CA1073440A - Triaryl phosphate ester functional fluids - Google Patents

Abstract

ABSTRACT OF THE INVENTION:
There are disclosed triaryl phosphate ester functional fluids, such as lubricants and hydraulic fluids, which contain as the oxidatively stable component, a mixed tertiary-butylphenyl/phenyl phosphate containing about 15 to 60% by weight t-butylphenyl radicals.

Description

This invention relates to improved synthetic phosphate ester functional fluids particularly suitable for use as lubricants, hydraulic fluids and the like. More particularly, the invention relates to triaryl phosphate ester functional fluid compositions derived from mixtures of tertiary-butyl- .
phenols and phenol which exhibit a high degree of resistance to oxidative and thermal degradation.
Triaryl phosphates and mixed alkylphenyl/phenyl phosphates are known and are described, for example, in U.S. Patent 3,576,923, issued April 27, 1971 to Randell et al. Synthetic functional fluids and lubricants containing triaryl phosphates of various types may be found in U.S. Patents 2,938,871 issued May 21, 1960 to MatuszaK; 3,012,057 issued December 5, =-1961 to Fierce et al; 3,071,549 issued January 1, 1963 to Stark; 3,468,802 issued September 23, 1969 to Nail; 3,723,315 issued March 27, 1973 to Sullivan and 3,780,145 issued December 18, 1973 to Malec.
The present invention is based on the discovery that phosphorylated mixtures of tertiary-butylphenols and phenol provide triaryl phosphate ester functional fluids which exhibit heretofore unrecognized thermal and oxidation stability which render such triaryl phosphate esters particularly suitable for use in the formulatlon of functional fluids such as lubricants, particularly turbine lubricants, hydraulic fluids . . .

and the like where extreme conditions such as hlgh temperatures or extended periods of use require fluids of unusual stability properties.
In accordance with the present invention, there are provided functional fluid compositions comprising 95 to 99.99% by weight of a mixed tertiary-butylphenyl/
phenyl phosphate containing between about 15 to 60%, preferably 30 to 50%, by weight mono-t-butylphenyl radicals or mixtures thereof with di-t-butylphenyl radicals, the di-t-butylphenyl radicals being present in an amount between about 1 to 10% by weight based on the weight of the mono-t-butylphenyl radicals, as the base stock, and in admixture with the base stock, of very minor amounts, about 0.1 to 5% by weight, of lubricant additives such as rust inhibitors, corrosion inhibitors, anti-foam agents, anti-wear agents, cavitation inhibitors and similar special purpose additives.
The mixed t-butylphenyl/phenyl phosphates of the present invention may be represented by the general formula (R0) 3PO where R represents radicals consisting of (a) about 15 to 60% by weight of mono-t-butylphenyl radicals or mixtures of mono-t-butylphenyl and di-t-butylphenyl radicals, from about 1 to 10% by weight of such mixtures being di-t-butylphenyl radicals and (b) about 85 to 40% by weight of phenyl radicals. Preferred are those mixed t-butylphenyl/phenyl phosphates wherein the R radicals consist of about 30 to 50% mono-t-butyl-phenyl radicals or mixtures of same with di-t-butylphenyl radicals, the mixtures containing 2% or less di-t-butyl-phenyl radi-cals and the balance of the R radicals are .
, .. :

1~73440 phenyl radicals. Rust and corrosion inhibitors commonly employed are compounds such as benzothiazole, benzotri- , azole, triethanolamine, phenothiazine, trialkyl phosphates, such as mixed mono- and dialkyl phosphates, N-acyl sarcosines, the acyl radical having 10 to 18 carbon atoms, propyl gallate, succinic acid and alkyl succinic acids. Other additives to inhibit foaming and cavitation -included organo-silicone compounds, dialkyl carboxylic acid esters, such as diethyl succinate or dioctyl sebacate, or lower alkanes such as butane, propane and isomers thereof.
Functional fluids formulated in accordance with the present invention which contain a mixed tertiary butylphenyl/phenyl phosphate as the base stock with small proportions of the specialty additives described above are particularly suitable for high temperature use appllcations, since they exhibit a kinematic viscosity stability of +5% when subjected to temperatures within the range of 175C to 220C for a period of 72 hours.
Particularly preferred embodiments are functional fluid formulations which consist essentially of a mixed t-butylphenyl/phenyl phosphate, the formulation containing 0.01 to 0.1% by weight of a member selected from the group of additives consisting of benzotriazole, N-oleoyl sarcosine, or a mixed mono- and dialkyl phosphate of the formula RH2PO4 and R2HPO4, the alkyl being C~-Cl2 and mixtures of these additives. These formulated compo-sitions may also contain very small proportions, that is, about 0.001%, of a silicone anti-foam agent, such as . .

