Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2002-08-16
2004-01-20
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S427000
Reexamination Certificate
active
06680398
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the synthesis of mercapto-functional organosilicon compounds ≡Si—(CH
2
)
n
SH, more particularly mercaptoalkylalkoxysilanes such as mercaptopropyltrialkoxy silane (MPTAS), using phase transfer catalysts. The process is capable of producing high purity mercaptopropyltriethoxysilane (MPTES), for example. Mercaptoalkylalkoxysilanes made by the process generally have a formula corresponding to Z—Alk—SH in which Z is one of a group consisting of —SiR
1
2
R
2
, —SiR
1
R
2
2
, and —SiR
2
3
; in which R
1
is an alkyl group with 1-12 carbon atoms, a cyclohexyl group, or a phenyl group; R
2
is an alkoxy group containing 1-12 carbon atoms; and Alk represents a divalent hydrocarbon radical having 1-18 carbon atoms and containing no unsaturation.
BACKGROUND OF THE INVENTION
Sulfur containing organosilicon compounds are known to be useful as reactive coupling agents between rubber and silica fillers, for improving the properties of cured rubber. They are also known to be useful as adhesion promoters, for adhering rubber compositions to substrates such as glass and metal. However, many sulfur containing organosilicon compounds are difficult to make in good yield, because undesirable byproducts are produced from various side reactions occurring when traditional methods are employed.
For example, U.S. Pat. No. 3,590,065 (Jun. 29, 1971) relates to a reaction between a haloalkylalkoxysilane and a thio-urea in the presence of ammonia. However, the necessity of handling bulky by-products such as guanidine hydrochloride is the major disadvantage associated with this particular method.
U.S. Pat. No. 3,849,471 (Nov. 19, 1974) is directed to another method involving reactions between haloalkylalkoxysilanes and hydrogen sulfide gas in the presence of amines. However, this reaction is carried out under a high pressure, and also has the disadvantage of producing a fluffy by-product salt which is difficult to filter from the end product.
U.S. Pat. No. 3,890,213 (Jun. 17, 1975) relates to yet another method involving reactions between hydrogen sulfide and alkenylalkoxysilanes. However, the major disadvantage associated with this method is that the mercaptosilane product itself can become associated with the alkenylalkoxysilane to form copious amounts of sulfide side products.
In British Patent 1,102,251 (Feb. 7, 1968), a method is described involving the reaction of sodium methoxide and hydrogen sulfide to produce sodium hydrosulfide, which is then further reacted with an haloalkylalkoxysilane. The disadvantage associated with this particular method however, is that the reaction of sodium methoxide with H
2
S produces sodium sulfide as a by-product, which in turn leads to large amounts of polysulfide silanes in the end product.
U.S. Pat. No. 5,583,245 ((Dec. 10, 1996) describes a process for making compounds generally corresponding to the formula Z—Alk—S
n
—Alk—Z, in which Z and Alk are the same as defined above, and in which n is 2-8. According to the process in the '245 patent, a compound of the formula Z—Alk—X where X is chlorine or bromine, is reacted with an ammonium hydrosulfide or an alkali metal hydrosulfide, and sulfur, using a phase transfer catalyst, in an aqueous phase.
The '245 patent teaches that an additional reactant corresponding to Alk—X may be present, where an unsymmetrical compound corresponding to Alk—S
—Alk—Z is desired, in addition to bis type end products. While the '
245 patent does describe a method for preparing MPTES in a 64.9% yield by reacting (i) sodium hydrosulfide flakes and (ii) chloropropyltriethoxysilane (CPTES), in a saturated sodium chloride solution and toluene solvent, in the presence of a phase transfer catalyst, the yield of MPTES was not optimal.
