US2491432A - Stabilized lubricant - Google Patents

Description

Patented n... s, 1949 STABILIZED LUBRICANT Ellis Ross White, Albany, Calif., assignor to Shell Development Company, San Francisco, Calif., a

corporation of Delaware No Drawing. Application August 12, 1946,

Serial No. 690,088 I 8 Claims. (01. 252-52) This invention relates to the stabilization of lubricating compositions against the deleterious effects of oxidation, said stabilization being effected by the addition of a certain outstanding oxidation inhibitor. More particularly, this invention relates to the stabilization of certain non-hydrocarbon lubricants with 1,2-dihydroxybenzene.

It has been previously suggested to use certain polymeric materials, such as polymers of propylene oxide, as lubricants. While such polymers have found a limited use as substitutes for mineral oil lubricants, their utility has been limited by their relatively great susceptibility to oxidation, and the poor response which they show toward standard antioxidants, such as those employed with petroleum base lubricants.

These polymeric lubricants, and the other nonmineral oil lubricants defined hereinafter, are especially distinguished from mineral oil lubricants by the volatility of their oxidation products. Petroleum oils have a tendency to form sludge and gummy or resinous products upon oxidation. Presumably, they polymerize under the influence of certain oxygen containing intermediates, probably peroxides, aldehydes, etc.

Contrary to these phenomena, the non hydrocarbon lubricants defined hereinafter do not form appreciable amounts of sludge and do not thicken to any great extent upon oxidation. Instead, the oxidation products are of such a volatile nature 2 positions, they are, as a group, substantially ineffective anti-oxidants for the non-hydrocarbon lubricants.

It is an object of the present invention to provide new lubricating compositions. It is another object of this invention to provide improved nonhydrocarbon lubricating compositions. It is still another object of this invention to provide a superior anti-oxidant for polymeric alky'lene oxides, and alkylene glycols, as well as for certain thioethers and polysulfides as more particularly defined hereinafter. It is a further object to provide improved non-mineral oil lubricants having a reduced tendency to oxidize and polymerize. Other objects will appear hereinafter.

Now, in accordance with this invention, it has been found that substances having units of the general formula wherein m, n, p and r are integers and the Rs are organic radicals, are stabilized to an outstanding degree against oxidation by the addition thereto of a minor amount of 1,2-dihydrcxybenzene. The action of 1,2-dihydroxybenzene as an anti-oxidant for substances having the above general formula is remarkably specifi since such closely allied compounds are alkylated 1,2-dihythat they escape from the lubrication system the stabilization of mineral oils is the group comprising substituted phenols. While many of these are good mineral oil anti-oxidants, and have inhibiting properties in other organic comuration .-ORS-R wherein the R's are organic radicals; monomeric or polymeric polysulfides having units of the general configuration --O-R-S--R-- wherein p is an integer and the Rs are organic radicals; and'copolymers of individual members of each group with other members of the same or different groups.

Alblene oxides, and particularly the alkylene oxides having the oxygen atom directly bound to adjacent carbon atoms, form polymers of the above configuration. have the general configurationwherein the free valences are satisfied with hydrogens or organic radicals.

Allwlene oxides which form polymers include ethylene oxide, propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide, isobutylene oxide, tetramethylethylene oxide, methylphenylethylene oxide, cyclohexeneoxide, methylcyclohexene oxide, 1,2-cetene oxide, and other substances containing the epoxide linkage, such as epichloro- ,hydrin, epibromohydrin, and glycides such as glycidol' and 1,2-epxybutanol-2, as well as derivatives and polymerizable homologs and analogs of the aforementioned and like substances.

Copolymers of the alkylene oxides useful in lubricants of the present invention include for example the copolymers of ethylene oxide and propylene oxide; the copolymers of ethylene oxide and isobutylene oxide; the copolymers of proylene oxide and epichlorohydrin; the copolymers of propylene oxide and 1,2-butylene oxide; and the copolymersof propylene oxide and isobutylene oxide.

Polymers similar to those above are formed from the alkylene glycols, including the polymethylene glycols arii the ethylene glycols. The monomeric and lower polymeric glycols have the general configuration V where m. and n are integers and the free valences are saitsfled with hydrogen atoms or organic radicals. when n is 1, the general formula is that of an ethylene glycol, wherein the glycollic hydroxyls are on adjacent carbon atoms.

