THIO-BIS-(HYDROCARBYL DIACID MATERIALS) AS OIL ADDITIVES

The present invention concerns hydrocarbonsoluble thio-bis-(C₄-C₁₀ qqq hydrocarbyl-substituted dicarboxylic acid materials), their method of preparation and their use in hydrocarbon fuels and lubricating oils as sludge dispersants, varnish inhibitors, antioxidants, antiwear agents and lubricity additives.

During the past decade, ashless sludge dispersants have become increasingly Important in keeping the automobile engine clean of deposits and permitting extended crankcase oil drain periods. One category

of ashless dispersants involves esters of alkenylsubstituted acids, e.g. polyisobutenyl succinic acids, with polyols e.g. pentaerythritol, as taught in U.S.

Patent 3,381,022; however, such dispersants often contain olefinic unsaturation tasking them susceptible to oxidative degradation especially under high severity conditions, such as elevated oil temperatures and extended drain intervals.

A second category involves chloro lactone

ester dispersants prepared by the esterification of alkenyl chloro lactone acids with pentaerythritol as taught in U.S. Patent 3,755,173; however, the inherent propensity of such dispersants towards elimination of corrosive HCl to give unsaturated products can promote decomposition of the hydrocarbon lubricant, corrode metal engine parts, and promote varnish deposition on the internal surfaces of the engine.

U.S. Patent 2,279,688 discloses the reaction

of maleic anhydride with olefins containing 18 to 30 carbon atoms, hydrolysis of the anhydride and reaction of the resulting alkenyl succinlc acid with either SCI2 or S2CI2 to form a product useful as corrosion preventive agent in lubricating oils. These chlorine-containing adducts are undesirable in lubricating oils subjected to high operating temperatures due to the formation of HCl with the resulting disadvantages mentioned above.

The present invention overcomes the shortcomings of one prior art by providing an oil-soluble reaction product comprising principally novel thio-bis-(hydrocarbyl dicarboxylic acid materials) with enhanced stability and potency. These materials comprise the dicarboxylic acids, anhydrides and asters but preferably are asters containing one to about four ester groups per molecule.

The esters of the present invention can be obtained by reacting a to C^q qqq hydrocarbyl-substituted to C-|_q dicarboxylic acid material, e.g. a succinic acid material, with a sulfur halide to form an adduct, removing substantially all the halogen in this adduct as hydrogen halide and then reacting the substantially halogen-free adduct with a polyol to form an ester. The succinic acid material may be succinic anhydride, succinic acid or a succinic ester, but is preferably succinic anhydride. The hydrocarbyl group is preferably a polyisobutenyl group with the polyisobutenyl succinic anhydride usually designated PIBSA.

The preferred sulfur halides are sulfur monochloride ^Clj) or sulfur dichloride (SC^) · The preferred polyol is pentaerythrito 1 (PE).. Since the thio-bis succinic derivative contains four acid groups, it can react with one to four polyol molecules, or two αr more hydroxy groups of a single polyol can react with several acid groups of the same bis-succinic derivative. The hydrocarbyl group preferably contains 4 to 400 carbon atoms, more preferably 16 to 400 carbon atoms, and most preferably 60 to 100 carbon atoms. The hydrocarbyl group is preferably an alkenyl group.

The preferred thio-bis acylating agents of the process of the present invention can be illustrated as follows:

¹¹

wherein R is selected from the group consisting of hydrogen, hydrocarbyl and substituted hydrocarbyl containing from 1 to 10,000, preferably 12 to 200, carbons with the restriction that at least one R has

at least about 4 carbons ; the bridging or coupling element, Y is selected from the group consisting of

S- (thio) , S-S (dithio) , S≈O (sulfinyl) , SC>2 (sulfonyl) , S-(CE^) S- where z is a number of from 2 to 10. The various R groups may be same or different.

The position of the double bond in II may vary depending on reaction conditions. The polyol esters of the above described thio-bis acylating agents can be synthesized via conventional esterification methods.

The polyol should contain 2 to 20 hydroxy groups

and a total of 2 to 100 carbon atoms. In some cases, depending on the mode of synthesis, the esterification of one mole of the thio-bis-acylating agent with one to about three moles of polyol may form macrocyσlic ring structures

of varying sizes and composition depending upon the nature

of the thio-bis-(acylating reagent) and the polyhydric alcohol. Two acylating reactants can combine with two polyols (2:2) to yield structurally larger macrocyσlic

esters of doubled molecular weight. Furthermore, equimolar ester products of thio-bis-(acylating agent) and polyol are capable of forming, under suitable reaction conditions, ever larger macrocyσlic structures, e.g. (3:3), (4:4), etc.

Usually, mixtures of linear and cyclic ester oligomers are formed^ and the ratio of cyclic to linear oligomers is a sensitive fuσtion of reaction“conditions, and the nature of the reactants.

U.S. “Patent 4,062,786 relates to the prepara-

tion of thio-bis-lactone oxazolines but in Examples 20

and 21 also discloses the formation of sulfur-bridged

(or thio-bis) adducts by the reaction of n-octenyl-

succinic anhydride with sulfur dichloride (SC^) or

sulfur monochloride (SjClj); the products are shown

to contain about 11 to 12% chlorine. There is no disclosure in this patent of converting the chlorine-

containing thio-bis adduct of n-octenyl succinic anhy-

dride to an ester nor the elimination of the chlorine

to form olefinic unsaturation. This chlorine-containing adduct is not shown to be useful as a dispersant and

the chlorine contained therein will result in corrosive

HC1 formation if the product were subjected to elevated temperatures, e.g. if it were used in an automotive

engine as a component of a lubricating oil or fuel.

German OS 2,757,767, corresponding to U.S.

Patent 4,123,373 (note column 8, lines 28-36) discloses

the addition of sulfenyl chloride to alkenyl succinic anhydride followed by dehydrohalogenation of the adduct

using water or alcohol and lactonization in the presence

of an acid catalyst. The lactonized acid can then be esterified with a polyol. This reference does not

teach the direct esterification of the sulfur-bridged

alkenyl succinic anhydride with a polyol, such as pentaerythritol, in the absence of an acidic lactonisation catalyst wherein the resulting product comprises primarily a sulfur-bridged non-lactone ester substantially free of chlorine. Minor amounts of lactone polyol esters can also be formed under suitable reaction conditions.

If substantial amounts of lactone ester products are desired, then the presence of a strong acid catalyst is required during the esterification of the thio-bis-acylating agent, which is preferably the chlorine-containing derivative.

