· Tetra-n-butylammonium Iodide
· (MW 369.43)
(phase-transfer catalyst;1 ether cleavage;1 alkyl iodide formation;1 salt effects1)
Physical Data: mp 148 °C.
Solubility: sol EtOH, H2O.
Form Supplied in: anhydrous white solid.
Analysis of Reagent Purity: tetraalkylammonium salts can be titrated with potassium 3,5-di-t-butyl-2-hydroxybenzenesulfonate and iron(III) chloride.1a
Purification: crystallize from toluene-petroleum ether, CH2Cl2-petroleum ether (or hexane), acetone, ethyl acetate, EtOH-ethyl ether, aq EtOH, or H2O. The solid is then dried at 90 °C under high vacuum for 2 d.2
Handling, Storage, and Precautions: highly hygroscopic solid.
Although Bu4NI is not as widely used as Tetra-n-butylammonium Bromide, it is often used in phase-transfer reactions. It was shown to promote several N-alkylation reactions3 of heterocycles such as pyrroles4 and of amides5,6 (eq 1).
It has also been used in phase-transfer carbene-mediated cyclopropanation reactions,7 metal-catalyzed carbonylation reactions of organic halides,8,9 and Wittig alkenation reactions.10
Several O-alkylation reactions11 were shown to proceed much faster if Bu4NI was added to the reaction mixture. One particularly interesting case is the benzylation of diethyl tartrate in which addition of a catalytic amount of Bu4NI was shown to be essential for obtaining high yield of the desired product (eq 2).12
A mixture of Zinc Chloride and Bu4NI catalyzes the synthesis of cyclic carbonates from oxiranes and carbon dioxide at rt and atmospheric pressure.13
Methyl, allyl, and benzyl ethers derived from alcohols and phenols are regioselectively cleaved by a mixture of Bu4NI and a Lewis acid (Boron Trifluoride Etherate14 or Aluminum Iodide15).
Alkyl and Vinyl Iodide.
Bu4NI can also be used as a source of iodide for nucleophilic displacement reactions. Neopentyl iodides can be prepared via SN2 displacement of the corresponding triflate (eq 3).16 Alkenyliodonium tetrafluoroborates can be converted to vinyl iodides upon treatment with Bu4NI (eqs 4 and 5).17
- 1. (a) Sjöberg, K. Aldrichim. Acta 1980, 13, 55. (b) Jones, R. A. Aldrichim. Acta 1976, 9, 35. (c) Weber, W. P.; Gokel, G. W. Phase Transfer Catalysis in Organic Synthesis; Springer: New York, 1977. (d) Starks, C. M.; Liotta, C. Phase Transfer Catalysis; Academic: New York, 1978. (e) Dehmlow, E. V.; Dehmlow, S. S. Phase Transfer Catalysis; Verlag Chemie: Deerfield Beach, FL, 1980. (f) Loupy, A.; Tchoubar, B. Salt Effects in Organic and Organometallic Chemistry; VCH: Weinheim, 1992.
- 2. Perrin, D. D.; Armarego, W. L. Purification of Laboratory Chemicals; 3rd ed.; Pergamon: Oxford, 1988.
- 3. (a) Baldwin, J. E.; Au, A.; Christie, M.; Haber, S. B.; Hesson, D. JACS 1975, 97, 5957. (b) van Leusen, A. M.; Bouma, R. J.; Possel, O. TL 1975, 3487.
- 4. Gonzalez, C. R.; Greenhouse, R. H 1985, 23, 1127.
- 5. Sato, R.; Senzaki, T.; Goto, T.; Saito, M. BCJ 1986, 59, 2950.
- 6. Keusenkothen, P. F.; Smith, M. B. SC 1989, 19, 2859.
- 7. Dehmlow, E. V.; Leffers, W. JOM 1985, 288, C41.
- 8. Lakshmi Kantam, M.; Prabhakar Reddy, N.; Choudary, B. M. SC 1990, 20, 2631.
- 9. For reviews on applications of phase-transfer agents in the metal-catalyzed organic transformations, see: (a) Alper, H. Fundamental Research in Homogeneous Catalysis; Plenum: New York, 1984; Vol. 4, p 79. (b) Alper, H. Adv. Chem. Ser. 1987, 326, 8.
- 10. Piechucki, C. S 1974, 869.
- 11. For a review of Bu4NI-catalyzed reactions of O-tin ethers and stannylenes, see: David, S.; Hanessian, S. T 1985, 41, 643.
- 12. Nemoto, H.; Takamatsu, S.; Yamamoto, Y. JOC 1991, 56, 1321.
- 13. Kisch, H.; Millini, R.; Wang, I.-J. CB 1986, 119, 1090.
- 14. Mandal, A. K.; Soni, N. R.; Ratnam, K. R. S 1985, 274.
- 15. Andersson, S. S 1985, 437.
- 16. (a) Binkley, R. W.; Ambrose, M. G.; Hehemann, D. G. JOC 1980, 45, 4387. (b) Harris, F. L.; Weiler, L. TL 1987, 28, 2941.
- 17. (a) Ochiai, M.; Oshima, K.; Masaki, Y. JACS 1991, 113, 7059. (b) Ochiai, M.; Oshima, K.; Masaki, Y. TL 1991, 32, 7711.
André B. Charette
Université de Montréal, Québec, Canada
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