US 3312620 A
Description (OCR text may contain errors)
United States Patent Ofitice Patented Apr. 4, 1967 This invention relates to novel synthetic lubricants. In particular, the invention relates to the use of certain N,N-disubstituted amides as lubricant base stocks.
The development of synthetic lubricants has been largely responsive to the very specific and stringent lubrication requirements of modern technology: suitable physical properties over a wide temperature range, high thermal and oxidative stability, and even resistance to nuclear radiation. A particular advantage of synthetic lubricants is the relative ease with which their physical, chemical, or performance properties can be regulated by a proper choice of starting materials. These considerations have given rise to a great number of novel products, some of which have found wide acceptance in industrial and military applications. Synthetic esters for aircraft gas-turbine engines are among the outstanding achievements in this field. As different and more demanding requirements are imposed on lubricants, newer, more stable compositions will be developed. The present invention is an outgrowth of the search for such lubricants.
It has now been discovered that certain N,N-disubstituted amides are effective lubricant base stocks. These compounds are either monoor diamides having the general formula R2 where X is a C to C preferably C to C hydrocarbylene group, preferably alkylene, arylene, alkarylene, or aralkylene; R and R are C to C preferably C to C alkyl or aryl groups, preferably alkyl, and R is selected from the group consisting of hydrogen and where R and R are C to C preferably C to C alkyl or aryl groups, preferably alkyl. Representative amides of the invention are N-butyl-N-phenyl-n-octanamide; N,N-di-n-octyl benzamide; N,N-di-n-butyllauramide; bis- (N,N di n hexyl)adipamide; N,N-dicyclohexylbenzamide; N cyclohexyl N propylbenzamide; N,N-di-npropyl p tertbutylbenzamide; bis(N,N di n propyl) phthalamide; bis(N,N-di-n-propyl)isophthalamide; and N-n-hexyl-N-n-propylisophthalamide. The present invention contemplates the use of these compounds and mixtures thereof as base lubricants; i.e., a major proportion (at least half) of the lubricant comprises the abovedefined N,N-disubstituted amides. It is preferred that amides of the invention comprise at least 75%, preferably at least 90% by weight of the final lubricant composition. These N,N-disubstituted amides are superior to unsubstituted amides and N-rnonosubstituted amides in that they are generally lower melting compounds having sub stantially less tendency to crystallize under conditions of low-temperature operation .or shutdown. Furthermore, although the disubstituted amides are lower melting than amides having a lesser degree of substitution, they do not have correspondingly high vapor pressures.
The present invention is based on the discovery that certain N,N-disubstituted amides, when used as lubricants e.g. for gas turbine engines, are particularly efliective regarding stability and ability to maintain engine cleanliness even at temperatures over 300 F. In accordance with this discovery, the invention contemplates a method of lubricating an engine, especially a gas turbine engine, which comprises maintaining on a surface to be lubricated such as bearings and other points of wear of the engine a film of lubricant comprising a major portion of N,N-disubstituted amide as defined above.
It has also been found that the amides of the invention are remarkably responsive to common oxidation inhibitors. Addition of small amounts of well-known inhibitors has a considerably greater inhibiting effect on the amides of the invention than on comparable ester lubricants; e.g. pentaerythrityl esters. Oxidation inhibitors which may be employed in the lubricants of the invention are, for example, aryl amines, thiodiarylamines, phenolic compounds, and mixtures thereof. Organic nitrogencontaining antioxidants, especially amines, are preferred. Examples of suitable antioxidants are phenyl-alpha-naphthylamine, dinaphthylamine, phenyl-beta-naphthylamine, diphenylamine, triphenylamine, 2,2-dipyridy1amine, 4,4- dipyridylamine, 2-arninopyridine, 4-aminopyridine, 2,6- diaminopyridine, phenyl-Z-pyridylamine, 3-aminoquinoline, phenyl-3-quinolylamine, phenothiazine, 3,7-dioctylphenothiazine, phenylthio-alpha-naphthylamine, phenylthio-beta-naphthylamine, beta,beta-thiodinaphthylamine, alkylated bisphenols, etc. These antioxidants are generally present in an amount of from about 0.1 to 10%, preferably 0.2 to 5%, by weight of the final lubricating composition.
Arnides of the invention were examined and compared to well-known ester lubricants in high-temperature airoxidation tests.. Air was bubbled at a rate of mls./ minute through a 20 gm. sample of oil maintained at 450 F. The induction period of the sample was defined as the test time required before two consecutive readings, one hour apart, showed that 5% v. or more of the oxygen passing through the oil was being absorbed. To provide a standard reference, all oils contained 1% w. phenylalpha-naphthylamine and 0.2% w. of a salt of monochloromethylphosphonic acid and mixed C to C primary amines. In addition, each sample contained 20 p.p.m. each of Cu and Fe, added as octoates, to simulate operating conditions. The test results are described in Table I below.
TABLE I.-RESULTS OF AIR OXIDATION TESTS Base stock: Induction period, hrs. Pentaerythrityl ester 1 5 N,N-di-n-butyllauramide 25 N,N-di-n-propylbenzamide 45 N,N-di-n-propyl-p-tertbutylbenzamide 43 Bis(N,N-di-n-propyl)phthalamide 45 Bis(N,N-di-n-propyl)isophthalamide 45 1 A mixture of 67% v. C4-C9 acid esters of pentaerythritol and 33% w. C5C1o acid esters of dipentaerythritol. As is apparent from the table, the induction periods of amide formulations are far longer than that of an identically-inhibited ester lubricant. Essentially no deposits or sludging were observed in any of the amides that were observed, except for N,N-di-n-butyllauramide which showed a slight amount of sludging. Benzamides and phthalamides, which are preferred lubricants of the invention, formed dark oils but did not contain insolubles even after over 40 hours of testing at 450 F.
