US3206401A

US3206401A - Lubricating oil compositions containing ester of mercapto acid and a phosphonate

Info

Publication number: US3206401A
Application number: US80016A
Authority: US
Inventors: O'halloran Rosemary
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1961-01-03
Filing date: 1961-01-03
Publication date: 1965-09-14
Anticipated expiration: 1982-09-14

Description

United States Patent 1 3,206,401 LUBRICATIN G OIL COMPOSITIONS CONTAIN- ING ESTER 0F IVERCAPTO AClD AND A PHOSPHONATE Rosemary OHalloran, Union, NJ, assignor to Ease Research and Engineering Company, a corporation of Delaware No Drawing. Filed Jan. 3, 1%1, Ser. No. 80,016 Claims. (Cl. 25246.6)

This invention relates to lubricating oil compositions which are useful in automobiles as automatic transmission fluids, as rear axle lubricants, and which are particularly useful in transaxle systems. Specifically, the invention is directed towards a mineral lubricating oil containing an alcohol ester of a mercapto acid in combination with a phosphonate, which composition may contain other additives.

Recently, in certain makes of automobiles the transmission and the rear axle systems have been combined into a single mechanical unit located proximate the rear wheels of the automobile. This combined unit is known as a transaxle unit and is primarily designed to eliminate the conventional hump extending along the floor of the automobile. The combined mechanism requires a lubricant which has the properties of both an automatic transmission fluid and a rear axle lubricant. The lubricant, therefore, must be extremely stable to heat and oxidation, have good antiwear properties and at the same time have the extreme pressure properties required for the hypoid gears associated with the rear axle. In addition to these basic properties, a transaxle lubricant must be inert to a wide variety of materials used in the construction of the combined units. The problem of formulating such a lubricant has been particularly difiicult since the conventional extreme pressure additives previously used in rear axle lubricants tend to attack the rubber seals, the nylon gears, and the resin bonded paper clutch discs of the transmission system. On the other hand, many of the mild extreme pressure additives used in transmission oils were insutficient in their extreme pressure properties to impart the desired degree of extreme pressure properties suitable for the rear axle unit. The present invention is based upon the discovery that a certain narrow class of alcohol esters of mercapto acid in combination with certain phosphonates solved the problems encountered. Both these types of compounds were found to be stable and had no bad effect upon the materials encountered. The ester additives primarily contribute the necessary extreme pressure properties, While the phosphonates contribute valuable antiwear properties.

The mercapto acid esters operable in the invention are those having the general formula:

HS(CH ),,COOR

wherein n is an integer of l to 4 and R represents an alkyl radical of a C to C alcohol, e.g. a C to C 3,26,4fll Patented Sept. 14, 1965 straight-forward esterification techniques, with or without catalyst, and preferably using a solvent such as hexane as a Water-entraining agent. If desired, the solvent-ester mixture may be washed with water and neutralized with sodium bicarbonate solution (if an acid catalyst such as NaHSO -H O is used), followed by more water washing before stripping and filtering.

In addition to being prepared by straight-forward esterification reactions between the alcohol and acid, the ester can also be prepared by ester interchange and other methods. For example, the ester of chloroacetic acid can be first made and then converted to the ester disulfide of mercaptoacetic acid by reaction with Na S or by reaction with thiourea followed by reaction with NaOH.

While the above type of mercato acid ester has been found particularly effective, other similar sulfur-containing esters had been found ineffective. Thus, in order to obtain the desired extreme pressure properties, it appears desirable that the sulfur atom of the compound be located proximate the end of the molecule. For example, esters prepared from materials having the sulfur in the center portion of the molecule, such as Kromfax glycols (plus fatty acids) having the formula:

while having excellent oxidation stability and good rubber resistance, have considerably less extreme pressure properties.

The phosphonates which are used in preparing the compositions of the invention are those having the general formula:

wherein R represents an alkyl group having from about 2 to 20, preferably 3 to 6, carbon atoms. These phosphonates are prepared from the corresponding phosphites by a Michalis-Arbusov rearrangement with an alkyl halide catalyst. The products used in the working examples of the invention were commercially available grades obtained from the Virginia-Carolina Chemical Co. of Richmond, Virginia. Examples of compounds coming under the above formula include dibutoxy butyl phosphonate; monopentoxy, dibutoxy lauryl phosphonate, diethyl-hexyl hexane phosphonate, didecyl decane phosphonate, etc.

While phosphonates of the above formula were found very eifective and stable, other rather related phosphorusoxygen compounds have various disadvantages. Thus phosphites, such as dibutyl phosphite, were found to have extremely poor temperature stability, while phosphates were also bad in this respect. The phosphites and phosphates attack rubber and clutch plates.

