Routes for reactions of alkylene oxides with R-β-hydroxyalkyl sulfides: Unusual exchange of functional groups

Article abstract of DOI:10.1134/S0965544112010069

Possible routes of the previously unknown exchange reaction of alkylene oxides with R-β-hydroxyalkyl sulfides have been considered. Each route has intermediates and transition states of its own, but all the directions in the final stage lead to the formation of a single intermediate cyclic bipolar ion with intramolecular hydrogen bonding, which determines the common nature and composition of end products for all routes. The features of the reaction have been analyzed. The quantitative description of each route has been given. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0965544112010069

ISSN 0965ꢀ5441, Petroleum Chemistry, 2012, Vol. 52, No. 3, pp. 194–203. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.D. Malievskii, 2012, published in Neftekhimiya, 2012, Vol. 52, No. 3, pp. 220–229.
Routes for Reactions of Alkylene Oxides with RꢀβꢀHydroxyalkyl
Sulfides: Unusual Exchange of Functional Groups
A. D. Malievskii
N.M. Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 117334 Russia
eꢀmail: chembio@sky.chph.ras.ru
Received June 13, 2011
Abstract—Possible routes of the previously unknown exchange reaction of alkylene oxides with Rꢀβꢀ
hydroxyalkyl sulfides have been considered. Each route has intermediates and transition states of its own, but
all the directions in the final stage lead to the formation of a single intermediate cyclic bipolar ion with
intramolecular hydrogen bonding, which determines the common nature and composition of end products
for all routes. The features of the reaction have been analyzed. The quantitative description of each route has
been given.
DOI: 10.1134/S0965544112010069
Earlier it was shown [1] that upon the interaction of The analysis and identification of the reactants and
alkylene oxides with organic compounds of the eleꢀ
ments of 5aꢀ and 6aꢀsubgroups of the periodic table
products were carried out using a variety of instrumenꢀ
tal methods (GLC [5–10], infrared spectroscopy
[11]); the structure of the compounds was determined
by the proton NMR technique [5, 6, 8, 9].
containing
βꢀhydroxyalkyl groups (βꢀhydroxyalkyl
sulfides, ꢀselenides, ꢀamines, ꢀphosphines) at S, Se, N
and P heteroatoms in the lower valence state an
unusual reaction of the exchange type was discovered.
In this reaction, alkylene oxide and an organic comꢀ
pound of a structure different from that of the original
RESULTS AND DISCUSSION
(1) with βꢀhydroxyalkyl group at heteroatom Z are
formed as products [1, 2, 3]:
The main feature of the reaction is that alkylene
oxide and
exchange radicals R1 and R3. As a result of this
exchange, alkylene oxide and ꢀhydroxyalkyl sulfide
βꢀhydroxyalkyl sulfide react as if they
1
R CH–CH2 + R2n – 1ZCH2CH(R3)OH
β
with radicals R3 and R1 are formed, respectively. Such
nonspecific exchange by functional groups is unusual.
A similar reaction of the exchange type has been
shown by numerous examples with R1 = H, CH3,
C2H5, CH=CH2, C6H5, CH2OC2H5, CH2OC4H9,
O
(1)
R3CH–CH2 + R2n – 1ZCH2CH(R1)OH
O
where Z is S, Se, N, or P; n is their lower valence state;
CH2OC6H5
CH3, C6H5, CH2OC6H5 [1, 2, 4–9]. In all the cases a
, ;
R2 =C6H5, C6H4CH3, C8H17 R3 = H,
and R1, R2, and R3 are radicals that do not contain
hydroxyl groups. Reaction (1) is reversible, and after
some time the system reaches the state of dynamic relationship between the structure of the product alkyꢀ
equilibrium.
lene oxide and the structure of the reactant
ꢀhydroxyalkyl sulfide, ꢀselenide, ꢀamine, and ꢀphosꢀ
phine has been established as well. This structure is
determined by the constitution of ꢀhydroxyalkyl
group of the parent alcohol containing the heteroatom
[1, 4, 7]. For example, the reaction of ꢀdihydroxyꢀ
ethylpropyl sulfide with phenyl glycidyl ether proceeds
to yield ethylene oxide from the hydroxyethylene
oxide group and propylene oxide from the hydroxꢀ
β
EXPERIMENTAL
ꢀhydroxyalkyl sulfides, βꢀhydroxyꢀ
alkyl disulfides, ꢀselenides, ꢀamines, and ꢀphosphines,
their purification, and elemental analysis were perꢀ
formed by standard methods [4–8]. The experiments
were conducted in temperatureꢀcontrolled glass and
metal ampoules in chlorobenzene and other solvents
β
Synthesis of
β
β,β'
at temperatures ranging from 75 to 180°С [1, 4, 6, 9]. ypropylene oxide group [4]:
194

ROUTES FOR REACTIONS OF ALKYLENE OXIDES
195
Table 1. Mass balance between the consumed reactant
= 145 C; solvent, chlorobenzene)
n
ꢀoctylꢀ
10
βꢀhydroxyethyl sulfide and the product ethylene oxide
(
T
°
τ
, min
0
20
30
40
50
60
70
Reactants
ꢀOctylꢀ ꢀhydroxyethyl sulfide mol/L
n
β
1.94
0
1.86
0.08
100
1.79
0.15
99
1.72
0.22
100
1.67
0.26
100
1.65
0.29
98.5
1.64
0.29
98
1.64
0.29
98
Ethylene oxide (product) mol/L
Product balance, %
–
OH
+PhOCH CH–CH
2
2
O
CH2–CH2
CH2CH(CH2OPh)OH
O
+ S
CH2CH2
CH2CH(CH3)OH
CH2CH2OH
.
