US2346153A - Compounded oil - Google Patents

Description

Patented Apr. 11, 1944 2,346,153 v comocsnao on.

George H. Denlson, In, and Paul 0. Condit,

Berkeley, Calii'., asslgnors to Standard Oil Company of California, San Francisco, Call! a corporation of Delaware Application August 2, 1940, erial No. 350,062

22 Claims.

This invention relates to a new and useful composition of matter. More particularly, the invention relates to viscous hydrocarbon oils contaimng a new combination of stabilizing agents which give a synergetic eil'ect. This combination comprises an anti-oxidant and an activator therefor which increases the effectiveness of the antioxidant even though the activator alone may have substantially no anti-oxidant action in the oil being stabilized.

The production of improved hydrocarbon oils, and particularly of lubricating oils having desired characteristics, has been the subject of extensive research and investigation. A characteristic which has ben found particularly significant is the tendency of hydrocarbon oils to deteriorate or partially oxidize when subjected to high temperatures. It is important that resistance to such deterioration or oxidation be imparted to hydrocarbon oils, particularly to lubricating oils, in order that such compositions may be relatively free from the tendency to form sludge and other types of deposits.

A direct result of oxidation and deterioration of oils during lubrication of internal combustion engines is the tendency of the oil to cause or permit the sticking of piston rings or the deposition of adhesive varnish-like material on the cylinder walls of the engine. The crankcase lubricant in internal combustion engines is subjected to extremely severe operating conditions, andin engines of the Diesel type the lubricant encounters in the piston ring zone temperatures of from approximately 425 F. to approximately 650 F. and pressures from oxidizing combustion gases as high as 750 to 1150 pounds per square inch. In its more specific aspects, the present invention is directed to the improvement of hydrocarbon oils by imparting thereto increased resistance to oxidation at temperatures in the order of those above mentioned. Anti-oxidants which are effective at lower temperatures often become ineiiective at higher temperatures, such as 300 F. or above. Even those anti-oxidants which are effective to stabilize hydrocarbon oils against oxidation at 300 F. are often unable to impart to the oil sumcient stability to withstand these severe conditions for more than a relatively short period of time.

The development of the lubricating art has resulted in the use of highly refined and highly paramnic type lubricating oils. This development sems not to have helped in the solution of the problem of stabilizing the lubricants against oxl dation since the highly refined or highly paraiiinic lubricating oils are more diiiicult to satisfactorily stabilize, without introducing other undesirable properties, than were the less highly refined naphthenic base lubricating oils.

This invention provides a combination of comoxidant.

pounding agents capable of imparting to such highly parafiinic and/or other highly refined oils a high stability against oxidation or deterioration, even at 300 F. or above. Further, the invention provides a combination of compounding agents which does not increase the corroslvity of naturally non-corrosive lubricating oils and which actually reduces or inhibits the corrosive action that develops with certain highly paramnic or highly refined lubricating oils.

The combination of the invention comprises an anti-oxidant of the type represented by di-alkyl thioethers and an activating agent for the anti- Examples of thioethers operative for the purpose of the invention are high molecular weight di-alkyl thioethers containing at least one long carbon chain. By "long carbon chain" is meant a radical containing at least 8 to 10 carbon atoms. By high molecular weight thioethers it is intended to designate thioethers containing in the order of a total of 12 or more carbon atoms. Examples of such high molecular weight di-alkyl thioethers are the following monothioethers: di-octyl thioether; octyl decyl thioether; octyl dodecyl thioether; octyl tetra-decyl thioether; octyl cetyl thioether; di-decyl thioether; decyl dodecyl thioether; decyl tetra-decyl thioether; decyl cetyl thioether; di-dodecyl thioether; dodecyl tetra-decyl thioether; dodecyl cetyl thioether; di-tetra-decyl thioether; tetra-decyl cetyl thioether; di-cetyi thioether; di-octadecyl thioether. The preferred di-alkyl monothioethers contain one long chain and one short chain, for example, dodecyl methyl monothioether, dodecyl ethyl monothioether, dodecyl propyl monothioether; tetra-decyl methyl monothioether, tetradecyl ethyl monothioether, tetra-decyl propyl monothioether; cetyl methyl monothioether, cetyl ethyl monothioether, cetyl propyl monothioether.

