Initiation of liquid explosives by cavitation

It is known that in some circumstances liquid explosives can be initiated with unexpected ease, and in other circumstances only with great diffculty.Thus, Winning [1] has shown that nitroglycerine (NG) free of gaseous inclusions and poured into a vessel so as to leave no wall surfaces free of liquid is not exploded even by the action of a fairly strong shock wave from a detonator immersed in the NG.On the other hand, in handling liquid explosives there have been quite a few cases in which relatively weak vibrations or impacts have led to unexpected explosions, which have sometimes had serious consequences. For example, a British report [2] describes an unfortunate accident that resulted from dropping a polyethylene bottle containing NG. Upon hitting the ground the NG exploded.The initiation of explosion by hot spots resulting from the adiabatic compression of gaseous inclusions even before the arrival of the shock wave has been reliably demonstrated in numerous experiments [1, 3]. However, some cases of initiation of liquid explosives simply cannot be attributed to the heating of such gaseous inclusions, since in these cases the adiabatic compression temperatures of the gas are so small that it is not possible to talk of a hot spot. Such puzzling cases include, for example, the above-mentioned explosion of NG in a polyethylene bottle. In other experiments [4] the role of gaseous inclusions has been completely eliminated by first subjecting the liquid explosive to a constant high pressure. This so reduced the degree of compression of the gaseous inclusions by a weak shock that strong heating of the gas in the bubbles, if any were present in the liquid explosives, was completely excluded. Nonetheless, there was no reduction in the sensitivity of the explosive to weak shocks.In attempting to explain such puzzling cases it is usually pointed out that explosion can be initiated by cavitation [1, 5], which may develop in a liquid even as a result of a weak impact or vibration. So far, however, no one has offered any direct experimental evidence of the possibility of cavitational initiation of explosion in liquid explosives. The object of our research was to fill that gap.     

Synthesis and properties of 2-hydroxyethyl derivatives of methylene-bis(1-oxy-3, 3-dialkyl-1-triazene 2-oxides)

Russian Chemical Bulletin - Synthetic approach to 2-hydroxyethyl derivatives of methylene-bis(1-oxy-3, 3-dialkyl-1triazene 2-oxides), promising NO donors, which can release NO in living organisms...     

Chiral epoxides via borane reduction of 2-haloketones catalyzed by spiroborate ester: application to the synthesis of optically pure 1,2-hydroxy ethers and 1,2-azido alcohols

An enantioselective borane-mediated reduction of a variety of 2-haloketones with 10% spiroaminoborate ester 1 as catalyst is described. By a simple basic workup of 2-halohydrins, optically active epoxides are obtained in high yield and with excellent enantiopurity (up to 99% ee). Ring-opening of oxiranes with phenoxides or sodium azide is investigated under different reaction conditions affording nonracemic 1,2-hydroxy ethers and 1,2-azido alcohols with excellent enantioselectivity (99% ee) and in good to high chemical yield.     

Turbulent liquid metal flow in rectangular shaped contraction nozzles for target applications

Owing to the high beam power densities envisaged in advanced nuclear targets, liquid metal-operated free surface targets are conceived as one feasible option. There, the free surface is formed by an adequately shaped upstream located nozzle. Target boundary conditions necessitate a detailed knowledge on the turbulent flow in contraction nozzles in order to identify turbulence models accurately predicting experimental findings within the velocity range of interest for nuclear target and hence can then act as design optimisation tools. In this context, a combined experimental and numerical study is conducted on the basis of the turbulent flow in the contraction nozzle of the Super-FRS target. Two aspects determining the turbulent flow in the nozzle have been investigated. The first is a potential relaminarisation of the boundary layer caused by the acceleration within the contraction and the second is a development of the secondary flows due to the pressure gradient in the rectangular shaped ducts cross-section. Regarding the three different turbulence models investigated here only the V2F model exhibited the capability to predict the relaminarisation of the turbulent boundary layer both qualitatively and quantitatively. All turbulence models are able to predict the development of secondary flows induced by pressure gradients in transverse direction with an acceptable accuracy.     

Radiation-induced nitration of organic compounds in aqueous solutions

Radiation-induced nitration of organic compounds in aqueous solutions was studied. It was found that γ-irradiation of solutions containing acetic and nitric acid and/or their salts gives nitromethane. Dependences of the product yield on the absorbed dose and the contents of components were established. The mechanism of radiation nitration involving radicals is discussed.     

Switching the nature of catalytic centers in Pd/NHC systems by solvent effect driven non-classical R-NHC Coupling

A well-established oxidative addition of organic halides (R-X) to N-heterocyclic carbene (NHC) complexes of palladium(0) leads to formation of (NHC)(R)Pd^II(X)L species, the key intermediates in a large variety of synthetically useful cross-coupling reactions. Typical consideration of the cross-coupling catalytic cycle is based on the assumption of intrinsic stability of these species, where the subsequent steps involve coordination of the second reacting partner. Thus, high stability of the intermediate (NHC)(R)Pd^II(X)L species is usually taken for granted. In the present study it is discussed that such intermediates are prone to non-classical R-NHC intramolecular coupling process (R = Me, Ph, Vinyl, Ethynyl) that results in removal of NHC ligand and generation of another type of Pd catalytic system. DFT calculations (BP86, TPSS, PBE1PBE, B3LYP, M06, wB97X-D) clearly show that outcome of R-NHC coupling process is not only determined by chemical nature of the organic substituent R, but also strongly depends on the type of solvent. The reaction is most favorable in polar solvents, whereas the non-polar solvents render the products less stable. © 2019 Wiley Periodicals, Inc.