US3929654A - Ortho alkyl phenol and ortho alkyl phenol sulphide lubricating oil additives - Google Patents

Abstract

An additive mixture for lubricating oils and fuel oils having good antioxidant and anticorrosion properties comprising: (a) 4575 wt.% of an ortho alkyl phenol, (b) 5-20 wt.% of an ortho alkyl phenol disulphide and (c) 15-40 wt.% of an ortho alkyl phenol trisulphide. Optionally the additive may also contain small amounts of the corresponding mono- and tetra-sulphide. Such additives may be made by reacting an alkyl phenol with sulphur in the presence of an organic amine having a pKb of between 2 and 12, e.g. morpholine.

Description

Unite States Patent Brewster et al.

[ 1 Dec. 30, 19'? ORTl-lO ALKYL Pl-lENOL AND ORTHO ALKYL PHENOL SULPHIDE LUBRICATING OlL ADDITIVES Inventors: Phillip William Brewster, Wyoming,

Canada; Peter Collen Hamblin,

Cheadle; James Pennycook Rutherford, Abingdon, both of England Exxon Research & Engineering Co., Linden, NJ.

Filed: Sept. 5, 1974 Appl No.: 503,370

Assignee:

Related U.S. Application Data Continuation-in-part of Ser. No. 417,121, Nov. 11, 1973.

Foreign Application Priority Data Sept. 7, 1973 United Kingdom......... 1980/73 May 23, 1974 United Kingdom 23068/74 U.S. Cl. 252/482; 44/76; 44/78; 252/52; 252/393; 252/404 Int. CL ClOM l/38;C1OM 3/32; ClOM 5/28; ClOM 7/36 Field of Search 44/76, 78; 252/482, 52, 252/493, 404

Primary Examiner-Delbert E. Gantz Assistant Examinerl. Vaughn Attorney, Agent, or Firm-Frank T. Johmann [57] ABSTRACT An additive mixture for lubricating oils and fuel oi having good antioxidant and anticorrosion propertii comprising: (a) 45-75 wt.% of an ortho alkyl phenc '(b) 5-20 wt.% of an ortho alkyl phenol disulphide ar (0) 15-40 wt.% of an ortho alkyl phenol trisulphid Optionally the additive may also contain smz amounts of the corresponding monoand tetr sulphide. Such additives may be made by reacting z alkyl phenol with sulphur in the presence of an o ganic amine having a pl(, of between 2 and 12, e. morpholine.

16 Claims, No Drawings ORTHO ALKYL PHENOL AND ORTHO ALKYL PHENOL SULPHIDE LUBRICATING OIL ADDITIVES This invention relates to additives which act as antioxidant and anti-corrosion additives in lubricating oils.

This application is a continuation-in-part of our prior filed application Ser. No. 417,121 filed Nov. 19th, 1973.

It has been found that certain mixtures of hydrocarbyl substituted phenols and sulphurised hydrocarbyl substituted phenols have very good antioxidant and anti-corrosion properties when added to lubricating oils.

According to this invention an additive mixture suitable for addition to lubricating oils and fuel oils comprises (a) 45-75 wt.% of a phenol substituted with one or two hydrocarbyl groups, one of which must be in the ortho position, (b) -20 wt.% of a hydrocarbyl substituted phenol disulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group and (c) 15-40 wt.% of a hydrocarbyl substituted phenol trisulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

Optionally the additive also contains not more than by weight of the other three components, of (d) a hydrocarbyl substituted phenol tetrasulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group. Also the additive may contain not more than 5% by weight of the three components (a), (b) and (c), of (e) a hydrocarbyl substituted phenol monosulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

In components (a), (b), (c), (d) and (e) the hydrocarbyl substituents are preferably in aliphatic group, e.g. alkyl, cycloalkyl or alkenyl. If desired these substituents may be aromatic such as aryl, aralkyl or alkaryl, e.g. tolyl, phenylethyl or phenyl butyl.

It is preferred that the or each aliphatic group has at least 3 carbon atoms, e.g. from 4 to 20 carbon atoms. Examples are t-butyl, sec-butyl, amyl, hexyl, cyclohexyl, octyl, isooctyl, nonyl, decyl, dodecyl, octadecyl or eicosyl groups. It is preferred that the alkyl groups be branched, and especially tertiary alkyl groups such as t-butyl, t-octyl and t-dodecyl.

