GB2199324A - Process for the preparation of catechols - Google Patents

Abstract

A process for the preparation of a compound of the general formula <IMAGE> in which each of R<1> and R<2> independently represents a hydrogen or halogen atom or a C1-6 alkanoyl, optionally substituted C1-6 alkyl, optionally substituted phenyl or CN group, provided that when R<2> represents a hydrogen atom, R<1> represents a hydrogen atom, which comprises dehydrogenating the corresponding 1,2-dihydroxycyclohexa-3,5-diene using a dehydrogenation catalyst in the presence of gaseous oxygen. 3-Trifluoromethylcatechol is claimed per se.

Description

PROCESS FOR TES PRELPARATION OF CATEMOLS This invention relates to a process for the preparation of certain catechols from the corresponding dihydroxycyclohexadienes using a dehydrogenation catalyst, and to a novel catechol.

It is kncwn that certain catechols ray be obtained from the corresponding dihydroxycyclohexadienes using a dehydrogenation catalyst under mild conditions. Thus Nakajima et al; Chew. Ber.

1959, 92, 163 discloses the conversion of 1, 2-dihydroxycyclohexadiene to catechol using a dehydrogenation catalyst. 11aug et al; Biochem. Biophys. Res. Common. 1973, 54, 760 discloses the conversion of the conpound of formula

to the corresponding catechol by heating the compound under reflux in water in the presence of palladium on charcoal. Wegst and Lingens, FEMS Microbiol. letters 1983, 17, 341 further discloses the conversion of the compound of formula

to the corresponding catechol under the same reaction conditions as those described in Ilaug et al (loc cit).

Taylor and Brown, Performance Chemicals, November, 1986, pages 18 to 22 disclose the dehydrogenation of dihydrocatechols, e.g. cis-1,2-dihydroxy-3-fluorocyclohexa-3,5-diene using a precious natal catalyst, to afford the equivalent catechols, e.g. 3-fluorocatechol, and also states that catechols are unstable in aerated aqueous systems.

Unfortunately, the catechols prepared using the above-described methods tend to be obtained in relatively low yield. TbLs is because the dinydroxycyclohexadienes disproportionate in the presence of the dehydrogenation catalyst. In other words, some of the dihydroxycyclohexadiene is converzec to dinydroxycyclohexene.

Surprisingly, it has now been found that when the dehydrogenation reaction is effected in the presence of gaseous oxygen, disproportionation is substantially eliminated, and moreover there is no observed oxidation through to undesired quinone.

Accordingly the invention provides a process for the preparation of a compound of the general formula

in which each of R anc R independently represents a hydrogen or halogen atom or a lower alkanoyl, optionally substituted lower alkyl, optionally substituted phenyl or COIN group, provided that when R represents a hydrogen atom, R represents a hydrogen atom, which comprises dehydrogeriating a compound of the general formula

in which R1 and R2 are as defined above by treatment of a compound of formula II with a palladium or platinum catalyst in the presence of gaseous oxygen and an organic solvent at a temperature in the range of 20 to 1200C.

In the process according to the invention, the substituent R is preferably in the para-position relative to R.

Preferably R represents a hydrogen atom.

R preferably represents a hydrogen or halogen atom or a CF3 or CN group. Mbre preferably, R2 represents a fluorine atom or a CF3 group.

Unless otherwise stated in this specification, any reference to a lower alkanoyl or optionally substituted lower alkyl group preferably means a group having up to 6, for example up to 4 carbon atoms. An optionally substituted alkyl group may be, for example, an unsubstituted alkyl group or a haloalkl group. A halogen atom may be, for example, a fluorine atom.

The solvent employed in the process according to the invention is conveniently selected from an alcohol, e.g.

methanol or ethanol; an ether, e.g. tetrahydrofuran; an aromatic hydrocarbon e.g. benzene or toluene; an ester e.g. ethyl acetate; and mixtures thereof. Preferably an alcohol is employed. When an alcohol is employed, water may be present.

It has been found that the process may advantageously be effected when the concentration of the compound of formula (II) in the organic solvent is in the range of from 0.0001 to 0.05 moles per litre.

The palladium or platinum catalyst employed in the process according to the invention may conveniently be supported on a carrier. Any conventional carrier may be employed, for example carbon or asbestos.

Preferably the process according to the invention is effected at a temperature in the range 40 to 800C, more preferably 50 to 600C.

The gaseous oxygen employed in the process according to the invention may be in the form of pure oxygen gas, but it may very conveniently be in the form of air. The gaseous oxygen can also be generated in situ from hydrogen peroxide.

It has been found that the process according to the invention may conveniently be effected in a continuous manner by passing the solution of the compound of general formula (I) over the catalyst in a stream of gaseous oxygen.

