Phase titrations-V: Nitroalkanes: Improving the phase-titration end-point

End-points for direct phase titrations of binary solutions of nitropropanes in water-miscible solvents are fair and, because of the steepness of the calibration curve, results are adequate. Nitroethane, in binary combination, gives poor end-points but, over part of the optimum titration range, results are good. Nitromethane gives end-points which are almost useless. Addition of standard amounts of nitrobenzene, which gives excellent phase-titration end-points, improves the composite nitromethane-nitrobenzene-water-miscible component end-point markedly. Because the nitrobenzene concentration is constant, the water titre is a function only of the nitromethane concentration. Addition of constant amounts of nitrobenzene also increases the optimum titration range. Results given for all systems are comparable in accuracy with systems previously reported which are favourable to direct phase titration.