US3450634A - Extreme pressure additives prepared from overbased lead naphthenate and partially or unneutralized dialkyl dithiophosphoric acid - Google Patents

Description

United States Patent US. Cl. 25232.7 6 Claims ABSTRACT OF THE DISCLOSURE Extreme pressure additives, especially for use with a lubricant composition comprising the class of materials produced by reacting an overbased lead naphthenate with a dialkyl dithiophosphoric acid or a partially neutralized dialkyl dithiophosphoric acid.

This application is a continuation of application Ser. No. 553,316, filed May 27, 1966, now abandoned.

The present invention relates to extreme pressure additives and a method for their preparation, and more particularly, is concerned with certain phosphosulfurized materials and metal derivatives thereof useful as additives in lubricants which are required to operate under extreme load conditions.

The need for extreme pressure lubricants and additives for the production of such lubricants is well known. When a lubricating film that separates two moving surfaces is subjected to increased pressure as a result of high load conditions, the lubricant tends to be squeezed out. The compression action of the high loads also tends to cause an increase in the internal heat of the lubricating film, resulting in a thinning out of the film due to its decreased viscosity. This combined squeezing and thinning of lubricant film permits the metal surfaces to make point contacts and generate friction which augments the heat effect on the film. Continued movement of the surfaces under these conditions results in high wear and ultimately in seizure and destruction of the surfaces under severe conditions.

It has been repeatedly observed that lubricating oil fractions alone do not have the required film strength to prevent excessive wear and seizure of highly loaded parts such as gears. It has been further observed, however, that certain materials, i.e., extreme pressure agents, can be added to lubricants to improve film strength and thus prevent wear and destruction of metal parts which are under high loads. A number of such agents have been found suitable for this purpose in the past, but there is a continuing search for new additives which are more effective or equally effective at lower cost, since such additives are usually more expensive than the equivalent amount of lubricant base that they replace.

This invention is concerned with certain compounds which, when added in small amounts to base lubricating oils, provide a lubricant composition with improved antiwear and extreme pressure characteristics. :In general, the compounds of this invention form three classes of extreme pressure agents which can be generally described as follows: Firstly, the class of materials produced by reacting a hydroxy dibasic acid and an ethoxy amine, which is then treated with phosphorus and sulfur, followed by subsequent neutralization with an alcohol and a metal oxide. Secondly, the class of materials produced by reacting an unsaturated dibasic acid and an alcohol, treating with phosphorus and sulfur, followed by subsequent 'ice neutralization with a metal oxide. Thirdly, the class of materials produced by reacting an overbased lead naphthenate with a dialkyl dithiophosphoric acid or a partially neutralized dialkyl dithiophosphoric acid.

Suitable hydroxy dibasic acids for use in producing the additives of the first class described above generally include those corresponding to the general formula (CHOH) (CH (COOH) where x is about 1 to 4 and y is about 0 to 6. Preferred dibasic acids include, among other, tartaric, mucic and malic acids. Monobasic hydroxy acids such as glycolic and tribasic hydroxy acids such as citric, may also be employed. However, dibasic hydroxy-acids are preferred. Suitable ethoxy amines include those of the general formula .zisO.

The reaction of the acid and amine can be conveniently carried out by heating a fluid mixture of the components containing about 1 to 1.5, preferably about 1.1 to 1.2 mols of amine per mol of acid at a temperature and for a time sufficient to completely react the acid and amine, e.g., until the theoretical amount of water is recovered from the reaction mixture. Suitable temperatures are from about 60 to 200 C., preferably about to 150 C. The time required for complete reaction will vary depending upon the temperature and particular reactants but usually falls in the range of about 1 to 20 hours. A preferred process is to reflux the acid and a small molecular excess of amine in a suitable solvent, e.g., toluene, until the theoretical amount of water is recovered.

