Efficient conversion of dimethyl phthalate to phthalide over CuO in aqueous media

Article abstract of DOI:10.1016/j.cattod.2015.10.014

An efficient conversion of dimethyl phthalate (DMP) to phthalide (PHT) over CuO in aqueous media was investigated. Among the catalysts we tested, various metals or metal oxides were effective for the conversion of DMP to PHT in water, and CuO showed excellent catalytic activity and gave the best result. The PHT yield of 85% was achieved when Zn acted as a reductant. Mechanism study for the conversion of DMP suggested that an intermediate 2-hydroxymethyl benzoic acid was produced in the process. The present study provides a useful route for the production of PHT from DMP.

Full text of DOI:10.1016/j.cattod.2015.10.014

Catalysis Today 263 (2016) 123–127
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Catalysis Today
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Efficient conversion of dimethyl phthalate to phthalide over CuO in
aqueous media
Jun Fu, Dezhang Ren, Lu Li, Yunjie Liu, Fangming Jin, Zhibao Huo∗
School of Environmental Science and Engineering, The State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University,
800 Dongchuan Road, Shanghai 200240, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2015
Received in revised form
28 September 2015
Accepted 6 October 2015
Available online 21 November 2015
An efficient conversion of dimethyl phthalate (DMP) to phthalide (PHT) over CuO in aqueous media
was investigated. Among the catalysts we tested, various metals or metal oxides were effective for the
conversion of DMP to PHT in water, and CuO showed excellent catalytic activity and gave the best result.
The PHT yield of 85% was achieved when Zn acted as a reductant. Mechanism study for the conversion
of DMP suggested that an intermediate 2-hydroxymethyl benzoic acid was produced in the process. The
present study provides a useful route for the production of PHT from DMP.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
Biomass
DMP
PHT
CuO
Conversion reaction
1. Introduction
biomass compound DMP to obtain PHT is an efficient method which
has the potential for the future commercialization. However, to
During the past several decades, the energy crises have led many
countries to seek renewable energy resources to reduce the over
dependence on fossil fuels [1,2]. After years of over-consumption
on unsustainable petroleum, the development of renewable and
“green” sources of energy to reduce this use of fossil fuels and
reduce CO2 emissions has become imperative [3–6]. Biomass is a
kind of abundant, renewable and relatively non-polluted resource,
these qualities make it an excellent candidate for the production
of high value-added chemicals. For this reason, the utilization of
biomass currently is receiving increasing attention.
PHT has wide applications in medicine, antiseptics and organic
synthesis. It is an intermediate chemical with important uses in, for
example, the treatment of circulatory and heart diseases. PHT can
also act as a versatile building block in organic synthesis, especially,
the PHT is useful in the synthesis of functionalized naphthalenes,
anthracenes and naphthacene natural products [7–11]. Due to its
beneficial industrial applications, much attention has been paid to
the synthesis of PHT. Currently, synthesis of PHT typically involves
an industrial process from petroleum-derived phthalimide. DMP,
an important biomass compound, can be easily obtained from the
plentiful biomass sources, says the celery [12]. Using renewable
date, very few studies have focused on this field. Franco Piacenti
et al. reported the hydrogenation of DMP into the corresponding
PHT using a ruthenium hydride complex H4Ru4(CO)8(PBu3)4 [13].
Toshiharu Yokayama et al. discussed turning DMP into PHT with a
yield of 55% over the ZrO2 and Cr–ZrO2 catalyst at a temperature
of over 350 ◦C [14]. Clarke et al. used LiHBEt3 as a catalyst for the
reaction and achieved a yield of 34% [15]. However, challenges still
lurk in these methods from both academia and industry perspec-
tive. For example, the high-pressure gaseous hydrogen, which is
often used, is difficult to store and is sometimes unstable; the PHT
yield is low; the use of expensive synthesized catalysts and organic
solvents are not economic and could be detrimental to the environ-
ment; and plus, a longer reaction time. Therefore, the development
of an efficient and scalable process to produce PHT from DMP is
very important.
