Method for the synthesis of acylamino organosilicon compounds

Abstract: Organosilicon compounds containing at least one acylamino-substituted hydrocarbon radical are prepared by reacting an organosilicon compound containing at least one amino-substituted hydrocarbon radical with an acyl halide in a nonaqueous solvent and in the presence of a metal alkoxide in a nonaqueous cosolvent.

Description: This invention relates to a method for preparing organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals. More specifically, the method involves the reaction of amino-alkylsilanes and siloxanes with acyl halides in nonaqueous media and in the presence of metal alkoxides to produce acylamino organosilicon compounds. Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in US-A-4,608,270 to Varaprath. As mentioned in US-A-4,608,270, acylaminoorganopolysiloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However, such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer especially when the acid chloride has other reactive vinyl functionality such as where the acid chloride is acrylyl chloride. An alternative method for the preparation for the amino organosilicon compounds involves the reaction of aminosiloxanes and silanes with an acid anhydride or ester at elevated temperature. Unfortunately, at the elevated temperatures of the reaction, arcylamide derivatives undergo Michael addition and amidation of the acrylic double bond resulting in unwanted byproducts and crosslinkage of the desired product which ultimately causes the polymer to gel. Finally, as taught in the above mentioned U.S. Patent No. 4,608,270 to Varaprath, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of aqueous sodium hydroxide. However, a problem arises from the fact that this reaction is carried out in a two-phase system in which the aminosiloxane is dissolved in an organic solvent that is immiscible with water. The HCl that is produced on addition of acyl chloride is neutralized by hydroxide in the aqueous phase. Because the amide function is generally highly polar and hydrophilic, it shows a great tendency to absorb moisture. Incorporation of these units into the siloxane backbone increases water miscibility causing the polymers to emulsify easily thus making phase separation difficult. To some extent, this problem can be overcome by using chlorinated solvents such as methylene chloride or chloroform but, unfortunately, such solvents are toxic. Moreover, when larger amounts of amide functionality or more resinous structure or both are used, it becomes very difficult to prepare such compounds using a two-phase system even when chlorinated solvents are used. Finally, because of the presence of the aqueous phase, it is impossible to prepare aminosilanes containing hydrolytically unstable groups using this process. Accordingly, the need remains for an improved method for preparing acylamino organosilicon compounds which avoids the phase separation and toxicity problems previously encountered. The need also remains for an expanded method which permits use of silane starting materials having hydrolytically unstable groups such as CH₃OSi. These needs are met by the present invention which is directed to a method for preparing organosilicon compounds that contain at least one silicon-bonded acylamino-substituted hydrocarbon radical using a nonaqueous solvent system. Accordingly, the present invention provides a method for preparing an organosilicon compound containing at least one silicon-bonded acylamino-substituted hydrocarbon radical comprising reacting in a non-aqueous solvent system an acyl halide with an aminosilicon compound having at least one silicon-bonded amino-substituted hydrocarbon radical containing at least one nitrogen-bonded hydrogen, all other silicon valences therein being satisfied by radicals selected from the group consisting of organic radicals and divalent, silicon-linking, oxygen atoms, in the presence of a non-aqueous solvent, a metal alkoxide and optionally a non-aqueous cosolvent for said metal alkoxide. Preferably, an aminoalkylsilane or siloxane, that is, an aminosilicon compound having at least