Reaction media, biocatalytic

The amount of Lewis acid to be used is depicted as an effective amount and a minimum limit of 0.5 mole equivalent with respect to the sulfmated compound concentration was mentioned. A wide variety of Lewis acids was mentioned to be useful for the present invention in the patent document, but only copper (II) compounds were claimed. The way in which the Lewis acid is used (either as a homogeneous or a heterogeneous phase), was reported to be irrelevant. So, it could be employed in solution in the reaction medium or insoluble as powders or on a solid support, such as alumina or a zeolite. The Lewis acid is supposed to be acting as a catalyst in the desulfination process. The temperature and pressure conditions for this reaction are substantially higher than the microbial conditions. The temperature and pressure conditions did not form part of any claim, but the document stipulates values between 50°C and 100°C, and 10 and 15psi, respectively. The quantitative effectiveness or conversion values of this reaction were not given, but it looks like it would diminish the advantages of a biocatalytic process. 

The innovating features of his disclosure are the incorporation of SOx sorbent within the catalytic system to separate the oxisulfides from the reaction medium and the inclusion of more than one biocatalytic stages with intermediate emulsion break-ing/making steps. 

In another research laboratory, surprised by the lack of success of other research groups and the previous statements about the impossibility of applying biocatalytic chemistry to polithiophenes and polypyrroles, special attention was paid to the enzymatic polymerization of the EDOT monomer [43]. In this case, the first trials succeeded and a blue-colored polymer solution was obtained after 16h of reaction (Scheme 4). As is well-known, an acidic reaction medium is suitable to increase the rate of polymerization. Protonic acids and a variety of Lewis acids catalyze the equilibrium reaction of EDOT to the corresponding dimeric and trimeric compounds without further oxidation or reaction [44]. In this work, three different pHs were evaluated (pH = 2, 4, and 6) in order to establish the optimum for adequate synthesis of EDOT. The UV-visible (UV-Vis) spectra for these three reactions are... 

For the asymmetric biocatalytic reduction of ketones with in situ cofactor regeneration an enzyme-compatible biphasic reaction medium has been developed (Fig. 34) [53],... 

Here, we will review the various issues related to biocatalytic reactions in ionic liquids. Biocatalyst tested in ionic liquids will be discussed firstly, and then the effect of ionic liquids on the activity, selectivity as well as on the stability of biocatalyst in ionic liquids will be surveyed. Finally, various applications of ionic liquids as reaction medium for biocatalytic transformations will be reviewed. 

The challenge for more widespread and industrial acceptance is to increase the productivity rates of many nonaqueous biocatalytic reactions. It is believed for many situations that this goal can be achieved through proper methodology and design of reaction medium and conditions. In particular, these specific and related design issues must be addressed ... 

Biocatalytic kinetic resolution of racemic hydroxymethylphosphinates 271 via their lipase-promoted acetylation in supercritical carbon dioxide as the reaction medium was investigated. The reaction was fastest when pressure was closer to the critical pressure at 11 MPa the reaction rate reached its maximum when the pressure was increased to 15 MPa. The optimal conditions were obtained at 13 MPa (yields 50%, 30% ee). The stereoselectivity of the reaction depended on solvent, substituents at phosphorus, and solubility of substrates in SCCO2. The best results were obtained with the Candida antarctica lipase (Novozym 435) (Scheme 89) [183, 184]. 

Reverse micelles have been associated with the idea of microreactors for enzymatic reactions, when snbstrates and/or products are lipophilic and low water content is desired. Microemnlsions provide an enormous interfacial area through which the conversion of hydrophobic snbstrates can be catalyzed. Increasing the interfacial area is of great technological interest because it results in the increase in the number of substrate molecules available to react. Enzymes in w/o microemulsions offer considerable advantages as a reaction medium is used for biocatalytic transformations ... 

Despite many efforts the use of classical organic solvents for biocatalytic transformations using whole cells remains limited. Water as a natural reaction medium limits the number of applications, since only a small number of substrates are sufficiently water soluble. As an alternative the use of an ionic liquid may be considered. A very early example for such a reaction has been reported by Cull in 2000 [360]. 

Full exploitation of cascade conversions by the true integration of biocatalytic and chemocatalytic procedures requires merging human s chemistry with nature s reaction conditions the latter impose a much stricter constraint with respect to reaction temperature, pressure and medium (Fig. 13.16). Consequently, a renaissance in the field of synthetic organic chemistry and catalysis is necessary to develop novel conversion processes that meet biocatalytic conditions. 

Any or all of these conditions may limit productivity, and whichever of the previously listed sequences occur in a particular process, the biocatalytic conversion needs to be selected and designed to cope with these issues. Such issues may be solved by process techniques (using purification or a change of medium/catalyst between the reactions) or potentially by alteration of the properties of the biocatalyst via selection or directed evolution. A further approach is to combine operations in a single-pot operation using process techniques, biocatalyst modification, and a degree of compromise. 

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