Topics in Current Chemistry (2019) 377:2
1 3
have focused on maximizing the interfacial area between the gas and liquid phase to
enhance mass transfer.
The laboratories at the University of Bergen and at Fluens Synthesis developed a
novel reactor platform called the multi‑jet oscillating disk (MJOD) reactor [130]. An
electric motor powers the up–down movement of a piston by a variable‑frequency
and variable‑amplitude oscillator (Scheme 31a). The reaction mixture moves from
one cavity to the next, and is pushed up the reactor through the jets of the MJOD
disks. The reactor was applied to the organocatalyzed Minisci aerobic epoxidation
of olefins by N‑hydroxyphthalimide (NHPI) [131]. The batch process for this reac‑
tion suffers from the limitation of long reaction times (24–48 h), which limits the
efficiency and throughput of the process. The changes in the flow created by the
oscillating disks resulted in very good mixing, which accelerated reaction rates and
enabled residence times of 1–4 h.
A nebulizer‑based continuous‑flow reactor has been developed for the photo‑
chemical
1
O 2 chemistry (NebPhotOX) by Vassilikogiannakis and co‑workers at the
University of Crete [132]. A solution containing the substrate and the photosensi‑
tizer is nebulized by using pure O 2 or air into a chamber that is enclosed by LED
light strips to form
1
O 2 as the reactive intermediate. The NebPhotOx system was
used for the photooxidation of β‑citronellol (Scheme 31b). The pneumatic nebulizer
generates aerosols consisting of fine droplets with an approximate 60 μm average
diameter corresponding to a droplet‑specific surface areas of 100,000 m
2
m
−3
. The
same group also reported the synthesis of cyclopent‑2‑enones from furans using the
NebPhotOx reactor in a similar manner [133].
Raston and co‑workers have developed a vortex fluidic device (VFD) for accel‑
erating and increasing the efficiencies of organic reactions [134]. The dynamic thin
film is generated by continuously adding a fluid from jet feeds to a rapidly rotating
surface (Scheme 31c). The reaction mixture is rotated at very high speeds (up to
9000 rpm) to produce the liquid phase as a thin film, thus providing a large surface
area between the liquid and gas phases. The reactor system was demonstrated on the
aerobic oxidation of thiols to disulfides [135]. In particular, the aerobic oxidation
of N‑acetyl‑l‑cysteine in water was investigated. Full conversion was achieved in
less than 2.5 min residence time within a VFD. The aerobic oxidation within a VFD
configuration performed significantly better compared to in batch where only 5%
conversion was observed after 1 h reaction time. However, the system was not com‑
pared to a segmented flow reactor setup.
George, Poliakoff and co‑workers at the University of Nottingham recently
reported the construction of a thermal and photochemical “vortex reactor” that uses
a rapidly rotating cylinder to generate Taylor vortices (Scheme 31d) [136]. The vor‑
tices result in a high interfacial area between the gas and liquid phases, thus ena‑
bling rapid dissolution of oxygen into the liquid phase. An interesting feature of the
reactor system is that it draws air in from the laboratory so does not specifically
need pressurized oxygen from a cylinder, with the optimal uptake of air observed
at 4000 rpm. The reactor was demonstrated for a number of reaction systems that
utilize
1
O 2 as a reagent, including the photooxygenations of α‑terpinene and furfu‑
ryl alcohol and the photodeborylation of phenyl boronic acid. The system was also
102
Reprinted from the journal
1 3
have focused on maximizing the interfacial area between the gas and liquid phase to
enhance mass transfer.
The laboratories at the University of Bergen and at Fluens Synthesis developed a
novel reactor platform called the multi‑jet oscillating disk (MJOD) reactor [130]. An
electric motor powers the up–down movement of a piston by a variable‑frequency
and variable‑amplitude oscillator (Scheme 31a). The reaction mixture moves from
one cavity to the next, and is pushed up the reactor through the jets of the MJOD
disks. The reactor was applied to the organocatalyzed Minisci aerobic epoxidation
of olefins by N‑hydroxyphthalimide (NHPI) [131]. The batch process for this reac‑
tion suffers from the limitation of long reaction times (24–48 h), which limits the
efficiency and throughput of the process. The changes in the flow created by the
oscillating disks resulted in very good mixing, which accelerated reaction rates and
enabled residence times of 1–4 h.
A nebulizer‑based continuous‑flow reactor has been developed for the photo‑
chemical
1
O 2 chemistry (NebPhotOX) by Vassilikogiannakis and co‑workers at the
University of Crete [132]. A solution containing the substrate and the photosensi‑
tizer is nebulized by using pure O 2 or air into a chamber that is enclosed by LED
light strips to form
1
O 2 as the reactive intermediate. The NebPhotOx system was
used for the photooxidation of β‑citronellol (Scheme 31b). The pneumatic nebulizer
generates aerosols consisting of fine droplets with an approximate 60 μm average
diameter corresponding to a droplet‑specific surface areas of 100,000 m
2
m
−3
. The
same group also reported the synthesis of cyclopent‑2‑enones from furans using the
NebPhotOx reactor in a similar manner [133].
Raston and co‑workers have developed a vortex fluidic device (VFD) for accel‑
erating and increasing the efficiencies of organic reactions [134]. The dynamic thin
film is generated by continuously adding a fluid from jet feeds to a rapidly rotating
surface (Scheme 31c). The reaction mixture is rotated at very high speeds (up to
9000 rpm) to produce the liquid phase as a thin film, thus providing a large surface
area between the liquid and gas phases. The reactor system was demonstrated on the
aerobic oxidation of thiols to disulfides [135]. In particular, the aerobic oxidation
of N‑acetyl‑l‑cysteine in water was investigated. Full conversion was achieved in
less than 2.5 min residence time within a VFD. The aerobic oxidation within a VFD
configuration performed significantly better compared to in batch where only 5%
conversion was observed after 1 h reaction time. However, the system was not com‑
pared to a segmented flow reactor setup.
George, Poliakoff and co‑workers at the University of Nottingham recently
reported the construction of a thermal and photochemical “vortex reactor” that uses
a rapidly rotating cylinder to generate Taylor vortices (Scheme 31d) [136]. The vor‑
tices result in a high interfacial area between the gas and liquid phases, thus ena‑
bling rapid dissolution of oxygen into the liquid phase. An interesting feature of the
reactor system is that it draws air in from the laboratory so does not specifically
need pressurized oxygen from a cylinder, with the optimal uptake of air observed
at 4000 rpm. The reactor was demonstrated for a number of reaction systems that
utilize
1
O 2 as a reagent, including the photooxygenations of α‑terpinene and furfu‑
ryl alcohol and the photodeborylation of phenyl boronic acid. The system was also
102
Reprinted from the journal