Calendula Oil as Paint Additive

During the last few years modern synthetic methods have been applied extensively to fatty compounds for the selective functionalization of the C,C-double bond of unsaturated fatty compounds and gave a large number of novel fatty compounds from which interesting properties are expected.[1] Presently our interest is focused to plant oils containing unsaturated fatty acids with a highly reactive hexatriene system such as calendula oil and tung oil. The latter – obtained from the nuts of the tung oil tree - is a drying oil and is used for a number of products including varnish, resins, inks, paints and coatings. Similar properties are expected from calendula oil. Octadec-8,10-trans-12-cis-trienoic acid (calendic acid) is the main fatty acid (ca. 60%) in the seed oil of calendula officinalis. We obtained calendic acid esters from the native oil by a simple transesterification method using alcohols, i.e. methanol, ethanol or isopropanol and sodium methoxide as catalyst. The solvent-free Diels-Alder reaction of methyl calendulate and maleic anhydride gave exclusively one highly functionalized cycloaddition product in 78% yield. The endo-8,12-cycloaddition product was formed with high regio- and stereoselectivity.[2] The reaction can be applied to the native oil as well.
In a patent by DSM methyl calendulate is described as a very efficient reactive diluent.[3] In addition to this we obtained even better results for ethyl and isopropyl calendulate as reactive diluent showing low viscosity and good drying properties.
In special applications e.g. in coating material used in the outskirt area the substitution of tung oil should be possible by calendula oil.

[1] U. Biermann, W. Friedt, S. Lang, W. Lühs, G. Machmüller, J.O. Metzger, M. Rüsch gen. Klaas, H.J. Schäfer, M.P. Schneider, Angew. Chem., 2000, 112, 2292-2310, Angew. Chem. Int. Ed. 2000, 39, 2206-2224.
[2] U. Biermann, W. Butte, T. Eren, D. Haase, J. O. Metzger, "Diels–Alder Reactions with Conjugated Triene Fatty Acid Esters", Eur. J. Org. Chem., 2007, 3859–3862.
[3] Z. Theodorus, DSM NV (NL): EP0685543, 1995.