(2)
S
CH2–CHCH3 + S
CH2CHCH3
OH
+PhOCH CH–CH
2
2
CH2CH(CH2OPh)OH
O
O
So, for the reaction of phenyl glycidyl ether (initial
oxirane concentration of 4.23 mol/L) with ꢀoctylꢀ
hydroxyethyl sulfide (initial concentration, 1.94 mol/L) ypropyl sulfide), the products are phenyl glycidyl ether
When reaction (3) is run in the opposite direction
n
βꢀ
(propylene oxide with ꢀoctylꢀ ꢀhydroxyꢀ ꢀphenoxꢀ
n
β
γ
conducted at 145.5
lished in 45–50 min after the start of the experiment
with an equilibrium constant of е= 0.013. In this proꢀ
°
С
, the equilibrium state is estabꢀ and
nꢀoctylꢀ
β
ꢀhydroxypropyl sulfide [1, 4]:
CH8CH17
К
cess, a permanent mass balance between the reactants
and the products is observed during the process (Table 1).
H3CCH–CH2 + S
O
CH2CH(CH2OPh)OH
(4)
The reaction of phenyl glycidyl ether with
βꢀhydroxypropyl) sulfide in chlorobenzene leads to
n
ꢀoctylꢀ
C8H17
(
K
'
e
+ S
propylene oxide and
octyl) sulfide [1, 4].
βꢀhydroxyꢀ
γ
ꢀphenoxypropylꢀ(
nꢀ
PhOCH–CH2
CH2CH(CH3)OH.
O
C8H17
'
For this reaction, Ke = 0.33 (150°С), while Ke =
PhOCH2CH–CH2 + S
O
'
'
1/Ke = 3.03 (150°С), where Kе and Ke are the equilibꢀ
rium constants measured in two experiments
described above.
CH2CH(CH3)OH
CH8CH17
(3)
K
e
It interesting that for the propylene oxide
+ S
H3CCH–CH2
(0.75 mol/L)–
mol/L) system at low reactant concentrations and
150 in chlorobenzene, the equilibrium state is
nꢀoctylꢀβꢀhydroxyethyl sulfide (0.063
CH2CH(CH2OPh)OH.
°
С
After a few hours, the system reaches the state of
dynamic equilibrium with an equilibrium constant of
reached in ~100 h [1].
Along with reaction (1) for compounds with Se, N,
or P heteroatoms, reactions leading to the formation
of carbonyl and unsaturated compounds [1] occur,
which impede establishment of the dynamic equilibꢀ
rium.
Ке =3.03 (150
between the reactants and products holds as well. The
equilibrium constant Ке (150 С) for reaction (3) is
constant to be 3.0–3.05 when the initial sulfide and
oxirane concentrations respectively vary from 2 to
4.2 and from 4.1 to 0.7 mol/L (molar ratio of 1 : 2, 1 :
°С). In this case, the material balance
°
In those rare instances when OH groups disappear
1, 2 : 1, and 5.5 : 1). With increasing temperature, the in the system, the state of dynamic equilibrium is not
equilibration time for reaction (3) decreases from 8– established. This is typical of systems with two
10 h at 140оС to 2 h at 180оС. The equilibrium conꢀ hydroxyl groups at the heteroatom. For example, in
stant Ке for the reaction in the temperature range of reactions involving bis(
140–190оС does not change (3.0–3.06), i.e., the heat which the exchangeꢀtype reactions were first observed
of the reaction is . In other cases, the heats of [2], we determined the presence of oxothianes as byꢀ
reactions for the phenyl glycidyl ether–Rꢀ ꢀhydroxꢀ products formed as a result of the dehydration of sulꢀ
βꢀhydroxyalkyl) sulfides, for
Q
≅ 0
β
ypropyl sulfide system (R = C6H5
C8H17) range from –3.7 to 0 kcal/mol.
,
pꢀ
CH3С6Н4, fides [1]. In this case, the system does not reach the
state of dynamic equilibrium. The same was observed
PETROLEUM CHEMISTRY Vol. 52
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196
MALIEVSKII
in the specific reaction of glycidol with
β
ꢀhydroxyproꢀ oxide in the same solvent were taken at 25°С (in the
pyl sulfide [1, 4]. The reason for this is apparently the region of stretching vibrations 3000–4000 cm–1) at
pinacol rearrangement [12] of dihydroxyalkyl sulfide sulfide concentrations varied from 2.72
formed during the exchange reaction; the rearrangeꢀ 4.34
10–2 mol/L [11]. Bands with maxima at 3655
ment leads to a compound that does not contain and 3559 cm–1 were detected for hydroxyethyl sulfide,
×
10–3 to
×
β
ꢀhydroxyl group (5):
which were attributed to the stretching vibrations of
free (in monomer) and bound (in dimer) hydroxyl
groups, respectively. The concentrations of the sulfide
monomeric and dimeric forms were calculated, and
their absorption coefficients and the constants of equiꢀ
librium between them were determined as well.
