FR3062392A1 - USE OF A LIPOIC ACID ESTER AS ANTI-WEAR ADDITIVE AND / OR FRICTION MODIFIER - Google Patents

Abstract

The present invention relates to the use of lipoic acid ester as an anti-wear additive and / or friction modifier as well as compositions comprising this type of additive.

Description

Holder (s):

OLEON NV.

O Extension request (s):

(© Agent (s): SANTARELLI.

© USE OF AN ESTER OF LIPOIC ACID AS ANTI-WEAR ADDITIVE AND / OR FRICTION MODIFIER.

The present invention relates to the use of lipoic acid ester as an anti-wear additive and / or friction modifier as well as the compositions comprising this type of additive.

FR 3 062 392 - A1

The present invention relates to the use of a certain type of ester as an anti-wear additive and / or friction modifier, to compositions comprising it, as well as to their preparation process.

Anti-wear and friction modifier additives are particularly used in the field of lubricants.

A lubricating composition generally comprises an oil, usually the majority constituent (ie the constituent whose content is the highest), and one or more additive (s).

An additive is used to reinforce one or more intrinsic property (s) of the oil and / or provide it with one or more additional property (s).

An anti-wear additive reduces wear on parts, such as metal parts, when brought into contact.

Among the anti-wear additives, mention may be made of polysulphides, dithiocarbamates, chlorinated paraffins, phosphates, and thio-phosphates. Zinc dialkyl dithiophosphate (ZDDP) is one of the most used additives because it is particularly effective as an anti-wear product. However, this additive has a high toxicity. The decomposition of ZDDP releases various sulfur gases, such as hydrogen sulfide (H ₂ S) and mercaptans.

There is therefore always a need for anti-wear additives of renewable origin, respectful of the environment and effective with a mineral oil.

A friction modifier additive (or friction reducer) reduces the friction of parts, such as metal parts, when brought into contact.

Among the most used friction modifying additives, there may be mentioned esters such as glycerol mono oleate (GMO), certain fatty acids and amides such as diethanolamide oleate (ODEA).

The publication Lipoate ester multifunctional lubricant additives; Biresaw et al .; Industrial & Engineering Chemistry Research (2016), 55, 373-383, describes monoesters of renewable origin and their use as a multifunctional additive in vegetable oil. In particular, these are esters of lipoic acid and C4-C18 monoalcohols. The authors show that these purified esters are additives that improve the performance of an oleic sunflower oil, such as its viscosity index, its antioxidant properties and extreme pressure. On the other hand, these monoalcohol monolipoates bring no anti-wear and friction-modifying properties to this vegetable oil. In fact, oleic sunflower oil additivated to 5% by mass of monoalcohol monolipoate has friction coefficients and results in terms of wear equivalent or superior to those obtained with non-additive oleic sunflower oil (see Table 8 of this publication).

However, the work of the inventors has made it possible to demonstrate that, unexpectedly, these same esters made it possible to improve the anti-wear property as well as the friction-modifying property of a mineral oil.

The invention therefore relates to the use of an ester of lipoic acid as an anti-wear additive and / or friction modifier for mineral oil.

Esters of lipoic acid have extreme pressure, antioxidant and / or viscosity index improving properties.

The invention therefore also relates to the use of an ester of lipoic acid as an anti-wear additive and / or friction modifier for mineral oil, and as an extreme pressure additive, anti-oxidant additive and / or additive improving the viscosity index.

Lipoic acid is also called 5- (1,2-dithiolane-3-yl) pentanoic acid, 6,8-dithiooctanoic acid or thioctic acid.

Mineral oils are oils from petroleum refining. They are essentially made up of carbon and hydrogen atoms, such as paraffinic oils, hydrorefined oils, hydrocracked oils and hydroisomerized oils.

