GB1592659A

GB1592659A - Lubricant compositions

Info

Publication number: GB1592659A
Application number: GB52661/77A
Authority: GB
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1976-12-23
Filing date: 1977-12-19
Publication date: 1981-07-08
Also published as: CH624142A5; DE2756488A1; NL7713918A; FR2375318B1; DE2756488C2; FR2375318A1; JPS5380402A

Abstract

A lubricant composition contains a compound of the formula I <IMAGE> in which the symbols R1, R2 and X are as defined in Patent Claim 1. The compounds of the formula I are used as lubricant additives and, in lubricants, deploy good extreme-pressure lubrication properties which manifest themselves by greatly reduced wear phenomena on the friction partners which are to be lubricated.

Description

(54) LUBRICANT COMPOSITIONS (71) We, CIBA-GEIGY AG, a Swiss Body Corporate, of Basle, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to the use of dithiophosphate derivatives as lubricant additives.

Various additives are usually added to mineral and synthetic lubricants to improve their performance properties. In particular there is a need for additives which will protect the devices to be lubricated from frictional wear. The requirement made of such wear inhibitors is that they shall increase the load bearing capacity of the lubricant and not have a corrosive action on the metal parts to be protected. From Russian patent 295,791 it is known to use N-monosubstituted dithiophosphate acetamide lubricating oil additives, and N-disubstituted dithiophosphate acetamides are known as pesticides from British patent specification 1,255,946.

The surprising invention has now been made that the dithiophosphates of the formula I are superior to the known high pressure lubricant additives, especially in respect of freedom from ashes, thermostability, non-corrosiveness to iron and nonferrous metals, and resistance to hydrolysis.

Accordingly, the invention provides lubricants which contain dithiophosphate lubricant additives of the formula I

wherein R1 and R2, each independently of the other, represents C3-C12-alkyl which can be interrupted by 1 or 2 oxygen atoms, C6-C10aryl or (C1-C12alkyl)-aryl or R, and R2 together represent C2-C12alkylene which can be interrupted by 1 or 2 oxygen atoms, and X represents -OH, -NR3R4,-OH.NR3R4R5, -N HCH,COOH -NHCH2COOR1, -N(CH2COOH)2, -N(CH2COOR1)2, -N(CH2COOH)2.NR3R4R5, -N(CH2COOH.NR3R4R5)2, -NHCH2OH or -N(CHCH2OH)2, wherein R3, R4 and R5, each independently of the other, represents hydrogen or C116alkyl, or R3 and R4 together represent C3-C 12 alkylene which can be interrupted by an oxygen or sulphur atom or by an -NH- or -N(alkyl)- group.

Alkyl represented by Rl and R2 is straight-chain or branched alkyl of 3 to 12 carbon atoms, such as n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, amyl, neopentyl, hexyl, I-methylpentyl, n-octyl, isooctyl, tert-octyl, 2-ethylhexyl, ndecyl, 2-ethyldecyl and n-dodecyl.

Alkyl represented by Rl and R2 which contains 1 or 2 oxygen atoms in the chain is straight-chain or branched alkyl of 3 to 12 carbon atoms, in particular alkoxyalkyl having a total of 3 to 12 carbon atoms, for example 2-methoxyethyl, 2ethoxyethyl, 2-n-propoxyethyl, 2-isopropoxyethyl, 2-n-butoxyethyl and 2-noctoxyethyl.

Alkylene of 2 to 12 carbon atoms represented by R, and R2 is straight-chain or branched alkylene, in particular ethylene or propylene-l, 3 which can be mono-or polysubstituted by C1-C4alkyl, in particular mono- or polymethylated propylene1,3- such as ethylene, propylene-1,3, butylene-1,4, 2-methylpropylene-l,3, 2,2dimethylpropylene- 1,3 and 1,1 3-trimethyipropylene- 1,3.

Aryl represented by Rl and R2 is in particular phenyl, alkylaryl, preferably phenyl which is di- tri-, or, especially, monosubstituted by C1-C12alkyl, preferably C1-C4alkylated phenyl, such as methylphenyl or isoproylphenyl.

Alkyl represented by R3, R4 and R5 is, in addition to the values given for Rl, also methyl or ethyl or C13-C18alkyl, such as n-octadecyl.

