PEYOTE (Hive Bee)
01-28-02 19:03
No 261882
      Halodecarboxylation of a,b-unsaturated Ar acids  Bookmark   

Tetrahedron Lett. 42:9253(2001)

A mild and efficient method for oxidative halodecarboxylation of a,b-unsaturated aromatic acids using lithium bromide/chloride and ceric ammonium nitrate

Subhas Chandra Roy, Chandrani Guin and Gourhari Maiti

Department of Organic Chemistry, Indian Association for the Cultivation of Science Jadavpur, Calcutta 700 032, India
Department of Chemistry, Jadavpur University, Jadavpur, Calcutta 700 032, India
Received 24 August 2001; revised 1 October 2001; accepted 12 October 2001

Abstract - A mild and efficient ecofriendly method for the halodecarboxylation of a,b-unsaturated aromatic acids has been developed by using lithium bromide/chloride and ceric ammonium nitrate in acetonitrile-water at room temperature to afford the vinyl halides in moderate to good yields.

The decarboxylation of organic carboxylic acids accompanied by a simultaneous replacement by a halogen under radical conditions is an extremely useful and selective reaction in organic chemistry for the synthesis of halogenated organic substances. The original method for oxidative halodecarboxylation, known as the Hunsdiecker reaction, is the reaction of a silver salt of a carboxylic acid with mainly bromine as the halogen1. The efficacy of the reaction has been improved by several groups to include carboxylates of mercury2, thallium3, lead4, and manganese5 besides the original silver of Hunsdiecker. In spite of that, the classical Hunsdiecker reactions have some limitations e.g. (i) the reaction of trans and cis cinnamic acids give b-bromostyrene in a very low yield6, (ii) generally, a high temperature is required for the reaction (iii) the use of toxic or hazardous reagents like molecular bromine and salts of mercury, thallium. lead and silver.

Later, classical Hunsdiecker reactions have been modified by using NBS/iodosyl benzene7, NBS/lithium acetate8, NBS/tetrabutylammonium trifluoroacetate9, and bis(collidine) halogen(I)hexafluorophosphate10. Very recently, microwave induced Hunsdiecker reactions using N-halosuccinimide/catalytic amount of lithium acetate11 and sodium halide/oxone(r) 12 have been reported. Although, most of these methods are quite satisfactory, the use of expensive and complex reagents, large amounts of solvent and prolonged reaction times demands some mild and efficient alternative reagents for the Hunsdiecker reaction.

Lanthanide salts have been used as shift reagents and reagents for organic synthesis13. Ceric ammonium nitrate (CAN) is one such reagent, which has been used extensively for functional group transformations in organic synthesis. The strong oxidising power of the ceric ion has been recognised for many decades. However, its synthetic utility to organic chemistry has only been explored recentlyl4. Asakura15 has demonstrated that CAN can be efficiently used as a one electron oxidant to generate electrophilic bromine from the metal salts. In continuation of our efforts16 to explore CAN as a one electron oxidant, we report here a simple and efficient methodology for the halodecarboxylation of a,b-unsaturated aromatic acids using LiBr or LiCl and CAN, at room temperature to afford the vinyl halides (Scheme 1). Thus, a series of trans-a,b-unsaturated aromatic acids were treated with Lix (X = Cl or Br) and CAN in acetonitrile-water (10:1) at room temperature to afford trans-b-halostyrenes17. The results are summarised in Table 1 . It is noteworthy that the amount of water in the solvent had a remarkable effect on the yield. An increase of water content in the solvent resulted in an increase in the yield of b-halostyrene12 and we obtained the maximum yield using a solvent to water ratio of 10:1. Moderate to good yields of the corresponding halides were obtained and it was observed that electron donating substituents in the aromatic ring accelerated the reaction.

In conclusion. we have developed a simple, efficient and environmentally friendly methodology for the halodecarboxylation of a,b-unsaturated aromatic acids using lithium bromide/chloride and ceric ammonium nitrate at room temperature.


