Friction Reducing Additives and Lubricating Oil Compositions Containing Same

This application is related to application Ser. No. 291,005, filed Aug. 7, 1981, now U.S. Pat. No. 4,402,842. The related application teaches the initial reaction product, i.e., the product made by reacting amine, aldehyde and mercaptan.

1. Field of the Invention

This invention relates to lubricant and fuel additives and compositions there of and, more particularly, to liquid fuel and lubricant compositions comprising fuels or oils of lubricating viscosity or greases prepared therefrom containing a minor friction reducing amount of products made by reacting together an amine, an aldehyde and a mercaptan and reacting this product with a boron compound.

2. Description of the Prior Art

Several means have been employed to reduce overall friction in modern engines, particularly automobile engines. The primary reasons are to reduce engine wear thereby prolonging engine life and to reduce the amount of fuel consumed by the engine thereby reducing the engine's energy requirements or fuel consumption. While it is commonly understood that lubricants by definition, reduce friction between moving surfaces, friction reducing additives are agents which when added to lubricants in minor amounts significantly enhance the frictional properties of those lubricants without modifying other physical properties such as viscosity, density, pour point, and the like.

Many of the solutions to reducing fuel consumption have been strictly mechanical, as for example, setting the engines for a leaner burn or building smaller cars and smaller engines. However, considerable work has been done with lubricating oils, mineral and synthetic, to enhance their friction or antioxidant properties by modifying them with friction reducing additives.

Although amines and other nitrogen-containing compositions have been added to lubricants for various purposes, the reaction products of this invention are, to applicants' best knowledge, novel, and they have no prior history of use in lubricating compositions as friction reducing additives or in the multifunctional additive areas of anti-corrosion, especially copper corrosion inhibiting, anti-wear or anti-oxidation.

No art is known which teaches or suggests the invention described herein.

In accordance with the invention, there is provided a product of reaction produced by (1) reacting an amine with a mercaptan and an aldehyde, and (2) reacting the product obtained with a boron compound. Also provided is a liquid fuel or a lubricant composition containing same. The lubricant comprises oils of lubricating viscosity or greases therefrom and the liquid fuel comprises liquid hydrocarbon fuels such as gasoline, fuel oil, and the like, as well as alcohol fuels, such as methanol and ethanol, or mixtures thereof.

The amines useful in this invention include hydrocarbyl mono- and diamines, wherein the hydrocarbyl portion, which can be alkyl, alkenyl, cycloalkyl, cycloalkenyl, alkaryl or aralkyl, may contain from 10 to 30 carbon atoms. Among the amines that are useful in the practice of this invention may be included cocoamine, decylamine, dodecylamine, tetradecylamine, oleylamine, isostearylamine, myristylamine, palmitylamine, stearylamine, N-oleyl-1,3-propylenediamine, N-coco-1,3-propylenediamine, N-tallow-1,3-propylenediamine and N-isomerictridecyl-1,3-propylenediamine.

Also included are the polyalkylene polyamines of the formula

wherein R is H or a C.sub.1 to C.sub.20 hydrocarbyl group, R.sup.1 is a C.sub.2 to C.sub.5 alkylene group and x is 1 to 10. Some specific members are ethylenediamine, N-oleyl-ethylenediamine, N-oleyl-propylenediamine, N-coco-triethylenetetramine, diethylenetriamine, tetraethylenepentamine, and the like.

The reaction product is prepared by reacting the amine with an aldehyde of the formula

wherein R.sup.2 is H or a C.sub.1 to C.sub.8 hydrocarbyl group (e.g., alkyl, alkenyl, cycloalkyl, alkaryl or aralkyl) and a mercaptan of the formula

wherein R.sup.3 is a C.sub.8 to C.sub.30 hydrocarbyl group, preferably an alkyl group. R.sup.3 can be a straight chain or branchd chain, with the straight chain mercaptans being preferred.

The useful aldehydes, of which formaldehyde and paraformaldehyde are preferred, include acetaldehyde, propionaldehyde, butyroaldehyde and 2-ethylhexylaldehyde.

