WO2004043910A2

WO2004043910A2 - Tungsten dithiocarbamate compositions and lubricating compositions containing the same

Info

Publication number: WO2004043910A2
Application number: PCT/US2003/036463
Authority: WO
Inventors: Shih-Ying Hsu; Randall Krinker; Hocine Faci; Omari Ansong; William M. Pastore
Original assignee: Castrol Limited
Priority date: 2002-11-13
Filing date: 2003-11-13
Publication date: 2004-05-27
Also published as: WO2004043910A3; AU2003287652A8; AU2003287652A1

Abstract

This invention generally relates to a new tungsten dithiocarbamate compound and a process for making the same by the reaction of divalent metal tungstates with dithiocarbamates in an alkaline sodium sulfide and/or sodium hydrogen sulfide solution. The tungsten dithiocarbamate compounds of the present invention are useful as extreme pressure agents and exhibit anti-wear properties.

Description

TUNGSTEN DITHIOCARBAMATE COMPOSITIONS AND LUBRICATING COMPOSITIONS CONTAINING THE SAME

Field of the Invention The present invention concerns a process for producing tungsten dithiocarbamates and the compounds made therefrom as well as lubricating oils containing said compounds.

Background of the Invention In the prior art molybdenum dithiocarbamates (Modtc) have been widely used as a friction modifier in automotive and industrial applications. Many Modtc are now commercially available under various brand names. Tungsten analogs to Modtc were previously attempted by Brown et al. in WO 99/66011 which claims a lubricant composition comprising a minor amount of a tungsten compound with a trinuclear tungsten core bonded to a ligand to render it oil soluble or oil-dispersible. The tungsten compound, prepared by a three-step process, was said to provide wear improvement and oxidative stability in lubricating compositions. The major step in the three-step process consists of reacting tungsten metal, elemental sulfur and bromine in a sealed quartz ampoule at 300°C for 48 hours to afford W₃S₇Br that was carried through to the next steps to obtain W₃S₇ (coco₂dtc)₄ and W₃S (coco₂dtc) . Brown and Smith reported in T. M. Brown and J. N. Smith, J.C.S. Dalton, 1614 (1972) the synthesis and characterization of tetrakistetramethylenedithiocarbamatometals (M[S₂CN(CH₂)₄]₄ (M=Nb^lv, Mo^lv, and W^ιv) by reacting ammonium tetramethlenedithiocarbamate and respective metal tetrachloride in acetonithle. In addition, the preparation of Wdtc was conducted by Lozano et al. They reported the syntheses of Tungsten(V) dimeric thio and oxo-complexes with dithiocarbamate ligands based on sodium tungstate and dithiocarbamate using hydrogen sulfide or sodium hydrosulfite as a reducing agent in Polyhedron, 2(6), 435 (1983) and Polyhedron, 3(8), 1021 (1984).

U. S. Patent No. 4,529,526 discloses a lubricating oil composition comprised of, among other components, a sulfurized oxymetal dithiocarbamate wherein the metal is molybdenum or tungsten. However, the examples only teach the preparation of molybdenum dithiocarbamates according to Japanese Patent Publication No. 6362/1974 which is entirely different from the process taught herein. An aim of this invention is to provide a method for producing oil-soluble tungsten dithiocarbamates and use of said products as antiwear/extreme pressure additives in lubricants.

In accordance with the present invention there is provided a process for producing a tungsten dithiocarbamate by the reaction of divalent metal tungstates with dithiocarbamates in an alkaline sodium sulfide and/or sodium hydrogen sulfide solution. The tungsten dithiocarbamate produced by this process is also structurally different from the organometallic dithio-compounds produced in the above-mentioned prior art methods. The tungsten dithiocarbamate produced in this process is a very good extreme pressure agent. It also exhibits very good anti-wear properties. These properties make the product useful and unique in lubricant formulations.

The divalent metal tungstate can be expressed by MWO₄, where M⁺² can be Mg+2, Ca+2, Ba+2, Cu+2, Zn+2 etc. These metal tungstates can be sourced commercially or generated in situ or prior to use by reacting tungstic acid, sodium tungstate or ammonium tungstate with the corresponding metal hydroxide or its equivalent.

