US2963434A

US2963434A - Method of preparing zing mercaptides and method of preparing a greases containing zinc mercaptides

Info

Publication number: US2963434A
Application number: US694520A
Authority: US
Inventors: Allen F Millikan; Ernest T Fronczak
Original assignee: Pure Oil Co
Current assignee: Pure Oil Co
Priority date: 1957-11-05
Filing date: 1957-11-05
Publication date: 1960-12-06
Anticipated expiration: 1977-12-06

Description

United States Patent i Allen F. Millikan and Ernest T. Fronczak, Crystal Lake, 111., assignorsto The Pure Oil Company, Chicago, 111.,

a corporation of Illinois No Drawing. Filed Nov. '5, 1957, Ser. No. 694,520 11 Claims. el. ,z1s2 42.7

This invention relates to a lubricating composition containing a major portion of a mineral lubricating oil and a sufficient amount of. a metal mercaptide to form a gel therein and impart to said lubricating oil the properties of a colloidal gel structure.

Numerous metal salts, polyvalent metal soaps, selenomercaptans, heavy metal alcoholates, alkaline earth metal phenates, aryl metal oxides, alkali metal naphthenates and .the like :aredisclosedas addends for mineral lubricating oils. .In general, .these .addends are used in small amounts ranging from 0.01 to 5.0 weight percent with the mineral lubricating oils for such purposes as inhibiting oxidation or sludgeyas :detergents, foam inhibitors, extreme pressure agents to prevent piston ring sticking, as oiliness agents, for ,color stabilization, to combat corrosion, and associated purposes. The present invention relates to the problem of iorminga solid phase of certain metal mercaptides in a colloidal solution in the mineral lubricating oil which resultant gel is stable and has utility as a grease or gel-lubricant exhibitingextreme pressure properties. The distinction :to :be drawn between the gelled lubricating ,oil composition of this invention and the prior art compositions "lies in its gel properties, the method of its formation, the materials used and their preparation, and the amounts found necessary to attain the stable gel or liquid-in-solid solution. 7

Because of these interdependent :discoveries, theinvention also distinguishes over such art as states that metal compounds and the like can be used to thicken lubricating oils. Atrue *geludiifers remarkably .firom athickened oil as will be demonstrated. Also, the invention distinguishes over the common gelling agents, such as the sodium, aluminum, lithium, barium, lead and magnesium soaps of fatty acids or naphthenic acids, 'orinorganic thickeners such asfinely .divided silica or bentonite, in that the gellingagen'tsrof this invention serve aldua'l func tion, rthatfof forming a true colloidal gel and imparting other useful properties to the mineral lubricating oil.

In accordance with :this invention, it has been discovered that the zinc salts of aliphatic, straight-chain mercaptans, in which the .alkyl group has *from 8 to 1-8 carbon atoms per molecule, incorporated in a mineral lubricating oil in a particular manner, form a gel or grease structure having stability and .extreme pressure qualities. The zinc mercaptides of this invention have the following general formula:

WhereinlRis a straight-chain, saturated alkyl group containing-f-rom 8 .to -18 carbonatoms. Thus, inaccordance with the foregoingqdefinition, R maylaenneoctyl, n-nonyl, n-decyl, nedodecyl, -n4etradecyl, n-hexadecyl, or n-octadecyl.

Specific. examples include:

, Zinc l-dotlecylmercaptide Zinc '1--n-octyl mercaptide ,Zinc l n-nonylmercaptide Zinc l-n-decyl mercaptide 12,963,434 Patented Dec. 6, 1960 Zinc l-n-tetradecyl mercaptide Zinc l-n-hexadecyl mercaptide Zinc l-n-octadecyl mercaptide Accordingly, it becomes a primary objective of this invention to provide a new type of gelling agent for mineral lubricating oils.

Another object of the invention is to provide a gelled mineral lubricating oil containing a metal mercaptide of the general formula:

wherein R is a straight-chain, saturated alkyl radical having from 8 to 18 carbon atoms.

Still another object of the invention is to provide a grease composition containing a sulficient amount of the foregoing specified metal mercaptide to form a gel structure, which grease exhibits extreme pressure characteristics, and is stable in storage and use.

These and further objects of the invention will become apparent as the invention is described in greater detail.

The invention will be demonstrated by reference to a number of examples to illustrate the technique of preparation, the physical properties of the completed compositions, comparative data showing metal mercaptides which do not work, and the relationship of the amounts necessary to form a gel.

