US3442804A - Lubricating composition containing a phosphorodithioate inhibitor - Google Patents

Description

United States Patent 3,442,804 LUBRICATING COMPOSITION CONTAINING A PHOSPHORODITHIOATE INHIBITOR William M. Le Suer, Cleveland, and William A. Higgins,

Gates Mills, Ohio, assignors to The Lubrizol Corporation, Wicklitie, Ohio, a corporation of Ohio No Drawing. Continuation of application Ser. No. 74,236,

Dec. 7, 1960. This application Jan. 19, 1967, Ser. No.

The portion of the term of the patent subsequent to Sept. 19, 1978, has been disclaimed Int. Cl. C10m 1/44 US. Cl. 25232.7 8 Claims ABSTRACT OF THE DISCLOSURE The invention disclosed herein relates to a lubricating composition containing a small amount, usually ranging from about 0.1% to about 20% by weight, of a particularly defined zinc phosphorodithioate. The zinc phosphorodithioate is illustrated by that derived from a dihydrocarbon phosphorodithioic acid in which the hydrocarbon radicals are primary alkyl radicals and consist of a mixture of lower molecular weight radicals (i.e., having less than carbon atoms) and higher molecular weight radicals (i.e., having at least 5 carbon atoms). In the particularly defined zinc phosphorodithioate, the ratio of the lower molecular weight radicals to the higher molecular weight radicals, expressed on a molar basis, is within the range of 1:1 to 3:1. Lubricating compositions disclosed herein have unusually high thermal stability and are characterized by corrosion inhibiting and oxidation inhibiting properties.

This application is a continuation of copending application Ser. No. 74,236, now abandoned, filed Dec. 7, 1960 which in turn is a continuation-in-part of earlier application Ser. No. 635,102, filed Jan. 22, 1957, now U.S. 3,000,822.

Zinc salts of phosphorodithioic acids have long been known and their utility in many applications widely acknowledged. They are useful as inhibitors of oxidation and corrosion and as such may be employed to combat such deteriorating influences on metal, asphalt, motor oils, and the like. Their principal use has been as additives for use in crankcase lubricants in which they are known to act to prevent corrosion of the relatively moving surfaces. Their use for such purpose is well established and their usefulness in this capacity has increased with the development and refinement of the internal combustion engine.

The performance of a particular lubricant in an engine is related directly to the design of a particular engine in which this performance is evaluated. A lubricant which performs well in one type of engine may perform very poorly in a different type of engine, and a very minor change in the design of a particular engine may be sufficient to pose an entirely new problem with respect to the lubrication of the new engine. The history of the development of lubricant additives therefore has been associated very closely with the development of the internal combustion engine.

Recent changes incorporated into internal combustion engines have pointed up a deficiency in the lubricant improving properties of zinc salts of phosphorodithioic acids which have been used heretofore. The somewhat higher operating temperatures of the newer engines have subjected the lubricant to correspondingly higher temperatures. Under these more severe conditions it has been observed that the zinc phosphorodithioate additive has shown a tendency to decompose so that the lubricant no longer ice affords protection to the moving metal surfaces from corrosion.

It is accordingly a principal object of this invention to provide novel compositions of matter.

Another object of the invention is the provision of compositions which are suitable for use in lubricants intended for use at high temperatures.

These and other objects of the invention are achieved by the zinc salts of a mixture of phos'phorodithioic acids having the structure in which R and R are the same or different primary aliphatic hydrocarbon radicals selected from the class consisting of lower molecular weight radicals having less than five carbon atoms and higher molecular weight radicals having at least five carbon atoms, the mole ratio of lower molecular weight radicals to higher molecular weight radicals in the zinc salt mixture being within the range of 1:1 to 3:1.

The above novel zinc salts, when used in lubricants, have been found to impart to the moving metal surfaces of the engine in which the lubricant is used a degree of protection from corrosion hitherto unrealized. Lubricants containing small proportions of the above novel zinc salts are enabled to withstand the higher operating temperatures of present-day engines to an extent not possible with previous lubricants.

