene, benzophenone, dipbenyl, anthraquinone, anthracene, and 9- phenyl fluorene are obtained. This may be avoided by the addition of salts of the alkali or alkaline-earth metals. (4) Freshly precipitated ferric oxide is suspended in water, potassium chloride dissolved therein, and the suspension then coated on to rough quartz fragments, quartz filter stones, or pumice or unglazed porcelain fragments. When used in the conversion of phthalic anhydride with the addition of reducing gases, e.g. water gas, illuminating gas, ethylene, or methanol vapour at 360‹-400‹ C., benzoic acid is obtained. Any other reduction or hydrogenation catalyst may replace the iron e.g. cobalt. nickel, copper, silver, gold, lead, thallium, or zinc, alone or admixed, and especially in association with stabilizers such as salts of the alkali forming metals. The potassium chloride may be replaced by other salts of the alkalis or alkaline earths e.g. phosphates, nitrates, and sulphates. The contact masses may be modified further by the addition of components containing one or more of the elements aluminium beryllium, strontium, titanium, zirconium, or tin. If unreacted phthalic anhydride is obtained, this may be separated from the benzoic acid by leaching with solvents which dissolve benzoic acid preferentially, such as benzene or chloroform, or by esterification and fractional distillation of the esters. (5) Freshly precipitated aluminium vanadate is coated on to unglazed porcelain fragments and used in the treatment of phthalic anhydride vapour admixed with reducing gases and some steam under the conditions previously described, yielding benzoic acid. Vapours of phthalic acid esters, such as dimethyl or diethyl phthalate, may be similarly treated, the products then comprising benzoic acid, methyl or ethyl benzoates, and some benzaldehyde. The salt used may be partially or wholly replaced by salts of the metal acids of the 5th and 6th periodic groups, e.g. columbic, tantalic, bismuthic, chromic, molvbdic, or tungstic acid, singly or in admixture. The basic radicle of the salts may comprise one or more of the following : aluminium, beryllium, magnesium, the alkaline earths, zinc. cadmium, copper, silver, titanium, zirconium, tin, lead, iron, cobalt, nickel, manganese. In particular, tin chromate is effective. Stabilizers may be used. (6) A solution of sodium water glass is treated with a cuprammonium solution prepared from copper nitrate, and aluminium nitrate solution is added until the mixture is neutral to phenolphthalein. The gelatinous zeolitic product is dried. Metallates, e.g. sodium aluminate, zincate, chromite or plumbite may be used singly or in admixture instead of the cuprammonium solution. The aluminium nitrate may be replaced by one or more metal salt solutions, e.g. containing titanium, zirconium, zinc, iron, chromium, vanadium or tungsten. The zeolites may be used directly, or treated with other salt solutions, e.g. calcium chloride or copper nitrate or solutions of iron, cobalt, nickel, zinc, magnesium, barium or lead salts. They may be diluted with kieselguhr, pumice meal, ground quartz, or glaucosil, or water or formed on carriers such as filter stones, granules of metals or metal alloys. Alkalies or alkaline earths may be used as cementing agents. They may also be treated, especially after base exchange, with acids, e.g. hydrochloric or phosphoric acid, and especially the metal acids of the 5th and 6th periodic groups. The base exchange substances may be leached with dilute acid, producing ultimately a reactive silicic acid, which may be used as a catalyst. A mixture of phthalic anhydride, hydrogen and steam is passed over these contact masses at about 380‹ C., yielding benzoic acid. (7) Sodium aluminate is obtained by dissolving freshly precipitated aluminium hydroxide in excess caustic soda solution. " Celite, " brick refuse, activated carbons, or polysilicates, e.g. of calcium, copper, iron, zinc, titanium, zirconium or thorium, are stirred into a solution of aluminium sulphate, which is then added to the aluminate sulphate, until the mixture is alkaline to litmus and preferably neutral to phenolphthalein. The product is freed from mother liquor, dried below 100‹ C., and broken up. The contact mass may be modified by trickling water or a salt solution over the fragments, thus hydrating or subjecting them to base exchange. Bases such as those containing iron, cobalt, copper, silver, lead, manganese or thorium may be thus introduced. The base exchange bodies may be impregnated with phosphoric or chromic acid to form the corresponding salts. The aluminate or aluminium sulphate may be partially or wholly replaced by other metallates or m