Preparative-scale chemical class

The materials boiling above 850°F, were subsequently separated into four fractions by a preparative scale chemical class separation in our laboratory. This was done as follows 2 gms of the residual material were ground and dissolved in tetrahydrofuran (HPLC grade, Fisher Products, Fairlawn NJ). Ten grams of 30-40pm silica gel ("Sepralyte", Analytichem Int., Harbor City, CA), which was previously washed with methanol and dried, was added to the THF... 

ScHLOGL and co-workers [80] have employed TLC on both analytical and preparative scale in their extensive work on syntheses and properties of ferrocene derivatives. It has been used in investigations like following chemical changes, such as oxidations [81] checking the purity of products of synthesis or separating isomers [21, 84]. TLC has further enabled compound classes such as the alkyl ferrocenes to be separated from acyl ferrocenes [82] and correlations between molecular structure and... 

Several dozens of aldolases have been identified so far in nature [23,24], and many of these enzymes are commercially available at a scale sufficient for preparative applications. Enzyme catalysis is more attractive for the synthesis and modification of biologically relevant classes of organic compounds that are typically complex, multifunctional, and water soluble. Typical examples are those structurally related to amino acids [5-10] or carbohydrates [25-28], which are difficult to prepare and to handle by conventional methods of chemical synthesis and mandate the laborious manipulation of protective groups. 

It should be noted that some commercial enzyme preparations may contain several enzyme isomers (enzymes derived from one source which belong to the same enzyme class but differ in specificity, stability or other properties). This is most often the case when the commercial preparation was developed for a process industry application rather than a specific chemical biotransformation application. Some fungal enzymes, such as laccase, are sometimes supplied as crude enzyme mixtures. Fungal laccases are manufactured on a huge scale (multitonne per annum) and are principally used in bulk processes such as wood... 

When reduced by electrolysis, nitrobenzene and its homologues yield the same products as may be obtained by the various chemical methods of reduction. Aniline, azobenzene, azoxybenzene, hydrazobenzene, and -amino-phenol, as well as phenylhydroxylamine, can thus be obtained from nitrobenzene, and most, if not all, of these products could be prepared satisfactorily on an industrial scale by electrolysis, by adjusting the manner of working so that economy of energy is combined with maximum yields. Many of these products demand a comparatively high price, so that low power cost is not so important in this class of manufacture as high percentage yields. 

As with another class of compounds, the scale of synthesis and time required at the research stage before product can be made influence which method is finally used. At small scale, a plethora of methods exist to prepare amino acids, in addition to isolation of the common ones from natural sources. The majority of these small-scale reactions rely on the use of a chiral auxiliary or template. At larger scale, asymmetric hydrogenation and biocatalytic processes come into their own. For the amino acids approaching commodity chemical scales, biological approaches, either as biocatalytic or total fermentation, provide the most cost-efficient processes. 

Technically almost any reaction can be classed as operating on a scale that is beyond the molecule whether it is the catalysis of polypropylene, the solidification of cement or gene transcription. What makes the concept of supramolecular chemistry attractive is that there is an implicit act of design in the use of existing molecules, or in the synthesis of new ones, to prepare molecular assemblies that have particularly desirable qualities. Such qualities may include detection of biologically important species in a hospital environment, monitoring agrochemicals in watercourses, controlled release of pharmaceuticals into a patient or even the ability for a supramolecular interaction to act as a bit of information on a chemical computer chip. 

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