DE1000372B - Process for the oxidation of nucleus-bonded alkyl groups to nucleus-bonded carboxyl groups in aromatic compounds - Google Patents

Description

GERMAN

The invention relates to a process for the oxidation of ring-bonded alkyl groups in aromatic Connections to carboxyl groups. The molecule of these compounds should not only contain the alkyl groups that must not be exposed to steric hindrance and at the same time at least one Must contain a hydrogen atom on the a-carbon atom, but they should also have a negatively polar group attached to the nucleus. The oxidation is in known manner carried out in the liquid phase, with a gas or a gas mixture, the molecular Containing oxygen, is used as an oxidizing agent.

The term "negative group" is used in context with the present method, unless expressly stated to the contrary, atoms or Atomic groups understood when they are present as substituents in the ring of an aromatic carboxylic acid are to increase their acidic character. Examples of such substituents include: the carboxyl, Carbonyl, cyano and nitro groups and the halogens.

There is currently a great deal of interest in the oxidation of the above class of compounds, in particular for the Oxidation of m- and p-alkylbenzoic acids, which belong to this class, to isophthalic acid and terephthalic acid.

These acids, which are technically very important, as their dimethyl esters for the production of synthetic ones Fibers and plastics are used and their higher esters can serve as plasticizers usually obtained by oxidation of the corresponding dialkylbenzenes, usually an alkylbenzoic acid is formed as an intermediate.

It was initially assumed that both alkyl groups at the same time in these oxidation reactions would be oxidized and the reaction would proceed via an intermediate in which both alkyl groups already contain oxygen and which could then easily be oxidized to dicarboxylic acid.

However, it was later found that the alkylbenzoic acid was predominantly formed as an intermediate product. and it has been found that it is very difficult to further oxidize them.

To overcome this difficulty and to achieve rapid oxidation of these alkylbenzoic acids, which oxidation could be used on an industrial scale with a good yield have already been made many embodiments proposed.

For example, US Pat. No. 2,479,067, which relates to the catalytic oxidation of p-toluic acid Terephthalic acid in an acetic acid medium in the liquid phase with air as the oxidizing agent, suggested an organic peroxide, a peracid, an aldehyde, an olefin or a ketone as the oxidation initiator Process of oxidation

of nucleus-bound alkyl groups

to core-bonded carboxyl groups

in aromatic compounds

Applicant: N.V. De Bataafsche Petroleum Maatsdiappij, The Hague

Representative: Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse

and Dr. E. von Pechmann, patent attorneys,

Munich 9, Schweigerstr. 2

Claimed priority:
Netherlands 20 September 1954

Jan Pieter Fortuin, Robert van Helden
and Eduard Cornells Kooijman, Amsterdam

(Netherlands),
have been named as inventors

or to add other organic compounds which show a tendency under the reaction conditions To form peroxides. The amount of initiator, calculated on p-toluic acid, is between 0.1 and 10 percent by weight, although in batch processes they are added at the beginning or during the reaction can. In this case, apparently after the reaction is set in motion, no further "foreign" Initiators added. The yields in continuous operation of this process are therefore also very low. When carrying out the reaction in batches, a maximum of 10 percent by weight Initiator is used, the weight ratio of toluic acid to foreign initiator is after it Add at least 10: 1 and then rise quickly 00: 1; but no further catalyst is added.

A similar method is proposed in British Patent Specification 664 667, in which in a similar one Way p-tolualdehyde or its mixture with p-toluic acid be oxidized to p-toluic acid in addition to a small amount of terephthalic acid.

The process described in British patent specification 623 836 relating to the oxidation of p-toluic acid in the presence of p-xylene, but not in-acetic acid as Solvent, is closely related to the above.

