Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Patent
1997-02-21
1997-11-04
Jordan, Charles T.
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C07C29110
Patent
active
H00016969
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention pertains to an improved process for making sulfonyl isocyanates from the corresponding sulfonamides and phosgene. Sulfonyl isocyanates are useful intermediates in the preparation of fine chemicals such as pesticides, including sulfonylurea herbicides, and pharmaceuticals.
U.S. Pat. No. 4,238,621 discloses the preparation of sulfonyl isocyanates from a reaction mixture of the corresponding sulfonamides and phosgene wherein the sulfonamide is generally present in molar excess in the reaction mixture relative to phosgene. In the present invention, the phosgene is always in molar excess relative to sulfonamide, thereby providing better yield and shorter reaction times.
SUMMARY OF THE INVENTION
The present invention pertains to an improved process for the preparation of sulfonyl isocyanates of Formula I comprising adding the corresponding sulfonamide of Formula II in small increments or continuously, perferably continuously, to a reaction mixture comprising inert solvent, phosgene and catalyst according to equation 1 ##STR1## such that there is in the reaction mixture an excess of phosgene relative to sulfonamide.
The most preferred sulfonyl isocyanate is methyl 2-(isocyanatosulfonyl)benzoate.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, sulfonamide II is fed to a reaction mixture of inert solvent, catalyst and phosgene wherein it is converted to isocyanate I. Elevated temperatures, typically in the range of 100.degree. to 200.degree. C., preferably 120.degree. to 135.degree. C., are usually required to make the reaction proceed at practical rates. Pressure can be ambient up to about 2 atmospheres (about 200 kPa). Phosgene is replenished to the reaction mixture so that at any point during the reaction there is always present a molar excess of phosgene (hereinafter referred to as "phosgene-rich") relative to sulfonamide; preferably there is at least 2% by weight of phosgene in the reaction mixture, more preferably at least 5%. Sulfonamide can be fed to the reaction mixture in small increments or continuously, preferably continuously, and can be in the form of a slurry or solution in solvent, preferably as concentrated as possible. The slurry can be preheated before admission to the reactor.
Solvent can be any inert solvent with a boiling point at or above the desired reaction temperature; examples include xylene, chlorobenzene, mesitylene, toluene, pentachloroethane and octane.
Catalysts include (U.S. Pat. No. 4,238,621) carbaryl isocyanates such as (DABCO). The full charge of catalyst can be added to the initial reaction mixture, or added incrementally or continuously during the course of reaction. Feeding the catalyst over the course of the reaction can reduce the total amount of catalyst needed and reduce side reactions.
Catalysts also include sulfonyl isocyanates (Res. Discl. (1983) 23210, 261), preferably the product sulfonyl isofonyl isocyanate. The sulfonyl isocyanate need not be isolated, and a small portion of the product reaction mixture (referred to as a "heel") from a previous batch can be employed as catalyst in a subsequent batch.
The reaction of sulfonamide and phosgene is very rapid and exothermic, and HCl is generated as a byproduct. It is preferable to drive the HCl out of the reaction mixture as rapidly as possible, preferably by maintaining vigorous reflux of phosgene, so that side-reactions caused by the HCl, and the resulting yield losses, are minimized. The HCl off-gas will typically be captured by scrubbers so as to avoid release to the environment; the phosgene can be condensed and returned to the reaction mixture. The HCl generation can be used to monitor the course of the reaction and can also be used to maintain an appropriate sulfonamide feed rate and concentration so that the reaction is kept under control and reaction times are as short as possible.
Once the reaction is complete, excess phosgene and dissolved HCl can be removed from the mixture by standard methods such as distillation. The sulfony
Adjei David Akueteh
Blaisdell Charles T.
Chelliah Meena
E. I. Du Pont de Nemours and Company
Jordan Charles T.
Katz Elliott A.
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