The sulfurization and phosphorization of the resulting reaction product can be accomplished by any of the various methods employed in the art but in each case should be conducted in a manner that provides the mixture with about 5 to 15% by weight of combined sulfur, preferably about 8 to 12%, and about 2 to 8%, preferably about 4 to 6% by weight of combined phosphorus. A particularly preferred method of conducting the sulfurization-phosphorization is phosphosulfurization which can conveniently be performed by adding a suitable amount, usually about 30 to 70 mol percent based on the acid component, of phosphorus sesquisulfide or phosphorus pentasulfide to the reaction product and heating the resulting mixture at a temperature and for a time suflicient to provide the aforementioned amounts of sulfur and phosphorus. Suitable temperatures are between about 100 and 200 C., preferably about to C. Again the reaction time will vary with the reaction temperature selected but will usually fall in the range of about 2 to 10 hours.

Alternatively, the sulfur can be added by first sulfurizing the reaction product with a sulfurizing agent such as sulfur flour or lump sulfur at a suitable temperature, e.g., about 150 to 250 C. and preferably about to 180 C. When sulfur flour is employed as the sulfurizing agent, it is preferred to actually add the desired amount of sulfur flour to the mixture and conduct the sulfurizing reaction so as to react substantially all of the sulfur with the mixture. The time required for complete reaction of the sulfur will vary depending upon the reaction temperature selected but usually falls in the range of about 3 to 15 hours. About 5 to 10 hours at C. is a preferred sulfurizing condition. After sulfurization of the reaction product, the sulfurized product can then be phosphorized employing a suitable phosphorizing agent such as a phosphosulfurizing agent. Phosphosulfurizing agents are the phosphorus sulfides such as P 8 P 5 etc., phosphorus sequisulfide (P 8 being particularly preferred. Since, when employing the phosphorus sulfides, the treatment is a phosphosulfurization, it may act to provide the reaction product with sulfur as well as phosphorus.

The phosphosulfurized reaction product of the hydroxy dibasic acid and ethoxylated amine is then treated with an alcohol to improve oil solubility. Suitable alcohols include alkanols having from about 5 to 24 carbon atoms. Fatty alcohols e.g., lauryl alcohol, oleyl alcohol, etc., having from 10 to 24 carbon atoms are preferred. The treatment with alcohol is preferably carried out by heating, e.g., refluxing a fluid mixture of the phosphosulfurized reaction product and alcohol at a temperature of from about 80 to 170 0, preferably about 110 to 150 C., for a time suflicient to improve the solubility of the reaction product which time will vary depending upon the temperature and reactants but is usually within the range of about 5 to hours. Conveniently, the reaction is terminated when no further water is evolved. A preferable method of carrying out this reaction is to reflux the reactants in a solvent such as toluene. In general, the alcohol is used in a slight excess, about 101 to 105 percent, referred to the acidic reaction component.

The phosphosulfurized reaction product, as treated with an alcohol, can be further neutralized or partially neutralized by methods employed in the art using, for example, metal oxides. Neutralization can be accomplished by heating a fluid mixture of the reaction product with a metal oxide such as lead or zinc oxide at a temperature of from about 100 to 200 C., preferably about 130 to 170 C., for a time sufficient to neutralize the alcoholtreated, phosphosulfurized reaction product the desired degree. The final product will generally have an acid number of less than about 100, preferably 60, and contain about 2 to 5 weight percent metal. The time for this neutralization required will vary depending upon the reactants and temperature, but usually is within the range of about 5 to 15 hours.

