EP0271368B1 - Polysulfurized olefin compositions, their preparation and their use as lubricant additives - Google Patents

Description

The invention relates to the field of organic sulfur additives used in particular to improve the extreme pressure properties of lubricants; it relates more particularly to new products of the polysulphurized olefin type, their preparation and their use as additives for mineral or synthetic lubricants.

There are described in the prior art a number of processes aimed at the preparation of polysulphurized olefins usable as extreme pressure additives for lubricants.

• (1) on fait réagir du monochlorure de soufre avec un excès d'une oléfine de 2 à 5 atomes de carbone, en particulier l'isobutène, à une température de 20 à 80_°C, de manière à former un "adduct" ;
• (2) on fait réagir l'"adduct" de la première étape avec un sulfure de métal alcalin (de préférence du sulfure de sodium) et du soufre élémentaire, utilisés dans un rapport de 1,8 à 2,2 moles de sulfure métallique par atome-gramme de soufre, la proportion de sulfure de métal alcalin étant en outre de 0,8 à 1,2 mole par mole d'"adduct", et la réaction étant effectuée en présence d'un alcool ou d'un solvant hydro-alcoolique, au reflux ; et
• (3) on fait réagir le produit obtenu, qui contient de 1 à 3 % de chlore, avec une base minérale en solution aqueuse au reflux, jusqu'à ce que la teneur résiduelle en chlore du produit soit inférieure à 0.5 %.

In particular, US patents US-A-3,471,404 and 3,697,499 describe a process, the main steps of which are as follows:

• (1) sulfur monochloride is reacted with an excess of an olefin of 2 to 5 carbon atoms, in particular isobutene, at a temperature of 20 to 80 _° C, so as to form an "adduct";
• (2) the adduct of the first step is reacted with an alkali metal sulfide (preferably sodium sulfide) and elemental sulfur, used in a ratio of 1.8 to 2.2 moles of metallic sulfide per gram atom of sulfur, the proportion of alkali metal sulfide being further from 0.8 to 1.2 moles per mole of "adduct", and the reaction being carried out in the presence of an alcohol or a solvent hydro-alcoholic, at reflux; and
• (3) the product obtained, which contains 1 to 3% chlorine, is reacted with a mineral base in aqueous solution at reflux, until the residual chlorine content of the product is less than 0.5%.

It is indicated in these prior patents that the sulfur content of the products obtained could be 40 to 60% by mass. In reality, it is most often close to 46% by mass. These products can be used as extreme pressure additives for lubricating oils, transmission fluids or greases, the lubricating bases considered consisting of mineral oils and certain synthetic oils.

• (1) on fait réagir à environ 30 - 100°C du monochlorure de soufre avec une monooléfine aliphatique de Cs à Ce (en général l'isobutène) de préférence en présence d'un promoteur consistant en un alcool inférieur, de manière à former un "adduct" ;
• (2) on fait réagir cet "adduct" avec du soufre et du sulfure de sodium (préparé par exemple à partir de NaOH, NaHS et/ou H₂S) dans un rapport de 0,1 à 0,4 atome-gramme de soufre par mole de sulfure de sodium, en milieu hydroalcoolique à une température allant de 50_°C au reflux ; et l'on récupère le produit obtenu sans traitement au moyen d'une base.

Furthermore, US Patent US-A-4,204,969 describes a fairly similar process for preparing polysulphurized olefins usable as extreme pressure additives for lubricating oils; this process includes the following main steps:

• (1) sulfur monochloride is reacted at approximately 30-100 ° C. with an aliphatic monoolefin of Cs to Ce (generally isobutene) preferably in the presence of a promoter consisting of a lower alcohol, so as to form an "adduct";
• (2) this "adduct" is reacted with sulfur and sodium sulfide (prepared for example from NaOH, NaHS and / or H ₂ S) in a ratio of 0.1 to 0.4 gram-atom of sulfur per mole of sodium sulfide, in an alcoholic medium at a temperature ranging from 50 _° C. to reflux; and the product obtained is recovered without treatment by means of a base.

JI is indicated in the single example that the product has a sulfur content of 49% by mass and a viscosity at 37.8 _° C (100 _° F) of 8.6 mm ² / s (cSt).