While U.S. Pat. No. 5,840,952 ((Nov. 24, 1998) describes a method of making mercaptopropylalkoxysilanes in good yield, by purging hydrogen sulfide gas in a sodium sulfide solution in methanol, and then reacting it with chloropropyltrimethoxysilane (CPTMS) in an anhydrous system, the disadvantage associated with this process is that sodium sulfide used must first be dehydrated. Another disadvantage of the '952 patent is that it requires the use of high pressure, i.e., 600 psi/4,140 kilopascal (kPa) hydrogen sulfide gas, to reduce sodium sulfide to sodium hydrosulfide.
In a prior copending application assigned to the same assignee as the present invention, i.e., U.S. patent application Ser. No. 09/895,719, filed Jun. 29, 2001, and entitled “Preparation of Sulfur Containing Organosilicon Compounds Using a Buffered Phase Transfer Catalysis Process”, there is described a process based on phase transfer catalysis. However, this process is directed to the production of bis-type sulfido silanes ≡Si—S—Si≡, which generally correspond to the formula (RO)
3−m
R
m
Si—Alk—S
n
—Alk—SiR
m
(OR)
3−m
, wherein R is a monovalent hydrocarbon group with 1-12 carbon atoms; Alk represents a divalent hydrocarbon group with 1-18 carbon atoms; m is 0-2; and n is 1-8. According to the process described in the copending application, (A) a sulfide compound M
2
S
n
or MHS wherein H is hydrogen, M is ammonium or an alkali metal, and n is as defined above, is reacted with (B) a silane compound corresponding to (RO)
3−m
R
m
Si—Alk—X, wherein X is Cl, Br or I, m is the same as defined above, and (C) sulfur, in the presence of a phase transfer catalyst, in an aqueous phase containing a buffering agent. However, no method is described in the copending application for making mercapto-functional organosilicon compounds, i.e., compounds containing the group
≡Si—(CH
2
)
n
SH.
The copending application, however, results in sulfidosilanes instead of mercaptosilanes. This is because of the presence of elemental sulfur in the copending application, and the use of different buffering agents in the copending application than the buffering agents (i.e., pH adjusting agents) used in the present application. In addition, pH is a controlling factor in these applications as to what is being prepared. The difference is based on (i) establishment of the equilibrium
or (ii) the equilibrium
and (iii) the fact that the disulfide anion is undetectable at a pH of about 9 or less.
Another way to view the difference is that when it is desired to make mercaptosilanes, rather than sulfidosilanes, the alkalinity of the reaction mixture must remain at a pH in the range of 4 to 9. Higher concentrations of alkalinity lead to disulfide anion formation from the mercaptide anion already present, without adding elemental sulfur. When it is desired to make the disulfide, it is necessary for the system to remain high in alkalinity, to inhibit any equilibrium leading to NaHS formation. As these reactants naturally react and form a neutral NaCl, the alkalinity of the brine will lessen over time, and can become low enough so that SH will form.
So the present application differs from the copending application in that (i) different pH adjusting agents are employed, (ii) the pH is different, i.e., a pH of 4 to 9, preferably a pH of 5-8, and more preferably a pH of 5 to less than 7, instead of a pH of 7-14, and (iii) the order of addition of the reactants is not the same. The result is that at the lower pH of 4 to less than 7, any sulfide present is converted to mercaptan in the aqueous phase.
The process of the present invention further differs from processes described above, in that it is capable of providing high yields of mercaptosilanes under mild conditions, without the use of solvents, toxic gas, and strictly anhydrous conditions. In addition, it is more economical, environment friendly, and capable of utilizing relatively inexpensive starting materials. When there is any byproduct present, it is simply an alkali metal salt, which can be easily removed by dissolution during the water and phase separation sequence of the process.
Other advantages provided by the present invention over the prior art include the benefit that the mercaptoalkylalkoxy silane yield is significan
Boswell Lisa Marie
Maki William Charles
Tomar Anil Kumar
DeCesare Jim L.
Dow Corning Corporation
LandOfFree
Method of making mercaptoalkylalkoxysilanes does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making mercaptoalkylalkoxysilanes, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making mercaptoalkylalkoxysilanes will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3230660