Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1993-10-12
1995-02-07
Lone, Werren B.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
502102, 502104, 568741, 568803, C07C 3760, B01J 3100
Patent
active
053877241
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for hydroxylating phenol and more particularly to a process in which phenol is hydroxylated using hydrogen peroxide in the presence of a catalyst.
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, 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.
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 leads to the recycling of an overwhelming fraction of unreacted phenol which in turn reduces the space yield of the plant. It would be desirable to develop a process which enabled a higher proportion of the phenol to be reacted to the desired end-products in each cycle.
It is an object of the present invention to ameliorate or overcome one or more of the difficulties indicated herein with regard to known processes for the catalysed hydroxylation of phenol.
According to the present invention, there is provided a process for the hydroxylation of a substrate comprising a phenol or related aromatic compounds by reaction with hydrogen peroxide in the presence of a catalyst, characterised in that the substrate is a phenol or phenolic ether and the reaction is carried out in a solvent containing an effective amount of an aliphatic carboxylic acid and the catalyst comprises amorphous or microcrystalline zirconium phosphate.
By the use of a process according to the present invention, it is possible to obtain good selectivity of reaction towards the introduction of a single additional hydroxyl substituent around the aromatic nucleus of the substrate, normally ortho or para to the existing substituent.
The substrate can be mono, bi or poly-nuclear and, preferably, is mono-nuclear. The nucleus or nuclei is or are particularly suitably carbocyclic. The most preferred nucleus is benzene. Although the substrate may contain more than one of the relevant substituents namely hydroxyl or ether, it is preferable for only one to be present. A particularly preferred substrate comprises phenol itself. The substrate nucleus may be further substituted, if desired, for example by an alkyl group, R.sub.a, preferably short chain such as methyl or ethyl. When the substituent is an ether, suitably of formula --OR.sub.b, R.sub.b is suitably alkyl and preferably short chain alkyl such as methyl or ethyl.
The catalyst employed in processes of the present invention comprises an amorphous or microcrystalline zirconium phosphate. The catalyst can be produced by the two stage method described by A. Clearfield and D. S. Thakur in Applied Catalysis, 26,1 (1986). In the first stage, zirconium oxychloride (ZrOCl.sub.2) is reacted with excess phosphoric acid in an aqueous medium, conveniently at laboratory ambient temperature or thereabouts, and amorphous zirconium phosphate precipitates from solution. In the second stage, a microcrystalline form is obtained by digesting the filtered amorphous material with concentrated phosphoric acid solution, at above ambient temperature, for example from 80 to reflux temperature, for at least 24 hours and often between 48 and 100 hours. The crystalline material so obtained is hydrated.
Preferably the microcrystalline form is at least partially dehydrated before it is emp
REFERENCES:
patent: 3416884 (1968-12-01), Stynes et al.
patent: 3514490 (1970-05-01), Marlard
patent: 5138104 (1992-08-01), Takahashi et al.
Chemical Abstracts, vol. 85, No. 24, 13 Dec. 1976, Abstract No. 178465Y.
Johnstone Alexander
Sanderson William R.
Wasson Robert C.
Lone Werren B.
Solvay Interox Limited
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