J. CHEM. RESEARCH (S), 1999 65
air-dried in the dark. Iodometric titrations,7 carried out
immediately, showed that they were of 92±98% purity.
Hence, they may be used as such in subsequent reactions.
So far, we have failed to chlorinate oxidatively 4-iodonitro-
benzene, 4-iodobenzonitrile and 2,4,6-trichloroidobenzene.
The same procedure is eective for the aromatic chlori-
nation of activated arenes. For example, we chlorinated
4-nitroanisole, 4-nitroacetanilide and 4-methoxybenzoic acid
to obtain the respective pure chlorinated products: 2-chloro-
4-nitroanisole (64%), mp 94±95 8C (from ethanol), lit.,15 mp
93±94 8C; 2-chloro-4-nitroacetanilide (58%), mp 138±139 8C
(from ethanol), lit.,16 mp 139±140 8C; 3,5-dichloro-4-
methoxybenzoic acid (42%), mp 202±204 8C (from ethanol),
lit.,17 mp 202±202.5 8C. Their purity was supported by
correct elemental analyses (C, H, Cl).
and melting points (with decomposition). Note: easily oxidizable
iodoarenes, e.g. 4-iodoanisole and iodotoluenes, should be added to
the reaction mixture after the addition of the whole portion of conc.
HCl. Otherwise, the ®nal yields of the corresponding ArICl2 are
very low.
Received, 1st July 1998; Accepted, 9th October 1998
Paper E/8/05063E
References
1 A. Varvoglis, The Organic Chemistry of Polycoordinated Iodine,
VCH, New York, Weinheim, Cambridge, 1992.
2 A. Varvoglis, Hypervalent Iodine in Organic Synthesis, Academic
Press, San Diego, London, 1997.
3 P. J. Stang and V. V. Zhdankin, Chem. Rev., 1996, 96, 1123.
4 A. Varvoglis, Tetrahedron, 1997, 53, 1179.
5 R. M. Moriarty and O. Prakash, Adv. Heterocycl. Chem., 1998,
69, 1.
Experimental
6 T. Kitamura and Y. Fujiwara, Org. Prep. Proced. Int., 1995, 3,
261.
7 C. Willgerodt, Die organischen Verbindungen mit mehrvertigem
Jod, Enke, Stuttgart, 1914.
8 H. J. Lucas and E. R. Kennedy, Org. Synth., Coll. Vol. III,
Wiley, New York, 1955, p. 482.
9 R. T. Taylor and T. A. Stevenson, Tetrahedron Lett., 1988, 29,
2033, and references therein.
The starting iodoarenes, ArI, were either commercial or obtained
by reported methods. They were puri®ed prior to use, and analyzed
(C, H, I). All the chlorination reactions were carried out under
a fume hood. The toxic residues containing chromium salts were
disposed of according to the local safety measures. Working on a
small scale, we did not recover or remove chromium salts from the
wastes. This should be taken into account, when preparations of
larger quantities are required.
10 A. Zanka, H. Takeuchi and A. Kubota, Org. Process Res. Dev.,
1998, 2, 270.
The melting points with decomposition (see Table 1) were
uncorrected and were measured as follows: after an approximate
mp had been taken in a capillary tube, a new sample was intro-
11 A. Tohl, Ber. Dtsch. Chem. Ges., 1893, 26, 2949.
12 B. Ya. Karele and O. Ya. Neiland, Latv. PSR Zinat. Akad.
Vestis, Kim. Ser., 1970, 587; Chem. Abstr. 1971, 74, 42033. They
failed to chlorinate three iodonitrobenzenes, 4-iodobenzoic acid,
and 2-iodoacetophenone; for ten appropriate iodobenzenes the
crude yields for ArICl2 were 73±96%.
13 D. I. Makhon'kov, A. V. Cheprakov and I. P. Beletskaya,
Zh. Org. Khim., 1986, 22, 681; Chem. Abstr., 1987, 106, 155951.
Only iodobenzene was chlorinated there to give PhICl2 (75%;
94% purity).
14 D. Koyuncu, A. McKillop and L. McLaren, J. Chem. Res.
(S), 1990, 21. They failed to chlorinate 2-iodonitrobenzene; for
®fteen appropriate iodobenzenes the crude yields for ArICl2
were 60±98%.
15 H. Fischli, Ber. Dtsch. Chem. Ges., 1878, 11, 1461.
16 A. Mannino and L. di Donato, Gazz. Chim. Ital., 1908, 38, II,
20.
duced about 10 8C below this point, and the temperature was raised
1
at a rate of 10 8C min
.
General Procedure.ÐPowdered CrO3 [either (see Table 1):
(a) 1.0 g, 10 mmol, 50% excess; (b) 2.0 g, 20 mmol, 200% excess;
(c) 3.0 g, 30 mmol, 350% excess] was dissolved in water (ca.
3±5 ml), this was added to glacial acetic acid (15 ml), then an
appropriate iodoarene (10 mmol) was either dissolved or suspended,
keeping the temperature below 30 8C. Concentrated (36%) hydro-
chloric acid (14 ml, 160 mmol, 300% excess) was added with
vigorous stirring at or near room temp. The reaction mixture
turned from orange to deep green, and a precipitate appeared
either immediately or within several minutes. The resulting
slurry was stirred for 0.5±5.0 h (see Table 1), then the whole was
poured into ice±water (100 ml). The yellow precipitate was collected
by ®ltration, washed well with ice-cold water until the washings
were colourless and neutral, then with CCl4. The crude product
was air dried% in the dark. See Table 1 for the crude yields
17 T. H. Durrans, J. Chem. Soc., 1923, 123, 1424.
18 F. M. Beringer and E. M. Gindler, Iodine Abstr. Rev., 1956,
3, 1.
19 C. K. Ingold, E. W. Smith and C. C. N. Vass, J. Chem. Soc.,
1927, 1245.
%By drying the crude ArICl2 in a vacuum desiccator, the chlorine
percentage was lowered: ArICl2 4 ArI Cl2.