Reactions of selected diazadienes with PBr 3 and BBr 3 in the presence of a tertiary amine yielding N-heterocyclic phosphanes (NHPs) and N-heterocyclic boranes (NHBs) were studied. It is demonstrated that heterocycle formation occurs even without an amine or another auxiliary reagent, and the amine acts mainly as scavenger of Br 2 formed as by-product, but also that the additive speeds up reactions and has an influence on the product selectivity. In extension of the results of earlier studies it is shown that the reactions can follow two different pathways to give either 2-bromo-or 2,4-dibromo-substituted heterocycles. Computational studies enabled to propose a reaction mechanism, which relates the

Since its discovery in 2012, multiple techniques to generate the CL‐20/HMX cocrystal have been published. However, as yet no assessment or trial has been reported of crystallisation methods capable of producing the cocrystal in a size region and production scale suitable for its use in polymer bonded explosives (PBX). This paper provides insight into the selection of suitable crystallisation methods, solvent selection and process optimisation with a focus on the efficient production of high‐quality cocrystals for use in PBX. Through extensive solvent screening, acetonitrile was identified as the best solvent for solution‐based crystallisation, due to its capability to produce compact parallelepipedic crystals and its comparably wide cocrystal phase region. Crystallisation conducted at 60 °C was found to increase the conversion rate and the material efficiency compared to room temperature. By application of an advanced seeding procedure, high‐quality cocrystals in the size region of 180–250 μm were produced in laboratory‐scale antisolvent and cooling crystallisations. By pilot‐plant‐scale batch reaction cocrystallization, cocrystals with a volume‐weighted mean diameter of 33 μm were produced in quantities of 250 g per day.

CL-20/HMX cocrystal is one of the most promising energetic cocrystals, but scaled-up production was prevented by the large inherent solubility difference of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX) and, therefore, unacceptable CL-20 efficiency. Reaction cocrystallization (aka. reaction crystallization or slurry technique) has been extensively used as an efficient, straightforward cocrystallization screening method, but only few attempts at utilizing this method for scaled-up cocrystal production have been undertaken and none have realized its full potential. By utilizing solid dosing and process analytical technology, semibatch reaction cocrystallization (SBRC) provided the first scale-up of high-quality CL-20/HMX cocrystal with a particle diameter D­(4,3) of 163 μm and a batch size of 100 g. The CL-20 recovery is 63%, which is over two times better than the theoretical recovery rate of the next best method (evaporation crystallization), and the crystal quality is comparable to crystals obtained from controlled antisolvent crystallization. It is shown that SBRC is a valuable crystallization technique for efficient scale-up of cocrystal systems whose coformers exhibit significantly different solubilities.

No abstract

Even though helium pycnometry is considered a very precise method of density determination, its use to analyse factors influencing crystal quality (e. g. solvent inclusions, amorphous states, crystal defects…) is limited due to the unknown inherent accuracy of the method. Previous studies have attempted to identify the best possible accuracy of helium pycnometry. However, no robust method has been proposed to validate even the precision obtained. This means that the often occurring, seemingly random density deviations have never been satisfactorily explained. In this study the influencing factors on density measurements of the CL‐20/HMX cocrystal and phase stabilised ammonium nitrate carried out with an AccuPyc 1340 TEC were quantified and a robust method of data analysis was developed to judge with certainty the quality and significance of the data obtained. This study shows that statistical tests such as the t‐test and ANOVA cannot be utilised to differentiate between samples or repeat measurements, even though the density data points exhibit a normal distribution. By utilising confidence intervals and quantifying the three major sources of error (sampling error, change in barometric pressure during the measurement, and weight in error), a repeatability of 0.015 % was achieved and a method was developed that enables differentiation between samples with a certainty as good as 0.05 %.