BACKGROUND OF THE INVENTION
The present invention relates to a novel process for producing
anhydrous alkali sulfides which are useful as synthetic intermediates of sulfur-containing
Since sodium polysulfide such as sodium tetrasulfide which
is produced by combination of sodium hydrosulfide or sodium sulfide and sulfur (Inorganic
and Theoretical Chemistry Vol. II, Longmans Green and Co., Ltd., (1961), p991) have
high water absorption properties, it is not easy to obtain anhydrides thereof. A
complex drying step is necessary in order to dehydrate these substances, which lowers
the yield of the object substance.
Much energy is required in order to obtain anhydrous sulfides
from hydrates of sulfides. In addition, since alkali polysulfides such as sodium
disulfide and sodium tetrasulfide are viscous liquids under drying conditions, for
example, at high temperatures of 120°to 130°C, it is difficult to treat
European Patent Publication No. 361,998
Japanese Laid-open Patent Publication No. 228588/1995
As another method of obtaining sodium sulfide, there is
a process wherein sodium alkoxide is allowed to react with hydrogen sulfide (
United States Patent No. 5,466,848
Japanese Laid-open Patent Publication No. 228588/1995
). Good anhydrous sulfide is obtained by this process. On the other hand,
since hydrogensulfide is toxic, it is necessary to treat it carefully, and an extra
step is required in order to avoid poisoning.
Furthermore, Inorganic and Theoretical Chemistry, Vol.
II, Longmans Green and Co., Ltd., (1961), p981discloses a process wherein metallic
sodium is allowed to react with sulfur in liquid ammonia or xylene. However, the
reaction using liquid ammonia is carried out at ultra-low temperatures, and treatment
of ammonia is also troublesome. Since the reaction in an aromatic solvent such as
xylene proceeds explosively at about 98°C, which is a melting point of the
metallic sodium, the reaction is not practical.
J. Inorg. Nucl. Chem., 1977, vol. 39, pages 1761-1766, Rauh
et al. disclose a preparation method of lithium polysulfide by the direct
reaction of sulfur with Li metal in an aprotic solvent.
US patent 5,039,506
relates to a method for preparing sodium sulfide from sodium and sulfur
under protective gas, without requiring a reaction medium.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method
of obtaining anhydrous alkali sulfides which are useful as synthetic intermediates
of sulfur-containing organosilicon compounds in a simple and safe manner without
treatment at ultra-low temperatures, high temperatures or high pressure in view
of the above-mentioned problems of the prior arts.
As a result of studies to achieve the above-mentioned objects,
the inventors found the following process for producing anhydrous alkali sulfides.
DETAILED DESCRIPTION OF THE INVENTION
The process according to the present invention comprises reacting sulfur with metallic
sodium or metallic potassium in the presence of an aprotic solvent.
In the process, sulfur is preferably anhydrous and preferably
takes the form of powder or flake for high solubility in the solvent used. The smaller
the particle diameter of sulfur having such a form, the higher does sulfur exhibit
reaction efficency. It is preferable to select sulfur having appropriate particle
diameter with respect to the solvent used in order to control the reaction. Since
the reaction is exothermic, sulfur having large particle diameter is sometimes preferable.
The alkali metal is metallic sodium or metallic potassium
and preferably metallic sodium.
In the process it is preferable to carry out the reaction
under an inert gas atmosphere such as a nitrogen gas or argon gas atmosphere dried
The aprotic solvent can be a solvent which does not have
an active hydrogen atom which reacts with the alkali metal, and it is preferable
to use a solvent dried to the utmost in order to prevent hydrolysis of alkoxide
due to water. Examples of the aprotic solvent which can suitably be used are aromatic
hydrocarbons such as benzene, toluene and xylene, and ether solvents such as tetrahydropyran,
dioxane and dibutyl ether. In particular, among these ethers, using a solvent which
solvates the starting material or the object substance, the reaction is promoted.
