Preparation background of 6-methyl-2-pyridinecarboxaldehyde
6-Methyl-2-pyridinecarboxaldehyde is an organic intermediate that can be prepared from 2,6-lutidine through a four-step reaction. 6-Methyl-2-pyridinecarboxaldehyde can also be condensed with primary amines to generate Schiff bases to generate bidentate chelating ligands, which are similar to 2,2′-bipyridine and 1,10-azophenanthrene. Ligands have similar properties to form complexes with transition metals.
Preparation of 6-methyl-2-pyridinecarboxaldehyde
Synthesis of (1)4b
Add 3b36.8g (300mmol), 70mL of glacial acetic acid and 50mL (500mmol) of 30% H2O2 into the reaction flask in sequence, stir at 75°C Reaction 6h. Add 50% H2O2 and react at 75°C for another 16 hours [TLC tracking, developing agent: A=V (petroleum ether): V (ethyl acetate) =1:3]. Rotary evaporate until half of the solution is removed, add 100 mL of water, and evaporate until no liquid drips out; repeat three times. The residue was adjusted to pH≈10 with saturated Na2CO3 solution, and extracted with CHCl3 (3×100mL). Combine the extracts and use Dry with anhydrous Na2SO4, rotary evaporate to remove CHCl3, and distill under reduced pressure to obtain yellow transparent oily liquid 4b (yield 78%, Rf=0.2).
Synthesis of (2)5b
Add 60mL of acetic anhydride into the reaction bottle, add 4b35.7g (300mmol) dropwise with stirring, complete the dripping, react at 100°C (micro reflux) for 10h (exothermic is severe, should be heated slowly, TLC tracking, developing agent: A=1:1). Distilled under reduced pressure to obtain light yellow slightly mucilage 5b (yield 59%, Rf=0.64).
Synthesis of (3)6b
Add 5b28.0g (170mmol) into the reaction bottle, slowly adjust pH≈14 with NaOH saturated solution while stirring (the color deepens from yellow to orange), and reflux the reaction (TLC tracking). Cool down, extract with CHC sodium bicarbonate 13 (3×100mL), combine the organic layers, and dry with anhydrous Na2SO4. Rotary evaporate to remove CHCl3 to obtain 6b.
(4) 7b is the synthesis of 6-methyl-2-pyridinecarboxaldehyde
Add active MnO259.6 g (700mmol), CHCl3250 mL and 6b17.7 g (140 mmol) into the reaction flask, stir and reflux the reaction ( TLC tracking). Cool down, filter, and evaporate the filtrate to obtain a dark brown liquid, which is decolorized by column chromatography (eluent: A=7:1) to obtain 7b, which is 6-methyl-2-pyridinecarboxaldehyde. 7b: Yellow solid, m.p.36℃～38℃, yield 76%, Rf=0.80(A=1:2);
1HNMRδ: 2.67( s,3H, CH3 ), 7.38～7.43( m, 1H, PyH), 7. n-Butylboronic acid 77( d,J=6.0 Hz, 2H, PyH), 10.05(s, 1H, CHO);
IRν: 3 408, 3064, 2927, 2827, 2684, 1914,1713, 1677, 1593 cm-1.