An attempt was also made to activate the catalyst with the aid of an activator, e.g. B. with help

3 4

of an aldehyde, as in U.S. Pat. No. 2,673,217 the entrainer does its job properly. It

is described. it has also already been found that the ratio of

The above oxidation appears neither in acidic entrainment to the compound to be oxidized,

Action media still in aqueous alkaline reaction - what ratio during the entire reaction period

media to run smoothly, as from the British patent 5 must be kept almost constant, a certain

font 679 400 can be seen, according to which aldehydes or must have a value that varies from case to case. the

compounds capable of generating radicals other than a compound to be used as an entrainment agent must be one

Catalysts are added. be organic compound that is under the reaction

This process, in which a new component is added to the conditions with sufficient speed and reaction mixture, has the disadvantage that 10 yield oxidizes oxidation products which do not interfere with the resulting one or more additional oxidation of the end product,
Contains borrowed compounds that are removed from it So that a compound as entrainment in the above must. In order to be able to use this disadvantage to a certain extent in the stated sense, it is necessary to overcome it, has already been proposed (cf. the use of the bindings which, if they are mentioned separately in the US Pat. No. 2,673,217 already mentioned above), as 15 Reaction conditions are subjected to an oxy-initiator to use the aldehyde which corresponds to the acid used as a solution amount of more than 1 g per liter per hour, so that the would have as.

Solvents used acid during oxidation, although in principle a large number of forms are formed will. bindings will usually be used

It has already been proposed earlier in the oxidation of alkyl-substituted benzene compounds that at least certain dialkylbenzenes contain, as a sterically unhindered alkyl group and alkylbenzoic acid formed as intermediate products, add at least one hydrogen to the α-carbon atom in order to thereby achieve faster oxidation. atom, preference is given
act, such as B. in British Patents For each oxidation it is preferable to have one of 677,363, 680,571 and 680,572 indicated. In order to choose the entrainment substance that forces the reaction to be oxidized in a given direction and shorten the bond and the ultimately desired product of the induction period, in this case reactions can be obtained one after the other, not just one connection that is already partially the ge examples of such compounds suitable as entrainment substances have desired degree of oxidation, but also fertilize are toluene, o-, m- or p-xylene, trimethylbene initiator can be added, such as. B. in the British 30 zole, ethylbenzenes, o-, m- or p-diethylbenzene, 1, 3, patent 680 572 is described. 5-triethylbenzene, 1, 2, 5-triethylbenzene, cumene, m- and

In the method according to the invention, p-diisopropylbenzene, 1,3,5-triisopropylbenzene, is now also used

the above oxidation in the presence of an aliphatic cyclane, e.g. B. cyclohexane, branched or non-branched

Carboxylic acid, preferably at an elevated temperature, branched paraffinic hydrocarbons, aldehydes, ketones

temperature, carried out in the presence of an "entrainer", 35 and alcohols.

as hereinafter defined, being during the whole of Oxidizable Antioxidants that are used during the

Reaction ensures that the molecular intended oxidation maintain its inhibitory effect.

keep the ratio of the compound to be oxidized to the entrainment substance, such as alkylphenols, can of course also be used as

between 1: 1 and 50: 1 is ensured and the water entrainers are used.

content of the reaction mixture less than 5 weight- 40 The compounds obtained with the help of the method according to

percent is. of the invention include e.g. B.

Surprisingly, it has been found that the oxy- ο-, m- and p-toluic acid, 3, 4-dimethylbenzoic acid, 4-

dation of the above type of compounds in the presence of methylbenzene-i, 2-dicarboxylic acid, o-, m- and p-chlorine

an aliphatic carboxylic acid very satisfactory through- toluene, o-, m- and p-cyantoluene, 1,3-dichloro-2-methyl-

can be performed, provided that 45 benzene, 1, 2-dimethyl-3-chlorobenzene, o-, m- and p-ethyl

ensures that during the entire reaction a verbenzoic acid, 3,4-diethylbenzoic acid, 2,4-diethylbenzoic acid

bond is present, which the oxidation of the oxy-acid, 4-ethylbenzene-i, 2-dicarboxylic acid, 6-ethylbenzene

causing connection. In contrast to the 1,2-dicarboxylic acid, 4-ethylbenzene-i, 3-dicarboxylic acid, o-, m-

above known processes in which and p-chloroethylbenzene, m- and p-isopropylbenzoic acid,

a special compound was added, called 50 or m- and p-chlorocumene.

