o-Phenylenediamine as a new catalyst in the highly regioselective conversion of epoxides to halohydrins with elemental halogens

Article abstract of DOI:10.1007/s00706-004-0179-5

The regioselective ring opening of epoxides using elemental iodine and bromine in the presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The results indicate that the complex [(Diamine)I]⁺·I5^- is formed, and we suggest that the major nucleophile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity observed attacking the less sterically hindered epoxide carbon. Springer-Verlag 2004.

Full text of DOI:10.1007/s00706-004-0179-5

Monatshefte f €u r Chemie 135, 1101–1111 (2004)
DOI 10.1007/s00706-004-0179-5
o-Phenylenediamine as a New Catalyst
in the Highly Regioselective Conversion
of Epoxides to Halohydrins with
Elemental Halogens
Hossein Eshghi1 , Sayyed Faramarz Tayyari , and Esmaiel Sanchuli
;ꢀ
2
1
1
Department of Chemistry, Sistan and Baluchestan University, Zahedan 98135-674, Iran
Department of Chemistry, Ferdowsi University of Mashhad, P.O. Box 1436,
Mashhad 91774-1436, Iran
2
Received December 2, 2003; accepted (revised) December 17, 2003
Published online June 24, 2004 # Springer-Verlag 2004
Summary. The regioselective ring opening of epoxides using elemental iodine and bromine in the
presence of o-phenylenediamine as a new catalyst affords vicinal iodo alcohols and bromo alcohols in
high yields. The major advantages of this method are versatility, high regioselectivity, a cheap and
commercially available catalyst, mild and neutral reaction conditions, and short reaction times. Fourier
transform Raman spectroscopy was used to study the reaction of iodine with o-phenylenediamine. The
þ
ꢂ
results indicate that the complex [(Diamine)I] ꢁ I5 is formed, and we suggest that the major nucleo-
phile is the pentaiodide ion. This bulky nucleophile has a fundamental role in the high regioselectivity
observed attacking the less sterically hindered epoxide carbon.
Keywords. Catalyst; Diamines; Epoxides; Halohydrin; FT Raman spectroscopy.
Introduction
Epoxides are useful substrates in organic synthesis due to their high reactivity [1].
Conversion of an epoxide to a vicinal halohydrin is a synthetically useful reaction,
which is typically performed with hydrogen halides [2]. Unless there is a structural
or a stereochemical bias, a couple of products is obtained due to the lack of the
regioselectivity in the ring opening step [3]. Moreover, the harsh reaction condi-
tions and the lack of chemoselectivity among various substituted epoxides limit the
synthetic utility of this reaction in multistep synthesis and have prompted a search
for more selective and milder procedures [2]. The ring opening of unsymmetrical
substituted epoxides with Li [NiBr ] [4], pyridine ꢁ HCl [5], haloborane reagents
2
4
[
6–9], Br =PPh [10], Ti(O-i-Pr) [11], chlorosilane [12], [n-Bu N]Br=Mg(NO )
2 3 4 4 3 2
ꢀ Corresponding author. E-mail: heshghi@hamoon.usb.ac.ir

