Chemistry Reference
In-Depth Information
RCO
2
H
caprolactone
peracid
generation
H
2
O
2
RCO
3
H
H
2
O
peracid
distillation
product
distillation
reaction
H
2
O
cyclohexanone
RCO
3
H
RCO
2
H,
cyclohexanone
to recycle
via Friedel-Crafts alkylation, in order to access
particular substitution patterns. Aldehyde to phenol
(the Dakin reaction) occurs only with strongly acti-
vating
o
- and/or
p
-substituents [241a,251]. Ketone
to phenol is common, owing to the ease of migra-
tion of phenyl groups relative to alkyl. A recent
system has employed H
2
O
2
in the presence of boric
and sulfuric acids [252].
Fig. 11.30
Caprolactone manufacture using the peracid
process.
The Baeyer-Villiger reaction and reagent systems
have been reviewed comprehensively [245]. Most
systems described to date are based either on
peracids or on electrophilic activation of peroxide by
various acid catalysts. Many Lewis acids are effective
[246] but tend to suffer deactivation sooner or later
owing to the water contained in or liberated from
the H
2
O
2
.
Inorganic peracid analogues such as perseleninic
acids, often derived from diselenides, have been
studied quite extensively [247]. Also, solid catalysts
including heteropolyacids [248], zirconium and
similar phosphates [249] and even uranium phos-
phate [250] have been described. Caprolactone is
particularly easy to hydrolyse but most other sub-
strates do give esters or lactones that are stable under
the reaction conditions.
The Baeyer-Villiger reaction can be a useful way
of making phenols from aldehydes or from ketones
4.2 Oxidations at nitrogen
There is a diverse range of specific oxidations at
nitrogen; a complete description of these, as they
relate to peroxygens, can be found elsewhere [1-4].
The ability to activate peroxygens selectively for a
given oxidation type is, as expected, very valuable in
such circumstances.
Oxidation of ammonia itself by peroxygens is of
importance in two industrial processes. One of the
main routes to hydrazine [253] involves reaction
of ammonia, hydrogen peroxide and 2-butanone
(MEK) to give an azine intermediate, which is then
hydrolysed to hydrazine, liberating the ketone for
