DE1085146B - Process for the preparation of dialkyl esters of iso- and / or terephthalic acid - Google Patents

Description

GERMAN

It is known to mix xylene or other dialkylbenzenes with air or oxygen in the presence of catalysts to oxidize. The oxidation of the hydrocarbons to the corresponding dicarboxylic acids does, however Difficulties, since essentially only one of the two alkyl groups of the starting hydrocarbon up to Carboxyl group is through-oxidized, while the other can only be oxidized with difficulty. To these difficulties In the case of the oxidation of xylene, for example, attempts have already been made to avoid those which are difficult to further oxidize Oxidation products, such as. B. toluic acid, into derivatives, e.g. B. esters, salts, amides or the anhydride, to transfer and to oxidize them further with oxygen-containing oxidizing agents. It succeeds on To get to the phthalic acids in this way, but such a process has the disadvantage that the Dicarboxylic acids are obtained in the form of their half-sided derivatives, which have to be broken down or, if the Diester wants to receive, must first be converted into this. The gradual conversion is also time consuming and requires additional work and equipment.

It is also known to dialkyl esters of phthalic acids from aromatic hydrocarbons and alkanols directly by mixing a xylene in the liquid phase in the presence of an alkanol with oxygen or treated such containing gases. The procedure was that in a pressure vessel Xylene heated to about 100 to 200 ° C in the presence of an oxidation catalyst and at low pressures from S to 20 atm of oxygen or air and methanol together or separately in an hourly amount of about 100 to 2001 air and 10 to 1000 g of methanol per 1000 g of starting xylene passed through the hydrocarbon. When transferring this known method of operation to other dialkylbenzenes, it has been shown that that the process only works satisfactorily when using xylene as the starting hydrocarbon, however, in the reaction of dialkylbenzenes with alkyl radicals having a higher carbon number, e.g. B. Isopropyl residues, no or almost no phthalic acid diesters are obtained.

It has now been found that dialkyl esters of iso- and or or terephthalic acid are obtained if an alcoholic solution of m- and / or p-diisopropylbenzene and alkanols with 1 to 4 carbon atoms, whose alkanol content is at least 60 percent by weight, advantageously 80 to 95 percent by weight, with gases containing oxygen, expediently with pure oxygen, at a temperature between 120 and 220 ° C and a pressure of at least 8 at, advantageously 10 to 40 at, treated.

Of the alcohols that can be used as starting materials, methanol is particularly suitable because it is procedure

for the production of dialkyl esters
of iso- and / or terephthalic acid

Applicant:

Aniline & Soda Factory in Baden
Aktiengesellschaft, Ludwigshafen / Rhein

Dr. Rudolf Keller, Dr. Joseph Schneider

and Dr. Gotthilf Wenner, Ludwigshafen / Rhine,

have been named as inventors

is practically not oxidized under the reaction conditions. Other lower alkanols, such as those with 2 to 4 carbon atoms, can also be used. The alcohols are expediently used in an anhydrous or practically anhydrous state, since water inhibits the reaction. Aqueous alcohols containing more than about 30% water, should be avoided if possible, however, to 80 or even 90 ° / ₀ owned alcohols readily be used.

The amount in which the alcohol is used in the oxidation of p- or m-diisopropylbenzene or their mixtures can be kept as large as desired, but it must be at least 60 percent by weight in the solution to be oxidized. Use solutions containing more than 98% alcohol by weight, is inadequate in that the process is then no longer carried out economically enough can be. It is advantageous to work with solutions containing about 80 to 95 percent by weight of alcohol.

The most suitable oxidizing agent is pure oxygen or gases containing oxygen which a high content of oxygen, e.g. B. 50 percent by volume and more have. Air or other oxygen-containing Mixtures with a low oxygen content can be used.

The oxidation succeeds even without the presence of substances that accelerate the reaction. However, it is expedient to use catalysts. The salts soluble in alcohols are particularly suitable as such of manganese, cobalt or vanadium. For example, let the salts of these metals be of fatty acids, of "unsaturated Acids, e.g. B. the oleic acid series, or called by naphthenic acids. The salts are used for oxidation or mixtures thereof, advantageously in amounts of 0.1 to 5 percent by weight, based on the total amount of starting solution to be oxidized is used.

