SE182805C1 - - Google Patents

Description

Inventors: RS Barker and A Saffer Priority Required as of March 18, 1955 (USA) The present invention relates to a process for the preparation of aromatic monacarboxylic acids by catalytic oxidation in the aqueous phase of an aromatic compound, which dunes a aliphatic substituent which Is oxidizable to a carboxyl group, whereby molecular oxygen such as oxidation medium In such a liquid phase oxidation, oxygen or oxygen-containing gas mixtures are brought into contact in the presence of an oxidation catalyst with a liquid reaction mixture containing the aromatic starting material.

Pet Ar can.t that any other heavy metal oxidation catalysts by oxidation with molekyMist oxygen in the water spoon of toluene and xylenes. Processes of this kind, which give a good yield of benzoic acid from toluene and of toluic acids from xylenes, have been previously described.

Pet has now realized that aromatic monocarboxylic acids can be produced by a more rapid reaction and with surprisingly high yield, which is very important from a commercial point of view, by oxidation of monoalkylbenzenes in the liquid phase with molecular oxygen in the presence of a heavy metal catalyst, if the reaction system contains a catalytic amount of bromine. This favorable result is obtained only with the use of bromine and has not been achieved with other halogens.

This special combination of one. Heavy metal oxidation catalyst and bromine have generally been found to be suitable for the production of aromatic monocarboxylic acids from aromatic compounds which contain a phatic substituent attached to the aromatic nucleus or from aromatic compounds which contain two. .or flora aliphatic substituents attached to the aromatic carnation, if one of these substituents is more oxidizable to the other substituents. The present invention relates to a process for the preparation of an aromatic monocarboxylic acid by oxidation in the aqueous phase of an aromatic compound containing an aliphatic substituent attached to the aromatic nucleus, which is oxidizable to a carboxyl group, the oxidation being carried out with molecular acid in each of a catalytic system that simultaneously contains bromine and a heavy metal.

The term «heavy metal» has been defined in the Oeriodic Chart of the Elements », p. 56 and 57, in the Handbook of Chemistry, Vol. 8, 1952, Handbook Publisher Sandusky, Ohio, USA, and the heavy metal oxidation catalysts are selected from the heavy metals zone shown in the d.

As heavy metal oxidation catalysts, it is possible according to the invention to use, for example, manganese, cobalt, jam or nickel, singly or in admixture. Manganese or cobalt or a mixture of manganese and cobalt is preferably used.

The heavy metal catalyst and bromine are typically added to the reaction mixture in the form of salts and are present in ionized form. The two components can be supplied, for example, in the form of a heavy metal bromide or in the form of various salts, one of which contains the metal and the other contains bromine. Thus, according to the invention, for example, manganese bromide and / or cobalt bromide can be added, which together form the catalyst system. The heavy metal can also be added as a carboxylic acid salt, e.g. such as the acetate or some other carboxylate and, moreover, in the form of the salt of the carboxylic acid to be prepared, while the bromine may be added in the form of a bromide, suitably with a non-metallic cation, e.g. ammonium brontide or an organic bromide which is soluble in the reaction mixture. The amount of all components of the catalyst system, calculated as MnBr2 or other heavy metal bromide, usually amounts to 0.1-10% by weight of the amount. aromatic compound to be oxidized. Manganese dibromide (MnBr 2) was suitably used in an amount of 0.3 to 2% by weight and preferably 0.5 to 1.7% by weight. The ratio between the amount of heavy metal and the amount of bromine does not need to be equal to the stoichiometric ratio, but when using, for example, manganese can vary from 1 to 10 atoms of Mn per 10 to 1 atoms of Br.

The oxidation is carried out in many cases with the advantage in the presence of an inert organic medium, preferably a matt, aliphatic monocarboxylic acid having about 2-8, preferably 24 carbon atoms in the molecule. When using such a medium, the amount thereof should not be greater than necessary for the reaction mixture to obtain a suitable consistency, for example 1 part by weight per part by weight thereof. aromatic compound to be oxidized. In general, the amount of inert medium is stated to be 1-1 and preferably 1-2.5 parts by weight per part by weight of the aromatic compound to be oxidized. Benzoic acid can also be used as the inert medium, which is particularly useful if the oxidation product consists of benzoic acid, as in the oxidation of toluene. The use of benzoic acid also makes it possible to carry out the process at atmospheric pressure.

The oxygen used in the process may consist essentially of pure oxygen, but may also be present in the form of a mixture of oxygen and inert gases, such as air, which contains about Vo oxygen. The total amount of oxygen fed to the reaction mixture may be 4-500 moles of oxygen per mole of the aromatic compound to be oxidized. Preferably 5 to 75 moles of oxygen per mole of aromatic compound are used and it is usually not unreasonable to use another oxygen moiety in 5 to 300 moles per mole of the aromatic compound.

The process according to the invention can be carried out batchwise, intermittently or continuously and only partially oxidized material can be returned to the reaction mixture after separation of the final product. Formed water can be deposited to maintain the desired concentration, e.g. by distillation or by the addition of acetic anhydride.

