Preparation and X-ray structure of 2-iodoxybenzenesulfonic acid (IBS) – A powerful hypervalent iodine(V) oxidant

Article abstract of DOI:10.3762/bjoc.14.159

The selective preparation of 2-iodoxybenzenesulfonic acid (IBS, as potassium or sodium salts) by oxidation of sodium 2-iodoben-zenesulfonate with Oxone or sodium periodate in water is reported. The single crystal X-ray diffraction analysis reveals a compl

Full text of DOI:10.3762/bjoc.14.159

Preparation and X-ray structure of 2-iodoxybenzenesulfonic
acid (IBS) – a powerful hypervalent iodine(V) oxidant
Irina A. Mironova1, Pavel S. Postnikov1, Rosa Y. Yusubova1, Akira Yoshimura1,
Thomas Wirth2, Viktor V. Zhdankin*1,3, Victor N. Nemykin4 and Mekhman S. Yusubov*1
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 1854–1858.
1The Tomsk Polytechnic University, 634050 Tomsk, Russia, 2School
of Chemistry, Cardiff University Park Place, Main Building, Cardiff
CF10 3AT, UK, 3Department of Chemistry and Biochemistry,
University of Minnesota Duluth, MN 55812, USA and 4Department of
Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
doi:10.3762/bjoc.14.159
Received: 14 May 2018
Accepted: 11 July 2018
Published: 20 July 2018
Email:
This article is part of the Thematic Series "Hypervalent iodine chemistry in
organic synthesis".
Viktor V. Zhdankin* - vzhdanki@d.umn.edu; Mekhman S. Yusubov* -
yusubov@tpu.ru
Associate Editor: J. A. Murphy
* Corresponding author
© 2018 Mironova et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
hypervalent iodine; iodine; 2-iodoxybenzenesulfonic acid; oxidation;
X-ray
Abstract
The selective preparation of 2-iodoxybenzenesulfonic acid (IBS, as potassium or sodium salts) by oxidation of sodium 2-iodoben-
zenesulfonate with Oxone or sodium periodate in water is reported. The single crystal X-ray diffraction analysis reveals a complex
polymeric structure consisting of three units of IBS as potassium salt and one unit of 2-iodoxybenzenesulfonic acid linked together
by relatively strong I=O···I intermolecular interactions. Furthermore, a new method for the preparation of the reduced form of IBS,
2-iodosylbenzenesulfonic acid, by using periodic acid as an oxidant, has been developed. It has been demonstrated that the oxida-
tion of free 2-iodobenzenesulfonic acid under acidic conditions affords an iodine(III) heterocycle (2-iodosylbenzenesulfonic acid),
while the oxidation of sodium 2-iodobenzenesulfonate in neutral aqueous solution gives the iodine(V) products.
Introduction
Recently, the interest in synthetic applications of hypervalent as for a variety of other synthetically useful oxidative transfor-
iodine compounds as stoichiometric reagents or catalysts has mations [10,11]. IBX and DMP are mild oxidants with a rela-
experienced an explosive growth [1-8]. Hypervalent iodine(V) tively low reactivity towards some substrates. Moreover, these
compounds represent an important class of oxidative reagents reagents are generally not suitable as active species in catalytic
extensively employed in organic synthesis [9-11]. 2-Iodoxyben- reactions due to the low reactivity and harsh conditions re-
zoic acid (IBX) and the product of its acetylation Dess–Martin quired for their in situ generation. In 2009, Ishihara and
periodinane (DMP) are the most common oxidants used for co-workers have reported an extremely active catalytic system
selective oxidation of alcohols to carbonyl compounds as well for oxidation of alcohols based on 2-iodoxybenzenesulfonic
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Beilstein J. Org. Chem. 2018, 14, 1854–1858.