To prove the formation of the Hꢀbonded complex
upon the interaction of propylene oxide with octylꢀβꢀ
hydroxyethyl sulfide, the IR spectra of their solutions
C8H17
HOCH2CH–CH2 + S
O
CH2CH(CH3)OH
C8H17
(5)
+ S
CH3CH–CH2
O
CH2CH(OH)CH2OH.
in ССl4 were measured. The sulfide concentration was
–H O
2
maintained constant (3.73–3.96)
the concentration of propylene oxide varied in the
range from 6.6
10–3 to 0.7 mol/L.
×
10–2 mol/L, when
C8H17SCH2COCH3
×
Propylene oxide is optically transparent in the freꢀ
quency range of 3000–4000 cm–1. The IR spectra of
octylꢀβꢀhydroxyethyl sulfide display two bands, at
Mechanism of the Exchange Reaction
As shown, the alkylene oxide–Rꢀ ꢀhydroxyalkyl
sulfide system is the simplest. In this case, only two
products of the exchange reaction are formed, alkyꢀ
lene oxide and βꢀhydroxyalkyl sulfide, and the system
3655 and 3559 cm–1. With increasing the propylene oxide
concentration, the intensity of the 3655 cm–1 band
decreases without shifting and the band at 3559 cm–1
shifts to lower frequencies to 3540 cm–1 with a simulꢀ
taneous increase in its intensity, which can be
explained by the formation of the complex. Thus, the
region of 3550–3540 cm–1 is characteristic of the OH
stretching vibrations of the dimeric form and the
Hꢀcomplex formed by the interaction of the hydroxyl
group of the monomeric form of hydroxyethyl sulfide
with the oxygen of the oxide ring. The evaluation of
the equilibrium constant for the formation of the
β
reaches the state of dynamic equilibrium.
Despite the seemingly simple nature of the reacꢀ
tion, a number of facts suggests otherwise. For examꢀ
ple, the discrepancy between the overall order deterꢀ
mined experimentally for concentrated solutions of
β
ꢀhydroxyalkyl sulfides and the value that follows from
the stoichiometric equation. The reaction order varies
from 1 to 2 with increasing sulfide concentration. In
addition, acceleration of the exchange by the action of
protonꢀdonor compounds was shown among other
things. In view of the complex nature of the reaction,
to select the right version of the mechanism, the reacꢀ
tion mixture composition for the “propylene oxide–
Hꢀcomplex leads to a value of
The results of processing the spectra of propylene
oxide and octylꢀ ꢀhydroxyꢀethyl sulfide solutions in
Кр = 3
2 l/mol.
β
CCl4 are shown in Table 2.
The [C]c–[A][B] curve, where Cc is the Hꢀcomplex
nꢀoctylꢀβꢀhydroxyethyl sulfide” system was studied in and A and B are hydroxyalkyl sulfide and propylene
detail, kinetic and spectral measurements were made, oxide, respectively, clearly indicates the formation of
and quantumꢀchemical calculations of the system the 1 : 1 complex only. Thus, the reaction mixture conꢀ
were performed.
tains free alkylene oxide, monomer and dimer of
ꢀhydroxyalkyl sulfide, and the Hꢀcomplex of alkyꢀ
β
In the kinetic study, the procedure consisted in the
determination of the dependence of the reaction rate
on the concentration of one component at a low conꢀ
stant concentration of the other. It was shown experiꢀ
lene oxide with one molecule of
βꢀhydroxyalkyl sulꢀ
fide.
In choosing the options for the exchange reaction
mentally [11, 13–15] that at a constant sulfide conꢀ mechanism, it was taken into account that the order in
centration, the reaction rate increases with an increase ꢀhydroxyalkyl sulfide changes with increasing its
in the concentration of alkylene oxide up to a definite concentration in the reaction mixture from 1 (for conꢀ
value of its concentration. Above this value, the reacꢀ centrations 0.3–0.5 mol/L) to 2 (for concentrations
β
≤
tion rate slows down and subsequently remains almost above 0.8–0.9 mol/L), whereas it is 1 in alkylene oxide
constant or close to a limiting value, since the sulfide and does not change over a wide range of its concenꢀ
is almost entirely bound in a complex at an excess of trations. This was shown by the example of propylene
alkylene oxide. Along with the
monomer and dimer, alkylene oxide and Hꢀcomplexes cidyl ether–phenylꢀ
involving the principal reactants starting materials are glycidyl ether–tolylꢀ
assumed to present in the mixture. To prove the formaꢀ other systems [1, 4, 11, 16, 17]. The discrepancy
tion of the complex, the IR spectra of octylꢀ ꢀhydroxꢀ between the overall reaction order in ꢀhydroxyalkyl
yethyl sulfide in ССl4 and its mixture with propylene sulfide determined experimentally for concentrated
β
ꢀhydroxyalkyl sulfide oxide–
n
ꢀoctylꢀ
β
ꢀhydroxyethyl sulfide, phenyl glyꢀ
ꢀhydroxypropyl sulfide, phenyl
ꢀhydroxypropyl sulfide, and
β
β
β
β
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ROUTES FOR REACTIONS OF ALKYLENE OXIDES
197
Table 2. Results of processing the IR spectra of an
25 C. Dm Dmix d, and Dc are the optical densities of monomer sulfide, mixture of the sulfide dimer with a complex,
dimeric sulfide, and a sulfide monomer–oxirane complex, respectively
nꢀoctylꢀβꢀhydroxyethyl sulfide–propylene oxide mixture in CCl4 at
°
,
, D
Concentrations of monomer,
dimer and complex
Concentration
Optical densities
Dmix
[A]o
mol/L
sulfide
Dm
Dd
ν =
Dc
ν ≈
3559 cm–1 3540 cm–1
×
104 [C]c
[A]m 2[A]d
mol/L mol/L
[B]o mol/L
propylene oxide
[B]b
(mol/L)2 mol/L
ν
=
ν
= 3559–
3655 cm–1
3540 cm–1
0.040
0.040
0.040
0.039
0.040
0.039
0.590
0.037
0
0.17
0.17
0.16
0.16
0.15
0.14
0.12
0.10
0.29
0.30
0.31
0.31
0.32
0.37
0.40
0.46
0.30
0.30
0.27
0.27
0.24
0.21
0.15
0.11
0
0.0128 0.0265
0.0128 0.0274
0.0120 0.0247
0.0120 0.0247
0.0113 0.0126
0.0105 0.0188
0.0090 0.0138
0.0075 0.0096
0
0
0.040
0.057
0.091
0.165
0.314
0.038
0.689
0.0
5.12 0.00
6.61 0.0028
10.62 0.0028
0.035
0.040
0.080
0.165
0.250
0.355
18.0
31.9
51.9
50.2
0.0066
0.0093
0.0150
0.0202
solutions and the value that results from the stoichioꢀ electron density during the course of the chemical
metric equation shows the complex nature of the
exchange reaction.