1
102
H. Eshghi et al.
[
13], Lewis acid metal halides [14–17] and Me SiBr [18], TiCl -LiX [14],
3 4
CeCl ꢁ 7H O–NaI [19], SmI [20], POCl or PCl =DMAP [21], HX or LiX=ꢀ-
3
2
2
3
3
cyclodextrin [22], and Et N ꢁ 3HF=MW [23] have been reported. However, these
3
methods are not always fully satisfactory and suffer from disadvantages such as
acidity, handling and in situ preparation of reagent, the noncatalytic nature of the
reagents, lack of versatility, and relatively long reaction times [8, 11, 24–26]. It has
been found that epoxides can be converted into iodohydrins and bromohydrins by
means of elemental iodine and bromine [27], but this method has some severe
limitations, such as low yield and lacking regioselectivity with long reaction times
and formation of acetonide byproducts in addition to the expected iodoadduct.
Furthermore, iodination does not occur using CH Cl , CHCl , C H , CH CN,
2
2
3
6
6
3
and THF as solvents.
Recently, Sharghi et al. [28–33] solved these problems by catalytic ring open-
ing of epoxides with elemental halogens. Some recently new synthesized macro-
cyclic diamides [28, 29], diamine podands [30], Schiff-base complexes of the
first-row transition metals (II) [31], metalloporphyrins [32], and 2-phenyl-2-(2-
pyridyl)imidazolidine [33] were applied successfully as catalysts for this ring
opening reaction. Advantages of these procedures are: high regioselectivity, in-
crease in chemical yield of halohydrin without any side product formation, short
reaction times, and neutral and mild reaction conditions in inert solvents such as
CH Cl .
2
2
In this study, we wish to report the results of the reactions of epoxides with
elemental iodine and bromine in the presence of a catalytic amount of the inex-
pensive and readily available o-phenylenediamine.
Results and Discussion
Aromatic diamines are valuable building blocks for the preparation of polyamides
[34], macrocyclic diamides [35], and azacrowns [36]. Because of these properties
they are inexpensive and commercially available. The diamines 1–3, which are
commercially available, were used as catalysts (Scheme 1). The results of the
Scheme 1

Regioselective Conversion of Epoxides to Halohydrins
1103
Table 1. Reaction of styrene oxide (1 mmol) with elemental iodine (1 mmol) in the presence of
ꢃ
representative catalysts in CH Cl at 25 C
2
2
a
Entry
Catalyst (0.1 mmol)
Conditions
Time=h
Yield=%
Ref.
1
2
3
4
–
–
–
I2, rt=acetone
I , excess=CH Cl
2
2
–
83
0
[27]
[27]
[24a]
2
2
LiI, AcOH, THF, rt
I , rt=CH Cl
1.3
1
87
50
2
2
2
2
5
6
I , rt=CH Cl
2
24
1
80
40
2
I , rt=CH Cl
2
2
2
7
8
I , rt=CH Cl
2
1
>98
>95
2
2
I , rt=CH Cl
2
0.75
[30]
2
2
9
I , rt=CH Cl
2
24
90
2
2
a
Relative yield according to GC
Scheme 2
reactions of styrene oxide with elemental iodine in the presence of 1–3, the above
catalysts, are summarized in Table 1 and are compared with the corresponding
results obtained in recently applied podand catalyst 4 [30] and the macrocyclic
diamide 5 (Scheme 2). In each case, cleavage of the epoxide ring occurs and upon
thiosulfate workup the corresponding iodohydrin was obtained. In comparison, the
cleavage behavior of styrene oxide with elemental iodine in the absence of catalyst
is given in entries 1–3. As shown in Table 1, yields of iodination with this meth-
odology are quite good and catalyst 3 is the most effective one (Table 1, entry 7).
However, iodination of styrene oxide with an excess of elemental iodine in the
absence of catalyst did not occur even under reflux and extension of reaction time
to several days, and unreacted styrene oxide was completely recovered.
Diamine 3 in comparison with the corresponding synthetic macrocyclic di-
amide 5 [28, 35a] and the diamino podand 4 [30, 35b] is the best selection because
it’s inexpensive and readily available with high conversion yield in short reaction
times. The catalyst was easily recovered and could be reused several times.
The results obtained with some representative epoxides in the presence of o-
phenylenediamine (3) as the catalyst are summarized in Table 2 and are compared