acid (IBS) as the active species [12,13]. IBS (or its sodium salt) with inorganic impurities. Because of the high solubility of IBS
is much more active as catalyst than IBX derivatives. In particu- in water, this mixture is difficult to separate. The resulting IBS
lar, it can be used as a highly efficient and selective catalyst is insoluble in nonpolar solvents (dichloromethane, chloroform,
(0.05–5 mol %) for the oxidation of primary and secondary etc.). Moreover, IBS has high reactivity towards polar organic
alcohols to the respective carbonyl compounds with Oxone® solvents (acetonitrile, DMSO, methanol) being readily reduced
(2KHSO5·KHSO4·K2SO4) in nitromethane, acetonitrile, or to 2-iodosylbenzenesulfonic acid upon contact with these sol-
ethyl acetate [13]. Recent research has revealed the extreme ac- vents. Despite these problems, IBS was previously character-
tivity of IBS as a catalyst in numerous other oxidations, such as: ized by 1H and 13C NMR, IR spectroscopy, high-resolution
the oxidation of benzylic and alkane C–H bonds [14], the oxida- mass spectrometry, and elemental analysis. However, all previ-
tion of phenols to 1,2-quinones [15], the cyclization and cross- ously reported attempts to grow single crystals of IBS from
coupling reactions [16], and the site-selective hydroxylative methanol or acetonitrile resulted in reduction with the forma-
dearomatization of 2-substituted phenols to either 1,2-benzo- tion of 2-iodosylbenzenesulfonic acid as confirmed by X-ray
quinols or their cyclodimers [17].
diffraction analysis [17]. In the present work, we report the
preparation and isolation of IBS (as potassium or sodium salts)
The first preparation and isolation of IBS (1) was attempted and its structural study by X-ray analysis. Furthermore, we have
in 2006 using two different approaches: direct oxidation developed a new method for the preparation of the IBS reduced
of 2-iodobenzenesulfonic acid (2) by Oxone or hydrolysis of form, 2-iodosylbenzenesulfonic acid (4), with the use of peri-
methyl 2-iodoxybenzenesulfate (3, Scheme 1) [18].
odic acid as an oxidant.
The hydrolysis of sulfonic ester 3 forms IBS as a mixture with Results and Discussion
methanol which is quickly oxidized by IBS in situ producing We have investigated the oxidation of 2-iodobenzenesulfonic
the corresponding iodine(III) heterocycle, 2-iodosylbenzenesul- acid as sodium salt and as a free acid using Oxone, sodium
fonic acid (4) as main product. The direct oxidation of periodate or periodic acid. The oxidation of sodium
2-iodobenzenesulfonic acid (2) with Oxone leads to the forma- 2-iodobenzenesulfonate (5) by Oxone was performed under
tion of the desired IBS (1, Scheme 1), however, contaminated Ishihara's conditions [13] in water at 70 °C (Scheme 2). NMR
Scheme 1: Previously reported preparation of IBS (1) [17].
Scheme 2: Oxidation of 2-iodobenzenesulfonate 5 by Oxone in water.
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Beilstein J. Org. Chem. 2018, 14, 1854–1858.
monitoring indicated 95% conversion of the starting sodium salt
5 to the iodine(V) product 6 after about 3 h stirring at 70 °C
(Figure S1 in Supporting Information File 1). After cooling the
aqueous solution to room temperature, the formation of a pre-
cipitate consisting of needle-shaped organic crystals and micro-
crystalline powder of inorganic salts was observed. The needle-
shaped organic crystals were manually separated from the inor-
ganic salts and analysed by NMR spectroscopy and X-ray crys-
tallography. 1H and 13C NMR spectra of these crystals were in
full agreement with the NMR spectra of IBS provided in the
Supporting Information of Ishihara's paper [13] and, in particu-
lar, displayed the characteristic signals of the ortho-protons
(relative to iodine(V)) at 8.28 ppm.
Figure 2: Simplified representation of structure 6-K. Selected inter-
atomic distances (Å): I(1)=O(1) 1.79; I(1)=O(2) 1.81; I(1)–O(3) 2.54;
O(2)–I(2) 2.46; I(2)=O(7) 1.81; I(2)–O(6) 1.88; I(2)–O(8) 2.60;
I(2)–O(16) 2.71; I(3)=O(11) 1.80; I(3)=O(12) 1.87; I(3)–O(13) 2.49;
I(3)–O(7) 2.63; I(4)=O(17) 1.8; I(4)=O(16) 1.81; I(4)–O(18) 2.60.
