Organosilane Stabilizers for Inorganic Silicates in Antifreezer/Coolant Compositions

1. Field of the Invention

The present relates to organosilicon compounds having hydroxyl and carboxyl groups or cyano group which are effective stabilizers for aqueous silicates, silica sols and other silica containing water, such as boiler water, antifreezer and coolant solutions.

2. Description of the Prior Art

It is well known that alkali metal silicates are effective metal corrosion inhibitor. It has therefore been desirable to use alkali metal silicates in antifreezer and coolant formulations. However, antifreezer and coolant compositions containing such silicates generally have the tendency to gel or form precipitates during the storage or after prolonged use at elevated temperatures. Thus, it has been previously proposed to use a stabilizer to prevent the gelation of the alkali metal silicates in the antifreezer compositions so that the silicates could be more persistent in their corrosion inhibiting properties.

A number of organosilicon compounds and organosilicon polymers or organosilicon copolymers with organic polymers such as polyethylene oxides have been known to be effective as the stabilizers for alkaline metal silicates corrosion inhibitor additives in antifreezer/coolant compositions.

U.S. Pat. Nos. 4,462,921, 4,287,077 and 4,485,025 disclose the use of organosilicon polymers or copolymers with organic polymer as the stabilizers for this purpose. Since the organic polymers have limited solubility in aqueous systems or in glycols, they are usually coupled with hydrophilic groups such as carboxylic acids, polyethers etc. Nonhydrolyzable linkage between the hydrophilc groups and organosilicon polymers can be obtained by hydrosilylation reaction. (Y. Lukevit M. G. Voronkov, "Organic Insertion Reactions of Group IV Elements", Consulant Bureau, New York, 1966). Unfortunately the reaction requires expensive platinum catalyst. In U.S. Pat. No. 4,514,315, there is disclosed that an aqueous or alcohol solution of a alkylene silane grafted polyether provides an aluminum corrosion inhibitor effect.

Organotrialkoxysilanes have been used in antifreeze compositions to improve the anti-gel characteristics of those compositions. U.S. Pat. Nos. 3,198,820, 3,265,623 and 3,312,622 disclose the use of organic acid silane compounds for this purpose. U.S. Pat. Nos. 3,203,969 and 3,248,329 also disclose the use of aminosilane compounds for this purpose. In U.S. Pat. Nos. 4,333,843 and 4,367,154, there is disclosed that the self life or gelation resistance of single phase aqueous glycol or glycol ether compositions can be improved by the addition to the glycol compositions of an effective amount of the hydrolyzate of organophosphorous-silicon compounds.

Pines et al described another system in U.S. Pat. Nos. 3,337,496 and 3,341,469 that was found useful for inhibiting corrosion in aqueous alcohol compositions. It consisted of a mixture of hydroxyalkylsilanes or hydroxyalkylether silanes and a silicate. The materials are stated as being remarkably soluble in aqueous liquids. The hydroxyalkylsilanes and hydroxyalkylether silanes were easily prepared by hydrolysis of the corresponding epoxyalkylsilanes in the presence of base. ##STR5##

The invention concerns organotrialkoxysilane stabilizers for inorganic silicate corrosion inhibitor additives in antifreezer/coolant formulations. The stabilizers have the following structure; ##STR6## Wherein R is an alkyl group of 1-4 carbon atoms, R.sub.1 is either ##STR7## and R.sub.2 and R.sub.3 may be same or different and selected from ##STR8## (wherein R is an alkyl gruop of 1-4 carbon atoms)

The glycols such as ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol can be used as major components in the present composition. The glycol ethers such as the methyl, ethyl, propyl, and butyl ether of ethylene glycol are also useful. Ethylene glycol is particularly preferred as the major antifreeze composition component.

Numerous corrosion inhibitors for antifreeze compositions have been proposed to date. Such inhibitors include both organic materials and inorganic materials. Illustrative of the organic materials that have been used as inhibitors in anti-freeze compositions are: guonidine, citrates, coal tar derivatives, petroleum bases, thiocyanates, peptones, phenols, thioureas, tannin, quinoline, morpholine, triethanolamine, tatarates, glycol monoricinoleate, organic nitrites,mercaptans, organic oils, sulfonated hydrocarbons, fatty oils and soaps. Illustrative of the inorganic materials that have been used as inhibitors are: sulfates, sulfides, fluorides, the alkali metal chromates, nitrites, phosphates, borates, tungstates, molybdates, carbonates, and silicates.

A number of known corrosion inhibitor and additives can be used in the present invention. The most preferred corrosion inhibitors are the alkali metal silicates, such as sodium metasilicate, potassium metasilicate and lithium metasilicate. Other corrosion inhibitors and additives may be used, such as alkali metal borates which include sodium tetraborate, potassium tetraborate and sodium metaborate. Other permissible component include alkali metal mercaptobenzotriazoles, alkali metal polytriazoles, alkali metal vanadates, alkali metal molybdates, and alakli metal nitrates such as sodium nitrate and potassium nitrate, alakli metal nitrites such as sodium and potassium nitrite, alkali metal phosphates such as sodium and potassium phosphate, alkali metal benzoates and various antifoaming agents and dyes, if desired.