Initiator acts and especially at the beginning of the process. It has already been mentioned several times in the foregoing

must be present, it is mentioned in the "steric hindrance" procedure. Although in general

It is essential to the invention that this substance in the re - this term indicates quite clearly what is meant by it,

action mixture during the entire reaction period and the expert generally knows where this

is present in order to expect the oxidation of the steric hindrance to be oxidized, let the following be

Effect connection. For this reason, it is carried out for the purpose of explanation.

preferred to speak of an "entrainer" to In general, methyl groups are few or even

He is not subject to steric hindrance from the substances given above. One

divorce who only act as initiators. Although the ethyl group is usually hindered when both

exact mechanism of the present reaction still 60 orthostations against this alkyl group with one

is not known, it has already been found that the substituents are occupied. So can the C ₂ H ₅ group

Presence of an aliphatic carboxylic acid as Re- are not oxidized in 1,3-dichloro-2-ethylbenzene,

Action medium is very important so that the entrainment substance while in 1, 2-diethyl-3-chlorobenzene is the ethyl group

works effectively. In British Patent 681455, is oxidized in the i-position; but the ethyl group in

which describes an oxidation, similar to that after 65 2-position, cannot be oxidized. An isopropyl

of the present invention, however, is only one group that is already sterically hindered when one of the

small amount of an inert solvent use ortho positions to it substituted with a substituent

made while watching the aliphatic carboxylic acids.

be discarded. These acids are, however, for the pre-alkyl groups that are sterically hindered can

It is essential to ensure that 70 does not oxidize by the method of the invention

are also not sterically unhindered alkyl groups, which have a quaternary a-carbon atom.

Although the optimal molar ratio of the compound to be oxidized to the entrainment substance depends on the case on the nature of the entrainment substance, the compound to be oxidized, the reaction temperature, the solvent and the concentration and reactivity of the catalyst depends, in general it can be said that this relationship between ι: ι and 50: ι should be. When using alkylbenzoic acids a dialkylbenzene are oxidized as entrainment substance and the alkyl groups in these compounds are lower, d. H. those having 2 to 4 carbon atoms inclusive, a ratio between 4: 1 and 12: ι preferred.

In the method according to the invention very good results are obtained if the reaction in one aliphatic medium from the lower aliphatic carboxylic acids having 1 to 4 carbon atoms inclusive or their mixtures. Acetic acid is preferably used for this purpose.

It has also been found that the water content of the reaction mixture is beneficial for obtaining results is essential. In order to achieve good results, the water content of the reaction mixture should be below 5 percent by weight, preferably below 2 percent by weight.

Molecular oxygen, either in pure or near pure form or mixed with other inert gases, can serve as an oxidizing agent. Preferably air is used in the method according to the invention.

The manganese or cobalt salts that are soluble in the reaction mixture, or mixtures of these metal salts are preferably used as catalysts. Salts of organic compounds are particularly preferred Acids, especially salts of the same acid as used as the solvent. Although the optimal one Temperature at which the oxidation is carried out, inter alia, from nature to the oxidizing one Compound and the entrainer used as well as the catalyst used and the solvent depends, it can be stated that very good results are obtained when working at a temperature between 100 and 2oo ° can be achieved.

The method according to the invention can also be carried out by adding a adding a small amount of organic peroxide to avoid or at least shorten the induction period, which often occurs at the onset of oxidation. Although this addition is by no means necessary, will this last-mentioned embodiment is often preferred in practice.

The invention is illustrated by the following examples.

Example I.

Mixed oxidation of p-toluic acid and
p-tert-butyltoluene

49 g (0.36 mol) of p-toluic acid, 25.2 g (0.17 mol) of p-tert-butyltoluene, 400 mg of cobalt acetate and 400 mg Manganese triacetate are dissolved in 100 ecm of butyric acid. 50 mg of di-tert-butyl peroxide are added to avoid an induction period, although this is the case is by no means essential. Oxygen was added to the vigorously stirring reaction mixture at one rate initiated by 4I per hour at atmospheric pressure and at a temperature of 150 °.