C3-C12alkylene represented by R3 and R4 together is in particular optionally mono- or polyalkylated, such as C1-C4alkylated, especially methylated, butylene 1,4 or pentylene-1,5, such as in particular butylene-1,4 or pentylene-1,5 itself. If such an alkylene radical is interrupted by an oxygen or sulphur atom or by an -NH- or -N(alkyl group it is, together with the nitrogen atom to which R3 and R4 are attached, preferably morpholino, thiomorpholino, piperazino or 4methylpiperazino.

Particularly suitable dithiophosphates are those of the formula I in which R1 has the same meaning as R2 and represents C3C8alkyl, or R1 and R2 together represent C2-C8alkylene, and X represents -NR3R4, -OH or -OH.NR3R4R5, wherein each of R3, R4 and r5 independently represents hydrogen or C1-C18alkyl.

Preferred dithiophosphates are in particular those of the formula I in which R1 has the same meaning as R2 and represents C,--C,alkyl, or R1 and R2 together represent C2-C8alkylene, X represents -NR3R4, and R3 has the same meaning as R4 and represents C1Cl8alkyl.

The most preferred dithiophosphates are those named in the Examples The compounds of the formula I, some of which are new, are obtained by methods which are known per se, either according to the process of British patent specification 1,255,946 to give compounds of the formula I in which X is -NR3R4, or by reacting an acid (R1O)(R2O)P(S)-S-CH2-COOH with an amine NR3R4R5 td give compounds of the formula I in which X is -OH.NRR4R5. However, it is also possible to react a dithiophosphoric acid ester with a correspondingly substituted chloroacetamide, such as with the disodium salt of N,N-biscarboxymethylchloroacetamide.

The compounds of the formula I, even when used in very small amounts, act as high-pressure additives in lubricants. Accordingly, mineral and synthetic lubricating oils, as well as mixtures thereof, which contain 0.001 to 5 percent by weight, based on the lubricant, and preferably 0.02 to 3 percent by weight, of a compound of the formula I, exhibit excellent high pressure lubricating properties which become evident due to the greatly reduced signs of wear of the friction surfaces to be lubricated. The suitable lubricants are known to the skilled person and are described for example in the "Schmiermittel Taschenbuch" (Hüthig Verlag, Heidelberg, 1974).

The lubricating oil formulation can contain still further additives which are added to improve certain performance properties, such as antioxidants, metal deactivators, rust inhibitors, viscosity index improves, pour-point depressors, dispersants/detergents and other wear resisting additives.

Examples of antioxidants are: a) Alkylated and non-alkylated aromatic amines and mixtures thereof, for example: dioctylidiphenylamine, mono-tert-octylphenyl-cr- and -p-naphthylamines, phenotriazine, dioctylphenothiazine, phenyl-a-naphthylamine, N,N'-di-sec-butyl-pphenylenediamine. b) Sterically hindered phenols, for example: 2,6-di-tert-butyl-p-cresol, 4,4'bis(2,6-diisopropylphenol), 2,4,6-triisopropylphenol, 2,2'-thio-bis-(4-methyl-6-tertbutylphenol), 4,4'-methylene-bis-(2,6-di-tert-butylphenol). c) Alkyl-, aryl- or aralkylaryl-phosphites, for example, trinonylphosphite, triphenylphosphite, diphenyldecylphosphite. d) Esters of thiodipropionic acid or thiodiacetic acid, for example: dilaurylthiodipropionate or dioctylthiodiacetate. e) Salts of carbamic and dithiophosphoric acids, for example: antimony diamyldithiocarbamate, zinc diamyldithiophosphate. f) A combination of two or more of the above antioxidants, for example: an alkylated amine and a sterically hindered phenol.

Examples of metal deactivators are: a) for copper, for example benzotriazole, tetrahydrobenzotriazole, 2mercaptobenzotriazole, 2,5-dimercaptothiadiazole, salicylidene propylenediamine, salts of salicylaminoguanidine. b) for lead, for example sebacid acid derivatives, quinizarine, propyl gallate. c) A combination of two or more of the above additives.

Examples of rust inhibitors are: a) Organic acids, the esters, metal salts and anhydrides thereof, for example: N-oleyl-sarcosine, sorbitan mono-oleate, lead naphthenate, dodecenylsuccinic anhydride. b) Nitrogenous compounds, for example: I. Primary, secondary or tertiary aliphatic or cycloaliphatic amines and amine salts of organic and inorganic acids, for example oil-soluble alkylammonium carboxylates.

