Chemical Properties
White to light yellow crystalline powder
Uses
2,6-Dibromopyridine is used as a tridentate chelating ligand and in the formation of macrocycles containing the terpyridine moiety. It is also used to produce 6-bromo-2-methoxypyridine.
Application
2,6-Dibromopyridine is an important organic chemical reagent with a wide range of uses:
(1) Spectroscopic studies: There is a satisfactory correlation between the normal Raman spectra of 2,6-dibromopyridine in aqueous solution and the surface enhanced Raman (SER) spectra in silver-pure sols. In the SER spectra, the compounds are notable for the stretching of the vibrational modes of (py)CBr and (CC,CN)(py) in 2,6-dibromopyridine to give enhanced vibrational intensities at 1175 and 1369 cm-1 , respectively[1].
(2) Reaction reagent: Friedel–Crafts-type acylation of alkenes with acyl chlorides has been successfully conducted with a wide substrate scope by the combined use of AlCl3 and 2,6-dibromopyridine. Trisubstituted alkenes afford allylketones or vinylketones depending on the presence or absence of hydrogen atom(s) at the β-position to the acylation site, while monosubstituted alkenes exclusively afford vinylketones[2]. In addition, 2,6-Dibromopyridine can be brominated to form 2,4,6-tribromopyridine by reacting with a mixture of bromine at 450~ 550 °C[3]. It can also be lithiated with butyl lithium for the synthesis of L-739,010[4].
(3) A selective palladium-catalysed arylation of 2,6-dibromopyridine has been developed by employing N-heterocyclic carbene ligands. Selective mono-arylation was performed in water/acetonitrile solvent system at ambient temperature with catalyst loading of 0.1 mol%. This reaction was also found to proceed smoothly in water although at a slightly elevated temperature of 80 °C. 2,6-Disubstituted and diversely substituted 2,6-pyridines were also obtained in high yields which will be of importance to organic and medicinal chemists[5].
Purification Methods
Purify 2,6-dibromopyridine by steam distillation, then recrystallise it twice from EtOH. It does not form an HgCl2 salt. [den Hertog & Wibaut Recl Trav Chim Pays Bas 51 381 1932, Beilstein 20/5 V 435.]
References
[1] S. CHATTOPADHYAY S. K B. Surface-enhanced Raman spectroscopy of 2,5-dibromopyridine and 2,6-dibromopyridine[J]. Spectrochimica acta. Part A: Molecular spectroscopy, 1992. DOI:10.1016/0584-8539(92)80253-S.
[2] SHINYA TANAKA*. Acylation of Alkenes with the Aid of AlCl3 and 2,6-Dibromopyridine[J]. Organic Letters, 2019. DOI:10.1021/acs.orglett.9b02688.
[3] H. J. HERTOG C. R K ;W Combe. Substitution reactions in the pyridine nucleus at elevated temperatures (I). The bromination of 2,6‐dibromopyridine[J]. Recueil des Travaux Chimiques des Pays-Bas, 2010. DOI:10.1002/RECL.19580770109.
[4] D. CAI T. V D Hughes. A study of the lithiation of 2,6-dibromopyridine with butyllithium, and its application to synthesis of L-739,010[J]. Tetrahedron Letters, 1996. DOI:10.1016/0040-4039(96)00336-X.
[5] PRAJAPATI D, SCHULZKE C, KINDERMANN M K, et al. Selective palladium-catalysed arylation of 2,6-dibromopyridine using N-heterocyclic carbene ligands?[J]. RSC Advances, 2015. DOI:10.1039/C5RA10561G.
