Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1993-08-03
1994-11-15
Lone, Werren B.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568741, 568800, 568803, C07C 3760
Patent
active
053649826
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the hydroxylation of phenol.
Phenol is a readily available raw material which can be hydroxylated using aqueous hydrogen peroxide and a catalyst to produce dihydric phenols, and particularly mixtures containing hydroquinone and catechol. However, two factors should be taken into account when seeking to hydroxylate phenol. First, the introduction of a second hydroxyl substituent onto the aromatic nucleus tends to activate the molecule towards further reaction and this leads to the formation of a mixture of unwanted tarry by-products. Self-evidently it would be desirable to hydroxylate selectively, i.e. favour dihydric phenol formation compared with tarry by-product formation. Secondly, hydroquinone and catechol tend to be used for different purposes. For example, hydroquinone is a photographic developer and catechol is an intermediate in the production of industrial anti-oxidants. Consequently, it remains an aim of producers to obtain one or other product selectively.
A commercial process has been developed for hydroxylating phenol based upon catalysed hydrogen peroxide which tends to produce mixtures containing a major fraction of catechol, but additionally a minor, significant fraction of hydroquinone, typically in a mole ratio of about 3:1. The proportion of tarry by-products has been controlled by limiting very strictly to the use of very low mole ratios of hydrogen peroxide to phenol, but inevitably this restricts the extent of conversion of the phenol and hence the space yield of the plant.
European Patent Application, Publication No 0 338 666A, inventors M Shimizu et al, describes a process in which a tri-alkyl substituted phenol is converted to the corresponding tri-alkyl benzoquinone using hydrogen peroxide and a heteropolyacid catalyst. The inventors Shimizu et al have applied a similar process to a wider range of alkyl-substituted phenol substrates and described the results obtained in a paper entitled "A convenient synthesis of alkyl-substituted p-benzoquinones from phenols by a H.sub.2 O.sub.2 /heteropolyacid system", published in Tetrahedron Letters, vol 30, No 4, pp471-474. These two publications teach that alkyl substituted phenols are converted through to the corresponding benzoquinone rather than selectively to an hydroxylated product. The only teaching regarding phenol itself was that it gave only a trace amount of p-benzoquinone. Accordingly, neither publication provides any clear teaching on how to hydroxylate phenol selectively.
It is an objective of the present invention to identify more exactly the conditions in which any one or more of the disadvantages in the aforementioned commercial process can be ameliorated or overcome.
According to the present invention, there is provided a process for the hydroxylation of phenol in which phenol is dispersed in a compatible organic reaction medium and brought into contact with hydrogen peroxide in the presence of a catalyst characterised in that the catalyst, which is at least partly soluble in the reaction medium, is selected from salts of heteropolyacids of general formula
i) Q.sub.3 PMo.sub.m W.sub.(12-m) O.sub.40 or
ii) Q.sub.3+v PM.sub.n V.sub.v O.sub.40 less than 6, M represents molybdenum or tungsten, v is an integer which is up to 3, and n is an integer such that n+v=12 and no more than a limited amount of hydrogen peroxide is employed.
In British Patent Application no 9103323.3, filed on 16th Feb. 1991 from which priority is claimed, the use was described of certain catalysts for selective phenol hydroxylation obeying the general formula: is less than or greater than 6. Herein, such catalysts when n is less than 6 are represented by general formula i, in which it will be observed that m has been substituted for n. Subsequent analysis of the catalyst tested in support of the formula in which n was greater than 6 showed that the anion in HPS11 had the formula PMo.sub.11 VO.sub.40, i.e. contained vanadium as a hetero metal atom rather than tungsten. The use of such catalysts in which n has a
REFERENCES:
Shimizu, et al., "A Convenient Synthesis of Alkyl-Substituted P-Benzoquinones from Phenols by a H2O2/Heteropolyacid System", Tetrahedron Letters, vol. 30, No. 4, 1989, pp. 471-474.
Takamitsu, et al., Chemical Abstracts, vol. 87, No. 25, 19 Dec. 1977, Abstract No. 201076Z, "Dihydric Phenols", p. 686, Col. 1.
Brown Scott W.
Hackett Anthony
Johnstone Alexander
King Angela M.
Sanderson William R.
Lone Werren B.
Solvay Interox Limited
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