- ~073440 a dimethyl silicone polymer. These formulated compo- ' sitions are highly significant in that they offer the desirable combined properties of oxidative stability at elevated temperatures, thereby eliminating the need for antioxidant additives, and excellent corrosion and rust resistance, which enable functional fluids pre-pared in accordance with the present invention to meet the most demanding commercial specifications.
Apparently, there are no commercially avail-able triaryl phosphate ester-based formulations which offer the,se combined properties. The remarkable stability of the compositions of the present invention at high temperatures is shown by their relatively un-, changed viscosity and acid number when compared withother available phosphate ester fluids.
A further embodiment of the present invention re- , sides in thermally and oxidatively stable mixed functional fluids comprising 10 to 90% by weight of a mixed tertiary-butylphenyl/phenyl phosphate as herein-before described and 90 to 10% by weight of anotherfluid composition useful in formulating functional fluids. Thus, mixtures may be prepared with other functional fluids such as the synthetic or natural hydrocarbon oils, halogenated aromatic hydrocarbons, organic esters such as the alkanoic acid esters of organic polyhydroxy compounds such as pentaerythritol, trimethylolethane and trimethylolpropane, neopentyl glycol esters and the like, the alkanoic acids generally having from about 5 to 10 carbon atoms.
Also suitable for formulating such mixtures are other - : . .... : ., phosphate ester functional fluids such as trialkyl phosphates, triaryl phosphates, alkyl substituted triaryl phosphates, other mixed alkyl phenyl/phenyl phosphates, with the foregoing phosphate esters being exemplified by tricresyl phosphate, tritolyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, di-phenyl ethylphenyl phosphate, butyl diphenyl phosphate, dicresyl xylyl phosphate, dibutyl phenyl phosphate, tributyl phosphate, triamyl phosphate, trioctyl phosphate, mixed isopropylphenyl/phenyl phosphates, such as those prepared by phosphorylating an isopropyl-phenol/phenol mixture prepared by alkylating phenol with 10 to 40% by weight of propylene.
Other functional fluids useful for formulating ~-mixtures include the alkoxypolysiloxane and organo polysiloxane fluids such as dimethylpolysiloxane, methylphenylpolysiloxane, dimethyldiphenylpolysiloxanes, methyl alkyl silicone fluids, siloxane esters, poly-phenyl ethers such as bis(m-phenoxyphenyl) ether, di-phenoxy biphenyl isomers, alkoxy aromatic ethers, poly-glycols such as polyalkylene glycols and polyoxyalkylene glycols, silicate esters, such as tetraalkyl, tetraaryl and mixed alkylaryl orthosilicate esters.
Particularly useful are oxidatively stable functional fluid compositions comprising 40 to 60% by weight of a mixed tertiary-butylphenyl~phenyl phosphate ester and 60 to 40% of a functional fluid selected from the group consisting of aliphatic or aromatic petroleum hydrocarbons of lubricating viscosity, a silicone functional fluid, a polyol alkanoic acid 1~73440 ester .functional fluid, particularly a pentaerythrltol ester, or other phosphate ester functional fluids as described above.
The mixed t-butylphenyl/phenyl phosphate ester fluids of the present invention, when formulated with the other useful functional fluids noted above, may require the presence of minor proportions of a co-solvent or coupling agent to render such fluids com-patible. Generally speaking, the phosphate esters use-ful in preparing the compositions of the present in-vention will generally be compatible and miscible with aromatic petroleum hydrocarbons, alkanoic acid ester functional fluids, other phosphate ester fluids, polyalkylene glycol fluids and the like. For formu-lation with other types of functional fluids such as the silicones, siloxanes, silicate esters, aliphatic hydrocarbons and similar fluids, the use in minor amounts, approximately 5 to 15~ by weight of the formulation, of couplers and co-solvents such as mono-hydric and polyhydric alcohols, polyalkylene glycols,ethylene glycol ethers, polyphenyl ethers, trialkyl phosphates, and the like, may be required.
The compositions of the present invention be-cause of their excellent stability at very high tempera-tures, are particularly suitable for use in applications wherein high use temperatures are routinely encountered such as in the lubrication of gas turbines, particularly aero gas turbines, power generating gas turbines, steam turbines and the like. Fluids formulated in accordance with the present invention containing the mixed t-butyl-phenyl/phenyl phosphate esters described hereln arealso especially suitable for use as hydraulic fluids, capacitator and transformer oils as well as for heat transfer fluids. In these applications, a high degree of oxidative stability is of importance. Since anti-oxidant additives are not present, filtration of such fluids in the course of their use for the purpose of removing impurities will not diminish their stability.
A further embodiment of the present invention re-sides in a method of lubricating metallic surfaces in frictional contact at elevated temperatures, that -is, in excess of about 50C, comprising applying to said metallic surfaces a lubricating composition con- ~
sisting essentially of an oxidatively stable phosphate -triester, said triester being a liquid mixed t-butyl-phenyl/phenyl phosphate containing about 15 to 60% of mono-t-butylphenyl radicals, or mixtures of mono-t-butylphenyl radicals and di-t-butylphenyl radicals, the di-t-butylphenyl radicals being present in such 20 mixtures in an amount between about 1 to 10% by weight -~
based on the weight of the mono-t-butylphenyl radicals or admixtures of said t-butylphenyl/phenyl phosphates with another fluid useful for formulating functional fluids as hereinbefore described. Mixed t-butylphenyl/
phenyl phosphates are particularly suitable for lubrication at high temperatures of metals present in the gears and bearings of a gas turbine such as copper, magnesium,-iron, steel, aluminum, silver and lead. Temperatures in the range of 50C to 400C are commonplace in the operation of steam and gas turbines.