The base oil used is preferably a mineral lubricating oil having a viscosity of about to '500 SUS at 100 and a viscosity index of about to 120. Preferred mineral oils are those having viscosities of 100 to 200 SUS at 100 F. and viscosity indexes of to 105. These mineral oils may be derived from either parafiinic or naphthenic crude oils which are refined by conventional methods. If the ester-phosphonate mixture is to be used for a heavy industrial gear oil application, however, heavy oils, asphalts, waxes, etc. may be used to thicken the product.

The esters and phosphonates of the invention are also useful in synthetic oil compositions uch as polysilicone oils, diester oils such as di-Z-ethylhexyl sebacate, glycol ether oils such as the Ucon oils, formals, polyearbonates, etc.

The final oil compositions will generally contain .5 to 10.0 wt. percent of the mercapto acid ester and about .5 to 10.0 wt. percent of the phosphonate depending on the molecular weight of the components and the end use of the oil. Preferred compositions will contain about 1.0 to 5.0 wt. percent of the ester and 0.5 to 3.0 wt. percent of the phosphonate. Concentrates of the ester and phosphonate in oil may also be prepared.

The above compositions may also contain various other additives such as thickeners, viscosity index improvers, .pour point depressants, antioxidants, rust inhibitors, other extreme pressure additives, antiwear additives, etc.

Preferably, a viscosity index improver is utilized in amounts of .5 to 10.0 wt. percent, preferably 1.0 to 5.0 wt. percent of active ingredient, based on the total weight of the finished composition. The viscosity index impr-overs can be used to thicken low viscosity base oils to the prefer-red viscosity for a transaxle lubricant (e.g. 150 to 300 SUS at 100 F.). These viscosity index improvers are long-chained polymers of about 10,000 to 1,000,000 molecular weight. Examples of such material include polyisobutylene; copolymers of vinyl acetate and dialkyl fumar-ates or maleates; polymethacrylates, etc.

The invention will be further understood by the following examples which include a preferred form of the invention.

EXAMPLE I PREPARATION OF ESTER FROM TALLOW ALCOHOL AND MERCAPTO ACETIC ACID (THIOVANIC ACID) An ester of the invention was prepared on a pilot plant scale. A commercial alcohol derived from the reduction of tallow fatty acids was used, which is manufactured by Archer Daniels Midland Corporation and known as Adol 63. It consists roughly of straight chain C alcohol and /3 C alcohol and is a solid with a melting point of 55 C. In the preparation of the ester, gallons of hexane was charged to a gal. Dowtherm jacketed glass-lined reaction kettle. A 50 lb. bag of tallow alcohol was added in chunks, and low heat turned on the jacket. After minutes the alcohol had dissolved in the hexane solvent, and the temperature rose to 107 F. in the kettle. The stirrer was turned on, 17.8 pounds of thiovanic acid was added and the vacuum adjusted to prevent fumes. I-Ieat was increased slowly for one hour until the hexane started a very gentle reflux (145 F. kettle temperature). This reflux was held for 24 hours while the water of reaction (1621 g.) was trapped off. Then the return was cut off and the hexane drawn off for 30 minutes. Vacuum and heat were gradually applied and the remainder of the hexane removed over one and one-half hours, reaching 220 F. and 29.3" Hg vacuum. The product was cooled to about 150 F. and drawn through a paper filter into pails for storage. The yield was 64.17 pounds of crude ester.

A base stock was prepared having the following ingredients by weight:

46.9 parts low cold test Coastal distillate of 76 SUS/ 100 F. and 63 V.I.

46.9 parts Mid-Continent neutral, 150 SUS/ 100 F. and

5.0 parts Additive A 1.0 part Acryloid 710 0.2 part Additive B The inspections on this base stock blend are:

Gravity, API 30.8 S.U.S. vis./100 F. 181.3 S.U.S. vis./2l0 F. 48.6 Pour, F 35 Cloud, F 6 Flash, COC, F 360 :Fire, coo, F s85 Additive A is a 33 wt. percent solution of polyisobutylene of about 10,000 molecular weight in 67 wt. percent of a solvent neutral mineral oil of 150 S.U.S. viscosity at 100 F.

The Acryloid 710 was a polymethacrylate viscosity index improver.

Additive B consisted of 37 /2 volume percent of a copolymer of Lorol B fumarate and vinyl acetate, 12.5 volume percent of the condensation product of chlorinated wax and naphthalene and 50 volume percent of a neutral mineral oil of S.U.S. at 100 F. The copolymer is primarily a viscosity index improver while the condensation product is a pour depressant.

