Purification of 3-Picoline

Subject: Purification of 3-Picoline Tue Aug 30, 2011 8:22 am

3-Picoline (CAS NO. 108-99-6) often contains 4-methylpyridine and 2,6-lutidine, neither of which can be removed satisfactorily by drying and fractionation, or by using the ZnCl2 complex. Biddiscombe and Handley after steam distn as for 2-methylpyridine, treated the residue with urea to remove 2,6-lutidine, then azeotropically distd with acetic acid (the azeotrope had b 114.5 °C/712mm), and recovered the base by adding excess of aqueous 30% NaOH, drying with solid NaOH and carefully fractionally distilling. The distillate was then fractionally crystd by slow partial freezing. An alternative treatment is to reflux the crude base (500mL) for 20-24h with a mixture of acetic anhydride (125g) and phthalic anhydride (125g) followed by distn until phthalic anhydride begins to pass over. The distillate was treated with NaOH (250g in 1.5L of water) and then steam distd. Addition of solid NaOH (250g) to this distillate (ca 2L) led to the separation of 3-methylpyridine which was removed, dried (K2CO3, then BaO) and fractionally distd. (Subsequent fractional freezing would probably be advantageous.)