Differential crystallisation

Resolution of compounds made as diastereoisomeric mixtures The synthesis of Jacobsen s Mn(III) epoxidation catalyst by resolution Resolution with half an equivalent of resolving agent Physical Separation of Enantiomers Chromatography on chiral columns Resolution of triazole fungicides by HPLC A commercial drug separation by chiral HPLC Differential Crystallisation or Entrainment of Racemates Conglomerates and racemic compounds Typical procedure for differential crystallisation (entrainment) Conventional resolution ofL-methyl DOPA Resolution ofL-methyl DOPA by differential crystallisation Finding a differential crystallisation approach to fenfluramine Resolution with Racemisation... 

Resolution of amino acids by differential crystallisation with racemisation Differential crystallisation and racemisation when enolisation is impossible Kinetic resolution with racemisation... 

The anorectic drug fenfluramine 85 is made by the alkylation of the simpler amine 84. Either compound could be resolved and, though a classical resolution of the camphoric acid salt of fenfluramine was known, chemists at Rouen were determined to achieve better results by differential crystallisation.21... 

Resolution of amino acids by differential crystallisation with racemisation... 

The separation of the enantiomers of most amino acids can be ach ie ved by differential crystallisation of their JV-acetyl derivatives, such as that of leucine. Racemic A-acetyl leucine 88 is dissolved in the right solvent mix cooled and seeded with 4% by weight of natural (.S )-88. Pure (.S )-88 crystallises out in good yield.22... 

Sometimes these differential crystallisations with racemisations are very easy to do. Racemic /V-butyrovl proline 91 gives a good yield of one enantiomer in moderate ee just by melting the racemic compound with catalytic acetic anhydride and seeding with one enantiomer. Further crystallisations improve the ee. The yield is 6.3 from 10.5 g or 60% of the total material. This process is clearly a great improvement on simple differential crystallisation both in simplicity of operation and because it is no longer necessary to alternate the isolation of enantiomers. 

Differential crystallisation and racemisation when enolisation is impossible... 

When the /V-acctyl derivative of the intermediate 94 was crystallised from isopropanol with seeding a good yield of enantiomerically pure l-DOPA could be crystallised out. Treatment of the residue from the mother liquor with NaCN in DMSO led to complete racemisation and the differential crystallisation could be repeated.23... 

B. Segregation Crystallisation, differentiation and accumulation Bushveld chromite still water complex Sukinda chromite... 

Parameters for tree differentiation are autumn colours and bud formation (with equal bearing). Parameters for fruit differentiation are degree and hue of blush, yellow ground (background) colour, shape of fruit, sheen, starch conversion, differentiation score on crystallisation pictures and luminescence. 

Eoams were extruded from low density polyethylene (LDPE) and blends of LDPE with syndiotactic polypropylene (sPP), using isobutane as the blowing agent. The extruded materials were characterised by measurement of dimensional stability at room temperature, density, tensile properties, dynamic stiffness, and crystallinity determined by differential scanning calorimetry. The sPP, with a slow crystallisation rate, did not interfere with the expansion of the LDPE, and enhanced the temperature resistance by in-situ crystallisation. The blends were flexible, dimensionally... 

Significantly, for macromolecular materials the rate of polymer crystallisation can be extremely slow and polymers that can potentially crystallise are often isolated in a kinetically stable, amorphous state. A potentially crystal-lisable polymer that is in an amorphous state can show an exothermic crystallisation transition T at elevated temperatures. The thermal transitions of a polymer are commonly investigated by the technique of differential scarming... 

Deposition of wax following crystallisation depends on the temperature differential between the bulk crude stream and the pipewall, and the Reynolds number. The larger the temperature differential, the greater the chance of wax deposition since molecular diffusion of dissolved wax to the pipewall intensifies as a result of the increase in wax concentration near the pipewall brought about by the temperature differential. With respect to Reynolds number, maximum wax accumulation is expected in the transition range (Reynolds number between 2000 and 4000). At low (laminar) flew, the net transport of wax to the wall 1s reduced by a relatively thick laminar layer adjacent to the pipewall and during turbulent flow, wax build-up 1s limited by erosion. 

At low temperatures, partial co-crystallisation was indicated by transmission electron microscopy and differential scanning calorimetry [156, 157]. Both electron microscopy of stained sections and optical microscopy showed that the segregated low molar mass material was present as small domains between the stacks of dominant lamellae within the spherulites/ax-ialites [115, 157, 158],... 

The depression of the melting point of a crystalline polymer in blends can be used to measure the Flory-Huggins interaction parameter of the mixture. The melting points on heating, or crystallisation points on cooling, can be measured using techniques such as differential scanning calorimetry or by turbidity measurements. 

Where several polymorphs crystallise in the same crystal system they may be differentiated by the Pearson symbol (see Sections IR-3.4.4 and IR-11.5.2). Greek letters are frequently employed to designate polymorphs, but their use is often confused and contradictory and is not generally recommended. 

Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) of amoxicillin trihydrate showed loss of the water of crystallisation from about 50 to 150 °C followed by decomposition of the amoxicillin from about 160°C upwards [18], DSC and TGA of amoxicillin sodium salt in an oxygen atmosphere showed loss of water at about 100°C and thermal decomposition in multiple events from about 200 to 500°C [19]. The techniques are of little practical value for these compounds. 

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