Due to the poor solubility of metal tungstate in sodium hydroxide solution with sodium sulfide or/and sodium hydrogen sulfide, the use of a phase-transfer reagent is very desirable, but not essential. With a phase-transfer catalyst, the chemical yield of the tungsten products is generally higher and the mechanical performance of the final products is often better than the ones produced without it. There are many phase-transfer catalysts that can be used, and Applicant does not intend to be limited to the ones mentioned in this invention. However, the preferred category of phase- transfer catalyst can be best described as follows:

Where Rι, R₂, R₃, R₄ are hydrocarbyl or aryl groups and may or may not contain heteroatoms such as oxygen, sulfur, nitrogen, etc. along the hydrocarbyl or aryl chains. These four R groups in the tetrasubstituted ammonium ion can either be identical or different and its counter ion X representing a halide that includes fluoride, chloride, bromide and iodide.

Not every dithiocarbamate can be used to yield the desired tungsten dithiocarbamates. Only those prepared by a secondary amine with carbon disulfide were found to be successful in reacting with metal tungstates. The two substituents (R₅ and R₆) in the secondary amine described below can be identical or different hydrocarbyl or aryl or substituted aryl groups with or without heteroatoms such as oxygen, sulfur, or nitrogen, etc.

\

R₅ and Re are preferred to be the sam ie. The carbon chain length of R₅ or R₆ can range from 1 to 100. However, the preferred length will be from 5 to 18. The disubstituted dithiocarbamates can be obtained through commercial sources or prepared in situ or prior to use. The reaction of the divalent metal tungstates with dithiocarbamates took place in a sodium hydroxide solution containing sodium sulfide or/and sodium hydrogen sulfide. The concentration of the sodium hydroxide in water can vary from 1 to 50 weight percent. However, 5 to 30 weight percent is preferred. The amount of sodium sulfide and sodium hydrogen sulfide used in a given sodium hydroxide solution is controlled by sulfur content % as measured by the Asoma instrument or through theoretical calculations based on the sulfur sources used. A wide range of sulfur content from 1.0 to 10 wt.% can be used for the reaction, but 2.0 -6.0 wt. % sulfur is preferred. Either sodium sulfide or sodium hydrogen sulfide or a combination of both can be used to make up the sulfur content. All ratios of sodium sulfide and sodium hydrogen sulfide will yield the desired tungsten products. However, sodium sulfide alone by itself is a preferred source of sulfur in the sodium hydroxide solution.

The weight ratio of metal tungstate to dithiocarbamate in a typical reaction is not crucial, but at least 1 to 4, respectively, is preferred. Any excessive or unreacted metal tungstate could be recovered and recycled. In a typical reaction, di(2- ethylhexyl)dithiocarbamate was added to a suspension of calcium tungstate in an alkaline sodium sulfide solution. The mixture was stirred at ambient temperature after initial exotherm for 4 hours. Hexane was introduced, followed by a neutralization step using glacial acetic acid or dilute hydrochloric acid to bring the reaction mixture to pH below 7, typically 6.1 as measured by a pH meter. More hexane was added, if needed. In the above process, any organic solvents, not only limited to hexane, such as toluene, xylenes, ether, THF, base stocks, etc. can be used. However, non-polar solvents or base oils such as pentane, hexane, heptane, or paraffinic base stocks are preferred. After the neutralization, the mixture was allowed to stand to allow the organic layer to separate. The organic layer was dried over sodium hydrogen carbonate or sodium carbonate or any drying agents typical for this purpose. Solvent, if used, was evaporated under reduced pressure to afford the tungsten dithiocarbamate as a dark brown to blue or green oil.

The reaction pathway leading to the tungsten dithiocarbamates of the present invention is represented by general formula (I):

R5

NaOH/Na2S

CaWO4 + _N <ζ »► WO_xSy(dtc)_z

SH

R6

dtc wherein x=1 to 4, y= 1 to 2; z = 1 to 4 and x+y+z = 6, 7 or 8. The tungsten dithiocarbamates thus formed can be a mixture at least two different tungsten dithiocarbamates whose structure can be represented by the general formula given above.

The tungsten dithiocarbamates produced in the process of the present invention exhibit load-carrying and antiwear characteristics. The tungsten dithiocarbamates may, for example, be incorporated into a standard grease formula. The present invention will now be described, by way of example only, with reference to the following examples:

Example 1

Preparation of Tungsten Di(2-ethylhexy0dithiocarbamate- Wdtc(di-isoC8) To a suspension of calcium tungstate (14.3 g, 0.05 mole) and tetrabutylammonium bromide (1.14 g) in a sodium sulfide or/and sodium hydrogen sulfide solution with a total sulfur content of 4.0 wt.% (250 ml) was slowly added Di