When, using the methods described in the prior art, it is sought to increase the sulfur content of the additives by bringing into play an increased proportion of elemental sulfur, compared to the sulfide or the alkaline hydrogen sulfide involved, obtains products which are no longer sufficiently soluble in synthetic lubricating oils (for example of the polyalphaolefin type) or even in mineral lubricating oils, to be usable as extreme pressure additives. Furthermore, the kinematic viscosity of the products thus obtained is generally too high.

• (1) on fait réagir au moins un composé choisi parmi le monochlorure et le dichlorure de soufre avec au moins une monooléfine de 2 à 5 atomes de carbone (en général l'isobutène), en une proportion de 1,5 à 2,5 moles de monooléfine par mole de monochlorure et/ou de dichlorure de soufre, formant ainsi un produit d'addition ou "adduct" ;
• (2) on met en contact ledit "adduct" et au moins un halogénure d'hydrocarbyle choisi parmi les chlorures, les bromures et les iodures d'alkyles de Ci à C)₂, de cycloalkyles ou de cycloalkyles substitués de Cs à C₁₂ et d'arylalkyles ou d'arylalkyles substitués de C₆ à C₁₂, la proportion dudit halogénure d'hydro- carbyle correspondant à 1 - 70 % en atomes-gramme d'halogène par rapport au nombre d'atomes-gramme d'halogène de l'ensemble formé par ledit "adduct" et ledit halogénure d'hydrocarbyle (soit 0,015 1,9 atome-gramme d'halogène pour 100 g d'"adduct"), avec au moins un composé sulfuré choisi parmi les sulfures, les hydrogénosulfures et les polysulfures de métaux alcalins, d'ammonium ou de métaux alcalino-terreux, mis en jeu en une proportion d'environ 0,4 à 0,8 mole par atome-gramme d'halogène contenu dans l'ensemble formé par ledit "adduct" et ledit halogénure d'hydrocarbyle, et une proportion de soufre élémentaire de 0 à 7 atomes-grammes par mole dudit composé sulfuré, au sein d'un milieu consistant en de l'eau ou un mélange d'eau et de monoalcool aliphatique ;
• (3) on chauffe le mélange résultant et, après séparation en deux phases, on récupère l'oléfine polysulfurée dans la phase organique ; et
• (4) on traite éventuellement le produit issu de l'étape (3) par un composé basique tel qu'une base minérale.

French patent applications FR-A-2 563 231 and 2 571 380, considered as a whole, or European application EP-A-159 936 teach a process for the preparation of polysulphurized olefins defined in substance by the following steps:

• (1) reacting at least one compound chosen from monochloride and sulfur dichloride with at least one monoolefin of 2 to 5 carbon atoms (generally isobutene), in a proportion of 1.5 to 2.5 moles of monoolefin per mole of monochloride and / or sulfur dichloride, thus forming an adduct or "adduct";
• (2) the said "adduct" is brought into contact with at least one hydrocarbyl halide chosen from chlorides, bromides and iodides of C 1 to C ₂ alkyl, of cycloalkyls or of substituted C ₅ to C ₁₂ cycloalkyls and of arylalkyls or substituted arylalkyls of C ₆ to C ₁₂ , the proportion of said hydrocarbyl halide corresponding to 1 - 70% by gram atoms of halogen relative to the number of gram atoms of halogen of the group formed by said "adduct" and said hydrocarbyl halide (ie 0.015 1.9 gram atoms of halogen per 100 g of "adduct"), with at least one sulfur compound chosen from sulphides, the hydrogen sulfides and polysulfides of alkali metals, ammonium or alkaline earth metals, used in a proportion of about 0.4 to 0.8 mole per gram atom of halogen contained in the assembly formed by said "adduct" and said hydrocarbyl halide, and a proportion of elemental sulfur from 0 to 7 gram atoms per mole of di t sulfur compound, in a medium consisting of water or a mixture of water and aliphatic monoalcohol;
• (3) the resulting mixture is heated and, after separation into two phases, the polysulphurized olefin is recovered in the organic phase; and
• (4) optionally treating the product from step (3) with a basic compound such as an inorganic base.

It is indicated in these previous applications that the products thus prepared are polysulphurized olefins, which can have a sulfur content generally ranging up to approximately 45-65% by mass. Their kinematic viscosity at 100 _° C varies according to their sulfur content. It can be around 4 to 20 mm ² / s. Their halogen content (mainly chlorine) is generally less than about 1% by mass and more often than about 0.6% by mass.