Other aliphatic groups which are suitable are those derived from the polymerization of a mono olefin, i.e. an alkenyl group. Suitable olefins are, for example, ethylene, propylene, butylene, l-hexylene, etc. Such alkenyl groups usually contain from 20 to 500 carbon atoms, e.g. from 60 to 70 carbon atoms.

For each component (a) to (e) there may be one or two hydrocarbyl groups per benzene ring, provided one of them is in the ortho position with respect to the hydroxyl group. When there are two hydrocarbyl groups per benzene ring it is preferred that both of the hydrocarbyl groups are in the ortho position with respect to the hydroxyl group, but one of them may, of course, be in another position i.e. meta or para with respect to the hydroxyl group.

It is to be understood that the hydrocarbyl groi may be the same or different both for each separ component and as between the separate componel Generally, however, the hydrocarbyl groups will be same for components (a), (b) and (c) and for com nents (d) and (e) if present. Usually the number hydrocarbyl groups per benzene ring will be the sa for all components and if there are two for each cc ponent usually they will all be in the same POSltlt with respect to the hydroxyl group.

For components (b), (c), (d) and (e) the sulpl linkage between the two benzene rings may be in ortho but is preferably in the para position with resp to the hydroxyl group.

Usually components (b), (c), (d) and (e) can represented by the formulae:

. where R is a hydrocarbyl group, preferably alkyl, wh

may be different in one or more cases, but is usually same; and wherein x for components (b), (c), (d) a (e) is respectively 2, 3, 4 and l.

The preferred proportions for components (a), 4 and (c) are respectively 55-65 wt.%, 10-15 wt.% 2 20-35 wt.%. Typical proportions for components 1 and (e) are respectively 3-7 wt.% and 1-2 wt.%, ba: on the weight of components (a), (b) and (0).

Thus, in a typical additive wherein component (a 2, 6, di-tert butyl phenol and the other components 1 the corresponding 2, 6, di-tert butyl phenol sulphit there is about 62 wt.% of component (a) about 12 wt.% of component (b) about 19 wt.% of component (c) about 5 wt.% of component (d) and about 2 wt.% of component (e) The additive can be made by mixing together individual components or by a novel method accord to this invention.

It is known to produce sulphurisedalkyl phenols reacting an alkyl phenol with sulphur monoor di-cl". ride, but such products tend to cause copper corros probably due to the presence of corrosive sulphur s cies e.g. sulphochlorinated alkyl phenol.

Attempts have been made to avoid the presence chlorine by sulphurising an alkyl phenol by sulp'. alone; but this has not been possible since the react is highly unreactive. We have not surprisingly foun method of preparing sulphurised alkyl phenols us sulphur as the sulphurising agent.

According to this invention sulphurised alkyl pher are prepared by a process in which an alkyl pheno the formula where R is an aliphatic group (eg an alkyl or cycli kyl group) and m and n are integers of from 1 t inclusive provided m plus n is not more than 6, is acted with sulphur in the presence of an organic am having a pK of between 2 and 12.