reaction and ascertaining the formation of the hydroꢀ
gen bond. The calculation showed that the probable
reaction mechanism involves three stages with two
The following routes of the development of the
exchange reaction were suggested: 1) for dilute soluꢀ intermediate products corresponding to the transition
tions of Rꢀ
βꢀhydroxyalkyl sulfides (concentration
states and final products [18].
≤
0.1–0.15 mol/L): monomolecular intramolecular
Let us describe in more detail the formation of the
preꢀreaction Hꢀcomplex and bipolar ion II, which
predetermine the course of the reaction and the comꢀ
position and nature of the final products (Figs. 1, 2).
The reactants (alkylene oxide and sulfide) are characꢀ
terized by uneven charge distribution and have noticeꢀ
attack of the sulfide sulfur atom on the carbon atom of
the oxide ring in the Hꢀcomplex; 2) for concentrated
solutions of Rꢀ
0.4 –0.7 mol/L): (a) the interaction of Hꢀcomplex
with a second molecule of ꢀhydroxyalkyl sulfide and
βꢀhydroxyalkyl sulfides (concentration
≥
β
(b) the interaction of two Hꢀcomplexes.
Experiments have shown that for all the directions
of the reaction the nature and composition of the
products are the same.
4
Dilute solutions of Rꢀβꢀhydroxyalkyl sulfides (conꢀ
centration 0.1–0.15 mol/L); forward reaction. For the
≤
3
first version of the exchange reaction mechanism,
semiempirical calculations (PM3) of changes in the
structure and energies of reactants, intermediates,
transition states and final products were carried out for
6
5
1
2
the model reaction of propylene oxide with methylꢀ
βꢀ
hydroxyethyl sulfide [18]:
17
11
20
8
CH3
7
CH3CH–CH2 + S
O
CH2CH2OH
CH3
(6)
CH –CH
2
2+ S
CH2CH(CH3)OH.
O
The structures of reagents and possible intermediꢀ
ates were determined, as well as the heat of formation,
charge distribution, and bond orders. The reaction
S
C
O
H
Fig. 1. Preꢀreaction complex I. Only the atoms that particꢀ
ipate in the exchange reaction are numbered.
order (n) was used for analyzing the “spillover” of
PETROLEUM CHEMISTRY Vol. 52
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198
MALIEVSKII
lene oxides with the RS– sulfide ion [19]. As a result,
the Hꢀcomplex transforms in the monomolecular
mode with the concerted rupture and formation of
corresponding bonds into the products through a
number of intermediates and transition states, includꢀ
ing intermediate cyclic bipolar ion II with intramolecꢀ
ular hydrogen bonding [1, 2, 18]. In this ion, the forꢀ
mation of the intramolecular hydrogen bond with the
proton at the center of the (О…Н…О)– fragment is
observed (Fig. 2). The charge on the bridging proton
changes little (+0.30, +0.28) in the process. The
bridging distances d(02ꢀ07) also change slightly: 2.68,
2.70 Å. The formation of complexes with fragments of
the (A…H…B) type with a central proton was also
observed in the ionization of organic compounds in
solutions of acids and bases [20–23].
In the bipolar ion II in accordance with the elecꢀ
Fig. 2. Intermediate II (a bipolar ion).
tronic structure of the sulfur atom three of four sp3
ꢀ
hybridized orbitals form σꢀbonds with C atoms, the
fourth is occupied by a lone electron pair. The S(4)–
C(3), C(5), C(6) node is a pyramid [18] with the sulfur
atom in the apex and C3–S4–C5, C5–S4–C6, and
able, although not very high dipole moments of 1.83
and 2.11, respectively. In alkylene oxide the largest
negative charge (–0.27) concentrates on the oxygen
atom; in methylhydroxyethyl sulfide, the highest posꢀ
itive charge (+0.19) is on the hydroxyl hydrogen atom.
Obviously, it is by these atoms that the reactants most
closely approach one another in the preꢀreaction conꢀ
formation and, hence, facilitate hydrogen bonding
(Fig. 1), confirming the results of earlier experiments
[11, 14].
C6–S4–C3 angles of 105°. The positive charge is conꢀ
centrated mainly on the S(4) sulfur atom (+0.58); the
negative one, on the O(7) oxygen atom (–0.75), and
the distance between them is 3.06 Å. As a result, the
dipole moment is rather high (7.6 D).