one silicon-bonded, amino-substituted hydrocarbon radical containing at least one nitrogen-bonded hydrogen, is reacted with an acyl halide in a nonaqueous and non-toxic solvent such as toluene or hexane. The silicon-bonded, amino-substituted hydrocarbon radical preferably has the formula -Q(NHQ') a NZH wherein Q and Q' are divalent hydrocarbon radicals, Z is H or a monovalent hydrocarbon radical and "a" is 0 or 1. The acyl halide preferably has the formula R''COX where R'' is a substituted or unsubstituted monovalent hydrocarbon radical and X is a halogen atom. An alkali metal alkoxide such as sodium methoxide which may be in the form of a dry powder, preferably dissolved in a small amount of a cosolvent such as methanol, is used to neutralize the HCl that is produced in the primary reaction. Preferably, the reaction is carried out at a temperature of from -10 to 10°C. The use of nonaqueous solvents allows the use of organosilicon compounds with hydrolytically unstable functional groups such as the methoxy group. Likewise, because no separate aqueous phase is present, there are no phase separation problems. Thus an improved process without many of the drawbacks of the prior art is provided for producing acylamino organosilicon compounds. As described in Varaprath Patent No. 4,608,270, the acylamino organosilicon products are useful for paper release coatings and coupling agents. They are also useful as conformal coatings, for example, as moisture and radiation dual cure coatings. Accordingly, it is an object of the present invention to provide an improved method for preparing organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals of the type described in Varaprath Patent No. 4,608,270. These and other objects of and advantages of the invention will become apparent from the following description and the appended claims. The preferred method consists of reacting an acyl halide with an aminosilicon compound having at least one silicon-bonded acylamino-substituted hydrocarbon radical containing at least one nitrogen-bonded hydrogen. The remaining silicon bonds are satisfied with organic radicals or divalent, silicon-linking, oxygen atoms or both. The improved reaction of the present invention is carried out in the presence of a nonaqueous solvent, a metal alkoxide and optionally a small amount of cosolvent for the metal alkoxide. Typically, the aminosilicon compound, a solvent, a metal alkoxide and a small amount of cosolvent are mixed together. An acyl halide is dissolved in a solvent and gradually added to the mixture. After the addition is complete, the resulting mixture is agitated until the reaction is complete. The by-product metal halide is removed by filtration and the solvent can be removed if desired. The acyl halide can have any structure such as a linear, branched or cyclic structure having aromatic heterocyclic, olefinic or paraffinic bonding and containing one or more carbon-bonded -COX radicals, where X denotes a halogen atom. Preferably, the acyl halide has the structure R″COX where X denotes a halogen atom such as I, Cl, Br or F, preferably chlorine and R″ denotes an unsubstituted or substituted monovalent hydrocarbon radical. Examples of monovalent hydrocarbon radicals, i.e. R'' radicals, include, but are not limited to, alkyl radicals such as methyl, ethyl, propyl, butyl, hexyl and octyl; cycloaliphatic radicals such as cyclohexyl; aryl radicals such as phenyl, benzyl, styryl, tolyl, xylyl and biphenyl (xenyl); and alkenyl radicals such as vinyl and allyl. Examples of corresponding acyl halides include acetyl chloride, benzoyl chloride and, most preferably, acrylyl chloride, methacrylyl chloride and cinnamoyl chloride. Examples of substituted R'' radicals include, but are not limited to, halogenated radicals such as -CF₃ and -C₆H₄Cl and other substituted radicals which are stable under the reaction conditions employed in the method of this invention such as -CH₂CH₂CN, -C₆H₄NO₂ and -C(CN)=CH₂. The aminosilicon compound that is to be acylated can have any structure as long as it contains at least one silicon atom bonded to an amino-substituted hydrocarbon radical that bears