In this case, when crown ether or the like is further added to the solvent as a
reaction accelerator, the reaction is much more promoted.
The preferred aprotic solvent in the process is a solvent
which can solvate metallic sodium or metallic potassium, ion or dissolve alkali
sulfide. The solvent which can solvate the alkali metal ion is a solvent which can
solvate the alkali metal ion by formation of chelate with the ion. The reaction
of sulfur with the alkali metal is promoted by using the solvent.
The solvents which can dissolve the alkali sulfide in the
present specification can be not only the solvents which can always and perfectly
dissolve the alkali sulfide which forms in the reaction system by the process for
production, but also the solvents can dissolve the alkali sulfide deposited in the
reaction system in the solvent successively and promptly under the reaction condition.
So far as the solvents can dissolve the alkali sulfide of necessary and sufficient
amount required for the progress of the reaction, the alkali sulfide can deposit
in the reaction system.
Examples of such a solvent are tetrahydropyran, crown ether,
and alkyl ethers of polyhydroxy alcohols such as dimethoxyethane (DME, ethylene
glycol dimethyl ether), diethylene glycol dimethyl ether, triethylene glycol dimethyl
ether, diethylene glycol dibutyl ether and propylene glycol dimethyl ether. It is
preferable to use a solvent dried to the utmost in order to prevent hydrolysis of
alkoxide due to water. In general, a low boiling point solvent requires less energy
to be recovered. However, it is particularly preferable to use dimethoxyethane,
etc. as the solvent since a reaction temperature of the latter step by the halogenoalkoxysilane
[I] is usually 60° to 100°C.
The anhydrous alkali sulfide which is the reaction product
obtained by the reaction of sulfur and the alkali metal in the aprotic solvent can
be taken out of the reaction liquid and used later, or the reaction liquid containing
it can be used in the later step as it is.
The alkali sulfide is represented by the general formula
(AIM)mSn (wherein AIM is an alkali metal, S is a sulfur atom, m is an integral number
of 2 or 4, and n is an integral number of 1 to 9). However, some of the substance
formed actually has composition distribution in a certain range. Examples of the
alkali sulfide are sodium sulfide (Na2S), sodium disulfide (Na2S2),
sodium trisulfide (Na2S3), sodium tetrasulfide (Na2S4),
potassium sulfide (K2S), potassium trisulfide (K2S3),
potassium pentasulfide (K2S5), potassium hexasulfide (K2S6),
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present process is specifically described hereinafter
by giving examples of the present invention. Unless the present invention deviates
from the spirit thereof, the present invention is not limited to these examples.
A three-necked flask (200 ml) equipped with a condenser,
a thermometer and a stirrer was first charged with 60 ml of dimethoxyethane (DME,
water content : 1 ppm or lower) treated with a molecular sieve as an aprotic solvent
while making dried nitrogen gas flow. To DME was added 6.4 g (0.2 mol) of powdered
sulfur of 200 mesh, and then 4.6 g (0.2 mol) of metallic sodium was introduced into
the flask at room temperature. Raising the temperature of the mixed liquid to about
65°C, a reaction of metallic sodium with sulfur began, and the mixed liquid
became a uniform solution in about 15 minutes. Stirring was further continued at
70°C for 45 minutes to form anhydrous sodium sulfide.
The same three-necked flask (200 ml) as used in Example
1 was first charged with 60 ml of the same treated DME as used in Example 1 as an
aprotic solvent while making dried nitrogen gas flow, and charged with 3.2 g (0.1
mol) of powdered sulfur of 200 mesh and then 4. g (0.2 mol) of metallic sodium at
room temperature. Raising the temperature of the mixture to about 65°C, a reaction
of metallic sodium with sulfur began. After 15 minutes, the mixed liquid became
a uniform solution. The reaction temperature was further kept at 70°C, and
the solution was heated while stirring it for 45 minutes. DME was evaporated under
reduced pressure to give sodium sulfide.