Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-12-30
2001-04-10
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06215022
ABSTRACT:
The present invention relates to a novel process for preparing 3-hydroxy-2-methylbenzoic acid.
It is known that 3-hydroxy-2-methylbenzoic acid is obtained by reacting sodium 2-naphthylamine-4,8-disulfonate with 50% strength NaOH at from 250 to 260° C. However, the yield is only about 10% (J. Chem. Soc. 95, 1883 (1909), see also J. Amer. Chem. Soc. 58, 749 (1936)). J. Chem. Soc. 2773 (1961) describes an improved yield of 76% when an initial pressure of 40 bar of nitrogen is used. However, the product obtained by this process is heavily contaminated; the actual yield is therefore significantly lower.
It was the object of the present invention to provide an improved, simple and industrially feasible process for preparing 3-hydroxy-2-methylbenzoic acid.
The present invention provides a process for preparing 3-hydroxy-2methylbenzoic acid of the formula (I)
which comprises reacting disodium 3-amino-1,5-naphthalenedisulfonic acid of the formula (II)
with 10 to 20 equivalents of potassium hydroxide and less than 55% by weight of water, based on the amount of potassium hydroxide, at temperatures from 250 to 300° C. and under a pressure of at least 100 bar.
Surprisingly, the process according to the invention results in higher yields of 3-hydroxy-2-methylbenzoic acid than the known processes. In addition, the product is obtained in such a high purity that it can be used without any further purification for further reactions.
The process according to the invention can be represented by the following formula scheme:
In general, 10 to 20 equivalents of potassium hydroxide, preferably 14 to 18, particularly preferably 15 equivalents, are used, based on the disulfonic acid of the formula (I) employed.
The amount of water used is generally less than 55% by weight, based on the amount of KOH, and preference is given to using from 15 to 50% by weight of water.
The reaction temperature is generally from 250 to 300° C., preferably from 260 to 290° C.
The reaction pressure is generally between 30 and 160 bar.
The reaction pressure is preferably at least 100 bar, preferably between 100 and 160 bar.
In general, the process according to the invention is carried out by initially charging the compound of the formula (I) in an autoclave with KOH and water, and applying the desired pressure (for example 40 bar) using nitrogen. The mixture is then heated to the reaction temperature, resulting in a reaction pressure of preferably at least 100 bar.
Work-up is generally carried out such that the reaction mixture is washed out of the autoclave using water and adjusted to an approximately neutral pH using an acid (preferably an inorganic acid, such as hydrochloric acid).
The mixture is then treated with montmorillonite, kieselguhr (for example (Celite®), activated carbon (for example Norite®), bleaching earth (for example Tonsil®) or bone charcoal, stirred and filtered. The mixture is then extracted with an organic solvent (for example methyl acetate, ethyl acetate, methylene chloride or diethyl ether) and the aqueous phase is adjusted to a pH between 1 and 4, preferably 2 and 3, using an acid (cf. above). The aqueous phase is then reextracted (cf. above), and the reaction product is isolated from the combined organic phases in a customary manner (compare also the working example).
3-Hydroxy-2-methylbenzoic acid is an important intermediate for the synthesis of insecticidally active compounds (see, for example, EP-A-0 602 794, EP-A-0 639 559).
REFERENCES:
patent: 5530028 (1996-06-01), Lidert et al.
patent: 639 559 (1995-02-01), None
J. Chem. Soc., (Month unavailable) 1909, pp. 1883 to 1889, Baudisch et al, The Reduction of of 6-Hydroxy-o-toluic Acid.
Amer. Chem. Soc. vol., 58, May 1936, pp. 749 to 753, Fieser et al, The Structure of Anthracene.
Bayer Aktiengesellschaft
Eyl Diderico van
Gil Joseph C.
Killos Paul J.
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