Their solubility in lubricating oils, in particular hydrogenated polyalphaolefins (PAO) depends on the operating conditions used for their preparation.

• (1) réaction d'un halogénure de soufre tel que le monochlorure de soufre S₂CI₂, le dichlorure de soufre SCI₂ ou un mélange des deux réactifs sur une oléfine aliphatique contenant de 3 à 6 atomes de carbone, pour obtenir un produit d'addition désigné par "adduct" ;
• 2) réaction dudit "adduct" avec du soufre, du sulfure de sodium Na₂S, un alkyl - mercaptan contenant de 1 à 12 atomes de carbone et éventuellement de l'hydrosulfure de sodium NaSH, dans un milieu hydroalcoolique et dans un domaine de température compris entre 50_°C jusqu'au reflux, pour former ladite oléfine sulfurée ; et
• (3) séparation de ladite oléfine sulfurée du milieu hydroalcoolique.

US Patent US-A-4,563,302 describes a process which also makes it possible to obtain polysulphurized olefins of increased solubility in polyalphaolefins (PAO) (up to 8% by mass); this process includes the following main steps:

• (1) reaction of a sulfur halide such as sulfur monochloride S ₂ CI ₂ , sulfur dichloride SCI ₂ or a mixture of the two reactants on an aliphatic olefin containing from 3 to 6 carbon atoms, to obtain a product addition designated by "adduct";
• 2) reaction of said "adduct" with sulfur, sodium sulfide Na ₂ S, an alkyl mercaptan containing from 1 to 12 carbon atoms and optionally sodium hydrosulfide NaSH, in an aqueous-alcoholic medium and in a domain of temperature between 50 _° C until reflux, to form said sulfurized olefin; and
• (3) separation of said sulfurized olefin from the hydroalcoholic medium.

United States patent US-A-3 873 454 describes an extreme pressure additive for lubricants obtained by reaction of isobutylene and a sulfur halide to form an "adduct", followed by the reaction of said "adduct" with an alkaline mercaptate, in an inert medium to form the compound of formula:

The alkaline mercaptate used can be sodium, potassium, lithium or calcium mercaptate. The reaction medium is generally a lower alcohol (C ₁ to C ₄ ). The desired compound (which has a sulfur content of about 53%) is obtained with a yield of about 45% by weight, the remaining 55% consisting of a mixture of sulfides and unsaturated polysulfides.

In the only example of preparation of the compound, it is indicated that a dispersion of solids is obtained by stirring sodium mercaptate in ethanol, before adding the "adduct" prepared separately.

The desired compound is finally obtained in the form of a solid, which is separated and purified.

However, such a compound has limited solubility in mineral oils and in synthetic oils of the polyalphaolefin type.

It has now been discovered that it is possible to prepare new (poly) sulfurized compositions whose solubility in mineral oils and synthetic lubricants, in particular of the hydrogenated polyalphaolefin type, is further increased and may even in some cases be total. These compositions are therefore advantageously usable as additives for lubricants. They improve notam extreme pressure properties.

• - une étape (1) dans laquelle on fait réagir au moins un composé choisi parmi le monochlorure et le dichlorure de soufre avec au moins une monooléfine aliphatique répondant à la formule générale R^1- C(R²)=CH₂ dans laquelle Rⁱ représente l'atome d'hydrogène ou un radical alkyle de 1 à 3 atomes de carbone et R² représente l'atome d'hydrogène ou un radical méthyle, de manière à former un produit d'addition ou "adduct" ;
• - une étape (2) dans laquelle on fait réagir, en général en milieu alcoolique, ledit produit d'addition avec au moins un mercaptate-polysulfure répondant à la formule générale R³ S_x M, dans laquelle R³ représente un radical aliphatique, renfermant par exemple de 1 à 14 atomes de carbone, ce radical aliphatique pouvant comporter au moins un groupement fonctionnel (par exemple au moins un groupe hydroxyle) ; un radical aromatique, éventuellement substitué par un ou plusieurs radicaux aliphatiques et renfermant par exemple de 6 à 14 atomes de carbone ; ou un radical hétérocyclique renfermant au moins un hétéroatome choisi parmi l'azote, le soufre et l'oxygène ; M représente un atome ou un groupement monovalent correspondant à une base minérale de formule générale MOH ; et x prend une valeur moyenne d'au moins 1,2 et pouvant aller par exemple jusqu'à environ 7 ; et éventuellement
• - une étape (3) dans laquelle le produit de l'étape (2) est mis en contact avec une solution aqueuse alcaline.

