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Org. Synth. 1986, 64, 189
DOI: 10.15227/orgsyn.064.0189
2,2' : 6',2' -TERPYRIDINE
Submitted by Kevin T. Potts, Philip Ralli, George Theodoridis, and Paul Winslow1.
Checked by B. L. Chenard and Bruce E. Smart.
1. Procedure
A. 3,3-Bis(methylthio)-1-(2-pyridinyl)-2-propen-1-one. A 3-L, three-necked flask is equipped with an efficient mechanical stirrer, pressure-equalizing dropping funnel with needle valve, and a reflux condenser fitted with a nitrogen gas inlet tube that is attached to a mineral oil bubbler. The system is flushed with nitrogen, and while the system is maintained under a static pressure of nitrogen, the flask is charged with 1000 mL of dry tetrahydrofuran (Note 1) and 96.5 g (0.86 mol) of potassium tert-butoxide (Note 2). Freshly distilled 2-acetylpyridine (50.0 g, 0.41 mol) (Note 3) is then added dropwise over a period of 5–10 min (Note 4). To the resulting reaction mixture 32.7 g (0.43 mol) of carbon disulfide is added over a period of 30–35 min. After the addition is completed, 122.1 g (0.86 mol) of methyl iodide is added over 1 hr to the viscous, heterogeneous orange reaction mixture. After the tan reaction mixture is stirred for 12 hr at room temperature, it is poured into 2 L of iced water and allowed to stand for 4 hr. The solid that precipitates is collected by filtration and air-dried to give 56 g (61%) of yellow crystals, mp 106–107°C. The filtrate is diluted with water to a total volume of 4 L, and chilled to afford an additional 16.5 g (18%) of product, mp 104–107°C (Note 5).
B. 4'-(Methylthio)-2,2' : 6',2''-terpyridine (Note 6). A 1-L, three-necked round-bottomed flask fitted with a mechanical stirrer and a gas inlet tube is flushed with nitrogen and charged with 500 mL of anhydrous tetrahydrofuran and 22.4 g (0.20 mol) of potassium tert-butoxide. Freshly distilled 2-acetylpyridine (12.1 g, 0.10 mol) (Note 3) is added, the solution is stirred for 10 min, and 22.5 g (0.1 mol) of 3,3-bis(methylthio)-1-(2-pyridinyl)-2-propen-1-one is then added. The mixture is stirred for 12 hr at room temperature, during which time it turns bright red and a red solid precipitates (Note 7). The mixture is next treated with 77 g (1.0 mol) of ammonium acetate and 250 mL of glacial acetic acid. A distillation head fitted with a thermometer is attached to the flask and the tetrahydrofuran is removed by distillation over a 2-hr period. The residual brown solution is chilled to 15°C, treated with 400 g of ice, and allowed to stand for 3 hr. Water (400 mL) is added, the mixture is chilled to 15°C, and the gray material that precipitates is collected by filtration, washed with iced water (3 × 200 mL), and air-dried. The crude product is taken up in 250 mL of boiling ethanol and filtered. The filtercake is rinsed with 50 mL of hot ethanol, and the hot filtrates are combined, diluted with 150 mL of water, concentrated to a volume of 400 mL, and allowed to cool to room temperature. After the mixture is thoroughly chilled in an ice bath, the precipitate is collected by filtration, washed with 50% aqueous ethanol, and dried under reduced pressure (23°C, 0.1 mm) to give 20.6–21.4 g (74–77%) of 4'-(methylthio)-2,2' : 6',2''-terpyridine as gray needles, mp 118–119°C (Note 8). This material is sufficiently pure for use in the following step.
C. 2,2' : 6',2''-Terpyridine. A 1-L, four-necked flask equipped with a mechanical stirrer, pressure-equalizing dropping funnel, thermometer, and a condenser fitted with a nitrogen gas inlet tube is flushed with nitrogen and charged with 300 mL of ethanol, 5.0 g (0.018 mol) of 4'-(methylthio)-2,2' : 6',2''-terpyridine and 42.8 g (0.180 mol) of finely ground nickel chloride hexahydrate (Note 9). The resultant green heterogeneous mixture is chilled in an ice bath while the system is maintained under a static pressure of nitrogen. To this chilled (0–5°C) mixture, a solution of 20.4 g (0.54 mol) of sodium borohydride in 128 mL of 40% aqueous sodium hydroxide is added dropwise over 4 hr (Note 10). After the addition is completed and the evolution of hydrogen subsides, the dark reaction mixture is refluxed for 12 hr. The hot mixture is then filtered through a Celite pad, and the pad is washed with hot ethanol (3 × 100 mL). The filtrates are combined and evaporated to dryness under reduced pressure to yield a gray solid residue (Note 11). This solid is suspended in 300–400 mL of water and chilled in an ice bath for 4 hr. The cold suspension is filtered and the gray solid is air-dried. The crude product is taken up in 100 mL of boiling hexane and filtered. The filtrate is concentrated to 50 mL, chilled in an ice bath, and filtered to give 2.48–2.53 g (59–60%) of 2,2' : 6',2''-terpyridine as cream-colored prisms, mp 84–86°C [lit.2 mp 85–86°C] (Note 12) and (Note 13). The mother liquor is concentrated to 10 mL to give a second crop of 0.37–0.40 g (8.8–9.5%), mp 81–84°C.
2. Notes
1. The checkers used tetrahydrofuran that was distilled from lithium aluminum hydride (Caution: See Org. Synth., Coll. Vol. V 1973, 976) and stored with a chip of sodium metal. Distillation from sodium/benzophenone is preferable.
2. Potassium tert-butoxide was obtained from the Aldrich Chemical Company, Inc.
3. The checkers obtained 2-acetylpyridine from the Aldrich Chemical Company, Inc. The submitters thank Reilly Tar & Chemical Corp. for a generous gift of 2-acetylpyridine used in their work.
4. A light yellow solid precipitates during this addition.
5. The product is pure by 1NMR (CDCl3) δ: 2.55 (s, 3 H), 2.65 (s, 3 H), 7.40 (d of d of d, 1 H, J = 1.5, 5.6, 7.5), 7.65 (s, 1 H), 7.85 (d of t, 1 H, J = 7.5, 2.0), 8.20 (d of t, 1 H, J = 7.5, 1.5), 8.65 (d of m, 1 H J = 7.5); IR (KBr) cm−1: 1484, 1471. Analytically pure material, mp 108–109°C, may be obtained by recrystallization from ethanol.
6. Recently, it has been shown that this product may be prepared without isolation of the precursors obtained in Step A.3
7. This solid is the potassium salt of the enedione intermediate.
8. The checkers also obtained material with mp 116–118°C. The submitters report product of unspecified purity with mp 120–122°C. The material obtained by the checkers shows the following 1H NMR (CDCl3) δ: 2.0 (s, impurity), 2.67 (s, 3 H), 7.30 (d of d of d, 2 H J = 1.8, 5.6, 8.0), 7.80 (d of t, 2 H, J = 1.8, 8.0), 8.35 (s, 2 H), 8.4–8.78 (m, 4 H). Mass spectrum m/e calculated: 279.0830. Found: 279.0815. IR (KBr) cm−1: 1558, 1390. The combustion analyses for the products obtained by the checkers were within accepted limits for H, but off about 2% for C, and 0.6–0.8% for N.
9. Nickel chloride hexahydrate was obtained from the Fisher Scientific Company.
10. This reaction, which generates nickel boride,4 is exothermic and evolves hydrogen. Frothing is prevented by keeping the reaction mixture at 0–5°C during addition of the sodium borohydride.
11. The submitters report obtaining tan material.
12. This material is analytically pure. Anal. calcd. for C15H11N3:C, 77.23;H, 4.75; N, 18.01. Found C: 76.82; H, 4.69; N, 18.17. The product shows 1H NMR (CDCl3) δ: 7.33 (d of d of d, 2 H J = 1.5, 5.0, 8.0), 7.86 (d of t, 2 H, J = 2.0, 8.0), 7.96 (t, 1 H, J = 8.0 H), 8.45 (d, 2 H J = 8.0), 8.62 (d, 2 H, J = 8.0), 8.71 (d of m, 2 H).
13. The submitters report that 4'-(methylthio)-2,2' : 6',2''-terpyridine also can be conveniently reduced to 2',2'' : 6',2''-terpyridine with Raney nickel in ethanol. The checkers found, however, that this procedure invariably gave product contaminated with 4'-ethoxy-2,2' : 6',2''-terpyridine. Raney nickel which was exhaustively washed with water to remove base still gave 15% of this by-product.
3. Discussion
The procedure described here is by far the most efficient synthesis of terpyridine.5 Previous preparations include the dehydrogenation of pyridine with ferric chloride,2 the Ullman reaction of 2-bromopyridine and 2,6-dibromopyridine,6 the action of copper on 2-bromopyridine and 6-bromo-2,2'-dipyridyl,6 the reaction of iodine or ferric chloride with 2,2'-bipyridyl,6 and the reaction of 2,2'-bipyridyl with 2-lithiopyridine (40% yield).7
Terpyridine is a very effective chelating agent.