Mineral oils are classified into three groups:

group I oils: these oils have a saturated hydrocarbon content of less than 90% by mass, an aromatic hydrocarbon content of more than 1.7% by mass, a sulfur content of more than 0.03% by mass, and a viscosity index of between 80 and 120;

group II oils: these oils have a saturated hydrocarbon content greater than 90% by mass, an aromatic hydrocarbon content less than 1.7% by mass, a sulfur content of less than 0.03% by mass, and a viscosity index of between 80 and 120;

group III oils: these oils have a saturated hydrocarbon content of more than 90% by mass, an aromatic hydrocarbon content of less than 1.7% by mass, a sulfur content of less than 0.03% by mass, and a viscosity index of more than 120;

the percentages by mass being given relative to the mass of the oil.

It should be noted that, within the framework of the present request, and unless otherwise stipulated, the ranges of values indicated are understood to be bounds included.

More particularly, the lipoic acid ester is represented by the following formula (I):

n being an integer between 1 and 8, representing the number of substituents L on R;

and in which R is an acyclic hydrocarbon chain, linear or branched, optionally substituted by oxygen atoms, that is to say, a chain made up of carbon, hydrogen atoms and optionally one or more oxygen atom (s).

Preferably, the lipoic acid ester has at least 16 carbon atoms, preferably at least 24 carbon atoms.

The lipoic acid ester can be a mixture of several lipoic acid esters.

Esters of lipoic acid are capable of being obtained by esterification of lipoic acid with an alcohol or by transesterification of lipoic acid with a triglyceride or a carboxylic acid ester other than a lipoic acid ester.

Preferably, the lipoic acid esters are capable of being obtained by esterification of the lipoic acid with an alcohol.

The esterification can be carried out by any known method, in particular by chemical or enzymatic means. The esterification can for example be carried out by heating the reagents, lipoic acid and alcohol, to a temperature of at least 90 ° C., in the presence or not of a catalyst. Esterification can also be performed using an enzyme by heating to 70 ° C.

Alcohol is understood to mean an acyclic hydrocarbon chain, linear or branched, substituted only by one or more hydroxyl function (s) and optionally comprising one or more oxygen atom (s). Alcohol has no other heteroatoms or other substitutions.

As alcohols comprising a hydroxyl function, also called monoalcohols, mention may be made of methanol, ethanol, isobutanol, heptan-1-ol, octan-1ol, 2-ethylhexanol, 7-methyl-octan -1-ol, 6-methyl-pentan-1-ol, nonanol (or nonan-1-ol or pelargonic alcohol), decan1-ol, dodecan-ol and octadecan-1-ol.

As alcohols comprising two hydroxyl functions, also called diols, mention may be made of 1,2-ethanediol or ethylene glycol, 1,6-hexanediol, 1,2propanediol or propyiene glycol, 1,3-propanediol, 1,4 -butanediol, 2-butyl-2ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, neopentylglycol, dimer diol, polyethylene glycol such as diethylene glycol and triethylene glycol.

As alcohols comprising three hydroxyl functions, also called triols, mention may be made of glycerol and trimethylolpropane.

As alcohol comprising more than three hydroxyl functions, mention may be made of pentaerythritol, di-pentaerythritol and polyglycerols.

Preferably, the alcohol has one, two or three hydroxyl functions. More preferably, the alcohol has one or two hydroxyl function (s), in other words, the alcohol is a monoalcohol or a diol.

Preferably, the alcohol contains at least 8 carbon atoms, more preferably at least 18 carbon atoms. In particular, it is chosen from the group consisting of n-octan-1-ol, 2-ethylhexanol, 7-methyl-octan-1-ol, nonanol (or nonan-1-ol or pelargonic alcohol), decan1-ol, dodecan1-ol, octadecan-1-ol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol and dimer diol.

By “diol dimer (s)” is meant a diol dimer or a mixture of diol dimers capable of being obtained by intermolecular dimerization of one or more unsaturated carboxylic acid (s), followed by a reduction reducing the acid functions into alcohol functions.

Each unsaturated carboxylic acid can have one or more unsaturations. Preferably, the unsaturation is a double bond.

Each unsaturated carboxylic acid preferably contains at least 16, more preferably at least 18 carbon atoms.

