1.Crystal structure of 2α-(1,1-di-phenyl-eth-yl)-4-methyl-4α,5α-diphenyl-1,3-dioxolane: the result of a non-acid pinacol rearrangement.
Kirchner RM1, Corfield PW2, Annabi M1, Regan J1, Speina K1, DiProperzio A1, Ciaccio JA2, Capitani JF1. Acta Crystallogr E Crystallogr Commun. 2015 Oct 3;71(Pt 11):1278-82. doi: 10.1107/S2056989015017752. eCollection 2015.
The title compound, C30H28O2, was obtained during recrystallization of (±)-1,2-diphenyl-1,2-propane-diol in 1-butanol, from an unexpected non-acid-catalyzed pinacol rearrangement followed by acetal formation of the newly formed aldehyde with the diol. The tri-substituted dioxolane ring has a twist conformation on the C-O bond opposite the methyl-substituted C atom. There is an intra-molecular C-H⋯π inter-action present involving one of the di-phenyl-ethyl rings and an H atom of the phenyl ring in position 4 of the dioxolane ring. In the crystal, mol-ecules are linked by weak C-H⋯O hydrogen bonds, forming chains along . The chains are linked by a second C-H⋯π inter-action, forming sheets parallel to the bc plane.
2.Solvent-Dictated Lithium Sulfur Redox Reactions: An Operando UV-vis Spectroscopic Study.
Zou Q1, Lu YC1. J Phys Chem Lett. 2016 Apr 12:1518-1525. [Epub ahead of print]
Fundamental understanding of solvent's influence on Li-S redox reactions is required for rational design of electrolyte for Li-S batteries. Here we employ operando UV-vis spectroscopy to reveal that Li-S redox reactions in high-donor-number solvents, for example, dimethyl sulfoxide (DMSO), undergo multiple electrochemical and chemical reactions involving S82-, S62-, S42-, and S3•-, where S3•- is the most stable and dominant reaction intermediate. In low-donor-number solvents, for example, 1,3-dioxolane:1,2-dimethoxyethane, the dominant reaction intermediate, is found to be S42-. The stability of these main polysulfide intermediates determines the reaction rates of the disproportionation/dissociation/recombination of polysulfides and thereby affects the reaction rates of the Li-S batteries. As an example, we show that dimethylformamide, a high-donor-number solvent, which exhibits stronger stabilization of S3•- compared with DMSO, significantly reduces Li-S cell polarization compared with DMSO.
3.Application of acetone acetals as water scavengers and derivatization agents prior to the gas chromatographic analysis of polar residual solvents in aqueous samples.
van Boxtel N1, Wolfs K1, Van Schepdael A1, Adams E2. J Chromatogr A. 2015 Dec 18;1425:62-72. doi: 10.1016/j.chroma.2015.11.020. Epub 2015 Nov 12.
The sensitivity of gas chromatography (GC) combined with the full evaporation technique (FET) for the analysis of aqueous samples is limited due to the maximum tolerable sample volume in a headspace vial. Using an acetone acetal as water scavenger prior to FET-GC analysis proved to be a useful and versatile tool for the analysis of high boiling analytes in aqueous samples. 2,2-Dimethoxypropane (DMP) was used in this case resulting in methanol and acetone as reaction products with water. These solvents are relatively volatile and were easily removed by evaporation enabling sample enrichment leading to 10-fold improvement in sensitivity compared to the standard 10μL FET sample volumes for a selection of typical high boiling polar residual solvents in water. This could be improved even further if more sample is used. The method was applied for the determination of residual NMP in an aqueous solution of a cefotaxime analogue and proved to be considerably better than conventional static headspace (sHS) and the standard FET approach.
4.Synthesis, structure and pyrolysis of stabilised phosphonium ylides containing saturated oxygen heterocycles.
Aitken RA1, Karodia N2, McCarron HB1, Rouxel C1, Sahabo N2, Slawin AM1. Org Biomol Chem. 2016 Jan 27;14(5):1794-804. doi: 10.1039/c5ob02467f.
A range of twelve stabilised phosphonium ylides containing tetrahydrofuran, tetrahydropyran or 2,2-dimethyl-1,3-dioxolane rings have been prepared and fully characterised, including one X-ray structure determination of each type. The X-ray structures confirm the P[double bond, length as m-dash]C and C[double bond, length as m-dash]O functions to be syn and all the compounds undergo thermal extrusion of Ph3PO to give the corresponding alkynes. In some cases there is also competing loss of Ph3P to give different carbene-derived products and evidence has been obtained for the generation of 2-phenyloxete in this way. Raising the pyrolysis temperature leads in several cases to new secondary reactions of the alkyne products involving a sequence of alkyne to vinylidene isomerisation, intramolecular CH insertion, and retro Diels Alder reaction.