Biomass-derived dibasic acids to diesters with inorganic ligand-supported catalyst: synthesis, optimization, characterization

Article abstract of DOI:10.1007/s11164-021-04570-z

Several attempts have been made to obtain aliphatic dicarboxylic diesters from esterification reaction to develop the biomass-derived platform molecules and green manufacturing processes. In this paper, Na₃(H₂O)₆[AlMo₆O₁₈(OH)₆], an Anderson-type polyoxometalate, firstly, was reported as a catalyst for diester synthesis from dicarboxylic acid to diester which showed an well productivity and selectivity characterized by ¹H and ¹³C. Response surface methodology (RSM) integrated with the desirability function approach was used to determine the best operative conditions, and the optimal reaction parameters for maximum dipropyl succinate yield (77 ± 2.5%) were identified as 1.19?mol.% catalyst loading, 4.9:1 propanol/succinic acid ratio, 113?°C, and 9.6?h. Three batches of tests were carried for catalyst recycling with 78–75% yield even after 6 cycles of esterification. In addition, the substrate carbon chain was increased for investigation of substrate scope achieving satisfactory results and all products were characterized by ¹H and ¹³C nuclear magnetic resonance spectroscopy.

Full text of DOI:10.1007/s11164-021-04570-z

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04570-z
Biomass‑derived dibasic acids to diesters with inorganic
ligand‑supported catalyst: synthesis, optimization,
characterization
Deli Lu1 · Yumeng Xu1 · Zhe Chen1 · Sheng Han1
Received: 5 July 2021 / Accepted: 11 August 2021
© The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract
Several attempts have been made to obtain aliphatic dicarboxylic diesters from
esterifcation reaction to develop the biomass-derived platform molecules and green
manufacturing processes. In this paper, Na3(H2O)6[AlMo6O18(OH)6], an Anderson-
type polyoxometalate, frstly, was reported as a catalyst for diester synthesis from
dicarboxylic acid to diester which showed an well productivity and selectivity char-
1
acterized by H and 13C. Response surface methodology (RSM) integrated with
the desirability function approach was used to determine the best operative condi-
tions, and the optimal reaction parameters for maximum dipropyl succinate yield
(77 2.5%) were identifed as 1.19 mol.% catalyst loading, 4.9:1 propanol/succinic
acid ratio, 113 °C, and 9.6 h. Three batches of tests were carried for catalyst recy-
cling with 78–75% yield even after 6 cycles of esterifcation. In addition, the sub-
strate carbon chain was increased for investigation of substrate scope achieving sat-
isfactory results and all products were characterized by 1H and 13C nuclear magnetic
resonance spectroscopy.
Keywords Diester · Catalyst · Esterifcation · Optimization · RSM
Introduction
The raw materials for many chemicals manufactured today perilously rely on the
fast-depleting traditional fossil energy resources. Fuels, lubricants, and solvents are
almost entirely derived from petroleum-based sources [1]. In this perspective, bio-
mass-derived platform molecules and green manufacturing processes have gained
*
*
Deli Lu
ldl@sit.edu.cn
Sheng Han
hansheng654321@sina.com
1
School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Haiquan
Road 100, Shanghai 201418, People’s Republic of China
Vol.:(0123456789)
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D. Lu et al.
growing research impetus among academia and industries [2–4]. It is possible to
derive potential chemicals from biomass-derived feedstocks and convert them into
other valuable products. At present, many biomass-based pathways to produce these
chemicals have been proposed in the literature instead of conventional methods
[5–8], which mainly include catalyzing monocarboxylic acids to obtain esters. The
preparation of diester products is urgently needed to be studied.
Acids like succinic, adipic acid, sebacic acid, etc., are essential bio-platform mol-
ecules that can be converted into valuable products through esterifcation reaction
[9]. It’s known that the efects of aliphatic dicarboxylic acids obtained from this
esterifcation reaction are necessary green chemicals widely used as intermediate for
the synthesis of fne chemicals, high-boiling solvents, lubricants, plasticizer, drugs,
food preservatives, pharmaceuticals, and cosmetics [10]. These diester products are
characterized by relatively high boiling and fashpoints, solubility, resistance, and
low viscosity and toxicity [11, 12]. Constant extension of an assortment of diesters
by synthesizing new individual compounds requires setting optimal conditions for
each particular process [13, 14]. Accordingly, it is relevant to determine the infu-
ence of diferent factors on the esterifcation reaction, which determine the maxi-
mum conversion of dicarboxylic acids. Besides, esterifcation processes are carried
out under harsh conditions with relatively high-energy demands and high costs.