Advantageously, the unsaturated carboxylic acid is an unsaturated fatty acid derived from a renewable substance, such as vegetable oils, animal oils and animal fats. In particular, the unsaturated carboxylic acid is an unsaturated fatty acid containing from 16 to 24 carbon atoms, preferably from 18 to 22 carbon atoms. More particularly, the fatty acid is oleic acid, linoleic acid or a mixture of fatty acids from a vegetable oil such as rapeseed oil, castor oil, sunflower oil, l soybean oil, linseed oil or safflower oil.

According to a first embodiment, the dimer (s) diol is a dimer diol. It is capable of being obtained by intermolecular dimerization of an unsaturated carboxylic acid, in particular of an unsaturated fatty acid.

Thus, preferably, the diol dimer has from 32 to 48 carbon atoms, more preferably from 36 to 44 carbon atoms, even more preferably, the diol dimer has 36 carbon atoms.

Generally, a diol dimer is a mixture of isomers, each of which may have an acyclic or cyclic structure.

Preferably, the dimer diol comprises more than 50% by mass, more preferably more than 70% by mass of acyclic isomer (s), the percentages by mass being given on the total mass of dimer diol.

According to a second embodiment, the diol dimer (s) is a mixture of diol dimers capable of being obtained by intermolecular dimerization of several (at least two, preferably at least three) unsaturated carboxylic acids, in particular, unsaturated fatty acids. More particularly, the diol dimer (s) is a mixture of diol dimers which may each and independently contain from 32 to 48 carbon atoms, preferably from 36 to 44 carbon atoms.

In particular, the mixture of diol dimers is obtained from fatty acids of a vegetable oil chosen from the group consisting of rapeseed oil, sunflower oil, soybean oil, linseed oil and safflower oil.

As indicated previously, each diol dimer present in the mixture of diol dimers can be in the form of different isomers.

Preferably, the mixture of diol dimers comprises more than 50% by mass, more preferably more than 70% by mass, of acyclic isomer (s), the percentages by mass being given on the total mass of dimer diol.

Advantageously, at least 50%, preferably at least 60% by mass of dimer (s) diol of the total mass of dimer (s) diol has 36 carbon atoms and more than 50% by mass, preferably more than 70% by mass of diol dimer (s), out of the total mass of diol dimers, is acyclic.

By total mass of dimer (s) diol is meant the total mass of molecules of dimer diol.

Advantageously, the dimer (s) diol is saturated.

Alternatively, the lipoic acid esters can be obtained by transesterification.

Transesterification can be carried out according to any known method, by chemical or enzymatic means. Transesterification can for example be carried out by heating the reagents, lipoic acid and, triglyceride or ester of carboxylic acid other than an ester of lipoic acid, at a temperature of at least 90 ° C., in the presence or not of catalyst . Transesterification can also be done using an enzyme, such as Novozym 435 by heating to 60 ° C.

Triglycerides advantageously come from renewable resources, such as oils and fats of vegetable and animal origin.

For example, triglycerides can come from rapeseed, sunflower, soy, safflower, flax and tallow oils.

The carboxylic acid esters have one or more ester functions, preferably one to three, more preferably one or two.

Advantageously, the esters of carboxylic acids are esters of fatty acids.

Preferably, in the esters of carboxylic acids, the carboxylic acid contains at least 8 carbon atoms, more preferably at least 18 carbon atoms.

In particular, the carboxylic acid ester is chosen from the group consisting of caprylic acid esters, capric acid esters, lauric acid esters, myristic acid esters, acid esters palmitic, esters of stearic acid, esters of oleic acid, esters of linoleic acid, esters of linolenic acid and mixtures thereof.

Preferably, the carboxylic acid ester is a methyl ester or an ethyl ester.

Whatever the method of preparation of the lipoic acid ester, advantageously, all the hydroxyl functions present on the lipoic acid ester are esterified.

Subsequent to the process for preparing the lipoic acid ester, there may be added one or more stages (s) of purification of the ester.

The purification can be done by any separation method known to those skilled in the art.

Advantageously, the purification of the lipoic acid ester (s) can comprise one or more of the following methods: filtration, evaporation, liquid / liquid extraction and / or passage over a mineral substrate or a resin such than silica.

