Lubricating oil compositions comprising a trinuclear compound antioxidant

Abstract

This invention relates to a lubricating oil composition comprising a Group I basestock and an antioxidant comprising an oil soluble trinuclear organomolybdenum compound of the generic formula (1): Mo 3 S x -(Q) wherein x is from 4 to 10 and Q is a core group, which may be a ligand, wherein the basestock has a kinematic viscosity at 100° C. (KV 100 ) from about 2 cSt to 50 cSt (2×10 −6 to 50×10 −6 m 2 /sec), a saturates content of <90% w/w, an aromatics content of >10% w/w and a sulphur content of >0.03% w/w. The composition has an improved stability when compared with either a Group II, III or IV basestock containing the same antioxidant or a Group I basestock containing a dinuclear molybdenum dithiocarbamate.

1 . A lubricating oil composition comprising a major amount of a Group I basestock and an antioxidant comprising an oil soluble trinuclear organomolybdenum compound of the generic formula: 
       Mo 3 S x -(Q)  (I) 
       wherein x is from 4 to 10 and Q is a core group, which may be a ligand.  
     
     
         2 . A composition according to  claim 1  wherein said basestock has a KV 100  in the range from 2-20 cSt, a sulphur content of >0.03% w/w (300 ppm) and a saturates content of <90% w/w.  
     
     
         3 . A composition according to any one of the preceding claims wherein the core group Q is a ligand capable of rendering the organomolybdenum compound of formula (I) oil soluble and ensuring that said molybdenum compound is substantially charge neutral.  
     
     
         4 . A composition according to any one of the preceding claims wherein the trinuclear organomolybdenum compound is represented by the formula (II): 
       Mo 3 S x L y   (II) 
       wherein L is the ligand and y is of a sufficient number, type and charge to render the compound of formula (I) oil soluble and to neutralise the charge on the compound of formula (I) as a whole.  
     
     
         5 . A composition according to  claim 4  wherein the ligands “L” are dihydrocarbyl dithiocarbamates of the structure (—S 2 CNR 2 ) wherein the dihydrocarbyl groups, R 2  impart oil solubility to the molybdenum compound.  
     
     
         6 . A composition according to  claim 5  wherein the group R is a substituent having carbon atoms directly attached to the remainder of the ligand and is predominantly hydrocarbyl in character.  
     
     
         7 . A composition according to any one of the preceding claims  4 - 7  wherein the total number of carbon atoms present among all of the hydrocarbyl groups of the organomolybdenum compounds' ligands is at least 21.  
     
     
         8 . A composition according to any one of the preceding claims wherein the trinuclear organomolybdenum compound is present in said composition in an amount from about 0.05 to 5.0 % w/w of the total composition.  
     
     
         9 . A composition according to any one of the preceding claims wherein the molybdenum metal is present in said composition in an amount from about 25 to 3000 ppm of the total composition.  
     
     
         10 . A method of improving the oxidative stability of a lubricant composition comprising a Group I basestock which has a kinematic viscosity at 100° C. (KV 100 ) from about 2 cSt to 50 cSt (2×10 −6  to 50×10 −6  m 2 /sec) and a saturates content of <90% w/w, an aromatics content of >10% w/w and a sulphur content of >0.03% w/w (300 ppm), said method comprising adding to the basestock an effective amount of an antioxidant comprising an oil soluble trinuclear organomolybdenum compound of the generic formula: 
       Mo 3 S x -(Q)  (I) 
       wherein x is from 4 to 10, preferably 7, and Q is a core group, which may be a ligand.