Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J1/00—Pistons; Trunk pistons; Plungers
  • F16J1/10—Connection to driving members
  • F16J1/14—Connection to driving members with connecting-rods, i.e. pivotal connections
  • F16J1/22—Connection to driving members with connecting-rods, i.e. pivotal connections with universal joint, e.g. ball-joint
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D18/00—Pressure casting; Vacuum casting
  • B22D18/02—Pressure casting making use of mechanical pressure devices, e.g. cast-forging
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D18/00—Pressure casting; Vacuum casting
  • B22D18/04—Low pressure casting, i.e. making use of pressures up to a few bars to fill the mould
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/27—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with oxides of nitrogen or nitrogen-containing mineral acids
  • C07C51/275—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with oxides of nitrogen or nitrogen-containing mineral acids of hydrocarbyl groups
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/48—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F110/00—Homopolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F110/02—Ethene
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S260/00—Chemistry of carbon compounds
  • Y10S260/25—Metal catalyst

Definitions

• the present invention mainly consists in a method of producing benzene polycarboxylic acids, comprising the steps of heating a benzene derivative consisting of a benzene ring substituted 2,9524 Patented Dec.
• the starting materials for the method of the present invention are chloromethylated alkyl benzene derivatives such as toluene, Xylenes, ethylbenzene, mesitylene, durol, and the like or mixtures thereof.
• chloromethylated alkyl benzene derivatives such as toluene, Xylenes, ethylbenzene, mesitylene, durol, and the like or mixtures thereof.
• chloromethylation is carried out by treating alkyl benzenes with chloromethyl ether or hydrogen chloride and formaldehyde (or its polymerides), whereby, depending on the reaction conditions, one or two chloromethyl groups are incorporated into the benzene ring.
• toluene can be converted into a derivative represented by the formula C H .CH (CH Cl) xylene is analogously converted into 0r C6H2(CH3)2 (CH2Cl)2, etc.
• the chloromethylated benzene homologues of the kind aforesaid are subjected to the twostage oxidation treatment of the present invention, the first stage being carried out at substantially atmospheric pressure to convert the chloromethyl group or groups to a carboxyl group or groups, and the second stage being carried out at superatmospheric pressure to convert the non-converted alkyl group or groups to a carboxyl group or groups.
• the number of carboxyl groups in the final benzene carboxylic acid is equal to the number of alkyl groups plus the number of chloromethyl groups present in the original benzene derivative.
• p-chloromethyltoluene is oxidized in the above described two-stage oxidation method to produce substantially pure terephthalic acid.
• the total number of substituents convertible to carboxyl groups by oxidation i.e. the total number of alkyl and chloromethyl groups is three, whereby a henzene tricarboxylic acid, such as trimellitic acid, is formed.
• the total number of three oxidizable groups may be reached by one chloromethyl group and two alkyl groups, or two chloromethyl groups and one alkyl group.
• the total number of alkyl and chloromethyl groups may be four, five or six whereby the resulting benzene carboxylic acid will be respectively pyromellitic acid, benzene pentacarboxylic acid or mellitic acid.
• the alkyl groups of the alkyl benzene are methyl groups, e.g. as in toluene, xylenes, mesitylene, durol and the like.
• the process of the present invention allows for the production of all the benzene carboxylic acids, including the trivalent acids and their derivatives up to mellitic acid, starting almost and in the most interesting cases from readily obtainable benzene derivatives, especially toluene, and pure and crude xylenes. Moreover, the process is extra-ordinarily simple in its performance, as will be seen from the following description.
• the most suitable temperature for the heating during the first stage is the boiling point of the nitric acid, about 105 C.
• the first stage should be carried out at about atmospheric pressure although a slight excess pressure may result in the speeding of the reaction in the first stage without adversely affecting the entire reaction.
• the superatmospheric pressure should be at least 3 atmospheres, preferably between 3 and 30 atmospheres and most preferably between 5 and 20 atmospheres.