1
104
H. Eshghi et al.
Table 2. Reaction of epoxides with elemental bromine and iodine in the presence of o-phenylenediamine (3) as the
catalyst
a
Entry Epoxide
1
Catalyst Mol % Reaction conditions Time=h Yield=%
Product(s)
Ref.
[27]
–
–
–
–
I2, acetone, rt
2
83
2
3
"
"
I2 excess=
CH Cl ,
–
–
No reaction
[27]
2
2
reflux
–
–
LiI, AcOH,
THF, rt
1.3
87 (2:1)
[24a]
4
5
6
7
"
"
"
"
3
3
–
–
10
10
–
I2, rt,
0.25
96
CH Cl
2
2
Br , rt,
2
Immed.
95
CH Cl
2
2
Br , rt,
2
1
5
31
[27]
[13]
CH Cl
2
2
þ
ꢂ
–
n-Bu N Br =
4
78 (1:5)
Mg(NO ) ,
3
2
CHCl , rt
3
8
"
–
–
(Me N) BBr=
2
12
75 (4.5:1)
[8]
2
CH Cl , N ,
2
2
2
atm, rt
9
0
1
2
3
4
5
"
"
–
–
4
3
3
3
3
–
HBr, rt,
CHCl3
0.25
0.25
10
>99
>99
90
[25]
[25]
[30]
1
1
1
1
1
1
–
HI, rt,
CHCl3
10
10
20
20
20
I2, rt,
CH Cl
2
2
2
2
"
"
"
I2, rt,
8
90
CH Cl
2
I2, rt,
4
93
CH Cl
2
Br , rt,
2
1.5
3
95
CH Cl
2
2
I2, rt,
92
CH Cl
2
2
(
continued)

Regioselective Conversion of Epoxides to Halohydrins
Table 2 (continued)
Entry Epoxide
1105
a
Catalyst Mol % Reaction conditions Time=h Yield=% Product(s)
Ref.
1
1
1
1
2
2
2
2
2
2
6
7
8
9
0
1
2
3
4
5
6
3
3
3
3
3
3
3
3
3
3
3
20
20
20
20
20
10
10
20
20
10
10
Br , rt,
2
1.5
4.5
2
94
88
92
85
88
94
96
75
80
82
87
CH Cl
2
2
I2, rt,
CH Cl
2
2
"
"
"
"
"
Br , rt,
2
CH Cl
2
2
I2, rt,
4
CH Cl
2
2
Br , rt,
2
2
CH Cl
2
2
I2, rt,
1
CH Cl
2
2
Br , rt,
2
0.5
5
CH Cl
2
2
I2, rt,
CH Cl
2
2
Br , rt,
2
2.5
3
CH Cl
2
2
I2, rt,
CH Cl
2
2
2
Br , rt,
2
2
CH Cl
2
2
a
Isolated yield
with the corresponding results obtained in the reaction of the same epoxides in the
absence of catalyst (Table 2, entries 1, 2, and 6). On the other hand, some other
methods for conversion of epoxides to the corresponding halohydrins are given in
Table 2, entries 3 and 7–10 for comparison.
When epoxides were allowed to react in the presence of 3, increases in yield
and regioselectivities were observed in all of the reactions studied. However, bro-
mination is faster than iodination cleavage. Generally, the optimum amounts of the
catalysts were found to be 0.1 mol per 1 mol of epoxide and halogen. Thus in the
case of the phenoxy epoxide (Entry 12), when the reaction was carried out using
ꢃ
0.1 equivalent of catalyst at 25 C for 8 h, the corresponding iodohydrin was
obtained in 90% yield. However, the use of a bigger amount of catalyst (0.2
equivalent) provided a shorter reaction time of 4 h to affording the iodohydrin in
93% yield. So, in the cases of entries 13–20, 23, and 24 reactions were reacted in
the presence of 0.2 mol of the catalyst.
In addition, other factors can have a pronounced effect on the observed ratio of
halohydrin isomers and overall yield e.g., rate and order in which the reagents are

