9,10,12-Trihydroxy octadecanoic acid rich fatty acid methyl esters (300 g) as prepared in example 1 was taken in one lit R.B.Flask and to this added propanoic anhydride (681 g), Dimethyl amino pyridine (DMAP, 300 mg) and xylene (100 ml) and stirred the contents magnetically at 180° C. for 6 hr. The course of the reaction was monitored by TLC. After completion of the reaction xylene and unconverted propanoic anhydride and propanoic acid were distilled under reduced pressure and the residue was taken in ethyl acetate. The ethyl acetate extract was washed with distilled water and passed through anhydrous sodium sulphate and concentrated under vacuum to recover the product (270 g) having an A.V. of 0.3, H.V. of 3.3 and I.V. of 2.0. The product was evaluated for viscosity, viscosity index (V.I.), pour point, flash point and copper strip corrosion and the data is provided in the following table.