The pressure should be sufficient to maintain a water phase. When carrying out the process in the temperature range of 120 to 27 ° C and depending on the starting material and the inert organic medium, if one is used, the pressure may vary between 1 and 105 kp / cm 2. When using an inert organic medium, such as a lower monocarboxylic acid, the liquid phase should contain at least some of the acid.

The reaction temperature should be sufficiently high for the desired oxidation to occur but not so. hag, that no 8nskad for charring or tar formation occurs. In general, a temperature between 120 and 275 ° C has proved suitable. The most suitable temperature range has in most cases been found to be between 150 to 250 ° C and preferably between 170 and 210 ° C. The reaction time should be sufficiently long to allow a satisfactory conversion of the aromatic starting material to the desired carboxylic acid, e.g. ex. about 0.5 to 25 'or more hours, and approximately up to about 4 hours.

The aromatic starting material used in the reaction may be a monoalkylbenzene or monoalkylnaphthalene which is in a technically pure form and contains free Iran impurities or substances which may interfere with the oxidation reaction. The alkyl substituent IjOr preferably contains 1 to 4 carbon atoms. The aromatic starting material may contain a small amount of matte aliphatic carbonates, which have similar boiling ranges and are relatively resistant to oxidation under the reaction conditions. As the starting material, according to the invention, for example, the following monoalkylated aromatic compounds can be used: methylbenzene, ethylbenzene, isopropylbenzene, n-butylbenzene, sec-butylbenzene, α-methylnaphthalene and fl-methylnaphthalene. Furthermore, polyalkyl compounds can be used in which one, alkyl group is more easily oxidizable than the others, e.g. tert-butyltoluene. By suitable choice of reaction conditions, the latter can be converted to tert-butylbenzoic acid without formation, of any nominal amount, dicarboxylic acid. However, one can also produce the corresponding dicarboxylic acid by Mining the temperature and pressure.

The invention is further illustrated by the following examples.

Example 1.

A suitable reaction vessel having a corrosion-resistant inner surface (for example, glass, ceramic or corrosion-resistant metal or alloy), provided with a stirring device, such as a mechanical stirrer or a gas stirring device, and having a. , device for heating or cooling the vessel contents, such as a loop or jacket (and optionally a backflow cooler, provided with a device for separating '' in water and intended for refluxing non-aqueous condensate into the reaction vessel, a gas inlet pipe and an outlet for diverting boiling water). material) was added with 100 parts, ethylbenzene, 125 parts acetic acid and 1 part manganese bromide. The reaction vessel was about half filled with the reaction mixture.

Air was introduced into the reaction mixture in an amount of 400 liters (determined at the outlet of the reaction vessel at atmospheric pressure and about 27 ° C) per hour, while the reaction mixture was bubbled at a temperature of 196 ° C under strong mechanical agitation for 3 hours. The pressure is maintained at approximately 29 kp / cm2.

The tertiary benzoic acid was isolated in solid form on an edge set. The yield amounted to 100% by weight (87% of theory).

Example 2.

The experiment of Example 1 was repeated using tert-butyltoluene instead of the ethylene, yielding tert-butylbenzoic acid in a yield of 104% by weight.

Example 3. 100 parts of cumulus, 150 parts of acetic acid, one part of manganese acetate and 0.75 parts of ammonium bromide are charged to a reaction vessel of the type described in Example 1. The oxidation is carried out at 28 kp / cm 2, with an effluent gas stream of 3000 volumes / hour / volume of reaction mixture and at 204-215 ° C in two. hours. The concentration of carbon dioxide in the exhaust gas reaches 6.6% • and the acid concentration in the exhaust gas reaches a minimum of 1.0%. The recovered reactor content is 275.1 parts and forms a clear solution. 275 parts of water were added thereto at room temperature. The precipitated solid is filtered and sealed with 250 parts of water. The precipitate is dried in an oven at 60 ° C and an amount of 52.4 g of benzoic acid is obtained. The filtrate and the wash water are combined and additional solid material precipitates. The second batch of solids is filtered and washed with 100 parts of water. A dry weight of 2.4 parts of benzoic acid is obtained. The precipitation procedure is repeated three more times, the water being combined with the main filtrate each time. P8. so salt is obtained 1.9 parts, 0.6 parts grated. 0.1 parts of benzoic acid. Thus, a total of 57.4 parts of benzoic acid of 100 g of starting cumulus are obtained.

Example 4.

The procedure set according to Example 3 is repeated using 100 parts of toluene instead of 100 parts of cumulus. The oxidation process and the recovery of benzoic acid are otherwise carried out in the same manner as described in Example 3. The yield of benzoic acid is 117 parts by weight, corresponding to a yield of 88 mol%.

Example 5.

The process feed of Example 1 is repeated except that the aromatic carbonate is 100 parts of toluene instead of ethylbenzene and the catalyst is 1.0 part of cobalt acetate and 0.75 parts of ammonium bromide in the place of 1.0 part of manganese bromide. The benzoic acid formed is recovered in 80 mol% yield.

Example 6.