In contrast to U.S.P. 4,123,373, the process of the present invention is designed to remove substantially all of hydrogen halide, such as HC1, from the adduct of the dicarboxylic acid material with the sulfur halide. The removal of said HC1 as by heating and/or passing nitrogen through the mixture, eliminates substantially the lactonlzation of the sulfur-bridged or thio-bis adduct when said adduct is esterified.

The preferred esters of the present invention have a number average molecular weight (Mn) ranging from about 400 to about 140,000 prepared by the reaction of a S_χCl2- diacid adduct wherein x is 1 or 2, with a polyol such as pentaerythritol, polypentaerythritol, or polyethylene glycol at about 20-240°C or preferably 50-200°C until the esterification is complete by IR analysis.

The stabilization of these novel dispersant systems may be ascribable to the presence of sulfide functionality which endow these systems with enhanced stability and antioxidant properties. The enhanced potency may be related, in part, to the macrocyclic and/or macrocyclic-like configuration assumed by the polar sulfur and oxygen (heteroatom) functionality in some of the dispersant molecules. Such circular-like arrangements of ligands endow these novel systems with remarkable binding and/or chelation properties making these dispersant systems uniquely effective even under high severity conditions. The present dispersant systems are believed to be based on hostguest chemistry wherein the polar head of the host molecule (dispersant) assumes or is capable of asstiming a macrocyclie-like configuration so that the resulting circular-like array of heteroatoms (e.g. sulfur, oxygen and nitrogen), on the polar head effectively binds guest ions and molecules, including metals and sludge components, within the cyclic-like structure, or between host molecules to form a sandwich-like structure with guest molecules in the middle,

The preparation of the mono- or dithio-bis(alkene dioic ester) or dithio-bis-(alkane dioic ester) involve the sulfur halide coupling or bis-sulfenyl halide-induced coupling or the oxidative coupling of HjS or thioacid adducts of an. olefin diacid. The olefin diacid is readily obtained via the reaction of an

olefin or a chlorinated olefin with an unsaturated C,

4 to C^q dicarboxylic acid, anhydride or ester thereof, such as fumarlc acid, itaconic acid, maleic acid, maleic anhydride, dimethyl fumarate, etc. The dicarboxylic acid material formed via the Ene reaction of an olefin with maleic anhydride can be illustrated as an alkenylsubstituted anhydride which may contain a single alkenyl radical or a mixture of alkenyl radicals variously bonded to the cyclic succinic anhydride group, and is understood to comprise such structures as:

with th℮Υ j δ -unsaturated isomers predominating and wherein R may be hydrogen or hydrocarbyl or substituted hydrocarbyl containing from 1 to about 10,000 and more carbons with the restriction that at least one R has at least 1 carbon, preferably from about 16 to about 400 carbons and optimally from about 60 to about 100 carbons. Thus, the hydrocarbyl group attached to the dicarboxylic group, preferably succinic anhydride group, contains at least 4 carbon atoms. The anhydrides can be obtained by well-known methods, such as the reaction between an olefin and maleic anhydride or halosuccinic anhydride or succinic ester (U.S. Pat. No. 2,568,876). In branched olefins, particularly branched polyolefins, R may be hydrogen, methyl or a long-chain hydrocarbyl group.

Suitable olefins include butene, isobutene, pentene, decene, dodecene, tetradecene, hexadecene, octadecene, eicosene, and polymers of propylene, butene, isobutene, pentene, decene and the like, and halogencontaining olefins. The olefins may also contain cycloalkyl and aromatic groups. The most preferred alkenyl succinic anhydrides used in this invention are those ih which the alkenyl group contains a total of from 4 to 400 carbon atoms; preferably 16 to 400, and more preferably 60 to 100 carbons. Many of these hydrocarbylsubstituted dicarboxylic acid materials and their preparation are well known in the art as well as being commercially available, e.g. 2-octadecenyl succinic anhydride and polyisobutenyl succinic anhydride.

Preferred olefin polymers for reaction with the unsaturated dicarboxylic acids are polymers comprising a major molar amount of C2 to monoolefin, e·g·, ethylene, propylene, butylene, isobutylene and pentene. The polymers can be homopolymers such as polyisobutylene, as well as copolymers of two or more of such olefins such as copolymers of: ethylene and propylene; butylene and isobutylene; propylene and isobutylene; etc. Other copolymers include those in which a minor molar amount of the copolymer monomers, e.g., 1 to 20 mole %, is a to C^g non-conjugated diolefin, e.g., a copolymer of ethylene, propylene and 1,4-hexadiene; etc.

The olefin polymers will usually have number average molecular weights (M_n) within the range of between about 500 and 140,000; more usually between about 700 and about 10,000. Particularly useful olefin polymers have (Mjj) within the range of about 700 and about 5,000 with approximately one terminal double bond per polymer chain.

An especially valuable starting material for a highly potent dispersant additive are polyalkenes, e.g. polypropylene and polyisobutylene, having about 90 carbons.

The dicarboxylic acid materials (Diels-Alder adducts) formed via the reaction of a chlorinated olefin with maleic anhydride also useful in the present invention. Useful chlorinated olefins include chlorinated di-isobutylene, tri-isobutylene, polyisobutylene, tetrapropylene, polyisopropylene, and alkenes which upon halogénation characteristically afford allylic halide structures.

Hemi-ester or diacid reactants can be constructed readily from the anhydride products obtained via the Ene process by the scission of the anhydride ring with a mole of alcohol or water. Normally, the ring opening process is effected by interacting equimolar amounts of anhydride and alcohol or water at temperatures of 25°C to about 120°C without diluent or with a suitable solvent such as tetrahydrofuran, p-dioxane, 1,2-dimethoxy-ethane, etc. In conversions to the diàcid, excess water may be added to accelerate the ring scission process. With alcohols, excess alcohol may lead to some di-ester formation, and accordingly equimolar reaction stoichiometry, is preferable. In the absence of strong acid catalysts, however, excess alcohol can be used to effect hemi-ester formation. Suitable alcohol reactants include methanol, ethanol, isopropanol, butanol or other simple monohydric alcohols which can be removed readily by evaporation or distillation.

The bridging or coupling of the precursor acylating agents can be achieved via a choice of synthetic options including (i) addition of sulfur halides or bis-sulfenyl halides or alkyl sulfenate/HCl reagent to unsaturated diacids, hemi-esters, diesters or anhydrides, (ii) the oxidative coupling of unsaturatεd acids previously thiylated with ΐ^S or R^C(≈O)SH, where represents a C1_-C5 alkyl group, or (iii) reaction of «HA’-alkanedithiols, ΐ^S, or a suitable thiylating agent, with epoxidized or halogenated alkene dioic acid or anhydride materials.