The above compounds are represented by the type formula RS--R1, where R and R1 may be the same or diiierent alkyl radicals. R and R1 may be either a straight hydrocarbon chain or a branched chain such as obtained from isobutylene polymers or interpolymers of butylene with isobutylene and other analogous olefin polymer derivatives.

Monothio or dithio di-alkyl di-ethers of the general formulae:

for example, monothioethane di-alkyl di-ethers,

or dithioethane di-alkyl di-ethers, are also effective in the combination of this invention. These latter compounds may be represented by the formulae:

where R andR1 may be any of the alkyl radicals previously listed above for these radicals, R2 and R3 may be either hydrogen or any one of such alkyi radicals and 11 may be any whole number. Sulfoxides such asare not precluded.

It is to be understood that the invention in its broader aspects does not preclude the use of substituted alkyl radicals in the thioether component of the composition. However, when such a substituent is present it should not be so close to the sulfur atom of the thioether group as to substantially destroy the essential thioether characteristics of the sulfur atom. Thus, functional groups in the alkyl radicals of thioether which are positioned on the alkyl chain relatively remote from the thioether sulfur atom may be utilized. For example, thioethers derived from oleic acid esters are eifective compounds in the combination of this invention. This type of compound may be represented by the formula:

where R, R1 and R2 are alkylradicals, R1 preferably being a relatively short chain such as an ethyl group. The carbonyl group of the above type compound is sufliciently far removed from the thioether group as not to mask or adversely affect the action of the thioether structure. Like wise, the thioethers remain essentially di-alkyl thioether, even though aryl or other nonaliphatic radicals be attached to the alkyl chain at a point remote from the thioether group, and such compounds may be utilized in the combination herein disclosed.

The thioethers utilized herein may be prepared by methods known in the art. For example, a mono-halogenated hydrocarbon may be reacted with a mercaptide to yield a thioether according to the reaction agent utilized in the compounded oils of this invention comprises an activator for the thioethers enumerated in the foregoing disclosure. The activator comprises either an acid ester of an acid phosphorus, i. e. a partially esterifled acid of phosphorus, or a salt of acids of phosphorus containing an organic substituent. Either the acid ester alone or the salt alone or mixtures of salts and acid esters may be used as an activator. These types of activators, when utilized in combination with the foregoing thioethers, give a synergetic efi'ect and greatly enhance the oxidation inhibiting action of the thioethers. This is true even though the activator may not, when added alone, inhibit oxidation of the oil being stabilized.

Activator-s which may be added to hydrocarbon oil, such as mineral lubricating oil. to provide the second component of the new composition claimed herein preferably comprise metal salts of substituted oxy acids of phosphorus and/or acid esters of oxy acids of phosphorus, although corresponding compounds of the thio acids of phosphorus are not precluded. Salts of metals selected from groups II, III, IV and VI of Mendeleeifs Table of the Elements are preferred. Specific examples of such metals are aluminum,

calcium, barium, strontium, chromium and mag nesium. Salts of iron, cobalt, nickel, tin, zinc and lead comprise additional examples of compounds falling within the broader aspects of the invention. Likewise, ammonium salts of substituted acids of phosphorus containing an organic substituent are not precluded.

The salts of.the substituted acids of phosphorus involved herein are preferably formed from substituted oxy acids of pentavalent phosphorus of the following type formula:

where B may :be alkyl, aryl, alkaryl, aralkyl or cyclic non-benzenoid radicals. Substituted phosphoric acids containing at least twelve carbon atoms are preferred, but where the salts are sufficiently soluble in oil, acids containing fewer carbon atoms may be utilized. Examples of preferred type acids are alkyl or alkaryl subsituted phosphoric acids having at least twelve carbon atoms in the molecule. It is to be understood that the broader aspects of the invention include salts of other types of acids ofphosph'orus containing more thantwelve carbon atoms. Additional examples of such substituted oxy acids of phosphorus are as follows:

aft.