The structure of IBS-K crystals obtained by this reaction
(Scheme 2) was established by single-crystal X-ray crystallog-
raphy (for crystallographic details, see Table S1 in Supporting
Information File 1). The X-ray structure of an independent unit O(16)) forms a long (≈2.46 Å for I(1)=O(2)···I(2) and ≈2.71 Å
of IBS-K is shown in Figure 1, and the corresponding structural for I(4)=O(16)···I(2)) secondary contact with the I(2) center. In
drawing with interatomic bond distances is presented in contrast, the third molecule of 6 has pentacoordinated iodine(V)
Figure 2.
center formed by two short I(3)=O bonds, one I–C bond, a rela-
tively long (≈2.49 Å) I···OSO2 intramolecular interaction and a
relatively long (≈2.63 Å) I(2)=O(7)···I(3) intermolecular inter-
actions. Unlike I(1)=O and I(4)=O centers, the I(3)–O(12) bond
distance is significantly longer (≈1.87 Å) compared to the other
I=O bond distances (≈1.80 Å), which is explained below.
Finally, the “inner” I(2) center is hexacoordinated with two
short (≈1.81 Å for I(2)=O(7) and ≈1.88 Å for I(2)–O(6)) bonds,
one regular I(2)–C bond, one usual (2.60 Å) I(2)···OSO2 intra-
molecular contact and two (≈2.71 Å for I(4)=O(16)···I(2) and
≈2.46 Å for I(1)=O(2)···I(2)) intermolecular contacts. Three
potassium ions were also identified in the crystal structure of 6.
In addition, a water molecule was observed in the crystal struc-
ture of 6, which forms two strong hydrogen bonds (≈2.05 Å for
O(21)–H(2)···O(11) and ≈2.07 Å for O(21)–H(3)···O(5)) with
neighbouring oxygen atoms and two short donor–acceptor inter-
actions with K(1) and K(2) potassium ions. Overall, the struc-
ture of the aggregate is indicative of only three potassium coun-
terions and a neutral water molecule thus leaving the anionic
iodine-containing tetramer. Careful examination of the electron
density map and the geometry of this tetramer indicates on the
two rather long I(2)–O(6) and I(3)–O(12) bonds
Figure 1: X-ray structure of an independent crystal unit of IBS 6-K.
The X-ray crystal structure 6-K is quite interesting. Each inde- (≈1.87–1.88 Å), their short (≈2.59 Å) O(6)···O(12) distance, and
pendent unit consists of a tetrameric aggregate, which holds a small electron density close to O(6) and O(12). Thus, a proton
together by relatively strong I=O···I intermolecular interactions was added at the small electron density region to the O(6) atom.
formed between molecules of 6 (Figure 2). Two out of three Such proton positioning results in the formation of an expected
molecules of 6 (those that include I(1) and I(4) centers) have strong hydrogen bond (≈1.87 Å ) in the O(6)–H(1)···O(12) frag-
very similar structures that consist of tetracoordinated iodine ment.
centers with two short (≈1.8 Å) I=O bonds, one regular I–C
bond and one relatively long (≈2.54–2.60 Å) I···OSO2 interac- Manual separation of organic crystals of 6-K from inorganic
tion. In each fragment, one of the I=O oxygen atoms (O(2) and salts resulting from reduction of Oxone is a time-consuming,
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Beilstein J. Org. Chem. 2018, 14, 1854–1858.
