Mechanism of α-acetyl-γ-butyrolactone synthesis

Article abstract of DOI:10.2478/s11696-013-0337-5

The mechanism of α-acetyl-γ-butyrolactone (ABL) synthesis from γ-butyrolactone (GBL) and ethyl acetate (EtOAc) was explored by detecting the material changes involved and the enthalpies of formation of the synthons, products, and possible intermediates were calculated using the density functional theory. GBL forms a carbanion of γ-butyrolactone by losing an α-H under strongly alkaline conditions. ABL is then obtained via two reaction mechanisms. One of the reaction mechanisms involves direct reaction of the carbanion of GBL with EtOAc to produce ABL. The other involves the formation of a carbanion of α-(2-hydroxy-tetrahydrofuran-2-yl)-γ- butyrolactone through the reaction of two molecules of GBL, and the subsequent combination of this anion with EtOAc to produce ABL. ABL is thus formed through the above two kinds of competitive ester condensation reactions. It is unnecessary to take into account synthons' local thickness, and their self-condensation under these conditions. Both reactions of the carbanion of GBL with EtOAc and GBL are exothermic, so the control of their reaction rate is the key to their security. Considering the reasons above, this work applied synthon as the solvent, and avoided environmental pollution by alkylbenzene; also, accidents such as red material and fire were avoided by specific surface area of sodium metal control. Effective isolation of the organic and aqueous phases was performed using the salting out method. Thus, an environmentally friendly, safe, simple, and efficient new method for the synthesis of ABL with the yield higher than 90 % has been established.

Full text of DOI:10.2478/s11696-013-0337-5

Chemical Papers
DOI: 10.2478/s11696-013-0337-5
ORIGINAL PAPER
Mechanism of α-acetyl-γ-butyrolactone synthesis
a,b
a
a
a
Wei Wang, Sheng-Wan Zhang*, Mei-Ping Li, Ying-Yu Ren
aSchool of Life Science, bSchool of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, China
Received 31 May 2012; Revised 20 November 2012; Accepted 21 November 2012
The mechanism of α-acetyl-γ-butyrolactone (ABL) synthesis from γ-butyrolactone (GBL) and
ethyl acetate (EtOAc) was explored by detecting the material changes involved and the enthalpies
of formation of the synthons, products, and possible intermediates were calculated using the density
functional theory. GBL forms a carbanion of γ-butyrolactone by losing an α-H under strongly alka-
line conditions. ABL is then obtained via two reaction mechanisms. One of the reaction mechanisms
involves direct reaction of the carbanion of GBL with EtOAc to produce ABL. The other involves the
formation of a carbanion of α-(2-hydroxy-tetrahydrofuran-2-yl)-γ-butyrolactone through the reac-
tion of two molecules of GBL, and the subsequent combination of this anion with EtOAc to produce
ABL. ABL is thus formed through the above two kinds of competitive ester condensation reactions.
It is unnecessary to take into account synthons’ local thickness, and their self-condensation under
these conditions. Both reactions of the carbanion of GBL with EtOAc and GBL are exothermic,
so the control of their reaction rate is the key to their security. Considering the reasons above, this
work applied synthon as the solvent, and avoided environmental pollution by alkylbenzene; also,
accidents such as red material and fire were avoided by specific surface area of sodium metal control.
Effective isolation of the organic and aqueous phases was performed using the salting out method.
Thus, an environmentally friendly, safe, simple, and efficient new method for the synthesis of ABL
with the yield higher than 90 % has been established.
ꢀ
c 2013 Institute of Chemistry, Slovak Academy of Sciences
Keywords: mechanism, enthalpy of formation, α-acetyl-γ-butyrolactone, synthesis
Introduction
as the solvent (Jedli n´ ski et al., 1987; Koehler & Uh-
lenbrock, 1998; Lipkin et al., 1988; Qian, 2008). How-
ever, this method also has many disadvantages; such
as serious safety issues, high costs, and environmental
pollution, etc. On the other hand, the use of synthon
as the solvent (Zhang et al., 2010a) is safe, proceeds
under mild reaction conditions, and causes minimum
environmental pollution and low energy consumption.
