US 2712526 A
Description (OCR text may contain errors)
HYDROCARBON 01L ADDITIVE John P. McDermott, Springfield, N. 1., assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application December 22, 1951, Serial No. 263,020
11 Claims. (Cl. 25232.7)
The present invention relates to an improved class of additives particularly suitable for use in lubricating oils and to the compounded mineral oils and other hydrocarbon products in which they are employed.
The application is a continuation-in-part of copending application Serial No. 100,741, filed on June 22, 1949, which has now issued as U. S. Patent 2,610,182 on September 9, 1952. 7
Modern developments in the design of internal combustion engines, with increasing engine speeds and compression ratios, have imposed a severe strain on the lubricants employed. in particular, the crankcase oil is raised to a high temperature and in the course of its circulation through the engine is repeatedly exposed to air under conditions highly conducive to destructive oxidation. Oxidative breakdown of the oil results in the formation of acidic products which corrode bearing surfaces and do considerable harm to the engine generally. Furthermore, the metallic corrosion products have the effect of catalyzing further oxidative breakdown of the oil.
A number of compounds, more especially those of the phenolic type, are known which exert an oxidation inhibiting effect when added to mineral lubricating oils and other hydrocarbon products. Their effect is to prevent oxidative breakdown of the oil both on storage (long potential reaction time and low temperature) and in use (short reaction time and high temperature). Although many antioxidants are known which stabilize the oil adequately on storage, the majority of them tend to break down with undesirable rapidity at high engine operating temperatures.
A principal object of the present invention is to provide a new class of lubricating oil antioxidants of good properties. Another object is to provide an antioxidant which is stable and effective at relatively high engine temperatures. Other objects and advantages will be apparent from the following description.
It has now been found, according to the present invention, that the salts formed by reacting thialdine or its homologs with sulfur-containing acids, such as sulfurized carboxylic acids, thiocarboxylic acids and the thio acids of phosphorus, are extremely effective antioxidants for hydrocarbon products liable to oxidation, especially mineral lubricating oils.
Thialdine, otherwise known as 5,6-dihydro-2,4,6-trimethyl-l,3,5-dithiazine,- is represented by the structural formula It is readily prepared by treating the condensation product of acetaldehyde and ammonia With hydrogen sulfide.
2,712,525 Patented July 5, 1955 Thialdine and the homologs of the same which are useful for the purposes of the present invention may be represented by the general formula where R represents an alkyl group of 1 to 10 carbon atoms. However, simple thialdine in which R is methyl is preferred.
Sulfur-containing acids which may be used in forming the thialdine salts of the present invention include sulfurized monoor dicarboxylic aliphatic acids which may be represented by the general formulas R 'COOH or COOH COOH where R represents a sulfurized aliphatic hydrocarbon radical having from 1 to 30 carbon atoms, preferably in the range of 4 to 20 carbon atoms. The radical R may before sulfurization be saturated or unsaturated, straight or branched chain, with or without cycloaliphatic, substituent chains, or it may be an alkyl substituted cycloaliphatic nucleus. Examples of suitable acidsare the lower monoand dicarboxylic acids such as 'butyric, adipic, sebacic, and decanoic acids. Higher acids include lauric, oleic, linoleic, ricinoleic, palmitic, and stearic acids. Mixtures of acids, such as those obtainedby the oxidation of parafiin Wax or other high molecular weight petroleum fractions, may also be used. The sulfurized acids may be prepared by heating the acid with elemental sulfur or with a sulfur halide. Examples are sulfurizedoleic, sulfurized linoleic, and sulfurized oxidized wax acids. Thio acids of the formulas R'COSH (thiol acids), and R'CSSH (dithio acids), where R is a sulfurized or unsulfurized aliphatic radical having the same significance as above, may also be used. Xanthic acids (ROCSSH) and the like may also be used. The most preferred products, however, are those prepared from the thio acids of phosphorus, such as thiophosphorous and dithiophosphoric acids, both from the point of view of effectiveness and from the point of view of ease of preparation. In general, partially esterified dithiophosphates or thiophosphites are preferred in making the monoor di-thialdine salt. These esterified compounds may be prepared by reacting an organic hydroxy compound with a sulfide of phosphorus. Thus, a compound of the formula ROH, where R" represents an organic radical, may be treated with phosphorus pentasulfide in a molar ratio of 4:1, as shown below.
The diester dithiophosphoric acids are preferred as a general rule. The compound R"OI-I used for making the esters of thio acids of phosphorus may be an alcohol,
such as a C2 to C20 aliphatic straight or branched chain or cyclic alcohol with or without substituent groups such as halogen, sulfur, amino, or nitro groups, or may be a phenol or an alkylated phenol, a hydroxy ester, hydroxy ether, etc. In general, the total number of carbon atoms in the group R should be from 2 to 30, preferably in the range of 4 to 20. Examples of suitable compounds are isopropyl alcohol, isobutyl alcohol, Z-ethylhexanol, iso-octyl alcohol, Ca Oxo alcohols, decyl alcohol, Lorol (CID-C16) alcohols, methylcyclohexyl alcohol, isopropyl cyclohexyl alcohol, mixed alcohols derived from paralfin wax or from chlorinated parafiin wax, phenol, p-cresol, 2,4,6-triiosobutylphenol, p-isooctylphenol, ptert.-octylphenol, p-tert.-octylphenol sulfide. butyl lactate, a-hydroxy butyl stearate, the various glycol ethers known as Cellosolves, such as the monobutyl ether of ethylene glycol, etc.