Preferably, the lipoic acid ester is a monoester, a diester, and / or a lipoic acid triester, more preferably a monoester and / or a diester. In particular, the lipoic acid ester is preferably a monolipoate, a dilipoate and / or a trilipoate, more preferably a monolipoate and / or a dilipoate.

More particularly, the lipoic acid ester is an ester or a mixture of lipoic acid esters represented by formula (I) in which n is between 1 and 3, preferably equal to 1 or 2.

In particular, the monoester is chosen from the group consisting of n-octyl lipoate, 2-ethylhexyl lipoate, 7-methyloctyl lipoate, nnonanyl lipoate, decyl lipoate, dodecyl lipoate, lipoate tetradecanyl, hexadecanyl lipoate, octadecanyl lipoate, dioleylglyceryl lipoate.

The diester is chosen from the group consisting of lipoic acid and 1,6-hexanediol esters, lipoic acid and 2-butyl-2-ethyl-1,3-propanediol esters, acid esters lipoic and oleylglycerol, and esters of lipoic acid and diol dimers.

According to the UIPAC nomenclature, the name of an R-COOR 'ester is based on the name of the corresponding carboxylic acid (R-COOH) whose ending "ique" becomes "ate", and on the name of the alkyl group. (R ') which ends with "yle".

However, it sometimes happens that the name of the ester is formed by the names of the reagents, such as acids and alcohols, used in the process for preparing the ester.

A third nomenclature used consists in using the name of the carboxylic acid in "ate" and the name of the alcohol as such.

Thus, n-octyl lipoate, ester of lipoic acid and n-octanol and n-octanol lipoate, denote the same compound.

The invention also relates to a method for improving the anti-wear and / or friction-modifying property of a mineral oil by adding an ester of lipoic acid.

The invention also relates to a composition comprising an ester of lipoic acid and a mineral oil.

The lipoic acid ester is as described above, including the advantageous and preferential modes.

The mineral oil is advantageously a group I, II and / or III mineral oil as described above.

Group II mineral oils are widely used in the metalworking industry. Also, advantageously, the oil of the composition according to the invention is a group II mineral oil.

Preferably, the composition according to the invention comprises a total amount of lipoic acid ester (s) of at least 2% by mass, more preferably at least 5% by mass, more preferably still at least 10% by mass relative to the mass of the composition.

A person skilled in the art knows how to choose the lipoic acid ester (s) best suited for the application chosen, as well as the appropriate quantity.

Preferably, the composition according to the invention further comprises an additive other than an ester of lipoic acid.

Advantageously, the composition according to the invention is a lubricating composition.

Preferably, the lubricant composition is a metalworking oil, a motor oil, a transmission oil, a hydraulic oil, or a gear oil.

In the field of lubricants, the oil represents at least 50% by mass of the mass of the lubricating composition.

Advantageously, the additive other than a lipoic acid ester is chosen from the additives used in the field of lubricants, such as antioxidant additives, anti-wear additives, additives improving the viscosity index, additives friction modifiers, extreme pressure additives, pour point lowering additives, anti-foam additives, demulsifying additives, corrosion inhibiting additives, thickening additives, detergent additives and dispersant additives.

A person skilled in the art knows how to choose the most suitable additive (s) according to the chosen application, such as a lubricant application.

The additive other than an ester of lipoic acid can be chosen from:

- antioxidant additives, such as dialkyl-dithiophosphates, substituted phenols and / or aromatic amines;

- anti-wear additives, such as zinc dialkyl-dithiophosphates and / or phosphorus derivatives, these can be added in an amount less than that usually used;

- viscosity index improving additives, such as polymers of olefin copolymers (OCP), polyisobutenes, polymethacrylates, diene polymers, polyalkylstyrenes and / or molybdenum derivatives;

- friction modifying additives other than an ester of lipoic acid, such as glycerol monooleate (GMO), these can be added in an amount less than that usually used;

- extreme pressure additives, such as organometallic derivatives of molybdenum, compounds derived from fatty acids, phosphosulfur molecules and / or borates;

- pour point lowering additives, such as metallic soaps, carboxylic acids, polymethacrylates, alkylphenols, dialkylaryl esters of phthalic acid, maleate-styrene copolymers, naphthalene paraffins and / or polyesters of vinyl fumarate acetate type;