In general, the polysulphurized olefin compositions of the invention can be defined as being obtained by a process which comprises:

• - a step (1) in which at least one compound chosen from monochloride and sulfur dichloride is reacted with at least one aliphatic monoolefin corresponding to the general formula R ^1- C (R ² ) = CH ₂ in which R ⁱ represents the hydrogen atom or an alkyl radical of 1 to 3 carbon atoms and R ² represents the hydrogen atom or a methyl radical, so as to form an adduct or "adduct";
• a step (2) in which said adduct is reacted, in general in an alcoholic medium, with at least one mercaptate-polysulfide corresponding to the general formula R ³ S _x M, in which R ³ represents an aliphatic radical, containing for example from 1 to 14 carbon atoms, this aliphatic radical possibly comprising at least one functional group (for example at least one hydroxyl group); an aromatic radical, optionally substituted by one or more aliphatic radicals and containing, for example, from 6 to 14 carbon atoms; or a heterocyclic radical containing at least one heteroatom chosen from nitrogen, sulfur and oxygen; M represents an atom or a monovalent group corresponding to an inorganic base of general formula MOH; and x takes an average value of at least 1.2 and which can range, for example, up to approximately 7; and eventually
• - a step (3) in which the product of step (2) is brought into contact with an alkaline aqueous solution.

The aliphatic monoolefin used in step (1) contains from 2 to 5 carbon atoms. Isobutene is most often used (R1 = Rz = CH _s ). The monoolefin is used more particularly in an amount of 1.5 to 2.5 moles per mole of mono- and / or sulfur dichloride. It is generally introduced into the liquid mono- and / or dichloride at 20-80 _° C, more specifically at 30-50 _° C.

The adduct, or "adduct", obtained at the end of step (1) consists of a mixture of sulfur compounds in which the average proportion of sulfur can be approximately 1 to 2 gram atoms per mole , depending on whether sulfur dichloride, sulfur monochloride or a mixture of the two is used at the start. The proportion of chlorine is approximately 2 gram atoms per mole of product.

The mercaptate polysulphides of general formula R ^3- S _x M used in step (2) can be more particularly prepared by reaction, preferably in alcoholic medium, of at least one mercaptan of general formula R ³ SH with a mineral base MOH, R ³ and M being defined as above, then with elemental sulfur in a suitable proportion so that the average value of x in the formula of the product obtained is approximately 1.2 to 7.

As examples of mercaptans of formula R ³ SH which can advantageously be used to prepare mercaptate-polysulphides, mention may be made of methylmercaptan, ethylmercaptan, n-propylmercaptan, n-butylmercaptan, isobutylmercaptan, tert.-butylmercaptan, tert .-nonylmercaptan, tert.-dodecylmer-captan, mercaptoethanol, 3-mercapto-propanediol-1,2, phenylmercaptan, tolylmercaptans, as well as 2-mercapto benzimidazole, 2-mercapto-benzothiazole, 2-mercapto-benzoxazole , mercapto-2 methyl-1 imidazole, mercapto-2 (and 4) pyridines, mercapto-2 pyrydinol-3, mercapto-2 thiazoline and mercapto-5 triazole.

The reaction between the mercaptan and the mineral base is generally carried out at a temperature of 20 to 100 ° C. The alcoholic medium can comprise at least one aliphatic monoalcohol containing, for example, from 1 to 5 carbon atoms. Most often methanol is used. In general, 200 to 400 ml of aliphatic monoalcohol are used per mole of mercaptan involved. Depending on whether the mineral base used is soda, potash or ammonium hydroxide, the product obtained is a sodium mercaptate, potassium or ammonium of formula R ^3- SM (M representing Na, K or NH ₄ ).

To prepare the mercaptate-polysulfide, the mercaptate thus formed is reacted with elemental sulfur, brought into play in a proportion ranging for example from about 0.2 to 10 gram atoms per mole of mercaptate. This reaction can be carried out at a temperature of 20-100 ° C.