In the present work, the method of ABL synthesis
using GBL, AcOEt, and metallic sodium as synthons
was systematically studied. First of all, changes in the
composition of the material in the reaction process
were tracked and detected by GC. The variation cor-
relation diagram of the content of the intermediates,
products, and by-products with the reaction time was
obtained. The values of the enthalpy of formation of
the synthons, products, and possible intermediates, as
As a five-membered oxygen-containing hetero-
cyclic derivative, α-acetyl-γ-butyrolactone (ABL) is
an important synthon in organic chemistry. As an in-
termediate product, ABL has been used in the synthe-
sis of vitamin B1 and chlorophyll, to delay heartache
and as an anti-angina agent. So far, there are only
two published methods for ABL synthesis. The first
one uses ethylene oxide and ethyl acetoacetate as syn-
thons (Elsasser & Korte, 1993). Ethylene oxide is an
inflammable and explosive chemical that has the dis-
advantages of very dangerous storage and reaction.
The reaction proceeds slowly, giving low yields, and
the product is difficult to purify. The other method
uses γ-butyrolactone (GBL) and acetyl chloride or
ethyl acetate (EtOAc) as synthons and alkylbenzene
*Corresponding author, e-mail: zswan@sxu.edu.cn

ii
W. Wang et al./Chemical Papers
well as the reaction enthalpies of each step accord-
ing to the proposed mechanism were calculated using
the density functional theory. The mechanism of ABL
synthesis was experimentally and theoretically inves-
tigated. On this basis, a new method for the synthesis
of ABL from GBL, EtOAc, and metallic sodium has
been established. Synthons were used as solvents and
they were added once. The purpose was to avoid envi-
ronmental pollution and the risks posed by the use of
alkylbenzene as the solvent, as well as to reduce the
costs.
the above basis set to ensure that no imaginary fre-
quency existed in the calculated structure and en-
thalpy of formation. Reaction enthalpies (Li et al.,
2011; Shafagh et al., 2011; Kiselev & Gritsan, 2008;
Vessecchi & Galembeck, 2008) of the generated inter-
mediates, by-products, and products were calculated.
The reaction enthalpy is an important physical param-
eter used to assess the stability of molecules and to
determine the energy amount released in the reaction
(Khrapkovskii et al., 2010; Fu et al., 1990). All cal-
culations were completed using the Gaussian 03 pro-
gram (Frisch et al., 2003) at the average temperature
of 298.15 K and average pressure of 101.325 kPa.
Experimental
Materials and methods
Synthesis of ABL
γ-Butyrolactone (GBL) and α-acetyl-γ-butyrolac-
tone (ABL) were purchased from J & K Scientific.
Ethyl acetate (EtOAc), ethanol (EtOH), petroleum
GBL (58.4 g, 0.68 mol), EtOAc (89.5 g, 1.02 mol),
and metallic sodium (17.2 g, 0.75 mol) with the spe-
cific surface area of 6.18 cm2
g
−1
were placed in a
◦
ether (60–90 C), and phosphoric acid (85 %) were
250 mL three-necked flask with an electric stirrer, a
condenser, and a thermometer. After the stirrer was
purchased from Beijing Chemical Plant. Distilled wa-
ter was prepared by a Milli-Q water system. Sodium
and silica gel (100–200 mesh) were purchased from
Chengdu XiYa Chemical Technology Co.
◦
started, the temperature was increased to 80 C for
◦
8 h (for acylation), and then decreased to 55–60 C
for 30 min. Phosphoric acid (51 mass %) (134.8 g)
1
◦
H NMR spectra were performed using a Bruker
was added at 55–60 C to adjust the pH to 3–4; stir-
Avance 600 spectrometer with tetramethylsilane
ring was stopped and the system was left to stand at
60 C for 1 h. The water phase was separated and the
◦
(TMS) as an internal standard and dimethyl sul-
foxide (DMSO-d6) as the solvent. Infrared spectra
organic phase was distilled at diminished pressure to
obtain the product.
(
3
4
in KBr pellets) were recorded on a FTIR Nicolet
−
1
80 instrument in the range of 4000–400 cm , with
To study the quantity changes of each reaction
component and to explore the reaction mechanism,
the reaction process was monitored via aliquots col-
lected at predetermined time intervals. Phosphoric
acid (51 mass %) was added to adjust the pH to 3–4
and the reaction mixture was allowed to stand for 1 h.
The organic phase was separated and analysed by GC
and GC–MS. The content was calculated by the area
normalisation method.
−
1
cm spectral resolution and 32 scan accumulation.