To 100 parts by weight of the above base stock was aded 2 parts by weight of the tallow alcohol ester of mercapto acetic acid prepared above, and 1 part by weight of dibutoxy butyl phosphonate (obtained from Virginia Carolina Chemical Co.).

The resulting final composition was subjected to a series of tests described as follows:

OLDSMOBILE 26A DOUBLE SHOCK TEST Here the oil composition was tested as a rear axle oil. First nineteen miles of warm-up driving was made between 40 and m.p.h. without any hard accelerations. Next, the auto was accelerated [at wide open throttle from to 100 m.p.h., then with closed throttle the auto was allowed to coast from 100 back to 60 m.p.h. This was repeated 10 times. The following shock cycles were then run:

(a) From a stop, a set brakes, fully open throttle with transmission in drive, release brakes and accelerate to 50 mph Pull shift lever into L0 range and allow car to coast to a stop with the throttle closed.

b) From a stop, set brakes, fully open throttle with transmission in drive, release brakes and accelerate to 60 m.p.h. Pull shift lever into L0 range and allow car to coast to a stop with the throttle closed.

(c) From a stop, set brakes, fully open throttle with transmission in drive, release brakes and accelerate to m.p.h. Pull shift lever into L0 range and allow car to coast to a stop with the throttle closed.

Following these shock cycles, ten more wide open throttle 60 to 100 m.p.h. accelerations with subsequent coastings were made.

The entire preceding test was then repeated, i.e. ten 60 to 100 m.p.h. accelerations, 3 shock cycles, ten 60 to 100 m.p.h. accelerations.

Upon completion of the 26A test the carrier was removed from the axle and disassembled for inspection. The composition passed the test. drive and coast sides of the tooth surfaces of the pinion and ring gear were negligible.

The very light trace scoring observed on the gears caused this test to be rated 2, a pass on the General Motors GMR rating scale.

CORVAIR SHOCK TEST This rear axle test was run on a 1960 Corvair with a standard transmission. The auto was driven as follows:

Step 1: 5 miles 50 m.p.h. Step 2: 5 miles 60 m.p.h. Step 3: 25 miles m.p.h. Step 4: Decelerate to 40 m.p.h.

The effects on the Step (a) Accelerate to 65 m.p.h. in third gear (b) Turnotf ignition (c) Disengage clutch (d) Coast to 60 m.p.h. 5 (e) Drop in clutch rapidly (f) Overrun to 40 m.p.h. (g) Turn on ignition Repeat steps (a) through (g) times gtep 5: Shift to second gear and decelerate to m.p.h.

tep 7:

(a) Accelerate to 45 m.p.h. in second gear (b) Turn off ignition (c) Disengage clutch (d) Coast to 40 m.p.h. 15 (e) Drop in clutch rapidly (f) Overrun to 20 m.p.h. (g) Turn on ignition Repeat steps (a) through (g) 10 times.

After the above test, the gears were examined, and showed no scoring, and were rated Pass.

L-89 POWERGLIDE TEST This test is the standard CRC L-39 test which was carried out on a Powerglide transmission over a period of 300 hours. The oil temperature in the sump was 275 F. while the oil outlet temperature from the converter was 300 F. No air was injected intothe transmisiso-n.

The results obtained are summarized in Table I as follows:

Table I TRANSMISSION TESTS Clutch plate condition Excellent. Nylon gear Trace wear. Valve body Clean. Screen Trace deposits. Sludge and varnish None.

Rating Pass, excellent.

CHEVROLET POWERGLIDE 5000 MILE= ACCELERATION TEST This test was carried out by operating a 348 cubic in. displacement engine connected to a 2-speed Chevrolet Powerglide transmission. This mechanism was automatically operated on a dynamometer stand by means of a tape controlled electronic system. From an engine speed equivalent to about 10 miles per hour, the engine was operated under maximum throttle until it shifted from L0 to drive gear and had reached its maximum speed r in drive gear, at which point the engine was decelerated to a speed of about 10 miles per hour. A brake signal was interposed every second cycle. This test was repeated for 5,000 miles at the rate of one full cycle every one and a half minutes for a period of time of about 10 days or 7,000 cycles. At the end of this time the transmission was disassembled and examined for wearor As indicated by the preceding data, the composition of Example I was excellent as a transmission lubricant, comparing favorably with the best of conventional detergent-inhibitor transmission oils.