In step (2), where the mercaptate-polysulfide of formula R ³ S _X M is reacted, preferably in an alcoholic medium, with "adduct" obtained at the end of step (1 ), said "adduct" is generally added to the alcoholic solution of said mercaptate-polysulfide in a proportion such that said mercaptate-polysulfide represents a molar excess of about 0.1 to 70% relative to the stoichiometry of 2 moles per mole of said "adduct", the reaction medium being maintained for example at a temperature ranging from -10 _° C. to the reflux temperature of the alcoholic solvent involved.

At the end of step (2), a polysulphurized olefin composition is obtained which can then be treated, in a step (3), with an alkaline aqueous solution, more particularly an aqueous solution of soda or potassium hydroxide having example a concentration of about 1 to 50% by mass. The amount of alkaline solution used can for example be from 0.1 to 5 times the mass amount of crude polysulphurized olefin to be treated.

The polysulfurized olefin compositions of the invention may have a sulfur content of about 25 to 60% by mass; their chlorine content is generally less than 0.1% by mass, most often less than 0.05% by mass. They can advantageously be used as extreme pressure additives for lubricating oils.

It is possible to adjust the solubility in oils and the extreme pressure properties by the choice of the mercaptan used and the proportion of elemental sulfur used relative to said mercaptan. In most cases, their solubility is complete.

A first application of the polysulfurized olefin compositions of the invention relates more particularly to the formulation of oils intended for the lubrication of gears. The base oils can be of mineral or synthetic origin. Synthetic oils include in particular oligomers of olefins such as triene, tetra- and pentamer of decene-1 obtained by oligomerization in the presence of LEWIS acids. Other α-olefins can of course be used, for example Ce to C ₁₄ α-olefins.

It is also possible to use alkylbenzenes, such as mono and dialkylbenzenes, or alternatively synthetic esters originating from mono- or polycarboxylic acids (such as sebacic acid, fatty acids, etc.) and monoalcohols or polyols, (such as 2-ethyl hexanol, trimethylol-propane, etc.).

The polysulphurized olefins considered can then be added to the lubricating oils at concentrations ranging for example from 0.5 to 10% by mass.

These additives can be used in combination with phosphorus additives, such as metallic dialkyl- or diaryldithiophosphates, phosphites and organic phosphates.

Other conventional additives can be added, such as antioxidants, anti-rust agents, copper passivators, anti-foam agents, friction reducers, in the usual proportions.

A second application of the polysulphurized olefin compositions of the invention as extreme pressure additives for lubricants relates more particularly to the formulation of oils intended for working with metals (cutting, forming, etc.).

In this application, the concentration of additive used is generally from 0.1 to 20% and preferably from 0.5 to 5% by mass relative to the lubricating oil. In this application, other conventional additives can be added, such as chlorinated paraffins in a proportion corresponding for example to 2-10% by mass of chlorine relative to the lubricating oil.

The following examples illustrate the invention; they should in no way be considered as limiting. Example 4 is given for comparison.

EXAMPLE 1

540 g of sulfur monochloride S ₂ CIz (4 moles) are introduced into a 2-liter reactor fitted with an agitator, then, under a dip tube, is introduced under the surface of S ₂ CI ₂ constantly stirred, 506 g of isobutylene (9.74 moles) in which 5 g of methanol have previously been dissolved. The temperature of the reaction medium is maintained between 45 and 50 _° C throughout the duration of introduction of isobutylene (1 hour). 1000 g of adduct are thus obtained, which is designated by the term "adduct".

In a second 2-liter reactor fitted with an agitator, 1 liter of absolute methanol and 96 g of sodium hydroxide pellets (2.4 moles) are introduced, the mixture is heated to approximately 60 _° C., until dissolved soda. 216 g of tert-butylmercaptan (2.4 moles) are then introduced dropwise into the alcoholic medium while maintaining the temperature around 60 ° C .; it is left to react for an additional half hour, then 38.4 g of flowering sulfur (1.2 gram-atom) are added to this homogeneous solution. The mixture is heated at reflux for 0.5 hour to promote the formation of sodium mercaptate-polysulfide. The S / mercaptan molar ratio involved is 0.5 / 1.

• S = 43,9 % masse ; CI < 0,05 % masse ; v loo-0 = 2,25 mm²/s.