Preferred among the useful mercaptans is n-dodecyl mercaptan. Others that may be used include n-nonyl, n-octyl, n-decyl, n-myristyl, n-hexadecyl, stearyl, and oleyl mercaptan.

The following formula depicts the structure of a product that may be present, at least to some extent, in the reaction product: ##STR1## Another possible structure may be: ##STR2## Since the products are mixtures of compounds, they will be referred to herein as "reaction products" or "products of reaction" or an equivalent expression.

The initial reaction products can be prepared by refluxing amine, aldehyde, and mercaptan at molar ratios of from about 1:1:0.5 to about 1:1:1, respectively, in either polar or non-polar solvents such as n-butanol, isopropanol, toluene, or benzene until an expected amount of H.sub.2 O is removed. A temperature of from about 80.degree. C. to about 160.degree. C. can be used, but from about 110.degree. C. to about 140.degree. C. is preferred.

Alternatively, the Mannich base-type condensation product can be prepared by reacting equimolar amounts of amine and aldehyde in an alcoholic solvent until an expected amount of H.sub.2 O is removed. The reaction is run for about 1 to 4 hours between about 80.degree. and 145.degree. C. Then, an equimolar amount, for example, of mercaptan may be added and reacted for about 3 to 6 hours at from about 110.degree. C. to about 160.degree. C.

The initial reaction product is then borated with any appropriate boron-containing compound. Preferred, because of ease of reaction, boric oxide or a boron compound of the formula

where R.sup.4 is a C.sub.1 to C.sub.6 alkyl, a is 0 to 3 and b is 0 to 3, the sum of a and b being 3, can be performed in the presence of an alcoholic solvent, such as butanol or pentanol, or a hydrocarbon solvent such as benzene, toluene or xylene, or mixtures of such solvents. Reaction temperatures of 90.degree. C. to 150.degree. C. or more can be used, but 95.degree. C. to 135.degree. C. is preferred. Reaction times can be 1 to 24 hours and more. Up to a stoichiometric amount of boric acid (included within the formula) or an excess thereof, can be used to produce a derivative containing from about 0.1% to about 10% of boron. Conversely, a stoichiometric excess of boric acid (more than an equivalent amount of borating agent compared to initial product) can also be charged to the reaction medium resulting in a product containing the stated amount of boron. The nitrogen/sulfur-containing products can also be borated with a trialkyl borate such as tributyl borate, often in the presence of boric acid.

In general, the product is employed in an amount from about 0.1% to about 10% by weight, and preferably in an amount of from about 0.5% to about 5% by weight of the total weight of the composition. When used in hydrocarbon or alcoholic fuels, they may be present to the extent of from about 0.00001 to about 1% by weight, preferably from about 0.001 to about 0.01% by weight.

Of significance also is the ability to counteract the accelerating effect of oxidation on metal and lubricant deterioration achieved by employing the aforementioned product. Thus, these products may be incorporated in liquid hydrocarbon fuels or in lubricating media which may comprise liquid hydrocarbon oils in the form of either a mineral oil or a synthetic oil, or mixtures thereof, or in the form of a grease, in which any of the aforementioned oils are employed as a vehicle. These can in addition contain detergents and dispersants, as well as antioxidants, inhibitors, antiwear, extreme pressure, antifoam, pour depressant, and viscosity index improving additives without negating the beneficial properties of the novel compositions of this invention. The compositions can include commonly used additives such as phenates, sulfonates, polymers, metal dithiophosphates, olefin copolymers, polymethacrylates, succinimides, and the like. In general, mineral oils employed as the lubricant or grease vehicle may be of any suitable lubricating viscosity range as, for example, from about 45 SSU at 100.degree. F. to about 6,000 SSU at 100.degree. F., and preferably from about 50 SSU at 210.degree. F. to about 250 SSU at 210.degree. F. These oils may have viscosity indexes varying from below 0 to about 100 or higher. Viscosity indexes from about 70 to about 95 are preferred. The average molecular weights of these oils may range from about 250 to 800. Where the lubricant is to be employed in the form of a grease, the lubricating oil is generally employed in an amount sufficient to balance the total grease composition, after accounting for the desired quantity of the thickening agent, and other additive components to be included in the grease formulation.