: :: ; ' `. ; -~073440 .
The compositions of the present invention are particularly suitable for lubricating at temperatures in excess of about 175C, because of their resistance to thermal degradation at these high temperatures.
The tertiary-butylphenyl/phenyl phosphates described herein also exhibit good extreme pressure and antl-wear properties. This property, in combination with their unusual degree of thermal stability, renders these materials particularly suitable for use in very minor amounts as additives for other functional fluids to improve the lubricating properties thereof. As special purpose additives, they may be added in amounts between about 0.1 to 5% by weight, based on the weight of the functional fluid. Thus, they may be employed as additives preferably for functional fluids such as the polyol alkanoic acid esters, the silicone fluids, natural and synthetic hydrocarbon oils as well as other useful functional fluids hereinbefore described. They function as suitable anti-wear or extreme pressure additives and offer the additional advantage of superior resistance to thermal and oxidative deterioration. -The mixed t-butylphenyl/phenyl phosphate esters ;
may be prepared by any suitable conventional technique, and preferably by phosphorylation of an isobutylene-phenol alkylation mixture prepared by alkylating phenol with from 10 to 40% by weight of isobutylene as disclosed, for example, in U.S. Patent 3,576,923 which results in a complex mixture of mono- and di-t-butylphenols and phenol. Alternatively~ appropriate mixtures of one or more isomeric t-butylphenols and phenol may be phosph~rylated to produce the mlxed t-butylphenyl/phenyl phosphate ror use in accordance wlth the present inventlon .
The followlng Examples are provided to further lllustrate this lnvention. The proportions ln the Examples and ln the rest of the speclflcation are by welght and the temperatures are ~n degrees centl-grade unless otherwlse lndicated.
EXAMPLE I
The preparation Or mlxed t-butylphenyl/phenyl phosphate ester fluids is set forth in the following Examples l(a) to l(f). Properties of the varlous mixed t-butylphenyl/phenyl phosphate triesters are -set forth in Table 1.
(a) Into a stlrred suspenslon of dried acid activated clay catalyst~ sold as "Super Filtrol", (75 ~
g, 2.0% by wt.) in phenol (3,765 g, 40 moles) was ~ ~-bubbled lsobutylene (664.4 g, 11.8 moles) at 80C.
Aluminum chloride (44 g, 1.0% by wt.) was added to 20 the stirred suspension and the temperature was in- -creased to 118 when the addition of phosphorus oxy-chloride (2,037 g, 13.0 moles) began. The addltion required 3.0 hours as the temperature was gradually increased to 220 where it was mainta~ned for an additional 3.0 hours after the addition. The hydrogen chloride which evolved was swept out of the system with nitrogen into a scrubber.
Without filtering the catalysts, the product was flash distilled out of the reactor. The main fractlon (4.062 g, 81%) boiled 180 to 230 at 0.4 torr.

