WO1990006302A1

WO1990006302A1 - Preparation of 2-halo-4-alkylsulfonylbenzoic acid

Info

Publication number: WO1990006302A1
Application number: PCT/US1989/005057
Authority: WO
Inventors: Peter K. Wehrenberg
Original assignee: Ici Americas Inc.
Priority date: 1988-11-25
Filing date: 1989-11-17
Publication date: 1990-06-14
Also published as: KR900701746A

Abstract

A process for the preparation of a 2-halo-4-(alkylsulfonyl)benzoic acid of structural formula (I), wherein halo is chloro or bromo and R is C1-C4 alkyl by the oxidation of 2-halo-4-(alkylsulfonyl)toluene under acid conditions.

Description

PREPARATION OF 2-HALO-4-ALKYLSULFONYLBENZOIC ACID

Background of the Invention

This invention relates to a process for the preparation of 2-halo-4-alkylsulfonylbenzoic acids.

2-Halo -4-alkylsulfonylbenzoic acids are intermediates useful for the preparation of certain 2-(2-halo-4-alky lsulfonylbenzoyl)-1,3-cyclo- hexanedione herbicides. 2-Halo-4-alky lsulfonylbenzoic acid is converted to its acid chloride and it is reacted with certain 1,3-cyclohexaendiones according to the process of U.S. Pat. 4,695,673.

Summary of the Invention

A process for the preparation of 2-halo-4-alkylsulfonylbenzoic acids is represented by the following reaction: o

wherein halo is chloro or bramo, preferably chloro; R is C₁-C₄ alkyl, preferably methyl, ethyl or n-propyl; and [0] is an oxidizing agent.

Detailed Description of the Invention

The reaction product of the process of this invention has the structural formula

wherein halo is chloro or bromo, preferably chloro and R is C₁ C₄ alkyl, preferably methyl, ethyl or n-propyl, most preferably methyl.

The desired reaction product is obtained by the oxidation of a compound of the structural formula

wherein halo and R are as defined.

The oxidation oust be run under acid conditions to insure that only the methyl group attached to the phenyl ring undergoes oxidation. If the oxidation is run under neutral or basic conditions, then both the methyl group attached to the ring and the alkyl group of the alkylsulfonyl moiety will undergo oxidation,.

The oxidation of only the ring methyl group when done under acid conditions is quite surprising and unexpected.

Many oxidizing agents can be used as long as the oxidizing step can be carried out under acid conditions. Sxamples of oxidizing agents are nitric acid, a cobalt acetate/soditsn bramide/oxygen/aoetic acid mix- ture or a vandium pentoxide/aqueous sulfuric acid mixture.

Preferably the oxidizing agent is concentrated nitric acid.

The following example teaches the process of this invention.

EXAMPLE I

Preparation of 2-Chloro-4-(methanesulfonyl)benzoic acid

A 25 milliliter (mL), three-neck, round-bottom flask was fitted with a glass thermowell, a narrow glass tube (sufficient to allow passage of a Teflon needle) topped by a septan, and a short path still head with a thermometer, 50 mL receiver, and nitrogen bubbler. A syringe was fitted with a Teflon needle, charged with 70% nitric acid and mounted in a syringe pump. The Teflon needle was passed through the septan, beyond the end of the glass tube, just into the 25 mL flask. A Love^● temperature controller (Model 49) connected to a thermocouple in the themmowell was used to control the temperature of an oil bath. Nitrogen was passed at a very slow rate via a needle through the septan to protect it from corrosive vapors. The 25 mL flask was charged with 5.0 grans (g) of 2-chloro- 4-(methanesulfonyl)toluene [24.5 millimoles (mmol)] and the contents were stirred magnetically and heated with an oil bath to 180ºC to give a pale yellow melt. The nitric cid was added at a rate of 0.087 mL /min. The pot temperature varied from 176-186ºC. The distillate, boiling point 98 -113ºC, was collected. The reaction was followed periodically by high pressure liquid chromatography (hplc). A 20 microliter (uL) aliquot was diluted with 1 mL CB₃CN and 1 mL one normal (1N) HCl, 10 uL of this was injected on a 25 x 0.46 cm Zorbax ODS column programed over 5 minutes from 70% of a 1% B₃PO₄ solution -1- 30% CH₃CN to 100% CB₃CN, flow =

3.0 ml/min, UV = 225 nm (5 t_R = 3.97 min, unknown t_R= 3.51 min, 6 t_R = 2.02 min). After 86 minutes, hplc analysis indicated that the amount of 2-chloro-4-(methanesulfonyl)toluene present (4 area percent) was less than the amount of developing inpurities, and the reaction was stopped (8.0 mL of 70% HNO₃ added, 124 mmol). After cooling, the reaction was stirred with 35 mL of water and 35 mL diethyl ether, adding 10% sodium hydroxide (NaOH) as needed to dissolve all solids (final pB = 13). The aqueous phase was separated and acidified to pB 1 with concentrated BCl. The resulting precipitate was filtered and dried to give 4.05 g of solid which assayed 94.3 weight percent pure 2-chloro-4-(methanesulfonyl)benzoic acid. The distillate was diluted with 5 mL water and extracted with 3 x 15 mL diethyl ether. The ether was stripped to 0.88 g of yellow oil which assayed as 16.4 weight percent 2-chloro-4-(methanesulfonyl)toluene and 84 weight percent of the desired product, 2-chloro-4-(methanesulfonyl)benzoic acid. Thus, the corrected yield based on unrecovered 2-chloro-4-(methane- sulfonyl)toluene was 81%.

Claims

I CLAIM:

1. A process for the preparation of a 2-halo-4-(alkylsulfonyl)- benzoic acid of the structural formula

wherein halo is chloro or bromo and R is C₁-C₄ alkyl by the oxidation of 2-halo-4-(alkylsulfonyl)toluene under acid conditions.

2. The process of Claim 1 wherein halo is chloro and R is methyl.

3. The process of Claim 2 wherein the oxidation is by nitric acid.