SYNTHESIS OF 2,2’-DINITROBIPHENYL

• Place 50g (0.32 mol) of o-chloronitrobenzene and 75g of clean dry sand in a 250-ml three-necked flask equipped with a mechanical stirrer and an air reflux condenser. 

• Heat the mixture in an oil or fusible metal bath to 215-225 °C and add, during 40 minutes, 50g (0.78 mol) of copper bronze or, better, of activated copper bronze(1). 

• Maintain the temperature at 215-225 °C for a further 90 minutes and stir continuously. 

• Pour the hot mixture into a Pyrex beaker containing 125g of sand and stir until small lumps are formed; if the reaction mixture is allowed to cool in the flask, it will set to a hard mass, which can only be removed by breaking the flask. 

• Break up the small lumps by powdering in a mortar, and boil them for 10 minutes with two 400 ml portions of ethanol; filter after each extraction. 

• Cool the filtered extracts in ice, and collect the crude product on a Buchner funnel. Concentrate the filtrate to about half the original volume and thus obtain a second crop of crystals. 

• The total yield of crude solid should be about 24g; if it is less than this, a third extraction of the reaction product should be made. 

• Dissolve the crude solid in about 400 ml of hot ethanol, add a little decolourising charcoal, boil for a few minutes, filter and cool in ice. 

• Recrystallise again from hot ethanol. The yield of pure 2,2'-dinitrobiphenyl, m.p. 123-124 °C, is 20-22g (54%). 

• The experimental conditions for conducting the above reaction in dimethylformamide as solvent are as follows. 

• In a 250-ml three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20g of o-chloronitrobenzene and 100 ml of dimethylformamide (dried over anhydrous calcium sulphate). 

• Heat the solution to reflux and add 20g of activated copper bronze in one portion. 

• Heat under reflux for 4 hours, add another 20g portion of copper powder and continue refluxing for a second 4-hour period. 

• Allow to cool, pour the reaction mixture into 2 litres of water and filter with suction. 

• Extract the solids with three 200 ml portions of boiling ethanol: alternatively, use 300 ml of ethanol in a Soxhlet apparatus. 

• Isolate the 2,2'-dinitrobiphenyl from the alcoholic extracts as described above: the yield of product, m.p. 124-125 "C, is 11. 5g (75%).

Notes to Keep in Mind:

1. If the temperature is allowed to rise above 240 °C, reduction of the nitro groups will occur and carbazole will be formed.