The formed water was distilled off during the reaction. After 11 hours, the terephthalic acid formed (2.1 g, 12.5 mmol; equivalent weight 83.4) was filtered off, and butyric acid and p-tert-butyltoluene were distilled off from the filtrate. After removing the butyric acid with 2η sodium hydroxide solution, the distillate gave 19.6 g (133 mmol) of p-tert-butyltoluene. The solid residue (53.6 g) was analyzed and contained 6.2 g of p-tert-butylbenzoic acid (35 mmol, yield 94%) and 46.6 g of p-toluic acid (343 mmol). The Terephthalsäureausbeute calculated p-toluic acid on reacted, was thus 73 ° / _0th

A further three tests were carried out in a similar manner under the same conditions with the Deviation that the molar ratios of p-toluic acid to p-tert-butyltoluene were 1: 1, 4: 1 and 6: 1 and with 100, 100 or 150 ecm of butyric acid as a solvent. The results together with those of the first experiment are summarized in the following table.

ao p-toluyl
_o 3, _lrA p-tert.-
Butyl Molver p-tert.-
Butyl Tere satire toluene ratio benzene phthalic acid I. II acid mmol mmol I: II mmol mmol 25 140.0 148.6 I: I 27.0 5.0 360.0 170.3 2: ι 35.0 12.5 685.0 170.0 4: 1 33.4 30.2 1020.0 I7M 6: 1 37.0 40.0

It can be seen that when a molar ratio of approximately 5: ι was used, the amounts of p-tert-butylbenzoic acid and terephthalic acid were the same.

Example II Mixed oxidation of p-chlorotoluene and

p-tert-butyltoluene

76.2 g (602 mmol) p-chlorotoluene, 30 g (203 mmol) p-tert-butyltoluene, 400 mg cobalt acetate, 400 mg manganese triacetate and 50 mg of di-tert-butyl peroxide were dissolved in 100 ecm of butyric acid. This mixture was 10 hours in the same way as indicated in Example 1, oxidized. During work-up, 66.8 g (528.4 mmol) of p-chlorotoluene, 8.3 g (53 mmol) p-chlorobenzoic acid, 23.1 g (156 mmol) p-tert-butyltoluene and 8.3 g (46.2 mmol) p-tert-butylbenzoic acid obtain.

An experiment was carried out in the same way in which the molar ratio of p-chlorotoluene to p-tert-butyltoluene was 2: 1.

The results of the two experiments are summarized in the following table.

Example III

Mixed oxidation of p-chlorocumene and p-tert.-butylcumene 30.8 g (199.4 mmol) p-chlorocumene, 17.9 g p-tert-Bu-

tylcumol (101.7 mmol), 300 mg of cobalt acetate and 300 mg manganese triacetate was dissolved in 100 cc of butyric acid and ¹ 7 Z as oxidized _{for 2} hours in the same manner in Example I.

Time
Stundea p-chlorine
toluene
I.
mmol p-tert.-
Butyl
toluene
II
mmol Molver
ratio
I: II p-chlorine
benzene
acid
mmol p-tert.-
Butyl
benzene
acid
mmol IO
12th 602.4
393.7 202.7
203.4 3: i
2: ι 53.0
23.4 46.7
31.O

The reaction mixture was worked up to give 8.3 g (53 mmol) of p-chlorobenzoic acid and 10.4 g (58.6 mmol) p-tert-butylbenzoic acid. Another attempt was made using a molar ratio of p-chloro cumene to p-tert-butylcumene of 3: 1 and an experiment carried out separately with p-chlorocumene, the other conditions remaining the same.

The results are given in the table below.