The second class of additives referred to above are the reaction products of unsaturated dibasic acids and an alcohol, treated with phosphorus and sulfur and followed by subsequent neutralization with a metal oxide. In general, the reaction is accomplished by heating a fluid mixture of the unsaturated dibasic acid and alcohol in about a 1:1 mol ratio so that the desired partial ester, e.g., the half ester, reaction product predominates. Conveniently, the acid and alcohol can be refluxed in a suitable solvent, e.g., toluene, with removal of water until no further water is evolved. However, the means by which this esterification is carried out in no way limits the scope of this invention, since the partial ester product is desired only as an intermediate reaction material and can be prepared in a variety of ways well known to the art. Suitable acids are maleic, fumaric, citraconic, mesaconic as well as high molecular weight materials such as linoleic dimer acids. Suitable alcohols are alkanols having about 4 to 24 carbon atoms and preferably about 6 to 18 carbon atoms. The ester, e.g., half ester, of the acid is neutralized with 9, metal oxide such as lead oxide. The neutralized ester, e.g. the lead salt or soap is then phosphorized and sulfurized, more accurately phosphosulfurized, for example, according to the procedure described above to produce a final product containing about 0.5 to 2% by weight, preferably about 0.75 to 1%, sulfur and about 0.5 to 5% by weight, preferably about 1 to 3%, phosphorus, and about 15 to 25% by weight metal, e.g., lead depending on the degree of esterification in making the partial ester and the molecular weight of the alcohol portion of the partial ester. Using a preferred alcohol of about 116 to 158 molecular weight for example, lead content will be about 18 to 22%.

The third class of additives encompassed by this invention are the reaction products of an Overbased lead naphthenate with a dialkyl dithiophosphoric acid or a partially neutralized dialkyl dithiophosphoric acid. Overbased lead naphthenate is produced by reacting naphthenic acids with an excess of lead oxide over the amount required for neutralizing the naphthenic acids. Generally, the lead naphthenate will contain about 35 to 50% by weight lead and preferably about twice the amount of lead calculated for theoretical neutralization of the naphthenic acids. For the usual naphthenic acids having an acid number in the range of about 190-220 the lead content preferably will be about 39 to 46%. The lead oxide is generally used in an excess of from about 50 to preferably about 75 to 125%. Suitable naphthenic acids are those having an acid number of about to 250, preferably about to 220 and an average molecular weight of about 220 to 320, preferably about 250 to 290 as calculated from the acid number. The basic lead naphthenate is reacted with a dialkyl dithiophosphoric acid in an amount suflicient to neutralize the excess basicity of the lead naphthenate. The basic lead naphthenate may be similarly reacted with a partially zincneutralized dialkyl dithiophosphoric acid, again in an amount calculated to neutralize the excess basicity of the lead naphthenate. The alkyl group of the dialkyl dithiophosphoric acid may have from about 4 to 24 carbon atoms, preferably about 6 to 18 carbon atoms.

The lubricating oil base stock used in the present invention is of lubricating viscosity and can be, for instance, a solvent extracted or solvent refined oil obtained in accordance with conventional methods of solvent refining lubricating oils. Often, lubricating oils have viscosities from about 20 to 250 SUS at 210 F. The base oil can be derived from paraffinic, naphthenic, asphaltic or mixed base crudes, and if desired, a blend of solventtreated Mid-Continent neutrals and Mid-Continent bright stocks may be employed. The oils can be thickened to grease consistency.

The base oil of the fluid lubricant or grease can also be a synthetic oil of lubricating viscosity. One type of synthetic oleaginous base which can be used is an ester synthetic oil of lubricating viscosity which consists essentially of carbon, hydrogen and oxygen, e.g., di-2-ethylhexyl sebacate. Various of these lubricating materials have been described in the literature and generally their vicosity ranges from the light to heavy oils, e.g., about 50 SUS at 100 F. to 250 SUS at 210 F. and preferably 30 to 150 SUS at 210 F. These esters are of improved thermal stability, low acid number and high flash and fire points. The complex esters, diesters, monoesters and polyesters can be used alone, or, to achieve the most desirable viscosity characteristics, complex esters, diesters and polyesters can be blended with each other or with naturally-occurring esters like castor oil to produce lubricating compositions of wide viscosity ranges which can be tailor-made to meet various specifications. This blending is performed, for example, by stirring together a quantity of diester and complex ester at an elevated temperature, altering the proportions of each component until the desired viscosity is reached.