- anti-foam additives, such as silicone oils, silicone polymers and / or alkyl acrylates;

- demulsifying additives, such as propylene oxide copolymers;

- anticorrosion (or anti-rust) additives such as alkali and / or alkaline earth metal sulfonates (Na, Mg, Ca salts), fatty acids, fatty amines, akenylsuccinic acids and / or their derivatives, benzotriazole, and / or tolyltriazole;

- thickening additives, such as fatty esters;

- detergent additives, such as calcium and / or magnesium salts of alkylaryl sulfonates, alkylphenates, alkylsalicylates and / or their derivatives;

- dispersing additives, such as alkenyl succinimides, succinic esters and / or their derivatives, and / or Mannich bases;

- metal deactivating additives, such as heterocyclic compounds containing nitrogen and / or sulfur, for example triazole, tolutriazole, and benzotriazole;

or their mixtures.

Note that an additive can have several properties, such as zinc dialkyldithiophosphate which is an antioxidant, anti-wear, anti-corrosion and slightly dispersing additive.

Due to the anti-wear, friction-modifying, viscosity index, antioxidant and extreme pressure properties of lipoic acid esters, the presence of one of these esters in the composition makes it possible to reduce the amount usually necessary additive other than an ester of lipoic acid, thereby reducing the environmental impact of this other additive, especially if it has a certain toxicity.

In particular, the amount of the additive other than a lipoic acid ester chosen from the group consisting of anti-wear additives, friction-modifying additives, additives improving the viscosity index, anti-additives oxidant and extreme pressure additives, may be adapted according to the amount of lipoic acid ester (s) present in the composition according to the invention.

The invention also relates to a process for preparing a composition according to the invention, comprising a step of mixing a mineral oil, with an ester of lipoic acid.

The mineral oil and the ester are as described above, including the advantageous and preferential modes.

The compositions according to the invention are particularly suitable for use as a lubricating composition and / or in the field of the petroleum industry.

The invention will be better understood in the light of the following examples, given by way of illustration, with reference to:

Figure 1, which is a graph representing Stribeck curves (i.e. curves representing the friction coefficient measurements as a function of the speed of rotation) obtained from a non-additive mineral oil and the same additive oil of 10% by mass of diol dimer dilipoate (1 test and 2 repetitions with each sample);

Figure 2, which is a graph representing the average improvement (on the test and the two repetitions of Fig. 1) of the coefficient of friction between a non-additive mineral oil and the same additive oil of 10% by mass of dilipoate of diol dimers;

Figure 3, which is a graph representing the average improvement (on the test and the two repetitions of Fig. 1) of the coefficient of friction between a non-additive mineral oil and the same additive oil of 7% by weight of lipoate of n-octyl;

Figure 4, which is a graph representing Stribeck curves obtained from a non-additive mineral oil, from the same additive oil of 10% by mass of dimer diol dilipoate, from the same additive oil of 7% by mass n-octyl lipoate and the same oil additive with 10% by mass of GMO.

Example 1 Preparation of Lipoic Acid Esters

1.1- Preparation of a diol dimer dilipoate

100 g of lipoic acid (98% lipoic acid, CAS number: 1077-28-7) and 132.5 g of diol dimers (Radianol ® 1990 sold) are added to a reactor equipped with a distillation circuit. by Oleon NV, composed of at least 98% of diol dimers, of which at least 95% of diol dimers containing 36 carbon atoms, and of at least 75% of acyclic isomers).

The mixture is heated to 140 ° C, with stirring. The progress of the reaction is followed by thin layer chromatography. After 24 hours of reaction, the alcohol conversion is complete.

The reaction mixture is purified on Combi-Flash by passage over a column of silica gel, with heptane as eluent with a gradient of 0 to 5% acetone.

After evaporation of the eluent, the dimer diol dilipoate is obtained in the form of a yellowish viscous oil.

The mixture of diol dimer dilipoate obtained contains 98.3% of diol dimer dilipoate containing 52 carbon atoms and 76% of acyclic isomers.

