Epithio compounds as additives for lubricants

Epithio compounds or mercaptans of the formula I ##STR1## wherein X is an oxygen or sulfur atom, --CH.sub.2 --, --CH(R.sub.1)--, --COO--, --NH-- or --NR.sub.1 --, each of Y and Z is hydrogen or together they are a direct bond, Q is hydrogen if Y and Z together are a direct bond, or is --OH, --SH, --OR.sub.1, --SR.sub.1, --OOCR.sub.1, --S--CH.sub.2).sub.n OH, --S--CH.sub.2).sub.n COOR.sub.1, --NHR.sub.1 or --N(R.sub.1).sub.2, n is an integer from 1 to 10, each of R and R.sub.1 independently is a cyclic or acyclic hydrocarbon radical of aliphatic or aromatic character containing 4 to 30 carbon atoms which can be interrupted by oxygen or sulfur, with the proviso that the groups R and R.sub.1 contain a total number of 8 to 30 carbon atoms. These compounds have excellent suitability for use as additives for lubricants, especially as extreme pressure and antiwear additives.

The present invention relates to .beta.-substituted epithio compounds and 
adducts thereof, and to their use as additives for lubricants, in 
particular as extreme pressure and antiwear additives. 
Compounds containing both sulfur and phosphorous, such as sulfur-containing 
esters of phosphoric and phosphorous acid and the use thereof as lubricant 
additives, have long been known in the art, cf. for example French Pat. 
No. 1,137,298 and Houben-Weyl, Methoden der organischen Chemie, Thieme 
Verlag, Vol. 12/2, pages 93-95 and 742-748. 
Among the known sulfur-containing esters of phosphoric acids, 
representatives have been developed which constitute effective EP/AW 
additives for lubricants. However, these esters are not without adverse 
characteristics. For example, triphenylthionophosphate has in many cases 
only an insufficient action. The trithiophosphites, in particular the 
trithiophosphites from PCl.sub.3 and SH-containing carboxylic acid esters 
described in U.S. Pat. No. 3,374,291, have a corrosive action on metal 
surfaces, especially at elevated temperatures. The alkyl trithio- and 
tetrathiophosphates proposed in U.S. Pat. No. 3,705,216 are also deficient 
in their effectiveness. It is held to be a drawback of the effective zinc 
dialkyldithiophosphates that they leave a residue on burning and therefore 
on account of the metal content and of the relatively low decomposition 
temperatures tend to form deposits, for example on contact with hot metal 
surfaces. 
There has therefore been a need to provide oil additives which do not 
contain phosphorus and metal and which leave no residues on burning. Thus, 
for example, N-substituted fatty acid amides which contain epithio groups, 
for example N,N-dibutyl-9,10-epithiostearamide or 
N,N-dibutyl-9,10,12,13-diepithiostearamide, are described as good EP/AW 
additives in Chemical Abstracts 79, 1973, 94496x and 82, 1975, 88387h. 
Fatty acid esters containing epithio groups and terpenes with similar 
lubricant properties are mentioned in the journal Tribology, 3(1970), 145. 
A conventional method for the production of such compounds is the addition 
of sulfur to the double bond of olefinic fatty acid derivatives. This 
reaction affords the desired epithio compounds usually only in 
insignificant yields (cf. Chem. Rev. 66 (1966), 297). In this same 
publication there are described epithio compounds which are substituted by 
alkyl and lower alkyl ether and are obtained in good yield from the 
corresponding epoxides by reaction with KSCN. 
Surprisingly, it has now been found that epithio compounds which are 
.beta.-substituted by aryl ether or long chain alkyl ether, arylthio or 
long chain alkylthio ether, arylamine or long chain alkylamine, and 
conversion products with protonic nucleophilic reagents, are very 
effective lubricant additives, in particular EP/AW additives, which are 
superior to other products which do not contain phosphorus and contain 
only sulfur. 
Accordingly, the present invention provides epithio compounds or mercaptans 
of the formula I 
##STR2## 
wherein X is an oxygen or sulfur atom, --CH.sub.2, --CH(R.sub.1)--, 
--COO--, --NH-- or --NR.sub.1 --, eacn of Y and Z is hydrogen or together 
they are a direct bond, Q is hydrogen if Y and Z together are a direct 
bond, or is --OH, --SH, --OR.sub.1, --SR.sub.1, --OOCR.sub.1, 
--S--CH.sub.2).sub.n OH, --S--CH.sub.2).sub.n COOR.sub.1, --NHR.sub.1 or 
--N(R.sub.1).sub.2, n is an integer from 1 to 10, each of R and R.sub.1 
independently is a cyclic or acyclic hydrocarbon radical of aliphatic or 
aromatic character containing 4 to 30 carbon atoms which can be 
interrupted by oxygen or sulfur, with the proviso that the groups R and 
R.sub.1 contain a total number of 8 to 30 carbon atoms. 