The thialdine and homologous salts of the present invention may be readily formed by contacting the thialdine compound with the sulfur-containing acid at room temperature'. Since heat is evolved, the reaction is preferably conducted in the presence of an inert solvent and by contacting the reactants gradually. Suitable solvents include chloroform, carbon tetrachloride, ethylene dichloride, benzene, and the like.
The following examples illustrate the preparation and testing of various thialdine salts according to this invention, but it is to be understood that these examples do not limit the scope of the invention in any way.
Example I.-Preparatin of thialdine di-nonyl di-thiophosphate A mixture of 115.2 grams (0.8 mol) of C9 0x0 alcohol and 44.4 grams (0.2 mol) of P285 was heated at 110 C. for 45 minutes with rapid stirring in a 1-liter, 3-necked flask equipped with a stirrer, thermometer, and reflux condenser. The resultant acid was then filtered and blown with nitrogen for minutes.
i A solution of 95.5 grams (0.25 mol) of this product (di-nonyl di-thiophosphoric acid) in 100 cc. of CHCls was added dropwise over a period of minutes to a solution of 40.8 grams (0.25 mol) of thialdine in 300 cc. of CHC13, maintaining the temperature below C. After stirring for an additional hour at room temperature, the product was filtered and placed on a steam bath k to remove the solvent. A viscous brown liquid was obtained, which upon analysis was found to contain 5.5% phosphorus, 22.1% sulfur, and 2.4% nitrogen.
Example 2.Preparati0n of thialdine di-methylcyclohexyl di-thiophosphate Di-methylcyclohexyl di-thiophosphoric acid was prepared by the method described in Example 1. using 114 grams (1 mol) of methylcyclohexanol and 55.5 grams (0.25 mol) of P2S5.
The thialdine salt was also prepared by the method described in Example 1, using 96.6 grams 0.3 mol) of methylcyclohexyl thiophosphoric acid and 49.0 grams (0.3 mol) of thialdine. A brown tacky solid was obtained which upon analysis was found to contain 6.0% phosphorus, 24.5% sulfur, and 2.1% nitrogen.
Example 3.Preparati0n 0f thialdine di-sulfurized oleyl di-thiophosphate Di-sulfurized oleyl di-thiophosphoric acid was prepared by the method described in Example 1, using Example 4.Preparation of thialdine sulfurized oleate A mixture of 113 grams (0.4 mol) of oleic acid and 12.8 grams (0.4 mol) of sulfur was heated for 1% hours at C.
The thialdine salt was prepared as described in Example 1. using 94.4 grams (0.3 mol) of sulfurized oleic acid and 49.0 grams (0.3 mol) of thialdine. A dark red liquid was obtained which upon analysis was found to contain 18.5% sulfur and 2.5% nitrogen.
Example 5.--Preparati0n of thialdine oleate Thialdine oleate was prepared substantially in accordance with the procedure of Example 4 using 113 grams (0.4 mol) of oleic acid and 65.2 grams (0.4 mol) of thialdine. An amber viscous liquid was obtained which upon analysis was found to contain 9.9% sulfur and 2.3% nitrogen.
These five products were then tested in the laboratory for their inhibiting action against the corrosion of lead in copper-lead bearings, as shown in the following examples.
Example 6 In this test theadditives were blended in 0.25% by weight concentration in an extracted Mid-continent oil of S. A. E. 20 grade and comparative tests run on these blends and on a sample of the unblended oil. The test was conducted as follows:
500 cc. of the oil was placed in a glass oxidation tube 13 inches long and 2% inches in diameter, fitted at the bottom with a /4 inch air inlet tube perforated to facilitate air distribution. The oxidation tube was then immersed in a heating bath so that the oil temperature was maintained at 325 F. throughout the test. Two quarter sections of automotive bearings of copper-lead alloy, of known weight and having a total surface area of 25 sq. cms., were attached to opposite sides of a stainless steel rod which was then immersed in the test oil and rotated at 600 R. P. M., thus providing sufiicient agitation of the oil during the test. Air was then blown through the oil at the rate of 2 cu. ft. per hour. At the end of each four-hour period, the bearings were removed, washed with naphtha, and weighed to determine the amount of loss by corrosion. The bearings were then repolished (to increase the severity of the test), reweighed and then subjected to the test for additional four-hour periods in like manner. The results are given in the following table as corrosion life, which indicates the number of hours required for the hearings to lose 100 mgs. in weight, determined by interpolation of the data obtained in the various periods.
The following data show that the salts of sulfur-containing acids were elfective oxidation and corrosion inhibitors. The salt of an unsulfurized carboxylic acid, however. was quite inefiective under the conditions employed in this test.
