2 u00b0 8 u00b0 c at this moment then with gaseous phosgene introducing at a rate of 100 g hour cold phosgenation was carried out at 4 u00b0 5 u00b0 c for 30 minutes the cold phosgenation produced a yellowish green slurry in the reaction flask due to the formation of carbamyl chloride and amine hydrochlorides the reaction flask was heated with a mantle heater to raise the temperature to 140 u00b0 c over about 45 minutes during the rise in temperature gaseous phosgene was charged at a rate of 100 g hour in the course of raising temperature the slurry was completely dissolved in orthodichlorobenzene with violent evolution of gaseous hydrogen chloride then hot phosgenation was conducted at 140 u00b0 c for 75 minutes while introducing gaseous phosgene at a rate of 100 g hour a total of 525 g of gaseous phosgene was introduced by the cold hot two state phosgenation this amount was equivalent to 8 1 times as much as the theoretical value then the reaction liquid was raised in temperature to 160 u00b0 c following which gaseous nitrogen was admitted thereto at a rate of 500 ml min for 2 hours to remove dissolved gaseous components and decompose fully unreacted carbamyl chloride after.