Selective Spectrophotometric Determination of Vanadium (II) in the Presence of 35 Common Cations by Means of Di-2-Pyridyl Ketone 2-Pyridylhydrazone (DPPH)

Abstract

DPPH was tested with 36 cations in slightly acidic medium, in the presence, of EDTA but only vanadium(II) formed a stable red complex. Based on these effects a method was worked out for the selective spectrophotometric determination of vanadium(II) in the presence of the remaining tested cations. A comparison of the sensitivity and selectivity of this method with recently reported methods is presented.     

DFT-assisted design and evaluation of bifunctional copper(I) catalysts for the direct intermolecular addition of aldehydes and ketones to alkynes

Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation.     

From (E)- and (Z)-ketoximes to N-sulfenylimines, ketimines or ketones at will. Application to erythromycin derivatives

Reactions of (E)- and (Z)-ketoximes with trialkylphosphines and diphenyl disulfide (PhSSPh) have been compared to gain insight into the mechanisms involved and their potential applications. N-Sulfenylimine isomers and ketimines have been spectroscopically characterised. Both the E and Z isomers of erythromycin A oxime, when treated with Bu₃P and PhSSPh (1:4:8 ratio), give the same N-phenylsulfenyl ketimine (of configuration E) as the major compound, whereas with Bu₃P or Me₃P and PySeSePy (1:8:4 ratio) afford the imine in good yield. Clarithromycin oxime behaves similarly.     

An acid-catalyzed Michael-aldol reaction

A tricyclic ketone is formed from cyclohexanone and cyclohexenone in strong acid solutions. The structure is confirmed by X-ray crystallography.     

Iodoarene-catalyzed one-pot preparation of 2,4,5-trisubstituted oxazoles from alkyl aryl ketones with mCPBA in nitriles

2,4,5-Trisubstituted oxazoles could be easily prepared in moderate yields by the reaction of alkyl aryl ketones, iodoarene, m-chloroperbenzoic acid, and trifluoromethanesulfonic acid in acetonitrile, propionitrile, butyronitrile, and isobutyronitrile, respectively. Here, reactive aryliodonium I(III) species is formed in situ by the reaction of iodoarene with mCPBA and trifluoromethanesulfonic acid, and the formed aryliodonium I(III) species reacts with alkyl aryl ketone to form β-keto aryliodonium species. This in turn, reacts with nitrile to form the corresponding oxazole. Iodoarene works as a catalyst. However, one equivalent of iodoarene is required because one equivalent of reactive aryliodonium I(III) species must be formed prior to the reaction with alkyl aryl ketone. Then, by introducing an ionic liquid group into iodoarene, to form ionic liquid-supported iodoarene, the isolation procedure of oxazole could be simplified. The addition of ethyl acetate to the reaction mixture, washing of the reaction mixture with aq NaHCO₃, removal of ethyl acetate, and extraction of the residue with ether provided oxazoles in moderate purity, and the residual ionic liquid-supported iodoarene could be reused in the same reaction.