Synthesis, characterization, X-ray structural analysis, and iodination ability of benzyl(triphenyl)phosphonium dichloroiodate

Article abstract of DOI:10.1002/hlca.201100198

Benzyl(triphenyl)phosphonium dichloroiodate (BTPPICl₂), BnPh₃P⁺(ICl₂)^-, is easily synthesized in a nearly quantitative yield by the addition of BnPh ₃P⁺Cl^- to a CH₂Cl₂ solution of iodine monochloride (ICl). BnPh₃P⁺Cl ^- can be prepared by the reaction of Ph₃P and BnCl. The compound was characterized by physicochemical and spectroscopic methods (elemental analysis, FT-IR, and ¹H-NMR). The use of phosphonium counterion improves the quality of the BTPPICl₂ crystals. BTPPICl₂ crystallizes in the monoclinic system, and its crystal and molecular structure has been determined at 100(1) K by X-ray diffraction. The structure was solved by the direct method and had refined R value of 0.0637 for 699 reflections (I>2σ(I)), space group P21/n with a=12.4700(3), b=13.2196(3), c=14.4580(3) A, β=102.6340(10)°, V=2325.67(9) A³, and Z=4. The I-atom is coordinated by two Cl-atoms as ligands in a linear geometry. This compound is a versatile reagent for the efficient and selective iodination of organic substrates, in particular of aromatic phenols to the corresponding iodo compounds, under mild conditions. To assess the generality of method, a wide variety of phenols with electron-donating and electron-withdrawing substituents were studied. BTPPICl₂ is a mild iodination reagent, which offers a new avenue for an expeditious iodination of phenols. The inexpensive, relatively non-toxic reagent, and mild conditions are the positive features of the procedure and reagent. Copyright

Full text of DOI:10.1002/hlca.201100198

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Helvetica Chimica Acta – Vol. 94 (2011)
Synthesis, Characterization, X-Ray Structural Analysis, and Iodination Ability
of Benzyl(triphenyl)phosphonium Dichloroiodate
by Hossein Imanieh*a), Shahriar Ghammamy*a), Mir Mohammad Alavi Nikjea), Farhang Hosseinia),
Zahra Shokri Aghbolaghb), Hoong-Kun Func), Hamid Reza Khavasid), and Reza Kiae)
a) Department of Chemistry, Faculty of Science, Imam Khomeini International University, Qazvin, Iran
(fax: þ 2813780040; e-mail: shghamami@ikiu.ac.ir,
shghamami@yahoo.com, imaniehhossein@hotmail.com)
b) Department of Chemistry, Payame Noor University, Abhar, Zanjan, Iran
c) School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
d) Department of Chemistry, Faculty of Science, Shahid Beheshti University, Tehran, Iran
e) Department of Chemistry, Science and Research Campus, Islamic Azad University, Poonak, Tehran,
Iran
Benzyl(triphenyl)phosphonium dichloroiodate (BTPPICl2), BnPh3Pþ(ICl2)ꢀ, is easily synthesized
in a nearly quantitative yield by the addition of BnPh3PþClꢀ to a CH2Cl2 solution of iodine monochloride
(ICl). BnPh3PþClꢀ can be prepared by the reaction of Ph3P and BnCl. The compound was characterized
1
by physicochemical and spectroscopic methods (elemental analysis, FT-IR, and H-NMR). The use of
phosphonium counterion improves the quality of the BTPPICl2 crystals. BTPPICl2 crystallizes in the
monoclinic system, and its crystal and molecular structure has been determined at 100(1) K by X-ray
diffraction. The structure was solved by the direct method and had refined R value of 0.0637 for 699
reflections (I > 2s(I)), space group P21/n with a ¼ 12.4700(3), b ¼ 13.2196(3), c ¼ 14.4580(3) ꢀ, b ¼
102.6340(10)8, V¼ 2325.67(9) ꢀ3, and Z ¼ 4. The I-atom is coordinated by two Cl-atoms as ligands in
a linear geometry. This compound is a versatile reagent for the efficient and selective iodination of
organic substrates, in particular of aromatic phenols to the corresponding iodo compounds, under mild
conditions. To assess the generality of method, a wide variety of phenols with electron-donating and
electron-withdrawing substituents were studied. BTPPICl2 is a mild iodination reagent, which offers a
new avenue for an expeditious iodination of phenols. The inexpensive, relatively non-toxic reagent, and
mild conditions are the positive features of the procedure and reagent.
Introduction. – In this article, we report the synthesis of the benzyl(triphenyl)-
phosphonium dichloroiodate (BTPPICl), Bn(Ph)3Pþ(ICl2)ꢀ, as iodination agent and
especially the X-ray diffraction data, concerning the crystal and molecular structure of
the compound. There were two primary incentives for the selection of BnPh3Pþ as
counterion. First, quaternary phosphonium ions are often used as phase transfer
catalysts. This could make BTPPICl2 a more efficient and reactive agent. Therefore,
this compound has been used for quantitative iodination of several organic substrates.
It turned out to be more efficient and to possess some advantages over similar
iodination agents in terms of the amount of reagent and solvent required, short reaction
times, and high yields [1 – 13]. Second, quaternary ions such as those with phosphorus
are used as crystal-growing agents. Hence, use of this counterion improved the quality
of the BTPPICl2 crystals. Indeed, the salt crystallized well and was structurally
characterized by single-crystal X-ray diffraction. Furthermore, this compound does not
react with MeCN, which is a suitable medium for studying kinetics and mechanism.
ꢁ 2011 Verlag Helvetica Chimica Acta AG, Zꢂrich