The lower molecular weight primary aliphatic hydrocarbon radicals having less than 5 carbon atoms include principally isobutyl, n-butyl, and n-propyl, although ethyl and methyl likewise are suitable for use in these novel zinc salts. The higher molecular weight primary aliphatic hydrocarbon radicals having at least 5 carbon atoms include principally the primary amyl radicals, n-amyl, primaryisoamyl, 2-methyl-1-butyl and neopentyl. These primary amyl radicals are preferred because of their economy and also because of the particular utility of Zinc salts which contain these primary amyl radicals as the higher molecular Weight primary aliphatic hydrocarbon radicals. In any particular zinc phosphorodithioate the higher molecular weight primary aliphatic hydrocarbon radicals may be a mixture of such radicals each of which contains at least 5 carbon atoms. Thus such a mixture may consist of 40 molar percent of n-amyl and 60 molar percent of primary isooctyl radicals, it being understood of course that such a zinc phosphorodithioate composition would contain also a sufiicient proportion of lower molecular weight primary aliphatic hydrocarbon radicals as to bring the ratio of lower molecular weight radicals to higher molecular weight radicals within the above-stated range of 1:1 to 3:1. A particularly preferred mixture of primary aliphatic hydrocarbon radicals having at least 5 carbon atoms is a mixture of n-amyl, primary-isoamyl and 2- methyl-l-butyl radicals. Zinc phosphorodithioates which contain this mixture of higher molecular weight aliphatic hydrocarbon radicals are especially valuable, both for reasons of economy and eificacy of use.

The zinc salts of this invention comprise mixtures of different salts as well as zinc salts prepared from mixtures of different phosphorodithioic acids and zinc salts of phosphorodithioic acids prepared from mixtures of alcohols. The mixtures of different zinc salts are prepared quite obviously by the separate preparation of the individual zinc phosphorodithioates and then mixing of these two diiferent salts. Such mixtures of salts may be illustrated by the separate preparation of zinc di-n-hexyl phosphorodithioate and zinc di-n-propyl phosphorodithioate, followed by mixing of these two dilferent salts in such proportions as to satisfy the mole ratio of npropyl to n-hexyl radicals as stated before. The zinc salts of mixtures of different phosphorodithioic acids is illustrated by the separate preparations of diisobutyl phosphorodithioic acid and di-n-amyl phosphorodithioic acid, followed by neutralization of an appropriate mixture of these acids with zinc oxide. The zinc salts of mixed phosphorodithioic acids is illustrated by the reaction of phosphorus pentasulfide with an appropriate mixture of nbutyl alcohol and n-octyl alcohol to prepare the corresponding phosphorodithioic acid, followed by neutralization of this mixed acid with zinc oxide.

The particular method by which the zinc salts of this invention are prepared is not critical. Any of the above illustrated methods may be used. It is necessary only that the zinc salt contain the primary aliphatic hydrocarbon radicals described earlier in the ratio stated.

It will be noted that there are two principal aspects which characterize the novel zinc salts of this invention: the first of these is the fact that the aliphatic hydrocarbon radicals are primary; the second is that these radicals include both lower molecular weight and higher molecular weight radicals. The first of these characterizing features is thought to be responsible for the peculiar thermal stability of the zinc phosphorodithioates of this invention. It appears that the attachment of CH; group to the oxygen of the phosphorodithioate is more stable than the similar attachment of CH or -C group. It appears furthermore that the difference in stability is sufficient to allow the zinc phosphorodithioates of this invention to perform satisfactorily as corrosion inhibitors in environments in which the zinc phosphorodithioates of the prior art have been found wanting.