(2-ethylhexyl)dithiocarbamate (57 g, 0.18 mole). A mild exotherm was observed during the addition of the dithiocarbamate and a maximum temperature of 60°C could be reached after the addition. The suspension was stirred at ambient temperature for 4 hours and its color changed from yellow to orange pink. Hexane (150 ml) was introduced, followed by dropwise addition of glacial acetic acid. At pH=7, the color of the mixture turned to brown. Additional glacial acetic acid was added until the pH reached 6.1. During and after the neutralization, a maximum temperature of 60° C was observed. Stirring was discontinued and the mixture separated into three layers after standing for one hour. The top layer was removed, washed with hot water, dried over sodium bicarbonate to afford the product as a viscous dark-green material (45grams) with a recovery of unreacted starting material- calcium tungstate (4.6 g). The tungsten dithiocarbamate thus produced from the reaction conditions discussed above was tested for friction-modifying activities and antiwear performance using the Optimol Instruments SRV III described below. Commercially available molybdenum and zinc counter parts were selected as a benchmark. Example 2 Friction & Wear Test Apparatus:

Optimol Instruments SRV III is used throughout the study. It employs a ball in oscillating sliding contact with a fixed disk, and directly measures and records dynamic coefficient of friction between the ball and the disk. Wear protection is assessed by post-test optical measurement of the scar generated on the ball at its point of contact with the disk. Before loading is applied and reciprocating motion is initiated, .06-.12 gm of sample oil is typically applied to the contact area. Test Specimens:

Ball 52100 steel, 60 Re hardness, .025 Ra surface finish, and 10 mm in diameter. Disk 52100 steel, 60 Re hardness, 0.45 - 0.65 Rz lapped surface, 24mm dia. x 7.9mm thickness. Specimens sourced from Optimol Instruments, Munich, Germany. Sample Preparation:

Preparations of the invention according to Example 1 , and analogous commercial organo-molybdenum preparations, were incorporated into standardized blends for friction and wear evaluation by SRV. The component blends were taken up in a petroleum base fluid, Exxon 150 Bright Stock: 0.5% w/w metallo-organic preparation 2.0% w/w isopropylated phosphate ester

1.3% w/w zinc di-ethylhexyl dithiophosphate Control - Incorporates the base fluid and all but the first among the above components, with the specific exclusion of a tungsten or molybdenum metallo- organic component.

WDTC examples - OA-04-93 and OA-04-97 represent neat preparations of WDTC. Examples OA-04-163B and OA-04-165A are two flash chromatography separation fractions originating from a neat preparation of WDTC, representing purified examples of active principles.

Organo-molybdenum examples - MoDTC and MoDTP are commercially available molybdenum alkyldithiophosphate and molybdenum alkyldithiocarbamate, believed to embody state of the art with respect to high-load friction and wear performance.

TABLE 1 Data on Friction and Wear Measured by SRV III

*Treat rate normalizes to 0.5% w/w, as these commercial preparations are sold 50% active in petroleum diluent.

Table 1 describes the performance data on friction & wear. The plot of the data as an attachment in terms of coefficient of friction as a function of test duration of 2 hours can be found as an attachment. From these data, it can be concluded that:

• WDTC gives a consistent, stable response in reduction of steel-on-steel coefficient of friction compared to MoDTC/MoDTP. At low treat rate the Mo has a more rapid initial response but fades away quickly. WDTC exhibits better wear properties than MoDTC/MoDTP. The WDTC preparations have equal or slightly better wear than the Control, while Mo preparations actually degrade anti-wear performance.

Claims

1. A compound having the formula WO_xS _y(dtc) ₂, or mixtures thereof, wherein: x=1 to 4, y= 1 to 2; z = 1 to 4 and x+y+z = 6, 7 or 8.

2. A lubricating composition comprising a major amount of an oil or grease and a minor amount of the compound of claim 1.

3. The composition of claim 2 further comprising one or more antioxidants, dispersants, detergents, pour point depressants, viscosity modifiers, surfactants and antiwear agents.

4. A process for producing a tungsten dithiocarbamate by the reaction of divalent metal tungstates with dithiocarbamates in an alkaline sodium sulfide and/or sodium hydrogen sulfide solution.

5. The process of claim 4 wherein the divalent metal tungstate is a calcium tungstate represented by the formula CaWO₄.

6. The process of claim 4 wherein the dithiocarbamate is represented by the following formula:

wherein R₅ and Re may be the same or different and are hydrocarbyl, aryl or substituted aryl groups, optionally with heteroatoms such as oxygen', sulfur, or nitrogen.