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up to 100% with 499% selectivity. Reactions were carried out in a basic
(K
2
CO
3
) aqueous medium, without any organic solvent and under atmos-
pheric pressure of air (or O
2
), with high yields and selectivities. Those mild
conditions are of industrial significance.
d
n
4
r
4
n
g
|
1
1.2.2.5 Porphyrins as Photosensitizers
Safari and co-workers introduced a new selective, economical and ecient
aerobic pathway for the selective photo-oxidation of a variety of aromatic and
aliphatic alcohols to the corresponding aldehyde and ketone derivatives.
33
Their method uses molecular oxygen (1 atm pressure of air) in the presence
of free base porphyrins and metalloporphyrins as sensitizers (Sens*) and
white light or sunlight in CH
3
CN at room temperature. Scheme 1.6 shows
the structures of the sensitizers used and the reaction conditions. This
method is broad in scope, exhibits chemoselectivity and proceeds under
mild reaction conditions. The resulting products are obtained in good
conversions within a reasonable time. The best results with both primary
and secondary alcohols were obtained with metallated H
2
TMP and iron-
porphyrins ClFeTMF.
1.2.2.6 Dimethylglyoxime
Transition metal species (ML
x
,M
ΒΌ
Co, Fe, Cu, Mn, Ni), which are usually
used in the form of metalloenzymes, synthetic porphyrins and Schiff base
.
OH
Sens*, air, sunlight or white light
O
CH
3
CN, r.t.
R
R'
R
R'
R
2
R
4
R
3
R
3
R
1
R
5
R
2
R
4
N
R
5
R
1
Sens* =
N
M
N
R
1
R
5
N
R
2
R
4
R
5
R
1
R
3
R
3
R
4
R
2
H
2
TPP
: R
1
=R
2
=R
3
=R
4
=R
5
=H,
M
: 2H;
H
2
TMP
: R
1
=R
3
=R
5
= CH
3
, R
2
=R
4
=H,
M
: 2H;
H
2
TPFPP
: R
1
=R
2
=R
3
=R
4
=R
5
=F,
M
: 2H;
M
: H, Fe, Mn and Zn
Scheme 1.6 Free base porphyrins and metalloporphyrins as sensitizers for selective
photo-oxidation.
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