• a pressure of about 5 atmospheres gives highly satisfactory results although the reaction proceeds faster at a pressure of about 15 atmospheres and at a temperature of about 150200 C.
• the method can be carried out in practice in a single reactor, so that isolation of the intermediate product is unnecessary and the operating conditions only need be intensified as soon as all the chlorine has been separated from the starting material.
• the difiicultly soluble crude acid of the first reaction stage can be separated and further oxidized in a second reactor.
• Isolation of the intermediate product and further oxidation in a second reactor have various advantages.
• the intermediate product can be freed by washing with a suitable alkyl benzene, e.g. toluene, from the last traces of impurities, such as non-converted chloromethyl alkyl benzene, and so be in the best form for obtaining an end product which fulfills the highest requirements of purity.
• the oxidation in two separate reactors is also of advantage since the corrosive action of the reaction mixture is very diiferent in the two stages.
• the oxidation of chloromethyl derivatives can be carried out equally well, as mentioned, in the same autoclave, merely by raising the pressure and temperature on completion of the first oxidation reaction.
• Such a process is particularly satisfactory since, in the first oxidation stage, a stronger nitric acid than in the pressure stage leads to the best results and the decrease in the ntiric acid concentration after the first oxidation stage leads to a suitable acid concentration for the second stage.
• nitric acid of about 30-47% concentration in the first stage and about 20-45% concentration in the second stage.
• concentration of nitric acid in the first stage is 38- 47% and most preferably, the concentration of nitric acid in the first stage is about 43-45%.
• concentration of nitric acid in the second stage is between 3038% when operating with a benzene derivative containing at least three constituents oxidizable to carboxyl groups and about 32-35% when starting with chloromethyltoluene.
• the consumption of the acid is known to be of great importance to the economy of a nitric acid oxidation, and is caused by the reduction of the acid to elementary nitrogen. With nitrogen, nitrous gases are separated out in such oxidation, which can be readily recovered by washing. However, the nitric acid reduced to nitrogen is lost for an oxidation method.
• reaction proceeds faster and with the best yields, since too great a lowering of the nitric acid concentration during the reaction is avoided. If operating instead without simulaneous introduction of oxygen, the second oxidation stage must be carried out with higher pressures and temperatures in order to achieve approximately equivalent results.
• nitric oxide evolved from the reaction mixture, but also hydrogen chloride, which can likewise be recovered.
• the gas is passed for instance through concentrated sulfuric acid. Nitrosylsulfuric acid is formed from which nitric acid can be readily obtained, while the hydrogen chloride gas evolves from the sulfuric acid and can be used again for preparing chloromethylated derivatives.
• a vertical heatable reaction tube is particularly suitable for continuous oxidation, in which the reaction components are introduced from below and the gas through a frit or the like.
• the reaction mixture rises in the tube according to the amount of fresh starting material supplied, without too great an intennixing of the reaction mixture occurring along the tube.
• the supply of new starting material is controlled so that reacted mixture always extends to the upper end of the tube.
• the mixture can be transferred to a container in which the desired acid separates. From the container, which can be cooled if required, the mother liquor flows over into a cooling tube.
• the nitrous gases flow downwards through the tube, wherein all the nitrous gases are surprisingly taken up again by the mother liquor, so that at the foot of the cooling tube nitric acid is obtained which is fully utilizable for the method and can be returned to the reactor if necessary. That all the nitrous gases are taken up by the nitric acid is shown since in the waste gas which is blown from the container through a valve from the enclosed system, substantially no nitrous gases remain.
• the oxidation can be carried out without interruption merely by changing the operating conditions in a single apparatus.
• This necessitates an apparatus resistant to hydrochloric acid and to nitric acid or mixtures thereof, respectively.
• it is preferable, however, to change the apparatus.
• it may be very advantageous to separate and to wash the intermediate oxidation product. This measure is especially recommendable when obtaining intermediate products difficultly soluble in nitric acid, since the separating does not cause any difficulty, resulting more safely in chlorine-free intermediate products.
