Counter current distribution

Geranylgeranyl pyrophosphate [6699-20-3 (NH4 salt)] M 450.5, pKEst(i)-<2, pKesk2) <2, pKEst(3) 3.95, pKes,(4) 6.26. Purified by counter-current distribution between two phases of a... 

When 1 mole of sucrose was treated with 2 moles of chloro-triphenylmethane in pyridine for 96 h at room temperature, it gave, after counter-current distribution and column chromatography, mono-O-tritylsucroses, di-O-tritylsucroses, and 6,l, 6 -tri-0-trityl-... 

Separating funnels for batch extraction special glass apparatus for continuous extraction automatic shakers used for discontinuous counter-current distribution. 

Sometimes requires large quantities of organic solvents poor resolution of mixtures of organic materials except by counter-current distribution which is slow. 

Two interlocking glass units for Craig counter-current distribution. 

Extraction scheme for a single solute by Craig counter-current distribution. (Figures represent the proportions in each phase for D= 1 and equal volumes. Only the first four extractions are shown). 

Table 4.6 Proportional distribution of a solute between extraction units for Craig counter-current distribution...

In a partition system the stationary phase is a liquid coated onto a solid support (p. 97). Silica gel, kieselguhr (diatomaceous earth) or cellulose powder are the most frequently used. Conditions closely resemble those of counter-current distribution so that in the absence of adsorption by the solid support, solutes move through the system at rates determined by their... 

From a preparative aspect, Peck et alX have employed the counter-current distribution technique with a partition system of water/ butanol/p-toluene sulphonic acid to separate and purify the neamine (neomycin A) present in commercial neomycin. 

A soln of Boc-Ala-Gly-Cys(Acm)-Lys(Boc)-Asn-Phe-Phe-Trp-Lys(Boc)-Thr(tBu)-Phe-Thr(tBu)-Ser-(tBu)-Cys(Acm)-OtBu (24.8 g, 0.01 mol) in DMF (1L) was poured in one portion (requiring about 30 s) into a well-stirred soln of I2 (30.5 g, 0.12 mol) in MeOH (9 L). After 5 min, a soln of ascorbic acid (23 g) in citrate buffer (2 L, pH 5) was added, producing within about 15 s a colorless and slightly turbid soln. This soln was concentrated to about 1.5 L. The resultant suspension was then diluted with H20 (2L) and stirred at 0 °C for 1 h yielding a white precipitate. This was collected, washed with Et20 (3 x 150mL), and then purified by counter-current distribution yield 16.8 g (78%). 

A method similar to the above was proposed recently by Kuhn, which uses a pair of solvents immiscible at a lower temperature but becoming miscible with elevating temperature5. To the present authors this method seems more easily applicable and perhaps more promising than the counter-current distribution, since no special instrumentation is necessary for the former. At any rate, it is obvious that these three methods do not allow fractionation of copolymers only by the composition without interference of the molecular weight, because they all are based on the solubility difference among constituent species. 

FL Rigby, JL Bethune. Counter current distribution of hop constituents The isolation and properties of cohumulone. Proc Am Soc Brew Chem, 1952, pp 119-129. 

When the separation procedures described in detail above are unsatisfactory for the separation of a mixture of organic compounds, purely physical methods may be employed. Thus a mixture of volatile liquids may be fractionally distilled (compare Section 2.26) or a mixture of non-volatile solids may frequently be separated by making use of the differences in solubilities in inert solvents. The progress of such separations may be monitored by application of the various chromatographic techniques detailed in Section 2.31, or indeed these techniques may be employed on the preparative scale for effecting the separation itself (e.g. flash chromatography, p. 217). The techniques of counter current distribution, fractional crystallisation or fractional sublimation (Section 2.21) may also be employed where appropriate. 

Russian comfrey (Symphytum x uplandicum Nyman) is widely recommended as a medicinal herb and an item of human diet. A previous investigation of this species led to the isolation of three alkaloids which were not fully characterized (cf. Vol. 7, p. 57). Culvenor and co-workers have separated eight pyrrolizidine alkaloids from the leaves of this perennial plant by counter-current distribution.21 The known alkaloids echimidine (51), symphytine (52), lycopsamine (53), and intermedine (54) were present. In addition, four new alkaloids, i.e. 7-acetyl-lycopsamine (55), 7-acetylintermedine (56), symlandine (57), and uplandicine (58), were characterized by spectroscopic methods, and by hydrolysis. The total alkaloidal extract caused chronic hepatotoxic effects in rats, and the authors... 

The alkaloids were best isolated from the ethanol extract of the plant material, partially fractionated by counter-current distribution, and subsequently purified by preparative chromatography. Of the 11 known Cephalotaxus alkaloids (105-115 in Figs. 8 and 9), cephalotaxine (105a) is ubiquitous and the most abundant (up to 64% of the total alkaloid extract) in all species examined. C. wilsoniana Hay., which yields only minor quantities of cephalotaxine, is the exception, however it is rich in Homoerythrina alkaloids,... 

DeCleyn and Verzele (3Q.3J-.32) isolated the four possible isomers from piperinic acid irradiated in an ultra-violet reactor, by counter-current distribution and also the piperidides obtained synthetically from the treated piperinic acid by high pressure liquid chromatography (figure 4). The structures of the isomers were derived mainly from NMR data. Their pungency was recorded, but possibly not by rigorous methods (31.32). The results confirmed the observation of Grewe t ail. (29) that piperine is the pungent principle of pepper, and that other isomers have little taste. ... 

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