14
1 Cavitation and Chemical Reactivity
• Weissler reaction: A KI solution is submitted to ultrasonic irradiation and the
oxidative production of iodine I 3
− is monitored by UV spectroscopy at around
350 nm.
• p-CBA probe reaction: The oxidative disappearance of para-chlorobenzoic acid is
monitored throughout time by UV detection at 234 nm.
Weissler reaction appears nowadays as the most implemented because it is the
easiest and most reliable chemical way to quantify OH° formation.
1.10 The Three Types of Sonochemical Reactions
The dynamic behaviour of the cavitation bubbles in homogeneous or heterogeneous
medium presents noticeable differences. Whereas they are rather spherical in homogeneous solutions, they appear to be deformed in heterogeneous conditions notably
in the presence of solid particles where they can be absorbed or even trapped within
the crevices of the solid network. In that case, collapsing bubble develops hot jet of
liquid directed towards the solid, eroding its surface together with secondary mechanical effects such as microstreaming, shock waves and micro-jets greatly impacting
kinetics and yields (Suslick 1988; Lepoint and Lepoint-Mullié 1998). This aspect
represents a large part of the literature related to heterogeneous organic environmental sonochemistry. On the other hand, in homogeneous conditions, mechanical effects
vanish and chemical effects predominate with more energetically violent collapses.
Cavitation originating from dissolved gas/volatilized molecules in a homogeneous
solution is usually referred as homogeneous cavitation and focuses on the creation
and subsequent faith of formed in situ radical species. Synthetic organic reactions
can be theoretically designed with reactants and solvents with adequate volatility,
affinity, miscibility and reactivity to draw up a synthetic route. An organic synthetic reaction occurring in heterogeneous conditions can be conjointly promoted
by both physical and chemical effects of ultrasound whereas the one occurring in
homogeneous conditions can be barely promoted by physical effects. Three classes
of sonochemical reactions have been established as early as 1993 by the late J. L.
Luche, leading pioneer in the field of organic synthetic sonochemistry. Indeed, he
published his first article about Barbier reaction with organolithium compounds in
a cleaning bath announcing the renewal of the discipline after almost 70 years of
silence following the first ever published paper in 1927 by A. Loomis.
• Type I: Sonochemical reactions occurring in homogeneous phase, also called
‘true’ sonochemistry that is driven by a radical pathway, in particular S.E.T (single
electron transfer) mechanisms. The formation of highly reactive intermediates
radical species able to initiate different mechanistic paths than under classical
conditions is enabled. The use of radical scavengers can reveal the radical nature
of the mechanism by quenching the reaction.
• Type II: Sonochemical reactions occurring in heterogeneous phase, also called
‘false’ chemistry. Physical effects arisen from collapsing bubbles generate reduc-
1 Cavitation and Chemical Reactivity
• Weissler reaction: A KI solution is submitted to ultrasonic irradiation and the
oxidative production of iodine I 3
− is monitored by UV spectroscopy at around
350 nm.
• p-CBA probe reaction: The oxidative disappearance of para-chlorobenzoic acid is
monitored throughout time by UV detection at 234 nm.
Weissler reaction appears nowadays as the most implemented because it is the
easiest and most reliable chemical way to quantify OH° formation.
1.10 The Three Types of Sonochemical Reactions
The dynamic behaviour of the cavitation bubbles in homogeneous or heterogeneous
medium presents noticeable differences. Whereas they are rather spherical in homogeneous solutions, they appear to be deformed in heterogeneous conditions notably
in the presence of solid particles where they can be absorbed or even trapped within
the crevices of the solid network. In that case, collapsing bubble develops hot jet of
liquid directed towards the solid, eroding its surface together with secondary mechanical effects such as microstreaming, shock waves and micro-jets greatly impacting
kinetics and yields (Suslick 1988; Lepoint and Lepoint-Mullié 1998). This aspect
represents a large part of the literature related to heterogeneous organic environmental sonochemistry. On the other hand, in homogeneous conditions, mechanical effects
vanish and chemical effects predominate with more energetically violent collapses.
Cavitation originating from dissolved gas/volatilized molecules in a homogeneous
solution is usually referred as homogeneous cavitation and focuses on the creation
and subsequent faith of formed in situ radical species. Synthetic organic reactions
can be theoretically designed with reactants and solvents with adequate volatility,
affinity, miscibility and reactivity to draw up a synthetic route. An organic synthetic reaction occurring in heterogeneous conditions can be conjointly promoted
by both physical and chemical effects of ultrasound whereas the one occurring in
homogeneous conditions can be barely promoted by physical effects. Three classes
of sonochemical reactions have been established as early as 1993 by the late J. L.
Luche, leading pioneer in the field of organic synthetic sonochemistry. Indeed, he
published his first article about Barbier reaction with organolithium compounds in
a cleaning bath announcing the renewal of the discipline after almost 70 years of
silence following the first ever published paper in 1927 by A. Loomis.
• Type I: Sonochemical reactions occurring in homogeneous phase, also called
‘true’ sonochemistry that is driven by a radical pathway, in particular S.E.T (single
electron transfer) mechanisms. The formation of highly reactive intermediates
radical species able to initiate different mechanistic paths than under classical
conditions is enabled. The use of radical scavengers can reveal the radical nature
of the mechanism by quenching the reaction.
• Type II: Sonochemical reactions occurring in heterogeneous phase, also called
‘false’ chemistry. Physical effects arisen from collapsing bubbles generate reduc-