In contrast to the modes of sulfur bridging outlined above, other possible synthetic options including the sulfurization of olefin diacid materials with elemental sulfur, and the Ene reaction of alkenyl sulfides do not provide discernable amounts of stable, sulfur-bridged olefin diacid materials.

The prior art clearly teaches that the sulfurization of alkenes with elemental sulfur gives complex mixtures of unsaturated, unstable polysulfides and polymeric sulfides up to about 140°C, and at higher temperatύres, ca. 170°C, the polysulfidic products owing to limited thermal stability, undergo extensive decomposicion to yield hydrogen sulfide, thiols, l,2-dithiole-3thiones and/or thiophenes as the major products. These results are in complete, harmony with published reports which elaborate upon the chemistry of sulfurized olefins:

(See L. Bateman and G. G. Moore, "Organic Sulfur Compounds", edited by N. Karasch, Pergamon Press, New York, 1961, Vol. I., pages 210-228). Moreover, sulfurization of alkenylsuccinic anhydrides with elemental sulfur also generates thioanhydride products which tend to eliminate hydrogen sulfide when treated with polyols.

- ii -

Finally, Che Ene reaction of disulfides with maleic anhydride does not engender the desired Ene product, but affords only low yields of 2-alkylthiasuccinic acid derivatives.

The preferred pathway to bridged acylating agents involves the reaction of sulfur halides, bissulfenyl halides or a sulfenate ester-HCl reagent with unsaturated diacids, hemi-esters, di-esters or anhydrides in the temperature range of -60°C to about 100°C, optimally from about 10°C to 50°C. If desired, solvents comprising hydrocarbons such as pentane, hexane, heptane, cyclohexane, mineral oil; halocarbons such as methylene chloride, chloroform, carbon tetrachloride, aromatics such as toluene, chlorobenzenes, xylene; ethers, such as diethyl ether and tetrahydrofuran (THF); and, acids such as acetic, propionic and trifluoroacetic acid, can be used in favorably controlling viscosity and reaction temperature. Usually, the sulfur halide is added dropwise to an unsaturated diacid, ester, or acid anhydride, preferably diluted in an inert diluent. With reactive diluents, namely those containing unsaturates including aromatics, and olefins such as polyisobutylene, sufficient sulfur halide must be added to effect complete bridging of the olefin diacid reactants.

The anhydride reactants can be the same or different so that mixtures of symmetrical and unsymmetrical bridged anhydride products can be prepared.

Higher conversions to unsymmetrical adducts can be achieved by the interaction of equimolar amounts of YCI2 and one type of alkene dioic acid or anhydride at low temperatures to generate a 1:1 adduct. Subsequent addition of a second type of unsaturated anhydride affords the unsymmetrical bridged acylating agent predominantly.

In some cases, it may be convenient to carry out bridging using an alkyl sulfenate ester since such esters are readily converted to sulfur halides upon treatment with a hydrohalide acid under mild conditions, e.g. 0<-20°C in the presence of an alkene diacid. Alkyl sulfenate esters, such as di-isopropoxy sulfide and/or disulfide are highly versatile, stable precursors to sulfur halides and accordingly, can be combined with an olefin diacid reactant in the proper molar ratio (1:2) and effectively bridge the diacid reagent via the in situ conversion of the sulfenate ester into sulfur halide by the gradual addition of gaseous HC1. Substantial yields of sulfur-bridged acylating agents can be realized via this novel route.

Increasing bridging temperature above about 50°C, and branching in the hydrocarbyl portion of the alkene dioic anhydride tend to accelerate the elimination of HC1 from the YC1₂-alkene dioic anhydride adduct. Since unsaturated bridged products can be further sulfenylated with YC1₂ reagent (re-addition), it becomes necessary in some cases, to modify the theoretical 2:1 stoichiometry to effect complete bridging. Accordingly, at higher temperatures, i.e. from 50°-100°C, ratios in the range of 1.5:1 to 1:1 may be required to realize higher conversions to bridged structures due to re-addition reactions, and the partial thermal decomposition of the sulfur halide reactant at elevated temperatures. While more sulfur halide reagent becomes necessary to achieve coupling, the additional sulfur incorporated into the dispersant precursor (and occasionally the diluent) tends to endow the resulting thio-ether products with enhanced oxidative stability.

When bridging in accord with the theoretical stoichiometry becomes desirable, high purity chlorosulfenylating reagent (distilled SC1₂), lower sulfenylating temperatures, and select thio-(bis-acylating reagents) comprising hemi-ester, and/or diacid materials, dissolved in a minimal amount of olefinic diluent, provide useful synthetic options in realizing more efficient coupling processes.

The polyhydric alcohols used in esterifying

the thio-bis-(acylating reagents) can have a total of

2 to about 100 carbon atoms and can be represented by

the formula :

?2

X, - C - CH-OH

έ3

wherein: is hydrogen, to alkyl, hydroxyl, hydroxyalkyl HO(CH2)_n wherein n is 1-10, hydroxyalkoxy HO(CIÎ2CH2θ)n_-, wherein n is 1-40, hydroxyalkylthio HOCI^CE^SCCΐ^C^S)^-, wherein n is 1 to 10; and hydroxyalkylamino HO(CH2CH2NCH2)_n“, wherein n is 1 to 10; and X2 and X^ may be the same or different and represent hydrogen, C^to C₅ alkyl and to C₅ hydroxyalkyl groups and their ester, ether, acetal or ketal derivatives.

An especially preferred class of polyhydric alcohols

for designing novel macrocyclic and macrocyclic-like ester products are typified by pentaerythritol, dipentaerythritol, tripentaerythritol, polypentaerythritols, sorbitol, mannitol, cyclohexaamylose, cycloheptaamylose and related polyhydric alcohols such as these prepared via the aldol condensation of formaldehyde with ketones such as acetone, and cyclohexanone, e.g· 2,2,6,6-tetra-methylol-l-cyclohexanol.

Typically, the esterification method is carried out by adding about one mole of polyol per 0.25 to 1 mole of S_χCl₂-alkene diacid adduct_in its HCl-free form with or without an inert diluent and heating the mixture at 20-240°C/ preferably 50-220°C until reaction is complete by infrared analysis of the product as indicated by maximal absorptions for ester functionality. If the adduct still contains chlorine, then mixtures of lactone and non-lactone esters can be produced. The superior stability and dispersant properties exhibited

by the sulfur-bridged hydrocarbyl esters of the present invention over the prior art compositions, namely esters of polyisobutenyl succinic anhydride and polyols, such as pentaerythritol, may be related in part, to the presence of sulfide functionality and in part, to the macrocyclic and macrocyclie-like configurations assumed by the polar heteroatoms in some of the dispersant molecules.

