Purification of the products

The mother liquors are concentrated under nitrogen atmosphere, reduced pressure to a small volume. The residue is adjusted to 20 cc with water, made alkaline at pH 9.5 with ammonium hydroxide and extracted with chloroform. The chloroform extract concentrated in vacuo at 30° C to small volume is passed through a column of400 g of silica gel in chloroform. By eluting with chloroform, a fraction is obtained containing ergocryptine which is evaporated to dryness. The residue is 

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The mixture should be colourless, otherwise difficulty will be experienced in the subsequent purification of the product. If the reaction mixture is coloured by iodine (due to volatilisation of some of the mercaptan), add just sufficient ethyl mercaptan to decolourise it. 

Electrolytic Reductions. Both nitro compounds and nitriles can be reduced electrochemically. One advantage of electrochemical reduction is the cleanness of the operation. Since there are a minimum of by-products, both waste disposal and purification of the product are greatiy simplified. However, unless very cheap electricity is available, these processes are generally too expensive to compete with the traditional chemical methods. 

In initial purification steps the goal is to obtain concentration with partial purification of the product, which is recovered either as a precipitate (precipitation), a solution in a second phase (liquid-liquid extraction), or adsorbed to solids (adsor ptiou, chromatography). 

The basis for the separation is that when two polymers, or a polymer and certain salts, are mixed together in water, they are incompatible, leading to the formation of two immiscible but predominantly aqueous phases, each rich in only one of the two components [Albertsson, op. cit. Kula, in Cooney and Humphrey (eds.), op. cit., pp. 451 71]. A phase diagram for a polyethylene glycol (PEG)-Dextran, two-phase system is shown in Fig. 22-85. Proteins are known to distribute unevenly between these phases. This uneven distribution can be used for the selective concentration and partial purification of the products. Partitioning between the two phases is controlled by the polymer molecular weight and concentration, protein net charge and... 

If sodium bicarbonate is used, large amounts of titanium oxide-containing emulsions tend to form which hamper the purification of the product. 

Although previous experience indicates that phosphorus is not essential for these reductions, purification of the product is more difficult with its omission. With iiydrocarbons sensitive to further reduction, phosphorus can have a deleterious effect through promotion of hydrogenation of the desired product. Whether or not phosphorus should be employed in an indi-... 

Additional purification of the product and improvement of particle size and shape can be achieved by re-ciystallization. The process consists of sequential dissolutions of potassium heptafluorotantalate in appropriate solutions at increased temperatures, filtration of the solution to separate possible insoluble parts of the product and cooling of the filtrated solution at a certain rate. The precipitated crystals are filtrated, washed and dried to obtain the final product. Re-crystallization can be performed both after filtration of the preliminary precipitated salt or after drying if the quality of the product is not sufficient. HF solutions of low concentrations are usually used for re-ciystallization. In general, even water can be used as a solvent if the process is performed fast enough. Nevertheless, practical experience suggested the use of a 30—40% HF solution within the temperature interval of 80-25°C, and a cooling rate of about 8-10°C per hour. The above conditions enable to achieve an acceptable process yield and good performance of the product. 

This gave a viscous sludge, and some ammonia was evolved. The temp was raised steadily to 59-61° over a period of 8 minutes, and held there for 23 minutes, while stirring the mixt continuously. After the mixt was cooled to 6°, a white ppt of methylnitroguanidine (MeNGu) was filtered off, washed with 30ml of cold w and dried. The crude product weighed about lQg (84.7% yield) and melted at 151—54°. Purification of the product was achieved by crystn, first from hot w (3ml per g) and then from 95% ethanol (8ml per g)... 

Analysis and purification of the product solution is best accomplished by gas chromatography. The submitters used a 500 cm. by 0.6 cm. aluminum or polyethylene column packed with 21% oxydipropionitrile on Chromosorb P with column, injector and detector operated at 25° and a flow rate of 50 ml./minute. Under these conditions the retention times of bicyclopentene and cyclopentadiene were 3 and 5 minutes, respectively, beyond that of the coinjected air. Since bioyclo-pentene is extremely labile with respect to acid catalysis any contact with water, hydroxylic solvents, and nonprotic acids should be avoided (Note 11). Bicyclopentene stored at —78° in anhydrous tetrahydro-furan is stable indefinitely. 