II. Heterocyclic compounds, for example substituted imidazolines and oxazolines. c) Phosphorus-containing compounds, for example: amine salts of phosphoric acid partial esters.

.d) Sulphur-containing compounds, for example: barium dinonylphthalenesulphonates, calcium petroleum sulphonates. e) Combinations of two or more of the above additives.

Examples of viscosity index improvers are: polymethylacrylates, vinyl pyrrolidone/methacrylate copolymers, polybutene, olefin copolymers, styrene/aerylate copolymers.

Examples of pour-point depressors are: polymethacrylates, alkylated naphthalene derivatives.

Examples of dispersants/detergents are: polybutenylsuccinic imides, polybutenylphosphonic acid derivatives, superbasic magnesium, calcium and barium sulphonates and phenolates.

Examples of other wear resisting additives are: compounds which contain sulphur and/or Phosphorus and/or halogen, such as sulphurised vegetable oils, zinc dialkyldithiophosphates, tritoylphosphate, chlorinated paraffins, alkyl- and aryldisulphides.

The invention is illustrated by the following Examples.

Example 1

83.2 g (0.33 mole) of the potassium salt of O,O-diisopropyl-dithiophosphoric acid are suspended in 200 ml of acetone and, with stirring, the suspension is treated with a solution of 53.3 g (0.3 mole) of chloroacetic N,N-diisopropylamide in 200 ml of acetone. The reaction mixture is then stirred for 12 hours at room temperature.

Precipitated potassium chloride is filtered off and the filtrate is completely concentrated and the oily residue is taken up in toluene. After washing three times with water, the organic phase is concentrated to dryness under reduced pressure, affording O,O-diisopropyl-S-(N,N-diisopropyl-carboxamidomethyl)-dithiophos- phate with a melting point of about 30"C. (Additive 1).

The corresponding O,O-dialkyl-S-(N,N-dialkylcarboxamidomethyl)-dithio- phosphates are obtained by repeating the above procedure, but substituting the homologues listed in Table 1 for O,O-diisopropyl-dithiophosphoric acid or chloroacetic-N,N-diisopropylamide or both: TABLE 1

5 t ,J Potassium salt ChloroacetamI.de mp. Thionophosphate Sl OH3 CiCH2C/CH3 CH3 /CH3 2 c3CHOSK NCH2CCH32 oil c3WCHO;SCH2CON CCHcH3 2 U U c\r 3 vr-a ~ > N(CH2CH2CH)2 oil 9 C 4 )3ȮHO 5pstc ClCH20N(C4Hgn)2 oil OHO PSllsOH2OoN(H9 OH3 2 OH3 2 0 S o 3 OH3 OH3 \,, f wf s

hl ii 011 /CH3 cHcHoPscHcoN 6 CH3 PSK H CH oil CH3 SI1 MCH3 CH3HCH2O2 CICH2C-NC2 CH3 2 CH3222 CH2C CH32 c, CH Il /CH3 CH3 FSK 0 /CH3 oil 2 CH3 2 \ CICH2CN CH CHCH2O PSCH2CON C\H 2 2 cH3 0 CH3 u CH3 II 8 3/CHCH2OSK ClCH2CN(CH2CH2CH3)2 oil c3)CHCH2O:SCH2CON ( CH2CH2 CH3 2 'o^ o o o CH3 5 v V" n 9 {CH3CHCH2O2PSK ClCH2C1N(C4H9n)2 oil 1 0=t O=V < w O=V 6 r C r Ex C r -C O < o < ~ 00 TABLE 1 (Continued)

Additive Potassium salt Chloroacetamide m.p. Thionophos phate i (nC4H9 0 5PSK 010H2{N )2c)$0H)2 oil (nH9o)2P5'scH2coN /CH3 c, c, s' S OCH S II CH3 ii (nC4H9O)2PSK OIOH2ONO\H oil (nHso)2FScH2OON C v S 9 OH32 OH3 2 S 0 S 12 (nC4H9O)2PSK ClCH2CN(C8 H 17n)2 oil (nC4H9O)2PSCH2CON(C8H17n)2 CH3 OH3 0 CH3-O 0 S CH3-C 0 S '3 1 ll I ll E PSK ClCH2CN(CH2CH2CH3)2 oil CH2 T n C '1, I OH3 =V CH3-CH-O l w C 0/ \0 E N N 9 | 9 t TABLE 1 (Continued)