In a tubular reaction vessel equipped with a stirrer and heater and with a water-cooled condenser, gas inlet and valve-provided gas outlet for regulating the effluent gas stream, 150 g of benzoic acid, 0.23 g of cobalt acetate and 0.42 g of manganese acetate (as the tetrahydrate) were charged. To this was added a solution of 0.64 g of tetrabromethane in 75 g of toluene, and the mixture was heated to 190-200 ° C. Air at a pressure of 5-6 standard liters / minute was passed through the mixture, while maintaining the pressure in the reaction vessel at about 27 kp / cm2. After 27 minutes, on analysis of the exhaust gases, it appeared that further oxygen absorption occurred. The contents of the reaction: the scarlet was cooled and analyzed. A yield of 95.7 g, or 96 mol% of benzoic acid is obtained with a melting point of 122 ° C and an acid number of 453.

Example 7.

In a rudder-shaped reaction vessel equipped with a stirrer and heating device and with a water-cooled condenser, gas inlet 'also valve-provided gas outlet f Or regulation of the exhaust gases is charged 25 parts of α-methylnaphthalene, 150 parts of glacial acetic acid and a solution of 1.2 parts of a mixture of cobalt acetate and manganese acetate (as the tetrahydrate) and 0.4 Mar. ammonium bromide in 6 parts of water. The mixture is heated at 204 ° C, while air under a pressure of 28 kp / cm 2 is passed through the mixture in an amount of 3.7 liters / minute, the pressure in the reaction vessel constantly at 28 kp / cm 2. Oxygen: the altitude of the exhaust gases drops to about 8.6% and rises, then to 20.8%. The reaction vessel is cooled, the contents are taken out and the solvent is removed by evaporation on a steam bath. The residue is dissolved in a dilute aqueous solution of alkali, filtered and the filtrate acidified with hydrochloric acid. The precipitated solids are collected on a filter, washed with water and dried to give 22.5 parts of α-naphthoic acid with a melting point of 159-161 ° C and a neutral equivalent of 171 (calculated value 172). The yield of α-naphthoic acid is 75 mol%, calculated on charged α-methylnaphthalene.

Example 8.

The procedure of Example 1 was repeated using 25 parts of the β-methylnaphthalene in place of the previously used amethylnaphthalene. It contains up to 25 parts of p-naphthoic acid with an ice melting point of 179-183 ° C and a neutral equivalent of 171 (calculated value 172). The yield of β-naphthoic acid was 83 mole percent based on. the. charged the p-methylnaphthalene.

Exempt 9.

To the reaction vessel described in Example 1 were charged 20 parts of α-isoamylnaphthalene, 150 parts of glacial acetic acid and a loading of 2.5 parts of a mixture of cobalt acetate and manganese acetate (as the tetrahydrate) and 1.0 part of ammonium bromide in 6.0 parts of water. The reaction 4-vessel was heated to 204 ° C and air under a pressure of 28 kp / cm 2 was passed through the mixture in an amount of 3.7 liters / minute, the pressure in the reaction vessel being kept constant at 28 kp / cm 2. The oxygen content of the exhaust gases dropped to a value of 12.4 and then gradually rose to 20.8%. The reaction vessel was then cooled, the contents removed and the solvent removed by evaporation on a steam bath. The residue was treated with a dilute aqueous solution of alkali and filtered to remove insoluble non-acidic material. The filtrate was acidified with hydrochloric acid and the precipitated solid was filtered off and washed with water. 10 parts of α-naphthoic acid are obtained, corresponding to a yield of 50 mol%.

Claims (8)

Patent claim: A process for the preparation of an aromatic monocarboxylic acid by oxidation of an aromatic carbonate having in the carnate an alkyl substituent which can be oxidized to a carboxyl group by means of molecular oxygen in the liquid phase in the presence of a catalyst and optionally in the presence of a lower monocarboxylic acid. of which the catalyst consists of a heavy metal oxidation catalyst in combination with a bromine-containing formation. Process according to Claim 1, characterized in that the aromatic carbon choice consists of a monoalkylbenzene, which in the alkyl group contains 1-4 carbon atoms. 3. A process according to claim 2, characterized in that the aromatic carbonate is constituted by toluene. 4. A process according to claim 1, characterized in that the aromatic carbonate consists of tert-butyltoluene. 5. A process according to any one of claims 1-4, characterized in that the heavy metal component in the catalyst consists of manganese and / or cobalt. 6. A process according to any one of claims 1-5, characterized in that the catalyst is introduced into the reaction mixture in the form of a heavy metal chromide. 7. A process according to any one of claims 1-5, characterized in that the heavy metal is introduced into the reaction mixture in the form of a salt other than a bromide and that the bromine is introduced in the form of a non-metallic bromine compound. Process according to any one of claims 1-7, characterized in that the reaction is carried out in the presence of a monocarboxylic acid having 2-8 carbon atoms in the molecule, in particular attic acid or benzoic acid, the reaction being carried out at a temperature of 1275 ° C and under a pressure of 1 to 106 kp / cm2. Request publications: Stockholm 1963. Kungl. Boktr. P. A. Norstedt & SiMer. 630089