Oxidation of drying oils containing non-conjugated and conjugated double bonds catalyzed by a cobalt catalyst

The oxidation of drying oil containing non-conjugated (linseed oil) and conjugated (tung oil) double bonds catalyzed by Co(II)-2-ethylhexanoate (Co-EH) is investigated. There is distinctive difference in the oxidation mechanism between the two model oils. For the non-conjugated linseed oil, H-abstra...

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Bibliographic Details
Published in:Progress in organic coatings 2005-11, Vol.54 (3), p.198-204
Main Authors: Oyman, Z.O., Ming, W., Linde, R. van der
Format: Article
Language:English
Subjects:
Alkyd
Applied sciences
Coatings. Paints, varnishes and inks
Cobalt catalyst
Drying oil
Exact sciences and technology
Film formation and curing, properties, testing
Oxidative drying
Polymer industry, paints, wood
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Summary:The oxidation of drying oil containing non-conjugated (linseed oil) and conjugated (tung oil) double bonds catalyzed by Co(II)-2-ethylhexanoate (Co-EH) is investigated. There is distinctive difference in the oxidation mechanism between the two model oils. For the non-conjugated linseed oil, H-abstraction occurs via the most susceptible double allylic H atom. A large amount of oxygen is taken up, leading to the formation of hydroperoxides; the hydroperoxides are then decomposed into alkoxy and peroxy free radicals, followed by the formation of cross-links and byproducts. In contrast, for the mainly conjugated tung oil, the oxidation has to start with H-abstraction from the monoallylic position. In comparison with linseed oil, a lower amount of oxygen is consumed, and much less hydroperoxides and byproducts are formed. It indicates that, once free radicals are formed, they tend to directly add to a conjugated double bond, instead of abstracting a monoallylic H atom. A tentative explanation is given in terms of bond dissociation energy of related bonds.
ISSN:0300-9440
1873-331X
DOI:10.1016/j.porgcoat.2005.06.004