Distribution coefficient, alkyl

Fischer, R.G. and Ballschmiter, K. Prediction of the environmental distribution of alkyl dinitrates - Chromatographic determination of vapor pressure p°, water solubility Sh2o, gas-water partition coefficient Kgw (Henry s law constant) and octanol-water partition coefficient K , FreseniusJ. Anal Chem., 360 769-776, 1998. 

Table 5 shows the evaluated distribution coefficients of the homologous alkyl alcohols. It is shown that the... 

Table 10.3 shows the comparison of Dg and for DCH18C6 and five N-alkyl aza-18-crown-6 in four different ILs. The distribution coefficients for both Sr + and Cs+ increase with the decrease of the alkyl chain length in ILs. Such dependence can be attributed to the ion-exchange capability of... 

Such reactions can take place predominantly in either the continuous or disperse phase or in both phases or mainly at the interface. Mutual solubilities, distribution coefficients, and the amount of interfadal surface are factors that determine the overall rate of conversion. Stirred tanks with power inputs of 5-10 HP/1000 gal or extraction-type equipment of various kinds are used to enhance mass transfer. Horizontal TFRs usually are impractical unless sufficiently stable emulsions can be formed, but mixing baffles at intervals are helpful if there are strong reasons for using such equipment. Multistage stirred chambers in a single shell are used for example in butene-isobutane alkylation with sulfuric acid catalyst. Other liquid-liquid processes listed in Table 17.1 are numbers 8, 27, 45, 78, and 90. 

Table 6. Relationship of the distribution coefficients Kd at pH 2 for Cu2+ and U02 + with cross-linking and alkylation for resins from BPEI and LPEP...

Vp and VL are the volumes of the extraction agent and the liquid sample, respectively, and Kle - Ce/Ce is the distribution coefficient. In practice, an extraction yield higher than 99% is usually considered to be quantitative. With the use of the same volumes of the extraction agent and the sample, this result can be obtained even in a single extraction step if Kle < 0.01. Sometimes the entire procedure can be complicated by a chemical reaction taking place, e.g., in the extractive alkylation (see p.59) or in the preparation of volatile metal chelates (see p.194), and the total yield of the extraction then involves, in addition to the interphase distribution of the initial compounds and products, also the chemical equilibrium which is attained by the reaction. If the quantitative yield of the extraction cannot be predicted on the basis of the character of the system, the extraction efficiency must be determined, otherwise the quantitative evaluation is questionable. 

Apart from the hydrophobic interactions provided by the alkyl part of the molecule, octanol has also hydrogen-bond acceptor and donor functions like lipid membranes have. This property of n-octanol made the octanol-water distribution coefficient that widely used. However, n-octanol or reversed phase materials cannot mimic the interfacial character of the bilayer structure. The ionic interactions between membrane phospholipids and solute are also not represented in the properties of octanol or reversed phase materials. To overcome this issue, alternative stationary phases... 

C X chains). Consequently, the mobile phases need to be more polar (e.g., CH3CN—H20, MeOH—H20) than the coated surface. During elution, separation of constituents of an applied sample mainly relies upon the differences in distribution coefficients between the mobile phase and the hydrocarbon coatings of the stationary phase. For all these reasons, the more polar constituents of a mixture in reversed phase chromatography are eluted before nonpolar components. Note also that although water is more polar than acetonitrile or methanol, it is a poorer eluent in reversed phase chromatography because of the alkyl surface character of the stationary phase. 

Table 6.13 Micelle/water distribution coefficients, P, for the solubilisation of benzoic acid by r>olkyl polyoxyethylene surfactants C E , (where n = alkyl (C) chain length and m = polyoxyethylene (E) chain length) os a function of temperature°...

A comparison of the effect of the structure of phosphate esters on uranium extraction from nitrate media shows that the esters from secondary alcohols give higher uranium distribution coefficients (D s) than those from primary alcohols, phenyl esters extract uranium less strongly than alkyl esters, and benzyl esters are intermediate in extractant strength for uranium (24). 

Three types of interaction mechanisms are known between the micelle and the analyte as shown in Figure 3.3 (1) incorporation of the analyte into the hydrophobic core, (2) adsorption of the analyte on the surface or on the palisade layer, and (3) incorporation of the analyte as a cosurfactant. Highly hydrophobic and nonpolar analytes such as aromatic hydrocarbons will be incorporated into the core of the micelle. The selectivity may not be very different among long alkyl-chain surfactants for this class of analyte but the distribution coefficient will be increased with longer alkyl-chain surfactants. Thus, selectivity will not be altered significantly for nonpolar hydrophobic analytes, even when different surfactants are used. However, bile salts may provide substantially different selectivity in comparison with long-alkyl chain surfactants, even for nonpolar hydrophobic analytes. 

Table 5.21 Micelle/water distribution coefficient, P, , for the solubilization of benzoic acid by n-alkyl-polyoxyethylene surfactants as a function of temperature [163].

Olivier and Berger335, who measured the first-order rate coefficients for the aluminium chloride-catalysed reaction of 4-nitroben2yl chloride with excess aromatic (solvent) at 30 °C and obtained the rate coefficients (lO5/ ) PhCI, 1.40 PhH, 7.50 PhMe, 17.5. These results demonstrated the electrophilic nature of the reaction and also the unselective nature of the electrophile which has been confirmed many times since. That the electrophile in these reactions is not the simple and intuitively expected free carbonium ion was indicated by the observation by Calloway that the reactivity of alkyl halides was in the order RF > RC1 > RBr > RI, which is the reverse of that for acylation by acyl halides336. The low selectivity (and high steric hindrance) of the reaction was further demonstrated by Condon337 who measured the relative rates at 40 °C, by the competition method, of isopropylation of toluene and isopropylbenzene with propene catalyzed by boron trifluoride etherate (or aluminium chloride) these were as follows PhMe, 2.09 (1.10) PhEt, 1.73 (1.81) Ph-iPr, (1.69) Ph-tBu, 1.23 (1.40). The isomer distribution in the reactions337,338 yielded partial rate factors of 2.37 /mMe, 1.80 /pMe, 4.72 /, 0.35 / , 2.2 / Pr, 2.55337 339. 

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