Previously, our group and others have reported on a series of
experiments concentrated on the conversion of biomass into value-
added chemicals using a process involving high-temperature water
[5,16–26]. In this process, water is not only an environmentally
friendly reaction medium, and it is also an abundant hydrogen
resource provided by the oxidation of active metal in water [27].
In addition, we have also reported a highly-efficient production of
diols from biomass-derived glycolide or lactic acid over CuO in a
high yield with high selectivity [28,29]. On the basis of these find-
ings, if we can extend this concept to the conversion of DMP, PHT
∗
Corresponding author.
E-mail address: hzb410@sjtu.edu.cn (Z. Huo).
http://dx.doi.org/10.1016/j.cattod.2015.10.014
0920-5861/© 2015 Elsevier B.V. All rights reserved.

124
J. Fu et al. / Catalysis Today 263 (2016) 123–127
Table 1
O
O
O
Effect of catalysts on the yield of PHT.a
Cat. CuO
OMe
OMe
Entry
Reductant
Catalyst
Yield of PHT (%)
O
1
2
3
–
Zn
–
–
–
Cu
0
24
0
Zn, H2O
1
2
4
–
CuO
Fe
Cu
0
5
6
7
8
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
47
61
43
85
55
0
26
57
58
42
12
24
15
Scheme 1. Conversion of DMP to PHT in the presence of CuO.
Co
CuO
Cu2O
Fe2O3
Fe3O4
TiO2
MnO2
ZrO2
CuFe2O4
Pd/C
Ni
may be produced in a similar manner. Herein, we present a highly
efficient conversion of DMP to PHT in the presence of CuO in aque-
ous media (Scheme 1).
9
10
11
12
13
14
15
16
17
2. Experimental
2.1. Experimental materials
a
Reaction conditions: DMP 0.5 mmol, reductant 25 mmol, catalyst 5 mmol,
250 ◦C, 2 h, water filling 25%.
DMP (>99%) as the initial reactant was purchased from J&K.
PHT (≥99%, chromatographic grade, J&K Scientific Ltd.) was used
for quantitative analysis. Zn (200 mesh, Aladdin) was used as the
reductant. Ni, Fe, Al, Mn, Mg, CuO, Al2O3, CuO, Cu2O, Fe2O3 and
Fe3O4 (200 mesh, Sinopharm Chemical Reagent Co., Ltd) were also
used in the experiment.
3. Results and discussion
3.1. Catalyst screening
2.2. Experimental procedure
Initially, we investigate the influence of metal or metal oxides on
the production of DMP to PHT. The reaction of DMP was conducted
in the presence of 5 mmol Cu and 25 mmol Zn at 250 ◦C for 120 min.
The result showed that the reaction proceeded efficiently and pro-
duced the desired PHT at a 61% yield, as determined by GC–FID
NMR and GC–MS (Figs. SI-2 and SI-3). Next, we screened a series
of metal or metal oxides to determine the most suitable one. The
results are summarized in Table 1. The reaction did not proceed at
all in the absence of both reductant and catalyst or in the presence
of the catalysts only (entries 1, 3–4). The reaction with 25 mmol Zn
but without the addition of any catalyst, gave the desired PHT at a
24% yield (entry 2), this result could be reckoned as an evidence of
the importance of the combined use of the reductant and catalyst.
Among the various catalysts we investigated (entries 5–17), the use
of CuO improved the transformation efficiency and afforded PHT at
a better yield (entries 8). However, the use of Fe3O4 is completely
ineffective (entry 11). CuFe2O4 and Ni gave lower yield (entries 15,
17).
All experiments were carried out in a Tefion-lined stainless steel
batch reactor with an internal volume of 30 mL. 0.5 mmol DMP was
used in all experiments. The typical procedure for the synthesis
of PHT was as follows. First, desired DMP, reductant, catalyst and
ultrapure water were loaded into the reactor. Then, the nitrogen
was charged into the reactor in order to exclude the effect of air and
then the sealed reactor was put into a drying oven, it will take about
20 min to be preheated to the desired temperature. After a desired
reaction time, the reactor was quickly moved out from the dry-
ing oven to cool down. Liquid sample was collected and extracted
by 10 mL ethyl acetate, then filtered with 0.45 ␮m Syringe Filter.