Helvetica Chimica Acta – Vol. 94 (2011)
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Results. – BTPPICl2 is an efficient, mild, and versatile reagent for the iodination of
phenols. The best reagent/substrate ratio was found to lie between 1.05 and up to 4.05
depending on the number of iodination positions. For example, the ratio for the
iodination of phenol to 2,4,6-triiodophenol was 3.05, and 2,6-dimethylphenol to 4-iodo-
2,6-dimethylphenol was 1.05. Using too low reagent/substrate ratios for substrates with
several positions for the iodination led to mixtures of mono and higher iodination
products. An excess reagent/substrate ratio affected neither the yields nor the reaction
time. The reaction of corresponding phenols was performed in CH2Cl2/MeOH 3 :1 at
room temperature (Table 1).
It is noteworthy to mention that all reactions should be conducted at room
temperature, since increasing the reaction temperature above 208 decreases the yields
of the reaction, probably due to oxidation [14 – 17]. To assess the generality of the
method, a wide variety of phenols with electron-donating and electron-withdrawing
substituents were examined.
BTPPICl2 was crystallized by slow evaporation over a week from a MeCN solution.
Discussion. – Benzyl(triphenyl)phosphonium dichloroiodate (BTPPICl2) can be
easily obtained by the addition of BnPh3PþClꢀ to a CH2Cl2 solution of ICl.
The advantages of the new method are: i) there is no side-product, ii) the reaction is
quite fast, iii) mild conditions, and iv) the accompanied color change, which provides a
visual evidence for ascertaining the progress of the reaction.
In summary, BTPPICl2 is an efficient and mild iodination reagent, which offers a
new procedure for an expeditious iodination of phenols. The inexpensive, relatively
non-toxic reagent and mild conditions are the positive features of the procedure.
BTPPICl2 crystallized in the non-centrosymmetric monoclinic space group P21/n
(Fig. 1). The cation and anion moieties were separated from each other and arranged in
an alternative AB layering pattern. The I-atom was coordinated by two Cl-atoms as
ligands in linear geometry. The results of the X-ray diffraction showed that the
structure of this dichloroiodate salt did not form a dimer, trimer, or more multi-nuclear
structures in the solid state (Fig. 2).
New iodination reagent BTPPICl2 was easily synthesized in a nearly quantitative
yield by the addition of BnPh3PþClꢀ to a CH2Cl2 solution of ICl. The compound was
characterized by physicochemical and spectroscopic methods such as CHN analysis,
and FT-IR and 1H-NMR techniques. The use of phosphonium counterion, improves the
quality of the BTPPICl2 crystals. BTPPICl2 crystallizes in the tetragonal system, and its
crystal and molecular structure has been determined at 100(1) K by X-ray diffraction.
The structure was solved by the direct method.
The authors thank Dr. Sadjad Sedaghat and Dr. Seyed Abolfazl Seyed Sadjadi for valuable
discussions.

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Table 1. Iodination of Phenols with BTPPICl2 as an Iodination Agent
Entry
1
Product
Reagent/
substrate
Reaction
time [min]
M.p. (Lit.) [8]
Yield [%]
73
3.05
2.05
2.05
1.05
2.05
2.05
3.05
2.05
150
380
330
220
200
200
80
157 – 159 ([14]: 158 – 159)
2
3
4
5
6
7
8
65 – 67 ([15]: 67)
70
73
82
86
85
92
91
85
99 – 102 ([16]: 102 – 102.5)
82 – 84
87 – 89
148 – 150 ([17]:149 – 150)
40
120 – 122

