CA1051011A - Monoepoxyendooxycyclohexyl compounds useful as acid scavengers - Google Patents

Abstract

ABSTRACT

A new class of monoepoxyoxocyclohexyl compounds useful as acid scavengers and corrosion inhibitors in func-tional fluid compositions.

Description

'~:
This invention relates to a new class of monoepoxy-oxocyclohexyl compounds and to functional fluid compositions, particularly hydraulic fluids, contai~ing such compounds to `
inhibit acid buildup.
Func-tional fluids have been utilized in many differ-ent types of applications such as electronic coolants, dif-fusion pump fluids,~lubricants, damplng fluids, bases for greases, power transmission and hydraulic fluidst hea-t trans~
fer fluids, heat pump fluids, refrigeration equipment fluids and as filter mediums for air-condi-tioning systems. Of these uses, hydraulic fluids intended for use in the hydraulic system of aircraft for operating various mechanisms and air-craft control systems must meet stringent functional and use requirements. One of the most important requirements -Eor an aircraft hydraulic fluid is that the fluid be chemically stable to resist oxidative and thermal degradation which can :'' ', ~' :' result in the formation of acid and the corrosive attack of metals in contact with the hydraullc fluid~
In order -to control the degree of acid buildup .j ,~, .
20~ during use of the fluid and inhibit corrosion of the compo- `
nents in the hydraulic system, it is conventional to add certain acid scavengers and/or corrosion inhibitors to the hydraulic fluid base stock.
Although a variety of compounds have been suggested for use as corrosion inhibitors, acid acceptors which act as proton acceptors and prevent the buildup of corrosive acids in the fluids when they undergo decomposition under pro~
longed use at high temperatures are generally preferred.
A particularly preferred class of such materials comprises `~
epoxy compounds, especially epoxidized naturally occurring ` -2-'~ ;~"..

ma-terials such as epoxidized unsaturated glycerides including epoxidized soybean oil, epoxidized castor oil, epoxidized linseed oil, epoxidi~ed fats and the like. Other suggested materials include epoxy esters such as butylepoxyacetoxy- ;
stearate, glyceryl triepoxyacetoxystearate, isooctylepoxy-:; , -`- stearate, epoxidized isooctyl phthalate and the like. Also ~ ~ ~
:: .
suggested are various alkyl and arylalkyl epoxides such as ~ ~ `
; epoxy decane, epoxy hexadecane, epoxy octadecane, epoxy ~ `
cyclododecane, and the like, and glyceryl and various glycidyl ethers such as phenyl glycidyl ether, glycidyl cyclohexyl ether, alkyl glycidyl ether, and the like.
. ` .
,j More recently it has been suggested that a parti-1 cular class of epoxy compounds, the 3,4-epoxycycloalkyl-3,4-;,epoxycycloalkyl carboxylates, are particularly useful as acid accep~ors for hydraulic fluids and are more effective than ~f ¦ the epoxy compounds used heretofore. A particularly pre-ferred compound is 3,4-epoxycyclohexylmethyl-3,4-epoxycyclo-! hexane carboxylate. These compounds are well known chemical ! entities which have been used as acid scavengers for -i 20 chlorinated diphenyl dielectric fluids prior to their intro-.j ., , , . , , , , ~.
¦ ~ duction as inhibitors for hydraulic fluids.
Although 3,4-epoxyc~cloalkyl-3,4-epoxycycloalkyl carboxylates are effective acid scavengers for common hy-I draulic fluid compositions, they have a disadvantage in that 'l . . .

! -they may cause resinous deposits to form around the fluid -, ¦ pump shaft at the point of seal. The formation of deposits ;~
i lS of particular concern in aircraft hydraullc systems whlch il operate under pressure and where the deposits soon result in fluid leakage through the seal. Although the problem of shaft ~ .

. .