10,000 MILE ACCELERATION TEST The test oil was used in the rear axle of the Chevrolet test car while 10,000 miles of acceleration testing was completed as described above. All parts of the axle were functioning and in excellent condition. Only a normal 6 burnishpattern was observed on the ring and pinion gear after the test period. This indicates that the oil of invention satisfactorily lubricates a rear axle under severe prolonged actual car operation.

EXAMPLE II A transaxle base oil composition was prepared by mixing 91.4 wt. percent of mineral lubricating oil, 6.78 wt. percent of Additive A, 1.6 wt. percent of Acryloid 710, 0.22 wt. percent Additive B and .0012 wt. percent of Dow Corning Silicone Fluid 200 as an antifoamant. To 96.8 wt. percent of this base oil composition was added 2.0 wt. percent of the ester of tallow alcohol and mercapto acetic acid, 1.0 wt. percent of dibutyl butane phosphonate, 0.1 wt. percent of Nonisol 210 as a rust inhibitor and 0.1 wt. percent of mercapto acetic acid as a supplemental extreme pressure agent. This lubricant composition was charged to the differential and transmission of a Corvair, wherein the differential and transmission had been piped together so that the lubricant approaches test conditions anticipated in a transaxle employing a common lubricant. 5500 miles of road test was satisfactorily completed with this composition.

EXAMPLE III 96.9 wt. percent of base stock (same as in Example I) containing 3.0 wt. percent of the tallow mercaptoacetate plus 0.1 wt. percent Nonisol 210 was subjected to testing in a 1960 Chevrolet in the Chevrolet Powerglide 5,000 mile acceleration test previously described. This oil contained no phosphorus additive. After 3,100 miles, the rear axle developed :a loud whine and the temperature rose sharply. On disassembly, the ring and pinion gears showed severe iidging distress. In comparison, Example I, the rear end oil containing both the mercapto-ester and the phosphonate had been allowed to run 10,000 miles without change, and at the end of this time all dif ferential parts were in excellent condition. This indicates that the combination of the ester and the phosphonate are required for adequate lubrication of the rear axle differential under these extreme conditions of re peated accelerations. The transmission parts of Example III when compared with those of Example I, showed several more small pits on the clutch plates and severe wear on the converter bronze thrust washer. While, the performance of the transmission in Example III was satisfactory, however, the combination of both the sulfur and phosphorus additives as in Example I gave superior performance over that obtained using the sulfur additive alone.

EXAMPLE IV A number of esterifications were carried out using the same equipment and procedure of Example I. Example I was repeated, except that 0.37 pounds of NaI-ISO -H O Was added as a catalyst. This resulted in the water coming off in about three hours.

The mercapto esters of other alcohols were made. In the case of alcohols below C chain length, it was necessary to wash the ester with N-aHCO in order for the product (when dissolved in oil) to perform satisfactorily in the 13-665 rust test with distilled water. It is also interesting to note that the esters of lower molecular weight alcohols required longer reaction times than tallow alcohol. The secondary alcohols also require long reaction times, but this is to be expected.

The esters prepared above were added to a base oil composition which was the same as that described in Example II, These compositions were tested for loadcarrying ability in a standard SAE laboratory test using a 3.4 rubbing ratio at 1,000 r.p.m., and were also tested for wear in a 4-bal-1 machine operating under 1-0 kilograms load, for ten minutes at 1,800 r.p.m. and C. It is very important that the ester does not deteriorate the buna rubber seals used in automatic transmission. Thus, the buna rubber seals themselves are relatively inexpensive, but it is necessary substantially to dismantle the entire unit in order to replace the seals. Rubber screening tests were carried out as follows: Sections of buna rubber compound (Acadia Rubber Co.) similar to the rubber us d for transmission seals were out to lengths of /2" to 2". These strips had a Shore A hardness of 71. The resulting strips were immersed in the oil composition in a 30 cc. beaker, covered, and stored in an oven at 300 F. for 100 hours. The strip was removed from the hot test oil, placed in a beaker of original cool test oil for /2 hour, washed in acetone, wiped and immediately subjected to a Shore durometer A hardness determination, The higher the number, the harder the rubber. The sides of the beaker mentioned above were also examined for deposits to check the stability of the composition at high temperatures.

A multiple oxidation test was also run as follows: the oil composition was stored for 5 days at 300 F. in a beaker while stirring with a steel wire stirrer, and in the presence of a copper strip. At the end of this time, drops of the oil composition was filtered through a #1 Whatman paper filter which was then examined for deposits. Also the copper strip was examined, as well as the wire stirrer for the existence of varnish deposits.