The oil-soluble sulfur-bridged ester products of the invention can be incorporated in a wide variety of oleaginous compositions. They can be used in lubricating oil compositions, such as automotive crankcase lubricating oils, automotive transmission fluids, etc., generally within the range of about 0.01 to 20 wt. %, e.g. 0.1 to 10 weight percent, preferably .3 to 3.0 weight percent, of the total composition. The lubricants to which the bridged polyol ester products can be added include not only hydrocarbon oils derived from petroleum but also include synthetic lubricating oils such as polyethylene oils; alkyl esters of dicarboxylic acid; complex esters of dicarboxylic acid, polyglycol and alcohol; alkyl esters of carbonic or phosphoric acids; polysilicones; fluorohydrocarbon oils, mixtures of mineral lubricating oil and snythetic oils in any proportion, etc.

When the products of this invention are used as multifunctional additives having detergent and antirust properties in petroleum fuels such as gasoline, kerosene, diesel fuels, No. 2 fuel oil and other middle distillates, a concentration of the additive in the fuel in the range of 0.001 to 0.5 weight percent, based on the weight of the total composition, will usually be employed.

When used as a friction modifier for auto35 matic transmission fluids, the additives of the inven36 tion preferably the thio-bis(hydrocarbyl diacid materials) are present in amounts ranging from about 0.05 to 2 weight percent based on the total weight of the fluid.

When used as an antifoulant in oleaginous, e.g. mineral oil, streams in refinery operations to prevent fouling of process equipment such as heat exchangers or in turbine oils, about 0*.001 to 2 wt. % of the inventive additive, preferably a thio-bis-(alkene dioate pentaerythritol ester) will generally be used.

The additive may be conveniently dispensed

as a concentrate comprising a minor proportion of the thio additive, e.g., 20 to 90 parts by weight, dissolved in a major proportion of a mineral lubricating oil, e.g., 10 to 80 parts by weight, with or without other additives being present. The alkenyl succinic anhydride reactants used in preparing the thio-bis-acylating agents of the present invention are featured below:

(1) Polyolefin and polyalkenylsuccinic anhydride molecular weights determined by Gel Permeation Chromatography (GPC).

(2) Saponification number according to AM-S 500.23.

(3) For convenience, Ene and Diels-Alder PIBSA will be identified as PIBSA and Cl-PIBSA, respectively.

Oil-soluble borated, polyol esters of the thio-bis-(hydrocarbyl-substituted acid materials) can be prepared by reaction of the esters with a boron-containing compound, usually by heating a mixture of the reactants at a temperature above about 60°C, preferably within the range from about 80C to about 20Q°C. However, when boric acid or oxide is employed, the process is carried out at a temperature of 100°C to 180°C, preferably at about 140°C. The use of a solvent such as benzene, toluene, naphtha, mineral oil, xylene, n-hexane, or the like is often desirable in the above process to facilitate the control of the reaction temperature and removal of water; mineral oil is preferred to facilitate the use of the products as lubricating oil additives.

If water of reaction is formed in thé reaction as with the preferred boric acid, it is necessary to remove all or a part of it from the reaction mixture by separating it overhead either by blowing with an inert gas, such as nitrogen, or by simple azeotropic distillation. Boration of the materials should provide from about 0.1 to 2.0 wt. %, preferably 0.2 to 1.0 wt. 7_β boron, based on the weight of said material.

Boron compounds useful in the boration reaction of the oil-soluble polyol esters of thio-bis-(hydrocarbylsubstituted acid materials) of the invention include boron oxide, boron oxide hydrate, boron acids such as boronic acid (e.g., alkyl-B(0H)2 or aryl-BCOH^) and boric acids, preferably H^BO^, and esters of such boron acids.

The boric acid esters include mono-, di-

and tri-substituted organic esters of boric acid with alcohols or phenols such as e.g., butanol, octanol, cyclohexanol, cyclopentanol, ethylene glycol, 1,3butanediol, 2,4-hexanediol, polyisobutene-substituted phenols. Lower alcohols, 1,2-glycols, and 1,3-glycols, i.e., those having less than about 8 carbon atoms are especially useful for preparing the boric acid esters for the purpose of this invention.

PREPARATION 1 - DEHYDROCHLORINATED ADDUCT OF S₂Cl₂ AND DIISOBUTENYLSUCCINIC ANHYDRIDE.

A tenth-mole (21.Og) of diisobutenylsuccinic anhydride in 150 ml of chloroform and 0.05 mole (6.8g) of sulfur monochloride (S₂C1₂) in 150 ml of HCCl^ were simultaneously added dropwise to 200 ml of chloroform at about 25°C. After addition, the mixture was stirred at ca 25°C for 2 days and concentrated by rotoevaporation at ca 25°C.

The concentrate analyzed for 10.317» chlorine and featured a gel chromatogram dominated by a peak corresponding to the S2Cl₂-diisobutenylsuccinic anhydride adduct. Refluxing the adduct in dioxane for 24 hours gave a concentrate consisting primarily of 5,5' dithio-bis-(4-neo-pentyl-3(4)-pentene-l,2-dicarboxylic acid anhydride) which analyzed for 2.127» chlorine. A plausible structure for the thio-bis-(alkene diacid anhydride) product, in part, is shown below:

PREPARATION 2 - TETRAMETHYL 5,5'-DITHIO-BIS-(4-NEO-PENTYL3(4)-PENTENE-1,2-DICARBOXYLATE).

A tenth mole (25.6g) of dimethyl diisobutenyl succinate In 100 ml CH₂C1₂ was treated dropwise with 0.05 mole (6.8g) of S₂C1₂^{at room t℮}rop^℮rature· After addition, the reaction mixture was stirred at room temperature for several hours and rotoevaporated at 50°C for 2 hours. The concentrate featured a gel chroma-Cogram with a dominant peak consistent with the sulfur-bridged ester product, dithio-bis(alkenylsuccinic acid dimethyl ester), corresponding to a M_n of about 400.

Heating the adduct at 225°C for 2 hours afforded a material with a gel chromatogram similar to that prior to heating. Clearly, the thermolytic conditions imposed on the bridge structures failed to cleave the sulfurlinked acid esters, and demonstrates the stability of the S~bridged esters towards the thermal conditions imposed during the esterification of the bridged structures .

PREPARATION 3 - TETRAMETHYL 5,5'-DITHIO-BIS-(4-NE0-PENTYL-1,2-PENTANEDICARBOXYLATE).

mole (10.5g) of diisobutenylsuccinic anhydride were dissolved in 30 ml of ether and stirred at room temperature overnight. Distillation of the mixture freed of solvent gave a fraction (8.0g) boiling at 180-185°C (0.1 mm).

