Extraction coefficient

Catalyst Cation. The logarithms of extraction constants for symmetrical tetra- -alkylammonium salts (log rise by ca 0.54 per added C atom. Although absolute numerical values for extraction coefficients are vastly different in various solvents and for various anions, this relation holds as a first approximation for most solvent—water combinations tested and for many anions. It is important to note, however, that the lipophilicity of phenyl and benzyl groups carrying ammonium salts is much lower than the number of C atoms might suggest. Benzyl is extracted between / -propyl and -butyl. The extraction constants of tetra- -butylammonium salts are about 140 times larger than the constants for tetra- -propylammonium salts of the same anion in the same solvent—water system. 

The ease of extraction may be represented by the extraction coefficient (Kex) for the system ... 

MCAm is the ion-pair formed between the crown (C) complex containing the metal ion (Mm+) and A- is the counter ion. It needs to be noted that the degree of extraction is anion-dependent. For example, the extraction of an alkali metal into an organic phase is enhanced when the counter ion is a large anion such as picrate. Alkali metal picrates undergo extraction into benzene in the presence of 18-crown-6 in the order K+ > Rb+ > Cs+ > Na+ (Iwachido, Sadakane Toei, 1978). Divalent ions may also be extracted. For 15-crown-5 in benzene, the picrate extraction coefficients (from water) fall in the order Pb2+ > Sr2+ > Ba2+ > Ca2+... 

Calculate the overall extraction coefficient based on the concentrations in the ketone phase, and the height of the corresponding overall transfer unit. 

Generally, it has been found that the organic acids and bases do exist in aqueous solution as equilibrium mixtures of their respective neutral as well as ionic forms. Thus, these neutral and ionic forms may not have the same identical partition coefficients in a second solvent therefore, the quantity of a substance being extracted solely depends upon the position of the acid-base equilibrium and ultimately upon the pH of the resulting solution. Hence, extraction coefficient (E) may be defined as the ratio of the concentrations of the substance in all its forms in the two respective phases in the presence of equilibria and it can be expressed as follows ... 

Curves similar to those in Fig. 4 have also been observed with cyclohexanone, tri-n-butyl phosphate and with solutions of TBP in a liquid hydrocarbon. The extraction increases rapidly upon the addition of small amounts of acid and, after a maximum value is reached, an exponential decrease is observed. Some of the higher extraction coefficients of organic liquids or solutions are given in Table 6. The values have been selected from data found by Boyd and Larson . 

Among the tertiary amines extraction coefficients decrease with decreasing basicity. Quaternary ammoniiun salts dissolved in inert solvents ensure efficient extraction not only from acid but also from neutral and alkaline solutions. 

The dependence of the extraction coefficient of pertechnetate on the salt concentration and kind of anions being an aqueous solutions is shown in Fig. 5. 

Pertechnetate in neutral and alkaline media can be extracted into solutions of tetra-alkylammonium iodides in benzene or chloroform. With tetra-n-heptylammo-nium iodide (7.5 x 10 M) in benzene distribution coefficients up to 18 can be obtained . A solution of fV-benzoyl-iV-phenylhydroxylamine (10 M) in chloroform can be used to extract pertechnetate from perchloric acid solution with a distribution coefficient of more than 200, if the concentration of HCIO is higher than 6 M The distribution of TcO between solutions of trilauryl-ammonium nitrate in o-xylene and aqueous solutions of nitrate has been measured. In 1 M (H, Li) NOj and 0.015 M trilaurylammonium nitrate the overall equilibrium constant has been found to be log K = 2.20 at 25 °C. The experiments support an ion exchange reaction . Pertechnetate can also be extracted with rhodamine-B hydrochloride into organic solvents. The extraction coefficient of Tc (VII) between nitrobenzene containing 0.005 %of rhodamine-B hydrochloride and aqueous alcoholic " Tc solution containing 0.0025 % of the hydrochloride, amounts to more than 5x10 at pH 4.7 . 

The time required for a system to reach equilibrium can be determined by shake-out tests, as described in earlier sections. Contact times are varied between about 0.5 and 15 min, at suitable intervals, and the extraction coefficient for each contact time plotted as a function of time. With this method, there is a lower practical limit on the contact time of about 0.25 min. These data will not be directly applicable to a continuous process because the rate of metal extraction is a function, in part, of the type and degree of agitation. However, a good idea of whether the extraction rate is sufficiently fast for the system to be suitable for use in a large contactor can be obtained. For example, if equilibrium is attained in less than 1 min, almost any type of contactor may be used. 

The selective cation binding properties ol crown ethers and cryptands have obvious commercial applications in the separation of metal ions and these have recently been reviewed (B-78MI52103.79MI52102, B-81MI52103). Many liquid-liquid extraction systems have been developed for alkali and alkaline earth metal separations. Since the hardness of the counterion is inversely proportional to the extraction coefficient, large, soft anions, such as picrate, are usually used. 

Interestingly, soluble polymeric crown ethers can have extraction coefficients up to 250 times larger than those of the corresponding monomers. Macromolecules such as polyvinyl [15]crown-5 and polyvinyl [18]crown-6 are readily soluble in organic solvents and many extraction systems involving their use have been developed (B-81MI52103). 

The interfacial pd selectivity coefficient, the factor multiplying a is determined by the ratio K /K, by the activity coefficient ratio, and by the mobility ratio, when the internal diffusion potential contribution is added. Clearly interferences should correlate with the ratio K /1C, which can be determined from salt extraction coefficients K KX/K K for a series of positive drugs, using common anion salts. This result is well documented in the literature (7,8). A curious correlation for N-based drugs studied by us and by Freiser ( ) is a trend in selectivity... 

The ion-pair model stipulates that formation of an ion-pai. occurs in the aqueous mobile phase (16, 18, 20). The retention time is governed by the extraction coefficient of the ion-pair. A longer alkyl chain on the pairing agent simply makes a less polar ion-pair, with a resulting higher extraction coefficient, and the retention of the ion-pair increases as a result of its greater affinity for the stationary phase. 

The influence of internal foam collapse on the parameters of foam accumulation has been experimentally studied by Khaskova and Kruglyakov [25,51,67], They evaluated the changes in the accumulation ratio and extraction coefficient of both NaDoBS and NaOL foams, that exhibit different kinetics of destruction [51,67]. Fig. 10.8 shows the kinetic dependence of the accumulation ratio and its constituents for NaDoBS foam (see Eq. (10.15)). 

A negative influence of the foam collapse on accumulation ratio and extraction coefficient has also been found [51,67] when separation of foams of various stability was carried out under gravitational drainage. Over a wide range of concentrations of the surfactant being extracted these coefficients decreased as a result of internal foam collapse. 

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