Water purification experimental procedure

For desymmetrization of diesters 3 via their hydrolysis in water, pig Hver esterase [12], o -chymotrypsin [12, 13a], and Candida antarctica Hpase (CAL-B) [14] were successfully used. However, further studies showed that respective anhydrides 5 can be used as substrates for enzyme-catalyzed desymmetrization in organic solvents [15]. The desired monoesters 4 were obtained in high yield in this way, using immobilized enzymes Novozym 435 or Chirazyme L-2 (Scheme 5.3). After the reaction, enzymes were filtered off, organic solvents were evaporated, and the crude products were crystalHzed. This was a much simpler experimental procedure in which control of the reaction progress was not necessary, and aU problems associated with extraction of products from aqueous phase and their further purification were omitted [15]. 

All enthalpy of solution measurements were carried out with an LKB 8700-1 precision calorimetry system. The experimental procedure and tests of the calorimeter have been reported previously (3, 4, 5). The purification of the solvent DMF (Baker Analyzed Reagent) and of all solutes used has been described in the same papers. The solvent mixtures were prepared by weighing and the mole fraction of water in the DMF-water mixtures was corrected for the original water content of the amide as measured by Karl Fischer titration. 

The enthalpies of solution were measured with a LKB 8700-1 precision calorimetry system. The experimental procedure and test of the instrument have been given before (6,7). EC (Fluka, purissimum) was distilled under reduced pressure and the middle fraction was stored over molecular sieves (4 A) for at least 48 hr. ACN (Merck, pro analysis) was dried over molecular sieves and used without further purification. The purity of both solvents (determined shortly before use), as deduced from GLC, was always better than 99.8%. The volume fraction of water, determined by K. Fischer titration (8) was always less than 3.10-4. The mixed solvents were prepared by weight as shortly as possible before the measurements. AH° of Bu4NBr in W-ACN mixtures have been measured at 25°C while those in W-EC are at 45°C, which is above the melting point of pure EC. 

These reactions are useful because they run under mild conditions, use inexpensive or easily recoverable starting materials, and have short reaction times. The major problem in purification is the separation of the sodium pyridone sulfonate from excess sodium sulfite, sodium bromide, and sodium bromoalkyl sulfonate. However, these latter compounds usually would not interfere with the use of the pyridone sulfonate as a water tracer. From a practical point of view, the pyridone sulfonates need not be purified, but can be used directly. A modified synthetic procedure involves the treatment of the pyridone sodium salt with a tenfold excess of a,iu-dibromoalkane in acetonitrile, followed by removal of the excess dibromide by vacuum distillation. The resulting product is treated with an excess of sodium sulfite in aqueous ethanol. Evaporation of the solvent yields a useful tracer. Procedures given in the experimental section were... 

After purification, quality control of solvent purity is necessary. For this purpose, many different analytical methods are utilized. Generally, chromatographic methods such as GC, GC-MS, and HPLC are used. Moreover, UV, infrared, and nuclear magnetic resonance spectroscopy can also be applied but they tend to be less sensitive toward trace impurities. Water in organic solvents is usually determined by Karl-Fisher titration. On the basis of experimental data obtained before and after purification, the efficiency of the clean-up procedure is determined. In general, the efficiency of purification, e.g., the recovery, is expressed by the coefficient R. This parameter is defined as the ratio of the amount of impurities removed to the amount of solvent before purification ... 

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