2 alkyl phenols which may be used have the ford n being integers of from 1 to 5. Preferred alkyl ols are those where m and n are both 1, but alkyl lroxy benzenes (m 2) and dialkyl phenols (n a quite suitable. It is to be understood that when n or more each alkyl group R can be different if ed. It is preferable that the or each aliphatic (alkyl cloalkyl) group R, has at least 3 carbon atoms e.g. 6 to 20 carbon atoms. Examples are t-butyl, samyl, hexyl, cyclohexyl, octyl, isooctyl, nonyl, dodecyl, octadecyl or eicosyl groups. tead of using an alkyl or cycloalkyl phenol it is ale to use other phenols having the same general 11a where the group R is an aliphatic group, e.g. derived from the polymerization of a mono-olee. an alkenyl group. Suitable olefins are for exam- :hylene, propylene, butylene, l-hexylene etc. Such yl groups usually contain from 20 to 500 carbon 5, e.g. from 60 to 70 carbon atoms. amine which is used must have a pK of between 12, and it is preferred that it has a pK of between 1 l0. pK is the negative logarithm (to base of quilibrium constant K of the reaction of the base water. Thus, for the reaction B+ H2O BH++0H- table primary amines include Primene 81-12 (a ry alkyl primary amine containing 12-14 carbon 3 pK 4.2) and the 2-, 3- and 4-amino pyri- (pK 7.1, 7.9 and 4.8 respectively). Suitable ldary amines include pyrrolidine (pK 2.73), azine (pK 4.19), piperidine (pl(;,= 2.80), mOrne (pK =5.67), pyrid-4-one (pK 10.70), imidpK 7.00), pyrazole (pK 11.5) and di-namine (pK 2.72). Tertiary amines which can be include pyridine (pK 8.86), the 2-, 3- and 4- yl pyridines (pK 8.0, 8.3 and 8.0 respectively), tzoline (pK 10.69), cinnoline (pK 11.36), azine (pK 11.90), quinoline (pK 9.15), isoline (pK 8.86) and acridine (pK 8.40). ferred amines are heterocyclic compounds having nino group, especially a secondary amino group. :ularly preferred secondary amines are piperidine norpholine. Very suitable secondary amines are which are liquid at ambient temperatures. a mole ratio of alkyl phenol to sulphur can vary, rom about 2:1 to about 1:2. The amounts of amine )8 small, e.g. 0.1 to 10 wt.%. especially from 1 to 722 based on the weight of alkyl phenol and sulphur. 2 sulphurised alkyl phenol is preferably prepared :ating with stirring the alkyl phenol, flowers of ur and secondary amine. The temperature to 1 the mixture is heated may be from 100 to I, e.g. 150C. The reaction mixture is preferably tained at this temperature with stirring for a perf time e.g. about 45 minutes. After being main- :1 at this temperature the reaction mixture is then 'd to a higher temperature e.g. 170 to 190C pref- 4 erably 180C, and held at this higher temperature for a period of time, e.g. 8 to 12 hours, preferably 10 hours. After being held at this higher temperature, the reaction mixture should be blown with nitrogen e.g. for about 2 hours.

As an even better method the alkyl phenol and sulphur may first be heated with stirring, e.g. to C, and then the secondary amine added.

In order to minimise or prevent solids formation by sublimation in the cold parts of the reactor, the solids being unreacted phenol and a reaction product between sulphur and the amine, it has been found advantageous to use an alcohol as a solvent when reacting the alkyl phenol with sulphur in the presence of the amine. Particularly suitable alcohols include n-butanol, amyl alcohol, isoheptanol and other alcohols having boiling points less than C.

The amount of alcohol used as solvent can vary greatly but amounts of between 5 and 25 wt.% e.g. about 15 wt.%, based on the weight of alkyl phenol, sulphur and amine have been found to be suitable.

Usually the additive mixture contains a diluent oil which may, for example, be any mineral lubricating oil. Other suitable diluent oils include synthetic ester lubricating oils. When making the additive mixture by the novel method described above the starting alkyl phenol is usually dissolved in the oil.

The amount of diluent oil can vary but usually the oil solution contains from 10 to 40 wt.% of oil, e.g. about 15-25 wt.% of oil.

The additive mixture can be added to a lubricating oil especially a crankcase lubricant, where it acts as an antioxidant and an anti-corrosion agent. It can also be added to a fuel oil, e.g. gasoline or diesel fuel, as a minor proportion by weight.

The lubricating oil may be any animal, vegetable or mineral oil, for example, petroleum oil fractions ranging from naphthas to spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, fish oils or oxidised mineral oil.

Suitable synthetic ester lubricating oils include diesters such as di-octyl adipate, dioctyl sebacate, didecyl azelate, tridecyl adipate, didecyl succinate, didecyl glutarate and mixtures thereof. Alternatively, the synthetic ester can be a polyester such as that prepared by reacting polyhydric alcohols such as trimethylol propane and pentaerythritol with monocarboxylic acids such as butyric acid, caproic acid, caprylic acid and pelargonic acid to give the corresponding triand tetraesters.

Also, complex esters may be used as base oils such as those formed by esterification reactions between a dicarboxylic acid, a glycol and an alcohol and/or a monocarboxylic acid.

The preferred quantity of sulphurised alkyl phenol added to the lubricating oil is between 0.01 and 10%, e.g. between 0.1 and 5% by weight based on the total weight of oil plus additive mixture.

Other additives, for example, dispersants (e.g. polybutene succinimides), Vl improvers (e.g. vinyl acetate/fumarate copolymers), corrosion inhibitors (e.g. diol' esters) or additional antioxidants (e.g. phenolic compounds) may be added to the lubricating oil.