THE METHOD OF PREPARATION 2NaOH+2C gH SeH+ 2C H SeNa-l-H O ZnSO +2C H SeNa (CHI-12586) 2ZH+N32S04 Also, the prior art shows that lead octadecyl selenomercaptan can be prepared by reacting basiclead acetate in a glacial acetic acid-alcohol solution with octadecylselenomercaptan. Aluminum alcoholates are prepared by the direct reaction of aluminum metal with an alcohol in the presence of iodine, and zinc alcoholates are prepared by direct reaction of zinc chloride with an alkali metal alcoholate. The reaction of. diisobutyl phenol with sulfurchloride-to yield diisob-utyl hydroxy phenyl sulfide, which is reacted with barium hydroxide octahydrate to yield the barium salt, proceeds quite readily when the mixture is blown with nitrogen and heated to 215 F. However, metal salts of these kinds, though used in con centrations of 10% by weight or more in a mineral lubricating oil to thicken same, do not form a stable gel structure. Such compositions break down during use and storage.

Attempts to react zinc oxide directly with a mercaptan by heating stoichiometric mixtures were unsuccessful; apparently .no reaction takes place. When calcium oxide was mixed with a mercaptan irra solution of liquid ammonia, orrefluxed with a mixture of mercaptan, toluene, and water, no reaction took place. "Similarly, an attempt --to react calcium chloride with a mercaptan inliquid ammonia was negative.

.It has been found, in accordance with this invention, that the higher-molecular-weight mercaptans react with zinc oxide, with or without the presence of mineral lubricatingoil, if liquid ammonia is used. Further, it has Example 1.Preparatin of zinc I-dodecyl mercaptide and grease therefrom To make a reaction medium, 12.2 g. (0.15 mole, 0.30 equiv.) of zinc oxide was aded to approximately 250 m1. of liquid ammonia with stirring. Then a mixture of 40.5 g. (0.2 mole, 0.2 equiv.) of l-dodecyl mercaptan, 50 ml. toluene, and 50 ml. of 85 vis/ 100 V1. neutral was slowly added as stirring continued. As the ammonia evaporated at room temperature, the mixture became somewhat gelatinous, and 300 ml. of toluene was added to the mixture. Heating and stirring over steam for an hour reduced the system to an essentially liquid phase. Excess zinc oxide was removed by vacuum filtration. Most of the toluene was removed by nitrogen stripping over steam. The product analyzed 8.0 wt. percent zinc and 7.2 wt. percent sulfur. Calculated on the basis of zinc content as found by analysis, the product contained 57.3% zinc l-dodecyl mercaptide, and on the basis of sulfur content as found by analysis, 52.5% zinc l-dodecyl mercaptide. In the formulation immediately below, this mercaptide solution was used as produced (average of 55% zinc mercaptide in 85 vis neutral oil) in an amount of 20%.

A grease was prepared using the following ingredients:

Zinc l-dodecyl mercaptide *11.0 85 vis/ 100 V1. neutral 9.0 200 vis/90 V.I. neutral 53.5 160 vis/90 V.I. bright stock 26.5

Wt. percent 100.0 From solution produced as described.

All components were blended together and heated to 110 C. with stirring. The hot liquid was poured into a shallow pan and cooled rapidly; in the process of cooling, a firm gel structure formed. The firm gel was then reduced to a softer, buttery grease texture by shearing the gel in a colloid mill. The resulting grease was of the order of a No. 0 or No. 1 N.L.G.I.-consistency-grade grease, with an A.S.T.M. grease dropping point of approximately 200 F.

Example 2.Preparation of zinc J-hexadecyl mercaptide Exacty 6.1 g. (0.075 mole, 0.15 equiv.) of zinc oxide was added to approximately 75 ml. of liquid ammonia with stirring. To this reaction medium, a liquid mixture of 25.9 g. (0.1 mole, 0.1 equiv.) of l-hexadecyl mercaptan, 31 ml. toluene, and 31 ml. or 85 vis neutral was added slowly. At room temperature, the ammonia was allowed to evaporate, with stirring. The toluene was then partially removed by heating and stirring over steam. A gelatinous product formed that was identical in appearance to that of the zinc l-dodecyl mercaptide product of Example #1.