1
106
H. Eshghi et al.
combined. For example, if iodine is added to the epoxide before the catalyst, two
isomeric iodohydrins are produced. However, if the epoxide is added to the cata-
lyst, and then iodine is added over a period of time (45 min), only one isomer is
formed. In this case, the rapid addition of iodine reduced the regioselectivity.
A comparison of the reaction of the same epoxide with elemental iodine in the
presence of 4 as the catalyst indicated that an increase in steric hindrance at the
catalyst structure results in a general decrease in the rate of halohydrin formation
(
long reaction times, Table 2, entry 11).
Recent studies of a halogenative cleavage of epoxides with elemental halogens
showed that in the absence of a catalyst, iodination does not occur in CH Cl ,
2
2
CHCl , C H , and CH CN as solvents, while it occurred in acetone solution with
3
3
6
6
some limitations [27]. Whereas in the presence of a catalyst halogenations proceed
28–33] most cleanly in CH Cl , CHCl , C H , and CH CN solutions, whereas,
those done in THF and acetone led to a lower yield of halohydrins. Now, our
[
2
2
3
6
6
3
observations showed that iodine solutions in CH Cl , CHCl , and C H cannot
2
2
3
6 6
produce a polyiodide ion, whereas in acetone concomitantly with the disappearing
of iodine bands a strong absorption band is observed at 364 nm corresponding to
ꢂ
ꢂ
I3 or I5 and the iodine bands have vanished. The intensity of this band in THF
and CH CN decreased in this order: acetone>THF>CH CN, presumably due to
3
3
the complex formation between iodine and electron pair donor ligands [37, 38]. So,
we suggest that the useful solvents for the catalytic cleavage of epoxide rings by
elemental halogens are those without electron pair donors, such as CH Cl , CHCl ,
2
2
3
and C H , whereas for non-catalytic cleavage acetone is a properly selected
6
6
solvent.
The variation in yield and rate of cleaving epoxides by elemental iodine or
bromine in the presence of a catalyst can be satisfactory rationalized in terms of the
suggested mechanism [28–33]. In support of this mechanism, the UV spectra of
iodine, catalyst 3, and complex formation between iodine and catalyst 3, and
complex formation of iodine with all used catalysts in dichloromethane solution
ꢃ
at 25 C are shown in Figs. 1 and 2. As can be seen from Fig. 1, none of the initial
Fig. 1. Absorption spectra of: (1) o-phenylenediamine 3; (2) iodine; (3) complex of o-phenylene-
diamine 3 with iodine in dichloromethane solution

Regioselective Conversion of Epoxides to Halohydrins
1107
Fig. 2. Absorption spectra of iodine (1) and complexes between iodine and the used catalysts:
macrocyclic diamide 5 (2); piperazine 2 (3); ethylene diamine 1 (4); diamino podand 4 (5);
o-phenylenediamine 3 (6)
reactants show any measurable absorption in the 315–445 nm region, whereas the
addition of diamine 3 to iodine results in a strong absorption band at 362 nm,
presumably due to the complex formation of iodine with diamine 3. It should be
noted that the band at 362 nm is characteristic for the formation of polyiodide ions
ꢂ
ꢂ
such as I3 and I , in the process of complex formation between iodine and
5
electron-pair-donating nitrogen atoms [37, 38]. It is well known that both ions
absorb in the same region around 360 and 290 nm with little deviation in their
absorptions [37c, 37e].
As shown in Fig. 2, in all cases a characteristic band at 362 nm was observed,
which is specific for the formation of polyiodide ion. The intensity of this band,
as evidence for the ease of formation of polyiodide ion, decreased in the order
3
>4>1ꢄ2>5. In the cases of 3 and 4 this band appeared immediately and
corroborated the much faster complexation of iodine with these catalysts.
Photometric titrations of 3 by iodine, monitoring the absorbance at 360 nm,
showed that until one equivalent of iodine is consumed, no absorption is detected.
However, with addition of an excess of iodine an absorption band developed at
ꢂ
360 nm that is characteristic for the formation of polyiodide ions, such as I and
I . The intensity of this band increased until three equivalents were consumed.
3
ꢂ
5
While the molar ratio of iodine:diamine was increased up to 4:1, a new absorption
band developed at 505 nm that is characteristic for excess of iodine. Accordingly,
þ
ꢂ
þ
the polyiodides complex might be identified as [(Diamine)I] ꢁ I . The proposed
5
þ
[
(Diamine)I] type of the cation is analogous to [(HMTA)I] reported by
Bowmaker et al. [39] in the reaction of iodine with hexamethylenetetramine (HMTA)
þ
þ
and also to [(TACTD)I] and [(TODACOD)I] reported by Nour et al. [38], to be
formed in the reaction of iodine with the cyclic polyamine 1,4,8,11-tetraazacyclo-
tetradecane (TACTD) and 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (TODA-
COD). On the other hand, the formation of I5 ions has been reported [40] to be
formed in the reactions of iodine with trimesic acid (TMA) and (CH ) NI.
ꢂ
3
4
On cooling, the mixture deposited a brown solid complex and the structure of
this complex was studied. The Raman and the far-IR spectra of the diamine-iodine
complex in the solid phase are shown in Figs. 3 and 4. According to the earliest
mentioned mechanism [28–33], we initially concentrated on the spectral features
of the triiodide systems [38–42], since we believed that these display the

