Reaction Product of Dialkyl Alkanephosphonate, Substituted Imidazoline, and Water in Lubricant Compositions

1. Field of the Invention

Farm, off-highway construction equipment and industrial tractors, especially those units employing a common fluid reservoir, presently use multifunctional lubricants. These lubricants are considered multifunctional because they must meet the requirements of the transmissions, differentials, final drives, hydrostatic transmissions, hydraulic systems, power steering systems, and fluid immersed disk brakes of the specialized equipment. Thus, for a lubricant to be considered for use in such equipment, it should desirably contain the following properties: oxidative and hydrolytic stability, good antiwear qualities, and compatibility with other lubricant compositions.

In addition, friction modifying characteristics are very important to assure proper, decisive operation of multi-disc transmission clutches and oil immersed brake discs. Water tolerance characteristics are especially important in friction modified lubricants for maintaining the performance integrity of the lubricant in the presence of water formed or introduced during operation.

This invention relates to lubricant compositions, which may be in the form of fuels, heat exchange fluids, lubricating oils or greases thereof, which possess improved water tolerance, friction modifying, antiwear, and antichatter properties. Such compositions are contemplated as being suitable for use in the specilized equipment described hereinabove.

2. Description of the Prior Art

British Pat. No. 1,247,541 discloses lubricant compositions containing alkanephosphonates as having friction modifying characteristics. The alkanephosphonates described therein have the formula: ##STR3## where R is methyl or ethyl, R' is a straight chain alkyl having 12 to 20 carbon atoms and X is a methyl, ammonium, alkylammonium or alkenylammonium group, the organic X group having from 1 to 30 carbon atoms. These compounds may be produced as follows: ##STR4## where R and R' are defined above and, R" and R'" are each alkyl or alkenyl of 1 to 30 carbon atoms.

In reaction (1), a dialkyl phosphonate is reacted with an olefin to produce a R' substituted dialkyl phosphonate. This product is partially hydrolyzed in step (2) by treatment with a base followed by acidification to produce an R' substituted monoalkyl acid phosphonate, which may be further reacted with an amine to form the corresponding salt by acid-base neutralization reaction (3 ) with a transfer of the acid hydrogen. An acid-base neutralization reaction involving a proton transfer, for example: HA + R.sub.2 NH .revreaction. A.sup.- + R.sub.2 N+H.sub.2 is reversible. If the equilibrium is destroyed such as by distillation of the acid or amine, the original reactants can be recovered. Due to the reverisibility of reaction (3) the salt products of the British patent may actually contain some acid phosphonate. Such compounds are sources of "reverse" acidity and tend to "deactivate" basic components of lubricant compositions by neutralization. It is further noted that the hydrolysis and acidification reactions of step (2) are very corrosive and, in addition, present problems with regard to emulsions, exotherms, solvents, solvent recovery, and comprise a multistep process.

In U.S. Pat. No. 3,793,199 an alkanephosphonate diester is reacted with a non-cyclic amine at temperatures of from 80.degree. to 150.degree. C, with 90-130.degree. C being preferred, according to the following formula: ##STR5## where R is a substantially straight chain aliphatic radical having from about 11 to 40 carbon atoms, R' is a lower aliphatic radical having from one to eight carbon atoms, R.sup.2 is a hydrocarbyl radical having from one to 40 carbon atoms and R.sup.3 and R.sup.4 are hydrogen, a hydrocarbyl radical having from one to 40 carbon atoms or a substituted hydrocarbyl radical having amino, alkylamino or hydroxy functional groups.

When R.sup.3 and R.sup.4 are hydrogen, a reversible acid-base reaction may occur. For example, if R.sub.3 were hydrogen, the following reverisble acid-base type reaction: ##STR6## would cause the production of acid phosphonate. The detrimental effect of the presence of acid phosphonate in a lubricant composition has already been discussed.

