DE2004047A1 - Trithiopyrophosphoric acid compounds, process for their production and use in lubricants - Google Patents

Description

The present invention relates to new trithiopyrophosphoric acid compounds which are particularly suitable as additives for lubricants. In particular, alkyl, aryl and alkaryltrithiopyrophosphoric acid compounds according to the invention have excellent properties as antioxidants, as anticorrosive agents and as antirust agents. They also improve the resilience of lubricants such as hydraulic fluids.

A number of multifunctional additives are known which improve the usability of lubricating oils in at least two respects, for example with regard to resistance to oxidation, the occurrence of metal corrosion, the dispersing effect, the rust protection effect or the load-bearing capacity. Such additives generally fall into two different classes, namely the class of the ash-forming or the class of the non-ash-forming additives. The non-ash-forming

Additives have a wider range of uses because they can be used in ashless lubricating oils as well as most other lubricants.

Very suitable, well-known, multi-purpose additives are metal dithiophosphates, for example zinc dialkyl dithiophosphates. However, these salts cannot be used as multifunctional additives in ashless lubricants because they are not ashless themselves. The new trithiopyrophosphoric acid compounds according to the invention now make it possible to solve this technical problem, since they can be used as multifunctional additives in a large number of lubricants and in particular hydraulic fluids.

The trithiopyrophosphoric acid compounds of the present invention have the following general formula in which X is oxygen, sulfur or the group = NH, R [deep] 1 and R [deep] 2 are identical or different and each have a C [deep] 1-9 alkyl group, a C [deep] 1-9 - Alkenyl group, a C [deep] 1-9 cycloalkyl group, a C [deep] 6-12 aryl group or a C [deep] 7-30 alkaryl group and in the event that all radicals X are sulfur and / or the group = NH are also a C [deep] 10-30 -alkyl group, C [deep] 10-30 -alkenyl group or a C [deep] 10-30 -cyolalkyl group.

In the trithiopyrophosphoric acid compounds of the above general formula I according to the invention, all radicals X can be

Group = NH and / or sulfur. The radicals X can be identical or differ from one another.

Particularly preferred within the scope of the invention are trithiopyrophosphoric acid compounds of the general formula I in which R [deep] 1 and R [deep] 2 are each a C [deep] 4-9 alkyl group, a phenyl group or an alkyl radical having 4 to 18 carbon atoms substituted phenyl group. Other very suitable representatives of the new phosphoric acid compounds are those of the general formula I in which X is oxygen, R [deep] 1 is identical to R [deep] 2 and is in each case the butyl, phenyl, octylphenyl or nonylphenyl group. Further preferred representatives of this class of compounds are those in which X denotes the group = NH, while R [deep] 1 and R [deep] 2 are identical and denote the oleyl, stearyl or dodecylphenyl group. Yet another group of preferred compounds is characterized in that X is sulfur, while R [deep] 1 and R [deep] 2 are identical and each mean the butyl, stearyl, phenyl or tridecylphenyl group.

The trithiopyrophosphoric acid compounds according to the invention can be prepared in two different ways, depending on whether aliphatic or aromatic compounds are to be obtained. The process according to the invention for the preparation of trithiopyrophosphoric acid compounds of the general formula I is characterized in that either an aliphatic thionothiophosphoric acid of the formula (RX) [deep] 2PS [deep] 2H in which X has the meaning given above and R denotes for R [deep] 1 and R [deep] 2 corresponds to the meanings given, with

N, N'-dicyclohexylcarbodiimide or that an aromatic thionothiophosphoric acid of the above formula is pyrolyzed.

