Process for the preparation of 5-chloro-2-hydroxy-4-alkyl-benzen

Details Process for the preparation of 5-chloro-2-hydroxy-4-alkyl-benzen Process for the preparation of 5-chloro-2-hydroxy-4-alkyl-benzen

1992-04-10

1994-03-08

Chan, Nicky

Organic compounds -- part of the class 532-570 series

Organic compounds

Sulfonic acids or salts thereof

562 73, 568709, C07C30930

Patent

active

052929329

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to a process for the preparation of 5-chloro-2-hydroxy-4-alkyl-benzenesulfonic acids which has been improved over the prior art.
5-Chloro-2-hydroxy-4-alkyl-benzenesulfonic acids, in particular 5-chloro-2-hydroxy-4-methylbenzenesulfonic acid and 5-chloro-2-hydroxy-4-ethylbenzenesulfonic are important precursors for the preparation of 3,5-dichloro-2-hydroxy-4-alkyl-1-nitrobenzenes, in particular 3,5-dichloro-2-hydroxy-4-methyl-l-nitrobenzene and 3,5-dichloro-2-hydroxy-4-ethyl-l-nitrobenzene, which in turn are used as intermediate products for the production of color couplers for color papers (German Offenlegungsschrift 2,216,804 and European Patent 175,151).
It is known from German Offenlegungsschrift 2,216,804 and German Offenlegungsschrift 2,501,899, for example, that 5-chloro-2-hydroxy-6-methylbenzenesulfonic acid can be obtained by sulfonation of 4-chloro-5-methylphenol, and this product can be converted into 3,5-dichloro-2-hydroxy-4-methyl-i-nitrobenzene by chlorination and desulfonating nitration, likewise in a known manner.
According to Japanese Patent 61/57536 (8/84) (FUJI), for example, 5-chloro-2-hydroxy-4-ethylbenzenesulfonic acid is obtained in an analogous manner from 4-chloro-5-ethylphenol, and this product can then likewise be converted into 3,5-dichloro-2-hydroxy-4-ethyl-l-nitrobenzene by chlorination and desulfonating nitration.
However, a decisive disadvantage of these known processes for the preparation of 5-chloro-2-hydroxy-4-alkylbenzenesulfonic acids, as described in detail in German Offenlegungsschrift 3,431,687, pages 4 and 5, is above all the difficult accessibility of the 4-chloro-5-alkylphenols required as starting compounds.
It has now been found that 5-chloro-2-hydroxy-4-alkyl(C.sub.1 -C.sub.6)-benzenesulfonic acids of the general formula (1) ##STR3## in which R is an alkyl(C.sub.1 -C.sub.6) group, preferably a methyl or ethyl group, and X is a hydrogen atom or an alkali metal atom, preferably a sodium atom, can be prepared in good yields and in a high purity, avoiding the disadvantages of the known processes of the difficult accessibility of the 4-chloro-5-alkylphenols required as starting compounds in those processes, by converting 5-chloro-2-amino-4-alkyl(C.sub.1 -C.sub.6)-benzenesulfonic acids of the general formula (2) ##STR4## in which R and X have the abovementioned meanings, into the corresponding diazonium compound using a diazotizing agent in a mineral acid at temperatures of about -5.degree. C. to about +25.degree. C., preferably about +5.degree. C. to about +20.degree. C., subsequently reacting this diazonium compound, without or after, preferably without, intermediate isolation, with aqueous mineral acid at temperatures of about 70.degree. C. to about 120.degree. C., preferably about 100.degree. C. to about 115.degree. C,. and isolating the resulting compounds of the above formula (1).
The process according to the invention can be represented by the following equation: ##STR5## In this equation, R has the meaning given above and Y.sup.- is any desired anion, preferably --SO.sub.4 H.sup.-, 1/2 SO.sub.4.sup.- or Cl.sup.-.
The diazotization of the 5-chloro-2-amino-4-alkylbenzenesulfonic acids is in general carried out in sulfuric acid or hydrochloric acid, aqueous acids preferably being employed in the concentrations customary for such reactions. An approximately 20 to approximately 70% strength aqueous sulfuric acid or an approximately 5 to approximately 30% strength aqueous hydrochloric acid, for example, is usually used. However, acid concentrations outside these concentration ranges can also be employed. The diazotization agents used are the compounds customary for this reaction, such as, for example, alkali metal nitrites or nitrosylsulfuric acid. Preferably, sodium nitrite is employed in the form of an aqueous solution.
The diazotization temperature and duration of the diazotization correspond to the customary conditions for such reactions and are in general between -5.degree. C. and about 25.degree. C. on the one hand an

REFERENCES:
patent: 3903178 (1975-09-01), Nakamura et al.
Sandler et al., "Organic Functional Group Preparations", Academic Press, New York, 1968, pp. 81-82.

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