Yield:-

Reaction Conditions:

with thionyl chloride in N,N-dimethyl-formamide at 70; for 4 h;

Steps:

14 Ethyl 2-chloro-5-iodonicotinate (20)

The mixture of 19 (29.8 g, 107 mmol), DMF (1.5 mL) and SOCl₂ (78 mL, 10 eq.) was stirred at 70 °C for 4 h.
The mixture was concentrated in vacuo and diluted with DMF (6 mL).
Water (90 mL) was slowly added to the mixture and then satd NaHCO₃ aq (200 mL) was slowly added.
The mixture was acidified to pH 4 by 1 N HCl (55 mL) and stirred at room temperature for 2 h and at 0 °C overnight.
After filtration, the solid was washed with water and dried in vacuo to yield a crude mixture of 2-chloro-5-iodonicotinic acid as a pale yellow solid (27 g).
The solid was suspended in CHCl₃ (135 mL) and SOCl₂ (13.9 mL) and the suspension was stirred at reflux for 0.5 h. DMF (0.5 mL) and SOCl₂ (27.8 mL) were added to make a clear solution and the mixture was stirred at reflux for 1.5 h, then cooled and concentrated in vacuo. EtOH (135 mL) was slowly added to the residue at 0 °C and the mixture was stirred at 0 °C for 15 min. and at room temperature for 30 min.
The mixture was concentrated in vacuo and partitioned between AcOEt (270 mL) and satd NaHCO₃ aq (135 mL).
The aqueous phase was extracted with AcOEt (135 mL) and the combined organic phase was washed with brine, dried over Na₂SO₄ and filtered.
The mixture was concentrated in vacuo and the residue was purified by silica gel column chromatography (AcOEt/n-hexane; 0:100 to 20:80) to yield 20 as a white solid (27.25 g, 95%).

References:

Takahashi, Bitoku;Funami, Hideaki;Iwaki, Takehiko;Maruoka, Hiroshi;Shibata, Makoto;Koyama, Makoto;Nagahira, Asako;Kamiide, Yoshiyuki;Kanki, Satomi;Igawa, Yoshiyuki;Muto, Tsuyoshi [Bioorganic and Medicinal Chemistry,2015,vol. 23,# 15,p. 4792 - 4803]