Reactivity of 2‐substituted imidazo[1,2‐b]pyridazines: Preparation of 3‐nitro,nitroso and chloro derivatives

The synthesis of 2‐substitutedimidazo[1,2‐b]pyridazines and their reactivity towards electrophilic substitutions are reported. The nitration was shown to be very dependent on the nature of the 2 substituent. Nitrosation using sodium nitrite in acetic acid media as a general method failed in all cases whereas chlorination was observed in warm hydrochloric acid. In order to ascertain the structure of some chloro derivatives, chlorination using N‐chlorosuccinimide was also reported. Depending of the nature of the substituent, the reaction occurred at the C‐3 imidazolic position and/or at the substituent on position 2. The 3‐nitroso‐2‐phenyl derivative was finally obtained using an alternative synthetic pathway by direct condensation of 3‐amino‐6‐chloropyridazine to ω‐chloro‐ω‐nitrosoacetophenone. The structural determinations were ascertained using high field ^lH and ¹³C‐NMR.     

Cation Complexation Properties of Hexakis(2-O-methyl-3,6-anhydro)-α-cyclodextrin: A 1H NMR Study

Abstract

The affinity of hexakis(2-O-methyl-3,6-anhydro)-α-cyclodextrin (3,6-α-CDM) for Ba²⁺, Pb²⁺, Ca²⁺ and Sr²⁺ has been tested by ¹H NMR. It was shown that 3,6-α-CDM forms strong complexes in water with Pb²⁺ and Ba²⁺. The comparison with the parent hexakis(3,6-anhydro)-α-cyclodextrin bearing hydroxyl groups instead of methoxy groups reveals that the O-CH₃ substitution significantly improves the anhydro-cyclodextrin selectivity.     

Preparation and characterization of MgB2 superconductor

The MgB₂ superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties. The upper critical field, irreversibility line and critical current density have been determined using magnetization data. The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition. The surface analysis using X-ray photoelectron spectroscopy shows that MgB₂ is sensitive to atmospheric degradation.