Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2003-02-19
2004-01-06
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06673954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for the preparation of an N-silylorganocarbamate from an aminoorganosilane and organocarbonate ester employing a basic catalyst.
2. Description of the Related Art
Organocarbamates have found widespread utility in such application as pesticides, herbicides, and pharmaceuticals, as well as their use in the manufacture of polyurethane foams, coupling agents and adhesion promoters. Although a number of methods currently exist for the synthesis of silylorganocarbamates, the simultaneous production in these processes of byproducts termed “heavies”, as well as the generation of large quantities of hazardous wastes has proved to be problematic for their use in all but a few applications. Thus, there continues to be a need for a process that will produce an organocarbamate without the resultant production of toxic and corrosive heavies.
Typically, the reaction of an aminoorganosilane and an organocarbonate ester in the presence of an alcoholate catalyst is conducted at low temperatures, i.e., 25° to 50° C. and over long periods of time, i.e., 4 to 6 hours. The process of preparing carbamates from primary amines without using volatile byproduct producing chloroformates has also been reported. Several processes also describe the manufacture of carbamates by the oxidative carbonylation of amines with carbon monoxide (CO) in the presence of transition metal compound catalysts such as palladium (Pd), ruthenium (Ru), and manganese (Mn). They can also be formed by the reductive carbonylation of nitro compounds such as nitrobenzene with alcohols and CO in the presence of Ru, rhodium (Rh), and/or Pd compounds. It has also been reported that azides are transformed into various carbamates by using Me
3
P and commercially available chloroformates.
Carbamates can be formed from the direct reaction of primary amines and organocarbonates such as dimethyl carbonate (DMC). European Patent No. A 391,473, for example, describes a process for producing carbamates using reduced amounts of catalyst by first reacting a suitable amine with a cycloalkyl carbonate in the presence of a carbamation catalyst to produce a mixture of carbamates and a urea. Further reaction of the urea with the carbonate produces the corresponding carbamates, which are eventually recovered from the reaction mixture.
In German Patent No. A 3,202,690 a process for preparing aromatic urethanes is described by the reaction of aromatic amines and alkylcarbonates in the presence of an alcoholate of an alkali metal or an alkaline earth metal.
More recently, a method of preparing carbamates has been described in U.S. Pat. No. 5,962,721 to Kim et al., by reacting an amine with an alcohol and a mixed gas of CO/O
2
in the presence of one or more monovalent copper catalysts.
Japanese unexamined Patent Publication No. 311452/1990 discloses a process for using a base as a catalyst in which an alcoholate of a suitable alkaline metal and alkaline earth-metal is employed. However, the base prepared by this method remained in the carbamate and thus must be removed by neutralization to prevent polymerization and/or coloration during the conversion of carbamate to isocyanate.
Alternatively, silylcarbamates have also been prepared by the reaction of a suitably functionalized silylorgano halide, a metal cyanate, and monohydridic alcohol in the presence of an aprotic solvent such as N,N-dimethyl formamide. Unfortunately the necessity for large quantities of expensive solvent and yields that do not typically exceed 85% currently make this process less economically attractive.
Silyl carbamates have also been prepared through the hydrosilation of suitably functionalized allyl carbamates and allyl isocyanates with trimethoxy silane as reported in U.S. Pat. No. 5,220,047. The commercial availability of allyl carbamates and or allyl isocyanates, however, has severely limited the commercial viability of this process.
Silylorganocarbamate formation has also been obtained from the direct reaction of a suitable dialkyl carbonate and the corresponding aminoorganosilane in the presence of a basic catalyst such as sodium methylate. See, in this regard, U.S. Pat. No. 5,218,133 the contents of which are incorporated herein by reference. The tendency of dialkyl carbonates to alkylate the amino functionality at elevated temperatures, however, produces an undesired side product and reduces the yield of the silylcarbamate.
According to the process described in aforementioned U.S. Pat. No. 5,218,133 the aminoorganosilane was combined with a mixture of dimethyl carbonate and sodium methoxide at ambient temperature over 30 minutes and held at this temperature for an additional 3 hours during which a reaction producing methyl N-3-(trimethoxysilyl)propylcarbamate took place. The reaction mixture was then heated to 50°±5° for an additional hour to complete the reaction
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for preparing an N-silylorganocarbamate, which can be used as a reactant in the further process of preparing an isocyanurate.
It is a further object of the present invention to provide the aforementioned process of preparing an N-silylorganocarbamate that can be utilized at an elevated temperature to increase the reaction rate while minimizing unwanted byproduct formation and thus resulting in greatly improved yield of the desired N-silylorganocarbamate.
In keeping with these and other objects of the invention, there is provided a process for preparing an N-silylorganocarbamate which comprises:
(a) providing a mixture of aminoorganosilane of the general formula:
R
3
n
R
2
3−n
SiR
1
NH
2
wherein R
1
is a divalent hydrocarbon group of from 1 to about 20 carbon atoms; R
2
and R
3
each is independently an alkyl group containing from 1 to about 20 carbon atoms, an alkoxy group containing from 1 to about 20 carbon atoms, an aryl group containing from about 6 to about 10 carbon atoms, or an aryloxy group containing from about 6 to about 10 carbon atoms with at least one of R
2
and R
3
being a hydrolysable alkoxy group; and where n is 0 to 3, and a catalytically effective amount of basic catalyst and;
(b) combining the mixture of aminoorganosilane and basic catalyst with an organocarbonate ester of the general formula:
R
4
OC(O)OR
4
wherein each R
4
is independently the same or different hydrocarbyl group of up to about 20 carbon atoms or halohydrocarbyl group of up to about 20 carbon atoms, or both R
4
groups together form a divalent alkylene group R
5
of from 2 to about 6 carbon atoms, the mixture of aminoorganosilane and basic catalyst, the organocarbonate ester or both being at elevated temperature at the time of their being combined, thereby producing N-silylorganocarbamate of the general formula:
R
3
n
R
2
3−n
SiR
1
NHC(O)OR
6
wherein R
1
, R
2
and R
3
have the aforestated meanings and R
6
is R
4
or R
5
H in which R
4
and R
5
have the aforestated meanings.
In contrast to the process described in U.S. Pat. No. 5,218,133, supra, in which aminoorganosilane is combined with a mixture of dimethyl carbonate (an organocarbonate ester) and a basic catalyst such as sodium methoxide (an alcoholate) at ambient temperature with the temperature of the reaction medium being increased only in the terminal phase of the reaction, the process of the present invention combines the organocarbonate with a mixture of aminoorganosilane and basic catalyst and does so with either the organocarbonate, the mixture of aminoorganosilane and basic catalyst or both being at elevated temperature at the time they are combined. As a result of this order of addition of the components of the reaction medium and the initially elevated temperature of at least the organocarbonate reactant or the mixture of the aminoorganosilane and basic catalyst, the process of this invention results in significantly increased production of the desired carbamate product.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the process of this invention, aminoorganosilane a
Childress R. Shawn
Gedon Steven C.
Jackson Melinda B.
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