US3867298A - Lubricant - Google Patents

Abstract

Triphenyl phosphates in which an average of at least one phenyl group per molecule is substituted with at least one alkyl group containing from 6-30 carbon atoms have been found to be excellent lubricants and functional fluids having much lower pour points and higher viscosity indices than conventional phosphate esters. These triphenyl phosphates are exceptionally useful as wear inhibitors in synthetic ester lubricants.

Description

United States Patent [1'91 Malec Feb. 18, 1975 LUBRICANT [75] Inventor: Robert E. Malec, Birmingham,

Mich.

[73] Assignee: Ethyl Corporation, Richmond, Va.

[22] Filed: Sept. 19, 1973 211 App]. No.: 398,645

Related US. Application Data [63] Continuation-impart of Scr. No. 117,095, Feb. 19,

1971. Pat. N0. 3,780,145.

3,012,057 12/1961 Fierce et al 252/49.8 X

3,790,478 2/1974 Rudston et al 252/49.8 X

\ OTHER PUBLICATIONS Chemical Abstracts Service, The Naming and Indexing of Chemical Cpds. for Chem. Abs, Vol. 56, (i962), pages l6N and l7N.

Primary ExaminerW. Cannon Attorney, Agent, or Firm-Donald L. Johnson; Robert A. Linn; Joseph D. Odenweller [57] ABSTRACT Triphenyl phosphates in which an average of at least one phenyl group per molecule is substituted with at least one alkyl group containing from 630 carbon atoms have been found to be excellent lubricants and functional fluids having much lower pour points and higher viscosity indices than conventional phosphate esters. These triphenyl phosphates are exceptionally useful as wear inhibitors in synthetic ester lubricants.

1 Claim, No Drawings LUBRICANT This application is a continuation-in-part of application Ser. No. 117,095, filed Feb. 19, 1971 now US. Pat. No. 3,780,145.

BACKGROUND Triaryl phosphates have been used both as lubricants and as hydraulic fluids. They are most useful in stationary turbine installations and in mining equipment where a non-flammable fluid is required. In the past, fluids such as tricresyl phosphate have predominated in such use. One deficiency of such fluids is their relatively high pour point and low viscosity index. An object of this invention is to provide a class of phosphate esters which has a low pour point and a high viscosity index.

SUMMARY The objects of the present invention are accomplished by providing a triphenyl phosphate ester in which an average of at least one phenyl group per molecule is substituted with a C alkyl group which preferably contains a linear alkyl chain of at least 5 carbon atoms.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention is a triphenyl phosphate ester in which an average of at least one phenyl group per molecule is substituted with at least one alkyl group containing from 6-30 carbon atoms. A further embodiment is a synthetic ester lubricant containing a wear-inhibiting amount of the above phosphate ester.

In stating that an average of at least one phenyl group per molecule is substituted with at least one alkyl group containing 6-30 carbon atoms, it is meant that the number of C alkyl-substituted phenyl groups present in the phosphate ester divided by the number of molecules of phosphate ester is at least one. From this, it is apparent that the ester need not be a single compound but can be. and as a practical matter generally is, a mixture of triphenyl phosphate esters containing varying amounts of C alkyl substituents on the phenyl ester groups in an amount such that an average of at least one phenyl group is C alkyl substituted per molecule of phosphate ester in the mixture.

The preferred phosphate esters contain an average of from l-6 C alkyl substituents per molecule of phosphate ester. As above, this is an average value determined by dividing the total moles of C alkyl substituents by the total moles of phosphate ester.

Although good results are obtained with all alkyl groups containing 6-30 carbon atoms, an especially useful product is obtained when the alkyl group has a substantially linear structure. By this, it is meant that the preferred alkyl substituents contain linear carbon chains of at least carbon atoms. Preferably this linear is unbranched. This is not to say that the alkyl groups need to be normal alkyl groups. For example, l-methyln-pentyl is a 6 carbon alkyl containing a 5 carbon linear alkyl chain. Likewise, l-ethyl-n-hexyl is an 8 carbon alkyl containing a 6 carbon linear chain. Similarly, l-nbutyl-n-pentyl is a 9 carbon alkyl group containing two 5 carbon linear chains. Some further examples of alkyl radicals containing from 6-30 carbon atoms and one or more linear alkyl chains of at least 5 carbon atoms are:

2 l-methyl-n-eicosyl, l-n-pentyl-n-hexyl, l,l-dimethyl-nheptyl, n-pentyl, n-hexyl, n-octyl, n-decyl, n-dodecyl, l-methyl-n-nonosyl, l-n-octyl-n-tridecyl, l-n-heptyl-ntricosyl, l-n-butyl-n-undecyl, l-methyl-n-heptyl, and the like.