The second characterizing feature of the zinc phosphorodithioates described herein is the particular distribution of lower and higher molecular weight aliphatic hydrocarbon radicals within the zinc salt composition. There are two apparently conflicting requirements which should distinguish a corrosion inhibitor: It should be oil-soluble, but it must also be inexpensive. Oil-solubility may be had by the use of higher molecular weight hydrocarbon radicals. The sources of such higher molecular weight hydrocarbon radicals, however, are relatively expensive alcohols. The cheaper lower molecular weight alcohols provide lower molecular Weight hydrocarbon radicals which do not contribute sufiicient oil-solubility to a zinc phosphorodithioate molecule. It is now possible, however, to provide a satisfactorily oil-soluble zinc phosphorodithioate which can be prepared economically from inexpensive alcohols.

The methods by which these zinc salts may be prepared are illustrated by the following examples.

EXAMPLE 1 To a mixture of 536 grams (6 moles) of mixed primary amyl alcohols (65% n-amyl, 3% isoamyl, and 32% 2- methyl-l-butyl) and 1332 grams (18 moles) of isobutyl alcohol there was added portionwise at 60-70 C. over a period of 4.5 hours 1332 grams (6 moles) of phosphorus pentasulfide. This mixture was heated for an additional 2 hours at 6070 C. then filtered to yield a clear, fluid filtrate. To a suspension of 358 grams (4.4 moles) of zinc oxide in 1796 grams of mineral oil there was added over a 2.5 hour period at 7577 C., 2080 grams (8 moles) of the above filtrate. The resulting mixture was freed of water and other volatile constituents by heating at 85- 95 C./ 120 mm. The mixture was filtered to yield a clear filtrate having the following analyses: P, 6.0%; S, 13.0%; Zn, 6.8%

EXAMPLE 2 A mixture of 1644 grams (6 moles) of di-isobutyl phosphorodithioic acid and 588 grams (2 moles) of a diamyl phosphorodithioic acid prepared by the reaction of phosphorus pentasulfide with a mixture (65 n-amyl, 3% isoamyl, and 32% 2-methyl-1-butyl) of amyl alcohols was prepared and added portionwise at 75-77" C. throughout a 2-hour period to a suspension of 358 grams (4.4 moles) of zinc oxide in 864 grams of mineral oil. The mixture was held at 75 C. for an additional hour, then heated to a final temperature of 95 C./120 mm. The residue was filtered to yield a clear filtrate having the following analyses: P, 8.0%; S, 16.8%; Zn, 8.5%.

EXAMPLE 3 The zinc salt of di-isobutyl phosphorodithioic acid was prepared by the reaction of isobutyl alcohol with phosphorus pentasulfide followed by neutralization of the resulting acid with zinc oxide. To 447 grams (0.36 mole) of the oil solution of this salt there was added 149 grams (0.12 mole) of a similarly prepared zinc salt of a phosphorothithioic acid prepared by the reaction of phosphorus pentasulfide with the mixture of primary alcohols referred to in Example 1. This mixture was shown to have the following analysis: P, 6.1%

EXAMPLE 4 To a mixture of 213 grams (2.4 moles) of mixed amyl alcohols (as in Example 1) and 176 grams (2.4 moles) of isobutyl alcohol there was added at 5560 C. over a 2-hour period 264 grams (1.2 mole) of phosphorus pentasulfide. The resulting mixture was heated for an additional 1.5 hours at 60-65 C., then filtered to yield a clear liquid filtrate. The zinc salt of this acidic filtrate was prepared according to the procedure of Example 1. The resulting zinc phosphorothioate showed the following analyses: P, 5.7%;S, 12.9%; Zn, 6.2%.

EXAMPLE 5 A mixture of 280 grams (1 mole) of the diamyl phosphorodithioic acid of Example 2 and 254 grams (1 mole) of the diisobutyl phosphorodithioic acid of the same example was prepared and added portionwise over a 1.5- hour period to a suspension of grams (1.1 mole) of Zinc oxide in 508 grams of mineral oil at 7577 C. This mixture was heated for an additional hour at 75 C. and then freed of water and other volatile constituents by heating to a final temperature of 8595 C./120 mm. The residue was filtered to yield a clear filtrate having the following analyses: P, 5.8%; S, 11.9%; Zn, 6.1%.

