Block 2 experiments

27 Novembro 2018, 11:03 • Christopher David Maycock

The experimental protocol for the last two experiments is described below.

5-Iodo-2-aminopyridine.

To a solution of 2-aminopyridine (5 g, 0.053 mol) in glacial acetic acid (31.9 mL) at r.t.,

was added KIO3 (2.3 g, 0.011 mol) dissolved in water (6.4 mL), and I2 (5.4 g, 0.021

mol), and the reaction was stirred at 80 °C for 3 h. The mixture was poured into 5%

aqueous Na2S2O3 (100 mL) and extracted with ethyl ether (3 x 50 mL), the combined

organic layers were washed with aqueous NaOH solution until pH 7-8 and this aqueous

phase was re-extracted with ethyl ether. The final combined organic layer was dried

(K2CO3) and concentrated. After filtration and evaporation under vacuum, purification

by recrystallisation (AcOEt) gave title compound (9.12 g, 78%) as large white crystals.

M.p. 126-130OC

 1H NMR (CDCl 3): δ 8.22 (1H, d, J=1.8 Hz, H-6); 7.62 (1H, dd, J=8.7 Hz, J=2.4

Hz, H-4); 6.35 (1H, d, J=8.7 Hz, H-3); 4.48 (2H, broad s, NH2).

Record the IR spectrum.

2-Chloro-5-iodopyridine.

To a solution of 2-amino-5-iodopyridine (3 g, 0.014 mol) in concentrated HCl (6.4

mL) at -5 °C, was added NaNO2 (2.4 g, 0.035 mol) dissolved in water (10.9 mL). The

temperature was allowed to rise slowly to r.t. and the reaction mixture was stirred for

1.5 h. At 0 °C aqueous NaOH solution was added until pH 7-8 (solid may be added as

before, with care) and the aqueous phase was extracted with ethyl ether (3 x 50 mL), the

combined organic layers were washed with water, and this aqueous phase was

reextracted with ethyl ether. The final combined organic layer was dried (K2CO3) and

concentrated. The residue was washed several times with hexane and this was

evaporated and not decanted, in order to remove the pink colour. No further purification

was needed, and the title compound was obtained as very light white crystals (2.44 g,

75%). M.p. 95-98OC

 1H NMR (CDCl 3): δ 8.60 (1H, d, J=2.1 Hz, H-6); 7.92 (1H, dd, J=8.4 Hz, J=2.4

Hz, H-4); 6.35 (1H, d, J=8.4 Hz, H-3).

Record the IR spectrum