Although alkyl groups containing from 6-30 carbon atoms are useful in providing the low pour point and high viscosity index properties of the present phosphate esters, it has been found that alkyls containing 6-l8 carbon atoms are a more preferred group. As above, these preferred alkyls have a structure such that they are substantially linear-that is, they contain linear alkyl chains of at least 5 carbon atoms. Some especially useful esters within this class are those in which the alkyl groups contain about 6-8 carbon atoms. In other words these are: n-hexyl, n-heptyl, n-octyl, l-methyl-npentyl, l-methyl-n-hexyl, l-ethyl-n-pentyl, l-methyl-nheptyl, l-ethyl-n-hexyl, l,l-dimethyl-n-hexyl, and the like.

Another highly preferred embodiment is a triphenyl phosphate in which an average of at least one phenyl group per molecule is substituted with an alkyl group containing l0-l2carbon atoms and having a linear alkyl chain of at least 5 carbon atoms such that the ester contains an average of from 1-6 alkyl groups per molecule. Preferably, in this embodiment an average of about one phenyl group per triphenyl phosphate molecule is substituted with l-3 alkyl substituents containing 6-30 carbon atoms each and having a linear carbon chain of at least 5 carbon atoms. More preferably, the alkyl substituent is a l-methyl-n-C alkyl. In a very useful embodiment the alkyl substituent contains 10-12 carbon atoms.

As stated above, the preferred esters contain an average of from l-6 alkyl groups per molecule. Another preferred embodiment is a triphenyl phosphate ester containing an average of about 5-6 alkyl groups per molecule of phosphate ester wherein the alkyl groups contain about 12 carbon atoms and have a structure such that they contain a linear alkyl chain of at least 5 carbon atoms.

The phenyl phosphate esters of this invention are an ester or mixture of esters having the formula:

ll i''@ 0 (10,,

wherein R represents an alkyl group containing from 6-30 carbon atoms and m, n and p are integers selected from 0, 1, 2 and 3. When the ester is a single compound the sum of m, n and p is from I-9, and when the ester is a mixture of different phosphate esters the sum of the average value of values of m, n and p is from l-6. The alkyl groups represented by R preferably have a linear alkyl chain of at least 5 carbon atoms in their structure. The more preferred R groups contain from 6-l8 carbon atoms. The most preferred are l-methyl-n-alkyl groups which can be derived from alpha-olefins.

The phosphate esters are made by' conventional methods. For example, phenol can be alkylated with a C olefin using a Friedel-Crafts catalyst to give a mixture of alkylphenols containing the required average of at least one alkyl for each 3 molecules of phenol, and preferably from l-6 alkyls for each 3 molecules of phenol. The alkylated phenol mixture containing the Friedel-Crafts catalyst can then be reacted directly with phosphorus oxychloride to form the phosphate ester of this invention or it can be first converted to its alkali metal salt by reaction with an alkali metal hydroxide or alkoxide and the salt then reacted with phosphorus oxychloride. These methods of alkylating phenols and forming aryl phosphate esters are well known. The following examples will serve to illustrate how the synthesis can be carried out. All parts are by weight.

EXAMPLE 1 In a reaction vessel was placed one mole part of the sodium salt of l-methyl-n-nonylphenyl (preparing by alkylating phenol with decene-l using a BF 'ether complex catalyst), one mole part of diphenyl chlorophosphate and 500 ml of benzene solvent. The mixture was stirred at 80-90C. until the reaction was completed and then cooled and filtered. The filtrate was washed and the solvent removed by vacuum distillation. The resultant product was dipheny1( l-methyl-nnonylphenyl)phosphate. The following physical properties were determined:

viscosity (cs.) 210F. 5.84

100F. 42.91 F. 4,650 viscosity index 81 pour point F.

