Photostabilization of polypropylene. II. Stabilizers and hydroperoxides

The effects of various polyolefin photostabilizers on the thermal and photodecomposition of model and polymeric hydroperoxides have been investigated, both in the liquid and solid phases. Several extremely effective ultraviolet stabilizers belonging to the metal chelate class can cause the rapid thermal decomposition of model and polymeric hydroperoxides. Although stabilizers did not reduce the quantum yield for polypropylene hydroperoxide photolysis, several additives can scavenge hydroxyl and macroalkoxy radical products which result from hydroperoxide photolytic cleavage. Ultraviolet stabilizers which were found to trap radicals were able to prevent the photodegradation of polypropylene which already contained a significant concentration of hydroperoxide groups. Highly effective polypropylene ultraviolet stabilizers probably operate by a range of mechanisms including hydroperoxide decomposition, radical scavenging and singlet oxygen quenching.     

Clean and selective oxidation of aromatic alcohols using silica-supported Jones’ reagent in a pressure-driven flow reactor

By exploiting the high surface to volume ratio obtained within continuous flow reactors, we are able to oxidise selectively an array of primary alcohols to either the aldehyde or carboxylic acid, depending on the flow rates employed, demonstrating a degree of reaction control unattainable in traditional stirred reactors.     

The use of electroosmotic flow as a pumping mechanism for semi-preparative scale continuous flow synthesis

By employing a series of reactions we demonstrate the use of electroosmotic flow as a continuous pumping mechanism suitable for semi-preparative scale synthesis, affording an array of small organic compounds, of analytical purity, with yields ranging from 0.57-1.71 g h(-1).     

Recent advances in synthetic micro reaction technology

Although in its infancy, the field of micro reaction technology is growing rapidly, with many research groups investigating the practical advantages associated with reaction miniaturisation. With this in mind, the following Feature Article aims to provide an overview of the progress made in the past decade, paying particular attention to the field of synthetic organic chemistry.     

Acid-catalysed synthesis and deprotection of dimethyl acetals in a miniaturised electroosmotic flow reactor

Through incorporating a series of polymer-supported acid catalysts into a miniaturised EOF-based flow reactor, we demonstrate a clean and efficient technique for the protection of aldehydes as their respective dimethyl acetal. In addition, we also report the acid catalysed deacetalisation of 11 dimethyl acetals to their respective aldehyde. In all cases, the compounds described are obtained in high yield (>95%) and excellent purity (>99%) without the need for further product purification.     

A study of the thermal degradation kinetics of tris dibromo alkyl phosphates

The thermal decompositions of a series of tris dibromo alkyl phosphates similar to tris(2,3-dibromopropyl) phosphate (T23DBPP), alone and incorporated in poly(ethylene terephthalate) (PET) fabric have been studied by non-isothermal thermogravimetry. Kinetic evaluation revealed that the decomposition rate for tris(2,3-dibromo-3-methyl butyl) phosphate (T23DB3MBP) was the fastest followed by tris(2,3-dibromo-2-methyl propyl) phosphate (T23DB2MPP). Tris(3,4-dibromobutyl) phosphate (T34DBBP) and tris(2,3-dibromo butyl) phosphate (T23DBBP) had only marginally faster decomposition rates than T23DBPP itself. Measured decomposition rates for PET treated with the chemicals were only marginally faster than those for the untreated fabric, except during the initial weight loss stages where some decomposition of the chemicals appears to be occurring. Calculated kinetic parameters using an isoconversional method, along with regression coefficients of compensation effect plots suggest that all the chemicals behave similar to T23DBPP in having an apparent detrimental effect on the condensed phase decomposition kinetics while relying on their combustion inhibition effects to act as gas phase flame retardants.     

The regioselective preparation of 1,3-diketones within a micro reactor

We demonstrate a simple method for the regioselective preparation of 1,3-diketones within a micro reactor from silyl enol ethers where the products are free from both competing O-acylation and diacylation products.     

Investigation of racemisation in peptide synthesis within a micro reactor

We demonstrate that peptides derived from alpha-amino acids may be prepared in a micro reactor. The peptides were prepared in 20 min with quantitative conversion, compared to batch reactions which require prolonged reaction times. We illustrate that by using dilute reagent concentrations and short reaction times, less racemisation is observed in micro reactions than in bulk reactions.