Method of making sulfur containing organosilicon compounds

Details Method of making sulfur containing organosilicon compounds Method of making sulfur containing organosilicon compounds

2002-11-12

2004-05-25

Barts, Samuel (Department: 1621)

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

Organic compounds

Silicon containing

Reexamination Certificate

active

06740767

ABSTRACT:

FIELD OF THE INVENTION
This invention is related to an improved method of making sulfur containing organosilicon compounds possessing better color. In particular, products with lighter colors can be obtained by modifying certain existing processes.
BACKGROUND OF THE INVENTION
Sulfur containing organosilicon compounds are known to be useful as reactive coupling agents in a variety of commercial applications. In particular, sulfur containing organosilicon compounds have become a necessary component in the production of tires based on rubber vulcanates containing silica. In that application, the sulfur containing organosilicon compounds improve the physical properties of rubber vulcanates containing silica, resulting in automotive tires with improved abrasion resistance, rolling resistance, and wet skidding performance. The sulfur containing organosilicon compounds can be added directly to the silica containing rubber vulcanates, or they can be used to pre-treat silica prior to addition to the rubber vulcanate compositions.
While a number of processes are known in the art for making such sulfur containing organosilicon compounds, a preferred one of such processes is described in a copending U.S. patent application Ser. No. 09/895,719, filed Jun. 29, 2001, entitled “Preparation of Sulfur Containing Organosilicon Compounds Using a Buffered Phase Transfer Catalysis Process”. The copending application is assigned to the same assignee as the present invention.
The process according to the copending application involves reacting (A) a sulfide compound having the formula M
2
S
n
or MHS where H is hydrogen, M is ammonium or an alkali metal, and n is 1-8, with (B) a silane compound with the formula (RO)
3-m
R
m
Si—Alk—X where X is Cl, Br or I, and m is 0, 1, or 2, and (C) sulfur. The reaction is carried out in the presence of a phase transfer catalyst and an aqueous phase containing a buffer. This process is characterized by addition of buffers to the aqueous phase which minimizes and/or prevents gelling of the sulfur containing organosilicon compounds.
The process according to the present invention, while being similar to the process described in the copending application, is not the same and is a significant improvement thereof. According to the present invention, it was discovered that one can dramatically reduce the color and any residual catalyst species present in the organic phase by heating the two phase product mixture in an additional step to a temperature of 80-100° C., preferably a temperature of 85-95° C., and most preferably to a temperature of 87-92° C. The heating should be continued for about 1-3 hours. This additional heating step results in a mild oxidation process which is enhanced by the basic species remaining in the aqueous phase, after completion of the reaction step in the process according to the copending application. This improvement is especially significant for commercial products where n corresponds to values of 3 or 4, or more, as product color is an important quality issue. Thus, there is a perception in the market place that quality is associated with less color. By implementing this additional heating step, one is enabled to obtain significant reductions of color of sulfur containing organosilicon compounds.
SUMMARY OF THE INVENTION
This invention is directed to a process for producing organosilicon compounds having the formula (RO)
3-m
R
m
Si—Alk—S
n
—Alk—SiR
m
(OR)
3-m
. In the formula, R represents independently a monovalent hydrocarbon having 1-12 carbon atoms, Alk represents a divalent hydrocarbon having 1-18 carbon atoms, m is an integer representing 0,1 or 2, and n is an integer with a value of 2-8, preferably 3-8, representing the average sulfur-chain length, i.e., the sulfur rank. The process consists generally of the steps of (I) heating and reacting (A) a sulfide compound having the formula M
2
S
n
or MHS wherein H is hydrogen, M is ammonium or an alkali metal, and n is 1-8, with (B) a silane compound having the formula (RO)
3-m
R
m
Si—Alk—X wherein X is Cl, Br or I; R and Alk are the same as defined above; and m is 0, 1, or 2, and (C) sulfur, in the presence of a phase transfer catalyst and an aqueous phase containing a buffer or a basic compound, to form a product mixture.
In a step (II), the product mixture, unlike the product mixtures manufactured according to previously known processes, is again heated but to a temperature of 80-100° C., preferably a temperature of 85-95° C., and most preferably to a temperature of 87-92° C., and then the desired organosilicon compound is obtained by separating it from the heated product mixture in a third step (III).
Separations can be obtained, for example, by (D) adding water or a dilute acidic solution to the product mixture, and (E) phase separating the product mixture into an organic phase containing the organosilicon compound and an aqueous phase. The organic phase containing the organosilicon compound can then be dried by (i) heating the organic phase at a reduced pressure, or (ii) drying it by contacting it with a solid desiccant such as sodium sulfate, magnesium sulfate, calcium sulfate, calcium chloride, magnesium chloride, lithium chloride, a molecular sieve, zeolite, aluminasilicate, or silica gel. The preferred desiccants are sodium sulfate and magnesium sulfate.
Other processing techniques can be included as steps according to the present invention such as the additional steps of (F) cooling the organic phase containing the organosilicon compound to a temperature below 15° C. to precipitate unreacted sulfur compounds, and (G) separating the organic phase containing the organosilicon compound from the precipitated unreacted sulfur compounds.
These and other features of the invention will become apparent from a consideration of the detailed description.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, the process herein involves the preparation of sulfur containing organosilicon compounds of the general formula (RO)
3-m
R
m
Si—Alk—S
n
—Alk—SiR
m
(OR)
3-m
in which R is a monovalent hydrocarbon having 1-12 carbon atoms, Alk is a divalent hydrocarbon having 1-18 carbon atoms, m is 0, 1 or 2, and n is 2-8, preferably 3-8. It consists generally of the steps of (I) heating and reacting (A) a sulfide compound such as M
2
S
n
or MHS where H is hydrogen, M is ammonium or an alkali metal, and n is 1-8; with (B) a silane compound of the formula (RO)
3-m
R
m
Si—Alk—X where X is Cl, Br or I; R and Alk are the same as defined above; and m is 0, 1, or 2; and with (C) sulfur. Step (I) is carried out in the presence of a phase transfer catalyst, and an aqueous phase containing a buffer or a basic compound, to form a product mixture. In step (II), the product mixture is again heated but to a temperature of 80-100° C., preferably a temperature of 85-95° C., and most preferably to a temperature of 87-92° C., for a period of time of about 1-3 hours, and the desired organosilicon compound can be obtained by separating it from the resulting product mixture.
Some examples of sulfur containing organosilicon compounds which nay be prepared according to the present invention are described generally in U.S. Pat. No. 5,405,985 (Apr. 11, 1995); U.S. Pat. No. 5,468,893 (Nov. 21, 1995); U.S. Pat. No. 5,583,245 (Dec. 10, 1996); and U.S. Pat. No. 5,663,396 (Sep. 2, 1997). Preferred sulfur containing organosilicon compounds which can be prepared according to this invention include the 3,3′-bis(trialkoxysilylpropyl) polysulfides such as 3,3′-bis(triethoxysilylpropyl) disulfide and 3,3′-bis(triethoxysilylpropyl) tetrasulfide.
The latter composition, i.e., bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT) with the formula [(CH
2
H
5
O)
3
SiCH
2
CH
2
CH
2
—S—S—]
2
—, is shown in more detail below. TESPT is a relatively commercially successful product, and therefore any process which can improve its quality can have significant value in the market place.
Sulfide compounds of the formula M
2
S
n
or MHS are used as component (A) in reaction step (I) of the process, in which M represen

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