Additional crystallisation steps

Crystallise benzhydrol from hot H2O or pet ether (b 60-70°), pet ether containing a Uttle benzene, from CCI4, orEtOH (ImL/g). An additional purification step includes passage of a benzene solution through an activated alumina column. It sublimes in a vacuum. Also recrystallise it three times from MeOH/H20 [Naguib J Am... 

Chiral phosphines are valuable as ligands in numerous important catalytic asymmetric processes. Intense research efforts have produced many classes of chiral phosphines with diverse steric and electronic properties, and researchers have examined how these properties influence activity and stereoselectivity in catalysis. Given the rapid development of new methods in asymmetric catalysis and the prominence of chiral phosphines in this area of ehemistry, it is surprising that few catalytic asymmetric syntheses of chiral phosphines have been described. Instead, enantiopure phosphines are most commonly prepared either via stereospecific reactions of resolved starting materials or through routes which require an additional resolution step, such as fractional crystallisation of diastereomers. On the other... 

Cocrystals are often prepared by a traditional solution crystalhsation approach such as solvent evaporation, coohng, or anti-solvent addition. There are a number of reasons for the popularity of the solution-based approach. Solution crystallisation can yield large, well-formed single crystals, from which one may easily evaluate crystal habit and surface features. Analysis of the diffraction pattern of a single crystal is typically the best means of obtaining an absolute crystal structure determination. Further, solution crystalhsation is an established and effective purification step. 

In these studies the protein was solubilised by the use of mild detergents and the protein in the micelle was the starting point for crystallisation using usual precipi-tants. The realisation that the detergent (its size and chemistry) played a direct role in crystallisation was an important step forward. The size and quality of the crystals were improved by addition of small polar organic molecules, which may act by improving packing of the micelles in the crystal lattice. 

In fact your suspicions may have been aroused by the quantity of material put in. We started with 150 g racemic 88, that is 75g of each enantiomer and we seeded with 6g of (.S )-88 making 81 g of (S)-88 altogether. But the yield of pure crystalline (.S )-88 was 112.6g - too much Clearly the other enantiomer is somehow being converted into the enantiomer that crystallises. The clue is the addition of that extra AC2O at step 4. This forms a mixed anhydride 89 that racemises by enolisation 90 and crystallisation can continue. 

The process from the FMC company involves as the pivotal step an intramolecular stereoselective [2 + 1 [-cycloaddition. In a Prins reaction [94] of chloral and isobutene, followed by an isomerisation, a racemic, trichloromethyl-substituted aUyl alcohol is obtained. Reaction with the isocyanate from (R)-naphthylethyl-amine enables separation ofthe diastereomers by crystallisation. The carbamate is cleaved by trichlorosilane/triethylamine, thus permitting the recycling of the chiral auxiliary. The optically pure (R)-aUyl alcohol is reacted with diketene, to produce the / -keto-ester. After diazo transfer and basic cleavage, the diazoacetate is obtained catalysed by a copper salt, this is converted in a [2 + 1 ]-cyclo-addition into a bicyclic lactone. The Boord reaction (discovered by Cecil E. Boord in 1930) [95] finally gives (IR)-cis-permethric acid. [96]... 

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