~ ~ , .... . . . . , . -1~51~
seal leakage is not serious from an aircraft operational .
point of vlew, it represents a sufficient nuisance that the aircraft industry and aircraft hydraulic Eluid manufacturers have actively sought alternative acld acceptors which are as effective and efficient as the 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate but which do not have the deposit and leakage problem associated with this material.
It is accordingly an object of this invention to provide an acid acceptor effective to prevent acid buildup in functional fluid composltions. Another object of this invention is to provide an acid acceptor which can be used ;
without adverse secondary effects in functional fluids which i may also contain a polymeric V.I. improver. A further object ~1 of this invention is to provide functional fluid compositions I which are resistant to thermal and oxidative degradation and ¦ which are suitable for use in aircraft hydraulic systems.
It is a yet further object of this invention to provide an aircraft hydraulic fluid con-taining a polymeric V. T . improver and an`epoxide acid acceptor which does not cause pump shaft .
seal leakage. Yet further objects will be àpparent from the following description of the invention.
In accordance with this invention, it was sur-prisingly found that compounds represented by the following formula effectively prevent acid buildup in functional fluid ~;

compositions:
R

~ PORMULA I

H' ~ ~ j 2 , ,:~

..... . . . . . . .. . . .. . .

~L~510~
wherein Rl is -(CH2)0 3 -C(O)OR, -C(O)R, or -CH2OR wherein R is an alkyl radical having from 1 to about 18 carbon atoms, . ~ ;, .
R2 is Rl, hydrogen or an alkyl radical having from 1 to about 9 carbon atoms, R3 and R4 are individually hydrogen or an ~^
alkyl radical having from 1 to 4 carbon atoms. Preferably, : ! :' :
R has 1 to 12 carbon atoms. : ~:
Representative compounds of this invention include the following; :
: DIESTERS ~ :
Diethyl-5,6-epoxy-1,4-oxocyclohexane-2,3-dicarboxyl-ate, dihexyl-5,6-epoxy-1,4-oxocyclohexane-2,3-dicarboxylate, diheptadecyl-5,6-epoxy-1,4-oxocyclohexane-2,3-dicarboxylate, butylmethyl-5,6-epoxy-1,4-oxocyclohexane-2,3-dicarboxylate, didecyl-5,6-epoxy-1-ethyl-1,4-oxocyclohexane-2,3-dicarboxylate, : ;
didodecyl-5,6-epoxy-1-methyl-4-butyl-1,4-oxocyclohexane-2,3- ~
dicarboxylate, ~ -ditetradecyl-5,6-epoxy-1,4-oxocyclohexane-2,3-di-(methylene-ca~boxylate~
-.
di(2ethyl-hexyl)-5,6-epoxy-1,4-oxocyclohexane-2,3-di(ethylene ~;
carboxylate) ETHERS ~ :
____ :

2-methoxy-5,6-epoxy-1,4-oxocyclohexane 2-hexoxy-5,6-epoxy-1,4-oxocyclohexane 2-decoxy-5,6-epoxy-1,4-oxocyclohexane 2-octadecoxy 5,6-epoxy-1,4-oxocyclohexane . . . . .
2-ethoxy-5,6-epoxy-1-methyl-1,4-oxocyclohexane 2-nonoxy-5,6-epoxy-4-ethyl-1,4-oxocyclohexane :`~

` ~ ::~ :
-5- ~ ~:

:,.' ;
.
., ~51~
DIETHERS
2,3-diethoxy-5,6-epoxy-1,4-oxocyclohexane 2,3-diheptoxy-5,6-epoxy--1,4-oxocyclohexane 2,3-didodecoxy-5,6-epoxy~1,4-oxocyclohexane :~
2,3-dipentoxy-5,6-epoxy-4-butyl-1,4-oxocyclohexane 2,3-dioctoxy-5,6-epoxy-1-methyl-4-butyl-1,4-oxocyclohexane KETONES
: , j, ...
~: propyl 5,6-epoxy-1,4-oxocyclohexyl ketone :: 2-ethylhexyl-5,6-epoxy-1,4-oxocyclohexyl ketone pentadecyl-5,6-epoxy-1,4-oxocyclohexyl ketone :. :
octadecyl-5,6-epoxy-1-propyl-1,4-oxocyclohexyl ketone nonyl-5,6-epoxy-4-butyl-1,4-oxocyclohexyl ketone DIKETO~ES
I dibutyl-5,6-epoxy-1,4-oxocyclohexyl diketone I dihexadecyl-5,6-epoxy-1,4-oxocyclohexyl diketone diethyl-5,6-epoxy-1,4-oxocyclohexyl diketone ~;~
didodecyl-5,6-epoxy-1-methyl-1,4-oxocyclohexyl diketone ~l Particularly preferred epoxy compounds that can `~
-, be employed in the practice of the present invention are ~:
those represented by the following structure: ~
:

(CH2)n-C-OR FORMULA II

~ S 2 'I , .
I wherein R2 is hydrogen or an alkyl of from 1 to 9 carbon ! atoms, R3 and R4 are individually hydrogen or an alkyl of from 1 to 4 carbon atoms, R is an alkyl of from 1 to 18 carbon - :
atoms and n is an integer of from 0 to 3. Preferably, R is an alkyl from 1 to 9 carbon atoms, R2, R3 and R4 are hydrogen and n is 0. Representative examples of this class of com-pounds include methyl 5,6-epoxy-1,4-oxocyclohexane-2-carboxylate, decyl 5,6-epoxy-1,4-oxocyclohexane-2-carboxylate, heptadecyl 5,6-epoxy-1,4-oxocyclohexane-2-carboxylate, ethyl~
5,6-epoxy-1-ethyl-1,4-oxocyclohexane-2-methylenecarboxylate, ~ ;~
2-ethyl-hexyl-5,6-epoxy-1,4-oxocyclohexane-2-carboxylate, methyl-5,6-epoxy-1,4-oxocyclohexane-2-ethylene carboxylate.
These compounds may be prepared by those proceduras well known in the art, for example~ those procedures described ~ ~
in U.S. 3,187,~18. ~1 The epoxy esters of this invention may be prepared by first reacting furan with an alkyl acrylate. The reaction product is converted to the epoxy esters of this invention by oxidizing the olefinic linkage contained in the reaction product. Peracetic acid is particularly well s~ited for this reaction, since it rnay be carried out under relatively mild conditions and with a minimum of operating difficulty.
The diesters of this invention may be prepared by first reactiny furan with maleic anhydride and then reacting this reaction product with an appropriate alcohol. Epoxi-dation is achieved by oxidizing the olefinic linkage with peracetic acid.
Epoxy mono ethers of this invention are prepared in the same manner as epoxy mono esters except an alkyl acrylyl ether is used in place of the alkyl acrylate. Di-ethers are prepared by using alkyl acrylyl ether.
Epoxy ketones of this invention are prepared by I
using alkyl or dialkyl vinyl ketones 1n place of the alkyl acrylate used to prepare the epoxy mono esters.

_7_ ~ ' Functional fluid compositions of this invention .
comprise a major amount of at least about 50 percent by weight of a base stock material selected from the group consisting of esters or amides of an acid of phosphorus, di- or tri~
carboxylic acid esters, esters of polyhydric compounds an~
mixtures thereof, from 0 to minor amounts of one or more -other base stock materials or base stock modifiers, and from about 0.1 to 10 percent by weight of one of the above mentioned compounds. The compositions may include polymeric V.I. im-provers and other conventional additives and are particularly ``
useful as aircraft hydraulic fluids.
The concentration of the epoxy compound in the func- ;~
tional fluid is adjusted according to the demands of the system and nature of the base stock being employed in order to provide compositions which contain sufficient amounts of epoxy material to inhibit acid buildup during normal operation. It has been found that the concentration of epoxy compound re-:, :
quired to inhibit and control acid buildup in a particular -, ~
~ base stock varies according to the composition of the base i 20 stock or blends of base stocks. It has generally been found , : .
that pr`eferred additive levels of epoxy compounds are from 0.10 weight percent to 5.0 weight percent, althou~h concen-trations of 10 percent or higher are also e~fective and may be used. Thus, included in the present invention are func~
tional fluid compositions comprising a base stock material and any of the epoxy compounds represented by Formula I in a concentration sufficient to control and inhibit acid buildup in the base stock.
The fluid compositions of this invention can be com~
pounded in any manner known to those skilled in the art for ;~
incorporating an additive into a base stock, as for example ;

