In a
5-l. three-necked flask, fitted with a reflux condenser and stirrer, are placed 2500 ml. of water and
50 g. of α-picoline (0.54 mole) (Note
1).
Ninety grams (0.57 mole) of potassium permanganate is added, and the solution is heated on a
steam bath until the purple color has practically disappeared (about 1 hour). A second
90-g. portion of permanganate is then introduced, followed by 500 ml. of water, and the heating is continued until the purple color is destroyed (2–2.5 hours). The reaction mixture is allowed to cool slightly, and the precipitated
oxides of manganese are filtered and washed well with 1 l. of hot water (Note
2). The filtrate is concentrated under reduced pressure to 150–200 ml., filtered, if necessary, and acidified to Congo red with
concentrated hydrochloric acid (65–70 ml., sp. gr. 1.19). This acid solution is then evaporated to dryness under reduced pressure. The solid residue is refluxed for one hour with
250 ml. of 95% ethanol and filtered, and the extraction is repeated with
150 ml. of 95% ethanol.
Dry hydrogen chloride is passed into the combined ethanolic filtrates until crystals begin to separate. The solution is then chilled to about 10° in a freezing mixture, the addition of
hydrogen chloride being continued until the solution is saturated. The crystals of
picolinic acid hydrochloride which separate are filtered and air-dried. The yield is
43–44 g. (
50–51%), m.p.
228–230° (Note
3).
This hydrochloride may contain traces of
potassium chloride, which can be removed by dissolving the hydrochloride in hot
absolute ethanol (50 g. requires 1 l.) and filtering from insoluble material. An equal volume of dry
ether is then added to the warm ethanolic solution, and, after cooling, the crystallized product is filtered. The recovery is
40–43 g., m.p.
210–212° (
230°) (Note
3) and (Note
4).