The IR spectrum of the product recrystallized from ether/ pentane (m.p. 72-73°C) featured intense anhydride and thiol ester carbonyl absorption bands at 5.64 and 5.95 microns. The crystalline product analyzed for 59.03% C, 7.57% H and 10.99% S. Theory requires 58.70% C, 7.57% H and 11.20% S. The proton and carbon magnetic spectra were consistent with the structure of the thioacetyl anhydride intermediate as shown below:

A tenth mole (7.6g) of thioacetic acid and 0.05

wherein R is neopentyl and T is CH^C≈O.

Oxidation of said thioacetyl anhydride was smoothly effected via the dropwise addition of 0.02 mole (2.7g) of sulfuryl chloride to ca 50 ml of a methanol solution of 0.02 mole (5.72g) of the thioacetyl anhydride. The addition produced an exotherm and the reaction temperature peaked at ça 50°C. The mixture was stirred at ambient temperatures for about an hour. Gel permeation chromatography (GPC) of the reaction mixture indicated that oxidative coupling was ça 80% complete; accordingly, additional SO2CI2 (ca 0.5g) was added until the GPC of the reaction mixture showed only a product peak. Upon standing, the reaction mixture crystallized. The solids recrystallized from ether/pentane melted at 82-83°C and, featured: an IR spectrum with a dominant carbonyl band at 5.72 microns, a proton spectrum with a double methyl proton signal centered at 6.3 tau, and a mass spectrum with a molecular ion peak at 578. The data are completely consistent with the bridged structure shown below. The product analyzed for 58.24% carbon, 8.48% hydrogen, 10.997. sulfur, and 22.24% oxygen. Theory requires: 58.09% C;

8.70% H; 11.08% S and 22.11% 0.

wherein R is neopentyl.

PREPARATION 4 - BRIDGING OF NOSA VIA SULFENYLATION WITH 1,34-THIADIAZOLE-2,5-BIS-SULFENYL CHLORIDE.

Two-tenth mole (42g) of n-octenyl succinic anhydride (NOSA) were dissolved in 100 ml of CHCl^ and 0.1 mole (21.9g) of 1,3,4-thiadiazole 2,5-bis-sulfenyl chloride in 100 ml of chloroform were added dropwise for a period of 15 minutes. An external cooling bath was provided to keep the addition at room temperature. The reaction mixture was then stirred at about 25°C overnight. The solution was filtered and the filtrate was concentrated with a stream of nitrogen. The oily residue featured an infrared spectrum with strong anhydride carbonyl absorption band at 5.65 microns. GPC analysis revealed that complete bridging had been achieved. Spectral analyses were in full accord with the desired thiobis-(acylating agent).

PREPARATION 5 - DEHYDROCHLORINATED ADDUCT OF SC1₂ AND n-OCTADECENYL SUCCINIC ANHYDRIDE (0SA).

Two hundred grams (0.57 mole) of n-octadecenylsuccinic anhydride were dissolved in 150 ml of chloroform. The resulting solution was stirred at room temperature and then bridged via the dropwise addition of 29.4g (0.286 mole) of sulfur dichloride. The bridging event was sufficiently exothermic to reflux the chloroform diluent. Evolution of HC1 gas was noted during the SC12 addition. Refluxing was continued for several hours after addition by applying external heating to the reactant. Rotoevaporation of the mixture for 2 hours at 100°C afforded the S-bridged anhydride adduct. Gel permeation chromatography revealed that coupling with SC12 was virtually complete. The S-coupled anhydride adduct featured an intense carbonyl absorption band at 5.68 microns and analyzed for 4.65% sulfur and 3.88% chlorine. The chlorine analysis indicates that the adduct had undergone extensive dehydrochlorination.

EXAMPLE 1 - BIS-PENTAERYTHRITOL ESTER OF THTO-BIS(POLYALKENE DIACID ANHYDRIDE).

Five hundred grams (0.385 moles) of PIBSA

having an of 776 and a Saponification (Sap.) No.

of 84 ware dissolved in 60 ml of methylene chloride and cooled to 0°C. While stirring at 0°C under a nitrogen blanket, 26g (0.192 moles) of sulfur monochloride were added dropwise over a period of half hour. The reaction mixture was allowed to warm up to room temperature and stirred for about ten hours to form an adduct of the PIBSA with S₂C1₂· 50g (ca 0.02 moles) of this adduct was heated to 190°C for 2 hours while stirring under nitrogen to remove substantially all the chlorine.

6.5g (0.048 mole) of pentaerythritol were added and

the stirred reaction mixture was heated to 220°C for

3 hours with nitrogen sparging. At the end of the third hour, an equal volume of Solvent 150 Neutral mineral oil was added to the residue to provide a 50 wt.% product solution. This solution was filtered through a Celite filter cake. The resulting product solution exhibited an infrared spectrum with prominent carbonyl absorption bands consistent with an aster product, featured a hydroxyl number of 106.1, and analyzed for 1.29 wt.% sulfur and 0.18 wt.% chlorine.

AND PIBSA WITH TRIPENTAERYTHRITOL.

210g (ca. 0.15 mole) of PIBSA, having a M_n

of 1050 and a Sap. No. of 78.9, were heated to 100°C while stirring under nitrogen. Then 13.6g (0.1 mole) of S₂C1₂ Were added dropwise over a period of 15 minutes.

Upon completion of the addition, the reaction mixture was nitrogen sparged for one-half hour at 100°C. Then 70g (ca. 0.025 mole) of the dithio-bis-(polyisobutylsuccinic anhydride) prepared as above were mixed with 9.3g (0.025 mole) of tripentaerythritol and gradually heated to 215°C.

The reaction mixture was kept at 215°C for 3 hours with nitrogen sparging. At the end of the third hour, an equal weight of Solvent 150 neutral mineral oil was added and the oil solution was filtered. The filtrate featured an IR spectrum characteristic of the polyol ester compounds and analyzed for 0.72 wt.% sulfur.

EXAMPLE 3 - PENTAERYTHRITOL ESTER OF AN SC1₂-

PIBSA ADDUCT FORMED AT 100°C.

Approximately 100g (about 0.077 moles) of polyisobutenyl succinic anhydride of M_∩ 776 by GPC and having a saponification number of 84 were charged into a reaction flask and heated to 100^βC. Thereafter 13.6g (0.1 mole) of S₂C1₂ were added while stirring at 100°C under a nitrogen atmosphere, for

a period of one half hour. When the addition was completed the reaction mixture was kept at 100°C for one half hour and then nitrogen sparged for another half hour. The adduct analyzed for 1.25 wt.7· chlorine.

