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Martyn Poliakoff

Publications and source records attributed to Martyn Poliakoff.

15 recordsLinked to original sources
PubMed2005

Selective monoprotection of 1,n-terminal Diols in supercritical carbon dioxide: a striking example of solvent tunable desymmetrization.

The reaction between 1,n-terminal diols (n = 3 or 6) with simple alcohols (MeOH, EtOH, and n-PrOH) in supercritical CO(2) over an acid catalyst (Amberlyst 15) leads to two possible products, a mono- and a bis-ether. At 150 degrees C, the selectivity of the reaction with 1,6-hexanediol and MeOH can be switched from 1:20 in favor of the bis-ether at 50 bar to 9:1 in favor of the desymmetrized mono-ether at 200 bar. It is demonstrated that the switch in selectivity is associated with the phase state of the reaction mixture, with monophasic conditions favoring the mono-ether and biphasic conditions favoring the bis-ether. A rationalization of this effect is also presented.

Journal Article↗
PubMed2005

Method for locating the vapor-liquid critical point of multicomponent fluid mixtures using a shear mode piezoelectric sensor.

A new approach to locating the critical point of fluid mixtures is reported, utilizing a shear mode piezoelectric sensor. This technique employs a single piece of quartz crystal that is installed at the bottom of a strongly stirred high-pressure vessel. The sensor response indicates whether liquid or gas is in contact with its surfaces. Thus, the sensor is able to identify vapor-liquid phase separation by registering a discontinuity in the impedance minimum of the sensor as a function of pressure. Two systems (methanol + CO2 and H2 + CO2) have been investigated using this method. The critical point data of the methanol + CO2 system were chosen to validate the approach against a wealth of literature data, and good agreement was obtained. The sensor behavior in the two-phase region, as well as the effect of stirring, is discussed. The method is general and can be used with other sensors.

Biosensing Techniques↗
PubMed2004

2DCOR-GC: an application of the generalized two-dimensional correlation analysis as a route to optimization of continuous flow supercritical fluid reactions.

A new approach for optimization and monitoring of continuous reactions has been developed using 2D correlation methods for the analysis of GC data (2DCOR-GC). 2DCOR-GC maps are obtained following perturbation of the system that allow the effect of changing reaction parameters such as time, temperature, pressure, or concentration to be both monitored and sequenced with regard to changes in the raw GC data. In this paper, we describe the application of the 2DCOR-GC technique to monitoring the reverse water-gas shift reaction in scCO(2). 2DCOR-GC is combined with FT-IR data to validate the methodology. We also report the application of 2DCOR-GC to probe the mechanism of the alkylation of m-cresol with isopropyl alcohol in scCO(2) using Nafion SAC-13 as the catalyst. These results identify coeluting peaks that could easily be missed without exhaustive method development.

Journal Article↗
PubMed2004

Supercritical hydrogenation and acid-catalysed reactions "without gases".

The high temperature catalytic decomposition of HCO2H and HCO2Et are used to generate the high pressure H2 and the supercritical fluids needed for micro-scale hydrogenation of organic compounds; our approach overcomes the problems and limitations of handling high pressure gases on a small-scale and opens the way to the widespread use of continuous supercritical reactions in the laboratory.

Journal Article↗
PubMed2003

Selective host-guest interaction of single-walled carbon nanotubes with functionalised fullerenes.

Exohedrally functionalised fullerenes have been inserted in single-walled carbon nanotubes (SWNTs) with the aid of supercritical carbon dioxide to form peapods; C(61)(COOEt)(2) are encapsulated in SWNTs in high yield, whereas C(61)(COOH)(2) aggregate via hydrogen bonding to form a supramolecular complex, which sterically hinders encapsulation and causes it to adhere to the exterior surface of the SWNTs.

Journal Article↗
PubMed2003

Probing the vapor-liquid phase behaviors of near-critical and supercritical fluids using a shear mode piezoelectric sensor.