- -_ g_ * Trade Mark ~' ~, ., Redistlrlatlon through a 12" Goodloe column ln the presence o~ 1.0% by wt. Or sodlum carbonate provlded 3,990 grams ( 80% ) of t-butylated phenyl/phenyl phosphates whlch boiled at 195 to 235 at 0. 4 torr.
(b) Using a process analogous to that ln Example l(a), phenol (4,220 g, 44.8 moles) and isobutylene (469 g, 8.38 moles) were reacted in the presence of ~uper Filtrol. The phosphorylation was similar except anhydrous magnesium chloride (1.0% by wt.) was used.
Distillation afrorded 4,714 grams (88%~ of t-butylated phenyl/phenyl phosphates which boiled at 195 to 220 at 0.25 torr.
(c) Using a process analogous to that in Example l(a), phenol (3,764 g, 40 moles) was reacted with 941 - -grams (16. 8 moles) of isobutylene. Phosphorylation and distillation afforded 4,856 grams (92%) of product which boiled at 210 to 240 at 0.15 torr.
(d) Phenol (2,069 g, 22.0 moles) and isobutylene (454 g, 8.1 moles? were reacted and phosphorylated in a manner as described in Example l(a).
(e) To a stirred solution (70) of phenol (2,760 g, 29.6 moles) and p-t-butylphenol (1,800 g, 12.0 moles) was added 2,195 grams (14.3 moles) of POCl3 in the presence of MgCl2 (30 g, 0.5% by wt.). The remainder of the preparation was carried out in an analogous manner as described in Example l(a) to yield 5,140 grams ( 94% ) Or triester.
(f) An alkylate prepared in an analogous manner to that described in Example l(a) was transalkylated by heating in a sealed system at 130 for 3. 5 hours * Trade Mark , in the.presence of 2.0% by wt. of Super Filtrol catalyst.
Comparative analyses before and after this treatment are given below.

Phenols - % by weight PhenoI ortho meta/para 2 4-di Alkylate Or Ex. l(a) 59.80 8.84 25.21 6.07 Transalkylated product5~.80 2.91 40.8 0.39 Phosphorylation of the transalkylated product as de-scribed in Example l(a) produced 2,870 grams (90~) which boiled at 190 to 240~ at 0.1 torr.
(g) Alkylate from Example l(d) was transalkylated in a simllar manner to Example l(e). Comparative analyses of the phenol dis'ributlon are agair set forth:

Phenols - % by weight Phenol ortho meta/~ara 2 4-di Alkylate of Ex. l(d) 52.80 7.09 35.50 4.47 Transalkylated -product47.40 3.21 48.60 0.68 Phosphorylation and distillation afforded a phosphate triester product.
E~AMPLE II
The mixed tertiary butyl substituted triaryl phosphates prepared in Example 1 were evaluated for oxidative stability and corrosivity according to Federal Test Method Standard No. 791B Method 5308.6 l'Corrosiveness and Oxidation Stability of Light Oils".
Comparisons of the products of this invention with other commercial triaryl phosphates via this procedure were m de. The results of these evaluations are presented in Table 2. The remarkable oxidative stability of the mixed tertiary butyl substituted triaryl phosphates is * Trade Mark ~.
,9~. .

mani~estly apparent when comparing acid number changes and viscosity differences with other triaryl phosphates.
The products were evaluated before and after exposure to 175C for 72 hours.
EXAMPLE III
Evaluations of the oxidative stability of the mixed tertiary butyl substituted triaryl phosphates were made according to the MIL-L-23699B 3.3.10 military specification at 204C and 218C after 72 hours, with data for 204C reported in Table 3 and data for 218C
reported in Table 4. The viscosity stability at very high temperatures is readily apparent.
EXAMPLE IV
The superior oxidative stability of the compounds of this invention is not diminished by treatment with additives known in the art to lnhibit metal corrosion, -rusting and foaming. Results of evaluations of mixed tertiary butyl substituted triaryl phosphates formulated with a copper passivator (benzotriazole), rust inhibitors - 20 (Sarkosyl O~ and Ortholeum 162~), a dimethyl silicone anti-foam agent (Dow-Corning "Compound A"), antioxidants and acid sumps (Kronox S~) are summarized in Tables 5 and 6. It is readily apparent from these results that the extraordinary thermal and oxidative characteristics of the compositions are maintained and their utility enhanced as indicated by the ASTM D-665 rust test.
EXAMPLE V
This example demonstrates the superior oxidative stability of mixtures of the phosphate esters of this inventicn with alkanoic acid esters. The table below ~073440 compares the stablllty Or an unstabillzed 65%/35%