Q CH3 0 CH3 CH3 -C -0 S II CH3-C-O S 14 J Sh CH2 PSK o 2 I CH3 wc CH-O CH3 CH a C, oil CH3-C-O S 15 \ii CH PSK CICH2CNCH2C\H I XI! yCH3 2 CH3 2 CH yPSCH2CON CH2C 3 C, , -3 CH3 CH3 CH3 -C -0 S C, CH3-C-OS CH3 16 . \ii CIOH2C0N 700C . II E PSK OH2 PSCH2CON " I I CH3 o OH3 OH3 OH3 -C -0 S 0 I Xii II OH3 -0-0 S E N viz < O Z I O 0== O ~ O < o7 \o o/ \o o/ \o o7 \o = P I P t e I 2 1 9 I 9 t e I D 1 Yo U X P e e S e e S s U U Q U U U U U T TABLE 1 (Continued)

Additive Potassium salt Chloroacetamide m.p. Thionophosphate 0 S OH S OH3 0H2-O %OQO\Jj Mo PSOH2OoN(O8H,7n)2 18 C PSK ClCH2CN(CH7n)2 oil OH3 OH2O N OH2 2 S 0 S 19 (iC8H170)2PSK ClCH2CN(CH2CH2CH3)2 oil (iC8H17 0) 2PSCH2CoN(CH2CH2CH3)2 S 0 S x (iC,H17OY2PSK ClCH2CN(C4H9n)2 oil v U e S 0 H S II /03 II MOH3 (i O8 H1 70)2 PS OH2OON OH 21 (iCH170)2PSK OIOH2ON OH oil A E S C S 0 /0H3 ii 11 22 (9H9O)2P1SK OIOH2ON OHOH32 oil U U 0)2 PSOH2 ON v o = V- V Qz t x t TABLE 1 (Continued)

= o2 o sa XE/ Vz o=tp (d m=t o O T CS Example 2

80 g (0.31 mole) of the potassium salt of O,O-diisopropyl-dithiophosphoric acid are dissolved in water and the solution is treated, with stirring, with a solution of 36.1 g (0.31 mole) of the sodium salt of chloroacetic acid in 10 ml of water. The reaction mixture is stirred for 10 hours at room temperature, then acidified with 50 ml of 6N hydrochloric acid and subsequently extracted with 200 ml of toluene. The toluene phase is washed twice with water and then completely concentrated under reduced pressure, affording O,O-diisopropyl-S-carboxymethyl-dithiophosphate as a light yellow oil.

The corresponding S-carboxymethyl-dithiophosphates are obtained as light yellow oils by repeating the above procedure, but substituting the potassium salt of O,O-diisobutyl-, O,O-di-n-butyl- or O,O-diisooctyl-dithiophosphoric acid for the potassium salt of O,O-diisopropyl-dithiophosphoric acid. O,O-diisooctyl-Scarboxymethyl-dithiophosphate is additive 42. Example 3

Primene 81R 5.12 g (0.02 mole) of O,O-diisopropyl-S-carboxymethyl-dithiophosphate are dissolved in 50 ml of toluene and the solution is treated, with stirring, with 3.8 g (0.02 mole) of Primene 8lR (mixture of primary C12-C15tertalkylamines, Rohm and Haas, USA -- Primene is a Trade mark). The solvent is completely distilled off under reduced pressure, yielding a yellowish transparent oil which is readily soluble in hexane or mineral oil. (Additive 24).

The corresponding ammonium salts are obtained by repeating the above procedure, but substituting the homologues listed in Table 2 for O,O-dusopropyl-S- carboxymethyl-dithiosphophate or Primene 81R or both: TABLE 2

Additive Carboxylic acid Amine m.p. Ammonium salt s t"' H2N04H9 n 25 2 c G z OH3 2 o S o u 26 2 OH3 2 900C OH OH3 OHOPSOH2O00H /OHNH OH3/22 OH3 2 v)=q 27 {OH3/ŎHO2PS OH2 COCH (i)C8H17NH2 oil - ;50H2000H. H2N08H17(i) a Z 28 OH3 2 (Primene JM-T) 3OH (Primene JM-T) OH3 \ V U 2 tO O U U U O o TABLE 2 (Continued)