When a THF-acetonitrile solution of any one of the CIOJ or BFJ salts of cations [112+], [25+], [99+] and [100+] was added to a deep green THF solution of K+[2 ] under argon in the dark, the colour immediately turned brownish orange, suggesting the formation of a covalent compound. After the isolation and purification of the product, the structures were determined to be the covalent compounds [112-2], [25-2], [99-2] and [100-2], as shown in Scheme 3. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

In mixed installations, reactions are often carried out batchwise, whereas the subsequent isolation and purification steps are performed continuously. Sometimes the character of the chemical reaction forces running the reaction in a continuous manner, while existing batch facilities for isolation and purification of the product are used to process the reaction mixture from the reactor. An example of this type of mixed plant is presented in Example 7.1.2. 

Spiroindolinobenzothiopyrans can be prepared by condensation of Fischer s base with thiosalicylaldehyde derivatives 46 in ethanol, as shown in Scheme 22.71,89 93 Reaction of 1,2,3,3-tetramethylindolinium salt with carbamoylthiobenzaldehyde,92 which is an intermediate for preparation of thiosalicylaldehyde, also gives the spirobenzothiopyran in high yield via the corresponding indolinium salt, as shown in Scheme 22.94 Conversion of spirobenzopyrans to the corresponding spirobenzothiopyran by phosphorous pentasulfide in pyridine or xylene is possible, but the purification of the product is difficult. 

Reactive distillation is the name given to the process where the chemical reaction and product separation are carried out simultaneously in one unit. Carrying out the reaction, with separation and purification of the product by distillation, gives the following advantages ... 

Tietze and coworkers developed two new domino approaches in the field of combinatorial chemistry, which are of interest for the synthesis of bioactive compounds. Combinatorial chemistry can be performed either on solid phase or in solution using parallel synthesis. The former approach has the advantage that purification of the products is simple and an excess of reagents can be used. This is not possible for reactions in solution, but on the other hand all known transformations can be used. The Tietze group has now developed a protocol which combines the... 

For purification of the product, tubes A and B are cleaned, dried, and reassembled with a dry glass-wool insert in B. Tube C, containing the initially formed product, is attached to tube B as shown in Fig. 2. The system is evacuated and this time left open to the vacuum. The two furnaces are separated by ca. 1.5 cm. Furnace I is heated to 80° and furnace II to 130 to 140°. Sublimation is allowed to continue until all the titanium(IV) iodide has left tube C (12 to 16 hours). The purified product crystallizes in tube B at the separation of the two furnaces. The major impurity, iodine, crystallizes in tube A and in the liquid-nitrogen trap. A fluffy tan residue of negligible weight (0.04 to 0.06 g.) remains in tube C. If desired, further purification can be accomplished by moving tube B farther into furnace II, which results in a second sublimation of the product. 

This procedure is a modification of that described by King3 and considerably facilitates the isolation and purification of the product. 

The on-column synthesis approach was also explored, followed by in situ purification of the products for the glycosylation reactions using trichloroacetimidates. The authors primed the top of a standard silica chromatography column with perchloric acid immobilized on silica. After charging both reactants, dissolved in dry CH2C12, onto the... 

In analogy to the thiohydantoin synthesis, the PEG-bound diamines have also been treated with various alkyl and aryl isothiocyanates and, after applying traceless cyclative cleavage, the desired thioxotetrahydropyrimidinones were obtained in excellent yields. In contrast to the thiohydantoin synthesis, purification of the products was more complicated if the excess of isothiocyanate amounted to more than 2.2 equivalents [85],... 

The last two decades have witnessed rapid development of organic synthetic methods based on benzotriazole derivatives. Thus, introduction of benzotriazole moiety to organic molecules provides several practical advantages. Among other benefits, a benzotriazolyl substituent activates the reaction center, stabilizes intermediates, increases regio- and stereoselectivity, and simplifies separation and purification of the products. After the desired molecular assembly is constructed, the bond with benzotriazole is cleaved off to provide the final product. A vast variety of... 

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