Phosphinlc acid In all of the formulae R and R1 may be alkyl,

' (chlorine,

aryi, alkaryl, aralkyl or cyclic non-benzenoid groups which, in turn, may be pure hydrocarbon constituents or oxygenated hydrocarbons such as alcohols, ketones, esters and ethers, or hydrocarbons containing substituents such as halogens bromine, iodine), amino, or nitro groups. Likewise, R and R may be an oil soluble heterocyclic constituent, for example, a .radical containing a nitrogen ring.

In general, salts of substituted derivatives of acids of phosphorus, such as phosphorou acid, HaPOa; hypophosphoric acid, HsPOs; orthophosphoric acid, H3PO4; pyrophoric acid, H4P=O1 and the sulfur analogues of these acids fall within the broadest aspects of the invention. By acids of phosphorus containing an organic substituent, or by "substituted acids of phosphorus wherever used herein it is intended to designate acids of phosporous containing an organic group of the types previously listed. The organic groups may be either directly attached to the phosphorus atom of the compound or attached thereto through an intervening atom, such as oxygen or sulfur. The term "oxy acids of phosphorus" is used to designate throughout the specification and claims acids of phosphorus in which only an oxygen atom may intervene between the hydrogen and phosphorus atoms of the parent acid.

The preferred acids are mono-esters of orthophosphoric acids or mixtures containing the mono-ester and the preferred salts compris the aluminum, calcium, barium, magnesium and chrominum salts of these acids. Examples of such salts are aluminum lauryl phosphate, aluminum cetyl phosphate, aluminum octadecyl phosphate, aluminum oleyl phosphate, aluminum (cetyl phenyl) phosphate, aluminum (di-amyl phenyl) phosphate, aluminum naphthenyl phosphate; calcium lauryl phosphate, calcium cetyl phosphate, calcium octadecyl phosphate, calcium oleyl phosphate, calcium (cetyl phenyl) flp'hosphate, calcium (di-amyl phenyl) phosphate, calcium naphthenyl phosphate; barium lauryl phosphate, barium cetyl phosphate, barium octadecyl phosphate, barium oleyl phosphate, barium (cetyl phenyl) phosphate, barium (di -amyl phenyl) phosphate, barium naphthenyl phosphate; magnesium lauryl phosphate, magnesium cetyl phosphate, magnesium octadecyl phosphate, magnesium oleyl phosphate, magnesium (cetyl phenyl) phosphate, magnesium (di-a'myl phenyl) phosphate, magnesium naphthenyl phosphate;

ess is not limited to the alkyl derivatives but includes aryl ethyl phosphoric acid, valkaryl ethyl phosphoric acid, aralkyl ethyl phosphoric acid and ethyl phosphoric acids containing a cyclic non-benzenoid group.

The metal salts of the various substituted oxy acids of phosphorus may be conveniently prechromium lauryl phosphate, chromium cetyl phosphate, chromium octadecyl phosphate, chromium oleyl phosphate, chromium (cetyl phenyl) phosphate, chromium (di-amyl phenyl) phoswhere R is an alkyl radical. The alkyl ethyl phosphoric acid is soluble in ether, while the ethyl metaphosphate is not, and the ether solution of the former may be separated from the latter by decantation. In preparing the metal salts herein involved, the ethyl group in the ethyl phosphoric acid above mentioned may be hydrolyzed to form the metal salt of the mono-alkyl orthophosphoric acid, i. e., the salt of RHZPOL This type of procpared by reacting the acid with sodium hydroxide or potassium hydroxide and then precipitating the desired metal salt from a solution of the sodium or potassium salt by the addition of the appropriate metal ion. The salt also may be prepared by the direct neutralization of the acid, as, for example, with lime where the calcium salt is to be obtained. The calcium salt may also be prepared in a non-aqueous environment by the reaction of calcium carbide with the free substituted acid of phosphorus.