105~
by adding the epoxy compound to the base ~tock ~ith stixxin~
until a uniform ~luid composition is o~tained.
As mentioned, the ~ase stock material which co~prises at least about 50~ b~ weight o~ the functional fluids of the present invention i5 selected from the ~roup consisting of esters and amides of an acid of phosphorus, di- or tricarboxylic acid esters, ester~ of polyhydro compounds, and mixtures there-.~ , of~ These base stock materials and examples thereof are des-cribed in U. S. Pa~.ent 3,723,320.
Hydrocarbon phosphates are preferred. Phosphorus ; ester base stocks include trialkyl phosphates, triaryl and/or alkyl substituted aryl phosphates and mixed aryl and/or substi-tuted arylalkyl phosphates. With respect to the alkyl groups, l~ it is preferred to have from about 2 to about 18 carbon atoms, more preferabIy from about 2 to about 12 carbon atoms and with :' ~
respect to the aryl and substituted aryl groups~ it is preferred to have from~about 6 to about 16 carbon atoms and moré preferab1y from a~out 6 to a~out 12 carbon atoms. Typical examples of ; preferred phosphates are dibutylphenyl phosphate, triphenyl ~ phosphate, tricresyl phosphate, tributyl phosphate, tri-2-:
ethylhexyl phosphate, trioctyl phosphate, the phosphates des-cribed in U. S. Patent 3,723,315, such as di~nonylphenyl) phenyl phosphate~ di~cumylphenyl) phenyl phosphate, (cumylphenyl) Cnonylphenylj phenyl phosphate, and mixtures of the above phos-phates such as mixtures of tributyl phosphate and tricresyl phos-phate r mixtures of triphenyl phosphate and 2-ethylhexyl diphenyl phosphate, mixtures of cumylphenyl diphenyl phosphate, nonyl-phenyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate and triphenyl phosphate. ~ preferred mixture contains !

- .~

~S~
45 to 65~ triphenyl phosphate, 25 to 45% by weight of the reaction product of l.S to 2 mo]es of nonylphenol, 0.5 to l mole of cumylphenol, 6 to 7 moles oE phenol with 3 moles of phosphorus oxychloride and 5 to 15% of 2-ethylhexyl diphenyl phosphate. All percentages are by weight based on the total weight of the mixture. In addition to these base stock ma-terials, the functional fluid may contain up to about 50 ~ -~
percent of one or more other base s-tock materials. Examples ,~
of these other base stock materials are given in U.S. Patent

3,723,320. Although lt is not permissible to employ these other base stock materials in major amounts in fluid composi-tions of the instant invention, they may be used singly or in combinations as a minor component of the total base stock present in amounts of less than about 50 percent by weight. `

In addition to the base stock materials and the ~-:
monoepoxy compounds, the fluids of the instant invention may ~ ~
also contain one or more base stock modifiers. As used herein, ~ ;
"base stock modifier" means any material which when added to ~ ~ `
the base stock effects a determinable change in the chemical ~`
or physical properties of the base stock. Examples of typical classes of such modifiers which are widely used in formulating hydraulic and other functional fluids include dyes, pour point depressants, antioxidants, antifoam agents, viscosity inclex ;
improvers such as polyalkyl acrylates, polyalkyl methacrylates, polycyclic polymers, polyurethanes, polyalkylene oxides and ; ;~
polyesters, lubricity agents and water.
The preferred polymeric viscosity index improvers which may be employed in the compositions of this invention are the polymers of alkyl esters of unsaturated monocarboxylic '`.

-10- ~ .
~: :