The compositions of this invention incorporate into the base oil a small, minor amount of one of the above described additives sufficient to provide the base oil of lubricating viscosity (which is the major portion of the composition) with improved anti-wear and extreme pressure properties. This amount is generally about 0.01 to 15 or 20 or more percent by weight of the lubricant depending on the particular base oil used and its application. The preferred concentration should be the minimum amount to give the desired properties for the particular application and usually will be about 0.2 to 20 percent by weight of the lubricant. In some cases where oil solubility might limit the amount of additive employed, dispersants may be used to increase the concentration. In these cases, it has been found that increased solubility is best obtained in highly refined oils by dissolving the dispersant in the oil before dissolving the additive.

Materials normally incorporated in lubricating oils and greases to impart special characteristics can be added to the composition of this invention. These include corrosion inhibitors, additional extreme pressure agents, antiwear agents, etc. The amount of additives included in the composition usually ranges from about 0.01 weight percent up to about 20 or more weight percent of the lubricant and, in general, they can be employed in any amount desired as long as the composition is not unduly deleteriously affected.

The following examples are'included to illustrate the advantages of the compounds of the present composition in lubricant compositions.

EXAMPLE I Ethomeen 18/12 (0.67 mol) and Ethomeen T/ 12 (0.73 mol) were reacted with tartaric acid (1.3 mols) by refluxing in toluene until the theoretical 2.6 mols of water were recovered from the reaction mixture.'Ethomeen 18/ 12 and T/l2 are tertiary amines containing one fatty alkyl group and two dioxyethylene groups, having the formula RN[(CH CH O),,H] The Ethomeens are commercial materials available from Armour Chemical Co. Ethomeen T/12 is derived from a mixture of amines having an average carbon chain ranging from C to C The predominant alkyl group in Ethomeen 18/12 is C This reaction product was then treated with 0.65 mol of P S for four hours at 110 C. and for 2 hours at 130 C. After removal of toluene solvent, the solid amber product analyzed: sulfur, 10.1%; phosphorous, 5.20%; acid No. 169. This product was found to be soluble in naphthenic-type lubricating oil base stocks, but to have limited solubility in paraffinic-type base stocks.

EXAMPLE II 640 grams of the product of Example I (1.94 acid number equivalents) were reacted with 400 grams (2 mols) lauryl alcohol by refluxing in toluene for 12 hours, recovering 11 ml. water of reaction. 200 grams of maleic acid (1.5 mols) were then added and the reaction was continued until approximately 68 ml. of water were collected and no further water was being evolved. After removal of toluene solvent, the dark amber fluid product analyzed: sulfur, 4.34%; phosphorus, 2.72%; acid No. 139.

EXAMPLE III 500 grams of the product of Example II were treated with 50 grams of zinc oxide at 150 C. for 8 hours. 200 grams of a 50 vis. 95 VI mineral oil were added to reduce viscosity, and the product filtered to remove unreacted zinc oxide and insoluble reaction products. The 600 gram yield of product analyzed: sulfur, 3.24%; phosphorus, 1.8%; zinc, 2.82%; acid No. 50.6.

EXAMPLE IV The half ester of maleic acid was prepared by refluxing 4 mols of maleic acid with 4 mols of mixed 0;

alcohols in the presence of toluene solvent until 73 mols of water were recovered and no further water was evolved. The product was filtered to remove traces of solid contaminants and the toluene solvent was removed by vacuum stripping.

EXAMPLE V 406 grams (1.9 mols est.) of the Example IV half ester reaction product were treated with 210 grams (0.95 mol) of lead oxide at 120 C. for one hour. The product was then diluted with approximately two volumes of benzene and filtered to remove unreacted lead oxide and insoluble lead salt of unreacted maleic acid. The fluid filtrate was treated with 77 grams (0.35 mol) of phosphorus sesquisulfide at C. for one hour, filtered, and the solvent removed by vacuum stripping. The resultant product analyzed: sulfur, 0.84%; phosphorus, 1.46%; and lead, 21.0%