While keeping the reaction temperature at 100^βC, 16.3g (0.12 mole) of pentaerythritol were added and the reaction temperature was gradually raised to 210-215^βC for a period of 3 hours. At the end of the third hour an equal amount of Solvent 150 neutral mineral oil was added and the product was filtered. An analysis of the product solution showed 0.36 wt.7o Cl and 2.05 wt.% S and a hydroxyl number of 66.1. An infrared spectrum of the product featured several broad absorption bands consistent with polyol ester product.

EXAMPLE 4 - BIS-PENTAERYTHRITOL ESTER OF THE S₂C1₂-PPSA ADDUCT.

Approximately 122g (ca. 0.1 mole) of a polypropenylsuccinic anhydride (PPSA), (prepared by the Ene process using polypropylene and maleic anhydride), having a M_n of 623 by GPC (peak maximum at M_∩ 938) and a saponification number of 92, were dissolved in 200 ml of THF and stirred at room temperature under a nitrogen blanket. Then, the above product was chlorosulfenylated via the dropwise addition of 6.8g (0.05 mole) of S₂C1₂ at room temperature. The reaction mixture was stirred ' at room temperature for 24 hours and then rotoevaporated under high vacuum 90°C for two hours.

About 60g (ca 0.025 mole) of the adduct prepared according to the above paragraph were mixed with 66g of mineral oil S150 neutral and 8.1g (0.06 mole) of PE and gradually heated to 215°C. The reaction temperature was kept at 215°G for 3 hours with i.

nitrogen sparging. After the third hour, the product was filtered and collected. The resulting product solution featured an infrared spectrum with prominent ester carbonyl absorption bands consistent with the desired product.

EXAMPLE 5 - PENTAERYTHRITOL ESTER OF A DEHYDROCHLORINATED sci2_-ci-pibsa ADDUCT (DIELS-ALDER).

Approximately 150g of PIBSA of 1044, having a saponifie a tien number of 103, were heated to 100°C.

While stirring under a nitrogen atmosphere, 15.5g of SCl2 were added dropwise for a period of 10 minutes, and then sparged with nitrogen for half hour. At this point, 80g of Solvent 150 neutral mineral oil were added and the reaction temperature was raised to 200°C;

thereafter 20.6g of PE were added and the mixture was heated at 215°C for 3 hours under a nitrogen blanket.

At the end of the third hour, 90g of S150 neutral were added and the product was sparged with nitrogen for another hour. The filtered product analyzed for 0.46% sulfur.

EXAMPLE 6 - PENTAERYTHRITOL ESTER OF AN SC1₂-C1-PIBSA ADDUCT (DIELS-ALDER).

Approximately 2000g of a PIBSA of of 1044, having a saponification number of 103 were dissolved in 4 liters of heptane and filtered through a filter cake of celite. The heptane was distilled off until constant weight and the residue analyzed for a saponification number of 90.2.

About 1500g (ca 1.21 mole based on a Sap. No.

of 90.2) were heated to 100°G, and 103g (1 mole) of SC12 were added dropwise over a period of one half hour. The stirred solution was kept at 100°C for one half hour and then sparged with nitrogen for another half hour. At this point, 450g of Solvent 150 neutral mineral oil and 190g (1.39 mole) of PE were added and the reaction mixture was gradually heated to 215 °C for 3 hours with nitrogen sparging. At the end of the third hour, 1227g of Solvent 150 neutral were added and the product solution was sparged with nitrogen for another hour. The filtered reaction mixture was analyzed for 0.45 wt.% S, and featured a hydroxyl number of 37.0.

EXAMPLE 7 - PENTAERYTHRITOL ESTER OF AN S₂C1₂-C1-PIBSA ADDUCT (DIELS-ALDER).

One hundred fifty grams (ca. 0.14 mole) of polyisobutenylsuccinic anhydride (M of 1055 and Sap. No. of ca 103) were successively reacted with 13.5g (0.1 mole) of sulfur monochloride and 22.5g (0.16 mole) of pentaerythritol as described in Exampie 5. The infrared spectrum of the residue featured broad bands at (2.9-3.0) microns and 5.75-5.85 microns. After dissolution in an equal weight of S150N mineral oil, the ester product analyzed for 0.61 wt.% sulfur.

EXAMPLE 8 - PENTAERYTHRITOL ESTER OF AN SC1₂-C1-PIBSA ADDUCT (DIELS-ALDER).

The procedure of Example 5 was followed except that the PIBSA (150g) had a M_n of 771 and a Sap.

No. of 112, the amount of S₂C1₂ was 20.3g and the amount of pentaerythritol was 20.δg (0.15 mole). The reaction product was dissolved in an equal weight of Solvent 150N mineral oil and analyzed for 0.61 wt.% sulfur.

EXAMPLE 9 - PENTAERYTHRITOL ESTER OF AN S₂C1₂-C1-PIBSA ADDUCT (DIELS-ALDER).

The procedure of Example 5 was followed except that 20.3g of S₂C1₂ and 20.6g (0.15 mole) of pentaerythritol were used and one-half, i.e. about 80g of S150N mineral oil, was added prior to the addition of pentaerythritol and the balance, i.e.

80g, of S150N mineral oil was added after esterification. The filtered reaction product analyzed for 0.78 wt » % sulfur.

EXAMPLE 10 - BIS-PENTAERYTHRITOL ESTER OF A DEHYDROCHLORINATED s₂ci₂-pibsa ADDUCT.

About 200g (ca 0.154 moles) of PIBSA having

a Mj^ of 1080 and a Sap. No. of 72 were dissolved in 100 ml of methylene chloride. While stirring at room temperature under a nitrogen blanket, 10.4g (0.077 moles) of sulfur monochloride were added dropwise for a period of 15 minutes. The reaction mixture was allowed to stir at room temperature overnight. One-half of the above adduct was heated to 150°C for approximately 4 hours. Analytical data on the dehydrohalogenated residue showed 2.08 wt.% sulfur and 0.15 wt.% chlorine. 26.5g of this dithio-bis-(polyisobutenylsuccinic anhydride) product was mixed with 2.9g (ca 0.022 moles) of pentaerythritol and heated to 200-220°C for 3 hours with stirring and nitrogen sparging. At the end of the third hour, an equal weight of Solvent 150 neutral oil was added to the residue to provide a 50 wt.% a.i. solution. The reaction mixture was filtered through a cake of Celite. The resulting product solution disclosed an infrared spectrum with broad hydroxyl and carbonyl absorption bands consistent with the bis-(pentaerythritol ester) of dithio-bis-(polybutenylsuccinic acid).

EXAMPLE 11 - BIS-PENTAERYTHRITOL ESTER OF DEHYDROCHLORINATED S₂C1₂-C1-PIBSA ADDUCT (DIELS-ALDER).

