Can sodium dithionite reduce o-nitrobenzoic acid to anthranilic acid under basic conditions with mild reflux?
If so, how could I separate anthranilic acid from the reaction mixture?
Just to add to Waylander's answer, sodium dithionate has been used successfully to reduce a wide variety of (more substituted) nitrobenzoic acids. Just as one example (there are many), this one used in Overman's synthesis of plectosphaeroic acids B and C (J. Org. Chem. 2013, 78 (17), 8766–8788):
In this case the product was extracted using ethyl acetate.
Yes I believe it can. Dithionite is a reliable reducing agent for aromatic nitro groups. The reaction of dithionite produces an acid solution which will need to be neutralised before isolation. Anthranilic acid is not very water soluble so an extraction with e.g. chloroform should separate the product cleanly. Tetrahedron Lett. 2013, 54 (21), 2600–2603 discusses dithionite reduction of o-nitrobenzamides and refers to other papers that have used dithionite on similar substrates.