Castor oil fatty acid based estolide esters and their derivatives as potential lubricant base stocks
Castor oil was hydrolysed to castor fatty acids and self condensed to get a ricinoleic acid-based estolide of about 95 acid value. The carboxylic group of the estolide on subsequent esterification with linear or branched chain alcohols and also on acetylation of free hydroxy group yielded castor oil fatty acids based estolide esters and their acetates. All the products were evaluated for total acid number (TAN), viscosity, viscosity index, pour point, flash point, and copper strip corrosion and found to be potential lubricant basestocks.
1. An estolide compound of general formula 1
wherein average value of n is equal to one having acid value of estolide equal to 95 which correspond to average of two molecules of ricinoleic acid in the estolide; R1 is branched or unbranched hydrocarbon of C1 to C8; and R 2 is CH 3 CO.
2. An estolide compound as claimed in claim 1 , wherein R 1 is selected from a group consisting of methyl, iso-propyl, butyl, hexyl, and 2-ethylhexyl.
3. A process for preparation of the estolide compound of claim 1 , wherein the process comprises
(i) saponifying castor oil to obtain the ricinoleic acid;
(ii) heating the ricinoleic acid at temperature ranging between 175 to 190° C. under inert atmosphere for a period ranging between 3 to 5 hr to obtain an estolide compound of
wherein the average value of n is 1 and, R1 and R2 are H;
(iii) reacting the estolide compound obtained in step (ii) with an alcohol of carbon C1-C8 in presence of a catalyst selected from sulphuric acid or SnCl 2 , at reflux temperature or a temperature ranging between 140 to 160° C. for a period ranging between 3 to 8 hr to obtain a corresponding estolide ester;
(iv) reacting the estolide ester obtained in step (iii) with acetic anhydride and pyridine to obtain the compound of general formula 1 wherein R1 is branched or unbranched hydrocarbon of C1 to C8; and R2 is CH 3 CO.
4. A process as claimed in claim 3 , wherein the acid number of the compounds is 0.5 mg KOH/g.
5. A process as claimed in claim 3 , wherein the compounds of formula 1 are suitable as base stock of functional fluids as such and with blends and additives.
6. A process as claimed in claim 3 , wherein the alcohol of carbon C1-C8 is methanol, isopropanol, butanol, n-hexanol, or 2-ethylhexanol.
7. A process as claimed in claim 3 , wherein R 1 of formula 1 in step (iv) is selected from a group consisting of methyl, iso-propyl, butyl, hexyl, and 2-ethylhexyl.