R and R.sub.1 as aliphatic hydrocarbon radicals can be linear, but 
especially branched, alkyl of 4 to 30 carbon atoms which may be 
interrupted by oxygen or sulfur atoms, or cycloalkyl or cycloalkylalkyl 
which is unsubstituted or substituted by 1 or 2 alkyl groups of preferably 
1 to 12 carbon atoms. As aromatic hydrocarbon radicals, R and R.sub.1 can 
be aryl or aralkyl which is unsubstituted or substituted by 1 or 2 alkyl 
groups of 1 to 12 carbon atoms. Alkyl in this connection contains 
preferably 4 to 22 carbon atoms, especially 8 to 22 and most preferably 8 
to 18 carbon atoms. Cycloalkyl contains 5 to 8 ring carbon atoms and is 
preferably cyclohexyl. Aryl is preferably phenyl and aralkyl is preferably 
benzyl, whilst each of cycloalkyl, phenyl or benzyl is preferably 
substituted by 1 or 2 alkyl groups. 
In particular, R and R.sub.1 in formula I are branched alkyl of 8 to 18 
carbon atoms. 
Examples of R are: n-butyl, isobutyl, tert-butyl, pentyl, hexyl, 
2-methylpentyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, 
dodecyl, 2-ethyldecyl, tetradecyl, octadecyl, eicosyl, docosyl, tetracosyl 
and the isomer mixtures thereof, methoxy-n-propyl, octoxyethyl, 
octylthioethyl, cyclopentyl, methylcyclopentyl, ethylcyclopentylmethyl, 
cyclohexylmethyl, methylcyclohexyl, methylphenyl, ethylphenyl, 
tert-butylphenyl, dimethylphenyl, hexylphenyl, 2-ethylhexylphenyl, 
dinonylphenyl, dodecylphenyl, methylbenzyl, nonylbenzyl, dodecylbenzyl. 
The above mentioned isomer mixtures are those which are derived from 
commercially available alcohols prepared via the oxo-synthesis. These 
products, also known as oxanols, normally consists of a mixture of 
branched chain, in particular primary, alcohols. 
Particularly interesting epithio compounds or mercaptans are those of the 
formula I wherein X is an oxygen or sulphur atom or the --COO-- group, Y 
and Z have the above meanings, Q is hydrogen if Y and Z are as defined 
above or is --SH, --SR.sub.1, --S--(CH.sub.2).sub.2 --OH, --S--CH.sub.2 
--COOR.sub.1, --NHR.sub.1, and each of R and R.sub.1 independently, is 
branched or unbranched C.sub.4 -C.sub.22 alkyl, with the proviso that the 
groups R and R.sub.1 contain a total number of 8 to 30 carbon atoms. 
Especially preferred epithio compounds or mercaptans are those of the 
formula I wherein X is an oxygen atom or the --COO-- group, Y and Z have 
the above meanings, Q is hydrogen if Y and Z together are a direct bond or 
is --SH, --SR.sub.1, --S--CH.sub.2 --COOR.sub.1 and --NHR.sub.1, and each 
of R and R.sub.1 independently is branched C.sub.8 -C.sub.22 alkyl, with 
the proviso that the groups R and R.sub.1 contain a total number of 8 to 
20 carbon atoms. 
The most preferred epithio compounds are those of the formula II 
##STR3## 
wherein R represents branched C.sub.8 -C.sub.18 alkyl and X represents an 
oxygen atom or the --COO-- group, and mercaptans of the formula III 
##STR4## 
wherein X has the given meaning, Q is --SR.sub.1 or --S--CH.sub.2 
--COOR.sub.1, and R and R.sub.1 are branched C.sub.8 -C.sub.18 alkyl, with 
the proviso that the groups R and R.sub.1 contain a total number of 8 to 
20 carbon atoms. 
The epithio compounds of the invention are obtained by known methods from 
generally known epoxides of the formula IV 
##STR5## 
wherein R and X have the given meanings, by reaction with alkali 
thiocyanate or alkaline earth cyanate or thiourea. A corresponding method 
of manufacture is described e.g. in Org. Synth., 32(1952), 39. The above 
epoxides can be prepared by known methods, for example by reaction of 
mercaptans with epichlorohydrin, optionally in the presence of suitable 
catalysts. 
For carrying out the reaction with thiourea, the calculated amount is 
suspended in approx. 10% sulfuric acid and the epoxide, dissolved in 
dioxan, is added dropwise with good stirring at about 0.degree. C. to 
5.degree. C. The reaction mixture is warmed briefly to 40.degree. C. when 
the dropwise addition is complete and then an approx. 20% aqueous 
equivalent sodium carbonate solution is added dropwise with efficient 
stirring. On heating to about 50.degree. C., any precipitate which may 
have formed is immediately dissolved again. 
To isolate the episulfides, the reaction mixture is acidified with dilute 
sulfuric acid and extracted repeatedly with ether. The ethereal extracts 
are washed neutral. The episulfides are isolated in a yield of over 90% 
from the ethereal solution after working up. 