About 312g (ca 0.28 mole) of PIBSA having

a M of 1044 and a saponification number of 103 was charged into a reaction flask and dissolved In 300 ml of methylene chloride while stirring under a nitrogen at 25°C. Thereafter 18.9g (ca 0.14 mole) of S₂C1₂ were added dropwise for a period of one half hour. The stirred reaction mixture was allowed to stand at room temperature for about 20 hours.

Approximately onethird (ca 0.037 mole) of

the above mixture was heated to distill off the solvent and then kept at 160°C for one hour. Hydrogen chloride evolution was observed during this period. A sample of this mixture analyzed for 0.50 wt.% Cl and 2.31 wt.% S. At this point, 12.4g (0.091 mole) of pentaerythritol were added and the mixture was gradually heated to 210-215°C for three hours while nitrogen sparging.

The resulting product was dissolved in hexane, filtered, and rotoevaporated at 100°C under high vacuum until constant weight. The residue was dissolved in an equal weight of solvent 150 neutral mineral oil. The infrared spectrum of said product solution was consistent with a polyol ester product.

The following comparison examples represent the prior art; thus Example 12 corresponds to Examples 18 and 19 of U.S.-F. 4,123,373. Example 13 describes another lactone ester similar to those described in U.S.P. 4,123,373. While Example 14 describes a borated lactone version, Example 15 describes a simple PIBSA/PE ester having no sulfur bridging.

EXAMPLE 12 - BIS-PENTAERYTHRITOL ESTER OF DITHIO-BIS(POLYISOBUTYL LACTONE ACID).

Five hundred grams (0.385 moles) of PIBSA having an (M_fl) of 776 and a Sap. No. of 84 were dissolved in 60 ml of methylene chloride and cooled to 0°C. While stirring at 0°C under a nitrogen blanket, 26g (0.192 moles) of sulfur monochloride were added dropwise over a period of half hour. The reaction mixture was allowed to warm up to room temperature and stirred for about ten hours. One-half of this product was diluted in 100 ml of p-dioxane and 6.9g of water (ca.

0.38 moles) were slowly added. The reaction mixture was refluxed for ten hours in the presence of a catalytic amount of sulfuric acid (HC1 evolution occurred during reflux). Thereafter, the solvent was removed by rotoεvaporation and the mixture further heated to 130-140°C for one hour. The product featured an infrared spectrum with strong absorption bands in the 5.65.8 micron region (lactone acid) and analyzed for 2.43 wt.7. sulfur and 0.05 wt.7. Cl. The IR spectrum of the diethylamine-treated product revealed a strong lactone carbonyl band at 5.63 microns. 80g (ca 0.03 moles) of this dithio-bis-(polyisobutyl lactone acid) product was heated to 190°C. While stirring under nitrogen blanket, 9.8g (0.072 moles) of pentaerythritol were added and the stirred reaction mixture was heated to 220°C for three hours with nitrogen sparging.

At the end of the third hour, an equal amount of Solvent 150 Neutral oil was added to the residue to provide a 50 wt.7. a.i. solution. This solution was diluted with 200 ml of hexane and filtered, and then rotoevaporated at 100°C for 3 hours. The resulting product solution disclosed an infrared spectrum with prominent carbonyl absorption bands ascribable to the desired lactone polyol ester product which featured a hydroxyl number of 90.8 and a GPC with peak maximum at M_t«4100 and 8100.

EXAMPLE 13 - TRIPENTAERYTHRITOL ESTER OF DITHIO-BIS-CPOLYISOBUTYL LACTONE ACID) .

Approximately 153g (0.15 mole) of polyisobutenyl succinic anhydride (M_n) of 757 having a Sap.

No. of 112 and prepared via the Ene reaction of PIB and maleic anhydride were dissolved in 200 ml of THF and stirred at room temperature under a nitrogen blanket.

Thereafter 10.7g (.077) of SjC^^were added dropwise for a period of 15 minutes. The mixture was stirred overnight at room temperature.

Approximately 56g of the above solution containing about 0.01 mole of the adduct was mixed with 3.7g (0.01 mole) of tripentaerythritol and gradually heated to 200-210°C for 3 hours while nitrogen sparging.

At the end of the third hour the reaction product was mixed with an equal weight of Solvent 150 neutral mineral oil. The filtered product featured and infrared spectrum with absorption bands at 2.9-3.0 microns, and a broad band at 5.75-5.85 microns characteristic of hydroxyl, lactone and ester functionality.

EXAMPLE 14 - BORATΞD PENTAERYTHRITOL ESTER OF DITHIO-BIS-(POLYISOBUTYL LACTONE ACID).

50g of the product solution of comparison Example 1 and l.lg of boric acid were heated at 120°C for 2 hours and then filtered hot. The resulting borated product solution contained 0.38 wt.% boron and 1.69 wt.% sulfur. The product solution prior to the above boration step featured an infrared spectrum with a prominent hydroxyl absorption band at 2.9 microns. This band was substantially reduced in the infrared spectrum of the borated product solution.

EXAMPLE 15 - PENTAERYTHRITOL ESTER OF PIBSA.

About 0.1 mole (200g of a 51 wt.7> solution in S150N oil) of PIBSA having a Sap. No. of 84 and M_R of 776 and 13.6g (0.1 mole) of pentaerythritol were mixed and heated to 200°C. The reaction mixture was stirred at 200°C for about 3 hours and then filtered. The filtrate (50% a.i.) featured an infrared spectrum with a strong ester carbonyl absorption band at 5.8 microns and analyzed for 5.04% oxygen. The hydroxyl number for the ester product in solution (50 wt.% a.i.) was determined to be 57.4. GPC analysis revealed that the peak maximum for this type of commercial dispersant was about 25,000.

EXAMPLE 16 - EVALUATION IN SLUDGE INHIBITION BENCH (SIB) TEST.

The products of the above examples were subjected to a Sludge Inhibition Bench (SIB) Test, which has been found after a large number of evaluations to be an excellent test for assessing the dispersing power of lubricating oil dispersant additives.

The medium chosen for the Sludge Inhibition Bench Test was a used crankcase mineral lubricating oil composition having an original viscosity of about 325 SUS at 100°F, that had been used in a taxicab that was driven generally for short trips only, thereby causing a buildup of a high concentration of sludge precursors.

The oil that was used contained only a refined base mineral lubricating oil, a viscosity index improver, a pour point depressant and zinc dialkyldithiophosphate antiwεar additive. The oil contained no sludge dispersants. A quantity of such used oil was acquired by draining and refilling the taxicab crankcase at 1,0002,000 mile intervals.

