Peter Styring

The use of a novel microreactor for high throughput continuous flow organic synthesis

Abstract The aim of this study was to investigate the performance characteristics of a flow injection microreactor with reference to both the chemistry and reactor design using a model system, the established synthesis of 4-cyanobiphenyl based on a modified Suzuki coupling of an aryl halide and an organoboron compound. The catalytic reaction was carried out in micro-channels (300 μm wide and 115 μm deep) etched into glass and sealed with a top plate. The mobility of the reagent solutions was achieved using electroosmotic flow (EOF) assisted by the incorporation of a microporous silica structure within the microreactor channels, which acted as both a micro-pump and an immobilisation technique for the catalyst bed (1.8% palladium on silica). The yield of 4-cyanobiphenyl was determined by GC–MS. The synthesis of 4-cyanobiphenyl at room temperature in a flow injection microreactor, using a supported catalyst, without the addition of a base gave a product yield of 67±7% ( n =6). This was achieved by injecting 4-bromobenzonitrile for 5 s, with a 25-s injection interval, into a continuous stream of phenylboronic acid. A series of injections were performed over a 25-min period and the product collected for analysis. Palladium contamination in the crude product was found to be in the range of 1.2–1.6 ppb, determined using ICP–MS, indicating a low leach rate from the immobilised catalyst. A conventional laboratory batch scale method was also performed for the same synthesis using the identical conditions as those used in the flow injection microreactor, with and without the addition of a base, at both room and elevated temperatures (75–80°C) in an inert atmosphere under reflux for 8 h. The product yield for the non-optimised bulk reaction was 10% (determined by GC–MS), significantly lower than with the flow injection microreactor illustrating the potential of microreactors for clean efficient synthesis.

Chirality and Frustration in Ordered Fluids

Abstract Chirality in liquid crystal systems is a complex and sometimes difficult concept to understand and appreciate. In this article we review some of the reduced symmetry aspects of calamitic liquid crystal phases with reference to point symmetry, space symmetry, and helicity. We utilize these concepts in the discussion of new results obtained on Twist Grain Boundary phases, inversions in chiral dependent properties such as the helicity in cholesteric and smectic C* phases and the spontaneous polarization in ferroelectric liquid crystals, and antiferroelectric behaviour in low molar mass systems. Our observations suggest that many novel effects found in chiral liquid crystals are a result of conflicts between the effects of reduced symmetry and the desire to form normal liquid-crystalline structures, i.e., a form of frustration exists.

The application of micro reactors to synthetic chemistry

A feature article describing the fundamental characteristics and emerging applications of micro technology in the field of synthetic chemistry.

A facile method for catalyst immobilisation on silica: nickel-catalysed Kumada reactions in mini-continuous flow and batch reactors

An unsymmetrical salen-type nickel(II) complex was readily immobilised onto functionalised silica using a convenient tethering method. The supported complex was an effective recyclable heterogeneous catalyst in a room temperature cross-coupling reaction between 4-bromoanisole and phenylmagnesium chloride. Leaching of the metal into solution from the supported catalyst proved almost negligible. The silica-supported catalyst was ideal for use in a mini-continuous flow reactor since it did not exhibit swelling which is common and a problem for organic polymer resin supports.

High CO2 solubility in ionic liquids and a tetraalkylammonium-based poly(ionic liquid)

Carbon dioxide (CO2) absorption in several imidazolium-based ionic liquids (ILs), pyridinium-based ionic liquids and a tetraalkylammonium-based poly(ionic liquid) (PIL), poly[(p-vinylbenzyl) trimethylammonium hexafluorophosphate] P[[VBTMA][PF6], was studied. The trend of CO2 solubility in all of the ILs increases dramatically with decreasing absorption temperature. Based on the same bis(triflamide) [Tf2N] anion, imidazolium, pyridinium and trihexyltetradecylphosphonium-based ionic liquids all show relatively similar CO2 solubilities, which were higher than for the [ES] anion. The highest CO2 absorption was found in a poly(ionic liquid) P[[VBTMA][PF6]], however, the monomer also showed higher CO2 capacity than the other ionic liquids. The poly(ionic liquid) is remarkable in that it can adsorb 77% of its body weight of CO2 with a selectivity over nitrogen of 70 : 1. The absorbed CO2 gas can be readily desorbed from ionic liquids and poly(ionic liquid) and the selectivity for CO2 over N2 was consistent over repeated cycles. The materials can be reused several times for consecutive sorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial adsorbers.