Example 3.Preparati0n of zinc t-dodecyl mercaptide Exactly 6.1 g. (0.075 mole, 0.15 equiv.) of zinc oxide was added to approximately 75 m1. of liquid ammonia with stirring. To this, a liquid mixture of 20.3 g. (0.1 mole, 0.1 equiv.) of t-dodecyl mercaptan, 24 ml. toluene, and 24 ml. of 85 vis/ 1000 V1. neutral was added slowly. After the ammonia had evaporated, toluene was stripped off by heating to 300 F. with stirring. Excess zinc oxide was removed by filtration of the hot product. The filtrate was clear yellow, and exhibited extreme pressure properties, as aforementioned, but the product was not gelatinous. Analysis: 8.3% zinc, corresponding to a 60.5% concentration of zinc t-dodecyl mercaptide in oil.

Exactly 12.2 g. of zinc oxide were added to 40.5 g. of l-dodecyl mercaptan, and the mixture was heated at 200 C. for 2 hours. At the end of this time, practically all of the zinc oxide separated from the mercaptan and there was no evidence of salt formation.

Example 6 Exactly 6.6 g. of calcium oxide were slurried in 200ml. of liquid ammonia. Then 33.4 g. of l-octyl mercaptan and 150 ml; of toluene were added with stirring. The mixture was heated as in Example No. 1. Again the metal oxide separated from the mixture after removal of the liquid ammonia, with no evidence of reaction.

Example 7 Example 6 was repeated using calcium chloride instead of calcium oxide with the same negative results.

Example 8 Exactly 12.2 g. of calcium oxide were mixed with 33.4 g. of l-octyl mercaptan in 300 ml. of toluene and 10 ml. of water. The mixture was heated to a reflux temperature of about C. for 20 hours. Again there was no evidence of reaction or salt formation.

Example 9 Exactly 20.3 g. (0.25 mole; 0.5 equiv.) of zinc oxide was added to approximately 200 ml. of liquid ammonia. To this was added slowly, with stirring, a solution of 59.1

g. (0.5 mole, 0.5 equiv.) of l-hexyl mercaptan in 150.

m1. of ether. The reaction mixture was stirred until the ammonia was substantially all evaporated. The product was filtered off and dried under vacuum. There Was 72.0 g. of mercaptide product, a yield of 96%. Analysis of zinc l-hexyl mercaptide: theor: 21.8% zinc, 21.4% sulfur; found: 21.9% zinc, 21.4% sulfur. It was not possible to form a gel with lubricating oil using the zinc l-hexyl mercaptide thus prepared.

Example 10 In the manner of Example 9, zinc cyclohexyl mercaptide was prepared in liquid ammonia using 8.2 g. (0.1 mole, 0.2 equiv.) of zinc oxide and 23.8 g. (0.2 mole, 0.2 equiv.) of cyclohexyl mercaptan in solution in ml. of ether. The yield was 32.1 g. of product (against 29.6 g. in theory) suggesting that the product was not completely dry. Analysis of product found: 21.2% zinc, 18.5% sulfur. Again, it was not possible to form a gel with lubricating oil using the zinc cyclohexyl mercaptide thus prepared.

Example 11 In the manner of Example 9, zinc l-octyl mercaptide was prepared in liquid ammonia using 15.9 g. (0.195 mole, 0.39 equiv.) of zinc oxide and 50.3 g. (0.34 mole, 0.34 equiv.) of n-octyl mercaptan in solution in 150 ml. of ether. There resulted 59.4 g. of mercaptide product, a yield of 96%. Analysis of zinc l-octyl mercaptide: theor: 18.4% zinc, 18.0% sulfur; found: 21.2% zinc; 16.1% sulfur. The analysis is partially explained by the excess of zinc oxide in the charge which was not separable from'the final product. The mercaptide thus prepared formed a weak gel structure with lubricating oil, but it was not possible to incorporate as much as 10% of the mercaptide in thc composition.

Example J2 In this experiment an attempt was made toprepare lead l-dodecyl mercaptide, Pb(SC H by the liquid ammonia technique used in Examples 9, 10, 11 and 12 (wherein no oil diluent was used). By reacting lead oxide with dodecyl mercaptan, a product was separated and dried under vacuum. Analysis of this product showed 52%lead and 6 .0% sulfur. Theoretically this product should contain 34% lead and 10.5% sulfur. This product exhibited no gelling tendencies.

vention between'about 1.0 to 15.0 wt. percent may be incorporated in .the oleaginous carrier. Other addends such as oxidation inhibitors, pour point depressions, VI improvers and the like may be incorporated in compositions of this invention. Greases prepared using at least an amount sufiicient to provide about 0.25 weight percent sulfur to as high as 2.0 wt. percent sulfur in the final composition are stable and qualify as greases.