1.2- Preparation of an n-octyl lipoate

The preparation uses lipoic acid (lipoic acid, 98%, CAS number: 1077-28-7) and n-octan-1-ol from Merck, according to the preparation process described in the publication Lipoate ester multifunctional lubricant additives; Biresaw et al .; Industrial & Engineering Chemistry Research (2016), 55, 373-383.

Example 2 Preparation of Samples of Compositions According to the Invention and Comparative Samples

Samples were prepared using as starting materials: mineral oil of group II Chevron Neutral oil 220R (hereinafter called “mineral oil”), the dilipoate of dimer diol of Example 1, the n-octyl lipoate of Example 1, the zinc dialkyldithiophosphate anti-wear additive (hereinafter designated "ZDDP"), and the friction modifying additive of glycerol monooleate Radiasurf® 7149 by Oeon (hereinafter designated "GMO") .

The content of the samples is indicated in Table 1 below:

Sample Content Mineral oil 100% mineral oil Composition C Mineral oil + 10% * by mass of diol dimer dilipoate Composition E Mineral oil + 2% * by mass of diol dimer dilipoate Composition I Mineral oil + 7% * by mass of n-octyl lipoate Composition K Mineral oil + 10% * by mass of n-octyl lipoate Comparative 1 Mineral oil + 1% * by mass of ZDDP Comparison 2 Mineral oil + 10% * by mass of GMO

* on the total mass of the sample

Table 1: Contents of the samples tested

The composition samples and the comparative samples are obtained by simple mixing, that is to say bringing the compounds into contact and manual stirring.

Example 3: Evaluation of the anti-wear property of the lipoic acid esters using the 4-ball test

The anti-wear property of the lipoic acid esters prepared in Example 1 was evaluated with the four-ball wear test according to standard ASTM D4172-94 (2016). To do this, the samples prepared in Example 2 were tested. The test consists in applying three balls disposed on the same plane and immersed in a sample, a weight of 40 kg with rotation at 1200 rpm for one hour at 75 ° C via the 4 ^th ball placed at the intersection of the other three marbles.

The test results are collated in Table 2 below:

Sample Wear (mm) wear gain (%) mineral oil 1.110 Composition C 0.625 -43.7% Composition E 0.650 -41.4%

Composition I 0.775 -30.2% Composition K 0.783 -29.5%

Table 2: Results of the four-ball wear tests

The addition of lipoic acid ester in mineral oil makes it possible to reduce the wear of the metal in contact with the compositions according to the invention. In particular, the addition of 2% by mass of diol dimer dilipoate in a group II mineral oil makes it possible to reduce the wear of the metal by more than 41%.

EXAMPLE 4 Evaluation of the Friction-Modifying Property of Esters of Lipoic Acid

To quantify the reduction in friction, the friction coefficient of the samples prepared in Example 2 (mineral oil, compositions C, E and I) was measured on an MCR-502 rheometer equipped with an MCR d tribometer 'Anton-Paar.

A 100Cr6 steel ball is brought into contact with 3 100Cr6 steel cylinders with a rotation ranging from 1000 mm / s to 0.01 mm / s at 25 ° C and applying a force of 10 Newtons. The three cylinders and the ball are immersed in 0.5 mL of the test sample. The coefficient of friction as a function of the speed of rotation is then measured to establish a Stribeck curve.

With mineral oil (not additive), it was observed that by repeating the test 2 times, the friction coefficient at low speed (<0.25 mm / s), increases appreciably each time (Fig. 1) .

Conversely, with composition C, the coefficient of friction remains stable after 2 repetitions, at values much lower than those obtained with mineral oil alone (Fig. 1).

At low speeds and therefore maximum metal-to-metal contact, a reduction in the coefficient of friction is observed up to 53% with composition C (Fig. 2).

The same results are obtained with composition E, by lowering the loading from 10% to 2% by mass of dimer diol dilipoate in mineral oil.

Similarly, at low speeds and therefore maximum metal-to-metal contact, a reduction in the coefficient of friction is observed up to 44% with composition I (Fig. 3).