A Shimadzu GC-2010 equipped with a split injector
and a flame ionisation detector was used. GC sepa-
ration was performed in a RTX-1 capillary column
(
30 m × 0.25 mm × 0.25 µm). Injector and detec-
◦ ◦
tor temperatures were 300 C and 250 C, respectively.
Temperature of the oven was maintained at 85 C for
5
to 250 C at 5.5 C min , and maintained at 250 C
for 30 min. Nitrogen was used as the carrier gas at
0
◦
◦
◦
min. Then, it was programmed to increase from 85 C
◦
◦
−1
Results and discussion
−
1
.5 mL min . The injection of 0.2 µL was made in
the split mode (60 : 1). Mass spectrometry was per-
formed using an Agilent GC7890-MS5975C under the
same GC conditions described above, except for he-
lium being used as the carrier gas. Mass spectrometer
was operated in the scan monitoring mode using elec-
tron impact ionisation (70 eV); MS transfer line and
First, the reaction mechanism of ABL synthesis
was explored by monitoring the changes of each com-
pound during the reaction process to obtain ABL un-
der mild reaction conditions with high yield, good sta-
bility, and minimal environmental hazard. Then, the
enthalpies of formation of the reactants, products, and
intermediates were calculated using the density func-
tional theory.
◦
the ion sources temperature were set to 280 C and
◦
2
30 C, respectively.
The density functional theory (Ochterski et al.,
995; Borges dos Santos et al., 2002; Fascella et
al., 2004; Francisco-Márquez et al., 2008; Waterlot
et al., 2011; Ghule et al., 2011) was used to verify
the proposed mechanism. The RB3LYP/UB3LYP/6-
1
Characterisation of reaction components and
their changes during the reaction
Gas chromatogram of the reaction mixture (or-
ganic phase) after 340 min during the synthesis of
ABL is shown in Fig. 1. Structures of ABL, EtOH,
EtOAc, GBL, and α-(2-hydroxy-tetrahydrofuran-2-
yl)-α-acetyl-γ-butyrolactone (2-HTABL) were deter-
3
1+G(d,p) basis set was used to optimise the struc-
ture of the synthons, intermediates, by-products, and
products for the ABL synthesis. Frequency of the ob-
tained molecular structure was then calculated using

W. Wang et al./Chemical Papers
iii
Fig. 1. Gas chromatogram of the reaction mixture after 340
min reaction time. Reaction components: EtOH (1),
EtOAc (2), GBL (3), ABL (4), Va (5), 2-HTABL (6).
Fig. 2. Content of the reaction components versus the reaction
time: EtOH ( ), EtOAc (
ꢁ), 2-HTABL ( ).
•
), GBL (ꢀ), ABL ( ), Va
(
mined by GC–MS using the NIST 05 mass spectral
library and the MS data analysis depending on stan-
dard samples. Moreover, retention time of the stan-
dard compounds was used to validate their structures.
and the contents of ABL and EtOH increased from
22.16 % to 46.57 % and from 17.64 % to 29.06 %,
respectively. The content of GBL remained at 1.46–
1.63 %. Thus, the increasing content of ABL is not de-
rived from GBL but from another pathway occurring
during this process. Contents of Va and 2-HTABL de-
creased from 13.02 % and 5.16 % to 2.11 % and 0.77 %,
respectively. This phenomenon shows that there is a
direct relationship between the increasing contents of
ABL, Va, and 2-HTABL. The formation of ABL es-
sentially reached the equilibrium in 460–580 min, the
content of ABL changed from 46.57 % to 47.12 %.
α-(2-Tetrahydrofuranylidene-γ-butyrolactone
(Va)
was purified by column chromatography and its struc-
1
ture was confirmed by H NMR, GC–MS, and IR spec-
tral data. More details are given in Table 1.
Changes of the components with the reaction time
during the ABL synthesis are shown in Fig. 2. Con-
tents of GBL and EtOAc decreased, whereas those of
ABL and EtOH increased. Contents of both Va and
2
1
-HTABL initially increased and then decreased. After
40 min of the reaction, contents of GBL and EtOAc
Mechanism of ABL synthesis
decreased from 35.50 % to 3.08 % and from 64.50 % to
3.87 %, respectively. Contents of Va and 2-HTABL
3
The density functional theory was used to calcu-
late the enthalpies of formation (∆f H ) of synthons,
0
reached a maximum of 13.02 % and 5.16 %, respec-
tively. During the process, the formation rate of ABL
and EtOH is relatively high. Contents of ABL and
EtOH increased from 0 to 22.16 % and 17.64 %, re-
spectively. For the reaction time of 140–560 min, the
formation rates of ABL and EtOH are relatively low,
products, and potential intermediates (Table 2). The
reaction enthalpies were calculated for each step of the
reaction and the energy changes were used to explain
the mechanisms (Przyby ꢀl ek & Gaca, 2012) shown in
Fig. 3.