References and Notes
  1. Department of Chemistry, Rensselaer Polytechnic Institute, Troy, NY 12181.
  2. Morgan, G.; Burstall, F. H. J. Chem. Soc. 1937, 1649.
  3. Potts, K. T.; Usifer, D. A.; Guadalupe, A.; Abruna, H. D. J. Am. Chem. Soc. 1987, 109, 3961.
  4. Truce, W. E.; Perry, F. M. J. Org. Chem. 1965, 30, 1316.
  5. Potts, K. T.; Cipullo, M. J.; Ralli, P.; Theodoridis, G. J. Am. Chem. Soc. 1981, 103, 3584, 3583; J. Org. Chem. 1982, 47, 3027.
  6. Burstall, F. H. J. Chem. Soc. 1938, 1662.
  7. Kauffmann, T.; König, J.; Woltermann, A. Chem. Ber. 1976, 109, 3864.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sodium/benzophenone

nickel boride

2',2'' : 6',2''-terpyridine

6-bromo-2,2'-dipyridyl

ethanol (64-17-5)

acetic acid (64-19-7)

ammonium acetate (631-61-8)

hydrogen (1333-74-0)

sodium hydroxide (1310-73-2)

nitrogen (7727-37-9)

copper (7440-50-8)

nickel (7440-02-0)

iodine (7553-56-2)

pyridine (110-86-1)

sodium (13966-32-0)

carbon disulfide (75-15-0)

ferric chloride (7705-08-0)

Methyl iodide (74-88-4)

nickel chloride hexahydrate (7791-20-0)

Tetrahydrofuran (109-99-9)

lithium aluminum hydride (16853-85-3)

2-Bromopyridine (109-04-6)

hexane (110-54-3)

sodium borohydride (16940-66-2)

2,2'-bipyridyl (366-18-7)

TERPYRIDINE

2-acetylpyridine (1122-62-9)

3,3-bis(methylthio)-1-(2-pyridinyl)-2-propen-1-one (78570-34-0)

2,6-dibromopyridine (626-05-1)

2-lithiopyridine

potassium tert-butoxide (865-47-4)

2,2' : 6',2' -TERPYRIDINE,
2,2' : 6',2''-Terpyridine (1148-79-4)

4'-(Methylthio)-2,2' : 6',2''-terpyridine (78570-35-1)