With the rapidly expanding industrial and research applications of near-critical and supercritical technology there is a pressing need for a simple and inexpensive sensor that may be used to determine the phase coexistence regions of fluid mixtures and to establish whether a fluid system is below, at, or above, a critical point. Mechanically vibrating AT-cut quartz plates may be used to determine the product of the fluid density and viscosity of a fluid in which it is immersed, through measurement of the impedance minimum of the electrical equivalent circuit or of the corresponding frequency. The density-viscosity product changes abruptly between fluid phases and rapidly along the isotherm corresponding to the critical temperature, enabling such a plate to act as a sensor of these fluid features. We consider the limitations and linearity of such a sensor and its behavior when a liquid-gas meniscus crosses its surface. We demonstrate for the first time the effective use of an AT-cut quartz sensor in mapping the phase behavior of fluids, using measurements made on carbon dioxide and ethane for calibration and then investigating an ethane-carbon dioxide mixture. The advantages of this experimental approach are that (i) piezoelectric sensors are available for operation up to 1,000 degrees C and at extremely high pressures and (ii) the measurement of the density-viscosity product of supercritical fluids is inherently simpler than traditional techniques for determining phase behavior.

Journal Article↗
PubMed2002

Supercritical fluid-mediated alumination of mesoporous silica and its beneficial effect on hydrothermal stability.

We have investigated the use of supercritical fluids (SCFs) as carriers/solvents during the postsynthesis alumination of mesoporous silica. SCFs were found to be ideally suited for transport of Al into mesoporous silica and to lead to Al-grafted aluminosilicate materials that exhibit exceptional hydrothermal (steam) stability even for highly aluminated materials. The improvements in steam stability arising from the use of SCFs as grafting media (as compared to aqueous or organic solvents) are remarkable, especially for Al-grafted MCM-41 materials with high (Si/Al < or = 10) Al contents. It is proposed that under supercritical fluid conditions Al is sorbed on the surface of the pore walls of the host Si-MCM-41 with little penetration into the pore wall region, that is, the low solvating power of SCFs ensures the deposition of Al onto rather than into the silica framework. This is because the host silica framework cannot undergo any significant hydrolysis (to allow penetration of Al into the pore wall region) during the SCF-mediated alumination. Removal of the Al (i.e., dealumination) which occurs during steaming is therefore less detrimental to the structural integrity of SCF-grafted Al-MCM-41 materials since any dealumination that occurs will not involve removal of Al from deep within the pore walls.

Journal Article↗
PubMed2002

Green chemistry: science and politics of change.

The chemical industry plays a key role in sustaining the world economy and underpinning future technologies, yet is under unprecedented pressure from the effects of globalization and change in many of its traditional markets. Against this background, what will be needed for the industry to embrace efforts to make it "greener"? We explore some of the issues raised by the development of "green chemistry" techniques and identify potential barriers to their implementation by industry.

Carbon Dioxide↗
PubMed2001

The Structure of

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Journal Article↗
PubMed1998

Synthesis and Properties of Polyether Adducts of Hexafluoropentanedionatosilver(I).

A series of polyether [CH(3)O(CH(2)CH(2)O)(m)()CH(3), with m = 2 (diglyme), 3 (triglyme), 4 (tetraglyme)] mono- or hemiadducts of hexafluoropentanedionatosilver(I) have been synthesized and in selected cases structurally characterized. Decomposition of [Ag(hfa)(diglyme)](2) (hfa = hexafluoropentanedionato) in air affords a mixture of products including crystals of [Ag(2)(hfa)(O(2)CCF(3))(diglyme)(2)]. The structure of [Ag(hfa)(diglyme)](2) consists of two silver cations which are bridged by four oxygens from two hfa ligands; each Ag(I) ion is also coordinated to a chelating diglyme molecule. In comparison, ligation of a longer polyether chain results in a monomeric species [Ag(hfa)(tetraglyme)]. The compounds are soluble in a range of solvents including supercritical carbon dioxide (scCO(2)). Crystal data for [Ag(hfa)(diglyme)](2) (150 K): a = 21.376(3) Å, b = 8.4143(17) Å, c = 21.067(3) Å, beta = 124.05(1) degrees, monoclinic space group C2/c; Z = 8. Crystal data for [Ag(2)(hfa)(O(2)CCF(3))(diglyme)(2)] (150 K): a = 9.0945(12) Å, b = 9.4110(13) Å, c = 17.803(2) Å, alpha = 96.109(14) degrees, beta = 101.649(13) degrees, gamma = 105.06(2) degrees, triclinic space group P&onemacr;; Z = 2. Crystal data for [Ag(hfa)(tetraglyme)] (150 K): a = 14.152(3) Å, b = 16.996(3) Å, c = 8.620(2) Å, beta = 106.99(2) degrees, monoclinic space group P2(1)/c; Z = 4.

Journal Article↗