5 research outputs found
Continuous Flow Synthesis of a Key 1,4-Benzoxazinone Intermediate via a Nitration/Hydrogenation/Cyclization Sequence
The
preparation of a functionalized 4H-benzo-[1,4]-oxazin-3-one
was completed via a three-step nitration/hydrogenation/cyclization
sequence. The unstable nature of the nitro and amino intermediates,
in addition to the hazards associated with the nitration of organic
compounds in general, makes this procedure exceedingly difficult to
perform on industrial scale. To overcome these limitations, we have
developed a fully integrated continuous protocol in which the aromatic
starting material (2,2-difluoro-2-(3-fluorophenoxy)-<i>N</i>,<i>N</i>-dimethylacetamide) is subjected to an initial
continuous flow dinitration using 20% oleum in combination with 100%
HNO<sub>3</sub> (2.5 equiv) using a microstructured device heated
to 60 °C. This was followed directly by continuous flow hydrogenation
of the dinitrointermediate over a Pd/C fixed bed catalyst at 45 °C.
The resulting air-sensitive diamino derivative was then directly cyclized
to the desired 6-amino-2,2,7-trifluoro-4H-benzo-[1,4]-oxazin-3-one
target compound via an acid-catalyzed cyclization step at 80 °C
using a tubular reactor. Uninterrupted continuous flow processing
was achieved by integrating liquid–liquid membrane separation
technology and the inline removal of excess of hydrogen gas using
gas permeable tubing into the process. The overall product yield for
the continuous flow process was 83%, a significant increase compared
to yield reported for the batch process (67%)
Planar Biphenyl-Bridged Biradicals as Building Blocks for the Design of Quantum Magnets
We have synthesized and investigated a new biphenyl-4,4′-bis(nitronyl
nitroxide) radical with intermediately strong antiferromagnetic interactions.
This organic biradical belongs to a family of materials that can be
used as a building block for the design of new quantum magnets. For
quantum magnetism, special attention has been paid to coupled <i>S</i> = <sup>1</sup>/<sub>2</sub> dimer compounds, which when
placed in a magnetic field, can be used as model systems for interacting
boson gases. Short contacts between the oxygen atoms of the nitronyl
nitroxide units and the hydrogen atoms of the benzene rings stabilize
a surprisingly planar geometry of the biphenyl spacer and are responsible
for a small magnetic interdimer coupling. The strength of the antiferromagnetic
intradimer coupling constant <i>J</i>/<i>k</i><sub>B</sub> = −14.0 ± 0.9 K, fitting the experimental
SQUID-data using an isolated-dimer model. The deviations from the
isolated-dimer model are attributed to a small interdimer coupling <i>J</i>′/<i>k</i><sub>B</sub>, on the order of
1 K, consistent with the crystal structure
Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure
Electro-oxidation
of the quinoidal bisdithiazole BT in dichloroethane
in the presence of [Bu<sub>4</sub>N][GaBr<sub>4</sub>] affords the
1:1 radical ion salt [BT][GaBr<sub>4</sub>], crystals of which belong
to the trigonal space group <i>P</i>3. The packing pattern
of the radical cations provides a rare example of an organic kagome
basket structure, with <i>S</i> = 1/2 radical ion chains
located at the triangular corners of a trihexagonal lattice. Magnetic
measurements over a wide temperature range from 30 mK to 300 K suggest
strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i><sub>b</sub> ∼ 30 K, but reveal no anomalies
that would be associated with magnetic order. These observations are
discussed in terms of the symmetry allowed magnetic interactions within
and between the frustrated layers
Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure
Electro-oxidation
of the quinoidal bisdithiazole BT in dichloroethane
in the presence of [Bu<sub>4</sub>N][GaBr<sub>4</sub>] affords the
1:1 radical ion salt [BT][GaBr<sub>4</sub>], crystals of which belong
to the trigonal space group <i>P</i>3. The packing pattern
of the radical cations provides a rare example of an organic kagome
basket structure, with <i>S</i> = 1/2 radical ion chains
located at the triangular corners of a trihexagonal lattice. Magnetic
measurements over a wide temperature range from 30 mK to 300 K suggest
strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i><sub>b</sub> ∼ 30 K, but reveal no anomalies
that would be associated with magnetic order. These observations are
discussed in terms of the symmetry allowed magnetic interactions within
and between the frustrated layers
Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure
Electro-oxidation
of the quinoidal bisdithiazole BT in dichloroethane
in the presence of [Bu<sub>4</sub>N][GaBr<sub>4</sub>] affords the
1:1 radical ion salt [BT][GaBr<sub>4</sub>], crystals of which belong
to the trigonal space group <i>P</i>3. The packing pattern
of the radical cations provides a rare example of an organic kagome
basket structure, with <i>S</i> = 1/2 radical ion chains
located at the triangular corners of a trihexagonal lattice. Magnetic
measurements over a wide temperature range from 30 mK to 300 K suggest
strongly frustrated AFM interactions on the scale of <i>J</i>/<i>k</i><sub>b</sub> ∼ 30 K, but reveal no anomalies
that would be associated with magnetic order. These observations are
discussed in terms of the symmetry allowed magnetic interactions within
and between the frustrated layers