Purification of chemicals and solvents

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. 

Polymerizations induced by y radiation proceed by both cationic and free-radical mechanisms. Predominance of the cationic process can be assured by exhaustive purification of monomers and solvents or by employing high radiation dose rates (from electron beam sources). The rate of cationic polymerization has been shown to be strongly influenced by the dielectric constant of the medium, giving rise to discrepancies between radiation-induced bulk polymerizations and chemically initiated solution polymerizations. These discrepancies have been attributed to specific solvation of propagating ions by monomer and polymer. 

WorkingS olution Regeneration and Purification. Economic operation of an anthraquinone autoxidation process mandates fmgal use of the expensive anthraquinones. During each reduction and oxidation cycle some finite amount of anthraquinone and solvent is affected by the physical and chemical exposure. At some point, control of tetrahydroanthraquinones, tetrahydroanthraquinone epoxides, hydroxyanthrones, and acids is required to maintain the active anthraquinone concentration, catalytic activity, and favorable density and viscosity. This control can be by removal or regeneration. 

As a chemical raw material, ethanol is used for the production of a range of monomers and solvents, and is essential in pharmaceutical purification. In the presence of an acid catalyst ethanol reacts with carboxylic acids to produce ethyl esters. The two largest-volume ethyl esters are ethyl acrylate (from ethanol and acrylic acid) and ethyl acetate (from ethanol and acetic acid). Ethyl acrylate is a... 

According to Coimbra et solvents play a central role in the majority of chemical and pharmaceutical industrial processes. The most used method to obtain artemisinin (1) from A. annua is through the use of organic solvents such as toluene, hexane, cyclohexane, ethanol, chloroform and petroleum ether. Rodrigues et al described a low-cost and industrial scaled procedure that enables artemisinin (1) enhanced yields by using inexpensive and easy steps. Serial extraction techniques allowed a reduction of 65% in solvent consumption. Moreover, the use of ethanol for compound extraction is safer when compared to other solvents. Flash column pre-purification employing silicon dioxide (Zeosil ) as stationary phase provided an enriched artemisinin (1) fraction that precipitated in hexane/ethyl acetate (85/15, v/v) solution. These results indicate the feasibility of producing artemisinin (1) at final cost lowered by almost threefold when compared to classical procedures. 

Some information on hazards related to chemicals and solvents that are used in the book is listed together with the preparation procedures and in the appendix. However, the list is not exhaustive and the reader is referred to other sources (e.g., [55,56]).The description of a number of techniques that are used in organic laboratory during for analysis, separation, and purification of organic compounds is out of the scope of this book. Therefore, the reader is refeered to some exellent textbooks on practical organic chemistry (e.g. [57,58]. 

All solutions were prepared from reagent grade chemicals and solvents without further purification. Two of the new ligands which were tested for the Pfeiffer effect, 2-(2-pyridyl)-benzimidazoline and 2-(2-pyridyl)-imidazoline, were prepared by the method of Walter and Freiser 18). The other ligand which had to be synthesized, (ethanediylidenetetra-thio)tetraacetate (ETTA), was prepared by the method of Longo et al. 12). Tris(ethylenediamine)nickel(II) chloride was prepared by the method of State 17). Bis(salicylidene)triethylenetetramine alumi-num(III) iodide [A1(TS2)]I was prepared by the method of Das Sarma and Bailar 6). 

Chemicals and Solvents. Acetonitrile (Burdick and Jackson) and dichloromethane (Fisher) were stored over Davisson 3 molecular sieves for at least 24 h. before use. Tetra-n-ethylammonium hexafluorophosphate (TEAH) was purchased from Alfa and used without further purification. Tetra-n-ethylammonium perchlorate (TEAP) was prepared from the corresponding bromide salt (Eastman) with the use of a previously published procedure (7). Tetra-n-butylammonium hexafluorophosphate (TBAH) was prepared by dissolving the iodide salt (Eastman) in a hot, equivolume water/ethanol/ acetone mixture followed by addition of HPFg (Alfa). The solution was reduced to approximately half its original volume, then cooled to room temperature. The resulting white solid was filtered off... 

Purification. A 1-1 portion of diglyme (Ansul Chemical Co.) is stored over 10 g. of small pieces of calcium hydride for 12 hrs. and decanted into a distilling flask. Sufficient lithium aluminum hydride is added to ensure an excess of active hydride (see purification of THF), and the solvent is distilled at 62-63°/15 mm. and stored under nitrogen. 

Water quality Determination of the activity concentration of radionuclides by high resolution gamma-ray spectrometry Nuclear energy Chemical separation and purification of uranium and plutonium in nitric acid solutions for isotopic and dilution analysis by solvent chromatography... 

The clear evaluation of the experimental results is also hindered by the difficulties encountered in the perfect purification of non-aqueous solvents. Several of them are hygroscopic, and even an extremely low water content may cause fundamental changes in the chemical properties of numerous solvents. As an electron-pair donor, the water molecule may behave as a ligand, and as a consequence of the ability of its hydrogen atoms to form hydrogen bonds, it may also act as an acceptor. This may lead to the occurrence of unexpected side reactions. In acidic solvents water behaves as a base, and in basic solvents as an acid, thereby disturbing the courses of the reactions to be investigated. The removal of trace amounts of water and the performance of work under anhydrous conditions is a difficult task. 

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