Purification of products

Di- and trinucleotides may be used as units instead of the monomers. This convergent synthetic strategy simplifies the purification of products, since they are differentiated by a much higher jump in molecular mass and functionality from the educls than in monomer additions, and it raises the yield. We can illustrate the latter effect with an imaginary sequence of seven synthetic steps, c.g. nucleotide condensations, where the yield is 80% in each step. In a converging seven-step synthesis an octanucleotide would be obtained in 0.8 x 100 = 51% yield, compared with a 0.8 x 100 = 21% yield in a linear synthesis. 

The present method offers several advantages over earlier methods. The use of carbon tetrachloride instead of diethyl ether as solvent avoids the intrusion of certain radical-chain reactions with solvent which are observed with bromine and to a lesser degree with chlorine. In addition, the potassium bromide has a reduced solubility in carbon tetrachloride compared to diethyl ether, thus providing additional driving force for the reaction and ease of purification of product. The selection of bro-... 

This group, used for 5 -phosphate protection, has hydrophobicity similar to that of the dimethoxytrityl group and thus was expected to assist in reverse-phase HPLC purification of product from failure sequences in oligonucleotide synthesis. The group is cleaved with Bu4N F in DMSO at 70°. ... 

On the other hand, the corresponding tin precursor (63) undergoes smooth cycloaddition with a wide variety of aldehydes to produce the desired methylene-tetrahydrofnran in good yields [32, 33]. Thus prenylaldehyde reacts with (63) to give cleanly the cycloadduct (64), whereas the reaction with the silyl precursor (1) yields only decomposition products (Scheme 2.20) [31]. This smooth cycloaddition is attributed to the improved reactivity of the stannyl ether (65) towards the 7t-allyl ligand. Although the reactions of (63) with aldehydes are quite robust, the use of a tin reagent as precursor for TMM presents drawbacks such as cost, stability, toxicity, and difficult purification of products. 

In addition to the insoluble polymers described above, soluble polymers, such as non-cross-linked PS and PEG have proven useful for synthetic applications. However, since synthesis on soluble supports is more difficult to automate, these polymers are not used as extensively as insoluble beads. Soluble polymers offer most of the advantages of both homogeneous-phase chemistry (lack of diffusion phenomena and easy monitoring) and solid-phase techniques (use of excess reagents and ease of isolation and purification of products). Separation of the functionalized matrix is achieved by either precipitation (solvent or heat), membrane filtration, or size-exclusion chromatography [98,99]. 

Chemoselectivity of enzymatic reaction is the enzyme-catalyzed transformation of one type of functional group in the presence of other sensitive groups present in the substrate molecule. As a result, reactions catalyzed by enzymes generally tend to be cleaner and purification of product(s) from impurities can largely be omitted. Therefore, all enzymatic reactions generate less by-products and waste compared to chemical transformations. This simplifies all operations and reduces costs of transformation, which is of great importance for the industry. 

A procedure that is catalytic in Bu3SnH and uses NaBH4 as the stoichiometric reagent has been developed.201 This method has advantages in the isolation and purification of product. Entry 5 is an example of this procedure. The reaction was carried... 

A chemical process is based on the transformation of raw material into more valuable chemical products, and two of the steps commonly encountered in such processes are the chemical reaction equipment and the section for purification of product species. A common task in the chemical industry, therefore. 

In order to obtain the quantities of protein needed for HTP structure determination, scale-up and purification of products identified during expression... 

The main kinds of crystallizers are represented in Figure 16.10. They will be commented on in order. Purification of products of melt crystallization is treated separately. 

NOTE. Reaction (1) is quite clean and the reaction mixture obtained after irradiation contains up to 90-95% of the monosubstituted product. If Rh6(CO)i 5NCMe is to be used for a further synthesis involving separation or purification of products, the crude Rh6(CO)l5NCMe product can be obtained without chromatographic separation in the following manner. Heptane (20 mL) is added to the final reaction mixture, which is concentrated under reduced pressure until complete precipitation of the product as described above. 

In this paper we have developed a method to prepare the intermediates of type 1 with solid base catalysts it introduces advantages for industrial manufacture, such as an easily separation and regeneration of the catalyst and a more facile work-up and purification of products. 

Melt crystallization operates with heat as a separating agent, but a crystalline product is not generated in the process. Instead, crystals formed during the operation are remelted and the melt is removed as the product. Such operations are often used to perform the final purification of products after prior separation units for example, the purity of an acrylic acid feed may be increased from 99.5 to 99.9%. Melt crystallizers do not require solids handling units nor do they utilize solid-liquid separation equipment. Finally, in some instances the use of melt crystallization can eliminate the use of solvents, thereby reducing the environmental impact of the process. 

Solution-phase synthesis has both advantages and disadvantages over solid-phase synthesis, and the preferred approach in a particular case will depend on a variety of considerations. Solution-phase expertise is currently the stock-in-trade of most synthetic organic chemists and much of the wealth of developed reactions is potentially available for combinatorial work. Whilst solution-phase reaction development has often been employed prior to transfer to solid phase, it occupies an important position in its own right in the combinatorial armoury. Solution-phase work is free from a number of the chemical constraints which currently limit the general application of solid-phase methods, but has clear disadvantages with respect to purification of products and pool generation. 

Fixed Bed Catalysts. Noble metal, base metal, and other types of catalysts, including alumina, silica, resins, clays, zeolites, and combinations thereof are used in almost every type of chemical and petrochemical business segment. There are many different process applications ranging from the generation of suitable feedstocks, actual chemical reactions, and purification of products to the treatment of by-product streams. 

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