The reaction of an aliphatic thionothiophosphoric acid with N, N'-dicyclohexylcarbodiimide can be represented by the following reaction equation:

2 (RX) [deep] 2 PS [deep] 2 H + (C [deep] 6 H [deep] 11 N =) [deep] 2C -> [(RX) [deep] 2 P (S)] [deep ] 2 S + (C [deep] 6 H [deep] 11 NH) [deep] 2 C = S (II)

The acid used as the starting material can be prepared by reacting 4 moles of an aliphatic alcohol, an aliphatic amine or an aliphatic mercaptan with one mole of phosphorus pentasulfide, 2 moles of the desired thionothiophosphoric acid then being formed. Instead of the individual alcohols, amines or mercaptans, however, mixtures of alcohols, amines or mercaptans can of course also be reacted with phosphorus pentasulphide, which then gives thionothiophosphoric acids in which the groups R differ from one another.

The aromatic trithiopyrophosphoric acid compounds are obtained by reacting an aromatic alcohol, an aromatic amine or an aromatic mercaptan with phosphorus pentasulfide and then pyrolyzing the thionothiophosphoric acids according to the following reaction equation:

2 (RX) [deep] 2 PS [deep] 2 H -> [(RX) [deep] 2 P (S)] [deep] 2 S + H [deep] 2 S (III)

In this case too, a large number of aromatic alcohols, amines and mercaptans or mixtures of these compounds can be used for the preparation of the thionothiophosphoric acids. For example Substituted and unsubstituted phenols, aminobenzenes, thiophenols, naphthols, naphthylamines or thionaphthols can be used for this purpose. Aryl alcohols, alkaryl alcohols, amines or mercaptans with a single aromatic nucleus are particularly preferred. In the context of the invention, alkaryl compounds are particularly suitable in which only a single alkyl group having 1 to 24 carbon atoms and preferably 4 to 18 carbon atoms is bonded directly to the aromatic nucleus.

The new trithiopyrophosphoric acid compounds according to the invention can be incorporated into a wide variety of lubricants, for example synthetic oils and, in particular, mineral lubricating oils. Mineral lubricating oils suitable for this purpose can be derived from paraffin-based, naphthenic-based or mixed-basic crude oils and / or mixtures of such crude oils. For example, neutral oils with viscosities in the range from 100 to 6500 SSU at 37.8 ° C. are very suitable. The alkyl, aryl and / or alkaryltrithiopyrophosphoric acid compounds according to the invention can be added to the lubricating oils either individually or in combination, expediently in amounts of about 0.01 to 10% by weight, preferably in amounts of 0.05 to about 5% by weight -%.

In addition to the trithiopyrophosphoric acid compounds according to the invention, such lubricants can also contain other additives such as are usually used in technology to fulfill special functions in the lubricants, for example viscosity index improvers such as methacrylate polymers, antioxidants such as amines or phenolic compounds, especially phenyl-small alpha -naphthylamine, dioctyldiphenylamine and 4,4'-methylene-bis- (2,6-di-t-butylphenol). The lubricants can also contain anti-foam agents, corrosion inhibitors, anti-rust agents and similar additives.

Example 1 Compound Nos. 1 to 13 listed in Table I below were synthesized according to one of the procedures described below. Procedure No. 1 was used to prepare trithiopyrophosphoric acid compounds with alkyl groups, whereas procedure 2 was used to prepare trithiopyrophosphoric acid compounds which contain aryl or alkaryl groups.

Procedure 1 Synthesis of alkyltrithiopyrophosphoric acid compounds 0.1 mol of an alkylthionothiophosphoric acid are dissolved in anhydrous diethyl ether. In addition, a solution of 0.05 mol of N, N'-dicyclohexylcarbodiimide in anhydrous diethyl ether is prepared and this solution is added dropwise to the acid solution over a period of 4 hours, the reaction mixture being kept at room temperature. A white precipitate separates out after a short time. When the addition is complete, the reaction mixture is stirred for one hour at room temperature and then refluxed for 2 hours with constant stirring.

