K. Taniguchi, et al.
Molecular Catalysis 477 (2019) 110519
charged to the reactor at 323 K. The reactor was submerged into a sand
bath at the desired reaction temperature for a given reaction time and
then submerged into a water bath to cool quickly to ambient tem-
perature, after the reaction. The partial pressure of carbon dioxide at
values of erythritol and 1,4-anhydroerythritol at reaction time (t), re-
spectively, and [erythritol]int is the initial erythritol concentration
(0.5 mol dm ). The solid line in Fig. 1(a) is the fitting curve with the
−3
least square method based on the Eq.s (1) and (2). The rate constant
-
1
573 K was estimated to be 17.7 and 24.8 MPa corresponding to the
values for the reaction in water at 573 K were 0.58, 0.035, and 0.102 h
for k , k , and k , respectively (Table 1). They were reproduced with
initial pressure of 10 and 14 MPa at 323 K, respectively, using Charles’s
law. After the reaction, a mixture of the reactant and products was
taken out the reactor with distilled water. The quantitative analysis of
the unreacted erythritol and the liquid products was conducted by using
a gas chromatography with a flame ionization detector (GC-FID)
equipped with a DB-WAX capillary column (Agilent Technologies)
using 1-propanol (Wako Pure Chemical Industries) as an internal
standard. The products were identified by comparing the retention
times with those of standard materials: 1,4-anhydro-D-erythritol
1
2
3
the previous report (0.44, 0.023, and 0.097 for k
tively) [20].
1 2 3
, k , and k , respec-
The dehydration reaction of erythritol was studied at erythritol
−3
concentration at 0.25 and 0.30 mol dm . The reaction order of ery-
thritol concentration was estimated using the following rate equation,
α
r = k[erythritol] ꢀꢀꢀ,
(3)
where r, k, and α were initial 1.4-anhydroerythritol formation rate,
rate constant and reaction order. The initial formation rates at each
concentration were determined by the slope of the linear increase of
1,4-anhydroerythritol amount with reaction time. Fig. 2 shows the
logarithm of 1,4-anhydroerythritol initial formation rate versus loga-
rithm of erythritol initial concentration. The reaction order (slope in
Fig. 2) was roughly one, indicating that the intermolecular dehydration
was first-order for erythritol concentration. The validity of this first
order of erythritol concentration for the dehydration could be sup-
ported by the results in Fig. 1, in which the raw data were well-fitted
with the rate Eq.s ((1) and (2)) that are based on the first order of
erythritol concentration.
(
SIGMA-ALDRICH). The product yield is defined as follows.
Yield (%) = (the amount of 1,4-anhydroerythritol obtained (mmol))
/
(initial amount of erythritol (mmol)) ×100.
3. Results and discussion
3.1. Dehydration of erythritol in high-temperature liquid water
The aqueous erythritol solution (concentration: 0.5 mol dm−3) was
treated in a batch reactor for 30 and 60 min at 523 K to obtain 0.4 and
.8% yields of 1,4-anhydroerythritol, respectively, indicating that the
intramolecular dehydration hardly proceeded in water at 523 K. At
73 K, the dehydration proceeded in water and 1,4-anhydroerythritol
0
5
3.2. Dehydration of erythritol in high-temperature carbonic water
was obtained as the sole product as confirmed by GC-FID analysis. The
erythritol dehydration profile at 573 K is shown in Fig. 1 (a). The yield
of 1,4-anhydroerythritol for 8 and 14 min were 6 and 10%, respec-
tively, at 573 K which increased with an increase in reaction time (the
High pressure carbon dioxide (at 10 and 14 MPa) was added to the
−3
reactor with 0.5 mol dm of aqueous erythritol solution at 323 K and
treated at 573 K. The estimated carbon dioxide pressure values at 573 K
are 17.7 and 24.8 MPa, respectively, by Charles’s low. By the treatment
of the aqueous erythritol solution at 573 K, 1,4-anhydroerythritol was
obtained by the GC analysis. Erythritol and 1,4-anhydroerythritol yields
in water at 573 K under 17.7 and 24.8 MPa of carbon dioxide are shown
in Figs. 1(b) and (c).
-1
initial formation rate was 0.50 mmol h ) and became constant at 71%.
The product recovery after 180 min was ˜80% (Fig. 1c). Yamaguchi
et al. studied the dehydration of several sugar alcohols, such as ga-
lactitol, xylitol, ribitol, L-arabitol, erythritol and threitol (concentration
−
3
0
.5 mol dm ), in high-temperature liquid water at 523–573 K, and
reported that the final recovery values decreased with an increase in
reaction temperature because of the degradation and/or polymerization
of reactants and products [18,20]. The intramolecular dehydration,
degradation and/or polymerization of erythritol proceeded in liquid
water at 573 K (Scheme 1). The rate constants were calculated by the
fitting the data with a least square method based on the following
equations,
The 1,4-anhydroerythritol yield for 8 min under 17.7 and 24.8 MPa
of carbon dioxide were 19 and 29%, respectively. The initial product
formation rates under 17.7 and 24.8 MPa of carbon dioxide were 1.45
−1
and 2.10 mmol h , respectively. The yields at 180 min became con-
stant at 73% under 17.7 and 24.8 MPa of carbon dioxide, which is the
almost the same as that in water at 573 K (71%). Fig. 1 shows that the
initial dehydration rates was enhanced by the addition of carbon di-
oxide and increased with an increase in carbon dioxide pressure and the
final yields were the same independent of carbon dioxide pressure,
indication that carbon dioxide serve as a role of an acid catalyst. Savage
et al. reported that the carbonic acid was formed by the addition of
carbon dioxide in water and the proton concentration in water at
[
erythritol] = [erythritol]int exp{(-k
1
-k
3
) t} ꢀꢀꢀ,
(1)
-k
[
1,4-anhydroerythritol] = {k /(k -k
1
2
1
-k
3
)} [erythritol]int [exp{(-k
1
3
)
t}-exp(-k
2
t)],
(2)
where [erythritol] and [1,4-anhydroerythritol] are concentration
Fig. 1. Yields of 1,4-anhydroerythritol (closed symbols) and erythritol (open symbols) as a function of reaction time for the treatment of erythritol aqueous solution
−3
in water at 573 K (initial erythritol concentration: 0.5 mol dm , carbon dioxide partial pressure: 0 (a), 17.7 (b) and 24.8 MPa (c)).
2