Preparation of o- and p-nitrotoluene:
In a 250ml three-necked flask, equipped with overhead stirrer, dropping funnel and thermometer 0.1 mol of toluene are cooled to 10°C. Then from the dropping funnel a pre-cooled (10°C) mixture of 10ml 68% nitric acid (d. 1.42) and of concentrated (98%) sulfuric acid (d. 1.84) is slowly added drop by drop while the batch is vigorously stirred. The temperature of the batch is held between 5°C and 10°C by cooling in an ice-bath. After the addition of acids is finished, the mixture is then stirred for 3 hours longer at room temperature (20-22°C). Then the batch is dumped into 300ml of icewater (ice:water 1/1 by volume) and is vigorously stirred, the whole mix is then transferred into a sep funnel. The nitrotoluene (lower orange layer) is drained and the aqueous phase (upper layer) is extracted twice with 25ml of dichloromethane. The extracts + nitrotoluene are pooled, washed once with 50ml water, then in sucessive 50 ml portions with 5% sodium hydrogencarbonate solution until fizzing stops and the nitrotoluene gives a neutral to slightly alkaline reaction to pH paper. Then the mix is given a last wash with 50ml water. The nitrotoluene, which is always the lower phase in the washes, is then dried over 15g anhydrous sodium sulfate for 12 hours with occasional shaking.
The dichloromethane is distilled off, last traces of dichloromethane are removed by heating in a water bath at 50°C when a weak vaccum is employed (about 100 Torr is sufficient). The now yellow coloured mixture of nitrotoluenes is immersed in a salted ice bath, where the white needles of the p-isomer precipitate out (the mixture itself should not be cooled below -9°C!). The precipitate is filtered off quickly on a pre-cooled Büchner filter (freezer), the needles of p-isomer are then given a wash with 2 x 6ml of ice-cold petrol ether.
The filtrate, which consists largely of o-nitrotoluene, is subjected to fractional distillation over a well insulated 30cm Vigreux column in vacuum. o-nitrotoluene distills over at 95°C (10 Torr), under normal pressure o-nitrotoluene distills at 222°C. Only the constant boiling point fraction from 94-96°C is taken. The residue in the distilling flask is again subjected to freezing as already described, to get the rest of the p-isomer. The filtrate from the freezing step is discarded, it consists of mainly of m-isomer, o-isomer and a very small amount of p-isomer...workup of this mixture again would be too difficult, so simply forget about it.
Yield is about 40% of o-nitrotoluene and 20% of p-nitrotoluene.
Procedure taken from "Organikum", VEB Deutscher Verlag der Wissenschaften, 15
th ed., 1981, p. 381
Modified by old Herman to suit his needs..
Edit: You will have to use a pressure-equalized dropping funnel!!