The addition of 7% by mass of n-octyl lipoate or 2% by mass of dilipoate of dimers diol or in a mineral oil of group II makes it possible to reduce the friction respectively by 44 or 53% compared to a use non-additive oil.

Esters of lipoic acid can therefore be used as friction modifier additives.

Example 5: Evaluation of the anti-wear and friction-modifying property of the lipoic acid esters using the HFRR test

The anti-wear and friction-modifying properties of the lipoic acid esters prepared in Example 1 were evaluated using the HFRR test (“High Frequency Reciprocating Rig”), a device with high frequency reciprocating motion, in a similar manner to that is described in ASTM D6079-11 (2016).

To do this, the samples (mineral oil, compositions C and K) prepared in Example 2 were tested.

The test involves applying a weight to a moving ball on a disc to measure wear and the coefficient of friction at different temperatures. A few milliliters of each sample are used to immerse the ball before each test.

Wear (mm) Gain on wear (%) Coefficient of friction 70 ° C 100 ° C 130 ° C mineral oil 255.3x231.8 0.166 0.202 0.241 Composition C 153.9 x 156.6 - 40% x -32% 0.142 0.114 0.111 Composition K 213.6 x 176.5 -16% x -24%. 0.142 0.125 0.143 Table 3: Tesi results s HFRR

With composition C, the wear of the ball is reduced to 153.9 x 156.6, ie 40% x 32% decrease. There is also a decrease in the coefficient of friction of 14% at 70 ° C, 44% at 100 ° C and 54% at 130 ° C.

With composition K, a decrease in ball wear is also observed, a decrease of 16% x 24%. The coefficient of friction is also reduced by 14% at 70 ° C, 38% at 100 ° C and 41% at 130 ° C.

This HFRR test confirms the anti-wear property of lipoic acid esters and also shows their friction-modifying property.

Example 6: Comparison - Four-ball wear test with the anti-wear additive ZDDP

The comparative test was carried out under the same conditions as those described in Example 3.

The test carried out with Comparative 1 prepared in Example 2 leads to wear of 0.570 mm, ie a reduction in wear of 48.6%.

Dimer diol dilipoate has an anti-wear property (decrease of 43.7%) comparable to ZDDP, which is one of the most used anti-wear additives today.

Example 7: Comparative - Rheometer test with the GMO friction modifier additive

The test with Comparative 2 prepared in Example 2 was carried out under the same conditions as those described in Example 4.

This test shows that lipoic acid esters lower the friction coefficient of mineral oil, similar to GMO, especially in the case of dimer diol dilipoate (Fig. 4).

Claims (9)

1. Use of an ester of lipoic acid as an anti-wear additive and / or friction modifier for mineral oil. 2. Use of an ester of lipoic acid according to claim 1, and as an extreme pressure additive, antioxidant additive and / or additive improving the viscosity index. 3. Use according to claim 1 or 2, wherein the lipoic acid ester has at least 16 carbon atoms. 4. Use according to any one of claims 1 to 3, wherein the lipoic acid ester is a monoester, a diester and / or a lipoic acid triester. 5. Composition comprising an ester of lipoic acid and a mineral oil, 6. Composition according to claim 5, in which the mineral oil is a group II mineral oil. 7. Composition according to claim 5 or 6, further comprising an additive other than an ester of lipoic acid. 8. A method of preparing a composition according to any one of claims 5 to 7, comprising a step of mixing a mineral oil of group I, II and / or III, with an ester of lipoic acid. 9. Use of the composition according to any one of claims 5 to 7, as a lubricating composition. 1/2 Composition C Composition: = Repeat 1 Composition C - Repeat 2 Mineral oil --Mineral oil - Repeat 1 Mineral oil - Repeat 2 0.5 t — I CN χΓ 00 LO CN m LO t — I t — I O o O O o t — I m LO CN LD o O o O O o o o o t — I CN LD O o 'o' o 'o' o 'o' o 'o' o 'o' I-Î LH t — I m in m LO o o O O in 00 ^ f xT CN in in in 00 O in in in 00 LO CD 00 t — I t — I O t — I rn r < LH t — I in LH t — I t — I CD t — I m LO CN LD o CD t — I CN LD CD Speed mm / s