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Oxidation takes place in the liquid phase when the vessel is closed again. The draining of the react

Temperature from 120 to 220 ° C, advantageous about 140 tion solution and the introduction of the methanolic

to 180 ° C, and a pressure of at least 8 at. The fresh solution is made every hour with about the same

Pressure should be so high that under the chosen amounts, as indicated above, repeated, wherein

Working temperatures, also the alcohol used.

is at least largely in the liquid state. In the products of the fresh solution,

In general, the pressure used is up to about. The hot reaction solution is allowed to cool. Man

60 at, advantageously 10 to 40 at. If desired, the dimethyl terephthalate can be separated by filtration

you can also work at an even higher pressure, e.g. B. from and works up the mother liquor by distillation. From the

at 100 or 150 at. ίο the amount of reaction solution withdrawn every hour

The oxidation can be carried out in the manner known per se for dimethyl ester for the average of about 140 to 150 parts of crude terephthalic work in the liquid phase. In the case of fractional distillation, both in batches and in continuous operation of the mother liquor, about 550 parts of methanol are recovered. For example, one can proceed in such a way that one wins. In addition, oxyin, which is soluble in methanol, is obtained in a pressure-proof vessel, the alcoholic diisopropyl cation intermediates and about 150 parts of water. benzene solution and the catalyst, the vessel remains in the still in the still a small residue, which consists of darkly heated resins and colored after the reaction temperature has been reached.
Oxygen or gas containing it up to the selected working pressure. Dimethyl acid is about 70 to 80%, based on

It has proven to be useful to achieve a 20 to the hourly supplied fresh diisopropylbenzene

rapid reaction process the vessel from time to time. After the urine crystallization and a subsequent

at least partially decompressed, optionally after a vacuum distillation beforehand, is obtained from 150 parts

cooling down and injecting new oxygen. Crude ester 145 parts ester with a melting point of 141 ° C.
When working continuously, one draws appropriately

periodically remove some of the gases and replace them with 25 Example 2
Oxygen. You can also work continuously

Proceed in such a way that the pressure vessel is continuously fresh. In a pressure vessel with a volume of 0.35 parts by volume

Feed the starting solution and a corresponding amount is given to 30 parts of m-diisopropylbenzene, 170 parts of Me-

The reaction solution is drawn off while the ethanol and 1 part of manganese acetate are poured through. Heated with shaking

The solution in the vessel is passed through oxygen and the vessel is heated to 170 ° C. and oxygen is pressed up to

at the same time with the help of a pressure relief valve ensures a pressure of 50 at. After a short time it falls

that the pressure does not depend on the selected working pressure pressure to about 30 at. By pressing he becomes

increases. set back to 50 at and tracking of

From the exhaust gases can expediently be repeated before the full oxygen so long, until also about one constant relaxation by cooling entrained 35 longer period of a few hours no pressure solvent vapors condense. decrease in the vessel can be determined more. Man

The reaction solution is worked up after allowing the vessel to cool and relax. The vessel will known methods, e.g. B. by filtration and closed again, heated to 170 ° C and the oxygen distillation. Recovered starting materials and oxy treatment at 50 at in the above dation intermediates are repeated, expediently in the manner described above. All in all, the treatment separation is repeated of the lung still contained in the reaction solution eight times. Then you take the cooled off and and the water formed during the oxidation and the reaction mixture as a relaxed vessel. It exists Distillation residue remaining, dark-colored from 20 parts of dimethyl isophthalate, methanol, Resins, added back to the starting solution, or for water and about 8 to 10 parts of oxidation in between further oxidized. 45 products that, after distillation in vacuo, make a

The iso- or terephthalic acid esters obtained can be added to another batch of the same size,

substantially pure and may optionally after forwarding / ₀ is increased the yield by about 20 °,
crystallization and / or vacuum distillation without

further e.g. processed on polyester. Example 3

The parts given in the examples are, as far as 50

otherwise said, parts by weight. Parts by weight and 560 parts of a 35 ° / ₀ p- and 65 ° / ₀ m-diisopropyl

Parts by volume are in the ratio of grams to benzene of the existing mixture and 2240 parts of methanol,