Any mineral oil or lubricating oil may be used to formulate compositions using the zinc mercaptides of this invention. Mineral oils of Mid-Continent, West Coast, Texas or Pennsylvania origin may be used. Refined mineral oils of predominantly paraffinic'nature form a preferred class of 'liquid carrier agent for the zinc mercaptides. Such lubricating oil fractions as neutrals and bright stocks which have been solvent refined, dewaxed and clay treated in a manner known to the art form a preferred class of carrier useful in preparing greases and other gel compositions for lubrication where anti-wear properties are paramount. The physical properties of the particular oils used in the experiments described herein are given in the following table.

TABLE-PHYSICAL PROPERTIES OF MINERAL OILS API Viscosity Wt. Neut. Oil Grav. Flash, Fire Color, Pour, OR VI Percent N 0.

7 degrees F. NPA F. S (1948) 85/100 N eutral- 35. 8 385 430 79. 3 56. 0 37. 6 1. 0 5 0.0 103 0.07 0. 03 200/90 Neutral 29. 3 430 485 207 107 46.5 1V 0 0. 01 91 0. 4 0.09 160/90 Bright Stoe 23.9 575 650 3,291 1, 165 171.8 6 5 1. 2 92 0. 80 0. 42

. Example 14 v In addition to their unique gelling properties in mineral Using the technique of Example 13, an attempt was made to prepare stannous l-dodecyl mercaptide,

There was some evidence of a gelling effect, although it was distinctly minor as compared with the gel formation experienced with the zinc mercaptides. Analysis of the product-showed in one sample 34.8% metal and in another 10.6% metal, and in the first sample 13.4% sulfur and inthesecond sample 15.6% sulfur. Theoretically, this product should-contain 22.8% metal and 2.8% sulfur. I Example 15 In this experiment cadmium oxide and dodecyl mercaptan were reacted using the technique of Examples 9, 10, 11 and 12 to prepare cadmium l-dodecyl mercaptide, Cd(SC H Analysis of the product revealed in one sample 39.8% metal and in another sample 0.0% metal, and 9.0% sulfur for both samples. Theoretically, this product should contain 21.8% metal and 12.4% sulfur. There Was no evidence of gelling tendencies.

The foregoing experiments indicate that the straightchain zinc mercaptides coming within the definition of this invention are unique in their properties of forming a stable grease or gel. The co-existence of zinc and sulfur in the molecule points to their utility as extreme pressure agents. In general, between about 1.0 wt. percent to as high as 99.0 wt. percent may be used with a mineral lubricating oil base. Under certain conditions it is contemplated that the zinc mercaptides of this invention may be used as lubricants per se, without a mineral oil base. A composition containing an amount of the zinc mercaptides of this invention suflicient to incorporate about 0.25 weight percent of sulfur therein has been found to exhibit incipient gel properties. A thickened non-gel composition is formed when an amount of the zinc mercaptides of this invention is used to incorporate less than 0.25 Weight percent of sulfur in the total composition, i.e.,- 0.20 weight percent sulfur. For purposes of preparing greases using the zinc mercaptides of this inoils, the straight-chain zinc mercaptides should be of value for other uses where thickening, or bodying, and/ or extreme pressure properties are desired. In these applications where gelling is not requisite, the tertiary and secondarymercaptides are also of value. Thus the zinc mercaptides should be of value as additives to lubricating oils to increase viscosity and impart extreme pressure qualities, and in lubricant formulations for operations suchas metal cutting and stamping, and wiredrawing. They should also be of interest for protective coatings as agents to increase the viscosity of vehicles used in paints, varnishes and lacquers, to adjust consistency, to modify. brushing and spraying properties, to decrease the ra'teof sedimentation and prevent the formation of a hard cake, to improve flat-finish coatings, and to facilitate the grinding of fine particles for paints and lacquers. In the plastics industry they should have merit for formulating plasticizer compositions, and as internal lubricants. In the manufacture of inks, they should have value as thickeners and dispersion promoters.

