GB1561464A

GB1561464A - Oxidation of alkaryl compounds

Info

Publication number: GB1561464A
Application number: GB420277A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1977-02-02
Filing date: 1977-02-02
Publication date: 1980-02-20
Also published as: FR2379500B1; NL7801126A; NL187158C; NL187158B; JPS5395937A; JPS6148489B2; FR2379500A1; DE2804115A1; DE2804115C2; CH634811A5

Abstract

Process for the oxidation of a compound of the formula <IMAGE> in which X is a non-oxidisable group by reacting this compound with molecular oxygen in the presence of a cobalt carboxylate, a bromine compound and a carboxylic acid, characterised in that the reaction is additionally carried out in the presence of from 0.5 to 40 mole per cent, based on the carboxylic acid, of an agent which counteracts the oxidative formation of a carboxyl group, and in that a compound of the formula <IMAGE> is isolated from the product mixture.

Description

(54) OXIDATION OF ALKARYL COMPOUNDS (71) We, SHELL INTERNATION AtE RESEARCH MAATSCHAPPIJ BçV., a Company organised under the laws of the Netherlands, of 30 Carel van Bylandtlaan, The Hague, The Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process for the oxidation of p-substituted toluenes containing a non-oxidizable group as substituent. In particular the invention relates to a process for the preparation of p-substituted benzaldehydes.

It is known that toluene or substituted tt'luenes may be oxidized with oxygen in the presence of a cobalt carboxylate, a brominr compound and a carboxylic acid, the latter acting as solvent. Generally this results in the predominant formation of (substituted) benzoic acids e.g. terephthalic acid. Whereas these aromatic carboxylic acids are useful chemical compounds which may be applied as starting materials for the manufacture of such products as alkyd resins, it is sometimes desired to produce compounds in which the methyl group of the starting material is only partially oxidized. These partially oxidized compounds, e.g. p-alkyl-substituted benzaldehydes are likewise valuable chemical intermediates and, in some instances, may find special applications e.g. in the field of aroma chemicals.

Under the conventional reaction conditions these partially oxidated toluenes are only formed in relatively small amounts, whilst the separation thereof from the co-produced benzoic acids is often laborious and ineffective.

It has now been found that with feedstocks of the formula

in which X is a non-oxidizable group and applying certain oxidation conditions, considerable amounts of partially oxidized alkaryl compounds--in addition to substituted benzoic acids-are formed. Moreover, an effective method has been found to separate the partially oxidized alkaryl compounds from the co-produced benzoic acids.

The invention may be defined as relating to a process for the oxidation of a compound of the formula

in which X is a non-oxidizable group, and in which the aromatic nucleus may contain one or more inert substituents located at orthoor meta-positions in respect of the methyl groups, by reaction of the said compound with molecular oxygen in the presence of a cobalt compound, a bromine compound and a carboxylic acid, characterized in that the reaction is carried out in the further presence of 0.5 to 40% m, based on the carboxylic acid, of an agent capable of counteracting the oxidative formation of a carboxy group, and in that from the product mixture a compound of the formula

is recovered.

The group X may be any non-oxidizable group, e.g. a carboxy group, but is preferably a non-oxidizable hydrocarbyl group. Most preferably X represents a tertiary butyl group.

The aromatic nucleus in the compounds of the above formula may in addition contain one or more inert substituents located at ortho- or meta-positions in respect of the methyl group.

The cobalt compound is preferably a cobalt(II) compound, for example the carbonate, oxide or bromide, or a carboxylate derived from an alkanoic acid of 1 to 10 carbon atoms, in particular the acetate. The bromine compound used in the catalyst is preferably an alkali or alkaline earth metal bromide, in particular sodium bromide, or ammonium bromide. The molar ratio of bromide to the cobalt compound may be from 0.1:1 to 5:1, preferably from 0.5:1 to 2.5:1.

The carboxylic acid used as solvent is preferably an alkanoic acid of uD to 6 carbon atoms in particular acetic acid. The molar ratio of cobalt compound to carboxylic acid may be from 0.0005:1 to 0.03:1.