Despite the fact that the O7–H8 distance (1.72 Å)
is much greater than the O2–H8 distance (0.98 Å), the
O7–H8 bond order is not negligible yet (0.09); the
O7–H8–O2 hydrogen bond (due in part to the
sequence of charges on the atoms of the chain: –0.75,
+0.28, –0.39) stabilizes the eightꢀmembered structure
of the ion II. The O2–H8–O7 bridge is retained
throughout all the process until the formation of the
final products.
The calculations showed that the O2–C3 bond in
preꢀreaction complex I (Fig. 1) is somewhat weakened
(
n
= 0.94). The bond orders in the O2(–0.30)–
H8(+0.24)–O7(–0.37) bridge are 0.04 and 0.87 [18].
Being small (0.04), the bond order of the hydroxyl
n
hydrogen bond with the oxygen of propylene oxide is
still different from zero. The S4 sulfur atom of the sulꢀ
fide and carbon atom C3 of the oxirane experience
The unimolecular transformation of the cyclic
bipolar ion II into the final reaction products occurs in
the following way. When attacking the СН2 group
bonded to the sulfur atom by nucleophilic fragment
interaction, although weak (n = 0.02), but it is probaꢀ
bly sufficient for spatial orientation necessary for furꢀ
ther structure rearrangement (1). The supposed secꢀ
ond stage of the reaction is the nucleophilic attack of
the sulfide sulfur atom on the oxide ring inside the
Hꢀcomplex (rateꢀlimiting stage):
О7(q = –0.75), the reaction of the removal of sulfide
easily occurs with breaking the S4–C6 bond and the
simultaneous closure of the O7–C6 bond with the forꢀ
mation of oxirane. With O7 and C6 getting closer,
R2S
changes in the charge
0.5 (2.43, 1.93, 1.44 Å) to be –0.75, –0.59, and
0.28, respectively; the same for (C6), –0.29, + 0.13,
–0.03, and the (С6О7) bond order varied as follows:
–0.07, 0.47, 0.96. The reaction of the conversion of
the bipolar ion into the products is exothermic, Нr
q(О7) were fixed at intervals of
CH2
Å
R1C1H–C3H2 CH(R3)
⎯
q
n
(7)
…
H–O
CH2CH(R1)O
O
Δ
=
k
1
reaction
products
°
°
R2S+
CH2CH(R3)O
ΔHf (Pr) – ΔHf (II) = –18 kcal/mol, and the
–
H
enthalpy of activation is 32 kcal/mol, which is consisꢀ
tent with experimental data for related compounds
(28.4–32.1 kcal/mol) [2, 18].
Steric hindrances in the Hꢀcomplex exert a deterꢀ
mining effect on the direction of the attack of the S
Thus, the determining influence of the structure of
atom and on epoxide ring opening, which goes mainly the preꢀreaction complex I on the course of the proꢀ
on the unsubstituted C3 carbon atom. A similar effect cess as a whole was revealed, the role the of O…H…O
of the steric factor was observed in the reaction of alkyꢀ hydrogen bridge at all stages of the reaction until the
PETROLEUM CHEMISTRY Vol. 52
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ROUTES FOR REACTIONS OF ALKYLENE OXIDES
199
formation of the end products was shown: the reaction cess, the nature and composition of the final products,
occurs with the direct conversion of the bipolar ion II
into the reaction products.
but also the reversible nature of the reaction associated
with prototropic tautomeric equilibrium between
bipolar ions IIA and IIB with the intramolecular
The reaction mechanism involving the cyclic bipoꢀ
lar ion II explains not only the occurrence of the proꢀ hydrogen bond [7, 18, 25].
CH2CH(R1)O
H
CH2CH(R3)O⎯
CH2CH(R1)O–b
CH2CH(R1)O(2)
H(8)
CH2CH(R3)O(7)
R2S+
R2S+b
R2S+
H
CH2CH(R3)O
(IIB)
b
(IIA)
(II)
(8)
R2SCH2CH(R1)OH
R2SCH2CH(R3)OH
+
+
CH2–CHR3
CH2–CHR1
O
O
The intermediate IIA transforms with a simultaꢀ temperature range 120–160
°
С
in chlorobenzene [11].
neous shift of the electron density from O7–H8 bond For the forward direction of the reaction of the system,
to O2–H8 bond through II into the intermediate it was found that 1 =1.52 29400/RT) (for
109 (exp
cyclic bipolar ion IIB with the intramolecular hydroꢀ 150 1= 8.4
107 s–1) and ≠=12.2 en. units,
gen bond while retaining the O2–H8–O7 hydrogen the heat of the Hꢀcomplex I formation – = 2.0
bridge. Quantum chemical calculations showed that in 1.0 kcal/mol (for 150 Ke = 1.85).
k
×
×
⎯
°
С
k
–ΔS
Δ
Н
°
С
the above structures the hydrogen bridge is retained
throughout all the reaction pathway [18]. This reacꢀ
tion is thermally neutral, and the activation barrier is
as low as 4–5 kcal/mol. Intermediates IIA and IIB are
in dynamic equilibrium. The reversible nature of the
reaction was experimentally shown for many pairs of
Similarly, the kinetic characteristics have been
determined for the forward reaction of the ethylethylꢀ
ene oxide (0.10–1.10 mol/L)– R2ꢀ
βꢀhydroxypropyl
sulfide (0.15–0.18 mol/L; chlorobenzene solvent)
system with R2 = С6Н5, СН3С6Н4, C8Н17 [1, 14, 16].