• the chlorornethylation' of e.g. m-xylene results in 4-chloromethyl-l,3-dimethyl-' benzene and 4,6-bis-chlorornethyl-1,3-dimethylbenzene.
• This mixture is obtained for example by treating m-xylene at about -70 C. with four to five times its weight of hydrochloric acid and about the same amount by Weight of formaldehyde with introduction of hydrogen chloride and vigorously agitating.
• the bis-compound When formaldehyde is present in larger excess, the bis-compound is preferably obtained. The non-reacted formaldehyde, paraformaldehyde etc. is not lost but is completely consumed by repeated employment of the reaction solutions. If bis-compounds are to be produced exclusively, the mono-compounds are separated and subjected to another chloromethylation. In this way trimellitic acid or other benzene-tricarboxylic acids are obtained from toluene via the bischlo-romethyl-toluene as intermediate products, and pyromellitic acid is obtained from xylene via the bis-intermediate products mentioned above.
• a special advantage of the process of the invention is the fact that the processing of practically all the xylene isomers leads exclusively to trimellitic and/ or pyromellitic acid. Consequently, the new process offers the chance of producing these high-grade acids from the so-called crude xylenes. According to their origin these crude xylenes represent a varying mixture of 0-, mand p-xylene.
• the crude xylene of coke oven plants contains for example about of m-xylene, 20% of p-xylene, 5% of o-xylene, and, in addition, about 5% of ethylbenzene.
• the crude xylenes of the petroleum industry consist of isomers, too. Separating the single isomers is diflicult due to their boiling points being closely together.
• Derivatives of these compounds such as nitro-derivatives and all the mixtures of the starting materials concerned are suitable also, certainly all the benzene derivatives or their mixtures which, after having been chloromethylated, contain substantially at least 3 substituents oxidizable to carboxyl groups.
• the mixture mentioned already and consisting of monoand bis-chloromethylxylene is obtained by chloromethylation, representing already a commercially valuable mixture of acids consisting substantially of pyromellitic acid, in addition to trimellitic acid after having been oxidized according to the process of the invention.
• the mono-product (boiling range 105l25 C.) can be separated by distillation from the mixture of the monoand bis-chloromethylated products, and the distillate and the residue can be oxidized separately, thus yielding trimellitic acid as well as pyromellitic acid either or both in isolated condition.
• pyromellitic acid When cooling the oxidation Solution, pyromellitic acid precipitates quantitatively without simultaneous precipitation of the l,2,3,4-bcnzene-tetra-carboxylic-acid containing also four carboxyl groups, and can be readily separated from the oxidation solution. Trimellitic acid is highly soluble even in cold water, being not obtained therefore prior to evaporating the oxidation solution. If required, it can be readily freed from contaminations by l,2,3,4-benzene-tetra-carboxylic-acid and hemimellitic acid by sublimation or a similar method.
• terephthalic acid results as by-product in excellent purity and considerable amounts. It is known to be difiicultly soluble even in hot nitric acid and consequently can be readily separated from the hot oxidation solution of the pyromellitic acid crystallizing out not before being cooled. Instead of this, both acids can be first separated together from the cold oxidation solution and boiled with water whereby pyromellitic acid is dissolved, unlike terephtalic acid, which is then filtered off. The filtrate is cooled, the pyromellitic acid crystallizing out as the hydrate in pure condition.
• the terephthalic acid is obtained from the oxidation solution in this very stage of the process in addition to trimellitic acid.
• the terephthalic acid is formed from ethylbenzene contained in the crude xylene.
• the surprising purity of this acid is simultaneously explained, since the ethyl group can be oxidized more readily than the methyl group.
• Example I 100 parts of m-xylene, 200 parts of aqueous formaldehyde solution (30-40%) and 400 parts of concentrated hydrochloric acid are heated for six hours to 75% C. After adding another 200 parts of formaldehyde solution, the reaction mixture is heated to about 70 C. with introduction of hydrogen chloride for an additional ten hours.
