2434 Bull. Chem. Soc. Jpn., 74, No. 12 (2001)
© 2001 The Chemical Society of Japan
excess) [or: I2 (0.61 g, 2.4 mmol; 20% excess), when NaIO3 was
used as an oxidant] were suspended in a stirred mixture of glacial
AcOH (10 mL) with Ac2O (5 mL) cooled to 5 °C. Varied quanti-
ties (see Table 1) of concd (98%) H2SO4 were very slowly added
dropwise with vigorous stirring while keeping the temperature be-
low 10 °C. An appropriate arene (14 mmol; 0% excess) [or: arene
(10 mmol; 0% excess), when NaIO3 was used as an oxidant] was
added portionwise or dropwise with stirring. Then, the notably in-
dividualized reaction conditions shown in Table 1 [i. e. the differ-
entiated times of a further stirring at given temperatures to com-
plete the iodinating reactions] were applied for each of the arenes
iodinated (cf. Ref. 5). Dark-brown initial reaction mixtures faded
to be finally yellowish. The resulting reaction mixtures, contain-
ing optimized quantities of the respective ArISO4 intermediates,
were cooled to ca. 5 °C, and concd (36%) hydrochloric acid (15
mL, ca. 170 mmol) was added with stirring while keeping the tem-
perature at 5–10 °C. After ca. 30 min, the resulting suspensions
were poured into stirred ice-water (ca. 300 g). After 15 min, yel-
low precipitates were collected by filtration, washed well with ice-
cold water, until the filtrates were neutral, then with a little CCl4,
and air-dried9 in the dark. Their melting points (Table 1) were
taken immediately in the way explained in Refs. 7 and 8. The
crude yields (Table 1) were calculated from the total amounts of
the arenes, used in strictly stoichiometric quantities (0% excess).
Iodometric titrations3 indicated that the freshly prepared crude
ArICl2 had 90–96% purity.
To explain the present method, it is necessary to recall our
former paper;5 alternatively, see our review,2 p. 1337, where
the supposed structures of the I3+ species and ArISO4 interme-
diates are also shown and explained. In our former work,5 we
oxidatively substituted halobenzenes and deactivated arenes in
anhydrous liquid systems, I2/NaIO4 or NaIO3/AcOH/Ac2O/
concd H2SO4, in which the said transient species, I3+, played a
predominant role in electrophilic substitutions of the reacted
arenes, ArH. These species were generated there as Scheme 3.
Scheme 3.
Next, the said strongly electrophilic I3+ species readily sub-
stituted ArH (Scheme 1). After pouring the resulting reaction
mixtures into excess aq. Na2SO3 solutions, the corresponding
iodoarenes were afforded: ArISO4 + Na2SO3 + H2O → ArI
+ Na2SO4 + H2SO4. Alternatively, the same resulting reaction
mixtures were reacted upon with excess aq ammonium acetate
Note. Exceptionally, PhI (3.14 g, 15.4 mmol; 10% excess) was
oxidatively iodinated, but with strictly stoichiometric quantities of
NaIO4 (1.28 g, 6.0 mmol; 0% excess) and I2 (1.02 g, 4.0 mmol;
0% excess); see Table 1 for the other reaction parameters. The
crude yield for 4-IC6H4ICl2 (Table 1) was calculated from the total
amount of the diiodine consumed.
solutions to afford (diacetoxyiodo)arenes:2,6 ArISO4
+
2AcONH4 → ArI(OAc)2 + (NH4)2SO4. Consequently, in the
present work we added excess concd (36%) hydrochloric acid
to the same resulting (final) reaction mixtures to precipitate out
the corresponding (dichloroiodo)arenes, ArICl2 (Scheme 2).
For more details see Experimental and Table 1.
Our novel, environmentally benign method for the prepara-
tion of crude ArICl2 from the respective arenes (Table 1)
avoids the hazardous application of gaseous Cl2 and chlorinat-
ed solvents, and the use of costly iodoarenes, previously ap-
plied as starting substrates for preparing ArICl2. Strongly
acidic wastes obtained in the present method, after their neu-
tralization and dilution, did not contain any toxic by-products,
in contrast to many former methods.1,2 Thus, our present
method would be particularly suitable for large-scale prepara-
tions of, for example, (dichloroiodo)benzene; cf. Ref. 4. Of
course, only those isomeric RC6H4ICl2 may predominantly be
obtained from the monosubstituted benzenes, RC6H5, which
are formed in agreement with common orientation rules in the
electrophilic substitutions of the used RC6H5 (Table 1) by the
said strongly electrophilic I3+ transient species (Scheme 1).
References
1
a) A. Varvoglis, “The Organic Chemistry of Polycoordinat-
ed Iodine,” VCH, Weinheim (1992). b) P. J. Stang and V. V.
Zhdankin, Chem. Rev., 96, 1123 (1996). c) A. Varvoglis, “Hyper-
valent Iodine in Organic Synthesis,” Academic, San Diego (1997).
2
L. Skulski, “Organic Iodine(ꢀ, Ⅲ, and ꢁ) Chemistry: 10
Years of Development at the Medical University of Warsaw, Po-
mdpi.org/molecules/papers.51201331.pdf
3
C. Willgerodt, “Die organische Verbindungen mit mehrw-
ertigem Jod,” Enke Verlag, Stuttgart (1914).
A. Zanka, H. Takeuchi, and A. Kubota, Org. Process Res.
Dev., 2, 270 (1998).
4
5
P. Luliński and L. Skulski, Bull. Chem. Soc. Jpn., 73, 951
(2000).
Experimental
6
7
P. Kaźmierczak and L. Skulski, Synthesis, 1998, 1721.
B. Krassowska-Świebocka, G. Prokopienko, and L.
The melting/decomposition points of crude ArICl2 (Table 1)
were uncorrected and were determined as previously de-
scribed.7,8 All commercial reagents and solvents (Aldrich) were
purified or dried, if necessary, prior to use. Diiodine was finely
powdered in order to facilitate its dissolution in the reaction mix-
tures.
Skulski, Synlett, 1999, 1409.
a) P. Kaźmierczak, L. Skulski, and N. Obeid, J. Chem.
8
Res., Synop., 1999, 64. b) N. Obeid and L. Skulski, Pol. J. Chem.,
74, 1609 (2000).
9
By drying the crude ArICl2 in a vacuum dessicator, the
chlorine percentage was lowered: ArICl2 → ArI + Cl2.
10 A. S. Dnieprovskii, V. A. Shkurov, and T. I. Temnikova,
Zh. Org. Khim., 13, 2587 (1977).
Optimized Procedures for the Preparation of ArICl2 from
Arenes, ArH. NaIO4 (1.41 g, 6.6 mmol; 10% excess) [or: NaIO3
(1.43 g, 7.2 mmol; 20% excess)] and I2 (1.12 g, 4.4 mmol; 10%
Lulinski, Piotr
