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Abstract
A chemo-enzymatic approach for the conversion of oleic acid into azelaic and pelargonic acid is herein described. It represents a sustainable alternative to ozonolysis, currently employed at the industrial scale to perform the reaction. Azelaic acid is produced in high chemical purity in 44% isolation yield after three steps, avoiding column chromatography purifications. In the first step, the lipase-mediated generation of peroleic acid in the presence of 35% H2O2 is employed for the self-epoxidation of the unsaturated acid to the corresponding oxirane derivative. This intermediate is submitted to in situ acid-catalyzed opening, to afford 9,10-dihydroxystearic acid, which readily crystallizes from the reaction medium. The chemical oxidation of the diol derivative, using atmospheric oxygen as a stoichiometric oxidant with catalytic quantities of Fe(NO3)3∙9∙H2O, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), and NaCl, affords 9,10-dioxostearic acid which is cleaved by the action of 35% H2O2 in mild conditions, without requiring any catalyst, to give pelargonic and azelaic acid.
Highlights
The employment of renewable feedstocks in the chemical industry is steadily advancing to ensure more efficient use of natural resources, reduce the dependence on fossil raw materials, and give a contribution to achieving sustainable consumption and production patterns [1].Fats and oils represent an important class of renewable feedstock from which the so-called oleochemicals are obtained
The enzymatic synthesis of azelaic acid reported in 2013 by Song et al [19] (Figure 2) consisted of the use of recombinant Escherichia coli cells expressing at the same time the genes encoding an oleate hydratase from Stenotrophomonas maltophilia, an alcohol dehydrogenase (ADH) from Micrococcus luteus, and a BV monooxygenase (BVMO) from Pseudomonas putida KT2440 for the transformation of oleic acid into 9-(nonanoyloxy)nonanoic acid (7)
In a further development of the work [20], the oxidation of derivative 8 by an ADH from P. putida GPo1 completed the route to azelaic acid
Summary
Fats and oils represent an important class of renewable feedstock from which the so-called oleochemicals are obtained They are abundant in nature, biodegradable, and have nontoxic properties. The major process for transforming fats and oils into oleochemicals is hydrolysis, converting natural triglycerides into crude glycerine and mixtures of fatty acids The latter are submitted to reactions involving either the carboxylic group (to afford soaps, esters, amides, amines, and alcohols) or the reduction/oxidation of the C=C double bonds, if present. Among these procedures developed to obtain fine chemicals, the oxidative cleavage of unsaturated fatty acids for the production of dicarboxylic acids, hydroxy acids, and amino acids has received great attention in the last decade [2,3,4]. Only two dicarboxylic acids prepared from oleochemicals have been commercialized, i.e., sebacic acid (1), obtained by the alkaline cleavage of castor oil [5], and azelaic acid (2), which is produced together with
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