Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-08-17
2001-07-10
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S482000
Reexamination Certificate
active
06258971
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to a method for making organooxysilanes. More particularly, the present invention relates to a process involving the reaction of a tetraorganooxysilane in the presence of a metal hydride.
Organooxysilanes are silicon-containing compounds of the formula R
m
Si(RO)
n
where each R independently represents a monovalent hydrocarbon group such as an alkyl group, aryl group, aralkyl groups, alkaryl groups, cycloalkyl groups, or bicycloalkyl groups; “n” is in a range between 1 and 3; “m” is in a range between 1 and 3; and “n+m” is 4. Silicon-containing compounds with silicon-carbon bonds, such as organooxysilanes, are commonly made from silicon dioixide via elemental silicon. Unfortunately, elemental silicon is manufactured from silicon dioxide by an energy intrusive reduction process.
The process commonly used commercially for the production of silicones and more particularly, alkoxysilanes, was first described by Rochow et al., U.S. Pat. No. 2,473,260. The Rochow process uses silicon, also referred to as elemental silicon, as a starting material. To prepare elemental silicon, silicon dioxide must be reduced. The elemental silicon is then oxidized to yield alkoxysilanes via a reaction of the silicon with methanol in the presence of a copper catalyst. It is well known in the art that the silicon-oxygen bond in silicon dioxide is extremely stable. In order to break the silicon-oxygen bond, a large amount of energy is consumed when silicon dioxide is reduced to elemental silicon. Thus, due to the large amount of energy needed to break the silicon-oxygen bond, the synthesis of silicones from silicon dioxide using the Rochow process is expensive and not energy efficient.
In the past, the synthesis of silicon-containing compounds with silicon-carbon bonds has relied heavily on the reduction of silicon dioxide to elemental silicon. Unfortunately, the large amount of energy needed for synthesizing silicones such as organooxysilanes from silicon dioxide can be problematic. Thus, new synthetic routes are constantly being sought which can form silicon-carbon bonds.
SUMMARY OF INVENTION
The present invention provides a method for the preparation of organooxysilanes containing at least one silicon-carbon bond comprising reaction of at least one tetraorganooxysilane with at least one metal hydride.
DETAILED DESCRIPTION
The present invention relates to a process involving the reaction of at least one tetraorganooxysilane and at least one metal hydride to form an organooxysilane containing at least one silicon-carbon bond. Tetraorganooxysilanes are of the formula (RO)
4
Si where each R independently represents a monovalent hydrocarbon group such as alkyl groups, aryl groups, aralkyl groups, alkaryl groups, cycloalkyl groups, or bicycloalkyl groups. The term “alkyl group” is intended to designate both normal alkyl and branched alkyl groups. Normal and branched alkyl groups are preferably those containing carbon atoms in a range between about 1 and about 22, and include as illustrative non-limiting examples methyl, ethyl, propyl, isopropyl, butyl, tertiary-butyl, pentyl, neopentyl, hexyl, octyl, decyl, dodecyl. Aryl groups include an example such as phenyl. Cyclo- or bicycloalkyl groups represented are preferably those containing ring carbon atoms in a range between about 3 and about 12 with a total number of carbon atoms less than or equal to about 50. Some illustrative non-limiting examples of cycloalkyl groups include cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl, and cycloheptyl. Preferred aralkyl groups are those containing carbon atoms in a range between about 7 and about 14; these include, but are not limited to, benzyl, phenylbutyl, phenylpropyl, and phenylethyl. Typical tetraorganooxysilanes include tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, and tetraiso-propoxysilane; tetraaryloxysilanes such as tetraphenoxysilane; as well as tetra(alkoxyaryloxy)silanes such as dimethoxydiphenoxysilane. Typically, the level of purity of the tetraorganooxysilane is at least about 80% by weight and preferably, about 95% by weight.
Metal hydrides include, but are not limited to, sodium hydride, lithium hydride, potassium hydride, rubidium hydride, cesium hydride, magnesium hydride, calcium hydride, strontium hydride, barium hydride, aluminum hydride, and combinations thereof. The metal hydride is preferably sodium hydride. Metal hydrides also include metal borohydrides, for example, lithium borohydride, potassium borohydride and sodium borohydride. Although the present invention is not dependent upon theory, the presence of hydrogen in the metal hydride may act as a base as well as a nucleophile to promote the formation of the organooxysilane.
Organooxysilanes are compounds of the formula R
m
Si(RO)
n
where R is defined as above, “n” is in a range between 1 and 3, “m” is in a range between 1 and 3, and “n+m” is 4. Preferably, R is methyl or ethyl, n is 3 and m is 1.
The reaction commonly can be practiced in a fixed bed reactor. The method for preparation of organooxysilanes, however, can be performed in other types of reactors, such as fluid bed reactors and stirred bed reactors. More specifically, the fixed bed reactor is a column that contains the metal hydride wherein a carrier gas, such as an inert gas of hydrogen or argon, is passed through at a rate in a range between about 0.1 milliliters per minute (ml/min) and about 100 ml/min and preferably, in a range between about 0.5 ml/min and about 30 ml/min. The tetraorganooxysilane is typically fed into the carrier gas stream. A stirred bed is similar to a fixed bed in which there is mechanical agitation of some sort in order to keep the bed in constant motion. A fluidized bed reactor, on the other hand, is a bed comprising metal hydride which is fluidized; that is, the metal hydride is suspended in the gas, typically argon, that is passed through the reactor. Reaction typically occurs at a temperature in a range between about 50° C. and about 600° C. and commonly, in a range between about 200° C. and about 450° C.
The reaction of the present invention can be performed in batch mode, continuous mode, or semi-continuous mode. With a batch mode reaction, for instance, all of the reactant components are combined and reacted until most of the reactants are consumed. In order to proceed, the reaction has to be stopped and additional reactant added. A fixed bed and stirred bed may both be run under batch conditions. In contrast, a fluidized reactor is typically run under continuous conditions. With continuous conditions, the reaction does not have to be stopped in order to add more reactants.
The tetraorganooxysilane is typically added to the reactor via any convenient method to provide batch, continuous, or semi-continuous means of addition. A pumping device, such as a motor driven syringe, is an example of a continuous means of addition. A motor driven syringe allows for consistent amounts of tetraorganooxysilane to be added to the reaction mixture at given time intervals. Addition of the tetraorganooxysilane via a motor driven syringe is illustrative and non-limiting. Manual injection is also a common method for the addition of tetraorganooxysilanes. Typically, the tetraorganooxysilane is added at a rate in a range between about 0.1 milliliters per hour (ml/h) and about 10 ml/h, and preferably, in a range between about 0.5 ml/h and about 2.1 ml/h. The tetraorganooxysilane is typically added in a mole ratio of metal hydride to tetraorganooxysilane in a range between about 10:1 and about 1:100 and commonly, a mole ratio of metal hydride to tetraorganooxysilane in a range between about 5:1 and 1:10. The reaction is typically at about atmospheric pressure.
Products in the organooxysilane synthesis may be isolated by any convenient means. Typically, product(s) may be isolated by condensation into fractions typically referred to as condensate. Products may be purified by any convenient means such as distillation. Once the fractions are collected, the formation of the organo
Bennett Bernadette M.
General Electric Company
Johnson Noreen C.
Shaver Paul F.
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