vol./vol. blend Or phosphate ester Or Example l(a) and "Hatcol 1570~ with a similar 65%/35~ mixture o~
trlcresyl phosphate (TCP)/Hatcol 1570~ Hatcol 1570 ls a commercially available pentaerythritol alkanoic acid (C~-CiO acids) ester. It is clearly evident that by comparlson of the change ln viscoslty and acld number the composition of this invention is signlficantly more stable than the one based on TCP. The data are set forth below. Corrosion results are also shown.
Federal Test Method Standard No. 791B~
Method 5308 ~ 6 at 175C for 72 Hours Ex. l(a)~Eatcol TCP/~atcol 1570 r 570 (65%/35% ) (65%/35% ) ~TAN* (mg/KOH/g) 6 ~ 60 11 ~ 9 % Viscosity Change29 ~ 0 54 ~ 0 (cs. at 100F) Wt. Change (mg/cm2) Cu -0 ~ 67 -0.18 Steel +0.01 ~0.01 Mg -0.01 -0.01 Al 0.00 0.00 Ag -o.o6 -0.0 *~TAN = Change in total acid number.
EXAMPLE VI
This example shows the enhanced oxidatlve stability of mixtures of phosphate esters prepared by adding the fluids of this invention to commercially available phosphate esters. The improved oxidative stability of the blended materials is readily apparent in the data set forth below.

* Trade Mark 3W~6 ~073440 Federal Test Method Standard No. 791B, Method 5308.6 at 175/72 hrs.
- Composltion~ TAN*% Vlscosity Change IPP* 26 102 TCP* 4.8 16 Ex. l(a) 0 5 Ex. l(a) (10~)/
IPP*(90%) 15.7 88 Ex. l(a) (50~)/
IPP*(50~) 2.7 14 Ex. l(a) (10%)/
TCP*(90%) 1.5 6 10 Ex. l(a) (50%)/
TCP*(50%) .5 3 Ex. l(a) (90%)/
TCP*(10%) .4 .8 *As defined in Table 2.
EXAMPLE VII
The extreme pressure and anti-wear characteristics of the t-butylphenyl/phenyl phosphate ester fluids of the present invention were evaluated as indicated ~
by the following 4-ball test data carried out at ~ -80F +15F according to ASTM D-2596 (Load Wear Index and Weld Point) and ASTM D-2266 (Wear Scar Diameter).
Sample _ASTM D-2596 ASTM D-2266 Load Wear Weld Point, Wear Scar ~ -Index kg. Di2meter, mm.
Ex. l(a) 26.19 126 0.60 Ex. l(b) 26.03 126 0.60 Ex. l(d) 26.07 126 0.54 `~-IPP* 24.43 126 0.5~ ~-TCP* 24.75 126 0.57 CDP* 21.76 126 o.65 TXP* 26.27 126 0.54 *Same as Table 2.

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Claims (4)

The embodiments of the invention in which an ex-clusive property or privilege is claimed are defined as follows:

1. A lubricant characterized by improved thermal stability comprising about 5 to 0.1% by weight of a mixed liquid tertiary-butylphenyl/phenyl phosphate containing from 15 to 60% by weight mono-t-butylphenyl radicals, or mixture of mono-t-butylphenyl and di-t-butylphenyl radicals and 95-99.9% by weight of a base stock selected from the group consisting of polyol alkanoic acid esters, a silicone fluid, and a different phosphate ester selected from the group consisting of triaryl phosphates, trialkyl phosphates, alkyl substituted triaryl phosphates and other mixed alkylphenyl/phenyl phosphates.

2. The lubricant of claim 1 wherein said base stock is a polyol alkanoic acid ester.

3. The lubricant of claim 1 wherein said base stock is a silicone fluid.

4. The lubricant of claim 1 wherein said base stock is a different phosphate ester selected from the group consisting of triaryl phosphates, trialkyl phos-phates, alkyl substituted triaryl phosphates and other mixed alkylphenyl/phenyl phosphates.