The mercaptans of the formula VI 
##STR6## 
wherein R, X and Q have the given meanings, are obtained in the further 
reaction of the resulting epithio compounds of the formula V 
##STR7## 
wherein R and X have the given meanings, with protonic nucleophilic 
reagents of the formula VII 
EQU H--Q (VII) 
wherein Q has the given meaning, such as alkyl mercaptans, thioglycolic 
acid esters or primary or secondary alkylamines. The addition of protonic 
nucleophilic reagents to epithio compounds is described for example in 
JACS 69 (1947), 2675. It is normally effected at temperatures between 
50.degree. and 150.degree. C., preferably between 70.degree. and 
100.degree. C., in the presence of an acid catalyst, in particular a Lewis 
acid, for example BF.sub.3 etherate. The addition of H.sub.2 S is effected 
by the method described in J. Chem. Soc. 1948 (3), 1894 (London). 
The compounds of the present invention are liquid to viscous products which 
are very readily soluble in lubricants. They are pre-eminently suitable as 
enriching additives for lubricants, as they improve both the extreme 
pressure and the antiwear properties surprisingly well. In addition to 
this excellent action, the compounds of the invention also have very good 
anticorrosion and stabilizing properties. 
The compounds of the formula I act even in very small amounts as extreme 
pressure additives in lubricants. Thus mineral and synthetic lubricant 
oils and mixtures thereof which contain 0.01 to 5% by weight, based on the 
lubricant, and preferably 0.1 to 3% by weight, of a compound of the 
formula I exhibit excellent extreme pressure lubricant properties which 
become evident from the markedly reduced signs of wear of the parts to be 
lubricated. The suitable lubricants are known to the skilled person and 
are described for example in the "Schmiermittel Taschenbuch" (Huthig 
Verlag, Heidelberg, 1974). 
The lubricating oil can contain still further additives which are added to 
improve the performance properties, such as antioxidants, metal 
deactivators, rust inhibitors, viscosity index improvers, pour-point 
depressors, dispersants/detergents. The compounds of the present invention 
can also be used in combination with other extreme pressure/antiwear 
additives. 
Examples of antioxidants are: 
(a) Alkylated and non-alkylated aromatic amines and mixtures thereof, for 
example: dioctyldiphenylamine, mono-tert-octyl-phenyl-.alpha.- and 
-.beta.-naphthylamines, phenotriazine, dioctylphenothiazine, 
phenyl-.alpha.-naphthylamine, N,N'-di-sec-butyl-p-phenylenediamine. 
(b) Sterically hindered phenols, for example: 2,6-ditert-butyl-p-cresol, 
4,4'-bis-(2,6-diisopropylphenol), 2,4,6-triisopropylphenol, 
2,2'-thio-bis-(4-methyl-6-tert-butylphenol), 
4,4'-methylene-bis-(2,6-di-tert-butylphenol) or esters of 
2-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with e.g. 
hexane-1,6-diol, thiodiethylene glycol and pentaerythritol. 
(c) Alkyl-, aryl- or aralkylarylphosphites, for example: trinonylphosphite, 
triphenylphosphite, diphenyldecylphosphite. 
(d) Esters of thiodipropionic acid or thiodiacetic acid, for example: 
dilaurylthiodipropionate or dioctylthiodiacetate. 
(e) Salts of carbamic and dithiophosphoric acids, for example: antimony 
diamyldithiocarbamate, zinc diamyldithiophosphate. 
(f) A combination of two or more of the above antioxidants, for example: an 
alkylated amine and a sterically hindered phenol. 
Examples of metal deactivators are: 
(a) for copper: for example benzotriazole, tetrahydrobenzotriazole, 
2-mercaptobenzotriazole, 2,5-dimercaptothiadiazole, salicylidene 
propylenediamine, salts of salicylaminoguanidine. 
(b) for lead: for example sebacic acid derivatives, quinizarine, propyl 
gallate. 
(c) a combination of two or more of the above additives. 
Examples of rust inhibitors are: 
(a) Organic acids, the esters, metal salts and anhydrides thereof, for 
example: N-oleyl-sarcosine, sorbitan monooleate, lead naphthenate, 
dodecenylsuccinic anhydride. 
(b) Nitrogen-containing compounds, for example: I. Primary, secondary or 
tertiary aliphatic or cycloaliphatic amines and amine salts of organic and 
inorganic acids, for example oil-soluble alkylammonium carboxylates. II 
Heterocyclic compounds, for example substituted imidazolines and 
oxazolines. 
(c) Phosphorus-containing compounds, for example: amine salts of phosphoric 
acid partial esters. 
(d) Sulfur-containing compounds, for example: barium 
dinonylnaphthalenesulfonates, calcium petroleum sulfonates. 
(e) Combinations of two or more of the above additives. 
Examples of viscosity index improvers are: 
polymethylacrylates, vinyl pyrrolidone/methacrylate copolymers, 
polybutenes, olefin copolymers. 
Examples of pour-point depressors are: 
polymethacrylates, alkylated naphthalene derivatives. 
Examples of dispersants/surfactants are: 
polybutenylsuccinic imides, polybutenylphosphonic acid derivatives, 
superbasic magnesium, calcium and barium sulfonates and phenolates. 
Examples of other wear-resisting additives are: 
compounds which contain sulfur and/or phosphorus and/or halogen, such as 
sulfurised vegetable oils, zinc dialkyldithiophosphates, 
tritolylphosphate, chlorinated paraffins, alkyl- and aryldisulfides.