Preparation and Characterisation of ε-CL-20 by Solvent Evaporation and Precipitation Methods

Abstract

, et al. studied the crystal quality of ε-CL-20 obtained from different precursors and solvent systems.In the present study, it is focused to prepare and characterisation by both solvent evaporation and precipitation methods. The present evaporation method also relates for obtaining agglomeration free fine ε-CL-20 crystals by in-situ use of ultrasound to crystallisation solution. The obtained crystals were characterised using HPLC, FTIR, Raman, Powder XRD, SEM and DSC techniques. Particle size measurement of obtained ε-CL-20 was carried out using particle size analyser and true density by Helium gas pycnometer. EXPERIMENTAL WORKRaw CL-20 sample was obtained from Premier Explosive's Laboratories, India. All the solvents and allied chemicals used for the processes are of analytical grade with > 99 % purity. ε-CL-20 is prepared using both solvent evaporation and precipitation techniques. Raw CL-20 is dissolved in ethyl acetate solvent and then antisolvent, n-heptane is added into the solution to induce the crystallisation. For the effective recovery in the drowning-out crystallisation, the fraction of raw CL-20, ethyl acetate and n-heptane was applied as about from 1 : 15 : 35, AbSTRACT ε-CL-20 is prepared from raw CL-20 by solvent evaporation and precipitation methods. Experiments were also done using solvent evaporation coupled with in-situ ultrasonication method. Using precipitation method, ε-CL-20 is scaled up to 500 g batch. Raw CL-20 was assigned to α-CL-20. The chemical and polymorphic purity of prepared ε-CL-20 was found to be about 98 per cent and > 95 per cent, respectively. ε-CL-20 was obtained agglomeration free with well defined geometry in comparison with raw CL-20 and its crystal morphology is dominantly bi-pyramidal or lozenge crystal shapes. The obtained mean particle size of prepared ε-CL-20 by solvent evaporation method with and without in-situ ultrasonication and also by precipitation methods is about 30 µm -40 µm, 150 µm -200 µm and 150 µm -300 µm, respectively. The measured true density of prepared ε-CL-20 by precipitation method with 100 g and 500 g batch scale using Helium gas pycnometer was 2.038 g/cm 3 and 2.043 g/cm 3 , respectively. The lower value of calculated void percentage of ε-CL-20 (0.05-0.29%) indicate better crystal quality. Conclusively, prepared ε-CL20 has high true density with less percentage of voids, less total moisture content and free from agglomeration as compared with the starting raw CL-20 material.

Probing Crystal Growth of ε- and α-CL-20 Polymorphs via Metastable Phase Transition Using Microscopy and Vibrational Spectroscopy

“…[6][7][8][9] CL-20 is obtained as the low density α-form during most of the synthetic process and thus requires further re-crystallization to the high density ε-form. [10][11][12][13][14] Although, ε-is the thermodynamically most stable phase, even small amounts of water in the reaction medium 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 preferentially stabilizes the hydrated α-phase. Reports are also available [15][16][17] on 'one pot' synthesis of ε-CL-20 that involved in-situ conversion of firstly formed α-and/or γ-phases without being isolated from the reaction vessel.…”

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This article presents the evidence of possible route to the formation of ε-and α-polymorphic phases of 2, 4,6,8,10,4,6,8,10, studied through CL-20 solution using reverse and normal precipitation method. Reverse precipitation with instant addition facilitated with the opportunity to track the crystal phases from their immediate formation to end of phase stabilization.

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Experimental Studies on Advanced Sheet Explosive Formulations Based on 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and Hydroxyl Terminated Polybutadiene (HTPB), and Comparison with a RDX-based System

“…Basic experiments such as thin layer chromatography (TLC) were carried out for both RDX and CL-20. The spectroscopic data generated for CL-20 also matched reported data from our laboratory [13,19,20]. CL-20 and RDX were coated with 6% dioctyl phthalate (DOP) to enhance their safety aspects during the processing of the explosive formulations.…”

Synthesis of CL-20 from TADB in a One-Pot Method by Zeolite/HNO3as a New Nitrolysis System

“…3 It is a well-known caged nitramine with significantly higher density (e-form), 4 higher performance and minimum signature than the other nitramines (HMX, RDX); therefore, CL-20 has found numerous military applications. 5 All the processes for CL-20 synthesis are based on the same starting materials.…”

“…7 According to related literature, there are several methods for the preparation of CL-20, like reductive formylation/nitrolysis, debenzylation/nitrolysis and tetraacetyldibenzylhexaazaisowurtzitane (TADB) nitrosation/nitrolysis methods. In this regard, some nitrolysis systems such as NOBF 4 9 have been introduced for the synthesis of CL-20 from TADB. The preparation of CL-20 in the final step requires the use of HNO 3 /H 2 SO 4 which has many disadvantages including formation of environmentally unfriendly wastes that are expensive to dispose of, strong acidic media, over nitration and safety problems.…”