The compounds of formula II may be prepared according to methods known in the art. For example they may be prepared from the corresponding benzene compounds by the action of certain microorganisms such as micro-organisms of the species Pseudomonas putida, for example as described in European Patent Application publication number EP-A-76606.

According to another aspect of the invention, there is provided a compound of formula

which has the chemical name 3-trifluoromethylcatechol.

It may be prepared by the process according to the present invention, for example using cls-1,2-dihydroxy-3-trifluoro- methylcyclohexa-3,5-diene.

The preparation of cis-1,2-dihydroxy-3-trifluoro- methylcyclohexa-3 , 5-diene is described in our co-pending British patent application number 8616614.

Thus, cis-l , 2dinydroxy-3-trifluoromethylcyclohexa-3, 5- diene may be prepared by culturing a wild type P.putida micro-organism as defined below, supplying trif luoromethyl benzene to the culture in a suitable growth medium and subsequently recovering the cis-1,2-dihydroxy-3trifluoromethylcyclohexa-3,5-diene therefrom.

The P.putida referred to above is that deposited with effect from 6th December, 1985 with the National Collection of Industrial Bacteria, Torry Research Station, Aberdeen, Scotland and assigned the numerical designation NCIB 12190 and referred to herein as "P.putida NCIB 12190". The isolation of this type of micro-organism has been described by Axcell and Geary, Biochem. J., (1975), 146, p. 173-183 and Biochem.'J. 136, 927-934.

The culture of P.putida may be initially grown in the presence of any suitable carbon source. However, a preferred carbon source capable of producing a constitutive culture for the desired biochemical process is succinic acid, suitably in the form of a salt such as disodium succinate. Other similar, but less expensive,-carbon sources are those derived from citric acid and fumaric acid, e.g. trisodium citrate and disodium fumarate.

The use of such carbon sources as, for example, salts of succinic, citric and fumaric acid, is particularly useful in that the grown P.putida is found to be constitutive of the dioxygenase required for the process.

The growth medium employed is selected to optimise the yield of cis-l,2-dihydroxy-3-trifluoromethylcyclohexa-3,5-diene.

However the growth medium preferably includes salts of succinic, citric or fumaric acid, as described above for the initial carbon source.

The product compound may be recovered from the resulting fermentation broth by any suitable means, such as adsorption onto granulated charcoal, followed by stripping with a suitable solvent with further purification as necessary dependent on the intended use of the product. Alternative recovery means include solvent extraction.

Compounds of"general formula (I) have applications as intermediates in the preparation of, for example, pharmaceuticals and agrochemicals, as indicated for example by Taylor and Brown, Performance Chemicals, November, 1986, pages 18 to 22.

Preparation of cis-1,2-dihydroxy-3-trifluoromethylcyclohexa- 3,5-diene in a fermenter using P.putida NCIB 12190 Yeast extract medium (YEM): 10g/l disodium succinate.6H20 2g/l (NH4)S04 3g/l yeast extract (Difco) 0.4g/l MgSO4. 7H20 0.04g/l Bactopeptone in 25 mM potassium phosphate buffer, final pH 7.0.

8 Litres of YEM in a fermenter were inoculated with a 20h shake culture of P.putida NCIB 12190 (stock slant derived from a shake culture grown on benzene) grown on the same medium (SOml).

The organism was grown at 500rpm; 500ml air/min for 20h, with a continuous feed of concentrated nutrient (disodium succinate (320g) and (NH4)2S04 (64g) in 1 litre of 0.025M KPO4 buffer pH 7.2) at 40ml/h, reaching a cell dry weight of 2.8g/l. The aeration was then increased (550rpm; 750ml air/min) for lhr.

giving an oxygen tension of 20-30% air-saturated.

Benzotrifluoride was then added at 50 "l/min via an HPLC pump.

Using these settings no product was found in the reaction mixture by GLC. It was thus concluded that the combination of low substrate solubility and high aeration was stripping substrate into the exhaust gas before a high enough concentration could be reached for the reaction to occur. To reduce this effect while still maintaining an adequate oxygen tension ( > 308) the stirrer speed was raised to 650rpm while aeration was reduced to 300ml/min. 5g of substrate was added batchwise while still maintaining a flow of SOKl/min. Product formation commenced immediately as judged by CLC and reached 0.3g/l after 60min.Further additions of substrate (5ml) were made at approximately 2h intervals while maintaining the continuous addition (SOyAl/min). The product concentration reached 1.25g/1 after approximately 6h at which point the stirrer failed and the run was terminated. The product was adsorbed onto charcoal followed by stripping in a Soxhlet apparatus (Et20:MeOH 3:1). Evaporation of the solvent yielded about 60ml of aqueous solution of cis-1,2-dihydroxy-3trifluoromethylcyclohexa-3,5-diene which crystallised upon addition of a trace of NaCl. Recrystallisation from Et20: petrol 1:4 yielded approximately 12g ( 1.5g/l) of pure cis-1,2-dihydroxy-3-trifluoromethylcyclohexa-3,5-diene.