EXAMPLE VI A solution of basic lead naphthenate was prepared by reacting 260 grams of naphthenic acids (acid No. 212, avg. MW 260) with 223 grams (1 mol or 2 equiv.) of lead oxide in 1600 grams of 100 vis. naphthenic neutral oil. The resultant 22% lead naphthenate solution in oil analyzed 9.70% lead, equivalent to approximately 44% lead content in the lead naphthenate, or approximately twice the lead content required for neutralization of the naphthenic acid. 300 grams of the basic lead naphthenate solution were diluted with 200 grams of toluene, and to this mixture were added 48 grams of dioctyl dithiophosphoric acid (acid No. 181), and the reaction mixture refluxed for six hours with water of reaction being removed via a Dean-Stark trap. After removal of solvent by vacuum stripping, the resultant product analyzed; sulfur 2.94%; phosphorus, 1.53%; and lead, 7.57%

EXAMPLE VII 300 grams of the basic lead naphthenate solution prepared as in Example VI were treated with 262 grams of a partially zinc-neutralized dioctyl dithiophosphoric acid EXAMPLE VIII The eflicacy of the compounds of this invention as extreme pressure and anti-Wear additives is demonstrated by the data of Table I, which show performance in the Falex load test, the Four-Ball EP and wear tests, the SAE load test, and the Timken load and wear tests. The tests used in evaluating these lubricants are well known in the art and their description is not considered essential to this invention. The Timken wear test is run using the Timken machine described in CRC procedure L-18-545, modified so that the test block is continuously moved back and forth for a distance of about 0.13 inch approximately every 15 seconds.

TABLE Composition No Blank 1 2 Base oil A, wt. percent Base oil B, wt. percent Base oil 0, wt. percent...

Example II, wt. percent Example III, wt. percent. Example V, wt. percent Example VI, wt. percent... Example VII, wt. percent. Falex max. load, lbs

SAE machine, lbs. at 300 r.p.m .I

Timken machine, safe lbs- Four-ball weld point, kg MHL Four ball wear scar, mm., at;

7 kg. for 2 hrs 14 kg. for 1 hr Timken wear at 100 lbs, mg

1 Falls at break-1n:

Norm-Base oils A and B are solvent refined neutral oils, having 100 F. vlscosities of about 500 and 200 SUS, respectively. Base oil 0 is a solvent refined bright stock having a viscosity of SUS at 210 F.

It is claimed:

1. An extreme pressure additive comprising the reaction product of over-based lead naphthenates containing about 35 to 50 percent by weight lead with a compound selected from the group consisting of dialkyl dithiophosphoric acid and partially zinc-neutralized dialkyl dithiophosphoric acid, the alkyl group of the dialkyl dithiophosphoric acid having from 4 to 24 carbon atoms, said ovrebased lead naphthenate being produced by reaction of naphthenic acid having an acid number of about 175 to 250 and an average molecular weight of about 220 to 320 as calculated from the acid number with an excess of lead oxide over the amount required for neurtalization of the acid, said compound being used in an amount sufficient to neutralize the excess basicity of said overbased lead naphthenate.

2. The additive of claim 1 wherein the lead oxide is used in an excess of from about 50 to 150 percent.

3. An oleaginous lubricant composition consisting essentially of a base oil of lubricating viscosity and an amount sufiicient to give improved extreme pressure properties to the composition of the additive of claim 1.

4. The composition of claim 3 wherein said amount is from about 0.01 to 20 percent by weight of the lubricant composition.

5. An oleaginous lubricant composition consisting essentially of a base oil of lubrictaing viscosity and an amount sufiicient to give improved extreme pressure properties to the composition of the additive of claim 2.

6. The additive of claim 2 wherein the alkyl group of said compound is from about 6 to 18 carbon atoms.

References Cited UNITED STATES PATENTS 2,364,283 12/1944 Freuler. 3,222,280 12/1'965 Wolfram.

PATRICK P. GARVIN, Primary Examiner.

US. Cl. X.R