4 research outputs found
Pd-Catalyzed Regioselective Arylation on the C‑5 Position of <i>N</i>‑Aryl 1,2,3-Triazoles
We herein report a highly efficient
method for the arylation at
the C-5 position of <i>N</i>-aryl 1,2,3-triazoles via a
direct palladium catalyzed arylation reaction. The optimal reaction
conditions required a combination of Pd(OAc)<sub>2</sub> and tris(<i>o</i>-tolyl)phosphine as catalyst, and Cs<sub>2</sub>CO<sub>3</sub> as the base under inert atmosphere. A variety of C-5 substituted <i>N</i>-aryl 1,2,3-triazoles were prepared using these conditions
with yields in the 70–88% range. Regioselective C-5 arylations
were also performed on 1,4-disubstituted 1,2,3-triazoles. The regioselectivity
in triazole substitution at the C-5 position was confirmed by single
crystal XRD. In addition, computational investigations of key steps
of the catalytic cycle using the density functional theory have provided
a rationalization to the selective C-5 arylation of <i>N</i>-aryl 1,2,3-triazoles
Studies on CL-20/HMX (2:1) Cocrystal: A New Preparation Method and Structural and Thermokinetic Analysis
A new
preparation method for CL-20/HMX (2:1) cocrystal has been
established at the laboratory level that is amenable for scale up.
Solvent evaporation from a saturated solution of the stoichiometric
mixture in the presence of a high boiling antisolvent, comparatively
a very efficient and cheaper method, yielded pure cocrystals. Cocrystals
were well characterized by spectroscopic, thermoanalytical tools,
X-ray diffraction, and microscopic techniques. A correlation of percentage
of cocrystal formation with evaporation rate has been obtained through
quantitative analysis using Raman spectrometry. An evaporation rate
of <1 mL/min consistently produced pure cocrystal confirmed by
Raman and powder X-ray diffraction analysis. Thermokinetic analysis
suggests the cocrystal to be more stable than CL-20 with an energy
of activation of 65 kcal/mol, higher than CL-20 but inferior to HMX.
Significant augmentation in the values of <i>k</i> and <i>A</i> over CL-20 justified a faster decomposition rate. Enhanced
insensitivity toward friction and impact forces and higher measured
velocity of detonation indicate improved performance on incorporation
into high explosive formulations
Tailoring of energetic groups in acroyloyl polymers
<p>Acryloyl based novel energetic monomers having nitro acrylates and nitro triazole acrylates were synthesized and further used for polymerization. Due to scavanging properties of nitro groups, syntheses of nitro aromatic polymers are not facile at normal conditions. In this regard, we report a simple protocol to synthesize these energetic group embeded acroloyl polymers. These polymers were characterized by FTIR, and NMR spectroscopic techniques. gel permeation chromatography (GPC) technique was employed in order to understand molecular mass of these polymers along with average molecular weight, number average weight and poly dispersity index. Glass transition temperature (<i>T</i><sub>g</sub>) was determined by using DSC analysis. It was observed that with increase in nitro groups in polymers there is a decrease in glass transition temperature. Two steps degradation were depicted in the TGA thermograph in nitro containing polymers. Heat release during this reaction was found up to 951 J/g. Increase in nitrogen content in polymer unit enhanced the heat release of polymers.</p
Regiospecifically Fluorinated Polycyclic Aromatic Hydrocarbons via Julia–Kocienski Olefination and Oxidative Photocyclization. Effect of Fluorine Atom Substitution on Molecular Shape
A modular synthesis of regiospecifically
fluorinated polycyclic
aromatic hydrocarbons (PAHs) is described. 1,2-Diarylfluoroalkenes,
synthesized via Julia–Kocienski olefination (70–99%
yields), were converted to isomeric 5- and 6-fluorobenzo[<i>c</i>]phenanthrene, 5-and 6-fluorochrysene, and 9- and 10-benzo[<i>g</i>]chrysene (66–83% yields) by oxidative photocyclization.
Photocyclization to 6-fluorochrysene proceeded more slowly than conversion
of 1-styrylnaphthalene to chrysene. Higher fluoroalkene dilution led
to a more rapid cyclization. Therefore, photocyclizations were performed
at higher dilutions. To evaluate the effect of fluorine atom on molecular
shapes, X-ray data for 5- and 6-fluorobenzo[<i>c</i>]phenanthrene,
6-fluorochrysene, 9- and 10-fluorobenzo[<i>g</i>]chrysene,
and unfluorinated chrysene as well as benzo[<i>g</i>]chrysene
were obtained and compared. The fluorine atom caused a small deviation
from planarity in the chrysene series and decreased nonplanarity in
the benzo[<i>c</i>]phenanthrene derivatives, but its influence
was most pronounced in the benzo[<i>g</i>]chrysene series.
A remarkable flattening of the molecule was observed in 9-fluorobenzo[<i>g</i>]chrysene, where the short 2.055 Å interatomic distance
between bay-region F-9 and H-8, downfield shift of H-8, and a 26.1
Hz coupling between F-9 and C-8 indicate a possible F-9···H-8
hydrogen bond. In addition, in 9-fluorobenzo[<i>g</i>]chrysene,
the stacking distance is short at 3.365 Å and there is an additional
interaction between the C-11–H and C-10a of a nearby molecule
that is almost perpendicular