Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2002-02-25
2002-12-03
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06489500
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a continuous transesterification process. More particularly, the present invention relates to a continuous transesterification process for the conversion of alkoxysilanes to different alkoxysilanes.
2. Description of Related Art
The major portion of the chemical industry involved in the production of organofunctional silicon compounds has been working on processes and products that do not involve the handling of hazardous chlorositanes as raw materials. The direct preparation of hydroalkoxysilanes from alcohols and silicon metal (see for example, U.S. Pat. No. 4,762,939) as shown in Reaction (I) avoids the preparation of chlorosilanes as was done in the older, two-step, process shown in Reactions (IIa) and (IIb), involving the preparation of trichlorosilane from hydrogen chloride and silicon metal followed by its esterification to the corresponding hydroalkoxysilane.
Hydroalkoxysilanes are useful in a variety of hydrosilation reactions, of the kind shown in Reaction (III), known to and practiced by those skilled in the art to provide commercially useful organofunctional silicon compounds:
where, for example, R is a hydrocarbon group or a substituted hydrocarbon group, R′ is R, R″ is H or R, and X is a functional group, including Cl, NH
2
, NHR, O
2
CCMe═CH
2
, an epoxy-group containing moiety, and the like, and x is 1, 2, or 3.
Recent advances in the technology of hydrosilation reactions of hydroalkoxysilanes have provided such organofunctional silicon compounds in economically attractive yields (see, for example, U.S. Pat. Nos. 4,709,067, 5,041,595, and 5,559,264), overcoming earlier, well-recognized deficiencies, particularly for the hydrosilation of allyl chloride (U.S. Pat. No. 5,559,264).
Nevertheless, a problem remains in that the production efficiencies are highest when R is a methyl group, such that the ROH above is methanol, and the (RO)
3
SiH is trimethoxysilane, but various applications of organofunctional silicon compounds require other R groups derived from other alcohols for reasons of reactivity, stability, toxicity, volatility, solubility, and flammability, among others. Other R groups that are useful in products include ethyl, propyl, isopropyl, butyl, 2-methoxyethyl, and the like. Thus, there is a need in the industry for a highly efficient process for transforming lower alkoxy groups attached to silicon, such as methoxy groups, to higher alkoxy groups, such as ethoxy groups, to provide a variety of organofunctional silicon compounds as may be required for a particular use. There is also, on occasion, a separate need for the reverse process, i.e., the transformation of higher alkoxy groups to lower alkoxy groups. For reasons of high reaction rates, high efficiencies, and lower capital investments, such a process, heretofore known in the art only in batch or non-continuous modes, should be of a continuous nature. While continuous processes exist for the conversion of chlorosilanes to alkoxysilanes, e.g., esterification (Reaction (IIb) see, for example, U.S. Pat. Nos. 4,298,753 and 4,924,022), continuous technology does not appear to have been applied to transesterification, i.e., the replacement of one alkoxy group with another, even by organizations knowledgeable in continuous esterification technology (see U.S. Pat. No. 6,005,132 wherein the continuous removal of lower alcohol is disclosed, but the process itself is not continuous, i.e., all the higher alcohol is fed at once at the start). Batch transesterification is well known in the art, but is prone to long reaction times or lower efficiencies relating to the use of excess alcohol to provide the desired alkoxy group in a reasonable reaction time.
There is also a need to perform such continuous transesterification processes in giving consideration to minimized economics, including the minimized generation of hazardous wastes. This can be accomplished by the use of recycled raw materials and/or materials of lower purity, or through the performance of more than one process step concurrently, as by combining the neutralization of a feed stream with transesterification of the bulk of that stream, or by transesterification of more than one alkoxysilane concurrently, with later separation of the products, as by simple distillation.
SUMMARY OF THE INVENTION
The present invention provides a process for the conversion of alkoxysilanes to different alkoxysilanes, i.e., transesterification, that is efficient and continuous and can be practiced in commercially available equipment designed for continuous operation. The process comprises the reaction of an alkoxyorganosilicon compound containing at least one alkoxy group with one or more alcohols that provide different alkoxy groups on silicon according to Equation (IV).
wherein R and R′ are independently selected from the group consisting of unsubstituted and substituted hydrocarbon moieties and are different from one another. The other three bonds on the silicon in Reaction (IV) can be to the same or other alkoxy groups, hydrocarbon groups, functionalized hydrocarbon groups (as in the products of Reaction (III), silicon-containing moieties, and even halogen groups (esterification of Si-halogen groups may occur concurrently with transesterification of alkoxy groups on silicon).
More particularly, the present invention is directed to a method for the continuous transesterification of alkoxysilanes comprising reacting at least one alkoxyorganosilicon compound containing at least one alkoxy group with at least one alcohol that provides at least one different alkoxy group on the silicon in the presence of an effective amount of an acidic or basic transesterification catalyst at an elevated temperature with continuous separation of product streams.
The process of the present invention is not narrowly limited and is thus applicable to a very large variety of alkoxyorganosilicon compounds, including monomeric silanes having one to four alkoxy groups, silanes containing more than one silicon atom, including oligomers and polymers, alkoxysiloxanes, and alkoxypolysiloxanes, as well as blends or mixtures thereof
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of the present invention is a continuous process for the interconversion of alkoxysilanes, i.e., transesterification, according to the general Equation IV above. More specifically, when the alkoxysilane is a monomeric silane, said transesterification is expressed by Equation V, wherein R and R′ are as defined above and R
2
is the same as or different from R or R′.
with the added proviso that R and R′ contain no functional group that will not remain largely intact during the transesterification, and x is as defined above.
The process of the present invention can be performed in a variety of commercially available continuous units, including those typically used for continuous esterification, such as those described in U.S. Pat. No. 4,924,022, or in custom-designed commercial or laboratory scale units. Continuous stirred tank reactors, alone or in series, can be used, as can units designed for continuous countercurrent reactive distillation. Said units can be operated at or near atmospheric pressure, under vacuum, or under positive pressure; the choice being determined by the boiling points of the reactants and the desired operating temperature. The operating temperature will typically be an elevated temperature to maximize reaction rates and boiling point differences between reactants and products. Preferably, the elevated temperature is at least the boiling point of the lowest boiling alcohol at reaction pressure.
The catalysts operable in the present invention include those typically used for batch esterifications and transesterifications, i.e., acids and bases. The catalyst selection is determined in part by the alkoxysilane being transesterified. For example, an aminoalkylalkoxysilane would normally be transesterified with a basic catalyst, such as the corresponding sodium alkoxide, w
Bowman Mark P.
Childress Thomas E.
Mendicino Frank D.
Warren R. Ingrid
Crompton Corporation
Shaver Paul F.
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