Due to the presence of the agent capable of counteracting the oxidative formation of a carboxy group, the oxidation of the methyl group is considerably retarded. This results in the formation of significant amounts of intermediate oxidation products, in particular products containing a formyl group, which may be recovered from the reaction product mixture.

A very suitable agent is water which is preferably employed in amounts of 2535% m based on the carboxylic acid. Also tertiary amines may be used, such as trialkylamines in which each alkyl group is of 1 to 6 carbon atoms, for example triethylamine, or a hetero cyclic tertiary amine such as pyridine. However, water is most preferred.

The process may be conveniently carried out by mixing the solid and liquid components and passing gaseous oxygen over, or prefer ably through, this mixture. The reaction temperature is preferably maintained at 800C to 1300 C, more preferably between 90 and 100"C.

The oxygen may be applied as such, but is preferably mixed with an inert gas such as nitrogen. The use of air is recommended.

Suitable reaction pressures are in the range of 1-10 bar, the oxygen (partial) pressure is preferably from 1 to 3 bar. Reaction times are suitably from 1 to 2 hours.

The recovery of the compound of formula

from the reaction mixture may proceed according to conventional separation methods, for example by distillation. However, considerably improved results, as regards separability and purity of the product, are obtained, if the recovery of the compound of the said formula involves an extraction with water. Thus two phases are formed, an aqueous phase containing the catalyst and most of the carboxylic acid as well as small amounts of the oxidation products and an organic phase containing nonconverted starting material, most of the oxidation products and minor amounts of water and carboxylic acid. After phase separation the two phases can be separately treated for the recovery of the products, the non-converted starting material and the catalyst, which may be recycled, if desired. According to a preferred embodiment of the process the aforesaid aqueous phase is extractively treated with the compound of the formula

the amount thereof being preferably selected such that-together with non-converted starting material-it corresponds with the amount employed in the oxidation reaction. Again an aqueous and an organic phase are formed, the latter being suitably combined with that obtained from the extraction with water. After washing with water the separation between the compound of formula

and the co-produced benzoic acid is conveniently effected by neutralization with the acid of a caustic treatment followed by a further phase separation. The products are suitably recovered by distillation of the organic phase and acidification of the aqueous phase, respectively.

The invention is illustrated further in the following Examples.

EXAMPLE I.

4-Tert-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 mol) were stirred together at 940 to 990C while oxygen was passed at a rate of 101 per hour and a pressure of 1 bar through the mixture. After 1 h 10 min- it was shown by GLC and NMR that the conversion of starting material was 52%. The reaction mixture was then fractionally distilled.

The 4-tert-butylbenzaldehyde was obtained as a fraction boiling at 6 > 85 C at 0.3 mm Hg, yield 40% based on converted toluene.

The residue was then extracted with acetic acid and then recrystallized from acetic acid +water to give 4-tert-butylbenzoic acid as a white crystalline solid, m.p. 167"C, yield 60% based on converted toluene.

Comparative experiment.

The procedure of Example I was repeated in the absence of added water. After 3/4 hours it was shown by NMR that the conversion of 4-tert-butyltoluene was 54%, but the product contained less than 14% 4-tertbutylbenzaldehyde.

EXAMPLE II.

The procedure of Example I was repeated using pyridine (7.0 g, 25.3 mmol) in place of water. After 1 h 23 min it was shown by NMR that the conversion of 4-tert-butyltoluene was 48% and the product contained 44% 4-tert-benzaldehyde and 56% 4-tertbutylbenzoic acid.

EXAMPLE III.

A 1 m3-batch reactor (type STU 1200) provided with a stirrer and a dip pipe ending near the tip of the stirrer was charged with 302.5 kg p-tertiary butyl toluene (PTBT), 500 kg acetic acid, 9.7 kg cobalt acetate .4 H2O, 3.4 kg NaBr and 50 kg water.

The contents of the reactor were heated to a temperature of 93-1000C and air was introduced through the dip pipe. The pressure in the reactor was maintained at 5 bar gauge.

