Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Patent
1991-04-11
1992-08-18
Niebling, John
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
562418, C07F 96547
Patent
active
051396289
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the halogenation and oxidation of substituted alkyl benzene compounds and specifically to the halogenation and oxidation of the alkyl substituent in compounds that are further substituted by both a halo and a sulpho group.
One of the compounds that is of potential value as an intermediate in for example agrochemical preparations is 4-sulpho-2-chlorobenzoic acid, which is sometimes also referred to herein by the abbreviation "SCUBA". A suitable starting material for the preparation of this compound is the corresponding 2-chlorotoluenesulphonic acid which itself can be made conveniently by instant inventors team by nuclear chlorination of toluenesulphonic acid. Whilst in theory direct oxidation of the methyl substituent of the compound is possible, using for example potassium permanganate, such a reagent is normally difficult to regenerate, produces insoluble manganese dioxide powder as a by-product and is accordingly regarded unfavourably for bulk-scale activities.
It would be desirable to find an alternative route for the preparation of 4-sulpho-2-chlorobenzoic acid which employed a regenerable reagent and/or avoided the difficulties associated with production of a fine powder as byproduct.
The team investigating ways of providing such an alternative route has also been investigating oxidation of the methyl substituent in toluene to the carboxylic acid in a related molecule in which the benzene nucleus is substituted by a nitro substituent instead of by a sulpho substituent. The team investigated a multi-stage process in the first stage of which the methyl substituent was brominated, in the second stage of which the brominated substituent was hydrolysed to an alcohol or aldehyde and in the third stage of which, the second stage product was oxidised to the carboxylic acid. It was found by the team that when a nitro-substituent was present, the first stage could be carried out conveniently in a two phase aqueous/hydrophobic system employing hydrogen peroxide and hydrogen bromide to generate bromine in the aqueous phase which is maintained in contact with the organic substrate in the organic phase and irradiated with bromine-dissociating radiation. By carrying out such a process under appropriately selected processing conditions, they found that it was possible to obtain as product the dibrominated side-chain product to a reasonably high extent of selectivity. The resultant product could be hydrolysed reasonably well in a subsequent step to the corresponding aromatic aldehyde, whereas if the product of the bromination step comprised either mainly or a substantial fraction of the corresponding monobrominated side chain product, the subsequent hydrolysis step was found to be markedly more difficult with much reduced yield.
There is a substantial degree of similarity between nitrotoluene and 2-chloro-4-toluene sulphonic acid, in that for example both molecules contain a methyl substituent that is available for bromination and both contain a deactivating substituent. Accordingly, it might be anticipated reasonably that a similar technique might be employed successfully in respect of 2-chloro-4-toluene sulphonic acid as starting material and that similar constraints would apply in respect of the bromination and hydrolysis steps. However, it was found in an initial appraisal of the process that adoption of the bromination technique without substantial modification resulted in a surprisingly poor yield of side chain brominated product. Secondly, it was found that the constraints upon subsequent processing steps, including that of hydrolysis were markedly different from expectations. Thus, the inventors have found that certain changes were necessary and other changes unexpectedly became possible.
The inventors have identified a convenient multi-stage route for the preparation of 4-sulpho-2-chlorobenzoic acid (SCUBA) from 2-chloro-4-toluene sulphonic acid (SCT) in which in stage a, the methyl substituent in the alkylbenzene is selectively brominated, in stage b, the product of stage a
REFERENCES:
patent: 2666785 (1954-01-01), Feichtinger et al.
patent: 3151153 (1964-09-01), Keith et al.
Robert T. Morrison, Robert N. Boyd, Organic Chemistry, 3rd Edition, Allyn and Bacon, Inc., Boston, 1975, pp. 47-62.
Chemical Abstracts, vol. 80, No. 9, Mar. 1974, (Columbus, Ohio, US), see p. 332, abstract 47649k & CS, A, 15000 (J. Horyna, et al.), Aug. 15, 1973 & Chemical Abstracts, 9th Collective Index, 1978, p. 2064f, formula C.sub.7 H.sub.5 ClO.sub.5 S.
Dear Kenneth M.
Reeve Kevan M.
Turner Philip J.
Interox Chemicals Limited
Nguyen Dean
Niebling John
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