Regarding the method of preparation found to apply herein, the ammonia appears to act as a solvent and/or catalyst for the reaction. Assuming, without limiting the invention thereto, that the ammonia catalyzes the reaction, it may function to form an ammoniacomplex intermediate which is decomposed in the heating steps. In this regard other liquid nitrogenous bases may be used such as liquid primary and secondary amines. In carrying out the method, the zinc oxide is mixed with at least a molar equivalent of the corresponding mercaptan in a solution of the liquid nitrogeviscosity of the mixture and ease the handling thereof. After mixing the reactants at room temperature for about 1 hour, the ammonia, if used, is allowed to evaporate. If an amine is used, it can be removed by heating over a steam bath with nitrogen stripping or with a slight vacuum. Any excess zinc oxide is removed by filtration, preferably aided by a vacuum. The toluene or other solvent is removed by nitrogen stripping over stream.

Where the mercaptides of this invention are prepared in situ in a mineral lubricating oil or other oleaginous liquid, the resulting product solution can be readily blended to yield the compositions desired. By adding about to 30% by weight of an oil solution containing from 40% to 60% by weight of the zinc mercaptide, good grease structures may be formed. Where the mercaptides are prepared without a mineral oil present, they may be dispersed in a mineral oil to form a stable gel structure by violent mixing or homogenization. Although the method herein is applicable to the preparation of mercaptides having R groups of less than 8 carbon atoms, such mercaptides do not exhibit the gel forming propensities of the mercaptides having R groups of 8 to 18 carbon atoms.

The invention is only limited by the appended claims.

What is claimed is:

1. The method of producing zinc mercaptides of the general formula wherein R is a straight-chain, saturated alkyl group containing from 8 to 18 carbon atoms, which comprises mixing zinc oxide with at least a stoichiometric amount of the corresponding mercaptan in a solution of a liquid nitrogenous base of the group consisting of liquid ammonia, ethylamine and propylamine at ambient temperatures for a time sufficient to complete the formation of the zinc mercaptide, removing the nitrogenous base from said mixture and recovering said zinc mercaptide.

2. The method in accordance with claim 1 in which between about 0.075 to 0.15 mole of said zinc oxide is reacted with between about 0.1 to 0.2 mole of said mercaptan and said liquid nitrogenous base is ammonia.

3. The method in accordance with claim 1 in which the liquid nitrogenous base is liquid ammonia.

4. The method in accordance with claim 1 in which the liquid nitrogenous base is ethyl amine.

5. The method in accordance with claim 1 in which the liquid nitrogenous base is propyl amine.

6. The method of preparing a grease composition containing a mineral lubricating oil and a suflicient amount of a zinc mercaptide of the general formula.

wherein R is a straight-chain, saturated alkyl group containing from 8 to 18 carbon atoms, to impart a grease gel structure thereto which comprises dissolving at least a stoichiometric amount of zinc oxide in a liquid nitrogenous base of the group consisting of liquid ammonia, ethyl amine and propyl amine, adding thereto a mixture comprising the corresponding mercaptan and a mineral lubricating oil, maintaining said mixture at ambient temperatures until the formation of said zinc mercaptide is complete, removing said nitrogenous base from said reaction mixture, heating said mixture at about C. for a time sufficient to homogenize same to a homogeneous liquid, filtering any unrcacted zinc oxide therefrom, and blending the resulting oil solution of the zinc mercaptide with a mineral oil to form a grease consistency.

7. The method in accordance with claim 6 in which said blending is accomplished by heating said oil solution and added mineral oil, followed by rapid cooling, and the resultant gel is reduced to a grease texture by milling.

8. The method in accordance with claim 6 in which said product is zinc l-dodecyl mercaptide prepared by the reaction of 0.15 mole of zinc oxide with about 0.2 mole of l-dodecyl mercaptan in a liquid ammonia solution.

9. The method in accordance with claim 6 in which the liquid nitrogenous base is liquid ammonia.

10. The method in accordance with claim 6 in which the liquid nitrogenous base is ethyl amine.

11. The method in accordance with claim 6 in which the liquid nitrogenous base is propyl amine.

References Cited in the file of this patent UNITED STATES PATENTS 2,228,500 Bergstrom Jan. 14, 1941 2,229,528 Shoemaker Jan. 21., 1941 2,289,795 McNab July 14, 1942 2,350,544 Zimmer et al. June 6, 1944 2,413,531 Verbanc Dec. 31, 1946 2,480,823 Morris et al. Sept. 6., 1949 2,510,765 Stewart June 6, 1950

Claims

6. THE METHOD OF PREPARING A GREASE COMPOSITION CONTAINING A MINERAL LUBRICATING OIL AND A SUFFICIENT AMOUNT OF A ZINC MERCAPTIDE OF THE GENERAL FORMULA.