EXAMPLE 1 An additive mixture was prepared which had the following composition:

The additive mixture was tested in the Rotary Bomb Oxidation Test (RBOT) ASTM D 2272 method for its effect as an antioxidant in an oil. It was also tested as an anti-corrosion additive, using USA Federal Test Method Standard No. 7918 Method 5321-1 (modified to run for 20 hours). For comparison purposes similar tests were carried out using 2, 6, di-t butyl phenol itself and the corresponding mono-, di-, triand tetra sulphides. Also tests were carried out on the oil alone which was a typical W/30 ashless mineral lubricating oil containing a VI improver and a dispersant. The results obtained were as follows:

It can be seen that the additive mixture shows superior properties both as an antioxidant and as an anticorrosion agent.

EXAMPLE 2 Sulphurised alkyl phenols were prepared by the following method.

a. the alkyl phenol, sulphur, and piperidine were heated with stirring to 150C and maintained at that temperature for 45 minutes.

b. the temperature of the reaction mixture was then increased to 180C and held for 90 minutes.

0. the reaction mixture was then blown with nitrogen for two hours at 180C.

The reaction details and results of ASTM D-130 copper corrosion tests are given below. For comparison an alkyl phenol was sulphurised with sulphur but in the absence of a sulphur-free secondary amine.

Alkyl Phenol Mol.ratio Amine Amine wt.% S Free Cu (AP) APzSulphur of reactant Content AP Corrosion charge wt.% wt.%(a) ASTM D-l(b) Mixed nonyl/ 1 020.56 Nil 1.39 4c dinonyl 1.010.56 Piperidine 1.6 3.37 41 1 1.0:0.84 2.0 5.27 lb Dodecyl 1.0:] .0 2.0 5.54 33 2a (a)determined by liquid chromatography (b)2.5 wt.% in mineral base oil having a viscosity of 150 S.S.U. at 100F.

RBOT

induction Treat level (wt. 5) Period (minutes) Additive EXAMPLE 3 Mixture 1.5 80 Sulphurised alkyl phenols were prepared by heating phenol 1.5 114 h o moms! hide 155 67 wt stirring to 120 C the alkyl phenol and sulphur. disulphi e 0.78 61 Morpholine was then added and the temperature of the de gig :3 mixture raised to 180C with nitrogen sparging. When None 28 the level of H 8 trapped in a caustic soda scrubber including the 23 wt.% oil.

remained constant, usually after 5-15 hours, the temperature was reduced to 120C and the mobile liquid Corrosion was vacuum stripped at 150 mm Hg for 3-6 hours. in T- each case the product was diluted with a mineral base (WW1?) g g oil having a viscosity of 150 s.s.u at 100F to Add? 50 active ingredient.

l j :g 3:2 3-; The reaction details and results of ASTM D-130 disul hide 0,7 12,6 24 copper corrosion tests are given below. trisu phide 0.56 1.0 35.6 tetrasulphide 0.44 0.6 42.2 None 5000 including the 23 wt.% oil.

Alkyl Phenol MoLratio Amine Amine wt.% 8(a) Free(b) Product Cu(d) (AP) AP-Sulphur of reactant content AP yield(c) Corrosion charge wt.% wt.% ASTM D-l30 Nonyl 1 0:1.0 Morpholine 4 96 2c 2,6-di-t-butyl 1.0:1.0 4 7.1 91 'l ortho t-butyl l.0:1.0 4 25 89 2c 2,6di-t-butyl 1 0:2.0 4 14.6 15 4c 1 0:1.0 4 6.6 25 82 2c (a)Product diluted to 75% active ingredient with mineral lubricating oil having a viscosity of 150 S.S.U. at 'F. (b)Determined by thin layer chromatography (c)Excluding free alkyl phenol.

(d)1.0 wt.% of diluted product (75% active ingredient) in mineral lubricating oil having a viscosity of S.S.U. at 100F.

EXAMPLE 4 Antiwear Perfonnance Mole Ratio Shell 4- ball wear Scar (mm) 2,6-di-t-butylphenolzS Sulphurised alkyl phenols were added at 1.0 wt.% concentration to a mineral lubricating oil having a viscosity of 150 S.S.U. at 100F.