In South African Pat. No. 74/4882, there is described a lubricant composition which contains a salt of (a) an amine or an imidazoline which contains a straight chain aliphatic group of 12 to 22 carbon atoms and (b) an alkyl, long chain alkyl (C.sub.12 - C.sub.22) acid phosphonate.

It is noted that none of the products described in the prior art were formed by the reaction of a dialkyl alkanephosphonate, substituted imidazoline and water.

It has now been found that an improvement in the antiwear and friction modifying properties of a lubricant can be obtained by incorporating therein a product formed by reacting:

a. a dialkyl alkanephosphonate having the formula: ##STR7## where R' is a substantially unbranched paraffinic alkyl group containing from about 10 to about 36 carbon atoms, but preferably is a substantially unbranched paraffinic alkyl group containing from about 10 to about 20 carbon atoms, and most preferably is octadecyl; and R is a hydrocarbyl group containing from 1 to about 4 carbon atoms with at least one hydrogen atom present on the carbon atom which is bonded to oxygen, but R preferably is methyl or ethyl and most preferably is methyl;

b. a substituted imidazoline of the formula: ##STR8## where one of the R.sup.2 and R.sup.3 substituents must be a substantially unbranched paraffinic or olefinic hydrocarbyl group containing from about 12 to about 35 carbon atoms; and the other R.sup.2 or R.sup.3 substituent is selected from the group consisting of: paraffinic alkyl containing from 1 to about 35 carbon atoms, alkenyl, containing from 1 to about 35 carbon atoms, and hydroxy-alkoxy-, alkoxymethoxy-, and oxo-substituted alkyl and alkenyl containing from 1 to about 20 carbon atoms; and (c) water.

It is preferred that R.sup.2 be a substantially unbranched paraffin or olefin hydrocarbyl group containing from 12 to about 35 carbon atoms, and most preferred that R.sup.2 be a substantially unbranched alkenyl group containing from about 13 to about 21 carbon atoms; with an alkenyl group containing 17 carbon atoms being the most particularly preferred group.

The preferred R.sup.3 substituent is an alkyl group containing 1 to 20 carbon atoms, which most preferably is substituted with a hydroxy, alkoxy, alkoxymethoxy or oxo group. Of these, the particularly preferred substituent is a hydroxy substituted straight chain alkyl group containing from 2 to about 4 carbon atoms, with the --CH.sub.2 CH.sub.2 OH group being the most particularly preferred.

Non-limiting examples of the phosphonate compounds suitable for use herein include: dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl, di-isobutyl and di-sec-butyl decylphosphonate; dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl, di-isobutyl and di-sec-butyl dodecylphosphonate; dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl di-isobutyl and di-sec-butyl tetradecylphosphonate; dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl, di-isobutyl and di-sec-butyl hexadecylphosphonate; dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl, di-isobutyl and di-sec-butyl heptadecylphosphonate; dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl di-isobutyl and di-sec-butyl octadecylphosphonate; and dimethyl, diethyl, diisopropyl, di-n-propyl, dibutyl, di-isobutyl and di-sec-butyl cosanylphosphonate.

Non-limiting examples of the imidazoline compounds suitable for use herein include: 1-(2-hydroxycosanyl)-2-methyl-imidazoline, 1-(2-hydroxybutyl)-2-undecenylimidazoline, 1-(2-hydroxyhexyl)-2-tetradecylimidazoline, 1-(2-hydroxypropyl) -2-hexdecylimidazoline, 1-(2-hydroxyethyl)-2-heptadecenyl-imidazoline, 1-(2hydroxyethyl)-2-octadecylimidazoline, 1-(2-hydroxyethyl)-2dodecenylimidazoline, 1-(2-hydroxy-octadecyl) -2-heptadecylimidazoline, and 1-methyl-2-octadecenyl-imidazoline.

The imidazoline compounds may be prepared by reaction of appropriately substituted 1,2-diaminoethanes with alkylcarboxylic acids as described in U.S. Pat. No. 2,267,965. A particularly preferred acid is oleic acid. Imidazolines which include examples of the above cited compounds are items of commerce as, for example, Amine C, Amine O and Amine S marketed by the Ciba-Geigy Corporation.

