Organic Syntheses, Vol. 77, 206
Checked by Suzanne Patterson and David J. Hart.
1. Procedure
2. Notes
2.
Collidine (99% grade) from Aldrich Chemical Company, Inc. was used. Technical grade (from ACROS) can be used after purification by distillation from
calcium hydride (CaH
2).
3. The checkers always observed a small amount of undissolved solid and began the addition of
collidine when dissolution appeared to cease.
4. The range of melting is
210°-253°C. At 253°C the submitters observe solid decomposition. The checkers observed an mp range of
222-238°C (dec.).
5. The NMR spectrum was as follows:
1H NMR (250 MHz, CDCl
3) δ: 2.40 (s, 6 H), 2.78 (s, 12 H), 7.11 (s, 4 H).
13C NMR (63 MHz, CD
2Cl
2) δ: 21.6, 28.0, 124.4, 153.9, 158.2. Anal. Calcd for C
16H
22AgF
6N
2P: C, 38.81; H, 4.48; N, 5.66. Found: C, 38.73; H, 4.36; N, 5.59.
8. The submitters note that after recrystallization from
methylene chloride a white solid is obtained [mp
131-132°C (dec)]. No difference in reactivity is observed compared with the crude product.
9. This solid must be stored in the dark at 0°C. In these conditions it can be kept for several years, or for several months at room temperature.
10. The following spectra were obtained:
1H NMR (250 MHz, CDCl
3) δ: 2.41 (s, 3 H), 2.43 (s, 3 H), 2.65 (s, 6 H), 2.85 (s, 6 H), 7.11 (s, 2 H), 7.17 (s, 2 H);
13C NMR (63 MHz, CD
2Cl
2) δ: 21.5, 29.9, 125.9, 155.0, 158.3; IR (KBr) cm
−1: 2989 (vs), 1618 (s), 1461 (s), 1384 (s), 1312 (s), 1031 (s), 1003 (s), 829 (br). Anal. Calcd for C
16H
22F
6IN
2P: C, 37.37; H, 4.31; N, 5.45. Found: C, 37.45; H, 4.36; N, 5.42.
11. All the
bromine should have reacted before removal of the solvent. See (Note
7).
12. The submitters indicate that after recrystallization from
methylene chloride the mp is 125°C (decomposition). No difference in reactivity is observed compared with the crude product.
13. The following spectra were obtained:
1H NMR (250 MHz, CDCl
3) δ: 2.43 (s, 6 H), 2.78 (s, 12 H), 7.16 (s, 4 H);
13C NMR (63 MHz, CD
2Cl
2) δ: 21.6, 25.9, 126.3, 154.9, 156.4; IR (KBr) cm
−1: 2990 (vs), 1618, (s), 1463 (s), 1386 (s), 1313 (s), 1030 (s), 1005 (s), 828 (br).
All toxic materials were disposed of in accordance with "Prudent Practices in the Laboratory"; National Academy Press; Washington, DC, 1995.
3. Discussion
The advantages of the hexafluorophosphate salts compared to the perchlorate salts are the safety of preparation, ease of use, and their low hygroscopicities. This method of preparation can be applied to a large variety of mono aromatic amines (
pyridine,
chloropyridine,
2-methoxypyridine, etc.); however, in the reactions that the submitters have examined these salts are less reactive than the parent collidine salts.
Bis(2,4,6-trimethylpyridine)iodine(I) and -bromine(I) hexafluorophosphate have been used for specific electrophilic halogenations, such as the preparation of 7-membered ring lactones
3 and ethers,
4 medium ring lactones,
3,5 halogenation of phenols,
6 pyridinols
7 and acetylenic compounds.
8 Most of these reactions are impossible or difficult with other known halogenation reagents.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Bis(2,4,6-trimethylpyridine)iodine(I) hexafluorophosphate: Iodine(1+) bis(2,4,6-trimethylpyridine)-, hexafluorophosphate(1−) (12); (113119-46-3)
Bis(2,4,6-trimethylpyridine)bromine(I) hexafluorophosphate: Bromine(1+) bis(2,4,6-trimethylpyridine)-, hexafluorophosphate(1−) (14); (188944-77-6)
Silver(I)nitrate: Nitric acid silver(1+) salt (8,9); (7761-88-8)
Potassium hexafluorophosphate. Phosphate(1−), hexafluoro, potassium (8,9); (17084-13-8)
2,4,6-Collidine: Pyridine, 2,4,6-trimethyl- (8,9); (108-75-8)
Iodine (8,9); (7553-56-2)
Bromine (8,9); (7726-95-6)
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