esters (RME, ‘biodiesel’) was epoxidized using the same procedure (Warwel et al.,
1996); in this case, the composition of the epoxidized fatty acid esters also closely
matched the composition of the biodiesel.
7.3.3 Epoxidation of unsaturated fatty alcohols and their
derivatives
Unsaturated fatty alcohols may also be epoxidized by lipase-catalyzed perhydrolysis
(Ru ̈sch gen. Klaas and Warwel, 1998b). Generally, peroxy acid formation is not the
only lipase-catalyzed reaction to occur and interestingly, the outcome of the reaction
depends on the ester applied for peroxy acid generation (Figure 5).
Fatty acid esters such as butyric acid ethylester react to epoxy alkanol acylates in a
three-step – one-pot reaction. In the first step, the unsaturated alcohol is esterified,
after which the resulting unsaturated ester is then epoxidized. The nature of these
consecutive reactions is shown clearly in Figure 6. Both the alcohol and the ester
components can be varied widely (Tables 3 and 4), and even epoxy acrylates can be
made directly, implying the intermediate formation of peroxy acrylic acid.
The reaction has a completely different outcome using the perhydrolysis of diethyl
carbonate. Epoxidation byin situformation of a peroxy carbonic acid derivative
proceeds smoothly, but the corresponding acid is not stable and cannot esterify
the alcohols; therefore, the product (with a selectivity of98 %) is the epoxidized
alcohol.
In an extension of these syntheses, we explored lipase-mediated conversion of
unsaturated fatty alcohol trialkyl silyl ethers and identified a range of synthetically
useful one-pot – multi-step reactions (Figure 7) (Ru ̈sch gen. Klaas et al., 1999).
7.3 Lipase-mediated lipid oxidations 123
Table 2.Chemo-enzymatic ‘self’-epoxidation of plant oils by NovozymÒ435/H 2 O 2.
No. Plant oil Conversion^1 Selectivity^2 Oxirane oxygen^3
2–1 rapeseed 99 92 5.3
2–2 sunflower 88 100 5.8
2–3 soybean 99 94 7.1
2–4 linseed 98 98 9.9
2–5 castor 95 95 4.5
2–6 sunflower + linseed 434 95 3.8
2–7 soybean + linseed 514 84 4.0
(^1) Related to iodine value.
(^2) Epoxide formed per C¼C-bond converted.
(^3) Percentage of oxirane oxygen in weight % according to titration and elemental analysis.
(^4) Deliberate restriction of conversion to mimic vernonia oil.
C¼C:H 2 O 2 (35 %)¼1 : 1.5; 0.05 C¼C/g NovozymÒ435; 16--72 h at room temperature in toluene;
addition of 5 mol% free fatty acid.