P. V. Vyas et al. / Tetrahedron Letters 44 (2003) 4085–4088
4087
of 2-naphthol using an excess of hydrochloric acid and
hydrogen peroxide in boiling methanol. The desired
-chloro-2-naphthol 10 was isolated in excellent yield
Eq. (7)), while the bromine analogue 11 was success-
Experimental:
1
(
The reaction products obtained in this study were
purified by column chromatography on silica gel using
a suitable mixture of ethyl acetate and hexane and
showed satisfactory spectral and analytical data. A
representative example is described below.
fully prepared under ambient conditions (Eq. (8)).
Dibromination of 2-naphthol with excess reagent
resulted in the clean formation of 1,6-dibromo-2-naph-
thol 12 in high yield (Eq. (9)). This dibrominated
product is an intermediate in the preparation of the
industrially important 6-bromo-2-naphthol by a selec-
Preparation of 1,6-dibromo-2-naphthol: To a stirred
solution of 2-naphthol (1.44 g; 10 mmol) and hydro-
bromic acid (1.65 g; 3.39 mL of a 49% aq. solution;
27
tive debromination reaction.
2
0.5 mmol) in methyl alcohol (25 mL) was slowly
added hydrogen peroxide (0.68 g; 2.27 mL of a 30%
aq. solution; 20 mmol) over a period of 15 min at
10–15°C. The reaction was left at room temperature
for 20 h whilst monitoring its progress by TLC. After
the completion of dibromination, the solvent was
removed under reduced pressure and the crude
product was taken in ethyl acetate and washed with
water, brine and dried over anhydrous sodium sul-
phate. The pure product was isolated by careful
column chromatography on silica gel (100–200 mesh)
using a mixture of ethyl acetate in hexane (10%) to
give pure 1,6-dibromo-2-naphthol as a light brown
(
(
(
7)
8)
9)
28
solid (1.77 g; 84%); mp 106–107°C (lit. 105–107°C);
IR (KBr): w 3485, 3444, 1617, 1586, 1381, 1210, 1183,
−
1
1
9
28, 871, 805, 645, 536, 512 cm ; H NMR (200
MHz, CDCl ): l 6.20 (br s, 1H), 7.40–7.78 (dd, J=66
3
and 9 Hz, 2H), 8.15–8.36 (dd, J=33 and 9 Hz, 2H),
8
1
.76 (s, 1H). Anal. calcd for C H Br O: C, 39.74; H,
.99. Found: C, 40.06; H, 2.18%.
10 6 2
Another derivative, 1-chloro-6-bromo-2-naphthol 13
was prepared by bromination of 1-chloro-2-naphthol
Acknowledgements
(
Eq. (10)) opening several possibilities to prepare het-
We wish to thank Dr. Pushpito Ghosh for his help
and encouragement and the CSIR, New Delhi for
financial assistance under the Quick Hire Scheme to
A.V.B.
erohalogenated naphthols and phenols. Similarly, chlo-
rination of 1-bromo-2-naphthol yielded 1-bromo-6-
chloro-2-naphthol 14 in moderate yield (Eq. (11)).
References
(
10)
1
2
. Normant, H. Adv. Org. Chem. 1960, 2, 1.
. Wakefield, B. J. The Chemistry of Organolithium Com-
pounds; Pergamon Press: Oxford, 1976.
3. Davis, S. G. Organotransition Metal Chemistry: Applica-
tions to Organic Synthesis; Pergamon Press: Oxford,
1982.
4. Cannon, K. C.; Krow, G. R. Handbook of Grignard
Reagents; Dekker: New York, 1996.
(
11)
5
6
7
. Still, J. K. Pure Appl. Chem. 1985, 57, 1771.
. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
. Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000,
Thus, in this communication we have presented our
results towards an environmentally safe chlorination
and bromination of aromatic amines, hydrocarbons
and naphthols by the in situ oxidation of hydrohalic
acid with hydrogen peroxide. We have prepared sev-
eral important halogenated and heterohalogenated
compounds in moderate to excellent yields without
using any catalyst.
100, 3009.
8
9
. Cabri, W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2.
. Meijere, A.; Meyer, F. E. Angew. Chem., Int. Ed. Engl.
1994, 33, 2379.
10. Sonogashira, K. Comprehensive Organic Synthesis; Perga-
mon Press: New York, 1991; Vol. 3, p. 521.
11. De la Mare, P. B. Electrophilic Halogenation; Cambridge
University Press: Cambridge, 1976; Chapter 5.