CL Z I! ii 29 (nC4H90)2 PSCH2COOH (t)c12 H2,NH2 oil (nC4H9 g PSCH2COOH t ~ W v 81-R)E t u" 0H3\ I I /0H3 c: o NH oil OH-0H20P550H2000H 2 H3 2 2 OH3 2 OH3 0 OH3 u U OH3 ll EO A 2 OH3 e 32 (iC8H17 o)2PSCH2CooH (n)C4119N112 oil (iC8H17 0)2 PSCH2COOH 112 NC4llg(n) s v X S U to O V S S V V V' x V r < -s o ~ N TABLE 2 (Continued)

3:" O)2PSCH2COOH HN oN oil UO8H17o)2PSOiOoOH Vz OThH S 34 - ,, - H2NC12H25 (t) oil (iCsH17O)2PSCH2COOH' H2NC12H25(t) 0 0 35 - vX 36 - ,, - HN(C8H17 i)2 oil ,, - HN(CsHi, i)2 V o Example 4

25.4 g (0.01 mole) of the disodium salt of N,N-bis-carboxymethyl-chloroacetamide are charged into 100 ml of dimethyl acetamide together with 4 g (0.1 mole) of sodium hydroxide. Then 21.4 g (01 mole) of dithiophosphoric acid 0,0diisopropyl ester are added dropwise and the reaction mixture is stirred for 12 hours at room temperature. Then 17 ml of hydrochloric acid are added and the reaction mixture is poured into 1500 ml of water. After extraction with chloroform, the organic phase is completely concentrated, yielding O,O-diisopropyl-S-l(N,N- bis-carboxymethyl)-carbamoylmethyll-dithiophosphoric acid ester as a yellowish oil.

Example 5 The procedure of Example 4 is repeated, substituting an equimolar amount of dithiophosphoric acid O,O-diisooctyl ester for dithiophosphoric acid 0,0diisopropyl ester, to give the isobctyl homologue also as a yellowish oil. (Additive 30).

Example 6

15.5 g (0.04 mole) of O,O-diisopropyl-S-[(N,N-biscarboxymethyl)-carbamoyl- dithiophosphoric acid ester are dissolved in 100 ml of toluene and the solution is treated with 9.7 g (0.04 mole) of diisooctylamine. The solvent is completely distilled off under reduced pressure, yielding a reddish yellow oil which is readily soluble in hexane or mineral oil. (Additive 39).

Example 7 The procedure of Example 6 is repeated, substituting an equimolar amount of the corresponding diisopropyl ester for the O,O-diisopropyl ester and an equimolar amount of Primene 81R (vide Example 3) for the diisooctylamine, to give the corresponding ammonium salt as a yellowish oil. (Additive 40).

Example 8

The diammonium salt is obtained by doubling the amount of Primene 81--R in Example 7 and repeating the same procedure. (Additive 41).

Example 9 The exceptional load bearing properties of the lubricant additives are also observed in the test on the gearwheel deformation test stand of the "Forschungsstelle fur Zahnrader und Getriebe" (FZG).

To this end, mixtures of the additives of the present invention were prepared in a non-doped mineral lubricating oil (viscosity: 20 cS-SOOC) and tested with the FZG machine in accordance with DIN 51354 (normal test A/8.3/90). for comparison, non-doped lubricating oil without addition of the additives was also tested.

The results of these experiments are reported in Table 3.

TABLE 3

Concentration Ams Degree of Test Additive in % by weight [mg/KWhj damage I no - 0.61 2 1 0.5 0.1 12 3 5 0.5 0.2 10-11 4 5 1 0.18 11-12 5 14 0.1 0.175 9-10 6 14 0.175 0.12 11 7 14 0.25 0.1 12 8 24 0.5 > 12 9 33 0.5 > 12 Example 10 The following values were determined with a Shell four ball tester for lubricating oils: (Tentative Method IP 239/69, extreme pressure and wear lubricant test for oils and greases, four-ball machine).

I) I.S.L.: initial seizure load, i.e. the load at which the oil film breaks up within a load period of 10 seconds.

2) W.L.:weld load, i.e. the load at which the 4 balls weld together within 10 seconds.

3) W.S.D.: wear scar diameter in mm, i.e. the average wear diameter at a load of 70 kg and 40 kg respectively in 1 hour.