one or more amino radicals at least one of which has a nitrogen-bonded hydrogen atom. The other silicon bonds are satisfied by organic radicals other than amino-substituted hydrocarbon radicals noted above or by divalent, silicon-linking oxygen atoms. Thus the aminosilicon compound can be a silane, a siloxane, a silcarbane or a silcarbane-siloxane. The silicon-bonded amino-substituted hydrocarbon radical has preferably the formula -Q(NHQ′) a NHZ where Q and Q′ denote divalent hydrocarbon radicals, Z denotes a hydrogen atom or a monovalent hydrocarbon radical, i.e., an R radical as defined previously and "a" has a value of 0 or 1. Examples of Q radicals and Q′ radicals include, but are not limited to, alkylene radicals such as ethylene, propylene, isopropylene, butylene, isobutylene, hexylene, octylene and arylene radicals such as phenylene, xylylene, etc. Q is preferably ethylene and Q′ is preferably propylene or isobutylene. Examples of silicon-bonded amino-substituted hydrocarbon radicals include, but are not limited to, NH₂CH₂CH₂CH₂-, CH₃NHCH₂CH₂CH₂-, NH₂CH₂CH(CH₃)CH₂-, NH₂CH₂CH₂NHCH₂CH₂CH₂-, NH₂CH₂CH₂NHCH₂CH(CH₃)CH₂-, NH₂(CH₂)₆NH(CH₂)₃- and NH₂(CH₂)₆NHCH₂CH(CH₃)CH₂-. Silicon-bonded radicals, other than the above-noted amino-substituted hydrocarbon radicals, include organic radicals and divalent, silicon linking oxygen atoms. Examples of said organic radicals include, but are not limited to, divalent, silicon-linking hydrocarbon radicals such as the Q and Q′ radicals noted above and halogenated derivatives thereof, alkoxy radicals such as methoxy radicals, hydroxy radicals, acyloxy radicals and hydrogen atoms. Preferably, said organic radicals contain no more than 6 carbon atoms, such as methyl, 3,3,3-trifluoropropyl, phenyl and vinyl radicals and most preferably are methyl or methoxy radicals. The aminosilicon compounds to be acylated by the process of this invention are preferably silanes or siloxanes having the average formula R′ c (NH₂(Q′NH) a Q) d SiO (4-c-d)/2 where R′ denotes a monovalent hydrocarbon radical or an alkoxy radical as defined previously, where "a", is 0 or 1, "c" denotes a number having a value of from 0 to 3, such as 0, 0.5, 1.01, 2, 2.1 and 3, "d" denotes a number having a value of from >0 to 4, such as 0.01, 0.5, 1, 2 and 3 and "c" + "d" has a value of from 1 to 4 such as 1.5, 1.99, 2.01, 3 and 4. Q and Q′ are as defined previously. Of course, the aminosilane or siloxane must contain an average of at least one silicon-bonded, amine-substituted hydrocarbon radical per molecule. The siloxanes can contain siloxane units without amino-substituted hydrocarbon radicals such as R′ c SiO (4-c)/2 as exemplified by MeSiO 3/2 , PhSiO 3/2 , PhMeSiO 2/2 , Me₂SiO 2/2 , Me₃SiO 1/2 , Me₂(OMe)SiO 1/2 , ViMe₂SiO 1/2 and SiO 4/2 units where Me, Ph and Vi denote methyl, phenyl and vinyl, respectively, in addition to siloxane units that contain the required amino-substituted hydrocarbon radicals. Preferred aminosilanes to be acylated have the formulae R′ e Si(QNHCH₂CH₂NH₂) 4-e or R′ e Si(QNH₂) 4-e where "e" denotes a number having a value of 0, 1, 2 or 3. For example, the aminosilane can be Me₃SiCH₂CH(CH₃)CH₂NHCH₂CH₂NH₂, (MeO)₂MeSiCH₂CH₂CH₂NH₂, (MeO)₃SiCH₂CH(CH₃)CH₂NHCH₂CH₂NH₂, (MeO)₃SiCH₂CH₂CH₂NH₂ or (MeO)₂MeSiCH₂CH(CH₃)CH₂NHCH₂CH₂NH₂. Preferred aminosiloxanes to be acylated have the formula YR′₂SiO(R₂SiO) x (YR′SiO) y SiR′₂Y where each Y denotes, independently, an R′, -QNHCH₂CH₂NH₂ or -QNH₂ radical, at least one Y being an amino-substituted radical and "x" and "y" denote numbers having average values of from 0 to 5000 and 0 to 500, respectively. Examples of preferred amino-siloxanes to be acylated by the method of this invention include, but are not limited to, Aminosiloxanes can also have a cyclic or branched structure such as (YMe₂SiO)₄Si and (YMeSiO)₄, in addition to the linear structures noted above, wherein at least one Y denotes an amino-substituted radical. Aminosilicon compounds and their preparation are well known in the organosilicon art. Some are commercially available. The disclosures of U.S. Patent Nos. 2,557,803, 2,738,357, 2,754,312, 2,762,823, 2,998,406, 3,045,036, 