In instances where synthetic oils, per se, or synthetic oils employed as the vehicle for the grease, are desired in preference to mineral oils, or even where they may be desired in combination with the mineral oil, various compounds of this type may be successfully utilized. Typical synthetic vehicles include polyisobutylene, polybutenes, hydrogenated polydecenes, polypropylene glycol, polyethylene glycol, trimethylol propane esters, neopentyl and pentaerythritol esters, di(2-ethylhexyl) sebacate, di(2-ethylhexyl) adipate, di(butylphthalate) fluorocarbons, silicate esters, silanes, esters of phosphorous-containing acids, liquid ureas, ferrocene derivatives, hydrogenated mineral oils, chain-type polyphenols, siloxanes and silicones (polysiloxanes), alkyl-substituted diphenyl ethers typified by a butyl-substituted bis(p-phenoxy phenyl) ether, phenoxy phenylethers, etc.

The lubricating vehicles of the aforementioned greases of the present invention, containing the above-described products, are combined with a grease-forming quantity of a thickening agent. For this purpose, a wide variety of material may be employed. These thickening or gelling agents may include any of the conventional metal salts or soaps, which are dispersed in the lubricating vehicle in grease-forming quantities, in such degree as to impart to the resulting grease composition the desired consistency. Examples are the alkali and alkaline earth metal soaps of fatty acids having from 12 to 30 carbon atoms. The metals are typified by lithium, sodium, calcium and barium. Preferred thickeners from these include lithium stearate and lithium hydroxy stearate. Other thickening agents that may be employed in the grease formation may comprise the non-soap thickeners, such as surface modified clays and silicas, aryl ureas, calcium complexes and similar materials. In general, grease thickeners may be employed which do not melt and dissolve when used at the required temperature within a particular environment; however, in all other respects, any materials which are normally employed for thickening or gelling hydrocarbon fluids for forming greases, can be used in preparing the aforementioned improved greases in accordance with the present invention.

The liquid fuels include liquid hydrocarbons such as fuel oil, diesel oil and gasoline, alcohols such as methanol and ethanol and mixtures thereof. That is, the fuel can be one or more liquid hydrocarbons, alcohols, mixtures of alcohols and mixtures of alcohols with hydrocarbons or mixed hydrocarbons.

The following Examples will specifically illustrate the invention. It will be understood that they are meant to be illustrations of and not limitations to the invention.

A mixture of oleylamine (200 g), 95% formaldehyde (23.7 g), and n-dodecyl mercaptan (151 g) was refluxed in 175 cc toluene. The expected amount of water was removed by azeotropic distillation. The reaction temperature was raised to 135.degree. C., and no additional water formed. Toluene was removed by high speed rotary evaporation, and the product residue was filtered through diatomaceous earth. The product solidified to an off-white waxy solid at room temperature. The infrared spectrum contained no characteristic carbon nitrogen double bond absorption at 1010 and 910 cm.sup.-1, indicating formation of the Mannich base rather than just the Schiff base intermediate.

The condensation product of oleylamine, formaldehyde, and dodecyl mercaptan (200 g), prepared as described in Example 1, was dissolved in 150 cc toluene and 50 g n-butanol solvents and heated to 50.degree. C. Boric acid (8.4 g) was added, and the reaction temperature was increased. The reaction was refluxed between 95.degree. and 130.degree. C., and water was removed by azeotropic distillation. The reaction solution was filtered through diatomaceous earth, and the solvent was removed by high speed rotary evaporation. The product was refiltered through diatomaceous earch to yield a waxy, yellow fluid product.

A mixture of cocoamine (79 g), 95% formaldehyde (12.5 g), and n-butanol solvent (80 g) was refluxed until water no longer distilled over. The reaction solution was cooled to room temperature, and n-dodecyl mercaptan (73 g) was added in bulk. The reaction was allowed to reflux at 120.degree. C. for 31/2 hours. The solvent was removed by high speed rotary evaporation, and the product residue was filtered through diatomaceous earth. The infrared spectrum of the resulting off-white waxy solid contained no characteristic carbon nitrogen double bond absorption at 1010 and 910 cm.sup.-1, indicating formation of the Mannich base rather than Schiff base type product.

