Purification Methods
The Ca diester salt is washed with H2O (x3) and MeOH (x3) alternately and dried in a vacuum oven at 50o. If the Ca salt is contaminated with much Ca salt of the monoester, then it (10g) is converted to the free acid by adding 6N HCl (ca 10volumes) and Et2O (> 50volumes) is added to it and stirred vigorously to form the free acids. When no white precipitate remains (ca 5minutes), the Et2O is separated, washed with H2O (2x > 50 mL) and dried by filtering through a bed of anhydrous Na2SO4 (11 x 5 cm) which is then washed with Et2O (2x >50 mL). Evaporation gives an oil (TLC RF 0.81 for diester and 0.50 for monoester). The oil is dissolved in *benzene (ca 25mL) and extracted with ethane-1,2-diol (25mL, 10x). After ten washings, a small sample of the *benzene layer is washed twice with H2O to remove the diol and showed that it is pure bis-[4-(1,1,3,3-tetramethylbutyl)-phenyl]phosphoric acid by TLC, i.e. no monophosphate. To form the Ca salt, the oil is dissolved in MeOH and to it is added the equivalent amount of CaCl2 together with aqueous NaOH to keep the pH >10. The resulting white precipitate is collected, washed alternately with 3 batches of H2O and MeOH and dried in a vacuum oven at 50o. [Craggs et al. J Inorg Nucl Chem 40 1483 1978, Morton & Chung Anal Biochem 157 345 1986.] 2,4-Bis-(p -tolylthio)-1,3,2