EXAMPLE 6 A mixture of 447 grams (5.0 moles) of the mixed amyl alcohols of Example 1 and 370 grams (5.0 moles) of n-butyl alcohol was heated to 55 C. and then treated portionwise throughout a 1.75-hour period with 555 grams (2.5 moles) of phosphorus pentasulfide. The resulting mixture was heated for an additional hour at 6065 C. then filtered to yield a clear filtrate. This filtrate was neutralized by the portionwise addition thereof to a suspension of an approximately equivalent amount of zinc oxide in mineral oil. The water formed by the neutralization was removed by distillation and the residue filtered to yield a clear filtrate having the following analyses: P, 5.5%; S, 12.2%; Zn, 6.3%.

EXAMPLE 7 A mixture of 280 grams (1 mole) of the diamyl phosphorodithioic acid of Example 2 and 257 grams (1 mole) of di-n-butyl phosphorodithioic acid was prepared and added portionwise throughout a period of 75 minutes to a suspension of 90 grams (1.1 mole) of zinc oxide in 505 grams of mineral oil at 7577 C. The resulting mixture was heated for an additional hour at 75 C. then freed of water and other volatile constituents by heating to a final temperature of C./ mm. The residue was filtered to yield a clear filtrate having the following analyses: P, 5.6%; S, 11.8%; Zn, 6.0%.

EXAMPLE 8 A mixture of 962 grams (13 moles) of isobutyl alcohol and 624 grams (7 moles) of the amyl alcohol mixture of Example 1 was prepared and heated to 65 C. whereupon 1110 grams (5 moles) of phosphorus pentasulfide was added portionwise throughout a 3-hour period. This mixture was heated for an additional 3 hours at 6971 C. then filtered. A 2224-gram portion of this filtrate (8.0 moles) was added portionwise throughout a 27-hour period to a suspension of 358 grams (4.4 moles) of zinc oxide in 622 grams of mineral oil at 7577 C. The resulting mixture was heated for an additional hour at 75 C., then freed of water and other volatile constituents by heating to a final temperature of 7895 C./ 120 mm. The residue was filtered to yield a clear filtrate having the following analyses: P, 8.6%; S, 17.9%; Zn, 9.1%.

Each of the Zinc salt compositions prepared as in the above examples was tested by heating at 250 F. for 8 hours. In each case the composition was perfectly clear after this test, indicating its thermal stability. Furthermore in every case there was little or no evolution of hydrogen sulfide during the test.

A 75/25 molar mixture of the Zinc salts of di-isobutyl phosphorodithioic acid and di-n-hexyl phosphorodithioic acid, a 50/50 molar mixture of the zinc salts of the diamyl phosphorodithioic acid of Example 2 and di-n-butyl phosphorodithioic acid, a 50/50 molar mixture of the zinc salts of di-isobutyl phosphorodithioic acid and the diamyl phosphorodithioic acid of Example 2, and a 50/50 molar mixture of the Zinc salts of di-isobutyl phosphorodithioic acid and di-n-hexyl phosphorodithioic acid all were prepared as in Example 3. Each of these salt mixtures likewise was found to possess a high degree of thermal stability as measured by the test of heating at 250 F. for 8 hours. Each of these salt mixtures was clear at the conclusion of this test, and none of them evolved hydrogen sulfide throughout the test period.