EXAMPLE 2 One mole part of phenol was alkylated with 1.83 mole parts of dodecene-l using a BF 'ether catalyst to provide a mixture of 1-methyl-n-undecylpheno1s having an average of about 1.83 alkyl groups per mole of phenol. This was reacted with 0.33 moles of phosphorus oxychloride and 2 grams of aluminum chloride, giving a triphenyl phosphate ester having an average of 5.5 l-methyl-n-undecyl alkyl groups per molecule of phosphate ester. This ester mixture had the following physical properties:

viscosity (cs.) 210F. ll

0F. 6,990 viscosity index 108 pour point 35F.

EXAMPLE 3 In a reaction vessel was placed 1.33 mole parts of phenol, a small amount of BF 'ether catalyst and 1.6 mole parts of a mixture of olefins containing from about 12-30 carbon atoms. The olefin composition used was 81.4% olefin and 18.6% paraffin. Excluding the paraffin, the olefins were 2.46% C 23.8% C 15.5% C 13.5% C 10.9% C 6.3% C 8.1% C C24,5.9% C26, C23, and 1. C30 oleflns. The olefins were a mixture of alpha-olefins, branched olefins and internal olefins in the ratio of about 12:2. The

mixture was stirred at about 2590C. for an hour. The

yl-n-heptyl, *methyl-n-decyl, dodecyl, .1 -methyl-n-tridecyl,

resultant alkylphenol mixture was reacted with 1.3 moles of phosphorus oxychloride at C. for an hour to form a phosphate ester. A small amount of unreacted phosphorus oxychloride was then distilled out and then 3.5 mole parts of phenol added. The esterification was completed by stirring an additional 12 hours at -200C. Unreacted phenol was then washed out. Paraffin and other volatiles were distilled out. The product was a triphenyl phosphate having an average of about 1.5 alkyl groups per molecule in which the alkyl group contained from about 12-30 carbon atoms. The physical properties of the ester were as follows:

viscosity (cs.) 210F. 1 1.07 100F. 107.2

viscosity index 96 pour point 30F.

Any of the other triphenyl phosphate esters described herein can be readily prepared following the above or any other of the wellknown methods of alkylatingphenols and preparing aryl phosphate esters. As stated previously, the esters are useful as lubricants, es-

pecially in stationary turbine engines and as functional fluids such as hydraulic fluid where flame-retardant properties are desired. They are also very useful as flame-retardant plasticizers, especially in polyvinyl chloride. They are beneficially added to gasoline containing tetraethyllead such as that used in spark ignition internal combustion engines. In this use they function to extend spark plug life. Amounts of from about 0.1 to 0.5 theories are used (one theory being the amount required to convert the lead to lead phosphate). They can be used as antiwear agents in other lubricant formulations. For example, they are added to synthetic ester lubricants used in turbojet aircraft engines to reduce wear. In this use, amounts of from about 1-5 percent are blended with the ester lubricant together with the other additives normally required such as an antioxidant (e.g., phenyl-B-naphthyl amine, phenyl-anaphthyl amine, dioctyl phenylenediamine, etc. metal deactivators, silicone antifoam agents, and the like.

Thus, a preferred embodiment of the invention is a synthetic ester lubricant containing a wear-inhibiting amount of a triphenyl phosphate in which an average of at least one phenyl group per molecule is substituted with at least one alkyl substituent containing 6-30 carbon atoms. Preferably, the alkyl substituent contains a linear alkyl chain of 5 or more carbon atoms. Examples of such triphenyl phosphates are: tri-(Z-ethylhexylphenyl)phosphate, tri-( l l-methylpentylphenyl)- phosphate, phosphate, tri-[2,4-di(l-methylheptyl)phenyllphosphate, diphenyl-[2,4,6tri(l-methylundecyl)phenyl]- phosphate, and the like.

In a particularly preferred embodiment the alkyl substituent contains 6-30 carbon atoms, as a l-methyl-n- C alkyl group. These are made by alkylating phenol with a C alpha-olefin or mixture of such alphaolefins and reacting the resultant 1-methyl-n-C alkylphenol with POCl Alternatively, triphenyl phosphate can be alkylated with a C alpha-olefin to form the preferred 1-methyl-n-alky1-substituted triphenyl phosphates. Examples of the preferred alkyl substituents are: l-methyl-n-pentyl, l-methyl-n-hexyl, l-methl-methyl-n-octyl, l-methyl-n-nonyl, 1- l-methyl-n-undecyl, l-methyl-nl-methyl-n-tetradecyl,

di-(1-methyl-4-ethylhexylphenyl)phenyll-methyl-n-pentadecyl, 1 -methyl-n-hexadecyl, l-methyl-n-heptadecyl, l-methyl-n-octadecyl, l-methyl-n-eicosyl, l-methyl-n-docosyl, l-methyl-n-noncosyl, and the like.

