The present invention relates to new sulfurized or co-sulfurized metallic dithiophosphates and their use as extreme-pressure and anti-wear additives for lubricating oils.
U.S. Pat. No. 3,944,495 discloses that automatic transmission fluids can be improved by the addition of metallic dithiophosphates of the formula: ##STR2## in which:
R represents a C.sub.4 -C.sub.30 saturated aliphatic radical;
R' represents hydrogen, a C.sub.1 -C.sub.6 alkyl radical or a C.sub.6 -C.sub.9 aryl radical;
a is a whole number between 2 and 12;
n corresponds to the valence of the metal M; and
M represents an alkaline or alkaline-earth metal or a transition metal.
Such products are particularly well adapted for the problem associated with automatic transmission fluids, which do not require additives of great thermal stability. On the other hand, such products are not sufficiently thermally stable to be used as additives for crankcase oils and, in particular, for diesel crankcase oils.
It is also known that the properties of lubricating oils can be improved, according to French patent No. 1,310,171 (U.S. counterpart, U.S. Pat. No. 3,102,096), by using metallic dialkyl dithiophosphates prepared from monoalcohols of the "neo" type, that is to say, alcohols in which the carbon atom adjacent the carbon atom fixed to the hydroxyl group is completely replaced by alkyl groups. Such products have the drawback of being only of average effectiveness and, furthermore, of not being capable of industrial use because of the high cost of the "neo" monoalcohols.
By the present invention new thermally stable sulfurized or co-sulfurized metallic dithiophosphates have been discovered which can be used industrially, in particular, to improve the extreme-pressure and anti-wear properties of lubricating oils.
It is an object of the present invention to provide novel sulfurized metallic dithiophosphate oil additives which improve the extreme-pressure and anti-wear properties of lubricating oils which overcome the disadvantages of the prior art.
It is another object of the present invention to provide a novel process for the preparation of the sulfurized metallic dithiophosphate lubricating oil additives of the invention.
It is a further object of the invention to provide novel lubricating oil compositions containing the sulfurized metallic dithiosphophate additives of the invention.
Other objects will be apparent to those skilled in the art from the present description.