. 43-4160A

~L~JS~
acid~ havinq the ~ormula ' R~ - C - C - OR7 C-H

;:
where~n R5 and R6 ar~ eaah individually hydrogen or a Cl to about C10 alkyl group, and R7 i9 a Cl to about C1~ alkyl group. Illustration of ths alkyl qroups represented by R5, - R6 and R7 within their definitions as given above are for example methyl, ethyl, propyl, butyl, t-butyl~ isopropyl, ~ 2-ethylhexyl~ hexyl, decyl, undecyl, dodecyl and the like.
:; The~e polymers includel for example, poly(butylmethacrylates), ~:
~:~ poly(hexylmethacrylates), poly(octylacrylates), poly(dodecyl-acrylates3 and polymers wherein the ester i9 a mixture of compound~ obtained ~y esterifying the ~-~ unsaturated mono-; oarboxylia aaid with a mixture of monoalcohols containing from 1 to 12 carbon atom~. These and other "base stock modi-~: fiers" are described in U~S.~3,723,320.
In a preferred embodiment of the present invention the fu~ctional fluid~compositions comprise at least about ; : 50 percent by weight of a phosphate.ester or mixture of phos-~ phate e~ter~ represented by the structure .~ .
~ O
Rlo - O - p - O - R8 : : ~ o : ~
,1 , .

:
wberein R8, R~, and Rlo are hydrocarbon radicals~selected ` from the group~consisting of alkyl, alkoxyalkyl,~aralkyl, aroxyalkyl, aryl, aroxyaryl, alkoxyaryl, alkaryl, and mixtures ;:~.
~: thereof and halogenated and alkyl-substituted members-~hereof `
' ~

- . .

3Lo53L~
having up to about 18 carbon atoms, and from about 0.1 to 10 percent by weight of an epoxy compound as hereinbefore defined~
In addition to the phosphate e~ter and epoxy compound, these preferred fluid compositions can also contain certain addi-tives a~ hereinbefore defined and can also contaln minor amounts, e~g., le9s than about 50 percent by weight of one or more other base stock composition as hereinbefore defined.
Particularly preferred ~unctional fluid,compositions comprise at least about 65 percent by weight of such p~osphate esters and less than about 35 percent by weight of other ma~
tarials including base stock~ and base stock modifiers, and even more preferably contain at least about 80 percent by weight of such phosphate e~ters and less than about 20 percent by weight of o~her materials. Particularly pref~rred phosphate ~ ~ , e~ter~ for use in the compositions of this invention are di-alkylaryl phosphates wherein the alkyl radicals have 1 to 18 carbon atoms, e.g., di~utylphenyl phosphate, and mixtures of tri~lkyl phosphate and triaryl phosphate such as 88/12 tri-butyl phosphate/tricresyl phosphate.
The invention will now be illustrated by the follow-ing example. All parts, proportions and percentages are by weight unless o~herwise stated.
EX~MPLE I
,:: ' ~' Dibut ~ 6-epoxy~1,4;oxocyclohexane-2,3-dicarboxylate A. Preparation of the d1butyl ester of 7-oxabicyclo - [2.2.}1 hept-5-ene-2,3-dicarboxylic anhydride. -To a suitable reaction ~essel equipped with a reflux ~;
condenser and ~tirrer is charged 166.1 g (1.0 mole) of 7-oxa-bicyclo 12.2.1] hept-5-ene-2,3-dicarboxylic anhydride (Eastman ) lJA

~S~
practieal srade) ~ 280 g of n~-bu~anol, and 1 g o~ p-tolue21e-sulfonic acid and stirred for about 28 days. During this period the temperature is kept at 50 to 55 C . The pressure is maintained at 20 to 60 Torr for about 120 hours~ When it is under reduced presQure, refluxin~ occurs and water in the condensate steam removed.
Alt the e~d of this per~od, the acid number oi~ the reac ion mixture is 2 . 9 . The mixture is then washed at room temperature once with 250 ~ of water and 2 g of sodium car-0 bonate and once with 250 ml of waterO Butanol and water are stripped under reduced pressure at a maximum temperature of 57C. The yield of the desired ester is 150 g.
B~ ~_ To a suitable reaction vessel i5 charged 29.6 g t.lO mole) o~ Preparation A~ then 22.3 g ~.11 mole) o~ 85%
assav m-chloroperbenzoic acid dissolved in 200 ml o~ methylene chloride is added while the reac~io~ temperature is kept at 20 25C. The reaction is aontinued for 1-3 hours.
- It is then quenched with 250 g o water, 10 g of NaHC03 and 1.5 g of sodium metabisulfite. ~his mixture is then washed with llO g o water and 5 g o~ NaHC03 then lO0 g o~ water~ Solvent is removed by strippin~ under reduced pre~sure ~o final condition o~ 60C. at 20 mm o Hg.
, ; ~ The residue is the de~ired epoxide~
; EX ~ PLE II
A functional fluid~ is prepaxed ~y incorporating 4%
of dibutyl-5,6-epoxy-1,4-oxocyclohexane-2,3-dicaxboxylate of Example I'in a base fluid comprising~94.2~ dibutylphenyl phosphate; 5.1% polyalkylme~hacrylate polymer V.I. impxover and water 0.2%.

