the tmah decomposition by adjusting the reaction conditions at the end of coupling reaction example 1 for example d three different experiments were conducted following the procedure given in example 6 of u s pat no 6 140 538 wherein nitrobenzene was added in 2 hours 2 5 hours and 3 hours each followed by a 4 hour hold period at 75 u00b0 c and 57 mm hg pressure equivalent to 76 mbar in a typical reaction the coupling reaction was carried out in a 2 liter glass round bottom flask rb flask equipped with a stirrer u00bd moon blade teflon u2122 stirrer a thermometer a baffle and a dropping funnel for nitrobenzene addition initially an aqueous solution of tmah 35 01 w w 485 66 gm 170 03 gm on 100 basis 1 87 moles was charged into the rb flask aniline was then charged 995 92 gm 10 68 moles into the rb flask and distillation was continued under reduced pressure at 57 mm hg water and aniline mixture was removed by distillation until the molar ratio of water to total tmah was about 4 1 during this process the temperature of the reaction mass increased to 70 73 u00b0 c after attaining the required molar ratio of water to total base nitrobenzene 218 99 gm 1 78 moles was added continuously over a given period i e 120 or 150 or 180 minutes during the nitrobenzene addition water and aniline were continuously removed from the reaction by distillation under reduced pressure at 57 mm hg the reaction mass was maintained at about 75 u00b0 c 57 mm hg for 4 hours after completion of nitrobenzene addition the reaction mass was analyzed at the end.