The N, N'-dicyclohexylthiourea formed as a by-product and having a melting point of 180 to 181 ° C. is filtered off. This by-product is obtained in a yield of 95-100% of theory, based on the acid used. Afterward the solvent is removed from the filtrate by vacuum distillation. Depending on the chemical structure of the thionothioic acid used, the end product obtained is a yellow-colored liquid to a white solid. The average yield is about 90%, based on the acid used.

Procedure 2 Synthesis of aromatic trithiopyrophosphoric acid compounds 0.4 mol of an aryl or alkaryl alcohol, an amine or mercaptan are dissolved in tetralin and heated to 130 ° C. under nitrogen. Then 0.1 mol of phosphorus pentasulfide is added over a period of 3 hours. When the addition is complete, the mixture is kept at the reaction temperature until everything P [deep] 2 S [deep] 5 has reacted and the evolution of hydrogen sulfide ceases. The temperature is then increased to 165 ° C. This temperature is again maintained until no more hydrogen sulfide is released. The reaction mixture is then filtered and the solvent is distilled off in vacuo. The yields of the end products are in the range from 80 to 90% of theory, based on the P [low] 2S [low] 5 used.

Table I.

Example 2 In order to demonstrate the excellent properties of the compounds according to the invention as antioxidants, 11 different mixtures are prepared with compounds according to Example 1 and then subjected to the air oxidation test (AOT), with two further mixtures which contain commercially available zinc dithiphosphates being used as a comparison . the Results obtained in this test are summarized in Table II below:

Table II Air Oxidation Test (AOT) [high] b

a) The concentration of the additives in a base oil with a high viscosity index of the 250N (neutral) type, which contained 0.5% by weight of 4,4'-methylenebis (2,6-di-t-butylphenol), was in each case 3.10 [high] -4 moles.

b) Air Oxidation Test: In this test, air is passed through samples which each contain 20 ppm of soluble iron catalyst and soluble copper catalyst. The resistance to oxidation corresponds to the length of time, measured in hours, which is required to absorb 1 mmol of oxygen per gram of the oil.

c) Blotting paper test: This test is used to check the dispersing properties of the lubricants. At intervals, drops of oil are placed on a sheet of blotting paper and the

The time that elapses before insoluble particles appear serves as a measure of the dispersibility of the lubricant in question.

The above test results confirm that the trithiopyrophosphoric acid compounds according to the invention increase the oxidation resistance of the base lubricating oil quite significantly and that many of the additives examined also show a superior effect compared to the metal dithiophosphates. The results of the blotting paper test further confirm that the compounds according to the invention are in many cases superior to the dithiophosphoric acid salts with regard to the dispersibility.

Example 3 In order to demonstrate the anti-corrosion properties of the trithiopyrophosphoric acid compounds according to the invention, copper / lead corrosion tests are carried out on a number of mixtures which contain compounds according to Example 1. Mixtures containing zinc dithiophosphoric acid salts are again used for comparison. The results obtained are summarized in Table III below.

Table III Copper / lead corrosion test [high] b)

a) The concentrations of the additives in the base oil with a high viscosity index of the 250N type, which contains 0.5% by weight of 4,4'-methylenebis (2,6-di-t-butylphenol), are each 0.2 Wt%.

b) Copper / lead corrosion test: previously balanced spirals made of copper and lead are heated to 162.8 ° C. in an oil sample, with air being passed through the glass test tube at a rate of 30 ml / min. After 5 hours the coils are removed, washed and weighed again. The loss of copper or lead caused by corrosion is given in mg.

The test data from Table III confirm that all the compounds according to the invention have a practically non-coordinating effect on copper and reduce the lead corrosion from 17.1 mg to about 2 to 9 mg. The zinc dithiophosphate additive decreased on the other hand, lead corrosion by only 12 mg or, in another case, by 6 mg.

EXAMPLE 4 In order to show the favorable properties of the novel compounds according to the invention as anti-rust agents, a number of mixtures containing corresponding trithiopyrophosphoric acid compounds were subjected to the seawater immersion test on steam turbine oil in accordance with ASTM D 665. Samples which contained zinc dithiophosphates were again used for comparison. The results of this experiment are summarized in Table IV below.