The wear scar was determined after 1 hour at 60 kg load. The same oil having no additive gave a wear scar of 2.5 mm

ANTIOXIDANT PERFORMANCE A bearing corrosion rate described by Staudt et al. (SAE 680538) was used to evaluate the bearing weight loss and colour of Peter W1 bearings.

BWL (mg) 36 Bearing Base Oil hours at 140C Colour No additive 1810 Clean plus 1 wt.% sulphurised 2,6- di-t-butyl phenol (ratio as (b) above) 2 Clean The base .oil contained a polyamine dispersant and ethylene propylene copolymer as VI improver to SAE lW-30.

EXAMPLE 5 moles (2060 g) of 2,6-di-tert butyl phenol, 10 mole (320 g) of flowers of sulphur and 372 g of isoheptanol were placed in a reactor and the temperature was raised to 120C. 96 g (4 wt.% based on alkyl phenol plus sulphur) of morpholine was added. The temperature was raised to 180C and maintained at this level for 20 hours with a nitrogen purge. l g of hydrogen sulphide was trapped out in a caustic soda scrubber. The solvent was removed by vacuum stripping and the temperature was raised to 90C and a vacuum of 150 mm Hg absolute maintained until the exhaust gas from the vacuum pump did not discolour lead acetate paper, i.e. the product contained little hydrogen sulphide. The brown liquid product was diluted to 75% active ingredient (a.i.) with a 150 SSU lubricating oil and found to contain 6.4 wt.% sulphur.

EXAMPLE 6 The procedure of Example 5 was repeated using 1075 g of Ethyl 733 (which is a mixture of mono-, diand tri-t-butyl phenols in the ratio of about 15:75:10) instead of 2,6-di-tert butyl phenol, 160 g of sulphur, 25 g morpholine, 127 g of amyl alcohol instead of isoheptanol and a 7 hour reaction time at 180C instead of a 20 hour reaction time. The a.i. product contained 7.5 wt.% sulphur.

EXAMPLE 7 Example 6 was repeated exactly only using about g amyl alcohol and reacting at C for 20 hours. The 75 wt.% a.i. product contained 6.4 wt.% sulphur.

EXAMPLE 8 The procedure of Example 6 was used but using instead of amyl alcohol, 75.6 g of n-butanol. The 75 wt.% a.i. product contained 7.5 wt.% of sulphur.

What is claimed is:

1. An additive mixture comprising a. 45-75 wt.% of a phenol substituted with one or two hydrocarbyl groups, one of which must be in the ortho position,

b. 5-20 wt.% of a hydrocarbyl substituted phenol disulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group and c. 1540 wt.% of a hydrocarbyl substituted phenol trisulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

2. An additive mixture according to claim 1 which also contains not more than 10% by weight based on the weight of components (a), (b) and (c), of (d) a hydrocarbyl substituted phenol tetrasulphide, each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

3. An additive mixture according to claim 1 which also contains not more than 5% by weight based on the weight of the three components (a), (b) and (c), of (c) 1 a hydrocarbly substituted phenol monosulphide each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

4. An additive mixture according to claim 1 wherein the hydrocarbyl substituents in the components are aliphatic groups.

5. An additive mixture according to claim 4 wherein the aliphatic groups are alkyl groups containing 4 to 20 carbon atoms.

6. An additive mixture according to claim 5 wherein the aliphatic group is a tertiary alkyl group.

7. An additive mixture according to claim 6 wherein the tertiary alkyl group is t-butyl, t-octyl or t-dodecyl.

8. An additive mixture according to claim 1 wherein there are two hydrocarbyl groups in the ortho position with respect to the hydroxyl group in each of the components.

9. An additive mixture according to claim 1 wherein the sulphur linkage in any sulphide is in the para position with respect to the hydroxyl group.

10. An additive mixture according to claim 3 which comprises a mixture of compounds each having the formula:

where R is an alkyl group and x is 1, 2, 3 or 4.

11. An additive mixture according to claim 1 which comprises 55-65 wt.% of component (a), -15 wt.% of component (b) and -35 wt.% of component (c).

12. An additive mixture comprising about 62 wt.% of 2, 6, di-tert butyl phenol,

about 12 wt.% of 2, 6, di-tert butyl phenol disulphide,

about 19 wt.% of 2, 6, di-tert butyl phenol trisulphide,

about 5 wt.% 'of 2, 6, di-tert butyl phenol tetrasulphide, and

about 2 wt.% of 2, 6, di-tert butyl phenol monosulphide.