Via a dropping funnel, 247 g (1 theoretical mole) of the previously prepared "adduct" are added dropwise over 0.5 hour, the reaction temperature being fixed by the reflux temperature of methanol . It is left to react for 8 hours at reflux, then the methanol is distilled; the residual mixture is washed with 2 times 500 cm ³ of water; the polysulphurized olefin recovered is treated at reflux under vigorous stirring with 180 g of an aqueous sodium hydroxide solution at 10% by mass; after washing with water, the recovered polysulphurized olefin is dried over anhydrous sodium sulphate, filtered and then evaporated under reduced pressure at 100 ° C to constant mass; it is in the form of a low-viscosity mobile oil whose physicochemical characteristics are the following:

• S = 43.9% mass; CI <0.05% mass; v loo-0 = 2.25 mm ² / s.

Solubility in mineral oils at 20 _° C and - 5 _° C: total. Solubility in PAO oil (hydrogenated polyalphaolefin) SAE 90 at 20 _° C and -5 _° C: total.

EXAMPLE 2

The experiment of Example 1 is repeated under the same operating conditions, but this time 76.8 g of sulfur in flower (2.4 gram atoms) is used; the S / mercaptan molar ratio used is then 1/1.

• S = 47,91 % masse ; CI < 0,05 % masse ; v 1 oooc = 2,72 mm²/s.
• Solubilité dans les huiles minérales à 20_°C et à -5°C : totale.
• Solubilité dans une huiles PAO SAE 90 à 20_°C et à - 5_°C : totale.

After reaction and treatments, the polysulphurized olefin recovered is in the form of a fluid oil whose physicochemical characteristics are the following:

• S = 47.91% mass; CI <0.05% mass; v 1 oooc = 2.72 mm ² / s.
• Solubility in mineral oils at 20 _° C and -5 ° C: total.
• Solubility in PAO SAE 90 oils at 20 _° C and - 5 _° C: total.

EXAMPLE 3

• S = 53,9 % masse ; CI = 0,07 % masse ; v 100-C = 6,2 mm²/s.

The experiment of Example 1 is repeated under the same operating conditions, but this time 384 g of tert-nonylmercaptan (2.4 moles and 384 g of sulfur in flower (12 gram atoms) are used; the molar ratio S / mercaptan used is then approximately 5/1 After reaction and without treatment with an aqueous sodium hydroxide solution, a fluid oil is recovered whose physicochemical characteristics are the following:

• S = 53.9% mass; CI = 0.07% mass; v 100-C = 6.2 mm ² / s.

Solubility in an oil 100 Neutral Solvent: soluble up to about 20% by mass at 20 ° C.

EXAMPLE 4

The experiment of Example 1 was repeated once again, but this time no elemental sulfur was used.

• S = 36,0 % masse ; CI < 0,3 % masse ; v 100°C = 2,1 mm²/s.
• Solubilité dans les huiles minérales et PAO à 20_°C et -5_°C : totale.

The physico-chemical characteristics of the product obtained are as follows:

• S = 36.0% mass; CI <0.3% mass; v 100 ° C = 2.1 mm ² / s.
• Solubility in mineral and PAO oils at 20 _° C and -5 _° C: total.

EXAMPLE 5 Evaluation of the extreme pressure properties of additives according to the invention.

Tests have been carried out demonstrating the extreme pressure properties of additives prepared according to some of the preceding examples on the one hand in formulations of the gear oil type and, on the other hand, in formulations of the working oil type metals.

The additives obtained in Examples 1 and 2 were studied using a 4-ball machine according to the procedures of ASTM D 2266 and D 2783, in a synthetic oil PAO SAE 90 at concentrations such as the content of oil sulfur is 0.69% by mass; the results obtained are collated in table 1 below.

These results show that the additives according to the invention lead to a very significant increase in the load-wear index and that they significantly reduce the wear of the balls; this type of additive can be advantageously used for the formulation of extreme pressure oils for industrial or automobile gears, and the formulation of oils for working non-ferrous metals.

EXAMPLE 6

The extreme pressure properties of the additive obtained in Example 3 are evaluated from a formulation of the metal cutting oil type, using a 4-ball machine according to the ASTM D 2783 procedure.

