Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1993-03-23
1994-03-08
Lone, Werren B.
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568713, C07C20520
Patent
active
052929671
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
The present invention relates to an improved process for the preparation of 2,3-difluoro-6-nitrophenol in good yields and high selectivity. The compound is a useful precursor for the preparation of quinolonecarboxylic acid antibiotics.
BACKGROUND OF THE INVENTION
It was hitherto only possible to are the compound in question by reaction of sodium hydroxide with 2,3,4-trifluoronitrobenzene at 25.degree. C., subsequent acidification until the product precipitated and filtering off thereof according to the equation ##STR1## residual isomer contents of 2,3-difluoro-4-nitrophenol (3) occurring.
These isomer contents could be reduced by extraction of the product with non-halohydrocarbons (Ihara Chem. Ind. Co., JP 62/181,241 A2), while in the extraction with halohydrocarbons only a product of about 90 percent purity was obtained.
The addition of polar aprotic solvents proved essential for carrying out the reaction in this method because of the low solubility of 2,3,4-trifluoronitrobenzene (1) and the alkali metal salts of (2) in aqueous alkali metal hydroxide solution (Daiichi Seiyaku Co. Ltd., JP 61/246,150, 246,151, 246,171, 246,188, JP 58/135,840).
The removal of the solvent added (as a rule dimethyl sulfoxide) had to be carried out by extraction from alkaline solution by means of a further organic solvent (chloroform). After acidification of the aqueous phase removed, isolation of the product (2) was likewise carried out by extraction with chloroform (Daiichi Seiyaku Co. Ltd., JP 61/246,150, 1.11.86).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
There was therefore a need for a better process in which addition of solubilizers and extraction with organic solvents is unnecessary.
As a solution to the object thus set, it has now been found that isomerically pure 2,3-difluoro-6-nitrophenol can be advantageously prepared in good yields and high selectivity by reacting 2,3,4-trifluoronitrobenzene with aqueous alkali metal hydroxide solution or alkaline earth metal hydroxide solution or suspension, preferably potassium hydroxide solution, in the absence of solvents at temperatures of about 20.degree. C. to about 100.degree. C., preferably of about 30.degree. C. to about 60.degree. C., adjusting the reaction mixture to a pH of about 1 to about 6, preferably of about 2.5 to about 4.5, particularly preferably of about 1.5 to about 3.0, by addition of acid, steam-distilling the resulting product by passing steam into the reaction mixture and isolating the 2,3-difluoro-6-nitrophenol from the distillate after cooling.
It is advantageous to meter the aqueous alkali metal hydroxide solution or alkaline earth metal hydroxide solution or suspension slowly into an initially introduced mixture of water and 2,3,4-trifluoronitrobenzene. A selectivity of 95 to 96% is achieved in this way and the stirrability of the solution is retained.
The isomerically pure 2,3-difluoro-6-nitrophenol is isolated in a yield of 86% of theory by the process according to the invention, no organic solvent being used even in the isolation of the compound mentioned.
Examples of aqueous alkali metal hydroxide solutions which can be used are lithium hydroxide, sodium hydroxide or potassium hydroxide solutions or mixtures thereof, preferably potassium hydroxide solutions, and examples of alkaline earth metal hydroxide solutions or suspensions are calcium hydroxide, strontium hydroxide or barium hydroxide solutions or suspensions or mixtures thereof, preferably calcium hydroxide solutions or suspensions. These solutions are advantageously employed in the form of about 10 to about 80 percent strength solutions or suspensions, preferably of about 30 to about 50 percent strength solutions or suspensions.
Acidification can be carried out using the customary non-oxidizing mineral acids, such as, for example, dilute sulfuric acid, phosphoric acid, hydrochloric acid, hydrobromic acid or hydriodic acid, as well as with sufficiently strong organic acids, such as, for example, formic acid or acetic acid.
The produc
REFERENCES:
patent: 4310711 (1982-01-01), Muller et al.
patent: 4596893 (1986-06-01), Eifert et al.
patent: 5227535 (1993-07-01), Pfirmann et al.
Hackenbruch Joachim
Papenfuhs Theodor
Pfirmann Ralf
Hoechst Aktiengesellschaft
Lone Werren B.
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