Extract solution after precipitation nature

By the treatment of Cross and Bevan cellulose, or cellulose isolated by some other purification procedure, with 17.5% sodium hydroxide under carefully controlled conditions, and then carefully washing, a fibrous product is obtained which is termed a-cellulose. As previously indicated, Cross and Bevan used this procedure for determining the purity of cellulose preparations. This product upon further similar treatments continues to lose weight, indicating the empirical nature of the treatment and terminology. Upon acidif3ring the alkaline filtrate a precipitate is formed. This fraction is known as /3-celIulose. The alkali-soluble extract which remains in solution after acidification of the solution is termed -y-cellulose. Since continued extraction of a-cellulose with caustic causes the formation of increasing amounts of /3-and y-cellulose, the incomplete removal of these fractions in one operation or the conversion of o-cellulose into 0- and -y-cellulose is indicated. In practice... 

Pectin is made naturally in ripening fruit. It is obtained commercially by treating the raw material (citrus peel or apple pomace) with hot, acidified water. (Apple pomace is the residue remaining after pressing of apples.) The pectin in the peel or apple pomace dissolves in the hot water and is then purified by repeated filtrations. It is extracted from the water solution by adding alcohol or an aluminum salt to the solution, causing the pectin to precipitate out of solution. The precipitate is then dried and ground into a powder. 

Xylans are partially extractable with water from natural cell walls but typically are removed by alkaline solution extraction. To minimize contamination by lignin, the plant or woody material is usually treated with azeotropic ethanol-benzene and the lignin removed by its conversion to halocellulose. The alkaline extract can be neutralized, precipitating the more linear, less acidic xylans. The more acidic, more branched xylan is recovered as a precipitate after addition of ethanol. 

Fig. 5.15 Separation of the polymeric products obtained after masticating natural rubber containing 38.5% methyl methacrylate to 97% conversion (O) fractional precipitation by methanol from 10 ml of 1% benzene solutions (Q) fractional precipitation by acetone (3) fractional precipitation by methanol after removal of free rubber (- -) fraction extracted by petroleum ether [87].

A fractionation procedure has been established and widely applied to studies of humic materials [42-44]. The procedure begins with natural OM (i.e., humus) and uses an aqueous basic solution (e.g., 0.1-0.5 mol/1 NaOH and Na2C03) to solubilize a fraction of the OM. The basic extract is then acidified which causes a precipitate to form, i.e., humic acids (HA). The fraction, which remains in solution, is called fulvic acids (FA). Humin is the name given to the insoluble organic fraction that remains after extraction of humic and fulvic acids. At nearneutral pH (pH 5 - 8), which is characteristic of most natural water, the FA are the most water soluble of these three fractions. HA are somewhat less soluble, with their solubility increasing as the pH increases. Humin is insoluble at all pH values. 

B. Wet Processes.—These vary considerably in detail according to the nature and amount of constituents other than vanadium in the ore. An outline of the operations involved in the case of patronite is as follows The ore is roasted with common salt or sodium carbonate and then extracted either (a) with water to give an alkaline solution of sodium vanadate and soluble vanadates of other metals, any lead, zinc, copper, etc., being left in the residue or (b) with sulphuric acid to produce a solution of vanadyl sulphate. Acid extraction is usually employed when the vanadium content of the material is low. The alkaline extract from (a) is treated with excess of sodium carbonate in order to precipitate calcium and aluminium, after removal of which,... 

Slow addition of triflic anhydride to a stirred solution of trimethylsilylmethyllithium (2) in pentanes at 0 °C resulted in smooth reaction as evidenced by the gradual precipitation of lithium triflate with only a slight increase in the internal temperature (max. 10 °C). Basic aqueous quench, extraction with dichloromethane and strong acidification (cone. HC1) of the remaining aqueous phase followed by extraction with dichloromethane led to the isolation of methyleneditriflone (3) as a yellow oil which was essentially pure by H NMR but could be obtained as a low-melting white solid after vacuum sublimation. The acidic nature of 3, which has been estimated to have a pKa... 

Saponification of the extracts is generally desirable to remove unwanted lipid materials. However, this step is omitted in the isolation of carotenol esters, since these are hydrolyzed by this procedure. It is also omitted in the isolation of carotenoids such as fucoxanthin and peridinin, which are alkali-labile. If acetone has been used in the initial extraction, it is essential that all traces be removed before saponification. The general procedure used involves dissolving the total lipid fraction in an alcoholic (ethanol or methanol) solution of potassium hydroxide. The mixture is then either heated for a short period of time while kept in the dark, or left in the dark at room temperature for 12-16 h. There has been considerable discussion of the merits of these two procedures. Which method is used is dependent on the nature of the samples being analyzed and the requirements of the analysis (Davies, 1976 Liaaen-Jensen, 1971). After saponification, water is added, and neutral lipids (the unsaponifiable fraction) are extracted with diethyl ether or hexane. Acidic carotenoids remain in the alkaline phase and are extracted with diethyl ether or hexane after acidification with acetic acid. The unsaponifiable fraction usually contains sterols as well as carotenoids. If desired, sterol contaminants can be removed by precipitation from cold (- 10°C) petroleum ether or by precipitation of these compounds as their digitonides. 

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