impractical procedure. Therefore, we investigated the use of cyclic) structure of 2-OIC6H4SO2ONa. Indeed, X-ray analysis
oxidants different from Oxone for the oxidation of sodium of 2-iodosylbenzenesulfonic acid (4) indicated a cyclic struc-
2-iodobenzenesulfonate (5). It is known from the literature that ture with a I–O bond length of 2.38 Å in the benziodoxathiole
sodium periodate can oxidize various ArI to ArIO2 in boiling ring [18], while in the anionic iodine(V) benziodoxathiole ring
water or aqueous acetic acid [19,20]. We have found that in aggregate 6 (Figure 2) the I–O bonds are much longer
according to NMR monitoring (Figure S2 in Supporting Infor- (≈2.5–2.6 Å). It is known from the literature that the prepara-
mation File 1), the reaction of sodium 2-iodobenzenesulfonate tion of iodine(V) species from ArI and an oxidant involves
(5) with sodium periodate in water selectively affords the initial formation of ArIO followed by disproportionation to ArI
respective iodine(V) product after heating at 60 °C for 16 h with and ArIO2 [23]. Such disproportionation is significantly
almost quantitative conversion. The aqueous solution contain- impeded or even impossible in the cyclic structure of 2-iodosyl-
ing IBS-Na (as sodium salt) and inorganic products resulting benzenesulfonic acid.
from the reduction of NaIO4 was treated with silver nitrate to
precipitate I– and IO3– anions. The precipitate of silver salts was
filtered off, and the mother liquor was concentrated using
blowing air to about half of the initial volume. The concen-
trated aqueous solution was left for several days resulting in the
formation of a microcrystalline precipitate of IBS-Na isolated in
61% yield. 1H and 13C NMR spectra of this product in D2O
were identical to the spectra of IBS-K (6-K). Oxidation of sodi-
um 2-iodobenzenesulfonate 5 with periodic acid under similar
conditions afforded 6-Na in a mixture with 2-iodosylbenzene-
sulfonic acid (4, see Figure S3 in Supporting Information
File 1).
In order to avoid the formation of salts, we have investigated
the oxidation of free 2-iodobenzenesulfonic acid with periodic
acid (H5IO6). 2-Iodobenzenesulfonic acid (7) was prepared
from sodium 2-iodobenzenesulfonate (5) by ion exchange using
Scheme 3: Comparison of the oxidation of sodium 2-iodobenzenesul-
fonate (5) with NaIO4 and 2-iodobenzenesulfonic acid (7) with H5IO6 in
water.
Amberlyst 15 (Н+). The oxidation reaction was carried out at Conclusion
60 °С and monitored by NMR (Figure S5 in Supporting Infor- In conclusion, we have reported a selective preparation of IBS
mation File 1). To our surprise, only the organoiodine(III) prod- (as potassium or sodium salts) and investigated its structure by
uct 2-iodosylbenzenesulfonic acid (4) was formed under these X-ray analysis. Furthermore, we have developed a new method
conditions. Product 4 precipitated from the reaction mixture for the preparation of the reduced form of IBS, 2-iodosylben-
upon cooling to room temperature and was isolated in 87% zenesulfonic acid, by using periodic acid as an oxidant. We
yield by simple filtration. 1H and 13C NMR spectra of product 4 have demonstrated that the oxidation of free 2-iodobenzenesul-
are identical to the previously reported spectroscopic data for fonic acid under acidic conditions affords an iodine(III) hetero-
2-iodosylbenzenesulfonic acid [18,21,22]. In particular, the cycle, while the oxidation of sodium 2-iodobenzenesulfonate in
1H NMR displayed the characteristic signal of the ortho-proton neutral aqueous solution gives the iodine(V) products.
(relative to iodine(III)) at about 8.0 ppm and 13C NMR exhib-
ited the ipso C–I(III) carbon at 112.1 ppm.
Supporting Information
These results clearly indicate that the oxidation of free
Supporting Information File 1
2-iodobenzenesulfonic acid affords iodine(III), while the oxida-
tion of its salt gives the iodine(V) products (Scheme 3). It is a
potentially important observation allowing to selectively
synthesize IBS (as a salt) in neutral aqueous solution or
2-iodosylbenzenesulfonic acid under acidic conditions. This
result can be explained by a greater stability of the heterocyclic
molecule of 2-iodosylbenzenesulfonic acid towards dispropor-
tionation in comparison to the unknown salt of 2-iodosylben-
zenesulfonic acid, which probably has a noncyclic (or pseudo-
Experimental details and NMR spectra.
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-159-S1.pdf]
Supporting Information File 2
Crystallographic information file of compound 6.
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-159-S2.cif]
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