2.4. Solubility measurement of catalysts in methanol
Solubilities of the POM–ILs in methanol were measured using UV–vis spectroscopy. The quantitative determination of the amount of dissolved POM–ILs in methanol is based on the fact that the samples have charge transfer bands at 250–260 nm [28]. The calibration
curve for each sample was prepared based on absorbance valuesnvarying from 0.0 to 2.0. In this region the calibration curves were almost linear. To measure the solubilities of the POM–ILs, excess amounts of the sample were added in methanol (5 mL) and vigorously stirred for 6 h at different temperatures. An aliquot was separated by centrifugation and diluted by a factor of 5–20 times. The absorption values of these diluted solutions were measured. The amount of dissolved POM–IL can be calculated using calibration curves, considering the diluted factor.