Liter. 5 parts of manganese acetate and 5 parts of cobalt bromide are used

Beisniel 1 ™ · ^ ^as ^ ¹¹ ^ ^e ^ V ^ 1 described pressure vessel introduced

^P 55 and the vessel heated to 175 ° C. Through one of the feed

2240 parts of methanol, 560 parts of p-diisopropylbenzene, supply lines are then injected with 250 parts by volume of 3 parts of cobalt naphthenate and 3 parts of manganese naphthenate per hour (measured under normal conditions). The is in a pressure vessel provided with a stirrer, which is equipped with pressure in the vessel through a relief valve, two feed lines, bottom drain valve and gas, which is attached in the gas discharge line, to 50 at discharge line, and the 60 is set. After about 3 hours, it is removed through a vessel heated to 160 ° C. About 900 parts of the reaction lines are then pressed through one of the feed and bottom drainage valves every hour 250 parts by volume of solution and 800 parts of the 80 ° / ₀ methanol-containing oxygen (measured under normal conditions) are introduced. The fresh diisopropylbenzene solution, which is still 1.4 parts of pressure in the vessel, is added to the vessel through a relief valve, manganese acetate and 1.4 parts of cobalt bromide are added to the gas discharge line to 40 at 65. The draining of the reake is discontinued. After about 3 hours, the solution is removed and the fresh solution is introduced, the bottom drain valve is about 900 parts of the reaction solution hourly with about the same amounts as above and 800 parts of the 80% methanol-containing specified, repeated, the further below Fresh diisopropylbenzene solution, to which 0.8 parts of co-given oxidation intermediates of the fresh solution are added baltnaphthenate and 0.8 part of manganese stearate.

The reaction solution is freed from non-volatile catalyst constituents by distillation, with additional methanol vapor being introduced into the bubble of the column. The distillate is allowed to cool. The dimethyl terephthalate which has crystallized out is separated off from the mother solution by filtration. The filtrate is broken down into its components, such as methanol, water, oxidation intermediates and isophthalic acid dimethyl ester, which is contaminated with terephthalic acid dimethyl ester, by fractional rectification. The oxidation intermediates are added to the fresh solution. After adjustment of the stationary state is obtained every hour on the average about 150 parts of the Dicarbonsäureestergemisches, corresponding to a yield of 78.5 ° / ₀ corresponds to the theory.

Example 4

30 parts of p-diisopropylbenzene and 170 parts of anhydrous are placed in a pressure vessel with a volume of 0.35 parts by volume Ethyl alcohol and 1 part cobalt bromide. The vessel is heated to 170 ° C. with shaking and pressed Oxygen up to a pressure of 50 at. After a short time the pressure drops to 25 at. By repressing it is set back to 50 at and the replenishment of oxygen is repeated until no significant A decrease in pressure in the vessel is determined. Let the vessel cool down and relax it. The vessel will then closed again, heated to 170 ° C and the oxygen treatment repeated at 50 at in the manner given above. The oxygen treatment is carried out as a whole 4 times off. The reaction mixture is then removed from the cooled and relaxed vessel. It consists of 25 parts of diethyl terephthalate, ethanol, water and about 10 to 12 parts of oxidation intermediates, which after distillation in the Va- kuum can be added to another batch of the same size, which increases the yield by around 20% is increased.

Example 5

40

In a pressure vessel of 0.35 parts by volume are placed 30 parts of m-diisopropylbenzene, 170 parts of isopropanol, 1 part manganese acetate and 1 part cobalt bromide. The vessel is heated to 180 ° C. with shaking and pressed Air up to a pressure of 50 at. After a short time the pressure drops to 45 at. By pressing he becomes set to 100 at and, after falling to 90 at, brought to 150 at by again forcing air. so this pressure is kept approximately constant by forcing in air until there is no more gas absorption he follows. Let the vessel cool down and relax it. The vessel is closed again, heated to 180 ° C and repeating the air treatment in the above manner about 15 times.

The reaction mixture is then removed from the cooled and relaxed vessel. It consists of 25 parts Isophthalic acid diisopropyl ester, isopropanol, water and about 15 parts of oxidation intermediates, which according to a distillation in vacuo can be added to another batch of the same size, reducing the yield to 35 parts of isophthalic acid diisopropyl ester, corresponding to 76% of theory, is increased.

Claims (2)

Patent claims: 1. A process for the preparation of iso- and / or terephthalic acid dialkyl esters by oxidation of dialkylbenzenes with oxygen or gases containing such in the liquid phase in the presence of alcohols with 1 to 4 carbon atoms and optionally of oxidation catalysts at elevated temperature and pressure, characterized in, that a solution of m- and / or p-diisopropylbenzene in alkanols with 1 to 4 carbon atoms, the alcohol content of which is at least 60 percent by weight, with oxygen or gases containing such at a temperature between 120 and 220 ° C and a pressure of at least 8 at treated. 2. The method according to claim 1, characterized in that solutions with an alcohol content of 80 to 95 ° / ₀ are used. © 009 550/342 7.60