Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1995-08-03
1997-10-07
Shaver, Paul F.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568763, 568771, C07C 4104, C07C 4320
Patent
active
056750420
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for hydroxylating phenols and more particularly to a process in which phenols are 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.
In the course of the studies leading to the present invention, a range of metal catalysts have been tested for the hydroxylation of phenols with varying levels of success and failure, demonstrating that catalysts useful for other hydrogen peroxide reactions cannot necessarily be transferred to phenol hydroxylation with a guarantee of success.
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 one or both of tin (IV) or cerium (IV) 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 round 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 crystalline tin (IV) or cerium (IV) phosphate. The catalyst can be prepared by the reaction between a tin or cerium salt such as especially the chloride or the sulphate and phosphoric acid, producing a solid metal phosphate precipitate. The reaction can conveniently by conducted at, or around ambient temperature. The extent of crystallinity can be controlled by controlling the length of time that the precipitate remains in contact with its supernatant liquor, ie aging. An in
REFERENCES:
patent: 4847437 (1989-07-01), Wu
patent: 5387724 (1995-02-01), Johnstone et al.
patent: 5426244 (1995-06-01), Sugai et al.
Shaver Paul F.
Solvay Interox Limited
LandOfFree
Selective hydroxylation of phenol or phenolic ethers does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Selective hydroxylation of phenol or phenolic ethers, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Selective hydroxylation of phenol or phenolic ethers will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2358777