"Front Matter". In: Organosilanes in Radical Chemistry - Index of

Oxidation Studies on Silyl-Substituted Silicon Hydrides 191
Initiation steps:
ROO
Propagation steps:
Ph Ph Ph
Si O Si O Si
H
H
Termination steps:
+
AIBN
R + O2 Ph Ph Ph
Si Si Si
Ph Ph Ph
Si Si Si
H
Ph Ph Ph
Si O Si O Si
H
H
R
ROO
ROOH
Ph Ph Ph
Si Si Si
Ph Ph Ph
Si Si Si + O2 fast
Ph Ph Ph
Si Si Si
H H
H O
O
H
Ph Ph Ph
Si Si Si
fast
Ph
Si O
Ph
Si
Ph
O Si
H O
O
H
H
H
2
+
R i
H H H H H
k p, slow
2k t
Ph Ph Ph
Si O Si O Si
H H H
no radical products
+
Ph Ph Ph
Si Si Si
H
H H H
Scheme 8.3 The reaction mechanism for the radical chain oxidation of poly(phenylhydrosilane)
conversion and yield depend upon the experimental conditions. For example,
50 % conversion and yield > 95 % have been obtained after 1 h of air bubbled
into 1 ml of pure silane. The reaction is a radical chain process since it is
accelerated by radical initiation and retarded by common radical inhibitors.
SiMe3 Me3Si Si
H
SiMe3 +
SiMe3 + O2 Me3Si O Si
H
O SiMe3 (8.4)
The homologous (Me3Si) 2Si(H)Me does not react spontaneously with air or
molecular oxygen at room temperature. However, a reaction takes place at 80 8C
when air or molecular oxygen is bubbled into the pure material or its solutions to
form a major product that contains the siloxane chain (Reaction 8.5) [15]. In
general, yields of siloxane are about 50 %. Also in this case the reaction is
accelerated by radical initiation and retarded by common radical inhibitors.