• the crystalline bis-chloromethyl compound (75 parts) is heated to boiling with 750 parts of 40% nitric acid in a vessel having a ceramic coating, for two hours with introduction of oxygen.
• the resulting insoluble acid is filtered off and the filtrate-4f necessary after replenishing the nitric acid-is used for oxidizing other chloromethylated products.
• the carboxylic acid obtained is oxidized with 500 parts of 30% nitric acid for one hour at 170 C. under atmospheres pressure while simultaneously introducing air. 75 parts of pyromellitic acid are obtained which crystallize out of the oxidation solution upon cooling.
• Example II 100 parts of m-xylene are chloromethylated as described in Example I, but after the separation of the crystals (75 parts) the liquid fraction of the chloromethylated products is distilled off. At a pressure of 14 mm. Hg and a temperature of 100110 C. 45 parts of 4-chloromethyl-1,S-dimethylbenzene are obtained as distillate, while the distillation residue becomes crystalline upon being cooled, consisting of 50 parts of bischloromethylxylene.
• the aforesaid 45 parts of mono-chloromethylxylene are oxidized with 400 parts of nitric acid (density 1.27) for two hours at l05l10 C. with introduction of air.
• the acids obtained are filtered off and oxidized with 300 parts of nitric acid (density 1.20) for one hour at 165 C. and under 15 atmospheres of pressure, air being passed through the reaction mass. After evaporating the nitric acid, 45 parts of trimellitic acid are obtained.
• Example 11 shows the method of producing from 100 parts of m-xylene either 185 parts of pyromellitic acid or 45 parts of trimellitic acid and 130 parts of pyromellitic acid, said 130 parts of pyromellitic acid resulting by oxidizing the aforesaid (75+50) parts of the bis-chloromethyl-compound.
• nitric acid density 1.26
• the mixture of acids obtained is filtered off and oxidized with 1000 parts of 35% nitric acid for one hour at 175 C. under 10 atmoshperes of pressure, air being passed in, too.
• 160 parts of a mixture of acids consisting of pyromellitic, trimellitic, terephthalic acid and small amounts of 1,2,3,4-benzene-tetra-- carboxylic-acid, hemimellitic and phthalic acid.
• Example IV parts of crude xylene are chloromethylated as described in Example III, parts of chloromethylated products being obtained.
• the part precipitated upon cooling the oxidation solution is boiled with water and filtered in hot condition. 112 parts of pure pyromellitic acid crystallize as a hydrate out or" the filtrate.
• the substance insoluble in water (10 parts) consists of pure terephthalic acid.
• Example V 100 parts of crude xylene are treated with formaldehyde and hydrochloric acid as indicated in Example I. The chloromethylation having been completed, the mixture is allowed to cool and the oily crystal layer is separated from the aqueous reaction solution. The crystals are filtered off from the oily crystal layer and eventually recrystallized in petroleum ether. The liquid chloromethylated products are Washed with water and acid (density 1.28), air being passed through the reaction solution. The oxidation is carried out in a ceramic-coated vessel. The hot oxidation solution is pumped into a stainless steel reactor and oxidized for one hour at 170 under atmospheres pressure, with introduction of air. The insoluble part is filtered off and washed with hot water. 11 parts of terephthalic acid (acid number 674) are obtained.
• Example VI 100 parts of 2,4-bis-chloromethyl-toluene are heated for two hours to boiling with 850 parts of nitric acid (density 1.28) with introduction of air. The resulting crude acid is washed with toluene. A chlorine-free methylphthalic acid is obtained which is oxidized with 600 parts of 32% nitric acid for one hour at 165l70 C. under 10 atmospheres pressure, air being passed simultaneously through the oxidation solution. After evaporating the nitric acid, 105 parts of trimellitic acid are obtained.