1
108
H. Eshghi et al.
Fig. 3. The Raman spectra of [(Diamine)I] ꢁ I5ꢂ ( — ) and 3 (- - -)
þ
Fig. 4. The far-IR spectra of [(Diamine)I] ꢁ I5ꢂ
þ
fundamental role in the course of the reaction. The Raman spectra of the triiodide
ꢂ1
systems exhibit a sharp band at 110 cm and additional weak bands in the region
ꢂ
ꢂ1
ꢂ
ꢂ
of 130–170 cm , whereas the other polyiodides, such as I , I , and I , pro-
5
7
11
ꢂ1
duce an increase in intensity of the band at about 170 cm relative to the band at
ꢂ1
110 cm . This band also shifts to higher wavenumbers until it reaches that of free
iodine (approx. 180 cm ). Solid I is known [40] to show a Raman active stretch-
ꢂ1
2
ꢂ1
ing frequency near 190 cm which was not observed in our spectrum. The com-
parison of the Raman results with reported data [38b, 41, 42] (Table 3) on the
pentaiodide systems strongly suggests the identity of the major chromophore with
ꢂ
ꢂ1
the pentaiodide (I ) anion. The strong scattering band at 162 cm was assigned
5
ꢂ
to a fundamental normal mode of vibration in I . Thus we suggest that the major
5
nucleophile in the course of the reaction is I , and this bulky nucleophile has a
5
ꢂ
fundamental role in the high regioselectivity observed attacking on the less steri-
cally hindered epoxide carbon.
Accordingly, it is supported that the halogenative cleavage of epoxides occurs
by the following four-step mechanism: The first step involves the formation of a
1:3 or 2:3 molecular complex between diamine and elemental halogen, in which

Regioselective Conversion of Epoxides to Halohydrins
1109
Table 3. Fundamental stretching vibrations for some pentaiodide ions
ꢂ1
ꢂ1
Far-IR, ꢁꢀ =cm
Entry
Pentaiodide complexes
Ref.
Raman, ꢁꢀ =cm
þ
ꢂ
1
2
[(Diamine)I] ꢁ I5
162 vs, 154 sh,
141 m, 97 sh, 63 s
ꢅ170 s, ꢅ154 sh,
ꢅ110 w
183 w, 160 sh,
(
present work)
ꢂ
144 vs, 100 mw
þ
[Et S] I5 [41]
3
160 sh, 145 s, 85 m
þ
ꢂ
ꢂ
3
4
[(TODACOD)I] ꢁ I5 [38b]
164, 137 m, 110, 87
165 sh, 143 s
[(Mn(modtc) ]I ꢁ 2I [42]
3
2
Scheme 3
Scheme 4
ꢂ
the pentahalide ion (X ) exists as an intimiate ion pair: Diamine þ 3X !
5
2
þ
ꢂ
þ
ꢂ
5
(
Diamine. . .X )X
or 2Diamine þ 3X ! (2Diamine. . .X )X . In the second
ꢂ
5
5
2
step this complex is further decomposed to release X ion into solution as:
þ
ꢂ
þ
ꢂ
(
Diamine. . .X )X ! (Diamine. . .X ) þ X .
5
5
Thus, in this way molecular halogen is converted to a nucleophilic halogen spe-
cies in the presence of a suitable diamine. In the third step this ion participates in the
ring opening reaction of epoxides (Scheme 3). Finally, the catalyst is regenerated in
step 4 (Scheme 4). These steps occur continuously until all of the epoxides and
halogen are consumed and after workup, the catalyst can be recovered easily.
The decrease in regioselectivity that results by merely reversing the order of
mixing of epoxide and halogen, namely the slow addition of epoxide to bromine or
fast addition of bromine to epoxide before the catalyst was added can readily be
understood from this model. When the initial epoxide was introduced (in the
absence or presence of catalyst) it would encounter an excess amount of bromine;
electrophilic attack by bromine can then occur, giving the more stable carbonium
ion-like transition state, and bromine anions will attack the more substituted car-
bon. On the other hand, slow addition of bromine to the mixture of catalyst and
epoxide fosters the four-step mechanism presented above in which all of the ele-
ꢂ
mental bromine is converted to Br5 by the catalyst and it then attacks the less
substituted carbon selectively.
In conclusion, we have found that inexpensive and readily available 3 can
catalyze the regioselective ring opening of epoxides by elemental iodine and