Time
hours p-chlorine
cumol
I.
mmol p-tert-
Butyl
cumoi
II
mmol Molver
ratio
I: II p-chlorine
benzene
acid
mmol p-tert.-
Butyl
benzene
acid
mmol 7 ¹ / ·
7 ¹ I,
IO 199.4
300.0
358.0 101.7
102.7
Nile 2: ι
3: 1
00: ι 53.0
60.0
<8 58.6
57.1

10

Example IV ao

Mixed oxidation of p-isopropylbenzoic acid
and cumene

A. A mixture of 100 g of p-isopropylbenzoic acid and 1200 g of acetic acid, in which 2 g of cobalt acetate and 2 mg of manganese acetate were dissolved, was mixed with air in an autoclave made of V2A steel with a capacity of 2.5 l, equipped with a stirrer (1400 revolutions per minute) was oxidized. The oxidation temperature was 165 ⁰ , the pressure 30 at. The air stream was passed through at a rate of 2001 per hour until no further oxygen absorption took place, which was found to be the case after 1 hour 50 minutes. The terephthalic acid formed was filtered off from the reaction mixture. After washing and drying, the amount formed was weighed. The weight was found to be only 3 g.

B. The experiment as described under A has now been carried out

carried out in the presence of 30 g of cumene, the oxygen absorption not having ended until after 6 ^s / ₄ hours. The terephthalic acid formed was again filtered off, washed and weighed. Their amount was now found to be 44 g. 20 g of cumene were then added to the filtrate, whereupon this mixture was oxidized under the conditions given above until no further oxygen absorption occurred (4% hours). A further 8.5 g of terephthalic acid could be recovered from the reaction mixture thus obtained, so that the total amount of the obtained in this experiment, 100 g of p-isopropylbenzoic terephthalic acid 5 g ² .5 reached. This terephthalic acid was pure white and had a titration equivalent of 83.2 to 83.5 (theoretically 83.1).

The filtrate obtained in the last case contained, as was found, benzoic acid in addition to unreacted p-isopropylbenzoic acid.

Claims (11)

PATE NTA NS PB Oc HE: i. Process for the oxidation of nucleus-bonded alkyl groups to nucleus-bonded carboxyl groups in aromatic compounds whose molecule is not just an alkyl group that does not have any steric hindrance may be subjected and at the same time at least one hydrogen atom on the a-carbon atom must be present, contains, but also has a "negatively polar" nucleus-bound group, the oxidation in the liquid phase using a gas or gas mixture, the molecular Contains oxygen, is carried out as an oxidizing agent, characterized in that the oxidation is carried out in the presence of an aliphatic acid and an »entrainment substance care is taken during the entire oxidation that the molecular ratio of the Connection to the "entrainment substance" is between 1: 1 and 50: ι and the water content of the mixture is below 5 percent by weight, the reaction being preferably carried out at an elevated temperature. 2. The method according to claim 1, characterized in that that a compound is used as the "entrainment agent" which, when separately subjected to the reaction conditions, has an oxidation rate of more than 1 g per liter per hour would result. 3. The method according to claim 1 and 2, characterized in that that alkylbenzene derivatives which contain at least one non-sterically hindered alkyl group and in which at least one hydrogen atom is bound to the ct-carbon atom, as an "entrainment substance" be used. 4. The method according to claim 1 to 3, characterized in that that the "negative polar" group consists of a group of C, H and O. 5. The method according to claim 1 to 3, characterized in that that the negative polar group consists of a group that is essentially theirs negative character does not derive from a carbon and an oxygen atom. 6. The method according to claim 1 to 4, characterized in that that m- or p-isopropylbenzoic acid in the presence of m- or p-diisopropylbenzene as Entrainment is oxidized. 7. The method according to claim 6, characterized in that the ratio of the compound to be oxidized to the entrainment substance to between 4: 1 and 12: 1 is measured. 8. The method according to claim 1 to 7, characterized in that that the medium of aliphatic acids from lower aliphatic carboxylic acids with ι up to 4 carbon atoms including or mixtures of these acids. 9. The method according to claim 1 to 8, characterized in that the oxidation in acetic acid is carried out. 10. The method according to claim 1 to 9, characterized in that that the water content of the reaction mixture is kept below 2 percent by weight. 11. The method according to claim 1 to 10, characterized characterized in that salts of an organic acid, preferably an acid, are used as solvents will be used as a catalyst. © «OS 740/427 12.56