Glycols having three carbon atoms separating the glycollic hydroxyls are derived from propanediol-1,3 (trimethylene glycol) and have the gen- In 1... Liiai.

wherein n is an integer and R1 and R2 are hydrogen atoms or organic radicals.

If R1 and/or R: are not hydrogen atoms, they.

These monomeric oxidespropanedioi-1,3; 1,2,3,3-tetramethylpropanediol- 1,3; 1,1,2,2,3-pentamethylpropanediol-1,3; 1,1,2,- 3,3 pentamethylpropanediol 1,3; and hexamethylpropanediol-Lii.

5 "In place of the methyl groups other alkyl groups may be utilized, such as ethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl, etc., radicals, as well as their isomers. Preferably, when alkyl groups are the substituents R1 and R2, they have from 1 to carbon atoms, and still more preferably from 1 to 5.

It will be understood that R1 and R: may be similar or dissimilar groups. Thus, when expanding the general formula given hereinbefore to its indicated number of carbon atoms, it then becomes wherein R: through Rs are either hydrogen atoms or similar or dissimilar organic radicals. Those derivatives of trimethylene glycol, other than trimethylene glycol itself, which give the most satisfactory polymers for general use, have either one or two of the R's as lower alkyl groups. Thus, 2-methylpropanediol-1,3; and 2,2-dimethylpropanediol-1,3 form excellent lubricants when treated according to the method of the present invention.

Other lower alkyl substituted trimethylene glycols which polymerize readily are 1-methyl-2- ethylpropanediol-l,3; 2-methyl-2-ethylpropanediol 1,3; 1-methyl-3-ethylpropanediol 1,3; 2- methyl 2 propylpropanediol 1,3; 1 methyl- 2-isopropylpropanediol-1,3; 2-methyl-2-butylpropanediol-1,3; I 2-methyl-3-butylpropanediol- 1,3; and the homologs, analogs and derivatives of the same.

One or more of the substituents represented by R3 to Rs in the above general formula may be cycloaliphatic radicals. Thus, Ra through R: may be such radicals as cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, etc. However, open chain alkyl substituents give polymers having preferred properties.

The polymers have modified properties if the trimethylene glycol derivative contains other active groups, such as additional hydroxyls, carboxyls, carbonyls, halogens, sulfur, etc.

Other polymethylene glycols, having 6 or more carbon atoms separating the glycollic hydroxyls, form polymeric and copolyrneric lubricants which are readily stabilized with 1,2-dihydroxybenzene.

The higher polymethylene glycols from which lubricants of the present invention may be prepared have the general formula wherein a is an integer, 1! is an integer greater than 5 and the R's attached to 11 carbon atoms are hydrogen atoms or organic radicals. Preferably z is an integer less than 10, and more preferably is an integer from 1 to 4. Actually, when 2 is more than 1, the glycol is a dimer, trimer, etc., of the corresponding monomeric glycol. The polymethylene glycols polymerizing most readily are those in which 1! is an integer of from about Btoabout 20.

Monomeric, unsubstituted polymethylene glycols falling within the above formula include 15 hexanediol-1,6; heptanediol-L'I; octanediol-1,8;

nonanediol-LQ; decanediol-1,10; dodecanediol- 1,12; and polymerizable homologs, analogs and derivatives of the same.

The above glycols are those in which all of the R substituents attached to the 11 carbons are hydrogens. When one or more of the R's are substituents other than hydrogens, they may be hydrocarbon radicals, such as aliphatic, aromatic, or alicyelic, hydrocarbon radicals, or radicals containing non-hydrocarbon members, such as hydroxyl, carboxyl, or carbonyl groups, or sulfur, selenium, tellerium, phosphorus or nitrogen atoms. Preferably, however, any organic radicals attached to the polymethylene glycol are hydrocarbon radicals. Of these, the aliphatic hydrocarbons are preferred, and the saturated lower aliphatic radicals give the most stable polymers and have the widest utility. Hence, the preferred Rs, other than hydrogen, are the lower alkyl radicals, such as methyl, ethyl, propyl, isopropyl, butyl, secbutyl, tertbutyl, amyl, isoamyl, hexyl, etc., groups. Again even when Rs other than hydrogen are present, it is preferred .that the monomeric glycol contain a preponderence of hydrogen substituent R's. The most reactive glycols are those in which less than four R's are other than hydrogen, and the greatest reactivity -is possessed by those having two or less Rs which are organic radicals.