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Table 1 (cont.)
Entry Product
Reagent/ Reaction
substrate time [min]
M.p. (Lit.) [8]
Yield [%]
92
9
4.05
3.05
1.05
2.05
24
200
140
75
106 – 110
10
11
12
119 – 121 ([18]: 121)
60 – 62 ([19]: 62)
156 – 157 ([20]: 157)
89
75
95
13
14
2.05
1.05
30
30
233 – 235 ([21]: 233)
91
78
70 – 72
15
16
3.05
4.05
20
164 – 166 ([22]: 163 – 165) 88
260
236 – 238
82

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Fig. 1. ORTEP Drawing of the molecule structure of BnPh3Pþ(ICl2)ꢀ
Experimental Part
General. Iodine chloride (ICl; Merck, p.a.) was used without further purification. Solvents were
dried and purified by standard methods. All chemicals were purchased from Merck. The reaction was
followed by TLC monitoring the disappearance of starting materials. Some products are known and were
characterized by comparison of their physical and spectroscopic data with those of authentic samples.
M.p.: Gallekamp instrument; uncorrected. FT-IR Spectra: BOMEM MB-100 instrument, found to be
.
comparable with those reported; ˜n in cmꢀ1 1H- and 13C-NMR spectra: Bruker Avance DRX 500
spectrometer at 500 and 125 MHz, resp.; d in ppm rel. to Me4Si as external standard, J in Hz. All the
chemical shifts are quoted in ppm using the high-frequency positive convention. Elemental analyses:
Heraeus CHN analyzer.
Benzyl(triphenyl)phosphonium Chloride (BTPPCl). To a 500-ml flask equipped with a magnetic
stirrer were added BnCl (100 mmol, 12.65 g) and Ph3P (100 mmol, 26.2 g) at 40 – 508. The mixture was
stirred for 20 min, cooled to r.t., and filtered. The filtered solid was washed with Et2O (2 ꢁ 50 ml),
crystallized, and identified.
Benzyl(triphenyl)phosphonium Dichloroiodate (BTPPICl2). To ICl (16.2 g, 100 mmol) in CH2Cl2
(200 ml) was added at r.t. a soln. of BnPh3PþClꢀ (33.88 g, 100 mmol) in CH2Cl2 (100 ml). After 50 min,
Et2O (100 ml) was added to the mixture, and the mixture was cooled and filtered. Recrystallization from
Et2O afforded 44.57 g (89%) of BTTPPICl2. M.p. 164 – 1668. FT-IR (KBr): 3000 – 3150 (CꢀH, arom.),
2900 – 3000 (CꢀH, aliph.), 1480 – 1615 (C¼C, arom), 700 – 750 (arom.). 1H-NMR (CDCl3): 4.74 (d, J ¼
14.1, PhCH2); 6.96 (d, 2J(H,P) ¼ 7.00, 2 arom. H); 7.19 (d, J ¼ 7.5, 2 arom. H); 7.29 (t, J ¼ 7.8, 1 arom. H);
7.57 (dd, Jo ¼ 7.8, 3J(H,P) ¼ 12.4, arom. H); 7.70 (td, Jo ¼ 7.5, 4J(H,P) ¼ 3.5, arom. H); 7.83 (t, J ¼ 7.4, arom.
H). Anal. calc. for C25H22Cl2IP (551.20): C 55.37, H 4.06; found: C 53.75, H 3.97.
General Procedure for 2,4,6-Triiodophenol (1). To a 250-ml flask equipped with a magnetic stirrer
were added phenol (2 mmol) in CH2Cl2 (30 ml), MeOH (10 ml), BTPPICl2 (6.1 mmol), and NaHCO3
(2 g), and they were mixed at r.t. for 150 min. The progress of the reaction was monitored by TLC

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Fig. 2. Two views of the unit cell of BnPh3Pþ(ICl2)ꢀ
(AcOEt/hexane 2 :1). After the completion, the mixture was filtered, and the liquid was neutralized by
5% NaHCO3 and extracted with Et2O (4 ꢁ 20 ml). The extracted org. layer was separated, dried
(Na2SO4), and evaporated to afford the product. Recrystallization from aq. MeOH afforded 44.57 g
(89%) of 1. M.p. 155 – 1578. FT-IR (KBr): 3200 – 3500 (OH, phenol), 3050 (CꢀH, arom.), 1181 (CꢀO,
1
phenol; CꢀOH, str.), 1623 and 1470 (C¼C, arom., str.). H-NMR (CDCl3): 8.0 (s, 2 arom. H); 5.8 (s,
OH).

