D. Bradley G. Williams

Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants

Various commonly used organic solvents were dried with several different drying agents. A glovebox-bound coulometric Karl Fischer apparatus with a two-compartment measuring cell was used to determine the efficiency of the drying process. Recommendations are made relating to optimum drying agents/conditions that can be used to rapidly and reliably generate solvents with low residual water content by means of commonly available materials found in most synthesis laboratories. The practical method provides for safer handling and drying of solvents than methods calling for the use of reactive metals, metal hydrides, or solvent distillation.

Aluminium triflate: a remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols

Al(OTf)3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols.

Highly atom efficient aluminium triflate catalysed acetal formation

Aromatic and aliphatic acetals are formed in excellent yields under solventless conditions at room temperature within 30 minutes by treating aldehydes and ketones with 0.5 mol% Al(OTf)3 as a recyclable catalyst in the presence of only 1.2 equivalents of an orthoester as reagent.

STEREOSELECTIVE SMI2-MEDIATED CONVERSION OF CARBOHYDRATES INTO CYCLOPENTANOLS

Carbohydrate derivatives were employed as precursors in the synthesis of stereodefined cyclopentanols. This rapid conversion was effected by a zinc-assisted Grob-fragmentation, followed by a stereocontrolled SmI2-mediated cyclisation.

ONE-POT SMI2-PROMOTED TRANSFORMATION OF CARBOHYDRATE DERIVATIVES INTO CYCLOPENTANOLS

Abstract Selectively functionalised carbohydrate derivatives underwent SmI 2 -promoted Grob-fragmentation reactions. This was followed by an in situ , stereocontrolled SmI 2 -mediated cyclisation to afford the corresponding cyclopentanols.

Bubbles in Solvent Microextraction: The Influence of Intentionally Introduced Bubbles on Extraction Efficiency

Significant improvements to microdrop extractions of triazine pesticides are realized by the intentional incorporation of an air bubble into the solvent microdroplet used in this microextraction technique. The increase is attributed partly to greater droplet surface area resulting from the air bubble being incorporated into the solvent droplet as opposed to it sitting thereon and partly to thin film phenomena. The method is useful at nanogram/liter levels (LOD 0.002-0.012 μg/L, LOQ 0.007-0.039 μg/L), is precise (7-12% at 10 μg/L concentration level), and is validated against certified reference materials containing 0.5 and 5.0 μg/L analyte. It tolerates water and fruit juice as matrixes without serious matrix effects. This new development brings a simple, inexpensive, and efficient preconcentration technique to bear which rivals solid phase microextraction methods.

Mild water-promoted selective deacetalisatison of acyclic acetals

Various aliphatic and aromatic dimethyl and diethyl acetals and ketals were found to hydrolyse in essentially quantitative yield when heated to 80 °C in neat water or aqueous medium without a catalyst or any other additive, while cyclic acetals were stable under these conditions. Selective deprotection is possible when both types of acetal are present.

FRAGMENTATION AND CLEAVAGE REACTIONS MEDIATED BY SmI2. PART 1: X-Y, X-X AND C-C SUBSTRATES

2. C-C Fragmentation Reac a. Cyclobutane containing Substrates b. Cyclopropane containing Substrate s... ....................................... c. 1,4-Diketones in Non-strained and Strained Systems ...... ..................... 590 V. CONCLUSION ............................................. .............................................. 595 REFERENCES ............................. ...................................................

Cooperative ligand effects in phase-switching homogeneous catalysts.

Homogeneous catalysis is usually carried out by using a metal complex that contains ligands that solubilize the complex and control the selectivity of the reaction. Apart from simple ligands, such as carbon monoxide or halides, these complexes usually contain only one other type of ligand. Noyori-type hydrogenation catalysts often contain diamines and (di)phosphine ligands and both are required to obtain the desired reactivity and selectivity. Less usual are systems which give one product when one ligand is used, but the outcome is altered by adding a second ligand, which gives cooperative effects. We have recently reported two such cooperative effects. Xantphos is a bidentate phosphine ligand which has a wide bite angle and hence a high selectivity for the linear product in the hydroformylation of alkenes. The products of these reactions are invariably aldehydes. When PEt3 is used as the supporting ligand for alkene hydroformylation in alcoholic solvents, alcohols rather than aldehydes are the products, but the linear selectivity is poor. By using a mixture of PEt3 and xantphos, it is possible to obtain high selectivity towards the linear alcohol products. We have demonstrated that only xantphos, which controls the regioselectivity, is coordinated to the metal atom during the early part of the reaction, but PEt3 coordinates later in the cycle and directs the formation of alcohol products. In a second example, a xantphos ligand that is tagged with an imidazolium group (xantphos’) together with a sulfonated triphenylphosphine (PPh3’) were used for hydroformylation of alkenes in supercritical fluid/ionic liquid flow systems. The metal/PPh3’ complex alone gives a high rate of reaction with poor linear selectivity, whereas the xantphos ligand alone gives a high linear selectivity at a lower rate of reaction. By using the two together we obtained intermediate linear selectivity at a similar rate of reaction to the experiments that were performed with xantphos alone. These results suggest that both PPh3’ and xantphos’ are coordinated to the metal atom in the resting state of the catalyst. Herein, we report a third example in which two ligands that are tagged with amidate groups, trisSwitchPhos 1 and an amidated xantphos ligand 2, give a high selectivity and allow the catalyst to be efficiently switched from the organic phase into the aqueous phase by bubbling CO2 through the reaction mixture.

Solvent-Assisted Headspace Sampling Using Solid Phase Microextraction for the Analysis of Phenols in Water

Headspace analysis is used widely and relies on volatilization of analytes into the headspace above the matrix. We detail the dramatic influence that added solvent can have on headspace analysis of phenols, without the requirement for specialized headspace vials. The use of water-immiscible solvents is key and leads to a 1-3 orders of magnitude enhancement in the volatilization of these analytes and shorter fiber exposure times than are otherwise required.