Glycols which fall within the above classification include heptanediol-1,6; octanediol-1,6; nonanediol-1,6 dodecanediol-1,6 decanediol-1,6; octanedio1-1,'7; nonanediol-l,7; decanediol-1,7 dodecanediol- 1,7; nonanediol-1,8 decanediol-1,8; decanediol-1,9; dodecanediol-1,9; dodecanediol- 1,10; octanediol-2,7; nonanediol-2,7; decanediol- 2,7 dodecanediol-2,7; nonanediol-2,8; decanedim-2,8; dodecanediol-2,8; decanediol-2,9; dodecanediol-2,9; 2,3-dimethylhexanediol-1,6; 2,4- dimethylhexane 1,6; 2,5 dimethylhexane 1,6;

4,4-dimethylhexanediol-1,6 5,5-dimethylhexanediol-1,6; 2-methyl-3-ethylheptanediol-1,7; 2- ethyl 3 methylheptanediol 1,7; 3,3 diethylheptanedio1-1,7 3,4-diisopropyloctanediol-1,8 etc., and their polymerizable homologs, analogs and derivatives.

The polymers described hereinbefore may be homopolymers or may be copolymers. For example, an ethylene glycol-may be copolymerized with a trimethylene glycol to give copolymers having units of the general configuration wherein m and n are integers and the free valences wherein m, 1; and p are integers, y is an inte er are satisfied with hydrogens or organic radicals. I

These include copolymers of ethylene glycol and greater than 5, and the free valences are satisfied with hydrogen atoms or organic radicals. These include, for example, copolymers of ethylene glyco] and hexamethylene glycol; trimethylene glycol and hexamethylene glycol, etc.

The allwlene oxides usually are polymerized at temperatures from about -60 C. to about C. in the presene of'alkalies, acids, salts, or active catalysts such as aluminium chloride and boron trifluoride. The glycols are polymerized at higher temperatures (-300" C.) in the presence of dehydration catalysts, such as iodine, mineralacids of the type of nitric acid and sulfuric acid, hydrogen halides such as hydrogen iodide or hydrogen chloride; or organic sulfonic acids such as para-toluene sulfonic acid.

All of the polymers and copolymers described hereinabove have units of the general formula wherein m is greater than 1, and n is 1, thereby givng polymers having units of the general configuration 0n the other hand, when m is 1 and n is greater than 1, the non-hydrocarbon lubricants have units of the general configuration wherein p is an integer. These substances may be monomeric or polymeric thioethers or polysulfides.

The monomeric hydroxy thioethers and polysulfides are represented by the general formula have organic radicals R which are either similar or dissimilar. Preferably they are similar hydrocarbon radicals. The aliphatic hydrocarbon radicals, and especially the saturated aliphatic hydrocarbon radicals form polymers with the subject alkylene glycols having high stability against oxidation. When the Rs are saturated aliphatic hydrocarbon radicals, they may be of primary, secondary or tertiary character with relation to thethioether sulfur atom, dependent upon their method of formation. For example, the primary dihydroxythioethers have'the general formula wherein the Rs are saturated aliphatic radicals. Thioethers of this configuration are conveniently prepared by the abnormal addition of unsaturated alcohols to hydrogen sulfide. Thus, when allyl alcohol and hydrogen sulfide are reacted in the presence of ultra-violet light at moderate temperatures, one of the products is his 75 (gamma-hydroxypropyl) sulfide.

A typical preparation of this character is that of the condensation of hydrogen sulfide with allyl alcohol, as follows:

' Five hundred parts of allyl alcohol and 124 parts of hydrogen sulfide were mixed in a quartz tube and irradiated for two hours by rays from a 250 watt mercury arc lamp. During the first hour the pressure rose from 140 lbs. per sq. in. to 190 lbs. per sq. in., after which it fell to 160 lbs. per sq. in. In this time the temperature increased from C. to 100 C., due in part to the exothermic character of the reaction, but mainly due to the heat from the mercury arc lamp. The product was subjected to fractional distillation, the part remaining in the still above 134 C. at'0.3 cm. mercury pressure being his (gamma-hydroxypropyl) sulfide.

