Authors:Nathaniel B. Zuckerman, Maxim Shusteff, Philip F. Pagoria, and Alexander E. Gash
The secondary high explosive 2,6-diamino-3,5-dinitropyrazine-1-oxide, or LLM-105, has been synthesized using a commercially available flow microreactor system. Investigations focused on optimizing flow nitration conditions of the cost effective 2,6-diaminopyrazine-1-oxide (DAPO) in order to test the feasibility and viability of flow nitration as a means for the continuous synthesis of LLM-105. The typical benefits of microreactor flow synthesis including safety, tight temperature control, decreased reaction time, and improved product purity all appear to be highly relevant in the synthesis of LLM-105. However, the process does not provide any gains in yield, as the typical 50—60% yields are equivalent to the batch process. A key factor in producing pure LLM-105 lies in the ability to eliminate any acid inclusions in the final crystalline material through both a controlled quench and recrystallization. The optimized flow nitration conditions, multigram scale-up results, analyses of sample purity, and quenching conditions for purity and crystal morphology are reported.
Authors:R. Ceolin, V. Agafonov, A. Gonthier-Vassal, H. Szwarc, J. Cense, and Ph. Ladure
Flutamide usually crystallizes in the orthorhombic non-centrosymmetric space group Pna21 (from I) and melts atTfus=384 K with ΔfusH=30 kJ·mol−1. It may be obtained in the glassy state (Tg=272 K) by quenching the melt. Although evidence of polymorphism could not be obtained by means of crystallography, DSC studies
of the recrystallization process indicate that a metastable form (form II) occurs first and is transformed into the stable
form at room temperature. ΔH for the transition I→II (2.52 kJ·mol−1) is close to the difference in energy (about 2 kJ·mol−1) calculated for the two possible conformers of flutamide.
The kinetics of solute segregation to partial dislocations in a Cu–3.4 At.% Sb alloy was studied by using a phenomenological approach with differential scanning calorimetry and isothermal calorimetry. The material, severely deformed by repeated bending, presented an excess of dissociated edge dislocations with a dislocation density amounting to about 8.5·1014 m–2, calculated using a prior model of the authors, together with calorimetric recrystallization trace analysis. The kinetics was found to be ruled by two overlapping mechanisms: diffusion of solute atoms mostly through dislocation pipes in the initial and middle stages of the reaction process, acting together with bulk solute diffusion in these stages and later. Bulk solute diffusion increases as the reaction proceeds, as shown by the increasing values of apparent activation energy in the reaction. The exponent of the Mehl-Johnson-Avrami equation used in the phenomenological description was successfully fitted to a time—temperature-dependent function, increasing in agreement with the apparent activation energy behaviour, as may be expected.
The heterogeneous isotopic exchange reactions in strontium polymolybdates of Sr2+ and MoO42- ions in the strontium nitrate and sodium molybdate solutions have been studied using 90Sr and 99Mo as tracers. Electrometric methods have been used to study the compositions of strontium molybdates obtained by adding strontium chloride to a progressively acidified solution of sodium molybdate. It has been found that the exchange fraction increases with increasing chain length of strontium polymolybdate. The exchange equilibrium constant (Kex) has been calculated between 298 and 348 K as well as DG°, DH° and DS°. The results indicate that Sr2+ cations have a much higher affinity for exchangers than MoO42- anions. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm it has been shown that the exchange capacity (Xm) for both ions is affected by the ion adsorption process at low temperatures and by the ion exchange process at high temperatures. At high concentrations, the recrystallization process contributes to on the cation exchange but is ineffective on the anion exchange mechanism.
Authors:F. Rey, O. Chamorro, F. Martín Gil, and J. Martín Gil
The thermal stability of selected straight-chain (C6-C14) esters of fatty acids has been studied by TG-DTG and DTA analysis. In DTG, a peak is detected between 84° and 125° C followed
by a main effect in the range 105°–215°C, whereas in DTA only an exothermic peak appears in the range of 126.5° to 187°C (onset
temperatures). The temperatures of these effects have been related with ignition points, molecular weights and boiling points.
The characteristics of melting and recrystallization of the above fatty acid methyl esters and those with carbon numbers between
C14 and C24 have been established by DSC along the melting range between −83° and 50°C. Polymorphism appears in caproic, heptanoic, palmitic
and stearic acid methyl esters.