The stabilizers useful in the invention are organotrialkoxysilanes which have carbonyl or carboxyl groups and the solublizing hydroxyl group. Gelation resistant additive compounds of this type may be prepared by reacting commercially available epoxy substituted coupling agents such as gamma-glycidoxypropyl-trimethoxysilane and beta-(3,4-epoxycyclohexyl) ethyltrimethoxy-silane with the compounds of general formula 1 in the presence of base catalyst such as alkyllithiums, sodium hydride, Grignard reagents, and alkaline metal alkoxides.

wherein:

X and Y may be same or different and selected from a functional group of the class of ##STR9## --COOR(wherein R is an alkyl group of 1-4 carbon atoms).

The compound of general formula 1 have two acidic protons at alpha position which can be easily pulled off by the base. The resulting carbanions attack the epoxide ring to open up the ring and form a new carbon-carbon bond. This gives a alkoxide anion which will pick up the proton at alpha position to generate another carbanion. This is why only catalytic amount of base is required to complete the reaction. Although this reaction goes smoothly at room temperature, it will speed up at the elevated temperature. At the elevated temperature alkoxy groups on silicon may be reacted to form a dimers or oligomers as the byproducts. However, the contaminated byproducts do not significantly lower the antigel activity of the products. ##STR10##

The improvement in the anti-gel characteristics of the antifreeze compositions of the present invention is achieved because of the chemical reaction between the various silanol and silicate components of the composition. When the organosilane is added to a silicate containing antifreeze composition, it is hydrolyzed by the water present to form the corresponding silanol. The silanol reacts with the silicate in the composition to form a reaction product which is much more stable with respect to gel and precipitate formations than the original silicate. Thus, the silicate remains in solution in the antifreeze composition. It is theorized that the silanol formed polymerizes in some way, but it is unclear whether the silanol polymerizes with itself or whether it copolymerizes with the silicate. The important thing is that the silicate stays in solution and the part of the silicate which exhibits corrosion inhibition activity retains this activity.

The amounts of corrosion inhibitors discussed above known to be effective are well known in the art. Of course, the amount will vary for each inhibitor. It is not possible to set forth exactly the amount of silicate to be used in each instance due to the complicating influence of the other corrosion inhibitors such as the aforementioned borates, triazoles, nitrates, nitrites and phosphates. Simple, accelerated aging tests can be used to determine the amount of silicate which when added will give the desired corrosion resistance. Generally, the proportion of silicates should range from about 0.025 to 1.0 percent by weight, preferably about 0.05 to 0.5 percent by weight.

The gelation resistant organosiloxane compound should be used at levels of about 100 to 10,000ppm to prevent gelation of the inorganic silicates in antifreeze/coolant formulations. These limits are generally much lower than those found in much of the prior art.

Throughout this specification it is noted that the gellation inhibitor is first created and subsequently added to the alkylene glycol composition. However, an alternate approach, which may even turn out to be the preferred one in practice, is to form the gelation inhibitor in situ. The invention relates to a glycol composition containing these gelation inhibitors and is not restricted by the method by which this is accomplished.

This invention will be further illustrated by the following examples which are not intended to limit the invention, but rather to illuminate it.

To a one liter, three neck, round bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser was placed 160 g(lmole) of diethylmalonate under the dry nitrogen atmosphere. With stirring, 60 ml(about 0.1 mole) of 1.6M n-butyllithium solution in hexane was added dropwise through the dropping funnel. At this time the evolution of butane gas was observed by means of a mineral filled bubbler conected to the top of the condenser and white solids precipitated, as the reaction proceeded. When no further gas evolution was stopped, 236 g(lmole) of glycidoxypropyltrimethoxysilane was added dropwise for 2 hrs. The solid was dissolved and the solution turned to light yellow. The solution was refluxed to complete the reaction for another 30 minutes. Gas chromatography analysis showed that no reactants were left. The solvent of hexane was evaporated to give the product.

The product contained about 10% of lithium salt of the product. Since the salt reacts with water to give the product back, it was not necessary to remove the salt from the product before the usage as the stabilizer for the inorganic slicates in antifreeze formulation.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by 0.1 moles of Na-H dispersed in 50 ml of dry THF solution.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by 0.1 moles of methylmagnesiumchloride in THF.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by 0.1 moles of sodium methoxide in methanol solution.

The procedure of Example 1 was repeated using beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane instead of glycidoxypropyltrimethoxysilane.

The product was prepared using the same procedure as described in Example 5 except n-butyllithium was replaced by 0.1 moles of Na-H dispersed in 50 ml of dry THF solution.

The product was prepared using the same procedure as described in Example 5 except n-butyllithium was replaced by 0.1 moles of methylmagnesiumchloride in THF.

The product was prepared using the same procedure as described in Example 5 except n-butyllithium was replaced by 0.1 moles of sodium methoxide in methanol solution.

