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Abstract
The self-metathesis reaction of soy, rapeseed, tall, and linseed oil fatty acids was investigated for the synthesis of symmetrical long-chain unsaturated-α,ω-dicarboxylic acids. The metathesis reactions were carried out in the presence of a Grubbs catalyst under solvent-free condition at a catalyst loading of 0.01 mol% to fatty acid substrate at 50 °C. Under these conditions, the conversions of starting unsaturated acids to metathesis products were >80% and the isolated yields of unsaturated dicarboxylic acid products were >70% of theoretical. This approach represents an effective and efficient route for the synthesis of these potentially useful dicarboxylic acids since they can serve as important intermediates in the production of several materials such as biodegradable polymers.
Keywords Diacids * Fatty acids * Hydrocarbons * Olefin metathesis * Unsaturated fatty acids
Introduction
Fats and oils are readily available domestic renewable materials that serve as the primary source of long-chain unsaturated fatty acids. The conversion of these long-chain fatty acids to long-chain-oe,co-unsaturated dicarboxylic acids (diacids) therefore is of interest since in addition to being derived from renewable resources, they are biodegradable and environmentally benign materials. Such diacids have potential in the production of biodegradable polyamides, polyesters, and polyurethanes. Presently, α,ω-diacids can be produced industrially by fermentation. For example, α,ω-diacids of C^sub 11^-C^sub 18^ chain-length are produced in China and unsaturated α,ω-diacids, particularly α,ω-octadecenedioic acid, from vegetable and animal raw materials. Using the latter diacid, nylons, polyamides, polyesters, and polyacrylate esters were synthesized [1]. Although diacids can be successfully produced by fermentation, there are environmental concerns because the aqueous waste products from these processes typically contain bacteria and other waste materials of fermentation, which places significant burden on water treatment systems.
Catalyst-based syntheses are particularly important and account for ~60% of today's chemical products [2, 3]. An important reaction of this type is olefin metathesis, in which an olefin and a transition metal carbene complex react to generate new olefins. Common catalysts used in olefin metathesis are homogeneous ruthenium-based catalysts such as those developed by Grubbs [4, 5]. Grubbs catalysts are typically ruthenium-based alkylidene carbene complexes that are stable to moisture, often show good functional group tolerance and hence work well for functionally substituted alkenes [6].
Grubbs type catalysts previously have been used in metathesis reactions of unsaturated...