Preparation of silanol-containing organosilicon compounds

Details Preparation of silanol-containing organosilicon compounds Preparation of silanol-containing organosilicon compounds

2000-05-12

2002-01-08

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S012000

Reexamination Certificate

active

06337382

ABSTRACT:

This invention relates to a method for preparing silanol group-containing organosilicon compounds from organooxysilanes.
BACKGROUND OF THE INVENTION
Organosilanes and siloxanes having silanol groups in their molecule are known to be effective dispersants for use in the manufacture of silicone rubber compounds. Their dispersing capability tends to increase as the content of hydroxyl groups increases. More particularly, low molecular weight organosilanes and siloxanes having silanol groups have higher hydroxyl contents and hence, higher dispersing capability than high molecular weight ones. Therefore, the low molecular weight organosilanes and siloxanes have the advantage that they are effective as the dispersant even in small amounts, which in turn, is not detrimental to the working of silicone rubber compounds.
Currently, the low molecular weight organosilanes and siloxanes are industrially manufactured by hydrolyzing organochlorosilanes having a chlorine atom at the end of their molecular chain in a weakly alkaline aqueous solution so as to avoid cyclization. This method, however, has the problem that silanol groups undergo condensation reaction with HCl formed by hydrolysis, resulting in a product having a higher molecular weight than the desired organosiloxane or a cyclic product. It is also known that an organochlorosilane is treated with acetic acid to introduce acetoxy before hydrolysis is effected. With this method, however, it is difficult to effect hydrolysis to completion, leaving acetoxy groups in the product. Such organopolysiloxanes are inadequate as the dispersant for use in the manufacture of silicone rubber compounds.
U.S. Pat. No. 3,925,285 discloses a method for synthesizing a low molecular weight, linear, silanol-terminated polyorganosiloxane by reacting hexamethylcyclotrisiloxane with methanol, formic acid, and water. This method is uneconomical since relatively expensive hexamethylcyclotrisiloxane is utilized. The method fails to produce a low molecular weight, linear, silanol-terminated polyorganosiloxane having a degree of polymerization of less than 3. It is impossible to obtain a silanol-containing organosiloxane having a lower molecular weight.
In U.S. Pat. No. 5,057,620, a chlorosiloxane is added dropwise to a water-containing epoxy solvent such as propylene oxide or butylene oxide. This method uses relatively expensive hexamethylcyclotrisiloxane as the reactant, imposing a cost problem. The method also uses a low boiling solvent having the risk of electrostatic ignition, leaving a safety problem.
In U.S. Pat. No. 5,378,788, an alkoxysilane is hydrolyzed with acidic water and neutralized with a metal oxide. This method yields silanol-containing organosiloxanes having an average degree of polymerization of 3 or higher. It is difficult to obtain a silanol-containing organosiloxane having a lower molecular weight.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method for preparing silanol-containing organosilicon compounds having a low molecular weight using a relatively inexpensive organooxysilane as the starting reactant rather than expensive reactants.
It has been found that by adding a specific amount of water at pH 1 to 5 to at least one organooxysilane to effect hydrolysis and then adding a mono- and/or di-alkali metal salt of phosphoric acid thereto, low molecular weight, silanol-containing organosilicon compounds, especially organosilicon compounds containing hydroxyl (or silanol) groups and having an average degree of polymerization of more than 1 to less than 3 (that is, a mixture of silanes and siloxanes) can be produced in an easy, reliable and efficient manner.
The invention provides a method for preparing organosilicon compounds having silanol groups, comprising the steps of:
adding water adjusted at pH 1 to 5 to at least one organooxysilane of the following general formula (1):
(R
1
O)
a
SiR
4-a
  (1)
 wherein R
1
and R are independently substituted or unsubstituted monovalent hydrocarbon groups, and “a” is an integer of 1 to 4, in an amount of 0.5 to 3 mol per mol of the organooxy group in the organooxysilane, mixing them, thus forming a hydrolyzed organooxysilane mixture, and
adding a mono-alkali metal salt of phosphoric acid and/or di-alkali metal salt of phosphoric acid to the mixture.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The method for preparing silanol group-containing organosilicon compounds according to the invention starts with an organooxysilane of the general formula (1).
(R
1
O)
a
SiR
4-a
  (1)
Herein R is selected from substituted or unsubstituted monovalent hydrocarbon groups, preferably having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms. Exemplary are alkyl groups such as methyl, ethyl, propyl, butyl and pentyl, cycloalkyl groups such as cyclohexyl, alkenyl groups such as vinyl, allyl and propenyl, aryl groups such as phenyl and tolyl, aralkyl groups such as &bgr;-phenylethyl, and substituted ones of these groups in which some or all of the hydrogen atoms attached to carbon atoms are replaced by halogen atoms (e.g., fluorine and chlorine) and cyano groups, such as 3,3,3-trifluoropropyl and cyanoethyl. Of these, methyl, ethyl, vinyl, phenyl and 3,3,3-trifluoropropyl are preferred.
R
1
is selected from substituted or unsubstituted monovalent hydrocarbon groups as defined for R, preferably alkyl groups such as methyl and ethyl. Letter “a” is an integer of 1 to 4, and preferably equal to 2. When “a” is 2 or more, the R
1
groups may be identical or different.
Illustrative examples of the organooxysilane of formula (1) include dimethoxydimethylsilane, diethoxydimethylsilane, phenylmethyldimethoxysilane, methylvinyldimethoxysilane, trimethylmethoxysilane, trimethylethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, and phenyltrimethoxysilane.
These organooxysilanes may be used alone or in admixture of two or more.
In the practice of the invention, first of all, acidic water is added to the organooxysilane of formula (1) as hydrolytic water for hydrolyzing the organooxysilane. This hydrolytic water is a component necessary to hydrolyze the organooxysilane and is previously adjusted to pH 1 to 5, preferably pH 3 to 4.5. If the pH is below the range, hydrolytic reaction is immediately followed by rapid condensation reaction to invite a molecular weight increase and formation of cyclic compounds, making it difficult to produce low molecular weight organosilicon compounds having high silanol contents. If the pH is above the range, the catalysis necessary for hydrolysis is not obtained and hydrolysis proceeds no longer. The acids used to adjust the pH of water include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid and organic acids such as formic acid and acetic acid. Acidic water is preferably used in an amount of 0.5 to 3 mol, especially 1 to 1.5 mol per mol of the organooxy group in the organooxysilane. Less amounts of water fail to drive hydrolysis of organooxy groups to completion. If water is used in excess, a noticeable amount of unreacted water is left in the reaction mixture.
Reaction of the organooxysilane with acidic water is generally effected at a temperature of 0 to 70° C., and preferably 20 to 50° C. Since the organooxysilane and acid water do not mix with each other and remain separate as two phases at the initial stage of reaction, agitation is necessary in order to bring them in full contact. As hydrolysis proceeds, water is consumed, an alcohol forms, and the system becomes homogeneous.
The hydrolysis time varies with the pH of hydrolytic water and the type of organooxysilane reactant. For example, when dimethyldimethoxysilane is hydrolyzed with hydrochloric acid water at pH 3.5, a two-phase system forms initially. With the progress of reaction, the system becomes homogeneous. It takes about 2 minutes until the system becomes homogeneous. At this point, low molecular weight, silanol-containing organosilicon compounds such as dihydroxydimethylsilane and dihydroxytetramethyldisilo

Affiliated with

Also associated with

Rating

Preparation of silanol-containing organosilicon compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Preparation of silanol-containing organosilicon compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preparation of silanol-containing organosilicon compounds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2866246