The compositions tested and results obtained are summarized in the following table:

phosphonate in specific base oil compositions, said ester and phosphonate are equally applicable to other base oil compositions. Thus, the good efi'ects obtained by said ester and said phosphonate were independent of the other additives present, e.g. the V1. improvers and pour depressant, these other additives being present merely to give the required low pour point and viscosity-temperature relationship necessary tor commercial transaxle lubricants. In sum, the present invention relates to lubricants which can be used for transaxle lubrication and which have any suitable base oil composition to which is added the mercapto acid ester and phosphonate of the invention.

What is claimed is:

1. A lubricating oil composition suitable for lubrication of tr-ansaxle systems, comprising a major amount of mineral lubricating oil, about 0.5 to 10.0 wt. percent of a mercapto acid ester of the general formula wherein n is an integer of 1 to 4 and R represents a C to C alkyl radical, and about 0.5 to 10.0 wt. percent of a phosphonate of the general formula:

ROP=O wherein R is a C to C alkyl group.

Table IV Buna Rubber, Mult. Oxid. Test 5 Da./300 F. Wt SAE 4 Da./300 F. Alcohol Time, NaI-ISOl Perpercent Test 4 Ball Hrs. Catalyst cent S Ester in (Scale Test Oil Base lbs.) Shire Deposits Paper Cu Varn.

44 22. 5 0. 96 360 266 83 'Ir-l- Tr 42 22. 1 0. 96 410 .333 85 Tr+ O 3 21.8 0. 96 340 .419 82 Lt. 0 Cyclohexy] 72 17. 7 1.04 375 319 85 Tr+ 0 Cyclohexyl 4 l. 04 305 81 Tr 0 41 15. 8 1. 24 315 289 84 Tr+ Tr 15. 0 1. 24 400 452 86 Tr+ 0 42 14. 8 1. 24 305 469 81 0 0 30 12.5 1.60 310 289 82 Tr+ Gray Ta 0 24 12. 1 1. 74 325 255 79 Hvy. Blaek Blk. O 30 7. 9 2. 240 241 80 0 Gray Tan Blk 0 24 9. 8 2.0 310 82 1 The 011 base consisted of by weight, 46.2% Neeton 37, 45.2% Solvent 100 Neutral, 6.78% Additive A, 1.60% Acryloid 710, 0.22%

Additive B and .0012% DC-200 polysilicone antifoamant.

EXAMPLE V Using the base oil composition of Example IV, compositions were made up containing the tallow thiovanate of Example I, and the butyl phosphonate of Example I, as well as a mixture of the two. These compositions were then tested for rubber hardening following the procedure used in Example IV. Following are the results obtained.

Table V Shore A Treatment:

Untreated rubber Base oil composition 85 98 wt. percent base oil c0mp0sition-I-2 wt. percent ta'llow thiovanate 83 99 wt. percent base oil composition+1 wt. per

cent butyl phosphonate 72 97 wt. percent base oil composition-P2 wt. percent tallo-w t-hiovanate-ll wt. percent butyl phosphonate v 73 These data indicate that the oil of invention, will have no deter-iorative effect on rubber seals.

Similar laboratory screening tests with sections of clutch plate (G.M. part No. 3,748,703) and with nylon washers 1%" diameter indicate that the oil of invention should not be deleterious to transmission parts made of these materials.

While the preceding examples have illustrated the invention by using the combined mercapto acid ester and HS (CH CO OR wherein n is an integer of 1 to 4 and R represents a C to C alkyl radical, and about 0.5 to 3.0 wt. percent of a phosphonate of the general formula:

wherein R is a C to C alkyl group.

5. -A lulbricatingoil composition suitable for lubrication of transaxle systems comprising a major amount of 9 mineral lubricating oil, about 1.0 to 5.0 wt. percent of a mereapto acid ester of the general formula:

HS(H COOR wherein n is an integer of 1 to 4 and R represents a C References Cited by the Examiner UNITED STATES PATENTS Sullivan 25'2-49.8 =Rosen 252-336 X Burke et a1.

-Rosen '260481 X Moreton 252-499 DANI'EJL E. WYMAN, Primary Examiner.

JULIUS GREENWALD, Examiner.

Claims

1. A LUBRICATING OIL COMPOSITION SUITABLE FOR LUBRICATION OF TRANSAXLE SYSTEMS, COMPRISING A MAJOR AMOUNT OF MINERAL LUBRICATING OIL, ABOUT 0.5 TO 10.0 WT. PERCENT OF A MERCAPTO ACID ESTR OF THE GENERAL FORMULA: