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Process (48), sometimes termed Bennett mechanism, yields H
2
O
2
and two
carbonyl compounds. It has often been thought of as being concerted, proceed-
ing via two five-membered rings (Bennett and Summers 1974; Bothe and Schul-
te-Frohlinde 1978) or two six-membered rings involving two water molecules
(see above). This has been criticized on account of the excessive entropic re-
quirements of the bicyclic transition state, and, following the lateral cleavage
(55), reactions (56) and (57) have been proposed instead (Khursan et al. 1990; for
a discussion, see von Sonntag and Schuchmann 1997).
R
2
CHO
•
+
•
OOOCHR
2
→
R
2
C=O + HOOOCHR
2
(55)
HOOOCHR
2
→
HO
2
•
+
•
OCHR
2
(56)
HO
2
•
+
•
OCHR
2
→
H
2
O
2
+ O=CHR
2
(57)
As far as concerted reactions are concerned, it should be mentioned that two
other processes of considerable concertedness have been recognized in the stud-
ies of the fate of the peroxyl radicals derived from cyclopentane and cyclohexane
[e.g., reaction (58); Zegota et al. 1984] and acetate [reaction (59); Schuchmann
et al. 1985].
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