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Biomedical subjects

Philip G Jessop

Publications and source records attributed to Philip G Jessop.

10 recordsLinked to original sources
PubMed2006

Switchable surfactants.

Many industrial applications that rely on emulsions would benefit from an efficient, rapid method of breaking these emulsions at a specific desired stage. We report that long-chain alkyl amidine compounds can be reversibly transformed into charged surfactants by exposure to an atmosphere of carbon dioxide, thereby stabilizing water/alkane emulsions or, for the purpose of microsuspension polymerization, styrene-in-water emulsions. Bubbling nitrogen, argon, or air through the amidinium bicarbonate solutions at 65 degrees C reverses the reaction, releasing carbon dioxide and breaking the emulsion. We also find that the neutral amidines function as switchable demulsifiers of an aqueous crude oil emulsion, enhancing their practical potential.

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PubMed2005

Green chemistry: reversible nonpolar-to-polar solvent.

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

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PubMed2005

The reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with carbon dioxide.

Amidines have been reported to react with CO(2) to form a stable and isolable zwitterionic adduct but previous studies were performed in the presence of at least some water. However, spectroscopy of the reaction between DBU and CO(2) detects the rapid formation of the bicarbonate salt of DBU when wet DBU is exposed to CO(2) and does not indicate that an isolable zwitterionic adduct between DBU and CO(2) forms either in the presence or the absence of water.

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PubMed2003

Liquid poly(ethylene glycol) and supercritical carbon dioxide: a benign biphasic solvent system for use and recycling of homogeneous catalysts.

Poly(ethylene glycol) (PEG), having a molecular weight of 900 or 1500, is a solid at room temperature but a nonvolatile liquid at 40 degrees C under CO2 pressure. Homogeneously catalyzed hydrogenation can be performed in the molten PEG, followed by extraction of the product by supercritical CO2. The catalyst-containing PEG phase which remains in the vessel can be reused for hydrogenation without addition of further catalyst or PEG.

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PubMed2002

Low-temperature synthesis of tetraalkylureas from secondary amines and carbon dioxide.

The reaction of dialkylamines with CO(2) giving tetraalkylureas can be performed at 60 degrees C. The reaction requires CCl(4), is weakly promoted by DMAN or PPh(3), and is not promoted by a Pd catalyst. A two-step procedure, in which dialkylammonium dialkylcarbamate is produced in situ and then reacted with CCl(4) and free dialkylamine, gave greater yields of urea than a simple single-stage procedure.

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PubMed2002

Hydrogenation of carbon dioxide catalyzed by ruthenium trimethylphosphine complexes: the accelerating effect of certain alcohols and amines.

A trace amount of alcohol cocatalyst and a stoichiometric amount of base are required during the hydrogenation of CO(2) to formic acid catalyzed by ruthenium trimethylphosphine complexes. Variation of the choice of alcohol and base causes wide variation in the rate of reaction. Acidic, nonbulky alcohols and triflic acid increase the rate of hydrogenation an order of magnitude above that which can be obtained with traditionally used methanol or water. Similarly, use of DBU rather than NEt(3) increases the rate of reaction by an order of magnitude. Turnover frequencies up to 95,000 h(-1) have now been obtained, and even higher rates should be possible using the cocatalyst and amine combinations identified herein. Preliminary in situ NMR spectroscopic observations are described, and the possible roles of the alcohol and base are discussed.

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PubMed2002

Carbon dioxide as a solubility "switch" for the reversible dissolution of highly fluorinated complexes and reagents in organic solvents: application to crystallization.

Highly fluorinated organic or organometallic solid compounds can be made to dissolve in liquid hydrocarbons by the application of 20-70 bar of CO(2) gas. Subsequently releasing the gas causes the compounds to precipitate or crystallize, giving quantitative recovery of the solid. The resulting crystals can be of sufficient quality for single-crystal X-ray crystallography; the structures of Rh(2)(O(2)CCF(2)CF(2)CF(3))(4)(DMF)(2), Rh(2)(O(2)C(CF(2))(9)F)(4)(MeOH)(2), Cr(hfacac)(3), and P[C(6)H(3)(3,5-CF(3))(2)](3) have been determined from crystals grown in this manner.

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PubMed2002

In situ formation of ruthenium catalysts for the homogeneous hydrogenation of carbon dioxide.

A total of 44 different phosphines were tested, in combination with [RuCl(2)(C(6)H(6))](2) and three other Ru(II) precursors, for their ability to form active catalysts for the hydrogenation of CO(2) to formic acid. Half (22) of the ligands formed catalysts of significant activity, and only 6 resulted in very high rates of production of formic acid. These were PMe(3), PPhMe(2), dppm, dppe, and cis- and trans-Ph(2)PCH=CHPPh(2). The in situ catalysts prepared from [RuCl(2)(C(6)H(6))](2) and any of these 6 phosphine ligands were found to be at least as efficient as the isolated catalyst RuCl(O(2)CMe)(PMe(3))(4). There was no correlation between the basicity of monophosphines (PR(3)) and the activity of the catalysts formed from them. However, weakly basic diphosphines formed highly active catalysts only if their bite angles were small, while more strongly basic diphosphines had the opposite trend. In situ (31)P NMR spectroscopy showed that trans-Ru(H)(2)(dppm)(2), trans-RuCl(2)(dppm)(2), trans-RuHCl(dppm)(2), cis-Ru(H)(O(2)CH)(dppm)(2), and cis-Ru(O(2)CH)(2)(dppm)(2) are produced as the major metal-containing species in reactions of dppm with [RuCl(2)(C(6)H(6))](2) under catalytic conditions at 50 degrees C.

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