The Sludge Inhibition Bench Test is conducted in the following manner: The aforesaid used crankcase oil, which is milky brown in color, is freed of sludge by centrifuging for 1/2 hour at about 39,000 gravities (gs·). The resulting clear bright red supernatant oil is then decanted from the insoluble sludge particles thereby separated out. However, the supernatant oil still contains oil-soluble sludge precursors which on heating under the conditions employed by this test will tend to form additional oil-insoluble deposits of sludge.

The sludge-inhibiting properties of the additives being tested are determined by adding to portions of the supernatant used oil, 0.5 wt.% on a 100% active ingredient basis, of the particular additive being tested. Ten grams of each blend being tested is placed in a stainless steel centrifuge tube and is heated at 280°F for 16 hours in the presence of air. Following the heating, the tube containing the oil being tested is cooled and then centrifuged for 30 minutes at about 39,000 gs.

Any deposits of new sludge that form in this step are separated from the oil by decanting the supernatant oil and then carefully washing the sludge deposits with 15 ml of pentane to remove all remaining oil from the sludge. Then the weight of the new solid sludge that has been formed in the test, in milligrams, is determined by drying the residue and weighing it. The results are reported as milligrams of sludge per 10 grams of oil, thus measuring differences as small as 1 part per 10,000. The less new sludge formed, the more effective is the additive as a sludge dispersant. In other words, if the additive is effective, it will hold at least a portion of the new sludge that forms on heating and oxidation, stably suspended in the oil so it does not precipitate down during the centrifuging.

Using the above-described test, the dispersant activity of the additive compounds according to the present invention were compared with the pentaerythritol ester of PIBSA (product of Example 15) and a commercially available dispersant (Lz 936--sold by the Lubrizol Corporation), which is believed to be a 60 wt.% mineral oil solution of an about equimolar reaction product of PIBSA and pentaerythritol with M_n of 25,000 by GPC.

The test results are given in Table I.

SLUDGE DISPERSANCY TEST RESULTS

of Example Additive Mg Sludge/10g Oil at 0.5 wt.%

1 2.4

7 2.04

8 3.6

9 2.1

10 3.2

11 3.2

12 1.2

15 7.4

Lz 936 10.2, 6.4

Blank 10.0

The results set forth in Table I show that the sulfur-bridged polyol ester dispersants according to the present invention are more effective sludge dispersants than the commercial type pentaerythritol esters of PIBSA, i.e. Example 15 and Lz 936, and are essentially equivalent to the lactone ester of the prior art (Ex. 12). EXAMPLE 17 - EVALUATION IN VARNISH INHIBITION BENCH (VIB) TEST.

Each test sample consisted of 10 grams of lubricating oil containing a tenth of a gram of the additive concentrate (50% active), which results in a total of 0.5 wt.% additive present in the test sample.

The test oil to which the additive is admixed was 9.93 grams of a commercial lubricating oil obtained from a taxi after 2,000 miles of driving with said lubricating oil. Each ten gram sample was heat-soaked overnight at about 140°C and thereafter centrifuged to remove the sludge. The supernatant fluid of each sample was subjected to heat cycling from about 150°C to room teraperature over a period of 3.5 hours at a frequency of about 2 cycles per minute. During the heating phase, the gas containing a mixture of about 0.7 volume percent SO2, 1.4 volume percent NO and balance air was bubbled through the test samples and during the cooling phase water vapor was bubbled through the test samples.

At the end of the test period, which testing cycle can be repeated as necessary to determine the inhibiting effect of any additive, the wall surfaces of the test flasks in which the samples were contained are visually evaluated. The amount of varnish imposed on the walls is rated at values of from 1 to 7 with the higher number being the greater amount of varnish. It has been found that this test correlates with the varnish results obtained as a consequence of carrying out an MS-VC engine test. The results are recorded in Table II below:

TABLE II

0.5 WEIGHT PERCENT (100% ACTIVE)

Additive of VIB

The data in-Table II illustrate the outstanding varnish-inhibition activity of the additive compounds according to the present invention when compared with commercial-type pentaerythritol esters of PIBSA, i.e. Examples 15 and Lz 936. The materials of the invention are at least as good and in many cases superior to the lactone esters of the prior art, i.e.

Examples 12 and 14.

EXAMPLE 18 - ENGINE TEST.

The utility of the inventive additives was also measured by subjecting the product of Example 2 to a standard engine test of a blended formulation containing this additive. A 15W/50 SAE crankcase oil formulation was made up using 12.5 wt.% of the oil concentrate of Example 2, 2 volume % of an ashless dispersant additive, 1.1 volume % of an overbased magnesium sulfonate, 0.8 volume 7o of overbased calcium phenate, 0.5 volume 7c of an antioxidant, and 1.43 volume % of a zinc dialkyldithiophosphate and a mineral lubricating oil blend of base stocks. The above formulation was tested in the Sequence V-C Engine Test, which is described in "Multicylinder Test Sequences for Evaluating Automotive Engine Oils", ASTM Special Technical Publication 315F, page 133ff (1973). The V-C test evaluates the ability of a formulated oil to keep sludge in suspension and prevent the deposition of varnish deposits on pistons, valves, and other engine parts. The MS-VC test results are shown in Table III.

“ piston Skirt "Total Sludge Varnish Varnish

In the above tests, the ratings are on a scale of 0 to 10, with 0 being an excessive amount of sludge and varnish while 10 being a completely clean engine. The formulated oil containing the additive of the invention passed.

The sulfur-bridged polyol ester products of the present invention and commercial polyol ester dispersant additives diluted in an equal weight of mineral oil were evaluated by thermo gravimetric analysis (TGA) for evidence of thermal stability under oxidative conditions provided by air flow across each sample heated linearly from about 50°C to 450°G at a rate of 6°/min.

Each sample of 200 mg in a stainless steel planchette was continuously weighed and recorded as the temperature was programmed upwardly at a linear rate to provide a record of sample weight versus temperature. The results are found in Table IV.

Temperature at which the indicated percentage weight loss occurred

that the compositions of the present invention are significantly more stable towards heat and oxidation than the reference commercial PIBSA polyol ester dispersants, Lz 936 and Ex. 15, with some of the Examples showing superior stability compared to the lactone dispersants of the prior art. In addition, the TGA data show that the thio-bis-(polyol esters) of the present invention tends to stabilize the base oil, e.g. S-150N base stock oil, towards thermal oxidative degradation. Thus, the novel structural features built into the present dispersants endow these additives with enhanced thermal stability as well as the ability to inhibit oxidation of the base oil. It is believed that these inhibitor properties can be related in part to the presence of sulfide functionality present in the additive molecules of the present invention.