3,087,909, 3,355,424, 3,560,543, 3,890,269, 4,036,868, 4,152,346 and 4,507,455 further teach how to prepare aminosilicon compounds that can be used in the method of this invention. The acyl halide is admixed to the aminosilicon compound in the presence of a metal alkoxide preferably dissolved in a small amount of cosolvent. Preferably, the cosolvent is methanol. The metal alkoxide is preferably an alkali metal alkoxide such as sodium methoxide. While it is possible to conduct the instant reaction without use of a cosolvent, use of a cosolvent is greatly preferred. Because sodium methoxide is essentially insoluble in a solvent such as toluene, it is believed to be difficult for the undissolved sodium methoxide to adequately neutralize the amine hydrochloride which is formed as a part of the process. Unless the amine hydrochloride that is formed during the reaction is neutralized and the amine freed, further reaction with the acyl halide cannot take place. Use of a cosolvent system in which the bases are soluble to some extent overcomes this apparent problem. Preferably, a catalytic amount of cosolvent is used, i.e., an amount sufficient to effect transfer of the alkali metal alkoxide into the nonaqueous solvent. Thus for a mixture sodium methoxide and methanol cosolvent, the preferred range of methanol is about 1 to 25 wt.%. While it is possible to use larger amounts of methanol, limiting the presence of the cosolvent to such small amounts is greatly preferred. Thus, it has been found that when a relatively large amount of methanol cosolvent is used, such as that found in a 25 wt.% solution of sodium methoxide in methanol, long term stability may be impaired. This is believed to be due to the fact that in order to obtain an acrylamidoalkyl polysiloxane with a long term stable viscosity, it is desirable to convert a high percentage (>95%) of amine to amide. When a large amount of methanol cosolvent is used, the best conversion of amine to amide that could be achieved was found to be around 90-93%. This was apparently due to the occurrence of competing reactions, such as formation of methyl acrylate, which are facilitated in the presence of an excess of cosolvent. Thus in order to maximize amide formation and to minimize side reactions, it is desirable to reduce the concentrations of methanol to only a catalytic quantity when compared to sodium methoxide. For example, when one half the weight of methanol compared to the weight of solid sodium methoxide is used, the conversion of amine to amide was found to be >95% and the resulting product exhibited a stable viscosity for at least 3 months. In addition to the small amount of cosolvent for dissolving the metal alkoxide, a nonaqueous solvent is also used for the aminosilicon when the acyl halide is admixed to it. That solvent can be any suitable nonaqueous liquid that will not react with the components of the reaction. Preferably, the solvent is also a solvent for the organosilicon product of the reaction. Examples of suitable solvents include, but are not limited to, hydrocarbons such as toluene, xylene, hexane, cyclohexane and heptane; halogenated hydrocarbons such as methylene chloride, chloroform, trichloroethylene and trichloroethane; and oxygenated compounds such as ethyl ether and ethyl acetate. Mixtures of two or more solvents can also be used, it only being required that the mixture and not necessarily all of the components in the mixture, be a solvent for the aminosilicon compound. Preferably, solvents such as toluene or hexane are used. The amount of solvent that is used should be sufficient to dissolve the aminosilicon compound and, preferably, the organosilicon product as well. The preferred components of the reaction mixture, i.e., the acyl halide, the aminosilicon compound, solvent, metal alkoxide and cosolvent, can be mixed in any manner as long as the acyl halide is added to the aminosilicon compound in the presence of the solvent, metal alkoxide and its cosolvent. In a preferred embodiment, the acyl halide or a solution thereof is added to a well agitated mixture of a solvent solution of the aminosilicon material and a cosolvent