Absolute alcohol adsorption

The formation of silicon-flvxyride bonds on the surface of silica after treatment with hydrogen fluoride was never proven directly. However, there is a pronounced change in the adsorption and wetting properties. The silica becomes hydrophobic as was mentioned in a patent to Kimberlin (279a). Neimark and collaborators (279b) found a type V isotherm in the methanol adsorption on silica gel which had been treated with a solution of SiF in absolute alcohol. Wilska (280) obtained a water-repellent silica when solutions of HaSiPg were precipitated with ammonia. The Si—F bond is hydrolyzed only slowly. A considerable fluorine content of 7-10% F was reported in an older patent (281) for a silica that had been prepared by hydrolysis of SiF. ... 

Jensen and DeLawder9s purified commercial insulin by adsorption on activated carbon followed by elution with 90% phenol. The phenol eluate was diluted with water and the insulin that flocked out was washed with absolute alcohol and ether. Insulin thus prepared has an activity about equal to that of crystalline insulin. The activity was not further increased by a subsequent adsorption and elution. This finding is supported by data of Fisher and Scott,96 and is in contrast to an observation by Dingemanse97 that a product of greater activity than crystalline insulin can be prepared by this procedure. 

Preparation. The algae, dried and defatted, are extracted exhaustively with hot water and impurities are precipitated with alcohol and then lead acetate. The peptide is precipitated from the water-alcohol mixture by mercuric acetate and acetic acid. After removal of the mercury, the peptide is reprecipitated by addition of absolute alcohol and ether. The crude product is purified by adsorption on Amberlite IR-1, and then eluted. Four hundred grams of dry algae yield about 100 mg. of pure peptide. 

We have further attempted to suggest a procedure which would make use of the advantages of the method of competitive reactions, i.e. its simplicity and little time demand, and at the same time would yield separately the absolute values of rate constants and adsorption coefficients also for reactions with a more complicated kinetics. Using the values of relative reactivities S from the method of competitive reactions, the adsorption coefficients, for example, of the alcohols (Kb) in the reesterification reaction described by Eq. (26) can be evaluated from the relation... 

The most marked effect of solvents was observed on the rate constants of reactions by which l,5-hexadiene-3-ol is consumed, and on the adsorption coefficients of both alcohols related to l,5-hexadiene-3-ol. In solvents with preferential adsorption of l,5-hexadiene-3-ol (methanol, ethyl acetate, 1,4-dioxane) the rate constants had the lowest values. Such an interesting compensation of the kinetic and adsorption terms has also been observed in other cases (77). Correlations between the relative adsorption coefficients and the parameters (p satisfied Eq. (23) with the absolute term q [similarly to Eq. (22)], the physical meaning of which remains obscure. Correlation analysis confirmed the more general character of the parameter compared with the parameter t. ... 

The corresponding dependence b(nc) for normal alcohols is also shown. Both curves have the same slopes, which shows that the increments of b and hence the free energy of adsorption per methylene group = -2.75 kJ/mol are equal for the two series, while the absolute values... 

Figure 33 depicts a prednisolone calibration curve in dry ACN. The nonlinearity of this profile is obvious. Because there is absolutely no indication of adsorption effects, we hypothesize that there is a following second order chemical reaction. Hydrocortisone gives similar behavior in dry aprotic solvents. Both of these steroids are characterized by an aliphatic alcohol groip which is not associated with the other three ideally behaving steroids. This circumstantial evidence suggests that the anion radical electrode reaction product is being protonated by reactant diffusing toward the electrode. The likelihood that this is the process occurring is further enhanced by the fact that addition of sufficient amounts of a weak proton donor (e.g., H2O) leads to a linear calibration curve with lower sensitivity, as shown in Figure 34. The latter figure illustrates calibration curves for dry and wet ACN and DMF, as well as aqueous base.

Since it is difficult for one to assess the absolute strength values, in reality, one can only talk about the probability of rupturing the adsorption layer. This probability varies significantly in cases involving nonspecific (physical) and specific adsorption (chanisorp-tion). Both of these cases are presented in Figure 4.17, which illustrates the fractiou of the phase coutacts formed in solutions of alcohols in heptane (physical adsorption) and in the... 

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