The process for the commercial production of 4,7-dichloroquinoline (5) was developed according to the methodology of Price and Roberts (Scheme 1), which is centred on diethoxymethylene malonate (6) and meta-chloroaniline (7), with necessary modifications. The synthesis of 4,7-dichloroquinoline (5) commenced by the conjugate addition of diethoxymethylene malonate (6) and meta-chloroaniline (7) to afford the acrylate intermediate 8, which, upon thermal cyclisation in diphenyl ether (DPE), afforded the quinoline ester 9 in good yields (90-96%). Hydrolysis of the ester (9) in aqueous sodium hydroxide to the quinoline acid (10) was achieved in essentially quantitative yields, while thermal decarboxylation and subsequent chlorination with POCl3 gave the target product 5 in 81-90% yields. The GC-MS chromatogram (Figure ) of the crude product showed an extra peak at a retention time of 13.13 minutes with a similar mass to that of 4,7-dichloroquinoline (5). After isolation and characterisation using 1D and 2D NMR, the identity of the impurity was confirmed to be the 4,5-dichloroquinoline isomer (12, Figure ). The 1 H NMR spectrum of the isomer 12 displayed two doublets integrating for one proton each at δH 8.72 (d, J 4.68 Hz, 1H, H-2) and at δH 7.52 (d, J 4.68 Hz, 1H, H-3) for the protons on the B-ring. An ABX spin system was observed at δH 8.05 (dd, J1 8.32, J2 1.44 Hz, H-8); 7.67 (dd, J1 7.56, J2 1.42 Hz, 1H, H-6) and 7.60 (dd, J1 7.96, J2 7.96 Hz, 1H, H-7) for the A-ring aromatic protons. Additional distinguishing NMR correlations were observed in the COSY NMR spectrum, with protonproton correlation between the three protons H-6, H-7 and H-8 confirming that they were adjacent to each other. The ortho-meta (7.56, 1.42 Hz) coupling constants for H-6, ortho-ortho (7.96, 7.96 Hz) coupling constants for H-7 and ortho-meta (8.32, 1.44 Hz) coupling constants for H-8 provide further confirmation for the arrangement of these protons. Attempted recrystallization in hexanes, as reported by Price and Roberts afforded the pure product in moderate yields of 59-65% (Table , Entry 1). Several solvents and conditions were tried in order to improve the yields, with recrystallization in heptane resulting in a slight improvement in yields without compromising the purity (Entry 2). In contrast to the alkanes, OH-containing solvents such as ethanol and methanol resulted in a drastic decrease in yields (Entries 3 and 5). In an attempt to minimize the solubility of the product, 5% water was added to the recrystallization, this however showed an inverse relationship between purity and yields, as the purity significantly reduced from 99.5% to 86% and 90% for MeOH/H2O and EtOH/H2O respectively. Even though successful in its objective of removing the 4,5-dichloroquinoline isomer (12), the loss in yield and a need for an extra step outweighed the advantages. Another option to remove the isomer, would be to take advantage of solubility due to the difference in the acidity of the two chloroquinoline acid isomers during hydrolysis.