Front Matter

These workers also used these peracidsin situfor epoxidation (Bjo ̈rkling et al.,

1990; 1992; Godtfredsen et al., 1990). In the meantime, we investigated extensively

the potential of lipase-mediated catalysis for the generation of a variety of peroxy

fatty acids, together with theirin situapplication for oxidation reactions in oleo-

chemistry.

7.2 Lipase-catalyzed peroxy acid generation

7.2.1 Generation from fatty acids

While examining the substrate range of Novo’s peroxy acid synthesis (Ru ̈sch gen.

Klaas and Warwel, 1997), it was found that all unbranched fatty acids with four to 22

carbon atoms were good substrates for NovozymÒ435-catalyzed peroxy acid syn-

thesis. Beside these fatty acids, however, only very few carboxylic acids (e.g. 2-

phenyl acetic acid) produced peroxy acids in good yield. The onlya-branched car-

boxylic acid which yielded any peroxy acid at all wasi-butyric acid; other branched

or benzoic acids were completely inactive.

These results were not completely surprising. The lipase B fromCandida antarc-

tica, which was used for most of our experiments, is known to possess a notably

narrow entrance to the active site (Uppenberg et al., 1994). An obvious solution

to our substrate restrictions would thus have been to use another lipase. In total,

about 30 lipases were investigated; although most lipases had a certain activity

for peroxy acid generation from fatty acids and H 2 O 2 , stability was mostly – and

in contrast to NovozymÒ435-very poor. Hence, NovozymÒ435 was identified as

the enzyme of choice for any preparative application, the substrate range being en-

hanced by modifying the reaction conditions.

7.2.2 Generation from carboxylic acids esters

Kirk et al. (1994) referred earlier to the possibility of perhydrolysis by H 2 O 2 analo-

gously to ester hydrolysis, but did not carry out any investigations in that respect.

However, we were successful in developing a useful protocol for lipase-catalyzed

ester perhydrolysis by H 2 O 2 :

Perhydrolysis proceeds especially well if the ester is applied as the solvent, i.e. in a

large excess, as it then has certain advantages over the lipase-catalyzed generation of

peroxy acids from free fatty acids. In most cases, perhydrolysis works with common

35 % aqueous H 2 O 2 , whereas for the conversion of free fatty acids 60 % H 2 O 2 is used

preferably. Considering that 60 % H 2 O 2 cannot be obtained from fine chemicals

providers such as Merck or Aldrich, the possibility of using 35 % H 2 O 2 makes

7.2 Lipase-catalyzed peroxy acid generation 117