Front Matter

this method much more attractive to the organic chemist. It should be mentioned here

that the chemical industry may on occasion prefer to use 60 % or even 70 % H 2 O 2 in

order to avoid ‘buying and transporting large amounts of water’.

Of even more importance is the broad substrate range of perhydrolysis, as illu-

strated by the epoxidation of 1-octene witha-substituted carboxylic acids/acid es-

ters (Ru ̈sch gen. Klaas and Warwel, 1997). Epoxidation with these sources of peroxy

acids proceeded only by perhydrolysis; however, even with perhydrolysis the bulk-

iest branching accepted by NovozymÒ435 is a singlea-methyl group, but not ana-

ethyl or ana,a-dimethyl group. Nevertheless, this substrate range clears the way for a

biocatalytic route to chiral peroxy acids (Warwel and Ru ̈sch gen. Klaas, 2000).

NovozymÒ435-catalyzed perhydrolysis of ethyl acetate or methyl acetate leads to

peroxy acetic acid; thus treatment of olefins with NovozymÒ435/35 % H 2 O 2 /ethyl

acetate is a highly convenient general method for olefin epoxidation (Ru ̈sch gen.

Klaas and Warwel, 1998b). In contrast, the conversion of acetic acid with H 2 O 2

is a very poor method, as shown recently (albeit unintentionally) by Jarvie et al.

(1999). Other methods of obtaining peracetic acid by biocatalysis are mechanisti-

cally interesting, but of little synthetic value (Picard et al., 1997).

Other more unusual peroxy acids, such as peroxy acrylic acid, peroxy citric and

peroxy lactic acid, as well as derivatives of peroxy carbonic acid (Ru ̈sch gen. Klaas

and Warwel, 1999b) can also be prepared by perhydrolysis; peroxy acrylic and per-

oxy carbonic acid are also useful in oleochemistry (see Section 8.3.3).

7.3 Lipase-mediated lipid oxidations

Peroxy acids, which are generated by one of the methods described earlier, may be

used for various oxidation reactions such as C¼C-epoxidation, Baeyer – Villiger

oxidations (Lemoult et al., 1995; Pchelka et al., 1998), the oxidation of aldehydes to

carboxylic acids, and a variety of oxidative conversions of trialkyl silyl ethers (Ru ̈sch

gen. Klaas et al., 1999). Of these chemo-enzymatic oxidations, epoxidation is the

most important. Chemo-enzymatic epoxidation of simple olefins has been described

for the first time by Bjo ̈rkling et al. (1990), and the mechanism is shown in Figure 1.

As mentioned earlier, a similar system can be based on perhydrolyis, and it was

found later that perhydrolysis of dialkyl carbonates leads to a peroxy acid, that is a

superior oxidant for acid-sensitive substrates (Ru ̈sch gen. Klaas and Warwel, 1999a).

Apart from the oxidation of simple olefins, biocatalytic peroxy acid formation is

extremely useful for epoxidations in oleochemistry, because the carboxyl function

necessary for peracid generation and the C¼C bond are often conveniently situated

in one molecule.

118 7 Lipase-Catalyzed Peroxy Fatty Acid Generation and Lipid Oxidation