Catenex 41 (trade name of Shell) was used as base oil. TABLE 4

Conc.

Additive in % by weight ISL (kg) WL (kg) WSD (mm) none - 60 160 2.42 (70 kg) 1.1 (40 kg) 1 1% 95 235 | 0.77 (70 kg) 2 1% 110 225 0.90 (70 kg) 3 1% - 190 0.80 (70 kg) 4 | 1% | - | > 200 | 0.70 (70 kg) 5 1% - 200 0.86 (70 kg) 6 1% - 180 1.1 (70 kg) 7 1% - 190 0.8 (70 kg) 8 1% - 180 1.1 (70 kg) 9 1% - 180 1.0 (70 kg) 10 1% - 190 0.5 (40 kg) 11 1% - 180 0.6 (40 kg) 12 | 1% - 180 0.3 (40 kg) 13 1% - 190 0.7 (70 kg) 14 1% 120 205 0.61 (70 kg) 15 1% - > 200 0.70 (70 kg) 16 1% - 180 0.70 (70 kg) 17 1% 180 0.50 (40 kg) 18 1% - 190 0.4 (40 kg) 19 1% - 180 1.0 (70 kg) 20 1% - 180 1.3 (70 kg) 21 1% - 180 1.5 (70 kg) 24 1% 140 > 270 0.3 (40 kg) 25 1% 110 > 230 0.5 (40 kg) 26 1% - > 200 0.5 (40 kg) 27 1% 110 > 270 0.3 (40 kg) TABLE 4 (Continued)

Conc.

Additive in % by weight ISL (kg) WL (kg) WSD (mm) 28 1% 100 > 240 0.3 (40 kg) 29 1% - > 200 1.0 (40 kg) 30 1% - > 200 0.5 (40 kg) 31 1% - > 200 0.4 (40 kg) 32 1% - 190 1.0 (40 kg) 33 1% 120 190 0.4 (40 kg) 34 1% - 190 0.5 (40 kg) 35 1% - | 190 0.5 (40 kg) 36 1% - 190 0.5 (40 kg) 37 1% - 190 0.5 (40 kg) 42 1% 150 210 0;4 (40 kg) 23 1% 100 190 0.4 (40 kg) 22 1% - 190 0.4 (40 kg) 39 1% - > 200 0.4 (40 kg) 40 1% | - > 200 0.4 (40 kg) 41 1% 190 0.4 (40 kg)

Claims

WHAT WE CLAIM IS: 1. A lubricant which contains a dithiophosphate of the formula I.

wherein R1 and R2, each independently of the other, represents C3-C12-alkyl which can be interrupted by 1 or 2 oxygen atoms, C6-C10aryl or(C1-C1@alkyl)-aryl or R1 and R2 together represent C2-C12alkylene which can be interrupted by I or 2 oxygen atoms, and X represents -OH, -NR3R4, -OH.N R3R4R,,, -NHCH2COOH, -NHCH2COOR1, -N(CH2COOH)2, -N(CH2COOR1)2, -N(CH2COOH)2, NR3R4R5, -N(CH2COOH.NR3R4R5)2, -NHCH2OH or -N(CH2CM2OH)2, wherein R3, R4 and R5, each independently of the other, represents hydrogen or C1-18alkyl, or R3 and R4 together represent C3-C12- alkylene which can be interrupted by an oxygen or sulphur atom or by an -NH- or -N(alkyl)- group.
2. A lubricant according to claim 1, wherein R1 has the same meaning as R2 and represents C3-C8alkyl, or R1 and R2 together represent C2-C8alkylene, and X represents-OH, -NR3R4 or -OH.NR3R4R5, in which each of R3, R4 and R5 independently represents hydrogen or C-C18alkyl.
3. A lubricant according to claim 1, wherein R1 has the same meaning as R2 and represents C3-C8alk yl, or R1 and R2 together represent C2-C8alkylene, and X represents-OH, -NR3R4 or -OH.NR3RR5, in which each of R3, R4 and R5 R3 independently represents hydrogen or C1-C18alkyl.
4. O,O-diisopropyl-S-(N,N-diisopropyl-carboxamidomethyl)-dithiophosphate.
5. The compound
6. A lubricant as claimed in Claim I substantially as hereinbefore described with reference to any one of Examples 9 or 10 and Tables 3 or 4.