Method of preparing silacycloalkanes

Details Method of preparing silacycloalkanes Method of preparing silacycloalkanes

2002-03-05

2002-10-08

Shaver, Paul F. (Department: 1621)

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

Organic compounds

Silicon containing

C556S474000

Reexamination Certificate

active

06462214

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of preparing a silacycloalkane and more particularly to a method comprising adding an Si-substituted silacycloalkane to a suspension of lithium aluminum hydride in a glycol diether. The present invention also relates to a method of preparing a silicon carbide film using the silacycloalkane.
BACKGROUND OF THE INVENTION
Methods of preparing silacycloalkanes are known in the art. For example, Nametkin et al. teaches the preparation of silacyclobutane by reduction of 1,1-dichloro-1-silacyclobutane in n-butyl ether at 55-60° C. (Khim. Geterotsikl. Soedin., 1966, 4, 623).
Laane discloses, inter alia, the preparation of silacyclobutane in 60% yield by treatment of lithium aluminum hydride in ethyl ether with 1,1-dicholoro-1-silacyclobutane in n-butyl ether at −5 to +5° C. (J. Am. Chem. Soc. 1967, 89 (5), 1144-1147).
U.S. Pat. No. 4,973,723 to Cawthon et al. discloses the preparation of silacycloalkanes by reduction of halosilacycloalkanes with an alkylaluminum hydride. According to a preferred embodiment of the invention, the halosilacycloalkane is added to the alkylaluminum hydride under temperature and pressure conditions that cause the silacycloalkane to vaporize immediately after it is formed. The silacycloalkane product is vacuum distilled from the resultant mixture immediately upon formation, virtually eliminating the occurrence of further reactions of the silacycloalkane. According to the '723 patent, improved yields of product are achieved by the described process.
Although the aforementioned references describe the preparation of silacycloalkanes by reduction of halosilacycloalkanes, there remains a need for a method of producing silacycloaklanes having high purity in high yield that is scaleable to a commercial manufacturing process.
SUMMARY OF THE INVENTION
The present invention is directed to a method of preparing a silacycloalkane having the formula:
wherein n is 1, 2, or 3, comprising the steps of:
(A) adding a substituted silacycloalkane having the formula:
wherein X
1
is —F, —Cl, —Br, or —OR
1
and X
2
is X
1
or H, wherein R
1
is C
1
-C
8
hydrocarbyl and n is 1, 2, or 3, to a suspension of lithium aluminum hydride in a glycol diether at a temperature not greater than 50° C. to form a mixture, wherein the glycol diether consists essentially of a linear arrangement of oxyalkylene units having formulae independently selected from —OCH
2
CH
2
—, —OCH
2
CH(CH
3
)—, and —OCH
2
CH(CH
2
CH
3
)—, and end-groups having the formulae —R
2
and —OR
2
, wherein each R
2
is independently C
1
-C
8
alkyl, phenyl, or C
1
-C
8
alkyl-substituted phenyl, provided the glycol diether has a normal boiling point of at least 85° C. and a viscosity not greater than 3000 mm
2
/s at 25° C.; and
(B) distilling the mixture under reduced pressure at a temperature not greater than 50° C. to remove the silacycloalkane.
The method of the present invention produces silacycloalkanes having high purity in high yield. Importantly, the silacycloalkane can be readily and efficiently removed from the reaction mixture by distillation. This separation minimizes the occurrence of unwanted side reactions that can diminish purity and yield. Also, the silacycloalkane product is free of solvent, which can be deleterious in certain applications, particularly in the electronics field. Further, the method can be carried out economically with a stoichiometric amount or only slight excess of lithium aluminum hydride. Still further, the method can be scaled to a commercial manufacturing process.
The silacycloalkanes of the present invention can be used as coatings on solar panels and as precursors for synthesis of various sila drugs. Moreover, the silacycloalkanes can be used to prepare polycarbosilanes, which are useful as ceramic precursors.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, a method of preparing a silacycloalkane having the formula:
wherein n is 1, 2, or 3, comprising the steps of:
(A) adding a substituted silacycloalkane having the formula:
wherein X
1
is —F, —Cl, —Br, or —OR
1
and X
2
is X
1
or H, wherein R
1
is C
1
-C
8
hydrocarbyl and n is 1, 2, or 3, to a suspension of lithium aluminum hydride in a glycol diether at a temperature not greater than 50° C. to form a mixture, wherein the glycol diether consists essentially of a linear arrangement of oxyalkylene units having formulae independently selected from —OCH
2
CH
2
—, —OCH
2
CH(CH
3
)—, and —OCH
2
CH(CH
2
CH
3
)—, and end-groups having the formulae —R
2
and —OR
2
, wherein each R
2
is independently C
1
-C
8
alkyl, phenyl, or C
1
-C
8
alkyl-substituted phenyl, provided the glycol diether has a normal boiling point of at least 85° C. and a viscosity not greater than 3000 mm
2
/s at 25° C.; and
(B) distilling the mixture under reduced pressure at a temperature not greater than 50° C. to remove the silacycloalkane.
The substituted silacycloalkane of the present invention has the formula:
wherein X
1
is —F, —Cl, —Br, or —OR
1
and X
2
is X
1
or H, wherein R
1
is C
1
-C
8
hydrocarbyl and n is 1, 2, or 3. The hydrocarbyl groups represented by R
1
can have from 1 to 8 carbon atoms, alternatively from 1 to 4 carbon atoms. Hydrocarbyl groups having at least three carbon atoms can have a branched or an unranked structure. Examples of hydrocarbyl groups represented by R
1
include, but are not limited to, alkyl such as methyl, ethyl, propyl, pentyl, and octyl; cycloalkyl such as cylcohexyl; alkenyl such as vinyl and allyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl. Preferably, R
1
is alkyl and more preferably, R
1
is methyl, ethyl, or propyl.
Examples of substituted silacycloalkanes include, but are not limited to, 1,1-difluoro-1-silacyclobutane, 1,1-dichloro-1-silacyclobutane, 1,1-dibromo-1-silacyclobutane, 1,1-dimethoxy-1-silacyclobutane, 1,1-difluoro-1-silacyclopentane, 1,1-dichloro-1-silacyclopentane, 1,1-dibromo-1-silacyclopentane, 1,1-dimethoxy-1-silacyclopentane, 1,1-difluoro-1-silacyclohexane, 1,1-dichloro-1-silacyclohexane, 1,1-dibromo-1-silacyclohexane, and 1,1-dimethoxy-1-silacyclohexane.
Furthermore, the substituted silacyclolalkane can be a single substituted silacyclolalkane or a mixture comprising two or more different substituted silacyclolalkanes.
The substituted silacycloalkanes wherein X
1
and X
2
are —Cl and n is 1 can be prepared using the method of Laane (J. Am. Chem. Soc. 1967, 89 (5), 1144-1147). According to this procedure, (3-chloropropyl)trichlorosilane (0.94 mol) in diethyl ether was added dropwise to a vigorously stirred suspension of magnesium powder (1.7 g-atoms) in ether (500 mL) over a period of 3 hours. The stirred mixture was heated for 72 hours and then allowed to cool to room temperature. The magnesium chloride and excess magnesium metal were removed by filtration and washed several times with ether. The filtrate and washings were combined and distilled to give 1,1-dichloro-1-silacyclobutane (61%) having a boiling point of 113-115° C.
The substituted silacycloalkanes wherein X
1
is Cl, X
2
is H, and n is 1 can be prepared by substituting (3-chloropropyl)dichlorosilane for (3-chloropropyl)trichlorosilane in the above procedure.
Methods of preparing the substituted silacycloalkanes wherein X
1
and X
2
are—Cl and n is 2 (1,1-dichloro-1-silacyclobutane) or 3 (1,1-dichloro-1-silacyclopentane) are well known in the art. For example, these compounds can be prepared from the corresponding &agr;,&ohgr;-dichloroalkanes or &agr;,&ohgr;-dibromoalkanes and silicon tetrachloride by means of the Grignard reaction, as described in
Organosilicon Compounds
(Eaborn, C., Butterworths Scientific Publications: London, 1960, Chapter 13).
The substituted silacycloalkanes wherein X
1
is —Cl, X
2
is H, and n is 2 or 3 can be prepared by substituting trichlorosilane for silicon tetrachloride in the above procedure

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