Corrosion L'fe Thialdine Salt 1 (Hours) None (Base oil only) Dlnonyl dl-thiophosphate (Ex. 1) Di(znethylcyclohexyl) di-thiophosphate (Ex Di(sulfuri7.ed oleyl) di-thlophosphate (Ex. 3)..." Sulfurized cleate (Ex. 4) Oleate (Ex. 5)
Example 7 Weight Loss Oil per Bearing Base oil alone 9 Blend From the preceding examples it will be evident that the thialdine salts of sulfur-containing acids are effective antioxidants for lubricating oils.
As previously stated, any of the alkyl homologs of thialdine may be employed although thialdine itself is preferred. The acid radical may be that of a long chain thio acid such as oleic, palmitic or stearic thio acids, as heretofore mentioned. Sulfur-containing acids are preferred in the carboxylic acid class, and these may be readily prepared, for example, by heating the acid with elemental sulfur or with a sulfur halide.
The additives may be blended in the oil in amounts of from about 0.02 to by weight, 0.1 to 2% being the preferred range. For load-bearing purposes quantities of 2 to 15% may be used. For handling and storage, concentrates containing in the range of about 15 to 50% or more may be prepared. These may be added to base stocks to give blends of the desired concentration.
In addition to the additives of this invention there may also be added to the oil other conventional additives including detergent type additives, such as metal soaps, metal petroleum sulfonates, metal phenates, metal alcoholates, metal alkyl phenol sulfides, and the like. Examples of such additional additives are barium tert.-octyl phenol sulfide, calcium tert.-amyl phenol sulfide, cadmium or nickel oleates, calcium phenyl stearate, aluminum naphthenate, and zinc methylcyclohexyl thiophosphate.
The lubricating oil base stocks used may be straight mineral lubricating oils or distillates derived from any suitable or desired crudes, or, if desired, blended oils may be employed. The oils may have been subjected to any conventional refining treatment such as acid, alkali and/ or clay treatment, or solvent extraction. Synthetic oils such as those prepared by the polymerization of olefins or by the Fischer-Tropsch synthesis may alternatively be employed, alone, mixed, or in combination with mineral oils.
Further types of additives which may be present if desired include dyes, pour point depressants, heat thickened fatty oils, sulfurized fatty oils, organo-metallic compounds, sludge dispersers, thickeners, viscosity index improvers, oiliness agents, voltolized fats, waxes or oils, and colloidal solids such as graphite or zinc oxide, etc. Solvents and assisting agents such as esters, ketones, alcohols, aldehydes, and halogenated or nitrated hydro carbons may also be employed where necessary or desirable.
Particularly suitable assisting agents are the Ca and higher alcohols (preferably C8 to C12) such as lauryl and stearyl alcohols, and the 0x0 alcohols of corresponding chain length.
In addition to being employed in lubricants, the additives of the present invention may also be employed in other hydrocarbon products susceptible to oxidative breakdown. Among these may be mentioned motor fuels, mineral oil base hydraulic fluids, torque converter fluids, cutting oils, flushing oils, turbine oils, transformer oils, industrial oils and process oils, natural and synthetic hydrocarbon rubbers, and the like. They may also be used in gear lubricants, greases, and in other products containing hydrocarbon oils as ingredients.
What is claimed is:
l. A mineral oil composition having incorporated therein in the range of about 0.02 to by weight of the salt formed by reacting a thialdine-type compound of the general formula where R is a C1 to C10 alkyl radical, with a sulfur-containing acid selected from the group consisting of (1) carboxylic acids of the general formula R'(COOH)n where R is a C1 to C30 sulfurized aliphatic hydrocarbon radical, and n is an integer of from 1 to 2, and (2) esters of thiophosphorous and di-thiophosphoric acids in which at least one of the hydrogen atoms is replaced by an organic radical containing from 2 to 30 carbon atoms and is selected from the group consisting of alkyl, sulfurized alkyl, aryl, aralkyl, alkaryl and cycloalkyl radicals.
2. A composition as in claim 1 wherein said thialdinetype compound is thialdine.
3. A composition as in claim 2 wherein said carboxylic acid is sulfurized oleic acid.
4. A composition as in claim 2 wherein said ester of dithiophosphoric acid is dinonyl dithiophosphoric acid.
5. A composition as in claim 2 wherein said ester of dithiophosphoric acid is di-methyl cyclohexyl dithiophosphoric acid.
6. A composition as in claim 2 wherein said ester of said dithiophosphoric acid is di-(sulfurized oleyl)dithiophosphoric acid.
7. A composition as in claim 1 comprising a mineral lubricant base stock and in the range of about 0.02 to 5% by weight of said salt.
8. An oil concentrate consisting of a mineral lubricating oil and in the range of about 15 to 50% by Weight of the salt of claim 1.
9. A composition as in claim 1 wherein said R radical has in the range of 4 to 20 carbon atoms.
10. A composition as in claim 1 wherein said acid is dithiophosphoric acid having both hydrogen atoms replaced by said organic radicals.
11. A composition as in claim 10 wherein said organic radicals have in the range of 4 to 20 carbon atoms.
i CH-R No references cited.