Process for the preparation of diphenyl ether compounds

Details Process for the preparation of diphenyl ether compounds Process for the preparation of diphenyl ether compounds

2002-06-20

2004-09-14

Raymond, Richard L. (Department: 1624)

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

Organic compounds

Amino nitrogen containing

C562S438000

Reexamination Certificate

active

06790991

ABSTRACT:

The present invention relates to a process for the production of diphenyl ether compounds which are useful as herbicides. In particular, it relates to a process for obtaining herbicidal diphenyl ether products on an industrial scale.
The problems associated with producing diphenyl ether herbicides on an industrial scale are discussed in WO 97/10200 and WO 97/10199 in which there are disclosed processes for making compounds of formula
wherein R
1
is hydrogen or C
1
-C
6
alkyl, C
2
-C
6
alkenyl or C
2
-C
6
alkynyl (any of which may optionally be substituted with one or more substituents selected from halogen and OH) or COOH, COH, COOR
4
, COR
6
, CONR
4
R
5
or CONHSO
2
R
4
; R
4
and R
5
are each independently hydrogen or C
1
-C
4
alkyl optionally substituted with one or more halogen atoms; R
6
is a halogen atom or a group R
4
; R
2
is hydrogen or halo; R
3
is C
1
-C
4
alkyl, C
2
-C
4
alkenyl or C
2
-C
4
alkynyl, any of which may optionally be substituted with one or more halogen atoms, or halo or, where appropriate, a salt thereof. More especially the disclosures deal with the commercially known herbicides 5-(2-chloro-&agr;,&agr;,&agr;-trifluoro-4-tolyloxy)-2-nitrobenzoic acid (acifluorfen) and 5-(2-chloro-&agr;,&agr;,&agr;-trifluoro-4-tolyloxy)-N-methanesulphonyl-2-nitrobenzamide (fomesafen).
A preferred method of making fomesafen on an industrial scale is via acifluorfen which is made from 5-(2-chloro-&agr;,&agr;,&agr;-trifluoro-4-tolyloxy)-benzoic acid (CTTBA). This compound is produced by oxidation of the corresponding tolyl compound which is in turn obtained from the condensation of 3-hydroxybenzoic acid and 3,4-dichlorobenzotrifluoride.
Because the final product (fomesafen) is required in sufficient purity to meet strict product registration standards the process normally also involves one or more purification procedures.
The synthesis of acifluorfen and its conversion to fomesafen has been the subject of intensive research in an effort to improve one or more of the process steps. Thus for example in WO97/10200 there is disclosed a purification method for acifluorfen or fomesafen, while a set of improved nitration conditions is disclosed in WO97/10199. Another set of possible nitration conditions is disclosed in WO 98/19978. However no processes are known which can perform most or all of the above reactions using a single solvent. This is undoubtedly because the range of reaction conditions is very demanding and it is not at all apparent if a process using a single common solvent is possible.
The applicants have now devised a single common solvent process in which acifluorfen is converted to purified fomesafen. There is therefore provided a process for producing fomesafen from acifluorfen comprising the steps of
converting acifluorfen to its acid chloride
coupling the acid chloride so formed with methanesulphonamide (MSAM) to form crude fomesafen and
purifying the crude fomesafen characterised in that each of the steps is carried out in a single common solvent.
The product of each step may be isolated at the end of the step or, more preferably, the steps may be telescoped together so that there is no isolation until the purified fomesafen end product is obtained.
Suitable solvents are haloalkanes (such as 1,2-dichloroethane or tetrachloroethylene), halobenzenes (such as fluorobenzene, chlorobenzene and dichlorobenzenes), alkoxybenzenes (such as anisole or phenetole), haloalkylbenzenes (such as benzotrifluoride), and esters (such as ethyl acetate or butyl acetate). Preferred solvents are chloroalkanes especially 1,2-dichloroethane (or ethylene dichloride or EDC).
In a further aspect of the invention the acifluorfen is formed by nitration of
CTTBA in the same solvent used to convert acifluorfen to fomesafen, the solvent being a chloroalkane, especially EDC.
In yet a further aspect of the invention the CTTBA is formed by the oxidation of the corresponding toluene and the CTTBA is extracted from the reaction mass using the same solvent that is used to convert acifluorfen to fomesafen, the solvent being a chloroalkane, especially EDC.
