JPS6148489B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for oxidizing p-substituted toluene containing as a substituent a tert-butyl group as a non-oxidizable group. In particular, the present invention relates to a process for making p-substituted benzaldehydes. It is known that toluene or substituted toluene can be oxidized with oxygen in the presence of cobalt carboxylates, bromine compounds and carboxylic acids, the latter acting as a solvent. Usually this results in the preferential formation of (substituted) benzoic acids such as terephthalic acid. Since these aromatic carboxylic acids are useful compounds that can be used as starting materials for the production of products such as alkyd resins, it may be desirable to produce compounds in which only the methyl groups of the starting material are partially oxidized. . These partially oxidized compounds, such as p-alkyl-substituted benzaldehydes, are also valuable chemical intermediates and may in some cases find special use, for example in the field of aroma chemicals. Under conventional reaction conditions, these partially oxidized toluenes are only formed in relatively small amounts and are often laborious and unsuccessful to separate from the benzoic acid produced at the same time. formula

When using a raw material represented by the formula (in which X is a tert-butyl group) and applying certain oxidation conditions, a considerably large amount of partially oxidized alkylaryl compound is produced in addition to the substituted benzoic acid. was found to be formed. An effective method has been found for separating not only the partially oxidized alkylaryl compound from the co-produced benzoic acid. The present invention is based on the formula

A method of oxidizing a compound represented by the formula (in which X is a group that is not oxidized) by reacting it with molecular oxygen in the presence of a cobalt carboxylate, a bromine compound, and a carboxylic acid. The reaction is carried out in the presence of an additional 0.5 to 40 mol %, based on the carboxylic acid, of an agent capable of counteracting the formation of carboxyl groups, and the product mixture has the formula The above formula is characterized in that a compound represented by (In this formula, X has the above meaning.) It can be defined as relating to a method of oxidizing a compound represented by: The aromatic nucleus of the compound of the above formula may further contain one or more inert substituents located in the ortho or meta position to the methyl group. Cobalt compounds are divalent cobalt compounds such as carbonates, oxides or bromides, or
Preference is given to carboxylates derived from 10 alkanoic acids, especially acetates. The bromine compound used in the catalyst is preferably an alkali or alkaline earth metal bromide, especially sodium bromide or ammonium bromine. The molar ratio of bromide to cobalt compound is
The ratio is preferably within the range of 0.1:1 to 5:1, preferably 0.5:1 to 2.5:1. The carboxylic acid used as a solvent is preferably an alkanoic acid having up to 6 carbon atoms, especially acetic acid. The molar ratio of cobalt compound to carboxylic acid is 0.0005:1
It is preferable to set it within the range of ~0.03:1. Owing to the presence of agents capable of counteracting the oxidative formation of carboxyl groups, the oxidation of methyl groups is hindered quite significantly. This results in the formation of relatively large amounts of intermediate oxidation products, in particular products containing formyl groups, which can be recovered from the reaction product mixture. A very suitable agent is water, which is preferably used in an amount of 25 to 35 mol %, based on the carboxylic acid. Tertiary amines such as trialkylamines in which the alkyl groups each contain 1 to 6 carbon atoms, such as triethylamine, or heterocyclic tertiary amines, such as pyridine, can also be used. However, water is most preferred. The process can be conveniently carried out by mixing the solid and liquid components and passing gaseous oxygen over or preferably into the mixture.
The reaction temperature is preferably maintained within the range of 80°C to 130°C, more preferably 90°C to 100°C. Oxygen may be applied neat, but is preferably mixed with an inert gas such as nitrogen. Use of air is recommended. Suitable reaction pressures are in the range 1 to 10 bar, with oxygen pressure (partial pressure) preferably in the range 1 to 3 bar. A suitable reaction time is 1 to 2 hours. From the reaction mixture the formula The recovery of the compound can be carried out by conventional separation methods such as distillation. However, if the recovery of the compound of the above formula involves extraction with water, a rather significant improvement in product separation and purity is obtained. Two phases are thus formed: an aqueous phase containing the catalyst and most of the carboxylic acid and a small amount of oxidation product, and an organic phase containing unconverted starting material, most of the oxidation product and a small amount of water and carboxylic acid. . After the phases are separated, the two phases can be treated separately to recover product, unconverted starting material, and catalyst, which may be recycled if desired. According to a preferred embodiment of the present method, the aqueous phase has the formula Preferably, the amount is selected to correspond to the amount used in the oxidation reaction together with the unconverted starting material. Again an aqueous phase and an organic phase are formed, the latter suitably being combined with that obtained from the extraction with water. After-washing ceremony The compound and benzoic acid produced at the same time are conveniently separated by neutralization by caustic treatment and then further phase separation. The product is preferably recovered by distillation of the organic phase and acidification of the aqueous phase, respectively. Next, the following examples will be shown to further specifically explain the present invention. Example 1 4-t-butyltoluene (54 g, 0.36 mol),
Glacial acetic acid (88 g, 1.47 mol), cobalt acetate tetrahydrate (1.72 g, 6.9 mmol), sodium bromide (0.6
g, 5.8 mmol) and water (8.8 g, 0.49 mmol) were combined and the mixture was stirred at a rate of 10 per hour and at a pressure of 1 bar while oxygen was passed through the mixture.
After 1 hour and 10 minutes, gas-liquid chromatography and nuclear magnetic resonance showed 52% conversion of starting material. The reaction mixture was then fractionally distilled.
4-t-Butylbenzaldehyde was obtained as a fraction boiling between 60 and 85 DEG C. at 0.3 mmHg in a yield of 40% based on the converted toluene. The residue was then extracted with acetic acid and further recrystallized from acetic acid and water to give 4-tert-butylbenzoic acid as a white crystalline solid with a melting point of 167°C and a yield of 60% based on converted toluene. . Comparative Experiment The example method was repeated without adding water. After 3/4 hours, 4-t-
Conversion of butyltoluene was shown to be 54%, but the product contained less than 14% 4-t-butylbenzaldehyde. Example Pyridine (7.0g, 25.3mmol) instead of water
I repeated the example using . 1
After a time of 23 minutes, the conversion of 4-t-butyltoluene was
Nuclear magnetic resonance showed that the product contained 44% 4-t-butylbenzaldehyde and 56% 4-t-butylbenzoic acid. Example Batch reactor with a capacity of 1 ^m3 (type STU 1200) with a stirrer and a dip tube terminating near the tip of the stirrer
, pt-butyltoluene (PTBT) 302.5
Kg, acetic acid 500Kg, cobalt acetate tetrahydrate 9.7Kg,
3.4Kg of NaBr and 50Kg of water were charged. Heating the contents of the reactor to a temperature of 95-100 °C,
Air was introduced through the immersion tube. Gauge pressure within the reactor was maintained at 5 bar. After 2.5 hours, when the conversion reached 40%, the air supply was stopped and 90 Kg of water was added to cool the reactor to 40°C. Extraction was performed by stirring for 30 minutes and allowing precipitation for 30 minutes. The two phases were then separated.
The aqueous catalyst-containing phase was treated with 150 Kg of PTBT at 40°C. The mixture was stirred again for 30 minutes, allowed to settle for 30 minutes, and then extracted. The two phases formed were separated and the organic phase was combined with the organic phase obtained from the first extraction. The combined organic phases (565Kg) were washed with 90Kg of water. After stirring for 30 minutes and settling for 30 minutes to separate the phases, the aqueous phase was drawn off and stored for the next batch, while the organic phase was flashed to remove the PTBT portion, some residual water and traces of acetic acid. Distilled. Add 10% NaOH aqueous solution to the residual mixture of PTBT, pt-butylbenzaldehyde (PTBAL) and pt-butylbenzoic acid (PTBAC).
% excess was added. Two phases are formed, the aqueous phase is
Contained dissolved sodium salt of PTBAC. After acidifying with sulfuric acid and filtering, 64 kg of PTBAC could be isolated. The organic phase was subjected to fractional distillation and then PTBT
A fraction, PTBAL fraction (53Kg >98% purity) and a small amount of heavy final fraction were obtained. PTBT was recycled to the reactor. The aqueous catalyst-containing phase resulting from the PTBT extraction was distilled to remove some water and then recycled back to the reaction. Examples: cutting board, gas introduction pipe, high-speed stirrer, cooler,
Using a 0.25 volume reaction vessel equipped with a thermometer and a heating jacket connected to a constant temperature bath,
A number of recirculation experiments were conducted. Run No. 1 was conducted under the conditions described in the example. Next stage operation (2~
5) were each carried out using feedstock containing a recirculated portion of the previous run. The following methods were followed unless otherwise stated. The reaction product was fractionated into three fractions and one distillation residue. The residue is 50 ml of the first distillate (4th run).
No. 40 ml) and stored at 10°C for 16 hours (Run No. 4: 45 hours). After washing twice with 10 ml each of the filtered and condensed first fraction and drying at 100° C., PTBAC was isolated. The liquor and the remainder of the first fraction are combined and used as the charge for the next run after addition of make-up PTBT and acetic acid to the recycled second fraction and condensate. No catalyst was added. In run number 2, the partitioning of the components across the three cuts was unsatisfactory, probably due to the high molar ratio of water/AcOH of 0.44. This run therefore followed a different recirculation method.
After recovery of PTBAC, the liquid was combined with the remainder of the first fraction and distilled at atmospheric pressure to remove excess water. Upper layer (PTBT3ml) and lower layer (AcOH14.7
g and 5.3 g of H ₂ O) was removed and the bottom layer was discarded. The top layer was combined with the distillation bottoms and the second fraction from run #2 and then recycled to add make-up PTBT and AcOH before being used as the input oil for run #3. The product of Run No. 5 was not processed further. The conditions applied to the various runs and the results obtained are shown in the following table.