The lubricant formulation used consists of a 100 Neutral Solvent oil containing 3% of chlorine in the form of chlorinated paraffin, and 1% of sulfur in the form of sulfur additive of Example 2; the results obtained are collated in table 2 below.

From these results, it appears that the additive can be used very satisfactorily in the formulation of oils for working ferrous metals.

Claims (14)

1. An olefin polysulfide composition characterized in that it is obtained by a process comprising the steps of:

(1) reacting at least one compound selected from sulfur monochloride and dichloride with at least one aliphatic monoolefin having 2 to 5 carbon atoms, complying with the formula R^1-C(R²)=CHε, wherein R¹ is the hydrogen atom or an alkyl radical having from 1 to 3 carbon atoms and R² is a hydrogen atom or a methyl radical, so as to form an addition product, and

(2) reacting said addition product with at least one mercaptate-polysulfide complying with general formula R3S_xM, wherein R3 represents an aliphatic radical, optionally carrying a functional group, an aromatic radical, optionally substituted with at least one aliphatic radical, or a heterocyclic radical, M is a monovalent atom or group corresponding to an inorganic base of formula MOH, and x has an average value of at least 1.2.

2. A composition according to claim 1, characterized in that, in step (1), said aliphatic monoolefin is used in a proportion of 1.5-2.5 moles per mole of sulfur mono- and/or dichloride.

3. A composition according to claim 1 or 2, characterized in that said aliphatic monoolefin is isobutene.

4. A composition according to one of claims 1 to 3, characterized in that, in the formula R³S_xM of the mercaptate-polysulfide used in step (2), R3 represents an aliphatic radical having from 1 to 14 carbon atoms, an aliphatic radical having at least one hydroxyl group, an aromatic radical optionally substituted with at least one aliphatic radical having 6-14 carbon atoms or an heterocyclic radical containing at least one heteroatom selected from nitrogen, sulfur and oxygen, M represents the sodium or potassium atom or the ammonium group and x has an average value up to about 7.

5 A composition according to one of claims 1 to 4, characterized in that step (2) is performed in the presence of an aliphatic monoalcohol having from 1 to 5 carbon atoms, used in a proportion of 200 to 400 ml per mole of mercaptate-polysulfide.

6. A composition according to one of claims 1 to 5, characterized in that the mercaptate-polysulfide used in step (2) is obtained by a process wherein at least one mercaptan of general formula R³SH is reacted with an inorganic base MOH, then with a suitable amount of element sulfur.

7. A composition according to claim 6, characterized by the use of about 0.2-10 gram-atoms of element sulfur per mole of mercaptan.

8. A composition according to one of claims 6 and 7, characterized in that the inorganic base is sodium hydroxide, potassium hydroxide, or ammonium hidroxide, the operation being conducted within an aliphatic monoalcohol of 1-5 carbon atoms, at a temperature from 20 to 100°C.

9. A composition according to one of claims 1 to 8 characterized in that :

- step (1) is conducted at a temperature from 20 to 80_°C, and

- step (2) is performed within an aliphatic monoalcohol of 1-5 carbon atoms, used in a proportion of 200-400 ml per mole of mercaptate-polysulfide, said mercaptate polysulfide being used in molar excess of about 0.1 to 70% in proportion to the stoichiometry of 2 moles per mole of said addition product, said reaction medium being maintained at a temperature from -10_°C to the reflux temperature of said monoalcohol.

10. A composition according to one of claims 1 to 9, characterized in that it is produced by a process further comprising a step (3) wherein the product obtained at the end of step (2) is contacted with an aqueous solution of inorganic base.

11. A composition according to claim 10, characterized by the use in step (3) of an aqueous solution of sodium hydroxide or potassium hydroxide at a concentration of 0.1 to 50% by weight, in a proportion of 0.1 to 5 times the amount by weight of the resultant product from step (2).

12. A process for preparing an olefin polysulfide composition as defined in any one of claims 1 to 11.

13. The use of an olefin polysulfide composition according to one of claims 1 to 11 as additive for gear- oils, wherein said composition is added in a proportion of 0.5-10% by weight to a mineral or synthetic lubricating oil.

14. The use of an olefin polysulfide composition according to one of claims 1 to 11 as additive for an oil destined to metal working, wherein said composition is added in an amount of about 0.1-20% by weight in proportion to the oil.