2-Chloropyridine

2-Chloropyridine is an aryl chloride with the formula C₅H₄ClN. It is a colorless liquid that is mainly used to generate fungicides and insecticides in industry. It also serves to generate antihistamines and antiarrythymics for pharmaceutical purposes.^[2] It is one of three isomers of chloropyridine.

2-Chloropyridine

Names
Preferred IUPAC name 2-Chloropyridine
Identifiers
CAS Number	109-09-1 Y
3D model (JSmol)	Interactive image
Beilstein Reference	105788
ChEBI	CHEBI:39174 Y
ChEMBL	ChEMBL509579 Y
ChemSpider	7689 Y
ECHA InfoCard	100.003.316
EC Number	203-646-3
Gmelin Reference	130818
PubChem CID	7977
RTECS number	US5950000
UNII	8HMD45AYEJ Y
UN number	2822
CompTox Dashboard (EPA)	DTXSID8024810
InChI InChI=1S/C5H4ClN/c6-5-3-1-2-4-7-5/h1-4H Y Key: OKDGRDCXVWSXDC-UHFFFAOYSA-N Y InChI=1/C5H4ClN/c6-5-3-1-2-4-7-5/h1-4H Key: OKDGRDCXVWSXDC-UHFFFAOYAI
SMILES Clc1ncccc1
Properties
Chemical formula	C5H4ClN
Molar mass	113.54 g/mol
Appearance	colorless liquid
Density	1.2 g/mL
Melting point	−46 °C (−51 °F; 227 K)
Boiling point	166 °C (331 °F; 439 K)
Solubility in water	27 g/L
Acidity (pKa)	0.49 [1]
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H301, H310, H315, H319, H330, H400
Precautionary statements	P260, P261, P262, P264, P270, P271, P273, P280, P284, P301+P310, P301+P312, P302+P350, P302+P352, P304+P340, P305+P351+P338, P310, P311, P312, P314, P320, P321, P322, P330, P332+P313, P337+P313, P361, P362, P363, P391, P403+P233, P405, P501
Safety data sheet (SDS)	MSDS
Related compounds
Related compounds	3-Chloropyridine 3-Bromopyridine 2-Chloromethylpyridine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Preparation

2-Chloropyridine is produced by direct reaction of pyridine with chlorine. The initially formed 2-chloropyridine reacts further to give 2,6-dichloropyridine.^[2]

Alternatively, 2-chloropyridines can be conveniently synthesized in high yields from pyridine-N-oxides.^[3]

2-Chloropyridine was originally prepared by the chlorination of 2-hydroxypyridine with phosphoryl chloride.^[4]

Main reactions and applications

2-Chloropyridine reacts with nucleophiles to generate pyridine derivatives substituted at the second and fourth carbons on the heterocycle. Therefore, many reactions using 2-chloropyridine generate mixtures of products which require further workup to isolate the desired isomer.^[2]

Some commercial products include pyrithione, pyripropoxyfen, chlorphenamine, and disopyramide. In these conversions, chloride is displaced.^[2] Pyrithione, the conjugate base of 2-mercaptopyridine-N-oxide, is a fungicide found in some shampoos. Oxidation 2-chloropyridine gives 2-chloropyridine-N-oxide.^[5] The antihistamine pheniramine may be generated via the reaction of phenylacetonitrile with 2-chloropyridine in the presence of a base.^[6]

Environmental properties

Although pyridine is an excellent source of carbon, nitrogen, and energy for certain microorganisms, introduction of a halogen moiety significantly retards degradation of the pyridine ring. With the exception of 4-chloropyridine, each of the mono- and di-substituted chloropyridines were found to be relatively resistant to microbiological degradation in soil or liquid media.^[7] Estimated time for complete degradation was > 30 days. 2-Chloropyridine exhibits extensive volatilization losses from water, less so when present in soil.^[8]

Toxicity

The LD50 is 64 mg/kg (dermal, rabbit).^[2]

References

1. Linnell, R. H., J. Org. Chem., 1960, 25, 290.
2. Shimizu, Shinkichi; Watanabe, Nanao; Kataoka, Toshiaki; Shoji, Takayuki; Abe, Nobuyuki; Morishita, Sinji; Ichimura, Hisao (2007). "Pyridine and Pyridine Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_399. ISBN 978-3-527-30673-2.
3. Narendar, P.; Gangadasu, B.; Ramesh, Ch.; China Raju, B.; Jayathirtha Rao, V. (2004). "Facile and Selective Synthesis of Chloromethylpyridines and Chloropyridines Using Diphosgene/Triphosgene". Synthetic Communications. 34 (6): 1097–1103. doi:10.1081/SCC-120028642. S2CID 95706122.
4. Pechmann, H. V.; Baltzer, O. (1891). "Ueber das α-Pyridon (α-Oxypyridin)". Berichte der Deutschen Chemischen Gesellschaft. 24 (2): 3144–3153. doi:10.1002/cber.189102402155.
5. Cheng, Hefeng; She, Ji. 14. Improved preparation of 2-mercaptopyridine-N-oxide. Zhongguo Yiyao Gongye Zazhi. 1990, 21, (2), pp. 55-56. ISSN 1001-8255
6. Botteghi, Carlo et al. New Synthetic Route to Pheniramines via Hydroformylation of Functionalyzed Olefins. 1994, 59, pp. 7125-7127. doi:10.1021/jo00102a044
7. Sims, G. K. and L.E. Sommers. 1986. Biodegradation of pyridine derivatives in soil suspensions. Environmental Toxicology and Chemistry. 5:503-509.
8. Sims, G. K. and L.E. Sommers. 1985. Degradation of pyridine derivatives in soil. Journal of Environmental Quality. 14:580-584.