In exploratory experiments, we observed isolation of the resultant hydrogen bonded complexes to be rather problematic; we suspect that autoxidation of the uncomplexed nitropyridine to the n-oxide occurs rapidly, thus the pyridine dosing is substoichiometric, leading to a mixture of acid, n-oxide and the desired complex. We therefore purify the resultant complexes from the reaction solution using Machine Vision Aided Crystallisation (MVAC). This process takes advantage of the near total insolubility of the precursor acid in acetone, the insolubility of the complexes in acetone/DCM mixtures, and the solubility of the pyridines and their N-oxides in both solvent systems. For MVAC the reaction suspension is filtered through a 0.2 micron PTFE filter to remove any uncomplexed carboxylic acid, before transferring to a 7 ml vial and concentrating to a volume of ~ 2 ml (Fig ). The vial containing the filtered solution of hydrogen-bonded complex is placed on a hotplate (IKA RCT Digital) at ambient temperature, and vigorously stirred. A PC controlled syringe pump (New Era) delivers 100 µl of DCM (as an antisolvent) into the vial as a bolus every 300 seconds, with mixing ensured by stirring (500 rpm). Machine vision via a USB camera monitors the addition process; as antisolvent is added the solution becomes turbid due to precipitation, with homogeneity restored by mixing. When the turbidity/precipitation persists for more than 150 seconds the antisolvent addition is discontinued, the vial is then allowed to stand for 1 hour to allow total precipitation of the complex (