Authors:M. Cirri, F. Maestrelli, S. Furlanetto, and P. Mura
Natural crystalline (α-, β-, γ-) and amorphous derivative (hydroxypropyl-β- and methyl-β) cyclodextrins were selected as potential
carriers for obtaining, through a co-grinding technique, a stable activated amorphous form of glyburide with improved dissolution
properties. Differential scanning calorimetry (DSC) was used to investigate solid-state modifications of the drug induced
by co-grinding with the selected carriers in a high energy vibrational micro-mill. X-ray powder diffraction and FTIR spectroscopy
were employed as additional techniques to support DSC data. Equimolar drug : cyclodextrin physical mixtures were co-ground
for different times (up to 60 min) at constant vibration frequency (24 Hz). A progressive drug amorphization with increasing
grinding time was observed in all binary systems, but, interestingly, different degrees of sensitivity to the mechanical-chemical
activation were evident. In fact, blends with natural cyclodextrins, despite the initial higher crystallinity than those with
the amorphous derivatives, required the same or shorter co-grinding times (60 min) to achieve complete drug amorphization.
Stability studies indicated no appreciable drug recrystallization in co-ground products after 4 months storage in sealed containers
at 25°C or 1 month at 25°C and 75% RH. No stability differences were detected between products with natural or derivative
cyclodextrins. The results accounted for the suitability of cyclodextrin co-grinding technique to obtain and stabilize glyburide
in the activated amorphous form.
Authors:S. Romero, P. Bustamante, B. Escalera, M. Cirri, and P. Mura
Differential scanning calorimetry (DSC), supported by hot stage microscopy, IR spectroscopy and X-ray powder diffractometry,
was used to investigate the characteristics of the solid phases of mefenamic, niflumic, and flufenamic acids and of paracetamol,
before and after equilibration with saturated solutions in different solvents. Mixtures of Lewis base (dioxane and ethyl acetate)
and amphiprotic solvents (ethanol and water) were prepared for evaluating the influence of both nature and polarity of the
solvents. Solid-state analysis performed on the original samples (commercial products) made it possible to establish that
paracetamol, mefenamic acid and flufenamic acid were in their respective Form I. No polymorphic modifications are known for
niflumic acid. Paracetamol, niflumic and mefenamic acids did not show any change after equilibration with the various solvents
or solvent mixtures, regardless of their different chemical nature. In contrast, DSC, IR and X-ray analyses revealed the partial
recrystallization of flufenamic acid into its polymorphic Form III in solid phases at equilibrium with ethanol, ethyl acetate
and their blends, as well as in dioxane-water mixtures containing 30 to 100% dioxane and in ethanol-water mixtures with a
water content less than 50%.
Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scanning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool-heat modulation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool-heat method lead to an increase in the peak melting temperature and the final traces of melting. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crystal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible.
Authors:A. Yaghmur, A. Aserin, I. Tiunova, and N. Garti
The five-component system is quite unique since it allows formation of reverse micelles with hydrophilic ethoxylated alcohol in the presence of ethanol and it facilitates dilution by water/propylene glycol (1,2-propanediol, PG) aqueous phase, all the way from a water-in-oil (W/O) microemulsion via a bicontinuous phase to an oil-in-water (O/W) microemulsion.The surfactant/alcohol/PG can strongly bound water in the inner phase so that it freezes below –10°C and acts in part as bound water and in part as non-freezable water. Upon dilution to >30 mass% aqueous phase (water/PG at constant mass ratio of 1/1) the system becomes bicontinuous and the aqueous layers are composed again from bound water. Even after complete inversion to O/W microemulsions the water in the continuous phase is strongly interacting with the PG/surfactant and remains bound or non-freezable. Water/PG/ethanol have a strong effect on the head groups (freezing below -10°C) and also on the hydrophobic tails (recrystallizing and melting) at lower temperature when dilution exceeds 45 mass% water/PG (1/1).No free water was detected neither in the W/O microemulsion's inner droplet domains nor when the microemulsion was either bicontinuous or when it was inversed to O/W. Continuous phase of resulting O/W microemulsion apparently is based on water/PG at a mass ratio of 1/1.
Inorganíc polymers such as silicates, borates and phosphates can be transformed into amorphous solids by heating to an appropriate
temperature. Thermal amorphization can be obtained by: 1. thermal dissociation of a crystalline compound, 2. distortion of
the crystal structure of a solid during prolonged heat treatment, without change of its chemical composition. The specificity
of the materials received, the crystallochemical conditions necessary for the amorphization which takes place, and the high-temperature
processes of internal structure reconstitution and recrystallization in the amorphous products are considered.