The thermal stability of the zinc salt compositions of this invention is demonstrated also by data available from a so-called Panel Coke Test. According to the specification of this test procedure a reservoir of a sample of oil to be tested is agitated violently at room temperature so as to provide an oil mist which rises to contact a heated aluminum panel suspended above the reservoir of oil. The temperature of the aluminum panel is maintained at 570 F. and the duration of the test is 3 hours. The thermal stability of the oil sample being tested is measured by an inspection of the deposits which have accumulated on the aluminum panel. The aluminum panel is assigned a rating based upon 10.0 as an indication of the complete absence of any such deposits and 0.0 as an indication of complete coverage of the aluminum panel by such deposits.

The compositions of this invention were tested in a Midcontinent, solvent-extracted, SAE 30 oil which in each case contained also 0.67% (as sulfate ash) of a carbonated basic barium sulfonate and 0.06% (as phosphorous) of the particular zinc phosphorodithioate composition being tested. The results of these tests are shown below.

Zinc phosphorodithioate composition: Rating 1. The zinc salt composition of Example 8 9.5 2. A zinc salt composition prepared as in Example 2 except that the molar ratio of isobutyl radicals to primary amyl radicals is 65:35

rather than 75:25 9.5 3. Zinc di-(4-methylpentyl-2) phosphorodithi oate 5.5

4. The zinc salt of a 60/40 molar mixture of di (4-methylpentyl-2) phosphorodithioic acid and diisopropyl phosphorodithioic acid 6.8 5. Zinc di-methylcyclohexyl phosphorodithioate 1.5

It will be noted that each of the zinc phosphorodithioates of Numbers 3, 4, and 5 contain secondary alkyl groups and that the rating for each of these three compositions is quite inferior to the ratings which correspond to the compositions of this invention.

A further demonstration of the superiority of the compositions of this invention is available from the results of tests performed in a Buda Diesel Engine. These tests were run at an engine speed of 1815-1820 R.P.M., a water jacket temperature of 175180 F., oil temperature of -150 F., under a load of 3000 watts and using a fuel containing a minimum of 1% sulfur. In each case the lubricant tested was a Midcontinent, solvent-extracted, SAE 30 oil containing 0.67% (as sulfate ash) of a carbonated basic barium sulfonate and 0.06% (as phosphorus) of the zinc phosphorodithioate composition being tested. The results of the test were determined after 100 hours and again after hours of operation under the above conditions. The piston was inspected for over-all cleanliness and a rating based on a scale of 0 as completely dirty and 100 as completely clean assigned to the test lubricant. A further rating was also determined based upon the degree to which the top ring groove of the piston was filled with deposits. This latter rating appears as a percent figure so that it obviously ranges from 0 to 100 percent. The results of these tests are as follows:

Overall Percent 150 Hours It is apparent from the above data that the compositions of this invention possess a much higher order of thermal stability than that shown by the zinc phosphorodithioate compositions known heretofore.

Generally speaking, the concentration in a lubricating composition of the zinc salts described herein may range from 0.1% to as high as 20% by weight. When the contemplated use is for inhibition of corrosion or oxidation the concentration should be at the lower end of this range. When intended for use in gear lubricating compositions the concentration should be higher, e.g., 23% and in some instances higher. A preferred range of concentration is 0.5 to 2.0% particularly for use in crankcase lubricants.

Specific illustrations of lubricating compositions containing the zinc salts of this invention in various concentrations are as follows:

Percent 1. SAE 90 oil (gear lubricant) 96 Product of Example 1 4 2. SAE 80 oil (gear lubricant) 92 Chlorinated parafiin wax (40% Cl) 2 Product of Example 2 3 Sulfurized methyl oleate 3 3. SAE 30 oil 97 Product of Example 5 1 Carbonated basic barium petroleum sulfonate 2 4. SAE 30 oil 96 Product of Example 6 2 Carbonated basic calcium petroleum sulfonate 2 5. SAE 20 oil 96 Product of Example 7 1.5 Basic barium dodecyl benzene sulfonate 2.5

6. SAE 20 oil 96.5 Product of Example 8 0.5 Carbonated basic calcium petroleum sulfonate 1.0

Carbonated basic barium salt of phosphosulfurized-olefin polymer 2.0

7. SAE 30 oil 99.4 Product of Example 3 0.6

The lubricating oil base usually is a mineral oil al- 7 though the particular zinc salts of the above examples are also effective for their intended function in synthetic lubricants.

