Purification of reagents

Methods of preparing ultrapure reagents in the laboratory have been described in detail by Ziefand Mitchell (1976) and Howard and Statham (1993). This section therefore presents only the basic techniques for easily purified reagents such as, in addition to water, hydrochloric and nitric acid, ammonia solution, and some organic solvents. Procedures for the purification of special reagents will be outlined in the chapters of the book where analytical methods are described in detail. 

A review of purification operations suggests that sub-boUing distillation in quartz or Teflon equipment provides the purest acids ( Fig. 12-2). Kuehner et al. (1972), who investigated the non-boiling procedure in great detail, reported Zn, Cd, Pb or Cu concentrations for HCl and HNO3 of the order of 10 -1(T g/g when feeding with a.g. acids. 

Another rather simple sub-boiUng distillation apparatus for the preparation of HCl, HNO3 and HF as described by Mattinson (1972) is shown in Fig.12-3. l vo FEP bottles are coimected at right angles by a Teflon block, and heat is supplied by a 300 W IRlamp. The metal contents of the purified acids are comparably as low as those mentioned before. Special advantages of the system are minimum handling and operation in a dosed system. 

Isothermal (or isopiestic) distillation is another method for purifying very volatile acids such as HCl, HF or CH3COOH (see Fig. 12-4). This procedme can be performed in a desiccator at room temperature. T vo beakers, one filled with concentrated add (a.g.), the other with ultrapure water, are placed close to each other. The final acid concentration depends on the time of exposure and on the volume ratio of acid to water and should be determined experimentally. In our laboratory =0.1 mol/L HCl was obtained when pladng 25 mL of concentrated acid 5 cm apart from 25 mL of distilled water in a quartz beaker for 2 d. The purification of hydrofluoric acid by isothermal distillation requires inert materials such as FIFE. 

Ultrapure HCl of different concentrations can also be produced by gassing distilled water with pure HCl, obtained from a tank or from concentrated HCl solution (by heating). Gas from commercially available cylinders should be filtered through 0.4/im Nuclepore or Teflon filters to remove particles before entering the water. 

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Many methods exist for the purification of reagents and solvents. A number of these methods are routinely used in synthetic as well as analytical chemistry and biochemistry. These techniques, outlined below, will be discussed in greater detail in the respective sections in this Chapter. It is important to note that more than one method of purification may need to be implemented in order to obtain compounds of highest purity. 

The submitters, working on a kilogram scale without purification of reagent or solvent and with no precaution against moisture, obtained 6,7-dimethoxy-l-methyl-3,4-dihydroisoquinoline hydrochloride,2 m.p. 202-203°, instead of the dichlorophosphate at this stage. The checkers obtained this hydrochloride by either treating the free base with... 

The procedure described here incorporates a number of modifications to the Suzuki coupling that result in a sound, efficient and scaleable means of synthesizing biaryls. First, the catalytic use of palladium acetate and triphenylphosphine to generate palladium(O) eliminates the need for the expensive air and light sensitive tetrakis(triphenylphosphine)palladium(0). No purification of reagents is necessary, no special apparatus is required, and rigorous exclusion of air from the reaction mixture is not necessary. Furthermore, homo-coupled products are not present in significant levels (as determined by 500 MHz 1H NMR). 

A strict vacuum-line technique was used for purifications of solvent, monomer, and initiator, preparation of solutions and polymerization. Polystyryllithium of a degree of polymerization of about 15 was prepared by using n-butyllithium and was used as a seed polymer. Purifications of reagents were most carefully carried out. See the original literature for details 17). 

Wet digestions can be carried out in open vessels or in closed systems. In open systems, increased consumption of reagents requires the use of especially pure reagents. Considerable progress in the purification of reagent chemicals has been made over the... 

Recrystallized preparations of acrylamide are available commercially or may be prepared as follows. Dissolve acrylamide (70 g) in 1 liter chloroform at 50°C. Filter the solution hot and cool it to —20°C to bring about crystallization. Collect the crystalline acrylamide in a chilled Buchner funnel, wash with chilled (—20°C) chloroform and/or heptane, and dry. Additional discussion of the purification of reagents used for electrophoresis may be found elsewhere (35,36). 

The preparation stage involves purification of reagents and preparation of reagent streams for addition to the reactor. The unit operations may involve removal of impurities from reagents including purging with inert... 

Acetone, CH3COCH3, [1, 5, before Acetone cyanohydrin]. Mol. wt. 58.05, b.p. 56-57°. For commercial sources of pure acetone, see 1. 1110. For the purification of reagent required for the preparation of carbohydrate acetonides, Whistler and Wolfrom1 recommend that technical-grade acetone be refluxed with small amounts of permanganate until the purple color persists, distilled, and dried for 2 days over anhydrous potassium carbonate or calcium sulfate, filtered, and distilled. 

Purification of Laboratory Chemicals by D. D. Perrin, W. L. F. Armarego, and D. R. Perrin (Pergamon, 2009, ISBN 978-1-85617-567-8) is the standard reference for the purification of reagents and solvents. Special attention should be paid to the purification and storage of ethers. 

The submitters, working on a kilogram scale without purification of reagent or solvent and with no precaution against moisture, obtained... 

TABLE IV Total mercury determination in water -purification of reagents... 

Blatz [ ] developed a precise difference, method for the spec-trophotometric determination of cerium (IV) at micromolar concentrations. He studied such variables as suspended material, presence of organic (reducing) materials, purification of reagents and solutions, cell constants, stray light, interferences, optimum reagent concentrations, time factors, and blanks, finally achieving a probable error of 0.25% (I favor the school that deems the probable error to be neither probable nor an error and prefer to think of this as a standard deviation of 0.37%). 

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