1) Wilson, C. V. Org. React. 1957, 9, 332.
2) Cristol, S. J.; Firth, W. C. J. Org. Chem. 1961, 26, 280.
3) McKillop. A.; Bromley. D.; Taylor, E. C. J. Org. Chem. 1969, 34, 1172.
4) (a) Barton, D. H. R.; Faro. H. P.; Serebryakov, E. P.; Woolsey, N. F. J. Chem. Soc. 1965, 2438; (b) Sheldon, R. A.; Kochi, J. K. Org. React. 1972, 19, 275.
5) Chowdhury, S.; Roy, S. Tetrahedron Lett. 1996, 37, 2623.
6) Johnson, R. G.; Ingham, R. K. Chem. Rev. 956, 56, 219.
7) Graven, A.; Jorgensen, K. A.; Dahl, S.; Stanczak, A. J. Org. Chem. 1994, 59, 3543.
8) Chowdhury, S.; Roy, S. J. Org. Chem. 1997, 62, 199.
9) Naskar, D.; Roy, S. Tetrahedron Lett. 2000, 56, 1369.
10) Homsi, F.; Rousseau, G. Tetrahedron Lett. 1999, 64, 81; (b) Homsi, F.; Rousseau, G. J. Org. Chem. 1999, 64, 8l.
11) Kuang, C.; Senboku, H.; Tokuda, M. Synlett 2000, 1439.
12) You, H.-W.; Lee, K. J. Synlett 2001, 105.
13) Long. J. R. Aldrichimica Acta 1985, 18, 87 and references cited therein.
14) (a) Ho, T. L. Synthesis 1973, 347; (b) Ho, T. L. In Organic Synthesis by Oxidation with Metal Compounds; Mijs, W. J.; Jonge, R.-H. I., Eds.; Plenum Press: New York, 1986.
15) (a) Asakura, J.; Robins, M. J. Tetrahedron Lett. 1988, 29, 2855; (b) Asakura, J.; Robinson, M. J. J. Org. Chem. 1990, 4928.
16) Roy, S. C.; Guin, C.; Rana, K. K.; Maiti, G. Synlett 2001, 226.
17) General procedure: To a magnetically stirred solution of the cinnamic acid derivative (1.68 mmol), LiBr or LiCl (3.7 mmol) in acetonitrile-water (7.7 mL, 10:1) a solution of ceric ammonium nitrate (3.5 mmol) in acetonitrile (10 mL) was added dropwise at room temperature under nitrogen. After completion of the reaction (monitored by TLC) the reaction mixture was diluted with ether (25 mL). The organic layer was washed successively with saturated aqueous NaHCO3 solution (3x10 mL), water (2x10 mL), brine (3x10 mL) and then dried (Na2SO4). Volatiles were removed under reduced pressure and the residue was purified by chromatography over Al2O3 (2% ethylacetate in petroleum ether) to furnish the pure vinyl halides.

(Chief Bee)
01-30-02 00:45
No 262465
      Re: Halodecarboxylation of a,b-unsaturated Ar acids  Bookmark   

Where do we go from here? Reaction with hydroxylamine to form the acetoxime, which is then reduced to the PEA?
(Ubiquitous Precursor Medal Winner)
01-30-02 12:53
No 262715
      Re: Halodecarboxylation of a,b-unsaturated Ar acids  Bookmark   

This "one electron oxidation" business is a tale I have heard lately, I believe with respect to manganese (III) acetate, in the way it pulls its little stunt to condense acetone with benzene. That makes this a topic of some interest, as another example of the same phenomonon, if the one can help us better understand the other.

Ceria is an article of commerce, a polishing compound for e.g. optical glass, think telescopes; in this formulation, it will remain in a natural mix with other rare-earth oxides, so chemically identical they can't hurt. (Same mix is on the von Welsbach catalytic lantern mantle, Coleman lamp, forgot the Brit name, there mixed with thoria; same mix is in the flints of lighters, rare-earth oxides nominally "ceria".) Nitric acid digestion gives the nitrate, then ammonia the ammine complex, hence cerium ammonium nitrate, CAN. No harder to make than manganic acetate. Will it do the same job?

That it gives an activated halogen from lithium bromide or chloride doesn't prove it. I'm also mystified where the above halovinyl compound points, but I do like the reagent used!

~ ~ ~ C U N D C ~ ~ ~
~ ~ 4 / 20 / 003 ~ ~
1000000 heads high
(Chief Bee)
01-30-02 18:00
No 262771
      Re: Halodecarboxylation of a,b-unsaturated Ar acids  Bookmark   

Ce(III) has been tried instead of Mn(III) in the benzene/acetone condensation, but the yields fall through the floor.