solution of the metal alkoxide. Since acyl chloride reacts with methanol or sodium methoxide to form esters, about 10% excess acyl chloride, preferably acrylyl chloride, based on the amine content is preferably used for the reaction. A deficiency of acyl halide relative to the total number of reactive amino groups, although merely leading to the preparation of incompletely acylated product when the acyl halide is free of aliphatic unsaturation, leads to products which can undergo a Michael-Addition type reaction when the acyl halide contains aliphatic unsaturation. For this reason, it is preferred, although not required, to fully acrylate the aminosilicon compound when an acrylyl halide is used. An equimolar amount of sodium methoxide and acyl chloride are also preferably used so that the solution at the end of the reaction is neutral. A deficiency of sodium methoxide relative to the amount of hydrogen halide produced is to be avoided since an excess of hydrogen halide will inhibit the reaction from going to completion. Except when the acyl halide is an acrylyl halide, the method of this invention can be practiced at any reasonable temperature. Advantageously, this method proceeds readily at room temperature. When an acrylyl halide is used, this method should be practiced at a relatively low temperature to minimize the formation of byproducts. Accordingly, when using the method of this invention to prepare acrylyl-substituted aminosilicon compounds, the reaction should be conducted at a temperature of from -10°C. to +10°C. Lower reaction temperatures are suitable particularly since no aqueous phase is present, but higher reaction temperatures will substantially reduce the yield of desired product. During and after the addition of the acyl halide component to the aminosilicon component, the reaction mixture should be thoroughly agitated to maintain an intimate contact between the metal alkoxide and the hydrogen chloride. The usual low shear means such as stirrers, paddles and impellers are sufficient to maintain sufficient agitation. Agitation is maintained until the acylation reaction is finished, typically within an hour. After the reaction is finished, the product of the reaction can be separated from the solvent or allowed to remain in the solvent as desired. When acrylyl-substituted products are to be separated from the solvent, it is desirable to add a polymerization inhibitor such as sodium nitrite to the solution prior to any separating action such as distilling or fractionation. The products of this method are useful as polar silicon-containing additives for cosmetic compositions, coating compositions, textile treating compositions and paints. The compositions are useful as comonomers with polymerizable vinyl monomers such as styrene, butadiene, methyl methacrylate, ethyl acrylate, vinyl acetate, vinyl chloride, vinylidene chloride and acrylonitrile. In particular, the compounds having acrylylamine-substituted hydrocarbon radicals are useful as a reactive component in free radical curable compositions such as radiation curable coupling agents, as adhesion promoters and as a component of dual cure systems. The following examples are disclosed to further teach the practice of the invention and are not intended to limit the invention. Example 1 1-Methyl-1,1-bis(trimethylsilyloxy)-1-{3-N-(2-aminoethyl)-3-aminoisobutylsilane was reacted with acrylyl chloride in toluene in the presence of a 25 wt % solution of sodium methoxide in methanol. One and one tenth equivalents of acrylyl chloride and 1.1 equivalents of sodium methoxide based on the amine neutral equivalent (ANE) of the starting amine was used (10% excess). The sample was washed with a saturated sodium chloride solution. Conversion of amine to amide in the washed sample was determined to be 92-93%. Infrared analysis and proton NMR analysis were used to confirm the structure of the resulting product. Example 2 A one liter, three-necked flask equipped with a thermometer, stirring paddle, air tight stirring sleeve, N₂ inlet and dropping funnel was charged with aminopropyltrimethoxysilane (100.0 g, 0.558 moles), toluene (160.1 g), sodium