Chloroform, acid-base parameter

An empirical way of assigning acid/base parameters to polymers and other non-volatiles has been practised in our laboratories . Reference acid and base probes are used (generally chloroform and diethyl ether), along with the usual alkanes. TTie perpendicular distance identified as in eqn 11 is here identified directly as the AN and DN number of the stationary phase. Figure 4A illustrates the situation for polycarbonate. The retention datum... 

Acid-base parameters of some solvents are shown in Table 2.4. Among them, chloroform has a smaller alkaline parameter C and larger acid parameter E, so it is acidic. 

Fowkes and co-workers have used test acids (e.g., phenol and chloroform) and bases (e.g., pyridine and ethyl acetate) to determine Drago s parameters for polymers and metal oxides using essentially calorimetric heats and infrared (IR) measurements [13,27,37,38]. 

This approach introduces the concept of a Lewis acid parameter of surface energy, y+ and a Lewis base parameter of surface energy, y - This recognizes that a given solid or liquid (e.g. chloroform) may only exert acid properties, that is be monofunctional. In this case, y is zero. For a mono-functional base (e.g. triethylamine), y is zero. Some substances, such as water, show both electron donor and electron acceptor properties, so both y+ and y are finite. These are termed bifunctional . An inert molecule shows... 

S Physical Parameters. The crystals of clotrimazole has mp 147-149 C. It is a weak base, slightly soluble in water, benzene, toluene soluble in acetone, chloroform, ethyl acetate and DMF. It gets hydrolysed rapidly upon heating in aqueous acids. 

The 0-protection of A -protected amino acids 55 was achieved by decarboxylative esterification in solvent-free conditions by Colacino et al. (Scheme 4.13). It was found that the use of planetary ball mill was more effective than vibratory mill [8], Commonly used 0-activation reagents (diaUcyl dicarbonate (B0C2O), carbonate (A, A -disuccinimidyl carbonate, DSC), and alkyl chloroformates (ROCOCl, R=Bn, Et, allyl)) were employed in combination with DMAP as base. Reaction parameters had to be optimized for each individual reagent to achieve acceptable yields (selection of results. Table 4.3). Due to high reactivity of benzyloxy chloroformate (Z-Cl), the two-step cycled milling was executed by addition of Z-Cl in 2equiv. portions, so as to consume the chloroformate and reduce the formation of the undesired byproducts. Acidic workup with 10% aqueous citric acid of ether extracts eliminates DMAP and affords the A-protected amino ester derivatives 56 in good yields. 

The use of IGC data to obtain acid and base interaction parameters for polymer solids has been described in detail elsewhere [2,13,14]. The procedure calls for a reference relationship between RTln Vn and the normal boiling point of mobile-phase materials able to interact through dispersion forces only, represented in this work by n-alkanes (Cg-Cjj Vapours known to be acids and bases were then injected into the columns, again at extreme dilution. Following the theories of Gutmann [3], diethyl ether (DEE) and chloroform (CHE) were used as reference base and acid, respectively. As shown in Figure 7.6 for PVC as stationary... 

Because of the solubility characteristics of polystyrene, which has a solubility parameter value of 9.2 (cal/cm ) or 18.5 (J/M ) x 10 polystyrene-based polymer reagents or catalysts are especially suitable for organic reactions because they are readily soluble or swollen in common organic solvents such as benzene, chloroform, and methylene chloride for organic reactions. Some of the reactions run on polystyrene include epoxidations, peptide syntheses, separations of chiral molecules, and acid catalysis. 

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