Solid sample was collected and washed with deionized water and
ethanol several times to remove impurities and dried in the oven
at 50 ◦C for 24 h. The schematic of the reactor system was shown in
Fig. SI-1.
As the XRD patterns of solid residues after the reaction shown
in Fig. SI-4(a), the Cu still existes while Zn has been oxidized
into ZnO, it is obviously that the Cu acted as a catalyst and
Zn acted as a reductant in the reaction process. According to
the result of Fig. SI-4(b), unexpectedly, the Cu instead of CuO
is observed in the solid sample. Our previous work [28] had
confirmed that CuO could be reduced completely into Cu by in situ-
formed hydrogen by the oxidation of Zn in water. We measured
the Cu ion concentration in the solution by ICP and only a small
amount of Cu ions (<1 ppm) in the liquid sample was found. This
result suggested that Cu was most likely present in the solid
residual.
Next, we investigated the effect of the amount of CuO on
the yield of PHT. The reaction was conducted in the presence of
25 mmol Zn with 25% water filling at 250 ◦C for 120 min. The results
are shown in Fig. 2(a). The yield of PHT increased significantly at
first as the amount of CuO increased from 0 to 5 mmol, and the
maximum value of 85% PHT was achieved at 5 mmol CuO. The yield
decreased when the amount of CuO was further increased. These
results may be led from that more CuO would lead to the decompo-
sition of PHT to more by-products, which might result in a decrease
in PHT selectivity.
2.3. Product analysis
After the reaction, the solution samples were collected and fil-
tered for GC–MS analysis (Aglient GC7890A-MS5975C) equipped
with an HP-5 polyethylene glycol capillary column with dimen-
sions of 30 m × 250 ␮m × 0.25 ␮m, and GC–FID. Details on the
conditions of GC–MS/FID analyses are available elsewhere [15].
The total residual organic carbon concentration in liquid sam-
ples was also measured with a TOC analyzer (Shimadzu TOC-V).
The gas product was detected by thermal conductivity detector
(TCD, Agilent Technologies). Thin layer chromatography (TLC) was
performed on aluminum-precoated plates of silica gel 60 with
an HSGF254 indicator and visualized under UV light or devel-
oped by immersion in the solution of 0.6% KMnO4 and 6% K2CO3
in water. Solid samples were collected and analyzed by X-ray
diffractometer (Shimadzu XRD-6100) to determine the composi-
tion and phase purity. The yield of PHT is calculated as the following
equation:
the amount of PHT obtained
the amount of PHT in theory
The yield (%) =
× 100%

J. Fu et al. / Catalysis Today 263 (2016) 123–127
125
120 min, the XRD patterns of the solid samples were shown in Fig. 1.
Firstly, a quick oxidation from Zn to ZnO in water can be observed.
After 1 min, peaks of Zn gradually become smaller until it disap-
peared at 30 min, whereas peaks of ZnO became bigger gradually
as time increased. However, peak of Cu is also observed after the
reaction. These results indicate that the DMP can be converted to
PHT by in situ formed hydrogen by the oxidation of Zn in water over
CuO.
Next, we investigated the effect of the amount of Zn on the yield
of PHT. The reaction was conducted in the presence of 5 mmol CuO
with 25% water filling at 250 ◦C for 120 min and with Zn as reduc-
tant, of which, the amounts is from 0 to 30 mmol, the results are
shown in Fig. 2(a). As we mentioned above, no PHT is observed
without the addition of Zn. The yield of PHT increased significantly
at first as the amount of Zn increased from 0 to 25 mmol, and the
maximum value of 85% PHT is achieved at 25 mmol. The yield of PHT
decreases somewhat when the amount of Zn exceeds 25 mmol. The
results indicate that the improvement in hydrogen production with
an increased amount of Zn in water is better for the conversion of
DMP to PHT, but higher hydrogen partial pressure will cause the
decomposition of PHT and decrease the yield.
