Conglomerate separation

A molecule can be called chiral when it lacks an internal plane of symmetry and has a nonsuperimposable mirror image. There exist three different possibilities when a racemic mixture of molecules crystallizes. It may lead to the formation of (i) a conglomerate, in which the molecules form condensates comprised of only one enantiomer (ii) a racemic compound, in which both enantiomers are ordered in the same condensate or (iii) a solid solution, in which the condensate contains both enantiomers in a disordered arrangement. In three dimensions, more than 90% of the compounds crystallize in centrosymmetric space groups. Thus, only a minor part forms a conglomerate, separating the enantiomers... 

Mechanical resobdion of a dl conglomerate. Separation by hand of crystals exhibiting visible enantiomorphism. 

Truly porous, synthetic ion exchangers are also available. These materials retain their porosity even after removal of the solvent and have measurable surface areas and pore size. The term macroreticular is commonly used for resins prepared from a phase separation technique, where the polymer matrix is prepared with the addition of a hq-uid that is a good solvent for the monomers, but in which the polymer is insoluble. Matrices prepared in this way usually have the appearance of a conglomerate of gel-type microspheres held together to... 

Crystallization methods are widely used for the separation, or resolution, of enantiomer pairs. Enantiomer mixtures may essentially crystallize in two different ways. In around 8 per cent of cases, each enantiomer crystallizes separately, giving rise to a mechanical mixture of crystals of the two forms, known as a conglomerate. Conglomerates may usually be separated by physical methods... 

The first resolution of an octahedral complex into its enantiomers was achieved in 1911 by A. Werner, who got the Nobel Prize in 1913, with the complex [Co(ethylenediamine)(Cl)(NH3)] [10]. Obviously, resolution is to be considered only in the case of kinetically inert complexes whose enantiomers do not racemize quickly after separation. This is a very important remark since, as noted above, the interesting complexes are those containing exchangeable sites required for catalytic activity and thus more sensitive to racemization. We will not discuss here the very rare cases of spontaneous resolution during which a racemic mixture of complexes forms a conglomerate (the A and A enantiomers crystallize in separate crystals) [11,12]. 

Conglomerate crystallization in the above case indicates that the inclusion approach may be further extended into the realm of the salt-type associates. Such an attempt is especially interesting due to the obvious role in enantiomer separation which relies heavily on the solubility difference of the enantiomeric salts under certain circumstances 137). 

A young Louis Pasteur observed that many salts of tartaric acid formed chiral crystals (which he knew was related to their ability to rotate the plane of polarization of plane-polarized light). He succeeded in solving the mystery of racemic acid when he found that the sodium ammonium salt of racemic acid could be crystallized to produce a crystal conglomerate. After physical separation of the macroscopic enantiomers with a dissecting needle, Pasteur... 

In the 1930s Adolph Hitler combined these companies into a cartel called 1 G Farben (Farben means colors) that rapidly dominated prewar chemical production and then produced Germany s chemicals, munitions, and synthetic fuels during World War 11. After the War, in an effort to control the power of this conglomerate, the Allies spht 1 G Farben into three separate companies BASF, Bayer, and Hoechst, which specialized in commodity chemicals, pharmaceuticals, and fine chemicals, respectively. These companies have continued to grow since the war so that now the three of them are the top three chemical companies in the world. 

The two salts may separate together, each retaining its individuality, so that each may be recognized, and the two varieties of crystals may be separated mechanically. Such a product is called a conglomerate or a mixture. 

An equimolar mixture of two enantiomers is called a racemate. The separation of two enantiomers that constitute a racemate is called optical resolution or resolution. Their crystalline forms best characterize types of racemates. A racemic mixture is a crystal where two enantiomers are present in equal amounts. A conglomerate is a case where each enantiomer has its own crystalline form. Sometimes their crystals have so-called hemihedral faces, which differentiate left and right crystals. For over a hundred years, crystallization processes have been used for the separation and purification of isomers and optical resolution, both in the laboratory and on an industrial scale. 

Various methodologies can be applied for resolving racemates, depending on their type. The most useful method for separating racemates that crystallize as a collection of enantiomorphous left and right crystals (a conglomerate) is preferential crystallization (or crystallization by entrainment). It involves alternate... 

Emprise was one of the largest nonpublic, family-owned corporations in the world, a conglomerate with control or partial control over 450 separate companies. Its stated annual profit is 350 million, from holdings in North American and British... 

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