Chemical processes, carbohydrate transformation

V. Carbohydrate Transformation in Chemical Processes, Including Humus... 

In some chemical processes, including natural humus formation, non-enzymic carbohydrate transformation, in aqueous media, into noncarbohydrate products is important. 

Universitat Darmstadt) as Honorary Chairman. The CORM meetings were started by Lichtenthaler in 1990. Both volumes highlight the importance of carbohydrates for sustainable processes as abundant, renewable, and low-cost materials and show how sugars contribute significantly to the indispensable new processes for tomorrow s chemistry. With the chemical and biochemical transformations of readily available carbohydrates, we are on the way toward a more sustainable future. 

The use of renewable resources as substrates in chemical processes has recently been reviewed [1]. There are two major topics of current research (1) oleochem-ical reactions, and (2) chemical transformation of carbohydrates. Nevertheless, the chemical possibilities of renewable resources as substrates - using homogeneous catalysis - are still very far from being fully exploited. 

Some of the potential uses of the fats and oils found in plants have been reviewed and some uses of carbohydrate-based polymers briefly discussed. Plants contain a whole variety of other chemicals including amino acids, terpenes, flavonoids, alkaloids, etc. When the potential for these naturally occurring materials are combined with the secondary products that can be obtained by fermentation or other microbial processes or by traditional chemical transformations, the array of chemicals that can readily be created from renewable resources is huge. In this section a few of the more interesting examples are considered. 

Although the investigations of both Raunkjaer et al. (1995) and Almeida (1999) showed that removal of COD — measured as a dissolved fraction — took place in aerobic sewers, a total COD removal was more difficult to identify. From a process point of view, it is clear that total COD is a parameter with fundamental limitations, because it does not reflect the transformation of dissolved organic fractions of substrates into particulate biomass. The dissolved organic fractions (i.e., VFAs and part of the carbohydrates and proteins) are, from an analytical point of view and under aerobic conditions, considered to be useful indicators of microbial activity and substrate removal in a sewer. The kinetics of the removal or transformations of these components can, however, not clearly be expressed. Removal of dissolved carbohydrates can be empirically described in terms of 1 -order kinetics, but a conceptual formulation of a theory of the microbial activity in a sewer in this way is not possible. The conclusion is that theoretical limitations and methodological problems are major obstacles for characterization of microbial processes in sewers based on bulk parameters like COD, even when these parameters are determined as specific chemical or physical fractions. 

Furan Derivatives Catalytic processes used to obtain furan derivatives from carbohydrates and the catalytic routes from furan intermediates to chemicals and polymers have been reviewed by Moreau et al. [27]. Some of the main reactions are summarized in Fig. 3.2. From fructose or carbohydrates based on fructose (sucrose, inulin), the first transformation step is dehydration to 5-hydroxy methylfur-fural (HMF). Fructose dehydration at 165 °C was performed in the presence of... 

In many projects involving a transformation or isolation of carbohydrates, it is important to quantify the amount of product obtained. It is sometimes difficult to measure the content of a specific component in a mixture. The process can be laborious with instrumentation such as HPLC or GC, especially if the sample contains major impurities of different natures. Fortunately, knowledge of the properties of the desired product can suggest a specific method of analysis, several of which involve colorimetric analysis. With colorimetric analyses, a selective chemical transformation will produce color. The absorbance or transmittance of the colored sample is directly correlated with the presence of a certain functional group or product in the mixture. Various reactions that produce color are known to be selective for certain types of carbohydrates. 

Some other natural compounds have been transformed for their use in the synthesis of polymers via olefin metathesis processes. As mentioned in the introduction, furans, which are obtained from carbohydrates, are perfect precursors of monomers for ROMP via simple Diels-Alder cycloadditions (n) (Scheme 25) [26]. In this regard, the first example of the ROMP of 7-oxabicyclo[2.2.1]hept-5-ene derivatives was reported by Novak and Grubbs in 1988 using ruthenium- and osmium-based catalysts [186]. The number of examples of ROMP with monomers with this generic structure is vast, and it is out of the scope of this chapter to cover all of them. However, it is worth mentioning here the great potential of a renewable platform chemical like furan (and derived compounds), which gives access to such a variety of monomers. 

The environmental and economical benefits of one-pot catalytic fine chemical syntheses, in which various successive chemical steps are accomplished in the same reaction vessel, generally over a bifunctional (or multifunctional) catalyst, are obvious. The reduction in the number of synthetic and separation steps has various positive consequences environmentally more sustainable processes (higher atom economy and lower environmental factors), lower operating costs, lower production of wastes and in general an improvement in the safety conditions.[1 31 The environmental advantages are still more remarkable when the transformation of renewable raw materials, such as mixtures of natural terpenes or carbohydrates are concerned. 

The ability to perform even the simplest of muscle movement requires complex coordination of the physical and chemical activities of the tissue. In recent years, nutritionists and exercise physiologists have described how the primary energy sources in food carbohydrates, fats, and proteins are transformed into the universal "currency" of biological energy, ATP. Oxidative metabolism processes the substrates through a cascade of enzymatic events to Insure maximal efficiency in energy conversion. At every level of this conversion, one or more metal ions serve as a cofactor to facilitate these biochemical reactions. The requirement of metals in the production of... 

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