The Extraction of Alkali Metal Picrates with Dibenzo-18-Crown-6

Abstract

The distribution of alkali metal picrate complexes of macrocyclic polyether (dibenzo-18-crown-6) between water and benzene was investigated. The polyether-cation complexes were found to be of a 1:1 stoichiometry. The formation of 2:1 complexes was recognized for Rb and Cs in a large excess of the poiyether. The extractability of complex cation-picrate ion-pairs decreases in this sequence: K>Rb>Cs>Na>Li. The values of the extraction constants (logKex) were determined to be 4.65, 3.75, and 3.07 for K, Rb, and Cs compounds respectively. The thermodynamic quantities for the extraction process were calculated from the change in the extraction constants with the temperature. The extraction reactions are all exothermic, accompanied by an entropy decrease.

Ion-Association Reagents A Review

“…'s Dibenzo-l 8-crown-6 potassium complex cation reacts with picrate anion to form the ion-associate which is extracted into benzene. 16 As the crown coordinates to potassium to expel the water molecule on the cation, the extractability is increased. Extraction solvents for the ion-associate (18-crown-6, potassium and picrate) were investigated and the distribution ratio of the ion-associate is correlated closely with the solubility parameter and Dimroth's Er (solvent polarity)."…”

Structure-cation complexation relationships for ortho-, meta-, and para-substituted bis(oxymethylcrown)benzenes and α,α'-xylenes

“…Extraction constants (K ex ) 14 and association constants (K a ) 15 were calculated by reported procedures. The stoichiometry of each extraction complex was ascertained from the position of the absorption maximum for the picrate anion in the organic phase after dilution with THF.…”

“…In some cases, the organic phase concentration was determined by difference from the aqueous phase readings before and after extraction because of turbidity or formation of complexes insoluble in THF. The extraction constants (K ex ) 14 and association constants (K a ) 15 were calculated according to previously developed methods. Standard deviations from the analysis of the five samples were less than 10% of the K ex and K a values.…”

Synthesis of N-pivot lariat ethers and their metal ion complexation behavior

“…18,19 Thus, a 5.0 mM aqueous solution of the metal picrate was extracted with an equal volume of 5.0 mM ligand in deuteriochloroform. By comparison of the UV-visible spectra at the picrate absorption maximum for the organic solution before and after extraction, the percent extraction was calculated.…”

“…IR (neat): 1093 and 1124 (C-O) cm -1 . 1 18,19 extractions were conducted by adding 0.50 mL of a 5.0 mM crown ether solution in CDCl 3 to 0.50 mL of an aqueous 5.0 mM metal picrate solution in a centrifuge tube. The mixture was agitated with a vortex mixer of 60 sec.…”