Table IV Steam turbine oil seawater immersion test according to ASTM D 665

a) The concentration of the additives in a base oil with a high viscosity index of the 250 N type, which contained 0.5% by weight of 4,4'-methylenebis (2,6-di-t-butylphenol), was in each case 0, 2% by weight.

b) At the specified
<nonreadable>
for the rust attack, the mean values are from 2 parallel experiments.

The above results show that although the effect of the individual trithiopyrophosphoric acid compounds as anti-rust agents is not always the same, they all remarkably reduce the amount of rust, based on the base oil without additives.

Example 5 A series of tests were also carried out to determine the pressure absorption capacity of lubricants which contained a trithiopyrophosphoric acid compound according to the invention. Samples were therefore produced according to Examples 3 and 4 and tested in a four-ball apparatus. The test results obtained are summarized in Table V below.

Table V Four-ball apparatus test [high] a)

a) Four-ball apparatus test: This test is described in more detail in the journal "Engineer" Volume 136 of July 13, 1933. The mean Hertzian pressure is determined by performing a number of test runs of 10 seconds each at previously selected loads. The load is increased until the four balls weld together.

The results of Examples 2 to 5 clearly show that the trithiopyrophosphoric acid compounds according to the invention are very effective antioxidants, do not have a coordinating effect on copper, prevent lead corrosion, reduce rust attack and give a lubricant good high pressure resistance. These new compounds, which do not form ash, are therefore very inexpensive multifunctional lubricant additives. In addition, they can also be used in hydraulic fluids, especially if hydraulic fluids based on mineral oil are involved.

Claims (7)

1. Trithiopyrophosphoric acid compounds of the general formula in which X is oxygen, sulfur or the group = NH, R [deep] 1 and R [deep] 2 are identical or different and each have a C [deep] 1-9 alkyl group, a C [deep] 1-9 - Alkenyl group, a C [deep] 1-9 cycloalkyl group, a C [deep] 6-12 aryl group or a C [deep] 7-30 alkaryl group, and in the event that all radicals X are sulfur and / or the group = NH, also mean a C [deep] 10-30 alkyl group, C [deep] 10-30 alkenyl group or a C [deep] 10-30 cycloalkyl group. 2. Trithiopyrophosphoric acid compounds according to claim 1, formula I, characterized in that R [deep] 1 and R [deep] 2 each have a C [deep] 4-9 alkyl group, the phenyl group or one substituted by an alkyl group having 4 to 18 carbon atoms Mean phenyl group. 3. trithiopyrophosphoric acid compounds according to claim 1 and 2, characterized in that X is oxygen, that R [deep] 1 is identical to R [deep] 2 and denotes the butyl, phenyl, octylphenyl or nonylphenyl group. 4. trithiopyrophosphoric acid compounds according to claim 1 and 2, characterized in that X is the group = NH, R [deep] 1 is identical to R [deep] 2 and denotes the oleyl, stearyl or dodecylphenyl group. 5. trithiopyrophosphoric acid compounds according to claim 1 and 2, characterized in that X is sulfur, R [deep] 1 is identical to R [deep] 2 and denotes the butyl, stearyl, phenyl or tridecyl group. 6. Process for the preparation of trithiopyrophosphoric acid compounds according to claim 1, formula I, characterized in that either an aliphatic thionothiophosphoric acid of the formula (RX) [deep] 2 PS [deep] 2 H in which X has the meaning given above and R corresponds to the meanings given for R [deep] 1 and R [deep] 2, is reacted with N, N'-dicyclohexylcarbodiimide or an aromatic thionothiophosphoric acid of the above formula is pyrolyzed. 7. Use of trithiopyrophosphoric acid compounds according to claim 1, formula I, as additives in lubricants, in particular in engine lubricating oils, steam turbine oils and hydraulic oils.