Sugar solutions, solvent extraction

A 100-mL, two-neck, round-bottom flask, equipped with two addition funnels was charged with pyridine (0.43 mL, 5.3 mmol) and 20 mL of methylene chloride. A solution of triflic anhydride (0.86 mL, 5.11 mmol) dissolved in 10 mL of methylene chloride was placed in one addition funnel. The sugar (2.55 mmol) dissolved in 10 mL of methylene chloride was placed in the other addition funnel. The flask was cooled to - 10°C in an ice-acetone bath, and the triflic anhydride solution added drop wise. A thick white precipitate began to form during die addition. After addition was complete, the suspension was allowed to stir for an additional 10 min. The sugar solution was added drop wise and stirring continued for an additional 1.5 h. The reaction mixture was poured into 50 mL of ice water, die layers were separated, and the aqueous layer was extracted with two 50-mL portions of methylene chloride. The combined extracts were dried over sodium sulfate, and the solvent was removed in vacuo. Hexane extraction, followed by in vacuo solvent removal, gave the Inflate ester [10]. 

Small quantities of compounds in natural extracts are often a problem when these need to be evaluated in bioassays. Sometimes there is just not enough of the compound isolated to carry out the usual bioassay.20 Microassays have been developed10 1 to overcome this problem. Typically, a microassay is carried out on a thin-layer chromatography plate with a cellulose layer. A small droplet (1.5 pi) of the tested compound in a solvent (1-102 nmol cm-2) is then added on the plate. After the solvent has evaporated a small amount (5 pi) of sucrose solution lmoll-1 is added to the place where the compound was added. In the control the same procedure was followed on a different plate, but with the solvent alone, with no compound added. These two plates are then placed in a petri dish with the test insect species. In the past, when paper chromatography was widely used, a crude plant extract was placed on the origin of the paper and then eluted into bands. The paper was freed of solvent, sprayed with sugar solution, and used directly in a bioassay to see which parts of the paper were not eaten, and therefore of interest for further examination. 

Solvent Extraction of Sugar Solution Coming from the Washing of Raw Sugar. The solvent or extract layer from the washing of impurities from the raw crystals was settled to remove dirt and other small solid particles. The solvent was evaporated for immediate recycle, leaving behind a first molasses. 

A tube reactor is to be used to contact an aqueous sugar solution with 5% by volume of a solvent of density 0.780 g/cm for extraction. The aqueous solution has a density of 1.080 g/cm, and a viscosity of 1.201 centipoise. 

Organic compounds such as aldehydes, alcohols, aliphatic, and aromatic 1,2-diols, nitrocompounds, and sugars have been determined by using two types of redox reactions. The analyte may be reduced with a metal ion in solution and the metal precipitate formed dissolved in nitric acid, and determined by AAS. Alternatively, the unreduced metal may be determined. The other type of method is based on the oxidation of the analyte with periodic acid or potassium permanganate, and addition of metal ion solution. The added metal ion forms, with the oxidized form of the analyte, either an insoluble compound or an uncharged metal complex which can be extracted into the organic phase. The atomic absorption of the metal ion is determined after dissolution of the precipitate or solvent extraction. 

Cases where the phases are solutions (or mixtures) containing but one common component occur more frequently. Selective solution of a component from a solid mixture by a liquid solvent is known as leaching (sometimes also as solvent extraction), and as examples we cite the leaching of gold from its ores by cyanide solutions and of cottonseed oil from the seeds by hexane. The diffusion is, of course, from the solid to the liquid phase. If the diffusion is in the opposite direction, the operation is known as adsorption. Thus, the colored material which contaminates impure cane sugar solutions can be removed by contacting the liquid solutions with activated carbon, whereupon the colored substances are retained on the surface of the solid carbon. 

In some cases the soluble material is distributed in small isolated pockets in a material which is impermeable to the solvent such as gold dispersed in rock, for example. In such cases the material is crushed so that all the soluble material is exposed to the solvent. If the solid has a cellular structure, the extraction rate will generally be comparatively low because the cell walls provide an additional resistance. In the extraction of sugar from beet, the cell walls perform the important function of impeding the extraction of undesirable constituents of relatively high molecular weight, and the beet should therefore be prepared in long strips so that a relatively small proportion of the cells is ruptured. In the extraction of oil from seeds, the solute is itself liquid. 

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