The CTTBA is suitably generated by the oxidation of the corresponding toluene using oxygen together with a catalyst (such as a cobalt or vanadium salt), at a temperature of 70° C. to 150° C.
The product of the extraction step and/or the nitration step may be isolated at the end of the step or, more preferably, the steps may be telescoped together so that there is no isolation of product at the end of each of the extraction and nitration stages.
In one suitable method for the nitration reaction, the nitrating agent may be nitric acid or a mixture of nitric and sulphuric acids although other types of nitrating agent may also be used. It is also advantageous to conduct the reaction in the presence of acetic anhydride and, in this case, it is preferred that the molar ratio of acetic anhydride to CTTBA is from about 1:1 to 3:1. The reaction temperature may be from about −15° to 15° C., more usually from about −10° to 10° C. It is advantageous to add the nitrating agent, over a period of time from 5 to 15 hours, or, more preferably, 6 to 12 hours. Most preferably the reaction is carried out using a mixture of nitric and sulphuric acids at 0-5° C. The resultant product solution is water washed, to remove mineral acid and acetic acid then topped to remove residual water.
The conversion of acifluorfen to the acid chloride may be carried out by conventional methods, for example as set out in EP-A-0003416. It is preferred to perform the reaction with a suitable chlorinating agent such as thionyl chloride or phosgene in the presence of a catalyst such as triethylamine or dimethylformamide at temperature of 60 to 80° C., preferably 70° C. The acid gases (SO
2
and HCl) may be removed, together with excess of the chlorinating agent by addition and distillative removal of further organic solvent.
The acid chloride may then be reacted with methane sulphonamide to give fomesafen. This step may suitably be carried out by conventional methods, for example as set out in EP-A-0003416. In a preferred process the acid chloride is coupled with MSAM using an excess of base such as potassium carbonate at 60 to 80° C., preferably at 80° C. The inorganic by-products and excess MSAM are removed by washing with water. The final product solution is topped to remove water. The organic solvent level, in the final product solution, is adjusted by topping off excess or by further additions and the product is then isolated by cooling to −10 to 30° C. preferably 0° C.
A particular advantage in the use of EDC in the coupling reaction with MSAM is that the boiling point of the solvent is the upper temperature limit for process operation and thermal decomposition of the acid chloride during the reaction is avoided.
The product may then be purified using a chloroalkane solvent. The purification may suitably involve filtration and washing with cold solvent or further recrystallisation from the solvent.
Using the process invention, it is possible to obtain fomesafen of desired quality in good yield enabling the industrial operation of the process with a single solvent.
The invention will now be further illustrated with reference to the following examples.


REFERENCES:
patent: 4285723 (1981-08-01), Cartwright et al.
patent: 4405805 (1983-09-01), Giacobbe et al.
patent: 4874846 (1989-10-01), Chene
patent: 5792888 (1998-08-01), Subramanian
patent: 6028219 (2000-02-01), Atherton et al.
patent: 274 194 (1988-07-01), None
patent: 2103214 (1983-02-01), None
patent: 2140417 (1984-11-01), None
patent: 97/10199 (1997-03-01), None
Xu Jin, “An Exploratory Study of the Synthesis of the Effective Herbicide Fomesafen” Shanghai Huagong, vol. 22(2), pp. 18 22 (1997) Chinese-Language and English Translation.*
Vulakh, E. L. et al, “Use of Phosphorous Oxychloride for the Synthesis of Aromatic Carboxylic Acid Chlorides” Khimicheskaya Promyshlennost (Moscow, Russian Federation), vol. 1, pp. 16-19 (1979)—Caplus Abstract.

Affiliated with

Also associated with

Rating

Process for the preparation of diphenyl ether compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for the preparation of diphenyl ether compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the preparation of diphenyl ether compounds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3188650