As has been previously pointed out, the present invention embraces the discovery that the combination of a. thioether and an activator therefor imparts to hydrocarbon oils greatly enhanced stability against oxidation and gives a synergetic effect. The following data illustrate the synergetlc action of thioethers and salts of substituted acids of phosphorus in hydrocarbon oils:

TABLE I oxidator data C. 0. oxygen absorbed at 300 F. Oil

2 hrs. 4 hrs. 6 hrs.

White 0a.... Q.

Greater than 1,000 c. c.

first 5 hr. White oil+1% cetyl ethyl thioether Do.

White oil+l% calcium cetyl phosphate. Do.

White oil+1% calcium eetyl phosphate+ 50 69 88 0.25% cetyl ethyl thioether.

White oil+l% di-octyl thioether 3B0 White oil-|-.l% di-octyl thioether+1% 40 calcium cetyl phosphate. 1 White oil+2% cetyl methyl thioether.. 650 c. c first hour. White oii+2% cetyl methyl thioether+ i l0 l5 1% calcium cetyl phosphate. f

. placing a weighted amount of oil in an oxygen absorption cell. The oil is completely saturated with oxygen by maintaining a foam with bubbles formed at a perforated glass surface in the cell. Constant temperature is maintained by an oil bath in which the cell and the intake line for the oxygen supply are immersed. Oxygen is circulated by means of a leakless oil-free p mp and is preheated to bath temperature, passed through the oil in intimate contact therewith by means of the perforated glass surface and certain volatile oxidation products carried out with the gas stream are condensed in a water-cooled column and returned to the oil. The procedure of taking measurements consists in placing the weighed amount of oil in the cell as previously stated, evacuating the apparatus. filling with oxygen at atmospheric pressure and then accurately determining the decrease in the volume of oxygen caused by its absorption in the oil by the measurement of the oxygen volume in the system at the stated intervals during the test.

Additional oxidator data on combinations of other thioethers and an activator therefor are given in Table II,

Teams II C. c. absorbed at 340 FJ Oil 2 hrs. 4 hrs. 6 hrs.

Greater than 1,000 c. e. White oil... 1 h h t r White oil+l calcium cety p osp a e-.- o

hite oil+2g dicctadecyl thioether 2,400 White oil+2% dioctadecyl thioether+1% 107 168 257 calcium cetyl phosphate. White oil+1 ethane dioctyl thioetheL 360 White oiii-l-l 0 etth amla1 dlo tytl thloether+ 45 l calcumce p osp ae. Highly refined ngphthenic base oil Greater than 1,000 c. o.

s r. Highly refined naphthenic base oil+l% 100 588 dilauryi thioether. Highly refined naphthenic base oil+l% 12 24 53 dgaurgltthioether+l% calcium cetyl 0s a e. H ghly reiined nsphthenic base oil+2% 50 l,000

dicetyl thioether. Highly refined naphthenic base oii+2% 40 135 200 dicetyl thioether+l% calcium cetyl phosphate.

1 Results given in number c. c. per 100 grams oil.

TABLE III 300 F. corrosion test Loss Ou-Pb Loss Cd-Ag mg. weight mg. weight 72 hrs. 72 hrs.

White oil White oil+i% calcium cetyl phosphate White oil+l% cetyl ethyl sulfide White oil-{4% cetyl ethyl sulfide+l% calcium cetyl phosphate The above corrosion tests were carried out in the following manner. Glass tubes 2 inches in diameter and 20 inches long were immersed in an oil bath, the temperature of which was automatically controlled to within :1 of the 300 F. test temperature. Approximately 300 c. c. of oil under test was placed in each tube and air was bubbled through it at the rate of liters per hour. Strips of the different types of bearing metals were placed in the oil; in most cases the copper-lead and cadmium-silver bearing alloys were tested simultaneously in the same sample of oil. The weight loss of each strip was recorded. Before weighing, each strip was washed in petroleum ether and carefully wiped with a soft cotton cloth. The duration of the test was 72 hours.