After 2.5 h when the conversion was 40% air supply was discontinued and the reactor was cooled to 40"C by addition of 90 kg water. The extraction was effected by 30 min stirring and 30 min settling. Then the phases were separated. The aqueous catalyst containing phase was treated at 40"C with 150 kg of PTBT. Again the extraction was effected by 30 min stirring and 30 min settling. The phases formed were separated and the organic phase was combined with the organic phase obtained in the first extraction. The combined organic phases (565 kg) were washed with 90 kg water. After stirring during 30 min, settling during 30 min and phase separation the aqueous phase was withdrawn and stored for a further batch, whereas the organic phase was subjected to a flash distillation in order to remove part of the PTBT, some remaining water and traces of acetic acid.

To the remaining mixture of PTBT, ptertiary butylbenzaldehyde (PTBAL) and ptertiary butylbenzoic acid (PTBAC) an aqueous solution of 10% NaOH was added in a 1% excess. Two phases were formed, -the aqueous phase containing the dissolved sodium salt of PTBAC. By acidification with sulphuric acid and filtration 64 kg PTBAC could be isolated. The organic phase was subjected to fractionated distillation from which resulted a PTBT fraction, a PTBAL fraction (53 kg purity 98%+) and a small heavy ends fraction.

The PTBT was recycled to the reactor.

The aqueous catalyst containing phase obtained as a result of the PTBT extraction was distilled to remove some water and was subsequently recycled to the reactor.

EXAMPLE IV.

A number of recycle experiments were carried out, using a 0.25 1 reaction vessel, provided with baffles, a gas inlet tube, a high speed stirrer, a condenser, a thermometer and a heating jacket connected with a thermostat bath. Run No. 1 was performed under the conditions indicated in Example I. Each of the subsequent runs (2-3) was performed with an intake, containing recycled portions of the previous run. Unless otherwise stated the following procedure was followed: The reaction product was fractionally distilied into 3 fractions and a distillation residue.

The residue was taken up in 50 ml of the first fraction (run No. 4:40 ml) and stored for 16 h at 100C (run No. 4.45 h). By filtration, 2 washings, each with 10 ml of condensed first fraction, and drying at 100"C PTBAC was isolated. The filtrate, and the remainder of the first fraction were combined and, together with the second fraction recycled, to be used as intake for the next run, after addition of make-up PTBT and acetic acid. No catalyst was added.

In run No. 2 the distribution of the components over the three fractions was not satisfactory, probably due to the high molar ratio water/ACOH of 0.44. Therefore in this run a different recycle procedure was followed.

After recovery of PTBAC the filtrate was combined with the remainder of the first fraction and distilled at atmospheric pressure to remove excess water. An amount of 23 ml was topped, consisting of an upper layer (3 ml PTBT) and a lower layer (14.7 g AcOH and 5.3 g H20) which was discarded. The upper layer was combined with the bottoms of the distillation and with the second fraction of run No. 2 and subsequently recycled to be used as intake for run No. 3 after addition of make-up PTBT and AcOH.

The product of run No. 5 was not worked up further.

Conditions applied in the various runs and results obtained are indicated in the Table below.

TABLE

. Yield Yield Recycled PTBAL PTBAC Intake GLC fraction I + Re- (on (on (not including Re- Re- product Fractionation conditions and composition of Filtrate covered con- con Run recycled por- action action analysis (after PTBAC PTBT, verted verted No. tions if any) period temp. mol % Fracion I Fraction II Fraction III recovery) % PTBT) PTBT) 53.3g PTBT 47.7 PTBT bp37-80 C/ bp80-95 C/ bp60-85 C/ 84.3g AcOH 15mm 15mm 0.3mm 88.2g AcOH 25,4 PTBAL 83.9g AcOH 0.95g PTBAL 11.0g PTBAL 10.7g PTBT 1 8.8g H2O 1h10' 94- 26.8 PTBAC 11.6g H2O 11.15g PTBT 3.3g PTBT 5.5g PTBAC 96 39.2% 33.1% 98 C 1.72g Co(OAc)2. 10.3g PTBT 8.9g H2O 4 H2O 0.6g NaBr 3.7g AcOH 42 PTBT bp -80 C/ bp80-94 C/ bp -115 C/ 85.0g 15mm 15mm 0.3mm 2 32.15g PTBT 3h 94 C 17 PTBAL 77.9g AcOH 7.1g PTBT 3.7g PTBT 90 36.1% 55.8% 41 PTBAC 9.7g PTBT 0.8g PTBAL 6.8g PTBAL 3.5g PTBAL 0.1g PTBAC 0.6g PTBAC 5.9g PTBAC 9.9g H2O 37.5g PTBT 42.2 PTBT bp -80 C/ bp80-90 C/ bp60-92 C/ 5.4g H2O 15mm 15mm 0.25mm 3 25.8g AcOH 55' 94 C 18.3 PTBAL 64.7g AcOH 6.9g PTBT 3.7g PTBT 61.9g AcOH 82.5 40.4% 61.3% 39.3 PTBAC 6.6g H2O 0.7g PTBAL 9.7g PTBAL 12.3g PTBT 13.9g PTBT 0.7g PTBAC 1.9g PTBAL 11.2g PTBAC TABLE (cont'd)

