period of 45 minutes the temperature is now increased to 330 u00b0 c in the course of 45 minutes the vacuum is now improved stepwise to 0 5 mbar as soon as the distillation subsides the mixture is then stirred for 30 minutes at a temperature of 330 u00b0 c the results are summarized in table 1 22 83 g 0 1 mol bisphenol a 18 60 g 0 1 mol 4 4 u2032 dihydroxydiphenyl 44 99 g 0 21 mol diphenyl carbonate and 4 9 mg 8 u00b7 10 u2212 6 mol tetraphenylphosphonium phenolate is metered in as a mixed crystal with 30 wt phenol based on the mixed crystal are weighed into a 500 ml three necked flask with a stirrer internal thermometer and vigreux column 30 cm mirrored with a bridge the apparatus if freed from atmospheric oxygen by applying a vacuum and flushing with nitrogen three times and the mixture is melted at 150 u00b0 c the vacuum is adjusted to 100 mbar the temperature is increased to 190 u00b0 c and the phenol formed is distilled off over a period of 20 minutes the temperature is now increased to 235 u00b0 c and after 15 minutes the vacuum is adjusted to 60 mbar and the mixture is stirred for 15 minutes it is now heated to 270 u00b0 c and after 15 minutes the vacuum is increased slowly to 5 mbar after a further 15 minutes the temperature is adjusted to 300 u00b0 c in the course of 10 minutes after 15 minutes the vacuum is improved to 0 5 mbar the temperature is then set at 320 u00b0 c after 15 minutes and the mixture is stirred for 30 minutes the results are summarised in table 1.