Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-10-17
2002-07-16
Morris, Patricia L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06420564
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a novel process for preparing a tribromomethylsulfonylpyridine using a methylthiopyridine as an intermediate, and a novel process for preparing a methylthiopyridine using a halogenated pyridine as a starting material.
Tribromomethylsulfonylpyridines are useful compounds in that, if used as a constituent component of a photosensitive resin composition, a tribromomethylsulfonylpyridine will generate halogen radicals upon irradiation with active rays such as visible rays, ultraviolet rays or a laser beam, thus producing a hydrogen halide, and improving the adhesion between the photosensitive resin and a substrate.
BACKGROUND ART
An example of a process for preparing a tribromomethylsulfonylpyridine is, as shown in the undermentioned equation, to use a pyridinethiol as a starting material, produce a methylthiopyridine by thiomethylating using a methylating agent such as a methyl halide, next oxidize to produce a methylsulfonylpyridine, and then brominate to obtain the tribromomethylsulfonylpyridine.
The pyridinethiol as a starting material is generally obtained by reacting a halide compound and thiourea in an alcohol, but there is a problem that the reaction yield is low. Moreover, known methods of oxidizing a methylthio compound to synthesize a methylsulfone include a method using any of various oxidizing agents such as hydrogen peroxide in the presence of an acid catalyst, and a method using any of various oxides in the presence of an acid catalyst in an acetic acid solvent. However, if a pyridine derivative is oxidized in the presence of an acid catalyst using such a method, then the nitrogen atom in the pyridine ring will also be oxidized, resulting in generation of an N-oxide as a by-product. Such N-oxides are hazardous, being prone to explosion and the like, which creates a large problem in the industrial manufacture of sulfones.
Moreover, a method disclosed in J. Org. Chem. (Vol. 51, page 3369, 1986) is known as a method of obtaining a tribromomethylsulfonylpyridine by brominating a methylsulfonylpyridine. In this method, sodium hypobromite is used as the brominating agent, the methylsulfonylpyridine is dissolved homogeneously in a mixed dioxane-water solvent, and reaction is carried out at room temperature under strongly alkaline conditions, thus obtaining the tribromomethylsulfonylpyridine; 24 hours is required for the reaction. However, in this method, the amounts used of the alkali and the sodium hypobromite are extremely large, being 21.5 mol and 6 mol respectively per mol of the methylsulfonylpyridine as a starting material. In particular, the sodium hypobromite must be used in an amount double the theoretical amount (3 mol per mol of the methylsulfonylpyridine). Moreover, the required reaction time of 24 hours is long, and the tribromomethylsulfonylpyridine obtained has poor purity, resulting in recrystallization being necessary before use. The method is thus not particularly good from an industrial point of view.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a process for preparing a tribromomethylsulfonylpyridine that is industrially advantageous, allowing the tribromomethylsulfonylpyridine to be obtained easily, in a short time, and at a high yield and a high purity.
Another object of the present invention is to provide a novel process for preparing a methylthiopyridine, which is an intermediate in the preparation of a tribromomethylsulfonylpyridine.
The inventors of the present invention carried out assiduous studies to attain the above objects, and as a result discovered that by reacting a methylthiopyridine and a hypobromite in the presence of a base and water in a heterogeneous system, oxidation and bromination are carried out simultaneously, and hence a tribromomethylsulfonylpyridine can be obtained through a single stage reaction.
Moreover, the inventors of the present invention also discovered that by reacting a halogenated pyridine and an alkali metal salt of methanethiol in the presence of a base and water in a heterogeneous system, a methylthiopyridine can be obtained easily.
Furthermore, the inventors of the present invention also discovered that by continuing on to react a methylthiopyridine produced through the above reaction with a hypobromite in the presence of a base and water in a heterogeneous system, a tribromomethylsulfonylpyridine can be prepared using a halogenated pyridine as a starting material through a series of reactions in a single vessel.
The present invention thus provides processes for preparing a tribromomethylsulfonylpyridine and processes for preparing a methylthiopyridine as follows.
1. A process for preparing a tribromomethylsulfonylpyridine, which comprises reacting a methylthiopyridine and a hypobromite in the presence of a base and water in a heterogeneous system.
2. The process for preparing a tribromomethylsulfonylpyridine according to 1 above, wherein the hypobromite is sodium hypobromite.
3. The process for preparing a tribromomethylsulfonylpyridine according to 1 or 2 above, wherein the base is a hydroxide of an alkali metal.
4. A process for preparing a methylthiopyridine, which comprises reacting a halogenated pyridine and an alkali metal salt of methanethiol in the presence of a base and water in a heterogeneous system.
5. The process for preparing a methylthiopyridine according to 4 above, wherein the alkali metal salt of methanethiol is sodium methanethiolate.
6. The process for preparing a methylthiopyridine according to 4 or 5 above, wherein reaction is carried out in the presence of a phase transfer catalyst.
7. The process for preparing a methylthiopyridine according to 6 above, wherein the phase transfer catalyst is a quaternary ammonium salt or a quaternary phosphonium salt.
8. A process for preparing a tribromomethylsulfonylpyridine, which comprises reacting a halogenated pyridine and an alkali metal salt of methanethiol in the presence of a base and water in a heterogeneous system to obtain a methylthiopyridine, and then reacting the methylthiopyridine and a hypobromite in the presence of a base and water in a heterogeneous system.
9. The process for preparing a tribromomethylsulfonylpyridine according to 8 above, wherein the halogenated pyridine is 2-chloropyridine.
Preparation of Methylthiopyridine
A process for preparing a methylthiopyridine according to the present invention is characterized by reacting a halogenated pyridine and an alkali metal salt of methanethiol in the presence of a base and water in a heterogeneous system.
There are no particular limitations on the halogenated pyridine used in the present invention, but examples include 2-halogenated pyridines, 3-halogenated pyridines and 4-halogenated pyridines, with specific examples thereof including 2-chloropyridine, 3-chloropyridine, 4-chloropyridine, 2-bromopyridine, 3-bromopyridine and 4-bromopyridine. Out of these, 2-chloropyridine is preferably used.
There are no particular limitations on the alkali metal salt of methanethiol used in the present invention, but examples include the potassium salt of methanethiol (potassium methanethiolate) and the sodium salt of methanethiol (sodium methanethiolate). Of these, from an economic standpoint, sodium methanethiolate is preferably used. The amount used is generally in a range of 1 to 3 mol, preferably 1 to 2 mol, per mol of the halogenated pyridine. If the amount used of the alkali metal salt of methanethiol is less than 1 mol, then the amount of unreacted halogenated pyridine will become large, whereas it is economically disadvantageous to use an amount greater than 3 mol. since then effects commensurate with the amount used will not be obtained.
Examples of the base used in the present invention are alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Of these, from an economic standpoint, sodium hydroxide is preferably used. The amount used is generally in a range of 0.05 to 2 mol, preferably 0.1 to 1 mol, per mol of the halogenated pyridine. If the amount used of the base is less than 0.05 mol, t
Fujisawa Eiji
Hata Hiroyuki
Knobbe Martens Olson and Bear LLP
Morris Patricia L.
Sumitomo Seika Chemicals Co. Ltd.
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