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1
Crystal Analysis of BTPPICl2 ). Ayellow crystal of size 0.25 ꢁ 0.20 ꢁ 0.20 mm3 was used for intensity
data set at 100(1) K on a Bruker SMART 1000 CCD area detector diffractometer. The intensity data were
collected within the range 3.508 < q < 28.998 using graphite monochromated MoKa radiation (l ¼
0.71073 ꢀ). Accurate unit cell parameters and orientation matrix for data collection parameters, and
orientation matrix for data collection were obtained from least-squares refinements. Intensities of 5393
reflections were measured, from which 699 reflections with I > 2s(I) were used in the refinement. cf.
(Table 2). The crystal structure was solved by directed methods. Selected bond lengths and bond angles
are given in Table 3.
Table 2. Crystallographic Data and Structure Refinement of BTPPICl2
Empirical formula
Mr
C25H22Cl2IP
551.20
Crystall dimensions [mm]
0.25 ꢁ 0.20 ꢁ 0.20
100.0(1)
0.71073
monoclinic
P21/n
Temp. [K]
Wavelength [ꢀ]
Crystal system
Space group
Z
4
Unit cell parameters:
a [ꢀ]
12.4700(3)
b [ꢀ]
13.2196(3)
c [ꢀ]
14.4580(3)
b [8]
102.6340(10)
2325.67(9)
1.574
1.685
V [ꢀ3]
Dx [Mg mꢀ3
Absorption coefficient [mmꢀ1
]
]
F(000)
1096
q Range for data collection [8]
Index ranges
Reflections collected
3.50 – 28.99
ꢀ 12 ꢂ h ꢂ 12, ꢀ 12 ꢂ k ꢂ 12, ꢀ 7 ꢂ l ꢂ 7
5393
Independent reflections
Completeness to q ¼ 28.998
Absorption correction
Max. and min. transmission
Refinement method
716 (R(int) ¼ 0.0344)
99.1%
Semi-empirical from equivalents
0.488; 0.416
Full-matrix least-squares on F2
716/0/23
Data/restraints/parameters
Goodness-of-fit on F2
1.108
Final R indices (for 699 rfln. with I > 2s(I))
R Indices (all data)
R1 ¼ 0.0637, wR2 ¼ 0.0954
R1 ¼ 0.0390, wR2 ¼ 0.0870
ꢀ 0.03(7)
Absolute structure parameter
Largest diff. peak and hole [e ꢀꢀ3
]
1.587; ꢀ 0.842
X-Ray Data Collection, Structure Determination, and Refinement Procedures. The structure has been
solved by direct methods and refined by full-matrix-least squares techniques on F2. All non-H-atoms
were filtered anisotropically. The position of H-atom was assigned an isotropic thermal parameter. The
values of R, wR with a goodness of fit on F2 of 1.108 are 0.0390 and 0.0870, resp. The final difference
density map showed a maximum peak and hole of 1.587 and ꢀ 0.842 e ꢀꢀ3. All structural calculations
1
)
CCDC-698883 contains the supplementary crystallographic data for BTPPICl2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif.

Helvetica Chimica Acta – Vol. 94 (2011)
2255
a
Table 3. Bond Lengths and Angles for BTPPICl2
Bond angles [8]
)
Bond lengths [ꢀ]
I(1)ꢀCl(1)#1
I(1)ꢀCl(1)
2.6284(5)
2.4980(5)
1.8189(17)
1.7914(16)
1.7918(16)
1.7949(16)
0.9700
Cl(1)#1ꢀI(1)ꢀCl(1)
C(8)#2ꢀP(1)ꢀC(1)#3
C(14)#2ꢀP(1)ꢀC(1)
C(20)#3ꢀP(1)ꢀC(1)
178.220(15)
112.83(8)
107.33(8)
110.56(8)
109.44(8)
108.78(8)
107.81(7)
108.4
P(1)ꢀC(1)#2
P(1)ꢀC(1)#3
P(1)ꢀC(1)
C(14)#2ꢀP(1)ꢀC(20)#4
C(8)#3ꢀP(1)ꢀC(20)#4
C(8)ꢀP(1)ꢀC(14)#4
P(1)ꢀC(1)ꢀH(1A)
P(1)ꢀC(1)ꢀH(1B)
P(1)ꢀC(1)#4
C(1)ꢀH(1A)
C(1)ꢀH(1B)
0.9700
108.4
107.5
H(1A)ꢀC(1)ꢀH(1B)
a) Symmetry transformations used to generate equivalent atoms: #1 ꢀ x þ 2, ꢀ y þ 1, z; #2 ꢀ x þ 2, ꢀ y, z;
#3 y þ 1, ꢀ x þ 1, ꢀ z; #4 ꢀ y þ 1, x ꢀ 1, ꢀ z.
were carried out with SHELXTLV. 5.10 structure determination software; intensity data were collected
on a Siemens SMART CCD diffractometer with graphite-monochromated MoKa radiation. The
compound crystallized in the symmetric space group P21/n that belongs to the monoclinic system.
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Received May 11, 2011