What is claimed is:

1. A lubricating composition comprising a major proportion of a lubricating oil and a minor proportion, sufficient to improve the thermal stability thereof, of the zinc salts of a mixture of phosphorodithioic acids having the structure in which R and R are primary aliphatic hydrocarbon radicals selected from the class consisting of lower molecular weight radicals having less than five carbon atoms and higher molecular weight radicals having at least five carbon atoms, the mole ratio of lower molecular weight radicals to higher molecular weight radicals in the zinc salt mixture being within the range of 1:1 to 3:1.

2. A lubricating composition comprising a major proportion of a lubricating oil and from about 0.1 to about of the zinc salts of a mixture of phosphorodithioic acids having the structure.

in which R and R are primary aliphatic hydrocarbon radicals selected from the class consisting of lower molecular weight radicals having less than five carbon atoms and higher molecular weight radicals having at least five carbon atoms, the mole ratio of lower molecular weight radicals to higher molecular weight radicals in the zinc salt mixture being within the range of 1:1 to 3:1.

3. A lubricating composition comprising a major proportion of a lubricating oil and a minor proportion, sufficient to improve the thermal stability thereof, of the zinc salts of a mixture of phosphorodithioic acids having the structure in which R and R are radicals selected from the class consisting of primary butyl radicals and primary amyl radicals, the mole ratio of butyl radicals to amyl radicals in the zinc salt mixture being within the range of 1:1 to 3:1.

4. A lubricating composition comprising a major proportion of a lubricating oil and a minor proportion, suf ficient to improve the thermal stability thereof, of the 8 zinc salts of a mixture of phosphorodithioic acids having the structure in which R and R are radicals selected from the class consisting of isobutyl and a mixture of amyl radicals, said mixture containing n-amyl, 3% isoamyl, and 32% 2-methyl-l-butyl radicals, the mole ratio of isobutyl radicals to amyl radicals in the zinc salt mixture being within the range of 1:1 to 3:1.

5. The lubricating composition of claim 1 characterized further in that the said zinc salts comprise a mixture of different salts prepared by the separate preparation of individual zinc phosphorodithioates and subsequent mixing of these salts.

6. The lubricating composition of claim 1 characterized further in that the said zinc salts are prepared by reaction of zinc oxide with a mixture of different phosphorodithioic acids.

7. The lubricating composition of claim 1 characterized further in that the said zinc salts are prepared by reaction of zinc oxide with phosphorodithioic acids prepared by the reaction of phosphorous pentasulfide with mixtures of alcohols.

8. A lubricating composition comprising a major proportion of lubricating oil and a minor proportion, sufficient to improve the thermal stability thereof, of the zinc salts of a mixture of phosphorodithioic acids having the structure in which R and R are radicals selected from the class consisting of isobutyl radicals and a mixture of amyl radicals said mixture containing 65% n-amyl, 3% isoamyl, and 32% 2-methyl-1-butyl radicals, the mole ratio of isobutyl radicals to amyl radicals in the zinc salt mixture being within the range of 1:1 to 3:1, said zinc salts prepared by the reaction of zinc oxide with a mixture of phosphorodithioic acids prepared by the reaction of phosphorus pentasulfide with a mixture of alcohols.

References Cited UNITED STATES PATENTS 2,3 64,283 12/ 1944 Freuler. 2,689,220 9/ 1954 Mulvaney. 2,723,236 11/1955 Assetf et a1. 2,838,555 6/1958 Goldsmith. 3,000,822 9/1961 Higgins et al.

PATRICK P. GARVIN, Primary Examiner.

US. Cl. X.R. 260-4293