It has also been observed that the thioether increases the efliciency of the substituted acids of phosphorus in stabilizing the hydrocarbon oil against the formation of gums or adhesive deposits on hot metal surfaces, for example, in the piston ring belt of internal combustion engines.

Mention has been made of acid esters of acids of phosphorus, i. 6. partially esterified acids of phosphorus, as an activator for the thioethers. Examples of such acid esters are monocetyl orthophosphoric acid and dicetyl ortho phosphoric acid exemplifying respectively acids of the type formula in which R and R1 may be alkyl, aryl, a'lkaryl, aralkyl or cyclic non-benzenoid radicals. The activating effect of acid esters of acids of phosphorus is illustrated by the following data:

Team: IV

Oxidator data C. c. 0: absorbed at 340 F.

1% cetyl ethyl thioether. White oil+1%monocetyl phosphoric acid.

White oil+1% monocetyl phosphoric acid +l% cetyl ethyl thioether.

1 Results given in number 0. e. per grams oil.

The compounded lubricant herein disclosed may have one or more advantages, depending upon the particular compounds selected, the proportions utilized and the environment which the lubricating oil is to encounter. It should be observed, for example, that even though a compounded oil may be somewhat corrosive to copper-lead or cadmium-silver bearing alloys, Babbitt bearings are little, if at all, affected by such corrosive action. Hence, combinations of compounding agents which may not be particularly desirable for lubrication of copper-lead or cadmium-silver bearings at high temperatures where corrosion becomes a factor of importance may be highly useful and extremely advantageous in conjunction with the operation of internal combustion engines having bearings of Babbitt or other corrosive-resistant bearing metals. Likewise, combinations of compounding agents which may not be sumciently powerful to stabilize a particular oil stock against oxidation under the most severe conditions may, none the less, be highly advantageous in such oils where the environment to be encountered is not so severe as, for example, in turbine oils, cable oils, electric switch oils, transformer oils, and the like. The present invention in its broader aspects is, therefore, not limited to the particular combination of ingredients giving the greatest stability or having all of the advantages of the preferred agents. The invention embraces various of the less advantageous combinations of addition agents which may find utility in particular applications where all possible improvements in properties of the oil may not be required or where the standard-of performance may not be so high.

The compounding ingredients of this invention appear at present to find their greatest utility in highly refined or highly paraifinic mineral lubricating oil stocks, which stocks have heretofore been the most diificult to stabilize. However, it is to be understood that the invention is not limited to any particular base stock. The advantages herein disclosed may be obtained with various oil stocks, the selection of which will be determined by conditions and services which the Greater than 1,000 c. c.

1st 5 hr.

ing on the uses involved and the properties desired. As little as 0.05% by weight of the ac-' tivator gives measurable improvements, particularly as respects the color stability ot the compounded oil. From approximately 0.25 to 2% of the salts of substituted acids of phosphorus or of the acid esters oi acids of phosphorus may be added to lubricate containing thioethers where stability at high temperature comprises the principal property desired. More than 2% of these activators in mineral oils is not precluded. In general, however, more than 5% will be found unnecessary. The proportion of the thioethers present in the compounded oil may likewise vary widely, depending on the uses involved and the properties desired. As little as 0.05% of the thioether gives measurable improvement, although from approximately 0.1% to 2% is preferred where the compounded oil is to be used as a crankcase lubricant for internal combustion engines. 5% or more by weight of the thioethers may be dissolved in mineral oil or other suitable organic solvents for the purpose of preparing a concentrate capable of dilution with lubricating oils and the like. Concentrates containing high percentages, e. g. 50%, of the thioether and the activator comprise a convenient method of handling these ingredients and may be used as addition agents for lubricants in general, as well as for other purposes.