Suitable alcohols for the preparation of primary dihydroxythioethers include, isopropenyl alcohol, allyl alcohol, crotyl alcohol, methallyl alcohol, and their homologs, analogs and substitution products. Dihydroxythioethers formed by the above method include his (beta-hydroxyethyl) sulfide and his (gamma-hydroxypropyl) sulfide.

If the thioether has hydroxyl groups on other than terminal carbons, the dihydroxythioethers include his (alpha-hydroxyethyl) sulfide, and his (alphaand beta-hydroxypropyl) sulfide. Mixed hydroxythioethers are useful in forming the lubricants of the preesnt invention. These include beta-hydroxyethyl-gamma-hydroxyprm pyl sulfide, hydroxymethyl-beta-hydroxyethyl sulfide, alpha-hydroxyethyl-alpha-hydroxypropyl sulfide, as well as their homologs, analogs and derivatives. Higher thioethers of this class may be prepared having hydroxybutyl, hydroxyamyl, hydroxyexyl, etc., groups.

Those hydroxythioethers having the general formula in which the Rs are similar saturated aliphatic radicals having from 1 to 6 carbon atoms are preferred in preparing the lubricants of the present inventio'n.

When the monomeric sulfur compound is a polysulfide having the general formula it is preferred that p be a number between 2 and 6, and that the R's be similar or dissimilar saturated aliphatic hydrocarbons. However, the latter may have functional groups attached thereto, such as carboxyl, carbonyl, hydroxyl, etc., radicals. Preferably, the Rs are similar saturated aliphatic radicals having from about 2 to about carbon atoms. While the R groups may be of primary, secondary or tertiary nature,

with respect to the sulfur atom, those forming lubricants of the greatest utility have the general formula gamma-mercaptopropyl alcohol. It is isolated by distillation of the irradiated condensation mix- ,8 ture. the fraction distillation at 132-134 C. (16

cm. mercury pressure) being gamma-mercaptopropyl alcohol, in a yield of 18.0% based on the charge.

One mol of gamma-mercaptopropyl alcohol was mixed with an aqueous solution of one mol of potassium hydroxide. Starting at room temperature, the calculated quantity of iodine was added slowly to the mixture. The solution was subjected to distillation, all products volatilizing below C. at 0.2 mm. mercury pressure bein removed, leaving his (gamma-hydroxypropyl) disulfide.

Polysulfldes having the preferred structure include bis (gamma-hydroxypropyl) disulfide, bis (beta-hydroxyethyl) disulfide, bis (hydroxymethyl) disulflde, hydroxymethyl-gamma-hydroxypropyl disulfide, hydroxymethyl-beta-hydroxyethyl disulfide, beta-hydroxyethyl-gammahydroxypropyl disulflde, etc., and their homologs and analogs.

The various substances described above are chain-like monomers or polymers containing one or two terminal hydroxyl groups. These hydroxyls may be acted upon by the usual methods with such materials as etherifying or esterifying agents in order to obtain products having altered properties, such as solubility, or improved action as lubricants, plasticizers, etc.

Various etherifying agents may be used for etherifying the terminal hydroxyls. These include alkyl halides, such as methyl iodide, methyl bromide, ethyl chloride, propyl iodide; aralkyl halides such as benzyl chloride and methylbenzyl chloride; hydroxyalkyl chlorides such as hydroxyethyl chloride; carboxyalkylating agents such as sodium mono-chloracetate; and alkylene halides such as allyl chloride. Ordinarily, the etheriilcation is carried out in strongly basic environments; sodium hydroxide, liquid ammonia and quaternary ammonium bases and salts being the usual basic substances present.

Esterification of the terminal hydroxyls may be accomplished with various inorganic groups such as nitrates, phosphates or sulfates. However, preferred esterifying agents are the organic acids, anhydrides or acid chlorides, and especially fatty acid anhydrides and their chlorides, including for example formic, acetic, propionic, butyric, hexoic, 2-ethyl-hexoic, and higher fatty acids such as lauric, stearic, myristic, palmitic and capric acids. Usually, the esters are formed by treatment of the hydroxylated polymer with the anhydride of the acid in the presence of 'a catalyst such as sulfuric or phosphoric acid. The

saturated fatty acids form the moststable esters with the glycol polymers.

At times it is preferable to allow only partial mixed ethers, mixed esters or ether-esters.