The reaction rate constants
lows depending on the structure of the substituent in
the sulfide: 1.41, 1.58, 8.4 (160 С). The values of the
k ) change as folꢀ
1(107 s–1
the oxirane–R2ꢀ
βꢀhydroxyalkyl sulfide system [1–4].
°
With allowance for the formation of the Hꢀcomꢀ
plex I, the reaction scheme for (6) has the following
form
Hꢀcomplex formation enthalpies, the activation enerꢀ
gies of the rateꢀlimiting step of the exchange reaction
for several alkylene oxide–R2ꢀ
βꢀhydroxyalkyl sulfide
K
e
k
1
А + В
[І]
reaction products,
systems are given in Table 3.
For the reaction in the ethylethylene oxide– R2ꢀ
βꢀ
where A is hydroxyalkyl sulfide and B is oxirane.
Assuming that the equilibrium is established quickly
and the consumption of the complex for the formation
of the products does not violate the equilibrium, the
concentration of the complex can be expressed by
[І] = Кe[А]b[В]b. Since the oxirane concentration in
our case is much higher than the concentration of
hydroxyalkyl sulfide, it can be assumed that
hydroxypropyl sulfide system in a series of R2 = C6H5,
CH3C6H4, C8H17 an increase in the reaction rate conꢀ
stants and a decrease in the activation energies related
to an increase in the electronꢀdonating properties of
the substituents in the sulfide are observed (Table 3).
The heats of formation for the Hꢀcomplexes correꢀ
spond to the heats of formation of the hydrogen bonds
of oxiranes with alcohols [26–28]. The accuracy of
[В]b
tial concentrations of hydroxyalkyl sulfide and
oxirane, respectively. Then, [I] = e[A]o[B]o/(1 +
e[B]o), and the expression for the initial reaction rate
will be as follows:
Wо k1Ke[A]о[B]о/(1+
≅ [В]о, [A]b= [A]о – [I]; [A]o and [B]o are the iniꢀ
determination of both
E
and
Δ
Н
is ~1 kcal/mol.
Concentrated solutions of R2ꢀ
βꢀhydroxyalkyl sulfides
K
(
≥
0.3 mol/L, forward reaction). For concentrated solutions
K
of Rꢀhydroxyalkyl sulfides (concentration 0.3 mol/L),
≥
taking into account the first order in alkylene oxide
and the second order in sulfide after the formation of
the Hꢀcomplex I, the following step of the exchange
reaction occurs, namely, the nucleophilic attack of the
C–O bond of the oxide ring of the Hꢀcomplex I by the
=
Ke[B]о).
Transforming this expression, we get [A ]o /Wo
1 + 1/k1Ke[B]o
=
1/k
.
Using it, the values of k1 and Кe for the propylene sulfur atom of a second molecule of Rꢀhydroxyalkyl
oxide (0.15–1.95 mol/L)–octylꢀ ꢀhydroxyethyl sulꢀ sulfide. The epoxide ring opens at the unsubstituted
fide (0.062–0.067 mol/L) system were found for the carbon atom, as in dilute solutions of hydroxyalkyl sulꢀ
β
PETROLEUM CHEMISTRY Vol. 52
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200
MALIEVSKII
Table 3. Kinetic parameters of the exchange reaction and the values of the enthalpy of the Hꢀcomplex formation (direct
reaction) for systems ethylethylene oxide–R2ꢀ
diluted solutions (solvent, chlorobenzene)
β
ꢀhydroxypropyl sulfide and propylene oxide–R2ꢀ
β
ꢀhydroxyethyl sulfide for
Preexponential factor
Activation energy
E
,
Enthalpy –
ΔH,
Oxirane R1
Sulfide R2
Sulfide R3
A
×
10–9, s–1
kcal/mol
kcal/mol
C2H5
C2H5
C2H5
CH3
C6H5
CH3
CH3
CH3
H
2.2
1.6
0.17
1.52
–
32.1
31.5
28.4
29.4
2.9
2.8
3.3
2.0
–
CH3C6H4
C8H17
C8 H17
CH3
CH3
H
32 – calculation [18]
fides. We believe that the reaction results in the formaꢀ
In the case of the interaction of Hꢀcomplex I with
tion of sulfonium salt IIA as an intermediate species the second molecule of hydroxyalkyl sulfide for
[1, 4, 17, 29], including the rupture of the C–O bond the forward exchange reaction, it was found by the
of the oxide ring of the Hꢀcomplex; this reaction is the example of the propylene oxide–
n
ꢀoctylꢀ
β
ꢀhydroxyꢀ
rateꢀlimiting stage of the process as a whole.
ethyl sulfide system that k2 = 2.37
×
105 (exp
⎯
19350/RT) l/(mol s) [29]. The values of the constants
of the forward and reverse routes for several other alkyꢀ
In addition, we find that the formation of alkylene
oxides and sulfides, the reaction products, at the final
stage of the reaction is preceded by the formation of
cyclic ion II with intramolecular hydrogen bonding, as
in the case of systems with low hydroxyalkyl sulfide
concentrations. This explains the same composition
and the nature of the set of the end products of the
exchange reaction in both cases:
lene oxide–Rꢀ
βꢀhydroxyalkyl sulfide systems are
given in Table 4.