The phosphonate (a) may be reacted with the imidazoline (b) at proportions such that there is an excess of the stoichiometric amount of the imidazoline needed to react with the phosphonate, but preferably are reacted in a molar ratio of imidazoline to phosphonate of 1.2 : 1 and most preferably are reacted in stoichiometric proportions. Water (c) is reacted in proportions within the range from about 0.25 mole water per mole of imidazoline (b) to about 2 moles water per mole of imidazoline, with a molar ratio of 1 : 1 being preferred and the ratio of .5 moles water to 1 mole imidazoline being most preferred.

The reaction is conducted at a temperature from about 130.degree. to about 170.degree. C, however, it is preferred to use a temperature from about 140.degree. to about 160.degree. C and a temperature of about 150.degree. C is most preferred.

Reaction times may vary from 4 hours to as little as about 0.25 hour with shorter reaction times applicable at higher reaction temperatures. It is preferred to use times in the range of from about 1 to about 2 hours, with approximately 1.5 hours being the most preferred reaction time. Heating may be done at reduced pressure or at atmospheric pressure using an inert atmosphere, such as nitrogen or carbon dioxide to avoid oxidative degradation during processing may be advantageous.

The infrared spectra of the reaction products of the present invention differs markedly from the product obtained by reaction of the phosphonate (a) and the imidazoline (b) in the absence of water. In the spectra of the product of the present invention a strong band appears at about 1670 cm.sup.-1, and a medium strong band appears at 1550 cm.sup.-1. These were not observed for the products formed by reaction (a) and (b) in the absence of water. The strong band at 1610 cm.sup.-1, which is observed for the products of the reaction of (a) and (b) in the absence of water, is very substantially reduced in the spectra of the products of the present invention.

It is contemplated incorporating antiwear or anti-static friction improving amounts of the aforementioned reaction product in base oleaginous media. In this regard, from about 0.001 to about 7 percent, by weight, preferably from about 0.25 to about 1, and for many applications, from about 0.4 to 0.75 percent by weight may be incorporated into the base oleaginous media.

The oleaginous media may comprise any materials that normally exhibit insufficient antiwear properties or which require friction modifying characteristics. A field of specific applicability is the improvement of oleaginous media which may be selected from the group consisting of lubricating oils, greases, fuels, heat exchange fluids, hydraulic and other functional fluids. Of particular significance is the improvement in lubricating media which may comprise lubricating oils, in the form of either a mineral oil or a synthetic oil, or in the form of a grease in which any of the aforementioned oils are employed as a vehicle. In general, mineral oils, both paraffinic naphthenic and mixtures thereof, 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 6000 SSU at 100.degree. F, and preferably, from about 50 to about 250 SSU at 210.degree. F. These oils may have viscosity indexes varying from below zero to about 100 or higher. Viscosity indexes from about 70 to about 95 are preferred. 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. A wide variety of materials may be employed as thickening or gelling agents. These 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. Other thickening agents that may be employed in the grease formulation may comprise the non-soap thickeners, such as surface-modified clays and silicas, polyaryl 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, it all other respects any material which is normally employed for thickening or gelling hydrocarbon fluids for forming grease can be used in preparing the aforementioned improved grease in accordance with the present invention.

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

Of still further significance is the friction modifying improvement in petroleum distillate fuel oils having an initial boiling point from about 75.degree. to about 135.degree. F and an end boiling point from about 250.degree. to about 750.degree. F. It should be noted, in this respect, that the term "distillate fuel oils" is not intended to be restricted to straight-run distillate fractions. These distillate fuel oils can be straight-run distillate fuel oils, catalytically of thermally cracked (including hydrocracked) distillate fuel oils, naphthas and the like, with cracked distillate stocks. Moreover, such fuel oils can be trated in accordance with well-known commercial methods, such as acid or caustic treatment, hydrogenation, solvent-refining, clay treatment and the like.