Generally, the most common methods for the preparation of ester proceed via car-
boxyl group activation under catalyst and subsequent reaction with suitable alcohol.
Therefore, the choice of a catalyst, which should be afordable, simple to prepare,
and remove easily, is particularly important [15–17].
The conventional synthetic methods for preparing diesters involve the use of
homogeneous acid and base catalysts or heterogeneous catalysts. The most often
used Lewis or Bronsted acidic catalysts can efciently catalyze esterifcation reac-
tion but cause corrosion. These routes are riddled with the complexity of down-
stream processing, catalytic poisoning, and deactivation in the presence of impu-
rities or water [18–20]. In addition, these base-catalyzed routes are also prone to
disproportionation of diesters to monoesters in the presence of alcohols, which
reduce the yield of diesters and, therefore, the selectivity of the process. In contrast
to homogeneous systems, heterogeneous catalytic systems facilitate product separa-
tion and reusability and provide more active sites and among many other benefts.
However, the heterogeneous catalysts currently studied also have their limitations
[21–23]. Recent papers have demonstrated that the ion-exchange resin [24–27], such
as Amberlyst 15, Amberlyst 70® and Amberlyst XN-100, the low cross-linked sul-
fonated or only sulfonated resin, showed good performance as an acid catalyst. But
the superior performance also represents the complex processing technology of the
catalyst. While there are reports on the esterifcation of succinic acid (SA) using car-
bonaceous materials like DARCO-HSO3 or carbon-P-750, it’s difcult to be widely
used in the long reaction time or difculty in controlling the catalyst structure
[28–30]. Also, some researches on the montmorillonite clay and molecular sieve
[31, 32] about esterifcation of carboxylic acids have made good progress. Still, the
preparation of these catalysts requires harsh conditions with high-temperature cal-
cination and multiple processes. Therefore, it is necessary to fnd a type of catalyst
that is more green, economical, and easy to prepare.
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Biomass-derived dibasic acids to diesters with inorganic…
Polyoxometalate (POM) catalysts with a simple preparation process, no corro-
sion, and environmental friendliness are well explored for organic transformations
such as esterifcation, oxidation, and isomerization [33–37]. Its unique cage structure
can increase the catalytic activity of the catalyst and increase the selectivity of the
catalyst. At present, the most reported researches on polyoxometalates mainly focus
on the phosphotungstate and silicotungstate [38, 39]. However, the esterifcation of
succinic acid using polyoxometalate catalyst is rather scant [40, 41], and there are no
reports on esterifcation by POM catalyst from dicarboxylic acid to diester.
Here, Na3(H2O)6[AlMo6O18(OH)6] (named as [AlMo6]), an Anderson-type poly-
oxometalate, was frstly reported as a novel catalyst for diester synthesis with well
selectivity and productivity which was prepared as described in the literature earlier
[41–43]. Using succinic acid (SA) and propanol as a template reaction, the efect
of diferent variables like the initial molar ratio of alcohol to succinic acid, tem-
perature, reaction time, and the amount of catalyst on the molar yield was studied.
Furthermore, an attempt was made to optimize the process by RSM and obtain the
regression coefcients equation for yield. Finally, the carbon chain of the substrate
was increased to expand the substrate and prepare diferent diester products, includ-
ing adipate diesters and sebacate diesters which would be an ideal option for the
diester production.
Experimental section
Materials and methods
Materials
All the chemicals were purchased from Shanghai Titan Scientifc Co., Ltd such as
succinic acid, adipic acid, sebacic acid and alcohols of diferent chain lengths.
Catalyst preparation
According to the literature [43, 44], it is prepared by precipitation from an acidic
aqueous solution of AlCl3·6H2O (15 g, 0.63 mol), acetic acid, and Na2Mo6O4·2H2O
(35 g, 0.145 mol). The reaction mixture was kept in a container at room temperature.