methoxide (33.16 g, 0.614 moles) and methanol (10.11 g). The mixture was stirred under N₂ atmosphere and cooled to 0°C. using a dry ice/isopropanol bath. To this, 55.37 g (0.614 moles) of acrylyl chloride dissolved in 100 g of toluene was added gradually over a period of 30 minutes. The mixture was agitated for another 30 minutes. By-product sodium chloride was removed by filtration and the solvent was removed under reduced pressure to obtain acrylamidopropyltrimethoxysilane in essentially quantitative yield. Sodium nitrite (0.001 g) was added as an inhibitor. Example 3 A 500 ml three-necked flask equipped with a thermometer, mechanical stirrer and dropping funnel with a N₂ inlet was charged with 50 g of (amine neutral equivalent 703; 71.12 mmole of amine) dissolved in 100 ml of toluene. Sodium methoxide (4.22 g, 78.1 mmole) and 2.5 ml of methanol was added to the solution. The reaction mixture was stirred and cooled to 0°C. Acrylyl chloride (7.06 g, 78.1 mmole), dissolved in 20 ml of toluene was gradually added to the stirred reaction mixture, maintaining the temperature at 0°C. After the addition of acrylyl chloride was complete, the mixture was stirred for an additional half hour. Since the solution was slightly acid (6.5 by pH paper), 0.7 g of potassium carbonate was added and the mixture stirred for another 30 minutes. The salts were removed by filtration and the solvent removed under reduced pressure. The conversion of amine to amide was found to be quantitative since the residual amine content in the product was negligible as determined by perchloric acid titration. Example 4 In a 500 ml three necked flask equipped with a thermometer, a mechanical stirrer, a dropping funnel and a N₂ inlet tube was placed 25 g of amine functional phenylhydrolyzate resin (amine neutralization equivalent 720) dissolved in 100 ml of dry toluene. Dry methoxide (2.06 g) dissolved in 2 ml of dry methanol was added. The reaction flask was cooled in an ice bath. Acrylyl chloride (3.45 g) dissolved in 5 ml of toluene was added while stirring the ingredients in the flask, at a rate to maintain the reaction temperature below 5°C. After the addition was over, the contents were allowed to warn to room temperature. The salts were removed by filtration and the solvents removed under reduced pressure to obtain the product in more than 95% yield. Example 5 Using the procedure outlined in Example 4, 20 g of amine functional hydrolyzate obtained from the cohydrolysis of PhSiCl₃ and n-propylSiCl₃ (70:30 wt/wt, respectively) was dissolved in 80 ml of toluene and reacted with 1.72 g of NaOMe in 2 ml of methanol to obtain the corresponding acryl-amide functional resin in 95% yield.

Claims: A method for preparing an organosilicon compound containing at least one silicon-bonded acylamino-substituted hydrocarbon radical comprising reacting in a non aqueous solvent system an acyl halide with an aminosilicon compound having at least one silicon-bonded amino-substituted hydrocarbon radical containing at least one nitrogen-bonded hydrogen, all other silicon valences therein being satisfied by radicals selected from the group consisting of organic radicals and divalent, silicon-linking, oxygen atoms, in the presence of a non-aqueous solvent, a metal alkoxide and optionally a non-aqueous cosolvent for said metal alkoxide. The method according to claim 1 wherein said silicon-bonded amino-substituted hydrocarbon radical has the formula -Q(NHQ′) a NZH and the acyl halide has the formula R″COX, wherein Q and Q′ denote divalent hydrocarbon radicals, R″ denotes a substituted or unsubstituted monovalent hydrocarbon radical, X denotes a halogen atom, Z denotes a hydrogen or a monovalent hydrocarbon radical and "a" has a value of 0 or 1. A method according to claim 2 wherein said acyl halide is a compound selected from the group consisting of acrylyl chloride, methacrylyl chloride and cinnamoyl chloride.

Inventors: VARAPRATH PADMAKUMARI JANAKEY, VARAPRATH SUDARSANAN, VARAPRATH, PADMAKUMARI JANAKEY, VARAPRATH, SUDARSANAN
Applicants: DOW CORNING, DOW CORNING CORPORATION
Application year: 1990
Main classification: C08G77
IPC codes: C08G77, C07F7