Δ
ZnO • Cu ♦ Zn
♦
♦
Δ
Δ
Δ
1 min
♦
♦
Δ
Δ
Δ
Δ
Δ
♦
♦
Δ
Δ
♦
•
•
♦
Δ
Δ
Δ
Δ
Δ
•
Δ
Δ
Δ
Δ
♦
10 min
♦
Δ
Δ
•
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
Δ
•
•
•
30 min
Δ
Δ
Δ
120 min
•
10
20
30
40
50
60
70
80
2 Theta(° )
Fig. 1. XRD patterns of the solid samples.
Table 2
Effect of reductants on the yield of PHT.a
Entry
Reductant
Yield of PHT (%)a
3.3. Effect of other parameters
1
2
3
4
5
6
–
Al
Mg
Fe
Zn
Mn
0
2
0.4
0.4
85
0.1
Fig. SI-5 shows the effect of water filling from 15% to 45% on the
yield of PHT with the conditions of 5 mmol CuO and 25 mmol Zn at
250 ◦C for 120 min. Due to the reason of safety, the max water filling
is 45%. The yields of PHT are almost interestingly constant between
the water filling of 15% and 20%. The yield remarkably increases
from 20% to 25% and reaches the maximum value of 85%, and then
decreases after 25%. Probably, decreasing yield is because a higher
water filling causes the decomposition of PHT when water filling
increases.
a
Reaction conditions: DMP 0.5 mmol, CuO 5 mmol, reductant 25 mmol, water
filling 25%, 250 ◦C, 2 h.
3.2. Effect of the reductants
In the conversion of DMP, temperature was found to be a very
influencing factor. The effect of temperature was investigated at
different temperature values from 100 ◦C to 250 ◦C with the addi-
tion of 5 mmol CuO and 25 mmol Zn at water filling of 25% for
120 min, and the results are showed in Fig. 2(b). The reaction did
not give the desire PHT at 100 ◦C, indicating that a lower temper-
ature was completely ineffective in the conversion of DMP. The
yield of PHT increased continuously from 100 to 250 ◦C. Between
200 and 250 ◦C, the yields of PHT increased the most obviously. The
maximum value of 85% PHT was obtained at 250 ◦C. However, we
did not continue the optimization because 250 ◦C was the limited
temperature of the Teflon material.
Several active metals, such as Al, Mg, Fe, Mn and Zn, were inves-
tigated for a suitable reductant in the formation of PHT. Table 2
showed the effect of different active metals on the yields of PHT.
Among the various active metals tested, it can be seen that Al, Mg,
Fe and Mn were almost ineffective for the transformation, and gave
a very lower yields (entries 2–4, 6), while Zn powder had a much
higher selectivity for the conversion of DMP and gave the best 85%
yield of PHT compared to Al, Mg, Mn, and Fe. Thus, Zn was chosen
for the following experiments.
To monitor the oxidation process from Zn to ZnO during the
reaction at different time, such as 1 min, 10 min, 30 min and
Amount of Zn (mmol)
Reaction time (min)
10
15
Amount of Zn
4
20
25
30
60
80
100
120
140
160
180
90
85
80
75
70
65
60
55
50
45
40
35
100
80
60
40
20
0
Reaction time (min)
Amount of CuO
Temperature (°C)
(a)
(b)
80
100 120 140 160 180 200 220 240 260
2
6
8
10
Temperature (°C)
Amount of CuO (mmol)
Fig. 2. (a) Effect of CuO and Zn amount. (b) Effect of temperature and time.

126
J. Fu et al. / Catalysis Today 263 (2016) 123–127
O
O
O
OMe
OMe
OH
OH
O
O
PHT
DMP
2-hydroxymethyl
benzoic acid
10 min
30 min
120 min
5
10
15
20
Retention time (min)
Fig. 3. GC–MS chromatogram of compounds during the reaction.
Zn + H2O
O
ZnO + H2
O
O
H2
H2
OMe
OMe
OMe
H
OMe
OH
- CH3OH
1
3
4
O
O
O
O
H2O
- H2O
OH
OH
O
- CH3OH
5
2
Scheme 2. Proposed pathway for the formation of PHT from DMP.