The distillate fuel oils are characterized by their relatively low viscosity, pour point and the like. The principal property which characterizes these hydrocarbons, however, is their distillation range. As hereinbefore indicated, this range will lie between about 75.degree. and about 750.degree. F. Obviously, the distillation range of each individual fuel oil will cover a narrower boiling range, falling nevertheless within the above-specified limits. Likewise, each fuel oil will boil substantially, continuously throughout its distillation range.

Particularly contemplated among the fuel oils are Nos. 1, 2 and 3 fuel oils, used in heating and as diesel fuel oils, gasoline, turbine oil and jet combustions fuels. The fuel oils generally conform to the specification set forth in ASTM Specification No. D396-48T. Specifications for diesel fuels are defined in ASTM Specification D975-48T. Typical jet fuels are defined in Military Specification MIL-F-5624B.

The mineral oil heat-exchange fluids particularly contemplated in accordance with the present invention have the following characteristics: high thermal stability, high initial boiling point, low viscosity, high heat-carrying ability and low corrosion tendency.

Further, the transmission fluids of consequence to the present invention are blends of highly refined petroleum base oils combined with VI improvers, detergents, defoamants and special additives to provide lubricity characteristics. Varied transmission design concepts have led to the need for fluids with markedly different frictional characteristics, so that a single fluid cannot satisfy all requirements. The fluids intended for use in passenger car and light-duty truck automatic transmissions are defined in the ASTM Research Report D-2: RR 1005 on "Automatic Transmission Fluid/Power Transmission Fluid Property and Performance Definitions". Specifications for low-temperature and aircraft fluids are defined in U.S. Government Specification No. MIL-H-5606A.

It is to be understood, however, that the compositions contemplated herein can also contain other materials. For example, corrosion inhibitors, detergents, extreme pressure agents, viscosity index agents, antioxidants, other antiwear agents and the like can be used. These materials do not detract from the value of the compositions of this invention, rather these materials serve to impart their customary properties to the particular compositions in which they are incorporated.

The following data and example will serve to illustrate the novel products of the present invention and their efficacy as lubricant improvers in the antiwear and friction modifying characteristics of lubricant compositions. It will be understood, however, that it is not intended the invention be limited to the particular additives as described and that various modifications thereof can be employed as will be readily apparent to those skilled in the art.

A mixture of 35 g of dimethyl n-octadecylphosphonate, 35 g of 1-(2-hydroxyethyl)-2-heptadecenylimidazoline and 1.8 g of water was heated at atmospheric pressure under nitrogen at a temperature of 150.degree. C for 1.5 hr. Heating was then continued for a short time under a reduced pressure of about 200 mm of mercury during which some volatile material was distilled from the reaction mixture. Upon cooling, the reaction product remained a soft, amber-orange colored semi-solid.

A composition containing 0.5 weight percent of the product of the Example and 99.5 weight percent of a base oil were tested for water tolerance, antiwear and chatter characteristics.

The International Harvester Water Tolerance Test is fully described in the International Harvester Engineering Materials Specification, as Engineering Research Test Method BT-7. In this test, the clearness or turbidity of the compositions after water has been added is the critical property.

The standard Shell Four Ball Wear Test is described in U.S. Pat. No. 3,423,316. In general, three steel balls of SAE 52-100 steel are held in a ball cup. A fourth ball, positioned on a rotatable vertical axis, is brought into contact with the three balls and is rotated against them. The force with which the fourth ball is held against the three stationary balls is varied according to the desired load. The test composition is added to the ball cup and acts as a lubricant for the rotation. At the end of the test, the steel balls are investigated for wear-scar; the extent of scarring represents the effectiveness of the lubricant as an antiwear agent.

The John Deere Tractor Chatter Index Test is fully described in U.S. Pat. No. 3,652,410.

The test results are reported in the following table:

Thus, it is seen from the data presented in Table 1 that the products of the present invention impart effective antiwear and water tolerance properties to the base oil and perform excellently in the Chatter Index Test.