Yield Yield Recycled PTBAL PTBAC Intake GLC fraction I + Re- (on (on (not including Re- Re- product Fractionation conditions and composition of Filtrate covered con- con Run recycled por- action action analysis (after PTBAC PTBT, verted verted No. tions if any) period temp. mol % Fraction I Fraction II Fraction III recovery) % PTBT) PTBT) 34.3g PTBT 51.7 PTBT bp -80 C/ bp80-90 C/ bp90 C/ 57.6g AcOH 15mm 15mm 0.23mm 4 26.1g AcOH 2h10' 94 C 13.5 PTBAL 61.8g AcOH 0.5g AcOH 3.5g PTBT 17.5g PTBT 89 39.2% 52.7% 34.8 PTBAC 17.1g PTBT 8.2 PTBT 7.2g PTBAL 1.5g PTBAL 3.0g H2O 0.5g PTBAL 0.6g PTBAC 12.9g PTBAC 2.2g H2O 28.3g PTBT 57.2 PTBT 5 29.9g AcOH 1h40' 94- 9.8 PTBAL - - - - - - 100 C 33.0 PTBAC

Claims

WHAT WE CLAIM IS:1. A process for the oxidation of a compound of the formula

in which X is a non-oxidizable group and in which the aromatic nucleus may contain one or more inert substituents located at ortho- or meta-position in respect of the methyl group, by reaction of the said compound with molecular oxygen in the presence of a cobalt compound, a bromine compound and a carboxylic acid, characterized in that the reaction is carried out in the further presence of 0.5 to 40% m, based on the carboxylic acid, of an agent capable of counteracting the oxidative formation of a carboxy group, and in that from the product mixture a compound of the formula

is recovered.
2. A process as claimed in claim 1, characterized in that the cobalt compound is a cobalt carboxylate.
3. A process as claimed in claim 1 or claim 2, characterized in that as starting material a compound of the formula

is used in which X is a tertiary butyl group.
4. A process as claimed in any one of claims 1 to 3, characterized in that the reaction is carried out in the presence of cobalt acetate, an alkali metal bromide and acetic acid.
5. A process as claimed in any one of claims 1-4, characterized in that the reaction is carried out at a temperature in the range of 80 to 1300C.
6. A process as claimed in claim 5, characterized in that the reaction temperature is between 90 and 1000C.
7. A process as claimed in any one of claims 1-6, characterized in that the reaction is carried out at a pressure in the range of 110 bar.
8. A process as claimed in any one of claims 1-7, characterized in that water is used as the agent capable of counteracting the oxidative formation of a carboxy group.
9. A process as claimed in claim 8, characterized in that the amount of water is in the range of 2535% m, based on the carboxylic acid.
10. A process as claimed in any one of claims 1-9, characterized in that the recovery of the compound of formula

involves an extraction with water.
11. A process as claimed in claim 10, characterized in that the aqueous phase resulting from the extraction with water is treated with the compound of formula

in an amount which together with gon- converted starting material, corresponds to that applied in the oxidation reaction.
12. A process substantially as hereinbefore described with reference to each of the Examples.
13. t-Butylbenzaldehyde whenever obtained obtained by a process as claimed in any one of claims 1-12.