• Example VII 100 parts of pseudocumene (1,2,4-trimethylbenzene) are heated for 3 hours to 70 C. with 200 parts of aqueous formaldehyde solution (3040%) and 500 parts of concentrated hydrochloric acid. After adding 100 parts of aqeuous formaldehyde solution, the mixture is heated for another 7 hours to 70 C. with introduction of hydrogen chloride. The reaction solution is allowed to cool and the crystals are separated. Eventuallythey can be purified by re-crystallization in petroleum ether. 140 parts of bis-chloromethyl-tri-methyl-benzene (melting point 84 C.) are obtained.
• Example VIII 100 parts of durene (or isodurene) are heated for 8 hours to 75 C. with 300 parts of aqueous formaldehyde solution (30-40%) and 400 parts of concentrated hydrochloric acid, additionally introducing hydrogen chloride. The oily reaction layer is separated and cooled. The crystals obtained are filtered off and the liquid chloromethyl fraction is returned to the chloromethylation. 90 parts of bis-chloromethyl-durol (melting point 193 C.) are obtained. When using isodurol, the melting point of the bis-chloromethyl-compound is 107 C.
• Example IX 100 parts of p-chloromethyltoluene are heated to boiling for two hours at normal pressure in a vessel with a ceramic covering with 850 parts of 32% nitric acid, with simultaneous introduction of air. 90 parts of crude tolu'ic acid with 12% of chlorine are obtained. Its acid number is about 370.
• the crude acid is washed with toluene, whereby chlorine-free toluic acid is obtained having an acid number of 412. It is oxidized with 600 parts of 32% nitric acid for two hours at 160 C. and 5 atmospheres pres-
• Example X parts of pure 100 parts of p-chloromethyltoluene are heated for two hours at normal pressure at 105-110 C. with 900 parts of 45% nitric acid with the introduction of air. 97 parts of toluic acid are obtained in nitric acid solution, which is substantially free of hydrochloric acid.
• the hot emulsion is pumped into a stainless steel reactor and oxidized for one hour at 170 C. and 10 atmospheres of pressure, air being passed in simultaneously. Crude terephthalic acid with an acid number of 660 is obtained. This acid gives parts of terephthalic acid with an acid number of 673 after washing with methanol.
• Example XI 100 parts of p-chloromethyltoluene are heated for two hours at -110 C. with 900 parts of 45 nitric acid with the introduction of oxygen. After separation and washing of the crude acid, 97 parts of chlorine-free toluic acid are obtained. The toluic acid is admixed with 32% nitric acid and pumped into a stainless steel reactor. After oxidizing for one hour at C. and 10 atmospheres, crude terephthalic acid with an acid number of 665 is obtained. This acid yields 90 parts of terephthalic acid with an acid number of 674 after washing with methanol.
• a method of producing benzene polycarboxylic acids comprising the steps of heating a benzene derivative consisting of a benzene ring substituted with at least one saturated alkyl group containing less than 3 carbon atoms and with at least one chloromethyl group with nitric acid at substantially atmospheric pressure at a temperature sufiiciently high to oxidize said chloromethyl group until a substantially chlorine-free reaction product is formed, thereby converting said chloromethyl group to a carboxyl group without substantially affecting said alkyl group and thus forming an alkyl benzene carboxylic acid; and heating said chlorine-free reaction product with nitric acid under a superatrnospheric pressure of 3-30 atmospheres at a temperature sufiiciently high to oxidize said alkyl group, thereby converting said alkyl group to a carboxyl group and thus obtaining a benzene carboxylic acid consisting of a benzene ring substituted only with carboxyl groups.