The combination of ingredients of this invention may be added to hydrocarbon oils containing other compounding agents, such as pour point depressants, oiliness agents, extreme pressure addition agents, blooming agents, and compounds for enhancing the viscosity index of the hydrocarbon oil. The invention in its broader aspects embraces hydrocarbon oils containing, in addition to the thioethers and activator, thickening agents and/or metal soaps in grease-forming proportions or in amounts insufficient to form grease, as in the case of mineral castor machine oils or other compounded liquid lubricants.

As previously indicated, di-alkyl thioethers are highly susceptible to activation according to this invention. The invention in its broader aspects includes the substitution for the di-alkyl thioethers of cycloalkyl thioethers such as di-(cetylcyclohexyl) thioether, or mixed acyclic cycloalkyl thioethers like cetylcyclohexyl cetyl thioether or non-benzenoid cyclic thioethers of the thiophane type such as cetyl thiophane.

While the character of the invention has been described in detail and numerous examples oi the combination given, this has been done by way 0! illustration only and with the intention that no limitation should be imposed on the invention thereby. Numerous modifications and variations of the illustrative examples may be eilected in the practice of the invention which is of the scope of the claims appended hereto.

We claim:

1. A composition comprising a hydrocarbon oil, a high molecular weight dialkyl thioether oxidation inhibitor, and an activator for said thioether comprising a salt or an acid of phosphorus containing an organic substituent. said salt being present in an amount suflicient to enhance the action of said oxidation inhibitor.

2. A composition comprising a hydrocarbon oil, an oxidation-inhibiting amount or a high molecular weight dialkyl thioether containing at least one long carbon chain, and an activator for said thioether comprising a salt of anacid of phosphorus containing an organic substituent, said salt being present in an amount suflicient sub.- stantially to enhance the anti-oxidant action of said thioether.

3. A composition comprising a hydrocarbon 011, an oxidation-inhibiting amount of a high molecular weight dialkyl thiodiether containing at least one long carbon chain, and an activator for said thiodiether comprising a salt or an acid 0! phosphorus containing an organic substituent, said salt being present in an amount suflicient substantially to enhance the antioxidant action or said thiodiether.

4. A composition comprising a hydrocarbon 011, an oxidation-inhibiting amount of a high molecular weight dialkyl'monothioether containing at least one .long carbon chain, and an activator for said monothioether comprising a salt of an acid of phosphorus containing an organic substituent.- said salt belng present in an amount sufficient substantially to enhance the antioxidant action of said monothioether.

5. A composition comprising a hydrocarbon oil, an oxidation-inhibiting amount of a high molecular weight dialkyl dithiodiether containing at least one long carbon chain, and an activator for said dithiodiether comprising a, salt of an acid of phosphorus containing an organic substituent. said salt being present in an amount sufllcient substantially to enhance the antioxidant action of said dithiodiether.

6. A composition comprising a hydrocarbon lubricating oil, an oxidation-inhibiting amount of a thioether oi the type iormula:

R-S-Ri where R and R1 are alkyl radicals, at least one of which contains more than about ten carbon atoms and the sum of the number of carbon atoms in R and R1 is at least about twelve, said oil also containing a small amount of a metal salt or an acid 01 phosphorus containing an organic substituent.

7. A composition comprising a hydrocarbon lubricating oil, an oxidation-inhibiting amount of a thioether of the type formula:

R-S-O-C-S-Ri where R and R1 are alkyl radicals, at least one of which contains more than about ten carbon atoms and the sum of the number of carbon atoms in R and R1 is at least about twelve, said oil also containing at least about 0.05% or a metal salt of an acid of phosphorus containing an organic substituent.

8. A composition comprising a hydrocarbon oil solution containing at least about 0.05% of a high molecular weight dialkyl monothioether and at least about 0.05% or a polyvalent metal salt of an oxyacid 0i pentavalent phosphorus containing an organic substituent.

9. A composition comprising a hydrocarbon oil solution containing at least about 0.05% of a high molecular weight dialkyl monothioether and at least about 0.05% 01' an alkaline earth metal salt of an oxyacid of pentavalent phosphorus containing an organic substituent.