After one week, the precipitated white crystals were fltered, washed with water,
and dried in air to obtain the Na3(H2O)6[AlMo6O18(OH)6] crystals. The crystal was
matched with literature data through the infrared spectrum test: FTIR (KBR pel-
let, cm−1): ṽ=3390(m, HO str.), 955(s, Mo=O), 919(s, Mo=O), 906(s, Mo=O),
645(s), 568(w), and 445(w), which are consistent with literature data [43, 44].
Experimental design
In this work, Box-Behnken design (BBD) of RSM was used for optimizing the diester
yield. Because Box-Behnken designs often have fewer design points, they can be less
expensive to do than central composite designs with the same number of factors. The
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D. Lu et al.
RSM coupled with BBD design was developed with the Minitab software ver.17. A
3-level 4-factor design of BBD was employed in this study. The catalyst quantity (A),
reaction temperature (B), molar ratio (C), and reaction time (D) were the four factors
considered for optimization. The factors and their levels were chosen based on the
experimental trials conducted in laboratory. The experiments were conducted based
on the BBD design, and the feasibility of the design was analyzed with the regression
and variance analyses. Furthermore, RSM was integrated with the desirability func-
tion to identify the local solution for the best optimal response of diester yield.
Esterifcation
The esterifcation reaction was carried out in a reaction tube with oil bath pot stirred
magnetically. The esterifcation was carried at diferent temperatures by varying the
catalyst amount (0.5–1.5 mol.%), molar ratio (2:1–6:1), and reaction time (4-12 h).
Taking the preparation of dipropyl succinate as an example, 1.18 g of succinic acid,
2.4 g of propanol, and 0.1170 g of [AlMo6] were added to the reaction test tube and
then stirred at 100° C for 8 h. After esterifcation, the catalysts were separated from
reaction liquid by gravity separation method and subjected to subsequent extraction
and concentration to obtain purifed dipropyl succinate. Other diester products were
obtained by the same preparation method.
Characterization method of diesters
After the esterifcation reaction contents were purifed, products were taken out
and dissolved in CDCl3 and then characterized by NMR spectroscopy in a Bruker
AVANCE 500 MHz instrument.
Results and discussion
Process optimization by RSM
In this work, RSM technique was used to optimize the experimental parameters. The
regression results for yield (%) are shown in Table 1, and the results of RSM are
provided in Table 2. According to Table 1, the two terms of linear and square whose
p-values are both less than 0.05 are signifcantly efective. The p-value of lack of ft
was 0.092 suggesting that the developed model has adequately ft the experimental
data. However, the p value of interaction term is more than 0.05 indicating that the
regression efect (Table 2) of the term is not signifcant. Therefore, the optimized
estimated regression coefcients for yield (%) after eliminating the interaction terms
have been expressed as Eq. (1).
Yield(%) = −523.2 + 49.3A + 9.19B + 12.2C + 6.62D − 20.7A2 − 0.04075B2 − 1.228C2 − 0.346D2
(1)
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D. Lu et al.
Table 2 Experimental, predicted
A
B
C
D
Yield (%)
Yield (%)
and residuals of RSM
Catalyst Temperature Ratio Time Experimental Predicted
1.0
0.5
1.5
1.0
1.5
1.5
1.0
1.0
1.0
1.5
1.5
1.0
0.5
1.0
0.5
1.0
1.0
0.5
1.0
0.5
1.0
1.0
1.5
0.5
1.0
1.0
1.0
100
120
100
120
120
100
100
100
100
100
80
120
100
120
80
100
80
4
4
4
4
4
6
6
2
2
4
4
6
2
4
4
6
4
4
4
4
4
2
2
6
2
6
4
8
8
12
4
8
8
12
12
4
4
8
8
8
12
8
4
12
4
4
12
8
8
66.0
61.9
69.0
70.0
67.0
60.0
69.0
55.0
47.0
57.0
34.0
77.0
60.0
72.0
16.0
52.0
24.0
43.0
25.0
57.0
67.0
54.0
58.0
60.0
20.0
33.0
70.0
67.67
66.32
64.71
61.57
67.72
66.75
68.55
54.55
50.38
57.05
32.52
74.53
49.40
71.74
18.22
55.38
28.59
48.20
21.42
57.86
67.67
60.03
56.25
57.90
23.38
27.88
67.67
100
80
100
100
120
100
100
80
8
8
8
8
80
100
8
A-Cat. (relative to SA, mol.%); B-Reaction temperature (°C);
C-Molar ratio (Propanol: SA); D-Reaction time (h)
where A denotes the catalyst in % (compared with reactant acid), B denotes reaction
temperature (°C), C denotes reactant alcohol: reactant acid, and D denotes the reac-
tion time (h). The regression coefcient (R2) of the model was 93.04% showing that
the efect of quadratic polynomial regression is good. For the optimized regression
results, the terms of linear and square whose p-values are all less than 0.05 are sig-
nifcantly efective.
