Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow Until recently, however, the question, “Should we do this in flow?” has merely been an afterthought This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts

The Hitchhiker's Guide to Flow Chemistry

In many areas of chemistry the synthesis of chiral compounds is a target of increasing importance. They play a vital role in biological function and in many areas of society and science, including biology, medicine, biotechnology, chemistry and agriculture. Many pharmaceutical molecules, like their biological targets, are chiral and it is therefore easy to understand the growing demand for efficient methods of producing enantiomerically pure compounds. This is equally true for the preparation of chiral solids, which have potential applications in asymmetric catalysis, chiral separations and the like. In this Review we will consider recent progress and future potential in the development of methods for the preparation of chirally pure solids, in particular where the building blocks of the structure are achiral themselves. We will discuss strategies for the synthesis of both inorganic (for example, zeolites) and inorganic-organic hybrid (for example, metal organic framework) chiral porous solids.

Induction of chiral porous solids containing only achiral building blocks

The separation of molecules with similar size and shape is an important technological challenge. For example, rare gases can pose either an economic opportunity or an environmental hazard and there is a need to separate these spherical molecules selectively at low concentrations in air. Likewise, chiral molecules are important building blocks for pharmaceuticals, but chiral enantiomers, by definition, have identical size and shape, and their separation can be challenging. Here we show that a porous organic cage molecule has unprecedented performance in the solid state for the separation of rare gases, such as krypton and xenon. The selectivity arises from a precise size match between the rare gas and the organic cage cavity, as predicted by molecular simulations. Breakthrough experiments demonstrate real practical potential for the separation of krypton, xenon and radon from air at concentrations of only a few parts per million. We also demonstrate selective binding of chiral organic molecules such as 1-phenylethanol, suggesting applications in enantioselective separation.

https://www.adamkewley.com/files/Adam-Kewley_Nature-Materials-Paper.pdf

Separation of rare gases and chiral molecules by selective binding in porous organic cages

We report experimental results that show a large and symmetric population of D and L crystals moving
into complete chiral purity, with one of the enantiomers completely disappearing. The results indicate (i) a
new symmetry breaking process incompatible with the hypothesis of an initial single chiral phase or
‘‘mother crystal,’’ (ii) that total symmetry breaking and complete chiral purity can be achieved from a
system that initially includes both enantiomers, and (iii) that this is achieved through a nonlinear
autocatalytic-recycling process.

Chiral Symmetry Breaking during Crystallization: Complete Chiral Purity induced by Nonlinear Autocatalysis and Recycling

http://www.yxxb.com.cn:8081/apsb/homeAction!downloadArticleFile.action?attachType=PDF&id=6730

Fundamental aspects of solid dispersion technology for poorly soluble drugs.

The provision of pure enantiomers is of increasing importance not only for the pharmaceutical industry but also for agrochemistry and biotechnology. In general, there are two rival approaches to provide pure enantiomers. The "chiral" approach is based on developing an asymmetric synthesis of just one of the enantiomers, while the "racemic" approach is based on separating mixtures of the two enantiomers. In the last few years remarkable progress has been achieved in the latter area. This Review focuses in particular on enantioselective crystallization processes and preparative chromatography, including hybrid processes and the incorporation of racemization steps. Several examples from our research are used for illustration purposes.

/pdf/processes-to-separate-enantiomers-2o17sxes0g.pdf

Processes to separate enantiomers.

The steam reforming of glycerol (1,2,3-propantriol) was investigated with non-substituted and partially Ce substituted La 1− x Ce x NiO 3 mixed oxides where x  = 0, 0.1, 0.3 or 0.7, and the activities were compared with Pt metal catalysts. The catalysts were characterised by temperature-programmed reduction (TPR), X-ray powder diffraction (XRD), BET surface area and carbon content. The Ni was easily reduced in the La 0.3 Ce 0.7 NiO 3 structure. The experimental results were compared with the thermodynamic equilibrium concentrations, which were calculated for the system with non-stochiometric method. The La 0.3 Ce 0.7 NiO 3 catalyst was highly active in the glycerol steam reforming with conversions approaching to the equilibrium at temperatures between 500 and 700 °C. The formation of carbonaceous deposits on the La 0.3 Ce 0.7 NiO 3 was smallest among all the investigated La 1− x Ce x NiO 3 catalysts. Unchanged catalyst surface area (BET) during operation and low carbon deposition after reaction confirm the efficient operation and high stability of the non-noble, inexpensive catalyst of La 0.3 Ce 0.7 NiO 3 .

Steam reforming of glycerol : The experimental activity of La1 -XCeXNiO3 catalyst in comparison to the thermodynamic reaction equilibrium

The measurement of solubility in microsamples employing a differential scanning calorimeter (DSC) has been evaluated for several aqueous and nonaqueous systems:  substance A in acetonitrile, (RS)-mandelic acid, (S)-mandelic acid, adipic acid, diphenhydramine HCl, α-glycine, and terephthalic acid in water, (RS)-mandelic acid and β-succinic acid in ethanol and methanol, and adipic acid in ethanol. This technique requires samples in the range of milligrams and can be used at high temperatures and pressures. Results show that the solubility data of most compounds studied using this technique are within 5% of solubility data obtained from the literature. Factors that influence solubility measurement by DSC were examined along with methods to minimize associated errors.

Solubility measurement using differential scanning calorimetry

Pure enantiomers are of large interest for several industries. Chemical synthesis is frequently not selective and provides racemic mixtures causing a large interest in efficient separation processes. Preparative chromatography is nowadays a powerful and flexible but expensive technology. As an alternative there exists the possibility to apply cheaper crystallization processes. Based on classifying enantiomeric systems according to their type of solid–liquid equilibria, crystallization processes will be discussed which are capable to provide pure enantiomers. Two separation problems studied in our laboratory will be considered for illustration. Preferential crystallization was used to separate racemic threonine dissolved in water. Cooling crystallization was applied to separate a non-racemic solution of mandelic acid enantiomers dissolved also in water.

Heike Lorenz

Papers

Processes to separate enantiomers.

Steam reforming of glycerol : The experimental activity of La1 -XCeXNiO3 catalyst in comparison to the thermodynamic reaction equilibrium

Solubility measurement using differential scanning calorimetry

Crystallization of enantiomers

Coupling of simulated moving bed chromatography and fractional crystallisation for efficient enantioseparation