Table 1. Spectral data and retention time (tr) of reaction components
Compound
tr/min
Spectral data
MS, m/z (Ir/%): 46 (M+, 34), 31 (CH3, 100)
EtOH
EtOAc
GBL
7.55
7.15
10.93
17.67
MS, m/z (Ir/%): 88 (M+, 8), 73 (C3H5O2, 8), 70 (C4H6O, 19), 61 (C2H5O, 20), 43 (C2H3O, 100)
MS, m/z (Ir/%): 86 (M, 50), 56 (C3H4O, 33), 42 (C2H2O, 100)
ABL
MS, m/z (Ir/%): 128 (M+, 7), 113 (C5H5O3, 6), 86 (C4H5O2, 100), 85 (C4H4O2, 22), 43 (C2H3O,
85)
IR, ν˜ /cm 1: 1728 (C—O), 1680 (C—C), 1375 (C—H), 1258 (C—O—C)
−
Va
31.76
34.92
1
H NMR (DMSO-d6), δ: 2.05 (m, 2H), 2.79 (t, 2H), 2.97 (t, 2H), 4.23 (t, 2H), 4.28 (t, 2H)
MS, m/z (Ir/%): 154 (M+, 100), 125 (C7H8O2, 8), 113 (C5H4O3, 40), 96 (C5H4O2, 85), 83 (C4H4O2,
3), 69 (C4H6O, 10), 68 (C4H5O, 10), 55 (C2O2, 26)
MS, m/z (Ir/%): 214 (M+, 0), 171 (C8H11O4, 1), 154 (C8H10O3, 26), 153 (C8H9O3, 10), 129
1
2
-HTABL
(
(
C6H9O3, 13), 128 (C6H8O3, 32), 113 (C5H5O3, 22), 87 (C4H7O2, 100), 86 (C4H6O2, 96), 85
C4H5O2, 15), 69 (C4H6O, 31), 43 (C2H3O, 94)

iv
W. Wang et al./Chemical Papers
Table 2. Values of the theoretical absolute enthalpies of for-
The reaction of GBL and EtOAc is a typical α-H
Claisen ester condensation reaction of two ester group
containing compounds under strongly alkaline condi-
tions. In theory, at least four products can be gener-
ated (Fig. 4).
0
◦
mation (∆f H ) at 25 C of the reaction components
0
−1
)
Substance
∆f H /(kJ mol
Na2
Na
GBL
ABL
H2O
C2H5O
C2H5OH
H2
–852191.853
–426059.708
–804456.771
–1205125.477
–200582.161
–405189.739
–406848.425
–3050.910
+
However, the changes in the material showed that
the main reaction product is GBL, which loses an α-H
to form a carbanion of GBL, and then attacks another
carbonyl carbon of GBL and/or EtOAc in the reaction
process. The loss of an α-H of EtOAc to form a car-
banion which can attack another carbonyl compound
is a minor side reaction. This is in agreement with
the fact that the secondary carbanion is theoretically
more stable than the primary one. The p electrons of
the carbanion form a p–π conjugate with the adja-
cent carbonyl groups. The temperature of the reac-
−
CH3COOC2H5
–807590.252
–201633.858
–801894.309
–1610519.323
–1203440.563
–1607132.665
–1607373.449
–2414903.919
–2007728.829
–1408232.582
–2009672.671
+
H3O
I
II
III
IV
V
VI
VII
Va
VIa
◦
tion solution is high (80–88 C) in the inducing phase,
which increases also the temperature of the metallic
sodium. When the surface of the metallic sodium gets
into contact with the mixture of GBL and EtOAc,
Fig. 3. Mechanism of the transformation of GBL into ABL under alkaline conditions. Molar enthalpies (in kJ mol 1) for individual
−
reaction steps: i) 1073.238, ii) –1034.745, iii) 204.137, iv) 26.234, v) –633.207, vi) –781.571, vii) –240.789, viii) 59.789, ix)
187.987, x) –59.078, xi) –168.490, xii) –633.207, xiii) –389.614.