Polymorphic Ionic Mesogens of Silver(l): Ionic Materials Exhibiting a Thermotropic Cubic Mesophase

Abstract Reaction of tran.s-4-alkyloxy-4′-stilbazoles (n-OPhVPy) with silver dodecylsulphate (AgDOS) led to the complexes [Ag(n-OPhVPy)2][DOS] which showed thermotropic mesomorphism. All homologues from methyloxy (n=1) to dodecyloxy (n=12) have been synthesised. The complexes showed a nematic phase at short chain lengths, but at longer chain lengths, smectic C and A phases were observed in addition to an isotropic mesophase (Mt), similar to the recently characterised D phase. The mesomorphism was determined using optical microscopy, DSC and X-ray scattering.

Measurement of vapour pressures of ionic liquids and other low vapour pressure solvents

The vapour pressures of several ionic liquids, liquid polymers and derivatives of glycerol were investigated by thermogravimetric analysis (TGA). The experimental method is described and discussed. Vapour pressure data for various solvents with low vapour pressures are reported at 100–120 °C. The thermogravimetric method for vapour pressure measurement is useful for the rapid screening of solvents. Ionic liquids have a low but detectable vapour pressure at 100–120 °C. The vapour pressures of liquid polymers such as poly(ethylenimine) and polyethylene glycols are in the same range, which might make these substances a less expensive alternative to ionic liquids.

Comparative study of solvent properties for carbon dioxide absorption

Several inexpensive and non-toxic solvents with low vapour pressures were investigated for their suitability as alternative solvents for the absorption of carbon dioxide from flue gas. The solvents include poly(ethylene glycol)s, poly(ethylene glycol) ethers, poly(ethylenimine) and glycerol-based substances. Solvent properties such as thermal stability, solubility of carbon dioxide and selectivity over nitrogen were investigated in a systematic study using a thermogravimetric analyser. Absorption results are reported for pure carbon dioxide and nitrogen as well as a mixture of both gases. Desorption and long-term sorption behaviour are also discussed. Glycerol and poly(ethylene glycol)s show a high solubility of carbon dioxide. Due to the high viscosity of the solvent, carbon dioxide absorption in poly(ethylenimine) is very slow in spite of the presence of favourable amine groups. PEG 300 was found to be the best solvent in this study and shows a high carbon dioxide solubility as well as good selectivity over nitrogen. The advantages of high stability, low solvent loss and low desorption energy of PEG 300 may outweigh its lower absorption capacity compared to the state-of-the-art solvent monoethanolamine, making it a potentially advantageous solvent for industrial carbon dioxide absorption processes.

Kumada-Corriu reactions in a pressure-driven microflow reactor.

Reaction rates for the Kumada reaction (of Grignard reagents with aryl halides) catalysed by an immobilised nickel(II) catalyst have been shown to be enhanced when the reaction is carried out in a pressure driven microreactor (internal diameter 100-200 microm) rather than with conventional batch reaction techniques.

Supported phosphine-free palladium catalysts for the Suzuki–Miyaura reaction in aqueous media

The Suzuki–Miyaura reaction has been performed using a non-symmetrical salen-type palladium(II) catalyst that is readily immobilized onto Merrifield resin and functionalized silica. The catalysts combine high activity with the recoverability and reusability offered by a heterogeneous system, without the need for phosphine ligands or additives. The high content of water used in the reaction, which is more than 96% by volume, represents a green process that should have advantages for industrial applications. Leaching of the metal into solution from the supported catalyst proved to be negligible.