Efects of experimental factors
The efects of experimental factors on dipropyl succinate yield are shown in
Fig. 1(a–f). It can be observed from Fig. 1 that at fxed catalyst concentration
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Biomass-derived dibasic acids to diesters with inorganic…
Fig. 1 Efect of diferent factors on the diester yield
(1 mol.%), reaction temperature (120° C), and 6:1 alcohol-to-acid molar ratio, the
maximum diester yield of around 77% was achieved for 8 h reaction time. Fig-
ure 1a demonstrates the efects of reaction temperature and reaction time on the
dipropyl succinate yield. It could be observed that the diester yield signifcantly
increased from 80 to 100° C and increased gently thereafter. This trend disclosed
that most of the esterifcation reaction occurred for reaching a certain temperature
because of the maximum reaction rate achieved during this period. The infuences
of molar ratio and reaction time on diester yield are demonstrated in Fig. 1b.
It was observed that the diester conversion accelerated with an increase in the
reaction time from 4 to 8 h and decelerated thereafter. This was because of the
reversal efect of the esterifcation reaction. From the response plot (Fig. 1c), two
major observations were drawn. The frst observation was that the diester yield
was signifcantly decreased when the catalyst concentration was more than the
optimum quantity. The second major observation was that there was no obvious
incremental efect on the diester yield when the molar ratio was increased from
4:1 to 6:1. Thus, the addition of alcohol beyond the optimal point would increase
the production cost and also account for an additional treatment step to recover
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D. Lu et al.
excess alcohol. In general, it is obvious from Fig. 1 that the reaction temperature
plays a key role in this reaction system.
Sensitivity analysis
In order to identify the local solution for the best predicted response, the sensitiv-
ity analysis was conducted with the aid of the Minitab response optimizer tool. The
response optimizer plot is shown in Fig. 2. It could be observed from the diagram
that the maximum predicted diester yield of 77% was achievable with the identi-
fed global solution. Moreover, composite desirability (D) evaluates how the set-
tings optimize a set of responses overall. Desirability has a range of zero to one. The
composite desirability was 1, indicating the ideal case that the developed solution
was excellent. To experimentally test this result, four batch trials were conducted
and the average yield was found to be 77.0 2.5%, which agreed with the predicted
response.
Recyclability and reusability of [AlMo6]
After each reaction, the reaction solution was fltered after using a short time cen-
trifugation to obtain the solid catalyst. The recovered [AlMo6] catalyst was then
dried, recycling for the next reaction. Accordingly, [AlMo6] showed super stabil-
ity and recyclability, and the catalytic activity remained almost constant (from 78
to 75%, Fig. 3) even after 6 cycles of esterifcation. Three batches of tests were
Fig. 2 Response optimizer plot to determine the global optimum solution
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Biomass-derived dibasic acids to diesters with inorganic…
Fig. 3 Recycling stability of the PIC in the esterifcation reaction (reaction temperature: 113 °C, Catalyst
dosage: 1.19 mol.% of SA, reaction time: 9.6 h, molar ratio of propanol to SA: 4.9: 1)
carried out in each cycle, and the standard deviation are shown in Fig. 3. In addi-
tion, each recycling [AlMo6] was dried to obtain the FTIR spectra and the results
in the 1100–400 cm−1 regions are shown in Fig. 4 because the characteristic peaks
of the [AlMo6] are seen only in the regions 960–900 cm−1, 650–550 cm−1 and less
than 450 cm−1. The peaks located at 955 cm−1,919 cm−1and 906 cm−1 are assigned
to the stretching vibrations of the Mo=O groups; the 645 cm−1 peak is attributed
to the vibration of the Mo–O-Mo group, and the vibrational mode characteristic of
the bond between the Mo and the central heteroatom Al is observed at 567 cm−1
and 445 cm−1 for [AlMo6]. According to Fig. 4, new absorption bands (more than
960 cm−1) appeared when the catalyst was recycled, which were the residual SA
C-O band and product diester C–O–C band. The appearance of these new absorp-
tion bands confrmed the combination of the [AlMo6] with SA during the esterifca-
tion process. In addition, the intensity of the peak located at 445 cm−1 is weakened
after 3 cycles of esterifcation which is consistent with the beginning of a reduction
of yield in the circle 4 of Fig. 3.
