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Fractionation major impurities removed

Sulfolane (45 mL) and spray-dried KF (9.4 g, 0.16 mol) were heated at 160 C, and sulfolane (ca. 5 mL) was distilled off under reduced pressure. After the solution had cooled. 2-chloro-1,3-dinitro-5-(tri-fluoromethy])benzene (10.9 g. 40 mmol) and tetrafluorophthaloyl fluoride (20 g, 82 mmol) were added. After 1.5 h at 150 C, the mixture was distilled under reduced pressure (25 Torr). The fraction boiling at 70-120 C was collected, affording 12.3 g of a liquid that contained the difluoro derivative in 47% purity (79% yield/80% conversion). The major impurity was tctrafluorophthaloyl fluoride, which was removed by hydrolysis. The distillate was diluted with pentane and treated with 10% aq NaHCO,. The mixture was stirred for 3 h, and the organic layer was separated and dried (CaCI2). Redistillation at 53- 56 C/15 Torr gave the title compound yield 5g (55%). [Pg.234]

Finally, achievement of 99% radiochemical purity required two tedious runs—the first to fractionate the major impurities and the second to remove the residual tetraphosphonate from the final product. [Pg.154]

Separations for removing undesirable by-products and impurities, and making suprapure fine chemicals constitute a major fraction of the production costs. There is an enormous variety of methods for product separation and purification and many books on the subject have been published. Here, we deal with the problem in a very general way and we refer the reader to advanced books for details. Conventional techniques for product isolation and purification, such as fractional distillation, extraction, and crystallization, still predominate. Some guidelines for scale-up of these techniques and producing experimental data for scale-up are given in Chapter 5. More information on specific separation and purification techniques applied to particular problems of fine chemicals manufacture the reader can find in Chapter 6. [Pg.554]

Most sidestream columnsnave a small flow dedicated to removing an off-key impurity entering the feed, and that stream must be manipulated to control its content in the major product. For example, an ethylene fractionator separates its feed into a high-purity ethylene sidestream, an ethane-rich bottom product, and a small flow of methane overhead. This small flow must be withdrawn to control the methane content in the ethylene product. The key impurities may then be controlled in the same way as in a two-product column. [Pg.43]

Most of the common barbiturates contain a 5-ethyl substituent and some may contain 5,5-diethylbarb-ituric acid (barbitone) as an impurity. The presence of this compound at a concentration of only 1 to 2% can produce unexpected results. For example, if amylobarbitone containing 1% of barbitone as an impurity caused coma in an overdose complicated by renal failure, the barbitone would form a higher percentage in the blood. This is because amylobarbitone is removed by rapid metabolism in the liver, but barbitone is eliminated more slowly by renal excretion. In the case of coma with renal function being maintained, barbitone would be a major fraction of the barbiturate excreted in the urine in some cases the concentration has been so high that it has been regarded as a metabolite. [Pg.117]

Size separation in mineral processing circuits are used for a number of reasons, such as the beneficiation of the ore by rejecting a certain size fraction that may contain the majority of the impurities or to avoid the transfer of a certain size of material that may be unsuited for a subsequent processing step. Other reasons include removal of the final sized material from the grinding circuit to improve grinding efficiency. [Pg.73]

When the acid gas impurities make up an appreciable fraction of the total gas stream, the cost of removing them by heat regenerable solvents may be out of proportion to the value of the treated gas. This has provided the major impetus for the development of processes that employ nonreactive organic solvents as the treating agents. These materials physically dissolve the acid gases, which are then stripped without the application of heat by merely reducing the pressure. [Pg.1188]


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See also in sourсe #XX -- [ Pg.5 , Pg.299 ]




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