A.E.D.M. van der Heijden

The influence of a solvent on the crystal morphology of RDX

A solvent can have a large influence on the crystal morphology. A molecular modeling technique based on the adsorption of solvent molecules on a crystal surface has been used to predict the influence of a solvent on the morphology of RDX. The predicted morphology has been compared with the experimentally found morphology of RDX crystallized from several solvents by cooling crystallization.

Mcm-41 Materials as Catalysts for the Synthesis of Alkyl Fructosides

ABSTRACT Alkylation of saccharides combines the essential characteristics of two major renewable classes, viz. triglycerides and carbohydrates, while leading to biofriendly surfactants and emulsifiers. The development of alkylated derivatives of fructose has lagged because no efficient synthesis was available. We have found that mesoporous materials of the MCM-41 type are active and selective catalysts for the alkylation of fructose. Quantitative yields were obtained in the reaction of fructose with lower alcohols, up to C4. For long chain alcohols yields were moderate but the alkyl fructopyranosides could be easily purified. The other isomers could be isolated by chromatography.

Synthesis of Alkyl Fructosides Using Solid Acid Catalysts. Part I: Silica-Alumina Cracking Catalysts

Abstract Silica-alumina cracking catalysts and acid clays efficiently catalyze the 2-O-alkylation of d-fructose with long chain alcohols. Under the conditions applied virtually no degradation of fructose is observed. l-Sorbose and the aldopentoses also undergo silica-alumina-catalyzed alkylation. The rate of conversion is related to the solubility of the monosaccharide and the stability of the intermediate oxocarbenium ion. Best results in fructose alkylation are obtained by applying a recirculation method with butyl fructoside as soluble intermediate.

Microscopic characterization of defect structure in RDX crystals

Three batches of the commercial energetic material RDX, as received from various production locations and differing in sensitivity towards shock initiation, have been characterized with different microscopic techniques in order to visualize the defect content in these crystals. The RDX crystals are embedded in an epoxy matrix and cross‐sectioned. By a treatment of grinding and polishing of the crystals, the internal defect structure of a multitude of energetic crystals can be visualized using optical microscopy, scanning electron microscopy and confocal scanning laser microscopy. Earlier optical micrographs of the same crystals immersed in a refractive index matched liquid could visualize internal defects, only not in the required detail. The combination of different microscopic techniques allows for a better characterization of the internal defects, down to inclusions of approximately 0.5 μm in size. The defect structure can be correlated to the sensitivity towards a high‐amplitude shock wave of the RDX crystals embedded in a polymer bonded explosive. The obtained experimental results comprise details on the size, type and quantity of the defects. These details should provide modellers with relevant and realistic information for modelling defects in energetic materials and their effect on the initiation and propagation of shock waves in PBX formulations.

Impurity profiling of trinitrotoluene using vacuum-outlet gas chromatography-mass spectrometry

In this work, a reliable and robust vacuum-outlet gas chromatography-mass spectrometry (GC-MS) method is introduced for the identification and quantification of impurities in trinitrotoluene (TNT). Vacuum-outlet GC-MS allows for short analysis times; the analysis of impurities in TNT was performed in 4min. This study shows that impurity profiling of TNT can be used to investigate relations between TNT samples encountered in forensic casework. A wide variety of TNT samples were analyzed with the developed method. Dinitrobenzene, dinitrotoluene, trinitrotoluene and amino-dinitrotoluene isomers were detected at very low levels (<1wt.%) by applying the MS in selected-ion monitoring (SIM) mode. Limits of detection ranged from 6ng/mL for 2,6-dinitrotoluene to 43ng/mL for 4-amino-2,6-dinitrotoluene. Major impurities in TNT were 2,4-dinitrotoluene and 2,3,4-trinitrotoluene. Impurity profiles based on seven compounds showed to be useful to TNT samples from different sources. Statistical analysis of these impurity profiles using likelihood ratios demonstrated the potential to investigate whether two questioned TNT samples encountered in forensic casework are from the same source.

Cold plasma synthesis of high quality organic nanoparticles at atmospheric pressure

Atmospheric pressure cold surface dielectric barrier discharge (SDBD) plasma was used for the first time to produce nano-sized organic crystals. Nano-sized particles can have beneficial product properties, such as improved internal quality and dissolution rate, compared to conventionally sized crystalline products. In cold plasma crystallization a nebulizer system sprays the solution aerosol into the plasma with the help of a carrier gas. The plasma heats and charges the droplets causing solvent evaporation and coulomb fission to occur, after which nucleation and crystal growth commence within the small, confined volume offered by the small droplets. As a result nano-sized crystals are produced. The operation conditions of SDBD plasma to produce nano-sized crystals of the energetic material RDX were determined by scanning electron microscopy, and the product was investigated with X-ray powder diffraction and sensitivity tests. The sensitivity tests indicated that the nano-sized product had reduced sensitivity for friction, indicating a higher internal quality of the crystalline product.

Transesterification of lactulose with ethyl butanoate catalysed by Candida antarctica lipase

The enzyme-catalysed acylation of lactulose by ethyl butanoate was investigated. A slow conversion to a complex mixture of esters was observed at 40°C in tert-butyl alcohol in the presence of a number of lipases and a protease. With Candida antarctica B lipase, esterifications could also be performed at 82°C (reflux) to increase the rate. The reaction could be accelerated by a factor of 5 when 1,2-dimethoxyethane was used as solvent. In this way, a nearly quantitative conversion to a mixture of esters was accomplished within 24 h.

The III–IV phase transition in ammonium nitrate: mechanisms

Abstract The polymorphic phase transition III–IV in ammonium nitrate is well known to be catalysed by water. Owing to this predominant role of water, it has been suggested in the literature that this transition proceeds via dissolution and crystallization occuring at a disordered phase boundary or even in a “bulk” layer of solution. A systematic study on the similarity between projections of specific (hkl)III and (hkl)IV faces predicts various orientation relationships between both phases. Several of these (hkl) faces and orientation relationships are confirmed by microscopic observations of the III → IV and IV → III transitions, by texture goniometry results, as well as by microscopic observations reported in literature. The combined experimental and theoretical results substantiate the existence of a solid-solid transition mechanism especially for single crystals. The transition is supposed to be continuously catalysed from the surface of the crystals by solvent molecules. The presence of a solution layer at the transition front would be unlikely in view of the proposed solid-solid mechanism which implies a greater restriction than just a set of parallel faces, namely the requirement of matching of faces.

Growth of ammonium nitrate phase I and II dendrites

Ammonium nitrate (AN) phase I and phase II crystallize as dendrites from a melt containing respectively 0–4.5 and 4.5–12 wt% water. In-situ microscopic measurements show that the, for dendrites, characteristic ratio S / ϱ (where S = side branch spacing near the tip and ϱ = dendrite tip radius) varies between 2.3 and 5.1 for both AN(I) and AN(II). This agrees reasonably well with the theoretically derived value of 2.8 reported in the literature. The water concentration has a strong influence on the relation between the side branch spacing near the tip, S, and the tip growth rate, v, of the dendrites. The findings satisfy at least qualitatively the theoretically expected relationship between S and v.

Mesogenic ketohexose and aldopentose derivatives : anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.