The condensation product of cocoamine, formaldehyde, and dodecyl mercaptan (107 g), prepared as described in Example 3, was dissolved in 75 cc toluene and 50 cc n-butanol solvents and heated to 50.degree. C. Boric acid (5.2 g) was added and the reaction temperature was increased. The reaction was refluxed between 95.degree. and 130.degree. C., and water was removed by azeotropic distillation. The reaction solution was filtered through diatomaceous earth, and the solvent was removed by high speed rotary evaporation. The product was refiltered through diatomaceous earth to yield a clear, yellow liquid product.

The reaction products derived from the reaction of amines with formaldehyde and mercaptan were blended into a fully formulated engine oil (SAE 5W-30) containing an inhibitor package which includes detergent and dispersant and tested on the Low Velocity Friction Apparatus (LVFA). The fully formulated synthetic lubricating oil had the following general characteristics:

The Low Velocity Friction Apparatus (LVFA) is used to measure the friction of test lubricants under various loads, temperatures, and sliding speeds. The LVFA consists of a flat SAE 1020 steel surface (diam. 1.5 in.) which is attached to a drive shaft and rotated over a stationary, raised, narrow ringed SAE 1020 steel surface (area 0.08 in..sup.2). Both surfaces are submerged in the test lubricant. Friction between the steel surfaces is measured as a function of the sliding speed at a lubricant temperature of 250.degree. F. The friction between the rubbing surfaces is measured using a torque arm strain gauge system. The strain gauge output, which is calibrated to be equal to the coefficient of friction, is fed to the Y axis of an X-Y plotter. The speed signal from the tachometer-generator is fed to the X-axis. To minimize external friction, the piston is supported by an air bearing. The normal force loading the rubbing surfaces is regulated by air pressure on the bottom of the piston. The drive system consists of an infinitely variable-speed hydraulic transmission driven by a 1/2 HP electric motor. To vary the sliding speed, the output speed of the transmission is regulated by a lever-cam-motor arrangement.

The rubbing surfaces and 12-13 ml. of test lubricant are placed on the LVFA. A 500 psi load is applied, and the sliding speed is maintained at 40 fpm at ambient temperature for a few minutes. A plot of coefficients of friction (U.sub.k) over a range of sliding speeds, 5 to 40 fpm (25-195 rpm), is obtained. A minimum of three measurements is obtained for each test lubricant.

Then, the test lubricant and specimens are heated to 250.degree. F., another set of measurements is obtained, and the system is run for 50 minutes at 250.degree. F., 500 psi, and 40 fpm sliding speed. Freshly polished steel specimens are used for each run. The surface of the steel is parallel ground to 4 to 8 microinches. The percentages by weight are percentages by weight of the total lubricating oil composition, including the usual additive package. The data are percent decrease in friction according to: ##EQU1## Thus, the value for the oil alone would be zero for the form of the data used in the Table below.

From the the data it can readily be seen that friction was reduced significantly relative to the base oil, with a maximum reduction of 28% in the coefficient of friction.

The products were also evaluated for oxidation stability. In most cases, improvements in oxidative stability over the base oil were observed. Basically, the test lubricant is subjected to a stream of air which is bubbled through at the rate of 5 liters per hour at 425.degree. F. for 24 hours. Present in the composition are samples of metals commonly used in engine construction, namely, iron, copper, aluminum, and lead. See U.S. Pat. No. 3,682,980, incorporated herein by reference, for further details of the test. Reductions in viscosity increase or limiting of neutralization number (or both) show effective control. See results in Table 2. The oil used was a 200" solvent paraffinic neutral mineral oil.

Also, copper strip corrosion tests were run in accordance with ASTM D130-80, the results of which are shown in Table 3. Effective corrosion inhibition was observed. A 200" solvent paraffinic neutral oil was used.