Org. Synth. 2000, 77, 206
DOI: 10.15227/orgsyn.077.0206
PREPARATION OF BIS(2,4,6-TRIMETHYLPYRIDINE)IODINE(I) HEXAFLUOROPHOSPHATE AND BIS(2,4,6-TRIMETHYLPYRIDINE) BROMINE(I) HEXAFLUOROPHOSPHATE
[
Iodine(1+), bis(2,4,6-trimethylpyridine)-, hexafluorophosphate(1−), and Bromine(1+), bis(2,4,6-trimethylpyridine)-, hexafluorophosphate(1−)
]
Submitted by Fadi Homsi, Sylvie Robin, and Gérard Rousseau
1
.
Checked by Suzanne Patterson and David J. Hart.
1. Procedure
Caution! These procedures should be conducted in an efficient fume hood because of the toxicity of iodine and bromine.
A.
Bis(2,4,6-trimethylpyridine)silver(I) hexafluorophosphate
. A 2-L, three-necked, round-bottomed flask is equipped with a mechanical stirrer and a 250-mL pressure-equalizing dropping funnel. The flask is charged with 1 L of distilled water,
100 g of silver nitrate (0.588 mol) and
109.3 g of potassium hexafluorophosphate (0.594 mol)
(Note 1). When all the solids are dissolved,
221 mL of 2,4,6-collidine (1.67 mol) is added over 10 min while stirring (Note 2), (Note 3). A slight exothermic reaction is observed, corresponding to the formation of a white solid. The mixture is stirred for 1 hr at room temperature, the solid is suction filtered, and the filtercake is washed with 1 L of water. The solid is dried in the dark in a desiccator under high vacuum over
phosphorus pentoxide
(P2O5) for 1 week, to afford 262-291 g (90-99%) of silver salt as a white-gray solid, mp 210°C
(Note 4), (Note 5).
B.
Bis(2,4,6-trimethylpyridine)iodine(I) hexafluorophosphate
. A 1-L, three-necked, round-bottomed flask equipped with a mechanical stirrer, condenser topped with a drying tube containing calcium chloride, and a stopper is charged with
500 mL of dry methylene chloride
(Note 6),
82.5 g of bis(trimethylpyridine)silver(I) hexafluorophosphate (0.166 mol), and
41.9 g of iodine (0.165 mol). The mixture is stirred until all the iodine is consumed (1 hr - 2 hr) (Note 7). The resulting yellow solid (
silver iodide
) is suction filtered, and washed with
100 mL of dry methylene chloride
. The filtrate is concentrated on a rotary evaporator at a maximum bath temperature of 30°C to give 68-76 g (80-88%) of yellowish solid
bis(2,4,6-trimethylpyridine)iodine(I) hexafluorophosphate
(mp 132-133°C) (Note 8), (Note 9), and (Note 10). This product is suitable for reactions without further purification.
C.
Bis(2,4,6-trimethylpyridine)bromine(I) hexafluorophosphate
. A 1-L, three-necked, round-bottomed flask equipped with a mechanical stirrer, 50-mL pressure-equalizing addition funnel, and a drying tube containing calcium chloride is charged with
500 mL of dry methylene chloride
(Note 6), and
82.5 g of bis(trimethylpyridine)silver(I) hexafluorophosphate (0.166 mol). Then
8.3 mL of bromine (0.161 mol) is added in 10 min. The mixture is stirred until all the bromine is consumed (1 hr) (Note 11). The resulting yellowish solid (
silver bromide
) is suction filtered and washed with
100 mL of dried methylene chloride
. The filtrate is concentrated on a rotary evaporator at a maximum bath temperature of 30°C to give 65-74 g (83-95%) of
bis(2,4,6-trimethylpyridine)bromine(I) hexafluorophosphate
(mp 127-128°C) as a white solid (Note 9), (Note 12), and (Note 13). This product is suitable for reactions without further purification.
2. Notes
1.
Silver nitrate was obtained from ACROS
and
potassium hexafluorophosphate from Aldrich Chemical Company, Inc.
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.
6.
Methylene chloride was dried by distillation over CaH
2.
7.
It is important that all the
iodine reacts with the silver salt. After concentration, the presence of
iodine can catalyze the decomposition of
bis(trimethylpyridine)iodine(I) hexafluorophosphate. If necessary a small amount of silver salt can be added.
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)
.
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
These preparations of
bis(2,4,6-trimethylpyridine)iodine(I) and
bromine(I) hexafluorophosphate are adaptations of methods previously reported for obtaining the corresponding perchlorates.
2
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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