STUDY OF THE ALKALINE CLEAVAGE OF THE P[sbnd]C BOND IN PHOSPHINE OXIDES AND DERIVATIVES OF TRICHLOROMETHANEPHOSPHONATE

Abstract

A study of alkaline decomposition of several aromatic phosphine oxides containing p- and o-nitrobenzyl, and trichloromethyl as leaving groups, is reported. The property of the trichloromethyl group as leaving group, and the CCl^? ₃-group's further decomposition in the hydrolysis of diethyl and disodium trichloromethanephosphonates, have also been investigated.     

Unexpected Isolation of 4‐Isothiocyanatomethylene‐4H‐pyridine‐1‐carboxylic Acid Ethyl Ester as Potential Template in Organic Synthesis

The synthesis of 4‐isothiocyanatomethyl‐pyridine 4 in 36% yield by Hasegawa and Kotani (Japanese patent 49088878, 1974) has spurred us to investigate this preparation in detail. In addition to this compound, 4‐isothiocyanatomethylene‐4H‐pyridine‐1‐carboxylic acid ethyl ester 3 can be isolated. The synthesis of both compounds 3 and 4 were optimized to 75% and 50% yield respectively. Reaction of compound 3 with methylamine gave thiourea derivatives 5, the same product obtained on reacting 4‐isothiocyanatomethyl‐pyridine 4 with methylamine. We succeed in adjusting the reaction conditions to obtain high yield either from compound 3 or isothiocyanate derivatives 4.     

Freezing and Hydrate Formation in Aqueous Sodium Perchlorate Solutions

The determination of the phase diagram of the binary system sodium perchlorate – water is reported. Beside the eutectic point, two polymorph crystal structures of sodium perchlorate dihydrate were determined. The two crystal structures are discussed, compared to each other and to other known sodiumhalide dihydrate crystal structures. The two polymorphs of the perchlorate dihydrate represent the two variants of connected octahedra in the layer structure found for sodium halide dihydrates.     

Synthesis of the Methyl, 1-Octyl,and D-Trifluoro-Acetamidophentlethyl α-Glycosides of 3,6-Di-O-(α-D-Galactopyranosyl)-D-Glucopyranose and an Acyclic Analogue Thereof

Abstract

The title trisaccharides were synthesized from a common trisaccharide thioglycoside derivative, which was, in turn, prepared from monosaccharide thioglycoside precursors. An acyclic analogue, methyl 3-O-(α-D-galacto-pyranosyl)-6-O-[(2′-hydroxyethyl)oxymethyl]-α-D-glucopyranoside, which carries a 2′-hydroxyethyloxymethyl group in place of the 6-O-galactosyl residue, was also synthesized.     

Unprecedented Electron‐Poor Octahedral Ta6 Clusters in a Solid‐State Compound: Synthesis,Characterisations and Theoretical Investigations of Cs2BaTa6Br15O3

The crystal structure of Cs₂BaTa₆Br₁₅O₃ has been elucidated by using synchrotron X‐ray powder diffraction and absorption experiments. It is built from edge‐bridged octahedral [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^4? cluster units with a singular poor metallic electron (ME) count equal to thirteen. This leads to a paramagnetic behaviour related to one unpaired electron. The arrangement of the Ta₆ clusters is similar to that of Cs₂LaTa₆Br₁₅O₃ exhibiting 14‐MEs per [(Ta₆${{\rm Br}{{{\rm i}\hfill \atop 9\hfill}}}$ ${{\rm O}{{{\rm i}\hfill \atop 3\hfill}}}$ )${{\rm Br}{{{\rm a}\hfill \atop 6\hfill}}}$ ]^5? motif. The poorer electron‐count cluster presents longer metal–metal distances as foreseen according to the electronic structure of edge‐bridged hexanuclear cluster. Density functional theory (DFT) calculations on molecular models were used to rationalise the structural properties of 13‐ and 14‐ME clusters. Periodic DFT calculations demonstrate that the electronic structure of these solid‐state compounds is related to those of the discrete octahedral units. Oxygen–barium interactions seem to prevent the geometry of the octahedral cluster to strongly distort, allowing stabilisation of this unprecedented electron‐poor Ta₆ cluster in the solid state.     

1,1′,1′′-(2,4,6-Trihydroxybenzene-1,3,5-triyl)triethanone tautomerism revisited

It has recently been suggested that 1,1′,1′′-(2,4,6-trihydroxybenzene-1,3,5-triyl)triethanone may be tautomeric. Using ¹³C NMR chemical shifts and deuterium isotope effects on ¹³C chemical shifts, it is demonstrated that this is not the case. This compound occurs as a strongly hydrogen bonded benzene structure with hydrogen bonds between OH groups and the acetyl groups in both non-polar and hydrogen donating solvents. Quantum-chemical calculations using MP2 and M06-2X methods show substantial preference for the phenol structure in both the gas phase, and in cyclohexane and methanol. In addition, conventional UV–vis spectroscopy data suggest not tautomeric, but aggregation behaviour of the molecule in methanol and acetonitrile.     

Graphene-based sensors for detection of heavy metals in water: a review

Graphene (G) is attracting significant attention because of its unique physical and electronic properties. The production of graphene through the reduction of graphene oxide (GO) is a low-cost method. The reduction of GO can further lead to electrically conductive reduced GO. These graphene-based nanomaterials are attractive for high-performance water sensors due to their unique properties, such as high specific surface areas, high electron mobilities, and exceptionally low electronic noise. Because of potential risks to the environment and human health arising from heavy-metal pollution in water, G-/GO-based water sensors are being developed for rapid and sensitive detection of heavy-metal ions. In this review, a general introduction to graphene and GO properties, as well as their syntheses, is provided. Recent advances in optical, electrochemical, and electrical detection of heavy-metal ions using graphene or GO are then highlighted. Finally, challenges facing G/GO-based water sensor development and outlook for future research are discussed.     

Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates

Calcium pyrophosphate hydrate (CPP, Ca₂P₂O₇·nH₂O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca₂P₂O₇·H₂O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X‐ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT‐β) is discussed.