- 13 o ~)S~

While this invention has been described with respect to various specific examples and embodiment~, it is to be under-stood that the invention is not limited thereto and that it can be various1y pract.~ced within the scope oE the iollowins claims.

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. ' . ' ~.

Claims (15)

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound represented by the following formula wherein R1 is (CH2)0-3-C(O)OR, -C(O)R, or CH2OR wherein R is an alkyl radical having from 1 to about 18 carbon atoms, R2 is R1' hydrogen or an alkyl radical having from 1 to 9 carbon atoms and R3 and R4 are individually hydrogen or an alkyl radical having from 1 to 4 carbon atoms; when R1 is -(CH2)0?C(0)OR R2 is not H or-(CH2)0-C(0)OR.

2. A compound according to claim 1 wherein R1 is -(CH2)0-3-C(0)OR.

3. A compound according to claim 2 wherein R
contains 1 to 9 carbon atoms.

4. A hydraulic fluid composition comprising (A) at least about 50 percent by weight of a base stock material selected from the group consisting of esters and amides of an acid of phosphorus, di- or tricarboxylic acid esters, esters of polyhydric compounds, and mixtures thereof, and (B) from about 0.1 to 10 percent by weight of an epoxide compound represented by the structure wherein R1 is -(CH2)0-3-C(0)OR, -C(0)R
or -CH20R where R is an alkyl radical having from 1 to about 18 carbon atoms, R2 is R1, hydrogen or an alkyl radical having from 1 to about 9 carbon atoms, and R3 and R4 are individually hydrogen or an alkyl radical having from 1 to about 4 carbon atoms.

5. A composition of Claim 4 wherin R1 is -(CH2)0-3-C(0)OR.

6. A composition of Claim 5 wherein the base stock material is a phosphate ester represented by the structure wherein R8, R9 and R10 are hydrocarbon radicals selected from the group consisting of alkyl, alkoxyalkyl, aralkyl, aroxyalkyl, aryl, aroxyaryl, alkoxyaryl, alkaryl, and mixtures thereof and halogenated and alkyl-substituted members thereof having up to about 18 carbon atoms.

7. A composition of Claim 6 wherein R9 and R10 are C1-18 alkyl radicals and R8 is a C6-C18 aryl radical-

8. A composition of Claim 6 wherein the phosphate ester is dibutylphenylphosphate.

9. A composition of Claim 8 wherein the epoxide compound is C1-12 alkyl-5,6-epoxy-1,4-endooxycyclohexane-2-carboxylate.

10. A composition of Claim 6 wherein the phosphate ester is a mixture of tributyl phosphate and triaryl phosphate

11. A composition of Claim 10 wherein the epoxide compound is C1-12 alkyl-5,6-epoxy-1,4-endooxycyclohexane-2-carboxylate.

12. A functional fluid composition comprising a composition of Claim 6 and from about 2 to 20 percent by weight of a viscosity index improver which is a polymer of an ester having the structure wherein R5 and R6 are each individually hydrogen or a C1 to about C10 alkyl group, and R7 is a C1 to about C12 alkyl group.

13. A functional fluid composition comprising a composition of Claim 6 and from about 2 to 20 percent by weight of a viscosity index improver which is a polymer of an alkylene oxide having a polymeric molecular weight of from about 1,500 to 4,500.

14. In a method of operating a hydraulic pressure device wherein a displacing force is transmitted to a dis-placeable member by means of a hydraulic fluid, the improve-ment which comprises employing as said fluid a composition of Claim 4.

15. In a method of operating a hydraulic pressure device wherein a displacing force is transmitted to a dis placeable member by means of a hydraulic fluid, the improve-ment which comprises employing as said fluid a composition of Claim 12.