【table】

【table】

Claims (1)

[Claims] 1 formula (In this formula, X is a tertiary butyl group) A method of oxidizing the compound by reacting the compound represented by the formula with molecular oxygen in the presence of cobalt carboxylate, a bromine compound, and a carboxylic acid, The reaction is carried out in the presence of an additional 0.5 to 40 mol % of water or pyridine, based on the carboxylic acid, as an agent capable of counteracting the formation of groups, and the product mixture is freed from the formula (In this formula, X has the above meaning) (In this formula, X has the above meaning.) A method of oxidizing a compound represented by: 2. Process according to claim 1, characterized in that the reaction is carried out in the presence of cobalt acetate, an alkali metal bromide and acetic acid. 3. The method according to claim 1 or 2, characterized in that the reaction is carried out at a temperature within the range of 80 to 130°C. 4. The method according to claim 3, wherein the reaction temperature is within the range of 90 to 100°C. 5. Process according to any one of claims 1 to 4, characterized in that the reaction is carried out under a pressure in the range 1 to 10 bar. 6. Process according to any one of claims 1 to 5, characterized in that water is used as agent capable of counteracting the formation of carboxyl groups due to oxidation. 7. The method according to claim 6, characterized in that the amount of water is in the range of 25 to 35 mol% based on the carboxylic acid. 8 formula 8. A method according to any one of claims 1 to 7, characterized in that recovery of the compound represented by includes extraction with water. 9. A patent claim characterized in that the aqueous phase resulting from the extraction with water, together with the unconverted starting materials, is treated with a compound of the formula [formula] in an amount corresponding to the amount used in the oxidation reaction. The method described in item 8.