W. Wang et al./Chemical Papers
v
Fig. 4. Claisen ester condensation of EtOAc and GBL.
◦
the low boiling point EtOAc (77 C) is vapourised,
a salt which is precipitated. Thus, the reaction process
favours the formation of ABL.
◦
while the high boiling point GBL (204 C) is adsorbed
on the surface of the metallic sodium, which leads to
the formation of a GBL carbanion. A reaction mech-
anism for ABL synthesis under strongly alkaline con-
ditions is proposed (Fig. 4), where sodium initially
attacks the α-H (H atom adjacent to the carbonyl
group) of GBL to form carbanion I (Fig. 3, reaction
scheme Eq. (1)). The molar enthalpy of formation is
In the synthesis of ABL, the second mechanism in-
volves GBL transformation to intermediate V, and its
conversion into ABL (Fig. 3, reaction scheme Eq. (3)).
Carbanion I attacks another carbonyl carbon of GBL
and consequently the π bond of the C—O double
bond opens to produce oxygen anion IV. The oxy-
gen anion and α-H of GBL rearrange to form car-
banion V. As spontaneous exothermic reactions, their
−
1
1
073.238 kJ mol . The reaction is endothermic and it
−
molar enthalpies of formation are –781.571 kJ mol
1
is required to provide sufficient energy for its comple-
tion, which was also confirmed by theoretical calcula-
tions. The absolute enthalpy of formation of carbanion
−
1
and –240.789 kJ mol , respectively. The p electrons
of carbanion V and the carbonyl π bond form a p–π
conjugate which is more stable than the intermedi-
ate oxygen anion IV. The centre of the activated car-
banion in carbanion V is connected to three neigh-
bouring carbon atoms attached to different groups,
which increased the steric hindrance of the carban-
ion. Collision frequency between the carbanion cen-
tre and the carbon atom in the carbonyl group of
EtOAc was decreased. The intermediate carbanion V
attacks the carbonyl carbon in EtOAc and opens the π
bond to form oxygen anion VI. The formation energy
−
1
I is –801988.367 kJ mol . Carbanion I is highly re-
active and it easily reacts with the carbonyl carbon of
GBL and EtOAc.
Another possible mechanism of the ABL synthe-
sis is the direct reaction of carbanion I with EtOAc
(Fig. 3, reaction scheme Eq. (2)). Carbanion I at-
tacks the carbonyl carbon atoms of EtOAc to form
a C—C bond. The C—O double bond is transformed
into a single bond to form oxygen anion II, and the
−
1
enthalpy of formation is –1034.745 kJ mol . Oxy-
gen anion II attacks the connected carbons to form a
C—O double bond. The ethoxy group is then elimi-
−
1
of the oxygen anion is 59.789 kJ mol . The oxygen
anion attacks the adjacent carbon to form a C—O
nated to form ABL and the enthalpy of formation is
double bond and to remove the ethoxy group to pro-
duce intermediate VIa with 187.987 kJ mol . Un-
−
1
−1
2
04.137 kJ mol . The highly reactive ethoxy anion
attacks the activated hydrogen of the β-dicarbonyl
group in ABL and its removal results in the forma-
tion of the π–p–π conjugate III. The energy needed
for this reaction is only 26.234 kJ mol . The rate-
controlling step of this reaction mechanism (Fig. 3,
reaction schemes Eq. (1) and Eq. (2)) is the formation
of intermediate I. Carbanion III and a sodium ion form
der strongly alkaline conditions, hydrogen is removed
from the hydroxyl group to form oxygen anion VII
−
1
with –59.078 kJ mol . The oxygen anion attacks the
connected carbon to produce a C—O double bond and
−
1
to form carbanion III as well as GBL. This reaction
occurs spontaneously and is exothermic with the en-
−
1
thalpy of formation of –168.490 kJ mol . The rate-

vi
W. Wang et al./Chemical Papers
controlling step of this reaction mechanism (Fig. 3,
reaction scheme Eq. (3)) is the formation of interme-
diate VI. In this mechanism, the content of GBL is
substantially constant while the content of ABL in-
creases drastically. The results revealed the presence
of intermediates Va and VIa, which further confirms
the feasibility of the proposed mechanism. Intermedi-
ate V is protonated to obtain intermediate Va by the
removal of a water molecule during the acid-catalysed
reaction (Fig. 3, reaction scheme Eq. (4)). The en-
−
1
thalpy of formation of Va is –389.614 kJ mol . Thus,
the content of intermediate Va is representative of the
content of intermediate V in the reaction system.