For the reaction of the phenyl glycidyl ether–R2–
β
ꢀhydroxypropyl sulfide system (for all sulfides,
R3 = СН3 in a series of R2 = C6H5, CH3C6H4, and
C8H17) an increase in the reaction rate constant (k2
×
104 l/(mol s), 150оС) from 0.7 to 1.9 to 8.4 and a decrease
in the activation energy from 15.6 to 14.1 to 9.6 cal/mol,
respectively, are observed; they are caused by the
enhanced electronꢀdonating properties of substituents
on the sulfide. On the other hand, the reaction rate
constants increase with the increasing electronꢀwithꢀ
drawing properties of substituents on alkylene oxides
R1CH–CH
2
R2
R2SCH2CH(R3)OH
+ S
…O
(I)
CH2CH(R3)OH
1
CH CH(R )O
2
k
–OCH(R3)CH2SR2
2
R2S+
(
k2 × °С): 3.7 for СН2ОС2Н5 and 8.4
104 l/(mol s), 150
H
for СН2ОС6Н5 (and a decrease in the activation
energy from 13.7 to 9.53 kcal/mol) at R2 = C8H17,
С6Н5, and R3 = CH3 in both cases. The influence of
substituents in the reactions for concentrated and
3
CH CH(R )OH
2
(9)
(IIa)
1
CH CH(R )O
2
dilute solutions of
The formation of alkylene oxides upon the degraꢀ
dation of sulfonium salts containing ꢀhydroxyalkyl
βꢀhydroxyalkyl sulfides is similar.
– + R2SCH2CH(R3)OH
R2S+
H
3
CH CH(R )O
2
β
(II)
groups is widely known [38, 39]. In our case the
decomposition of the sulfonium salt begins with the
proton loss by the OH group. Owing to a positive
charge on the sulfur atom of the sulfonium salt, the
OH hydrogen atom acquires additional mobility and
its separation becomes much easier. As a result of proꢀ
ton abstraction by the anion of salt IIa, the bipolar ion
II with intramolecular hydrogen bonding and delocalꢀ
ized negative charge is formed, while the original molꢀ
Reaction products
Sulfonium salt IIa contains two
β
ꢀhydroxyalkyl
groups, apparently linked by an intramolecular hydroꢀ
gen bond, because of its pyramidal structure [24].
Intramolecular hydrogen bonds with the formation of
fiveꢀmembered or larger cycles were observed for ethꢀ
ylene glycol monomethyl ether and in dilute solutions
of polyethylene oxide [30]. The energy of the intramoꢀ
lecular hydrogen bond formation for the eightꢀmemꢀ
bered selfꢀassociate of diethylene glycol monoethyl
ecule of Rꢀβꢀhydroxyalkyl sulfide is regenerated. The
decay of bipolar ion II leads to the final reaction prodꢀ
ucts.
Catalytic effect of protonꢀdonating compounds. In
ether is –4.1 kcal/mol [31]. Other examples of formaꢀ Hꢀcomplex I, the
tion of sulfonium salts in reactions with oxiranes are not only a reactant but also has a catalytic effect on the
known as well [32–37]. course of the reaction [17]. Thus, a sharp increase in
βꢀhydroxyalkyl sulfide molecule is
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ROUTES FOR REACTIONS OF ALKYLENE OXIDES
201
Table 4. Rate constants
k2 and k–2 for the forward and reverse directions of the exchange reaction for the systems alkylene
oxide–Rꢀ ꢀhydroxyalkyl sulfide (concentrated solutions [2, 4])
β
1ꢀAlkylene oxide ꢀhydroxyalkyl sulfide
β
Rate constants
k2, k–2 L/(mol s)
T, °C
sudstituent R1
mol/L
4.44
sudstituent R2 sudstituent R3
mol/L
2.86
3.3
×
×
102(exp – 5600/RT
)
15.2(exp – 12500/RT
102(exp – 14100/RT
3.85(exp – 11000/RT
C6H5OCH2
“–”
C6H5
CH3
CH3
CH3
CH3
H
118–189
140–180
140–180
)
1.2
)
4.12
2.78
C6H4 CH3
C8H17
2.64
2.82
)
3.54(exp – 9530/RT
1.24(exp – 9600/RT
)
)
“–”
1.8
2.8
1.1
6.1
×
×
×
×
102(exp – 13700/RT
102(exp – 13300/RT
102(exp – 13000/RT
102(exp – 10800/RT
)
)
C2H5OCH2
C6H5OCH2
2.45–2.83 C8H17
3.75–3.30 C8H17
2.81–3.17 141–182
1.25–1.45 140–170
)
)
CH3
CH3
0.747
–
C8H17
C8H17
H
H
0.0625
–
150
–
0.48
2.37
×
×
10–6; 1.94
105(exp – 19350/RT
×
10–3
)
the rate was observed in the presence of protonꢀdonatꢀ compounds are arranged in the following order of
ing additives (HA) [2, 29, 40, 41].
The effect of protonꢀdonor compounds on the
reaction rate for concentrated solutions of βꢀhydroxyꢀ
alkyl sulfides follows from the scheme of the exchange
process and, in terms of the mechanism proposed
above, is due to the formation of the Hꢀcomplex I in
the first stage of the reaction
'
increasing catalytic activity (k2
С8Н17SCH2СН2OH (0.2) С6Н5ОН (2.5)
CD3СООD (2.7) СН3СООН (7.5)
×
104 l/(mol s):
<
~
<
<
СН2СICOOH
(160) [41]. In addition, isotope effects in the reaction
rate constants was observed for acetic and perdeuterꢀ
ated acetic acids: the primary isotope effect upon the
replacement of H atom by D in the carboxyl group and
the secondary effect upon the introduction of D in the
methyl group.
