Separation fraction from acid-base

Table V. Fraction Yields from Adsorption Chromatography and Acid-Base Separations, Weight Percent...

Table VII. Proton NMR Data from the Acid-Base Separation Fractions...

Historical. Pyridines were first isolated by destructive distillation of animal bones in the mid-nineteenth century (2). A more plentifiil source was found in coal tar, the condensate from coking ovens, which served the steel industry. Coal tar contains roughly 0.01% pyridine bases by weight. Although present in minute quantities, any basic organics can be easily extracted as an acid-soluble fraction in water and separated from the acid-insoluble tar. The acidic, aqueous phase can then be neutrali2ed with base to Hberate the pyridines, and distilled into separate compounds. Only a small percentage of worldwide production of pyridine bases can be accounted for by isolation from coal tar. Almost all pyridine bases are made by synthesis. 

First, the tar acids were removed from the naphtha fractions of light oils and, in the case of CVR tars, carboHc oil. The oils were then mixed with 25—35% sulfuric acid. After separation of the sulfates, the aqueous solution was diluted with water and the resinous material skimmed off. The diluted sulfate solution was boiled to expel any neutral oils, dried by the addition of soHd caustic soda or a2eotropically with ben2ene, and fractionated to yield pyridine, 2-methylpyridine (a-picoline), and a fraction referred to as 90/140 bases, which consisted mainly of 3- and 4-methylpyridines and 2,6-dimethylpyridine (2,6-lutidine). Higher boiling fractions were termed 90/160 and 90/180 bases because 90% of the product distilled at 160 and 180°C, respectively. 

Steam distd from a soln containing 1-2 equivalents of 20% H2SO4 until about 10% of the base had been carried over with the non-basic impurities, then the acid soln was made alkaline, and the base separated, dried with NaOH and fractionally distd twice. Dried with Na and fractionally distd through a Todd column packed with glass helices (see p. 174). 

In coals alkylated in this manner, the number of acidic sites is substantially reduced, and acid-base associations are virtually precluded. Extracts from alkylated coals should, therefore, be amenable to GPC fractionation. Such fractionation, conducted on Bio Beads S-Xl and S-X2, results in separation by molecular weight and indicates that both benzene and chloroform extracts contain substantial amounts of high ( 6000) and fairly low (560-640) molecular weight fractions (Figure 2). While the extract yields from non-reductively ethylated vitrinite increase in the order benzene extr. chloroform extr. - pyrid. extr > the molecular weights determined by VPO in pyridine, decrease in this order. 

A technical challenge with this step is to achieve RNA extraction of uniform quality and efficiency for each fraction. This is because the amount of RNA in each sucrose gradient fraction varies considerably and the high concentration of sucrose in the bottom fractions interferes with phase separation in typical phenol-based extraction steps. To address these problems, we spike each fraction with an aliquot of a foreign (control) RNA, which can be used later to correct for differences in RNA recovery (and reverse transcription efficiency) between samples. We then remove sucrose from the samples by precipitation of total nucleic acid and protein with ethanol. To purify RNA, a standard Trizol (Invitrogen) extraction is performed as outlined later (also see product insert). 

PAHs were isolated from the crude extracts by a two-step procedure. The neutral fraction was separated by simple acid-base partitioning and then chromatographed on a silica gel column. The column was first eluted with TO ml of hexane. Subsequent elution with 200 ml of hexane containing 5 dichloromethane gave the PAH fraction. The solvent was carefully evaporated to produce the dry extract. The PAH fraction of SI and S2 were designated as S1-C2 and S2-C2, respectively. 

The one-phase liquid system is more frequently encountered since many organic reactions are carried out in solution. Direct fractional distillation may separate the product, if it is a liquid, from the solvent and other liquid reagents, or concentration or cooling may lead to direct crystallisation of the product if this is a solid. However, it is often more appropriate, whether the required product is a liquid or solid, to subject the solution to the acid/base extraction procedure outlined above and considered in detail on p. 162. This acid/base extraction procedure can be done directly if the product is in solution in a water-immiscible solvent. A knowledge of the acid-base nature of the product and of its water solubility is necessary to ensure that the appropriate fraction is retained for product recovery. In those cases where the reaction solvent is water miscible (e.g. methanol, ethanol, dimethylsulphoxide, etc.) it is necessary to remove all or most of the solvent by distillation and to dissolve the residue in an excess of a water-immiscible solvent before commencing the extraction procedure. The removal of solvent from fractions obtained by these extraction procedures is these days readily effected by the use of a rotary evaporator (p. 185) and this obviates the tedium of removal of large volumes of solvent by conventional distillation. 

Niederer [100] used ion trap mass spectrometry and negative ion chemical ionisation to determine nitro- and oxypolyaromatic hydrocarbons in soils. Meyer et al. [101] have described a simple and reproducible method which provides the simultaneous determination of polycyclic aromatic hydrocarbons and het-eropolycyclic aromatic hydrocarbons (N, S, O) and their metabolites in contaminated soils. Contaminants extracted from the soil sample were separated by polarity and acid-base characteristics using solid-phase extraction on silica gel and a strong basic anion exchange material. A subfraction containing PANHs and neutral metabolites was subsequently fractionated into neutral and basic... 

A series of Sephadex columns have been widely used in separation of intact or truncated LPS. The selection of the column is based on the repeating constitution of O-antigen in LPS. The intact LPS can be separated by Sephadex G-200 and eluted with detergent containing materials (Morrison and Leive, 1975 Peterson and McGroarty, 1985 Rivera et al., 1988). Sephadex G-200 was also used to separate the alkaline hydrolyzed LPS which can be eluted with pyri-dine/0.05 M acetate buffer (Chester and Meadow, 1975). Sephadex G-25, 50, and 75 have been applied to fractionate acetic-acid hydrolyzed LPS with distilled water or pyridine acetate buffer elution (Byrd and Kadis, 1989 Carlson, 1984 Koval and Meadow, 1977 Kropinski et al., 1982 Lacroix et al., 1993 Prehm et al., 1975 Temple et al., 1986). Biogel P6 has been used to fractionate the partially degraded LPS with 1% acetic acid, eluted with pyridine/0.05 M acetate buffer (Koval and Meadow, 1977). Sepharose 4B has been used to fractionate LPS from E. coli 0111 B4, eluted with 0.12 M Tris buffer (Morrison and Leive, 1975). 

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