To a one liter, three neck, round bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser was placed 113 g(lmole) of ethylcyanoacetate under the dry nitrogen atmosphere. With stirring, 60 ml(about 0.1 mole) of 1.6M n butyllithium solution in hexane was added dropwise through the dropping funnel. Butane gas was evolved and white solids precipitated, as the reaction proceeded. When the gas evolution was stopped, 236 g(lmole) of glycidoxypropyltrimethoxysilane was added dropwise for 2 hrs. The solid was dissolved and the solution turned to light yellow. The solution was refluxed to complete the reaction for another 2 hrs. Gas chromatography analysis showed that no reactants were left. The solvent of hexane was evaporated to give the product. The product contained about 10% of lithium salt of the product. Since the salt reacts with water to give the product back. It was not necessary to remove the salt from the product before the usage as the stabilizer for the inorganic silicates in antifreeze formulation.

The product was prepared using the same procedure as described in Example 9 except n-butyllithium was replaced by 0.1 moles of Na-H dispersed in 50 ml of dry THF solution.

The product was prepared using the same procedure as described in Example 9 except n-butyllithium was replaced by 0.1 moles of methylmagnesiumchloride in THF.

The product was prepared using the same procedure as described in Example 9 except n butyllithium was replaced by 0.1 moles of sodium methoxide in methanol solution.

To a one liter, three neck, round bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser was placed 113 g(lmole) of ethylcyanoacetate under the dry nitrogen atmosphere. With stirring, 60 ml(about 0.1 mole) of 1.6M n-butyllithium solution in hexane was added dropwise through the dropping funnel. Butane gas was evolved and white solids precipitated, as the reaction proceeded. When the gas evolution was stopped, 246 g (lmole) of beta-(3,4-epoxycyclohexyl)trimethoxysilane was added dropwise for 2 hrs. The solid was dissolved and the solution turned to light yellow. The solution was refluxed at 120.degree. C. to complete the reaction for another 4 hrs. Gas chromatography analysis showed that no reactants were left. The solvent of hexane was evaporated to give the product.

The product contained about 10% of lithium salt of the product. Since the salt reacts with water to give the product back. It was not necessary to remove the salt from the preduct before the usage as the stabilizer for the inorganic silicates in antifreeze formulation.

The product was prepared using the same procedure as described in Example 13 except n-butyllithium was replaced by 0.1 moles of Na-H dispersed in 50 ml of dry THF solution.

The product was prepared using the same procedure as described in Example 13 except-n-butyllithium was replaced by 0.1 moles of methylmagnesiumchloride in THF.

The product was prepared using the same procedure as described in Example 13 except n-butyllithium was replaced by 0.1 moles of sodium methoxide in methanol solution.

The procedure of example 1 was repeated using the same number of moles of ethylacetoacetate instead of dimethylmalonate to prepare the stabilizer.

The procedure of example 1 was repeated using the same number of moles of methylphenylacetate instead of dimethylmalonate to prepare the stabilizer.

To a one liter, three neck, round bottomed flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser was placed 160 g(lmole) of benzylcyanide under the dry nitrogen atmosphere. With stirring, 60 ml(about 0.1 mole) of 1.6M n-butyllithium solution in hexane was added dropwise through the dropping funnel. Butane gas was evolved and white solids precipitated, as the reaction proceeded. When the gas evolution was stopped, 236 g(lmole) of glycidoxypropyltrimethoxysilane was added dropwise for 2 hrs. The solid was dissolved and the solution turned to light yellow. The solution was refluxed to complete the reaction for another 30 minutes. Gas chromatography analysis showed that no reactants were left. The solvent of hexane was evaporated to give the product.

The product contained about 10% of lithium salt of the product. Since the salt reacts with water to give the product back. It was not necessary to remove the salt from the product before the usage as the stabilizer for the inorganic silicated in antifreeze formulation.

The procedure of example 13 was repeated using the same number of moles of ethylacetoacetate instead of ethylcyanoacetate to prepare the stabilizer.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by same number of moles of methyllithium.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by methylmagnesium bromide in THF.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by phenyllithium.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by phenylmagnesium bromide in THF.

The product was prepared using the same procedure as described in Example 1 except n-butyllithium was replaced by t-butyllithium.

One equivalent of the product prepared in Example 1 is hydrolyzed by refluxing with five times of aqueous sodium hydroxide to give the corresponding siliconate having the following formular. ##STR22##

In U.S. Pat. No. 4,367,154, there is disclosed an accelerated aging test method to estimate the gellation resistance of antifreeze compositions. The antifreeze samples were prepared according to GM 6038M of General Motor Co. The details of the compositions are 95.975% of ethylene glycol, 0.200% of sodium nitrate, 1.000% of sodium metaborate, 0.150% of sodium silicate, 0.200% of sodium tolyltriazole(50% aqueous solution), 0.450% of sodium orthophosphate, 0.20% of sodium hydroxide, 0.005% of pigment, and 2.000% of water.

The test was performed by placing a sample of the antifreeze composition in an oven controlled at 65.degree. C. or 100.degree. C. and measuring the number of days before the composition begins to gel. The gel stability of the sample at 65.degree. C. and 100.degree. C. and as well as those to which various stabilizing agents were added in the quantity of 100 ppm are presented in Table 1 wherein the time in days is the amount of time before the first visible formation of a gel was observed.