Etherification or. esterification of the endgroups may take place simultaneously with or subsequent to polymerization, and may be effected prior to or subsequent to any decolorizing and purifying processes. Preferably, the end-group modification is carried out immediately after polymerization and before purification or decolorizing, but a secondary preferred time for modiilcation is during the polymerization step itself.

In employing this last alternative, the exact about preferably from 1% to 2.5%

mechanism by which substitution of the endgroups occurs is obscure. However, by using an active modifying agent, such as an alcohol, as the diluent during the polymerization, reaction occurs to give polymers having at least one substituted end group, such as an ether group or ester group. For example, if alcohols such as n-octyl alcohol, n-decyl alcohol, n-dodecyl alcohol, etc., or their isomers, are used as diluents during the polymerization,the corresponding ethers of the polymers are formed. This provides a convenient method for modifying the properties of the polymer. It is preferred that the alcoholic diluent, or other modifying agent, have from 6 to 20 carbon atoms. The reactive diluent may be the only diluent present, or may be mixed with one or more inert diluents.

In accordance with the present invention, any of the above monomeric or polymeric lubricants are stabilized against oxidation by the presence of 1,2-dihydroxybenzene; The amountsof 1,2- dihydroxybenzene required to stabilize the lubricants defined hereinbefore varies somewhat with the conditions'to which the compositionwill be subjected, with the secondary additives in the composition and with the exact identity of the monomer or polymer to be stabilized. Ordinarily, the inhibitor gives optimum stabilization when present in amount between about 0.5% and 1,2-dihydroxybenzene may be used in combination with other-secondary additives such as corrosion inhibitors (including organic acidic materials capable of forming water-insoluble soaps), E. P. agents, etc., as well as gelling agents such as calcium, barium, sodium, potassium,

lithium or strontium soaps, for the preparation K from which the compositions are prepared in that lubricant consumption and oxidation product formations by the stabilized compostiions are relatively low.

The following example is presented for the purpose of illustrating the present invention, but it is not intended that the invention be limited specifically thereto:

A methylated polymer of ethylene glycol having the formula was inhibted with 1% 1,2-dihydroxybenzene. Seventy-five gram samples or the unihibited and stabilized oils were heated in a bomb at 140 C.

in the presence of 1 sq. cm. copper per gram oil under an initial oxygen pressure of 50 lb. per sq. in. The times were noted when the oxygen pressure dropped 10 1b., and 20 lb.,.as well as the point at which the rate of oxygen absorptionincreased appreciably beyond the initial rate. This latter period is called the induction period. The table .compares the stability. of the uninhibited and stabilized oils:

I claim as my invention:

1. A fluid lubricating composition which comprises essentially a polytrimethylene glycol fluid and 0.5-5% by weight of 1,2-dihydroxybenzene.

2. A fluid lubricating composition which comprises essentially a polyalkylene glycol fluid and 0.5-5% by weight of 1,2-dihydroxybenzene.

3. A fluid lubricating composition which comprises essentially a fluid selected from the group consisting of polyalkylene oxide fluids, polyalkylene glycol fluids and poly (alkylene oxide-alkylene sulfide) fluids, and 0.5-5% by weight of 1,2-di-hydroxybenzene.

4. A fluid lubricating composition comprising as the major lubricant therein a fluid selected from the group consisting of polyalkylene oxide fluids, polyalkylene glycol fluids and poly (alkylene oxide-alkylene sulfide) fluids, and 0.5-5% by weight of 1,2-dihydroxybenzene.

5. A fluid lubricating composition which comprises essentially a polyalkylene oxide fluid and 0.5 to' 5% by weight of 1,2-dihydroxybenzene.

6. A fluid lubricatingcomposition which comprises essentially a poly (alkylene oxide-alkylene sulfide) fluid and 0.5 to 5% by weight of 1,2-di hydroxybenzene.

7. A fluid lubricating composition which comprises essentially a polypropylene oxide fluid and.

0.5 to 5% by weight of 1,2-dihydroxybenzene. 8. A fluid lubricating composition which comprises essentially bis (hydroxypropyl) sulfide and 0.5 to 5% by weight of 1,2-dihydroxybenzene.

ELLISROBB WHITE.

REFERENCES CITED The following references are of record inthe Zisman et a1. Jan. 27, 1948