10. A composition comprising a hydrocarbon,

antioxidant i'or the'oil and an activator for said thioether comprising an acid ester of an acid of phosphorus in an amount suflicient substantially to enhance antioxidant action of said thioether.

13. A composition comprising a mineral lubricating oil, from approximately 0.1% to 5% of a high molecular weight dialkyl monothioether, and from approximately 0.1% to 5% of a polyvalent met-a1 salt of an oxyacid of pentavalent phosphorus containing an organic substituent.

14. A process of stabilizing hydrocarbon oil subject to deterioration at elevated temperatures which comprise incorporating in said oil a small amount of a high molecular weight dialkyl thioether antioxidant and enhancing the efiectiveness of said antioxidant by incorporating a small amount 01' an activator therefor.

ness of said antioxidant by incorporating a small amount of an activator therefor comprising a salt or an acid oi phosphorus containing an organic substituent.

17. A process of stabilizing a viscous hydrocarbon oil which comprises incorporating in said oil a high molecular weight dialkyl thioether in an amount sumcient substantially to inhibit deterioration oi' the oil at elevated temperatures and enhancing the eflectiveness of said thioether by incorporating in the oil a small amount or a polyvalent metal salt 01' an acid of phosphorus containing an organic substituent.

18. A stabilizer for hydrocarbon oils subject to deterioration by oxidation, said stabilizer comprising a high molecular weight dialkyl thioether antioxidant and a salt of an acid of phosphorus containing an organic substituent, said salt being present in an amount sufllcient to enhance the antioxidant action of thethioether.

19. A stabilizer as defined in claim 18, further characterized in that said salt is a polyvalent metal salt of an oxyacid of pentavalent phosphorus.

20. A stabilizer as defined in claim 18, further characterized in that it comprises a concentrated hydrocarbon oil solution or said antioxidant and said salt.

15. A process 01' stabilizing hydrocarbon oil subject to deterioration at elevated temperatures which comprise incorporating in said oil a small amount oi. a high molecular weight dialkyl thioether antioxidant and enhancing the eflectiveness of said antioxidant by incorporating a small amount or an activator therefor comprising an acid ester or an acid of phosphorus.

16. A process of stabilizing hydrocarbon oil subject to deterioration at elevated temperatures which comprise incorporating in said 011 a small amount of a high molecular weight dialkyl thioether antioxidant and enhancing the eflective- 21. A stabilizer for hydrocarbon oils subject to deterioration by oxidation, said' stabilizer comprising a high molecular weight dialkyl thioether antioxidant and an acid ester of an acid of phosphorus, said ester being present in an amount sufllcient to enhance the antioxidant action of the thioether. i

22. A composition comprising a hydrocarbon oil, a high molecular weight dialkyl thioether antioxidan't for said oil, and an activator for said thioether capable of enhancing the antioxidant action thereof and selected from the class consisting oi the esters and salts of phosphoric acid, said activator being present in an amount sufllcient to effect said enhancement.

GEORGE H. DENISON, JR. PAUL C. CONDIT.

Certificate of Correction Patent No. 2,346,153. April 11, 1944.

GEORGE H. DENISON, JR., ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 60, for

page 3, first column, line 13, for pyrophoric read pyrophosphom'c; line 19, for phos- 5 porous read phosphorus; and that the said Letters Patent should be read with these giigections therein that the same may conform to the record of the case in the Patent Signed and sealed this 4th day of July, A. D. 1944.

[SEAL] LESLIE FRAZER Acting Commissioner of Patents.

Certificate of Correction Patent No. 2,346,153. 7

GEORGE H. DENISON, JR., ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 60, for

' OH OH read |l\ 0 OH 0 OH 111165 69-7 3, for

page 3, first column, line 13, forpyrophoric read pyrophosphom'c; line 19, for phosporous read phosphorus; and that the said Letters Patent should be read with these gofrgections therein that the same may conform to the record of the case in the Patent Signed and sealed this 4th day of July, A. D. 1944.

[SEAL] LESLIE FRAZER,

Acting Commissioner of Patents.

April 11, 1944.