• a method of producing benzene polycarboxylic acids comprising the steps of heating a benzene derivative consisting of a benzene ring substituted with at least one saturated alkyl group containing less than 3 carbon atoms and at least one chloromethyl group, the total number of said alkyl and chloromethyl groups being at least three, with nitric acid of 30-47% concentration at substantially atmospheric pressure at a temperature sufiieiently high to oxidize said chloromethyl group until a substantially chlorine-free reaction product is formed, thereby converting all chloromethyl groups to carboxyl groups without substantially affecting said alkyl groups and thus forming an alkyl benzene carboxylic acid; and heating said chlorine-free reaction product with nitric acid of 20-45% concentration under a super-atmospheric pressure of 3-30 atmospheres at a temperature sufficient- 1y high to oxidize said alkyl groups, thereby converting said alkyl groups to carboxyl groups and thus obtaining a benzene carboxy
• a method of producing benzene polycarboxylic acids comprising the steps of heating a benzene derivative consisting of a benzene ring substituted with at least one saturated alkyl group containing less than 3 carbon atoms and with at least one chloromethyl group with nitric acid at substantially atmospheric pressure at a temperature corresponding substantially to the boiling range of said nitric acid so as to oxidize said chloromethyl group until a substantially chlorine-free reaction product is formed, thereby converting said chloromethyl group to a carboxyl group without substantially affecting said alkyl group and thus forming an alkyl benzene carboxylic acid; and heating said chlorine-free reaction product with nitric acid under a superatmospheric pres sure of 3-30 atmospheres at a temperature of about 150- 200 C. so as to oxidize said alkyl group, thereby converting said alkyl group to a carboxyl group and thus obtaining a benzene carboxylic acid consisting of a benzene
• a method of producing benzene polycarboxylic acids comprising the steps of heating a benzene derivative consisting of a benzene ring substituted with at least one saturated alkyl group containing less than 3 carbon atoms and with at least one chloromethyl group with nitric acid of between 30-47% concentration at substantially atmospheric pressure at about the boiling point of the reaction mixture at atmospheric pressure so as to oxidize said chloromethyl group until a substantially chlorine-free reaction product is formed, thereby converting said chloromethyl group to a carboxyl group without substantially affecting said alkyl group and thus forming an alkyl benzene carboxylic acid; and heating said chlorine-free reaction product with nitric acid of between 14 20-45% concentration under a superatmospheric pressure of 3-30 atmospheres at a temperature of about ISO-200 C. so as to oxidize said alkyl group, thereby converting said alkyl group to a carboxyl group and thus obtaining a benzene carboxylic acid consisting of
• 9.-A method of producing benzen'e polycarboxylic acids comprising the steps of heating a benzene derivativeiconsisting of a benzene ring substituted with at least one saturated alkyl group containing less than 3 carbon atoms and with at least one chloromethyl group with nitric acid at substantially atmospheric pressure at a temperature sufficiently high to oxidize said chloromethyl group while bubbling a gas containing free oxygen through the reaction mixture until a substantially chlorine-free reaction product is formed, thereby converting said chloromethyl group to a carboxyl group without substantially aifecting said alkyl group and thus forming an alkyl benzene carboxylic acid and evolving a gas including nitrogen oxide; and heating said chlorine-free reaction product with nitric acid under a superatmospheric pressure of 3-30 atmospheres at a temperature sufiiciently high to oxidize said alkyl group while bubbling a gas containing free oxygen through the reaction mixture, thereby converting said alkyl group to a carboxy
• a method of producing benzene polycarboxylic acids comprising the steps of heating mono-chloromethyl xylene and nitric acid at substantially atmospheric pressure at a temperature sufiiciently high to oxidize the chloromethyl group of said mono-chloromethyl xylene to a carboxyl group until a substantially chlorine-free reaction product is formed, thereby converting said chloromethyl group to a carboxyl group without substantially affecting the alkyl group of said mono-chloromethyl xylene, thus forming dimethyl-benzene mono-carboxylic acid; and heating said dimethyl-benzene mono-carboxylic acid with nitric acid of 20-45% concentration under a superatmospheric pressure of 3-30 atmospheres at a temperature sufficiently high to oxidize said methyl groups, thereby converting said methyl groups to carboxyl groups, thus otbaining trimellitic acid.

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