In an especially preferred embodiment the alkyl substituent is a l-methyl-n-alkyl containing 6 to about 18 carbon atoms. In other words, the alkyl substituent is a l-meth-yl-n-C alkyl.

The phosphate esters may be used in any of the wellknown synthetic ester lubricants. Representative examples of such lubricants are described in Brit. Pat. No. 715,933; Brit. Pat. No. 750,560; Brit. Pat. No. 847,664; Brit. Pat. No. 861,965; Brit. Pat. No. 887,343; Brit. Pat. No. 910,023; Brit. Pat. No. 971,901; U.S. Pat. No. 2,356,745; U.S. Pat. No. 2,499,984; U.S. Pat. No. 2,588,194; U.S. Pat. No. 2,628,974; U.S. Pat. No. 2,757,139; U.S. Pat. No. 2,815,368; U.S. Pat. No. 2,820,014; U.S. Pat. No. 2,991,297; U.S. Pat. No. 3,148,147; U.S. Pat. No. 3,223,637; and U.S. Pat. No. 3,309,318, all of which are incorporated herein by reference.

The synthetic esters may be esters of monocarboxylic acids with monoalkanols, esters of dicarboxylic acids with monoalkanols, esters of monocarboxylic acids with alkane polyols, or complex esters of monocarboxylic acids and dicarboxylic acids with alkane diols or other polyols, or dicarboxylic acid esters with monoalkanols and alk ane diols or other polyols, and the like.

Representative diesters are the C alkanol esters of dicarboxylic acids such as adipic, sebacic, and the like. Complex esters are readily made by esterifying a dicarboxylic acid (e.g., adipic) with a polyol (e.g., ethyleneglycol, pentaerythritol, trimethylolpropane, etc.) using as an end-blocking agent either a C monocarboxylic acid or a C monoalkanol. Hindered esters are made by esterifying neopentyl type polyols (e.g., pentaerythritol, trimethylolpropane, trimethylolethane, etc.) with C aliphatic monocarboxylic acids (e.g., hexanoic, octanoic, decanoic, etc.).

The present esters have a quite unexpected property when used as antiwear agents in synthetic ester lubricants. In synthetic ester lubricants, viscosity properties are quite important and, in fact, both the Air Force and Navy set stringent specifications on viscosity. It has Viscosity (cs.)

Phosphate ester Conc. 210F. F. -40F.

Tricresyl phosphate 2% 6.32 34.80 13,450 Example 1 2% 6.34 34.85 13.160

From the above data, it can be seen that the ester of this invention (Example 1) when compared with use of tricresyl phosphate has very little effect at 210F. or 100F. In fact, if any, the esters of this invention give a slightly higher viscosity at these higher temperatures which in itself is beneficial. A highly unexpected property of the present phosphate esters is their effect on viscosity at 40F. Here it can be seen that the ester containing 2 percent tricresyl phosphate has a =40F. viscosity of 13,450 cs. whereas the same synthetic ester lubricant containing the same amount of the phosphate ester of Example 1 exhibits a 40F. viscosity of 13,160 cs. This reduction in viscosity at -40F. is quite significant in meeting military specifications. Other additives routinely used in synthetic esters such as the phenyl-anaphthyl amine and phenylenediamine type antioxidants are known to increase the viscosity of the lubricant.

I claim:

1. A synthetic carboxylic acid ester lubricant in major amounts containing a wear-inhibiting amount of diphenyl-( l-methyl-n-nonylphenyl) phosphate.

Claims (1)

1. A SYNTHETIC CARBOXYLIC ACID ESTER LUBRICANT IN MAJOR AMOUNTS CONTAINING A WEAR-INHIBITING AMOUNT OF DIPHENYL-(1METHYL-N:NONYLPHENYL) PHOSPHATE.