To illustrate the lubrication properties of the amides of the invention, four-ball wear tests were conducted at various temperatures and bad conditions using a representative amide, bis(N,N-di-n-propyl)phthalamide. The four-ball wear test is a well-known method of determining lubrication properties; this test is described in detail by Larsen and Perry in Trans. Am. Soc. Mech.
ing, 67, 45-50 (1945). For comparison, similar tests lere conducted on a commercially available synthetic ster base oil which is known to have good lubrication haracteristics. Thisester (designated ester base in he table) is a mixture of 67% pentaerythrity tetraester If C C alkanoic acids, and 33% dipentaerythrityl hexaster of C C alkanoic acids. The results are shown n Table 11 below.
TABLE II.FOUR-BALL WEAR TEST RESULTS where R and R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons and a minor amount of an oxidation inhibitor.
' 2. A method of lubrication which comprises maintaining on surfaces to be lubricated a film of lubricant comprising a major amount of an N,N-disubstituted amide having the formula Speed Temp. Load Time Scar (r.p.m.) F.) (kg) (hr.) diameter Ester base 1,800 500 15 1 1. 08 3is(N,N-di-n-propyl)phthalamide 1, 800 500 15 l 1. Ester b 600 500 50 1 1. 25 lis(N,N-di-n-propyl)phthalami 600 500 50 1 0. 81 Est-er base 600 175 2 0.83 lis(N,N-di-n-propyl)phthalamide 600 175 15 2 0. 44
From these results it appears that the amides have ery good lubricating properties, even being superior to vell-known synthetic ester oils (under some conditions).
Several well-known methods are available for making he amides of the invention. Two methods which are generally applicable are illustrated below.
Example I.Preparati0n of N,N-di-n-pr0pylbe nzamia'e Example II.-Preparati0n of bis(N,N-di-n -pr0pyl)- phthalamide Two moles of di-n-propylarnine and one mole of phthalic acid were heated to 175 C. Water produced in the reaction was collected in a trap. The product was purified as in Example I; yield was about 75% w.
The amide lubricants of the invention may be blended with one or more additives to further enhance their properties. Such additives include viscosity-index improvers, pour point depressants, extreme-pressure agents, antifoamants, and the like.
The lubricants of the invention have general applicability for the lubrication of moving metal parts, and are especially preferred for high-temperature lubrication, e.g., over 300 F.
We claim as our invention:
1. A lubricant composition comprising a major amount of an N,N-disubstituted. amide having the formula R1 RX-CN/ where X is selected from the group consisting of alkylene, arylene, alkarylene, and aralkylene having 3to 12 carbons, R and R are selected from the group consisting of alkyl and aryl having 3 to 12 car-bons, and R is selected from the group consisting of hydrogen and.
' Ii R- -X-ON where X is selected from the group consisting of alkylene, arylene alkarylene, and aralkylene having 3 to 12 carbons, R and R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons, and R is selected from the group consisting of hydrogen and where R and- R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons.
3. A method of lubricating a gas turbine engine which comprises maintaining on the bearings and other points of wear of the engine a film of an N,N-dis-ubstituted amide having the formula where X is selected from the group consisting of alkylene, arylene, alkarylene, and aralkylene having 3 to 12 carbons, R and R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons, and R is selected from the group consisting of hydrogen and where R and R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons.
4. A method of lubrication which comprises maintainmg on surfaces to be lubricated a film of lubricant comprising a major amount of an N,N-disubstituted amide having the formula r f t a NOXCN R4 R2 major amount of an N,N-disubstituted amide having the formula Where X is selected from the group consisting of alkylene, arylene, alkarylene, and aralkylene having 3 to 12 carbons, R and R are selected from the group consisting of alkyl and aryl having 3 to 12 carbons, .and R is selected from the group consisting of hydrogen and i if where R and R are selected from the group consisting of .alkyl and aryl having 3 to 12 carbons and 0.1% to 10% by weight of an organic nitrogen-containing antioxidant.
8. The lubricant of claim 7 wherein the antioxidant is an organic amine. 9. The lubricant of claim 7 phenothiazine.
10. The lubricant of claim 8 wherein the amine is -an aromatic iamine.
11. The lubricant of claim 10 wherein the amine is phenyl-wnaphthylamine.
12. The lubricant of claim 10 wherein the amine is diphenylamine.
13. A lubricant as defined in claim 1 wherein the oxidation inhibitor is a phenolic oxidation inhibitor.
wherein the antioxidant is References Cited by the Examiner UNITED STATES PATENTS 2,691,010 10/1954 Anderson 260558 X 3,115,519 12/1963 Crouse et al. 252-56 X 3,121,691 2/1964 Eickemeyer 252- X 3,226,324 12/ 1965 Eickemeyer 252-51.5 X 3,251,661 5/1966 Retzlolf et .al. 252-464 X DANIEL E. WYMAN, Primary Examiner. P. P. GARVIN, Assistant Examiner.