In summary, GBL forms carbanion I by losing an
α-H under strongly alkaline conditions. ABL is then
obtained via two reaction mechanisms. One involves
direct reaction of carbanion I with EtOAc to produce
ABL. The other involves the formation of carbanions
IV and V, by the reaction of carbanion I with GBL,
followed by a proton shift (Fig. 3, I, IV, and V). The
subsequent combination of carbanion V with EtOAc
produces ABL. The formation of intermediates II, IV,
and V is spontaneous, releases a lot of energy, and
leads to by-products EtOH and EtOAc vapourisation
giving rise to the occurrence of red material, fire, and
explosion. It is very important to study the reaction
mechanism not only to provide effective theoretical
guidance, but also to design a reasonable production
process.
Fig. 5. Correlation diagram of the yield as a function of the
EtOAc/GBL mole ratio.
1.5 is preferable and completely avoids the environ-
mental pollution caused by using alkylbenzene. Thus,
the yield of GBL conversion into ABL reaches a max-
imum. Under these conditions, ABL was isolated with
a 90 % yield, which is by 10 % higher than the yield
of the process which uses toluene as the solvent.
It is shown that the π–p–π conjugate structure
with sodium cation formed by both mechanisms of
ABL synthesis is stable. In this study, the principle
of salting out was applied, a phosphate acid was se-
lected as the neutralising acid, and the effects of differ-
ent concentrations of the phosphate acid and different
separation temperatures of the organic and aqueous
phase on the separation result were investigated. The
results indicate that optimum separation is achieved
when the phosphate acid concentration reaches 51
mass % and the separation temperature of the organic
Selection of reaction conditions
Research on the above mechanism shows that the
rate of formation and the amount of generated car-
banion I represent the key information for the security
of the entire reaction in such an ABL synthesis pro-
cess. This study examines the temperature increase
rate and the specific surface area of metallic sodium.
When the EtOAc/GBL and the sodium/GBL mole
ratios are 1.5 and 1.1, respectively, the specific sur-
◦
and aqueous phases reaches 60 C. Under these reac-
tion conditions, the aqueous phase does not need to be
extracted by organic solvents, which greatly simplifies
the purification process.
2
−1
face area of metallic sodium is 6.18 cm g . The syn-
thons are added at once and heated up slowly until the
system starts to reflux; the reaction becomes steady
ensuring thus the safety of the whole reaction, and
the accidents, such as the production of red materials
and/or fire, are eliminated completely (Zhang et al.,
Conclusions
The mechanism of ABL synthesis was experimen-
tally and theoretically investigated. Theoretical sim-
ulations adopted the density functional theory. The
ABL synthesis was explored via two proposed mecha-
nisms. A rate-controlling step was determined for each
possible reaction mechanisms. The rate-controlling
step for the first reaction mechanism (Fig. 3, reac-
tion schemes Eq. (1) and Eq. (2)) was the forma-
tion of intermediate I, and that for the second reac-
tion mechanism (Fig. 3, reaction scheme Eq. (3)) was
the formation of intermediate VI. The overall rate-
controlling step was the formation of intermediate VI.
A new method for the ABL synthesis using synthon
as the solvent, where the synthons are added at once
while controlling the specific surface area of metallic
2
010b).
The mechanism of ABL synthesis indicates that
the two reaction mechanisms ultimately form the tar-
get product. Therefore, it is unnecessary to consider
problems of the synthon, either its local thickness or
self-condensation. In this study, synthon was used as
the solvent instead of alkylbenzene. The sodium/GBL
mole ratio was 1.1, and the effect of the EtOAc/GBL
mole ratio of 1.1 to 1.9 on the reaction was examined.
The correction diagram of the yield as a function of
the EtOAc/GBL mole ratio is shown in Fig. 5.
Fig. 5 shows that the EtOAc/GBL mole ratio of

W. Wang et al./Chemical Papers
vii
sodium, is presented. The proposed method can be
easily applied under mild reaction conditions avoiding
thus pollution of the environment by the use of alkyl-
benzene as the solvent. More importantly, the method
has been applied in a local industrial production and
a higher yield of ABL, 90 %, was obtained.
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(
GC, NMR, mass, and IR spectra) can be found in
the online version of this paper (DOI: 10.2478/s11696-
13-0337-5).
0
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