1
110
H. Eshghi et al.
bromine under neutral conditions with a variety of sensitive functional groups, as
well as that it is a convenient procedure, which makes this synthetic technique
highly useful. Resonance Raman spectroscopy indicated that the complex
þ
ꢂ
[
in the course of the reaction is the pentaiodide ion, I . This bulky nucleophile
(Diamine)I] ꢁ I is formed. Accordingly, we suggest that the major nucleophile
5
ꢂ
5
plays a fundamental role in the high regioselectivity observed. It is due to an attack
on the less sterically hindered epoxide carbon.
Experimental
All materials and solvents were obtained from Merck (Germany) and Fluka (Switzerland). Melting
points were determined in open capillary tubes in an Electrothermal IA 9000 melting point apparatus.
1H NMR spectra were recorded on a Bruker-80 MHz instrument using TMS as an internal standard.
UV-Vis spectra were obtained with a JASCO spectrometer. IR spectra were recorded on a Shimadzu-IR
ꢂ1
4
70 spectrometer. The far-IR spectrum in the region 650–50 cm was obtained using a Thermo
Nicolet NEXUS 870 FT-IR spectrometer equipped with a DTGS=polyethylene detector and a solid
ꢂ1
substrate beam splitter. The spectrum was collected with a resolution of 4 cm by coadding the results
ꢃ
of 125 scans. The Raman spectrum was recorded employing a 180 back-scattering geometry and a
Bomem MB-154 Fourier transform Raman spectrometer. It was equipped with a ZnSe beam splitter
and a TE cooled InGaAs detector. Rayleigh filtration was afforded by a set of two holographic
ꢂ1
technology filters. The spectrum was collected with a resolution of 4 cm by coadding the results
of 1000 scans. The purity determination of the substrates and reaction monitoring was accomplished by
TLC on silica gel polygram SILG=UV 254 plates or GLC on a Shimadzu GC-10A instrument with a
flame ionization detector using a column of 15% carbowax 20M chromosorb W acid-washed 60–80
mesh. Column chromatography was carried out on short columns of silica gel 60 (230–400 mesh) in
glass columns (2–3 cm diameter) using 15–30 g silica gel per 1 g of crude mixture. Compounds 4 and 5
were obtained according to Ref. [35].
General Procedure for Halogenative Cleavage of Epoxides
3
Epoxide (1mmol) in 5 cm of CH Cl was added to a stirred solution of 0.1–0.2 mmol of o-phenyl-
2
2
3
enediamine (3) in 5 cm of CH Cl at room temperature. Next, a solution of 1 mmol of elemental
2
2
3
halogen in 10 cm of CH Cl was added dropwise during 45min. The progress of reaction was
2
2
monitored by TLC and GLC. After complete disappearance of the starting material, the reaction
3
3
mixture was washed with 2ꢆ10 cm of 10% aqueous Na S O and 2ꢆ10cm of H O. The aqueous
2
2
3
2
3
layer was further extracted with 2ꢆ10cm of CH Cl . The combined organic layer was dried (anh.
2
2
MgSO ) and the solvent was evaporated. The crude product was purified by chromatography on a
4
column of silica gel. The halohydrins obtained throughout this procedure were identified by compar-
ison with authentic samples prepared according to literature procedures [17, 22, 24a, 28].
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Regioselective Conversion of Epoxides to Halohydrins
1111
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