Let us compare the rate constants for the reaction
of Hꢀcomplex I with a sulfide molecule with the corꢀ
responding rate constants for the reactions when aceꢀ
tic or monochloroacetic acid is added to the system.
'
K
e
R1CH–CH2 + HA
O
R1CH–CH2
HA
(10)
O
(I')
…
At the same time, the replacement of chlorobenꢀ
zene as a solvent by benzene, a mixture of chlorobenꢀ
zene with decane, or acetonitrile did not produce any
change in the rates of the exchange reaction [1, 29].
In the system with an admixed protonꢀdonating
compound, along with reactions without the proton
donor, the following new route appears [40, 41]:
'
In the presence of acetic acid in the system, k2
=
'
'
7.5
×
10–4 and the k2
/
k2 ratio is 34, whereas k2 = 1.6
×
10–2 l/(mol s) and k2
/k2
≈
730 in the case of
'
monochloroacetic acid.
Interaction of two Hꢀcomplexes I. The trend of the
initial reaction rate to a limiting value with increasing
oxirane concentration and a constant concentration
R2
CH2CH(R1)O
R2S+
CH2CH(R3)OH
'
k
H]A–
2
[
I' + S
of
βꢀhydroxyoxyalkyl sulfide was shown kinetically
CH2CH(R3)OH
[11, 14]. This means that at a large excess of oxirane, it
actually starts to play the role of a solvent. A large part
of the sulfide is bound in complex I, i.e., it is also necꢀ
essary to take into account the contribution of the
reaction between two Hꢀcomplexes I to the overall
reaction rate in any event. In this case, [sulfide]b =
[sulfide]o–[I], and [oxirane]b ~ [oxirane]o. The final
equation obtained in [17] is as follows:
(11)
–HA
reaction products
(II)
(IIa')
Sulfonium salt IIa' and bipolar ion II are formed as
intermediates; the decay of bipolar ion II leads to the
formation of the same products as in the absence
of HA.
Wo(1 + Ke[oxirane]o)2
Ke[sulfide]2o[oxirane]o
The catalytic action of protonꢀdonor compounds
(monochloroacetic acid, d4ꢀacetic acid, phenol, etc.)
on the forward reaction of propylene oxide with
Y = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
β
ꢀhydroxyethyl sulfide was studied in chlorobenzene
at 150 by measuring the initial rates of ethylene
oxide buildup. In this reaction, the protonꢀdonor
k1(1 + Ke[oxirane]o)
°
С
–
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ = k2 + k3Ke[oxirane]o
[sulfide]o
PETROLEUM CHEMISTRY Vol. 52
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202
MALIEVSKII
The values of
8.92
10–6 l2/(mol s) were determined from the cess; it largely determines the character of each eleꢀ
dependence of on [oxirane]o, whence it follows that mentary event. It is also noteworthy that at the final
for Ke = 1.85 l/mol [17], k3 = 4.71
10–6 l/(mol s) stage of the reaction. all the routes lead to the formaꢀ
150 ). The interaction of the two complexes leads tion of a single intermediate cyclic bipolar ion with
to the same products as in the case of the second direcꢀ intramolecular hydrogen bonding, which ion deterꢀ
k2 = 2.2
×
10–5 l/mol s and k3Kp
=
intact (albeit it is modified) throughout the entire proꢀ
×
Y
×
(
°C
tion.
For the reaction of two H complexes I in the system
octylꢀ ꢀhydroxyethyl sulfide–propylene oxide, which
leads to the same products as in the previous case
through the sulfonium salt IIa and complex II with
mines the final composition of the products.
The results reported in this paper represent only a
small fraction of the possibilities inherent in the
exchange reaction. We believe that the study of
exchange reactions involving organic compounds
containing other elements of 5a and 6a subgroups of
the periodic system is of no less interest. The prospects
for further study of reactions involving cycles, in which
the alkylene oxide oxygen atom is replaced by S or N
atom (thiirane and its derivatives, ethyleneimine and
its derivatives) are also of interest.
β
an interꢀion hydrogen bond, we have k3 = 8.2
103(exp – 17820/RT) (k3 = 4.71 10–6 l/(mol s)
150 ) against the rate constant for the reaction
of the Hꢀcomplex I with a molecule of hydroxyꢀ
ethyl sulfide 2 = 2.37 19350/RT) [17] (2.2
105(exp
10–5 l/(mol s), 150
) and k3 k2 = 0.21. This can be
×
×
(
°C
k
×
⎯
×
°С
/
explained by the fact that the steric hindrances in the
former case are higher than in the second.
The contribution of the reaction with two Hꢀcomꢀ
plexes I to the overall process rate increases with
increasing concentration of propylene oxide. At a
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ꢀhydroxyethyl sulfide concentration of 2.1 mol/L
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remainder being the reaction of the Hꢀcomplex I with
a second hydroxyethyl sulfide molecule (85.5%) and
unimolecular conversion of the Hꢀcomplex I (7.1%).
At a sulfide concentration of 0.6–0.9 mol/L and a proꢀ
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=
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'
3.66
I' + I
8.1
×
'
k
3
'
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'
×
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'
k
3
reaction I' + I
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PETROLEUM CHEMISTRY Vol. 52
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2012