13. An oil solution comprising 10 to 40 wt.% of diluent oil and 60 to wt.% of the additive mixture according to claim 1.

14. A lubricating oil composition comprising a lubricating oil and 0.01 to 10 wt.% of the additive mixture according to claim 11.

15. A lubricating oil composition comprising a major proportion by weight of a lubricating oil and a minor proportion by weight of the alkyl phenol additive mixture according to claim 1.

16. A lubricating oil composition comprising a major proportion by weight of a lubricating oil and a minor proportion by weight of the additive mixture of alkyl phenols according to claim 12.

Claims (16)

1. AN ADDITIVE MIXTURE COMPRISING A. 45-75 WT. % OF A PHENOL SUBSTITUTED WITH ONE OR TWO HYDROCARBYL GROUPS, ONE OF WHICH MUST BE IN THE ORTHO POSTION, B. 5-20 WT. % OF A HYDROCARBYL SUBSTITUTED PHENOL DISULPHIDE, EACH BENZENE RING HAVING ONE OR TWO HYDROCARBYL SUBSTITUENTS, ONE OF WHICH IN EACH RING BEING IN THE ORTHO POSITION WITH RESPECT TO THE HYDROXYL GROUP AND C. 15-40 WT. % OF A HYDROCARBYL SUBSTITUTED PHENOL TRISULPHIDE, EACH BENZENE RING HAVING ONE OR TWO HYDROCARBYL SUBSTITUENTS, ONE OF WHICH IN EACH RING BEING IN THE ORTHO POSITION WITH RESPECT TO THE HYDROXYL GROUP.

2. An additive mixture according to claim 1 which also contains not more than 10% by weight based on the weight of components (a), (b) and (c), of (d) a hydrocarbyl substituted phenol tetrasulphide, each benzene ring having one or two hydrocarbyl substituents, one of whicH in each ring being in the ortho position with respect to the hydroxyl group.

3. An additive mixture according to claim 1 which also contains not more than 5% by weight based on the weight of the three components (a), (b) and (c), of (e) a hydrocarbly substituted phenol monosulphide each benzene ring having one or two hydrocarbyl substituents, one of which in each ring being in the ortho position with respect to the hydroxyl group.

4. An additive mixture according to claim 1 wherein the hydrocarbyl substituents in the components are aliphatic groups.

5. An additive mixture according to claim 4 wherein the aliphatic groups are alkyl groups containing 4 to 20 carbon atoms.

6. An additive mixture according to claim 5 wherein the aliphatic group is a tertiary alkyl group.

7. An additive mixture according to claim 6 wherein the tertiary alkyl group is t-butyl, t-octyl or t-dodecyl.

8. An additive mixture according to claim 1 wherein there are two hydrocarbyl groups in the ortho position with respect to the hydroxyl group in each of the components.

9. An additive mixture according to claim 1 wherein the sulphur linkage in any sulphide is in the para position with respect to the hydroxyl group.

10. An additive mixture according to claim 3 which comprises a mixture of compounds each having the formula:

11. An additive mixture according to claim 1 which comprises 55-65 wt.% of component (a), 10-15 wt.% of component (b) and 20-35 wt.% of component (c).

12. An additive mixture comprising about 62 wt.% of 2, 6, di-tert butyl phenol, about 12 wt.% of 2, 6, di-tert butyl phenol disulphide, about 19 wt.% of 2, 6, di-tert butyl phenol trisulphide, about 5 wt.% of 2, 6, di-tert butyl phenol tetrasulphide, and about 2 wt.% of 2, 6, di-tert butyl phenol monosulphide.

13. An oil solution comprising 10 to 40 wt.% of diluent oil and 60 to 90 wt.% of the additive mixture according to claim 1.

14. A lubricating oil composition comprising a lubricating oil and 0.01 to 10 wt.% of the additive mixture according to claim 11.

15. A LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PROPORTION BY WEIGHT OF A LUBRICATING OIL AND A MINOR PROPORTION BY WEIGHT OF THE ALKYL PHENOL ADDITIVE MIXTURE ACCORDIDNG TO CLAIM 1.

16. A lubricating oil composition comprising a major proportion by weight of a lubricating oil and a minor proportion by weight of the additive mixture of alkyl phenols according to claim 12.