To examine the effect of different reaction time from 60 min to
was not effective for the product of PHT from DMP in high temper-
ature water.
300 min on the yield of PHT, the results in Fig. 2(b) indicates that
the reaction time plays an important role in the process. The yield
of PHT increases at the first 120 min and the maximum value of 85%
PHT is obtained. However, with further reaction time increases, the
yield of PHT decreases. To investigate the reason of decreasing yield
of PHT by using Cu and ZnO obtained after the reaction and PHT as a
reactant, the reaction of prepared 50 mmol/L PHT was performed in
the presence of 5 mmol Cu and 25 mmol ZnO with 25% water filling
at 250 ◦C for 120 min. The GC–FID results indicate that the initial
concentration of PHT has decreased from 50 mmol/L to 22 mmol/L.
These results suggest that Cu and ZnO can cause the decomposition
of PHT obtained at a long reaction time in the process [30].
O
O
5 mmol CuO/ 2.8 MPa H2
OMe
OMe
O
250 oC, 2 h
water filling: 25%
5.2%
O
4. Mechanism study
Initially, in order to investigate the pathway for the conver-
sion of DMP, we examined the peak changes of intermediates in
the process. At 250 ◦C we chose the 10 min, 30 min and 120 min
to check the intermediates. As shown in Fig. 3, it is obvious that
the peak of DMP is reducing with the increase of reaction time
and gradually disappears from 10 min to 120 min, while desired
PHT keeps increasing. However, we observed the intermediate 2-
hydroxymethyl benzoic acid marked with circular on the right
when the reaction time was 30 min though its peak was small.
Based on previous reports and results in this study, the path-
way for the conversion of DMP to PHT over CuO is proposed in
Scheme 2. First, hydrogen is formed via the oxidation of Zn in water
[31]. Then the in situ-formed hydrogen reacted with DMP molecule
to obtain an intermediate 2-hydroxymethyl benzoic acid 5 (see
Fig. SI-7) via intermediates 3 and 4 along with the loss of methanol
[32]. Finally, the intramolecular cyclization of the intermediate 2-
hydroxymethyl benzoic acid occurred and give the desired PHT.
Finally, a carbon balance was conducted at the optimal con-
dition. The results show that the conversion of DMP for liquid
products is approximately 98.2%. The main products observed for
this transformation were PHT and methanol. In addition, CO2 as
main gaseous product with trace amounts of other gaseous prod-
ucts is also observed in the transformation (see Fig. SI-6).
3.4. Investigation of gases hydrogen
The effect of gases hydrogen on the formation of PHT from DMP
in high temperature water was investigated. The reaction was con-
ducted in the presence of 5 mmol CuO by using 2.8 MPa H2 with 25%
water filling at 250 ◦C for 2 h (Procedure in details, see Supporting
Information). As a result, only peak of PHT was observed by GC–FID,
and the PHT yield of 5.2% was much lower than the yield of 85% by
in situ-formed hydrogen. The result suggested that gases hydrogen

J. Fu et al. / Catalysis Today 263 (2016) 123–127
127
O
Basic Research Projects of Science and Technology Commission
of Shanghai (14JC1403100). The Program for Professor of Special
Appointment (Eastern Scholar) at Shanghai Institutions of Higher
Learning (ZXDF160002). The Project-sponsored by SRF for ROCS,
SEM (BG1600002).
O
5 mmol CuO,
25 mmol Zn,
OH
OH
O
250 oC, H2O,
120 min
5
2, 17%
Appendix A. Supplementary data
Scheme 3. Conversion of intermediate 5 to PHT.
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.cattod.2015.10.
014.
O
O
O
5 mmol CuO,
25 mmol Zn,
Ο
OMe
OMe
+
OH
O
250 oC, 120 min
HO
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7
8
, 3%
6
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We developed a highly efficient conversion of DMP to PHT over
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Acknowledgements
Financially supported by the State Key Program of National
Natural Science Foundation of China (Grant No. 21436007). Key