The following examples illustrate the invention.

Example 1 Preparation of 3- (trifluoromethyl)catechol Cis-1,2-dihydroxy-3-trifluoromethylcyclohexa-3,5-diene (1.37g) in ethanol (548m1) was trickled at a rate of 4ml/minute, concurrently with a stream of oxygen gas passing at a rate of 20ml/minute, over a loosely packed bed of course palladised asbestos (14% Pd, 0.5g) in a jacketed column at a temperature of 56 C. Ethanol was then passed through the column until no further products were eluted. The eluants were then combined and the solvent was removed by evaporation. The residue was then dissolved in diethyl ether and extracted under nitrogen with aqueous sodium hydroxide. The aqueous extract was then acidified to pH5 and extracted with diethyl ether. The diethyl ether was then removed by evaporation to afford the title compound (0.36g).The product was then purified by sublimation in vacuo to afford the title compound as colourless crystals m.p. 53-56"C.

Mass spectrum: m/z 178 (78%, M+), 158 (100%), 130 (95%).

H-NMR (in CDC13): 5 7.09 (t,2H), 6.90 (t, 1H), 5.8 (broad, 2H; OH) p.p.m.

19 NOR (in CDC13): & -64.9 p.p.m. (d, J 6Hz).

Uv absorption (in ethanol): > max. 286nm ( 3820).

Example 2 Preparation of 3-fluorocatechol A solution of cis-l,2-dihydroxy-3-fluorocyclohexa-3,5-diene (15mg) in ethanol (12ml) was trickled at a rate of 4ml/minute, concurrently with a stream of air at lO0ml/minute, over a loosely packed bed of coarse palladised asbestos (14% Pd, 0.5g) in a jacketed column held at 56"C. The column was then washed with ethanol until no further products were eluted, and the combined eluants (20.7ml) were analysed by gas chromatography.

The percentage yield of each product in the eluantmeasured by the analysis is given below.

Compound 5 % Yield 3-fluorocatechol 67.0 cis-1,2-dihydroxy-3-fluorocyclohexa-3,5-diene 0 cis-1,2-dihydroxy-3-fluorocyclohex-3-ene 0 For the purpose of comparison, the procedure in Example 2 was repeated using nitrogen gas instead of air. It was found that no cis-1,2-dihydroxy-3-fluorocyclohexa-3,5-diene was present in the eluant. However, cis-1,2-dihydroxy-3fluorocyclohex-3-ene was present in the eluant, the ratio of 3-fluorocatechol to cis-1,2-dihydroxy-3-fluorocyclohex-3-ene being approximately 3:1.

Claims (13)

1. A process for the preparation of a compound of the general formula

in which each of R1 and R2 independently represents a hydrogen or halogen atom or a lower alkanoyl, optionally substituted lower alkyl, optionally substituted phenyl or Con group, provided that when R2 represents a hydrogen atom, R1 represents a hydrogen atom, which comprises dehydrogenating a compound of the general formula

in which R1 and R2 are as defined above by treatment of a compound of formula II with a palladium or platinum catalyst in the presence of gaseous oxygen and an organic solvent at a temperature in the range of 20 to 1200C.

2. A process as claimed in claim 1, in which R1is in the para-position relative to R2.

3. A process as claimed in claim 1 or claim 2, in which R1 represents a hydrogen or halogen atom.

4. A process as darned in any one of claims 1 to 3, in which R2 represents a hydrogen or halogen atom or a CF3 or CN group.

5. A process as claimed in claim 4, in which R2 represents a fluorine atom or a CF3 3 group.

6. A process as claimed in any one of claims 1 to 5, in which the gaseous oxygen is in the form of air.

7. A process as claimed in any one of claims 1 to 6, in which the solvent is selected from an alcohol, an ether, an aromatic hydrocarbon or an ester.

8. A process as claimed in claim 7, in which the solvent is methanol or ethanol.

9. A process as claimed in any one of claims 1 to 8, in which the palladium or platinum catalyst is supported on a carbon or asbestos carrier.

10. A process as claimed in any one of claims 1 to 9,in which the temperature is in the range of 40 to 800C.

11. A process as claimed in any one of claims 1 to 10, in which the compound of formula II is dissolved in the solvent at a concentration in the range of 0.0001 to 0.05 moles per litre.

12. A process for the preparation of a compound of formula (I) as defined in claim 1 substantially as described herein with reference to the Examples.

13. 3-Trifluoromethylcatechol.