Mechanism consideration
Based on these experimental results and POM catalysts that have been reported
[45–47], a tentative reaction mechanism of [AlMo6] catalyzed esterifcation that
rationalizes product formation as illustrated in Fig. 5. Note that any comment on
the specifc details of the mechanism is speculative at this stage. The acid center
on the surface of the [AlMo6] can accept the lone pair of electrons on the carbonyl
oxygen so that the electron cloud is strongly biased toward the oxygen atom, and the
carbonyl carbon is partially positively charged, which facilitates the attack of the
alcohol oxygen atom. The nucleophilic attack of alcohol to the carbocation produces
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D. Lu et al.
Fig. 4 FTIR spectra of [AlMo6] and its each recycling
a tetrahedral intermediate. Finally, proton migration and breakdown of the interme-
diate occur and eventually generate target product diester.
Investigation of substrate
The substrate expansion is carried out according to the above optimized conditions.
Since factor of the reaction temperature has the greatest infuence on the diester
yield, it is only necessary to adjust the reaction temperature to obtain the satisfed
1
results (Table 3). And all diester products were confrmed by H NMR and 13C
NMR.
NMR spectra
The chemical structure and composition of dipropyl succinate was character-
1
1
ized by H and 13C NMR analysis. The H NMR and the 13C NMR spectra are
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Biomass-derived dibasic acids to diesters with inorganic…
Fig. 5 Esterifcation of succinic acid and propanol catalyzed over the [AlMo6]
presented in Figs. 6 and 7, respectively, with dicarboxylic acid esters’ chemi-
cal structures (1H NMR (501 MHz, CDCl3) δ 4.02 (t, J = 6.7 Hz, 4H), 2.60 (s,
4H), 1.67–1.53 (m, 4H), 0.91 (t, J = 7.4 Hz, 6H); 13C NMR (126 MHz, CDCl3)
δ 172.70, 77.59, 77.33, 77.08, 66.58, 29.44, 22.20, 10.64). From Fig. 6, the
presented peaks were assigned to the protons of (CDCl3, ppm) -CH3 at about
δ = 0.91, labeled with b at about δ = 2.6 and-COO(CH2)2COO-(labeled with c) at
about δ = 1.67–1.53. The peak at 4.02 ppm labeled with d indicates a resonance
of characteristic peak for dicarboxylic acid esters (-COOCH2-). According to the
13C NMR spectra, peaks at about δ= 77.59, 77.33 and 77.08 ppm ascribed to the
CDCl3 solvent and the other peaks are corresponded to the chemical formula indi-
cated by the label. The spectrum results of other diester products are as follows,
and spectral pictures are presented in the supporting information.
1
Dimethyl Succinate, H NMR (501 MHz, CDCl3) δ 3.71 (s, 6H), 2.65 (s, 4H);
13C NMR (126 MHz, CDCl3) δ 173.04, 77.57, 77.31, 77.06, 52.14, 29.14.
Diethyl succinate, 1H NMR (501 MHz, CDCl3) δ 4.15 (q, J = 7.1 Hz, 4H), 2.62
(s, 4H), 1.26 (t, J = 7.1 Hz, 6H); 13C NMR (126 MHz, CDCl3) δ 172.63, 77.58,
77.32, 77.07, 60.94, 29.44, 14.43.
1
Dipropyl succinate, H NMR (501 MHz, CDCl3) δ 4.02 (t, J = 6.7 Hz, 4H),
2.60 (s, 4H), 1.67–1.53 (m, 4H), 0.91 (t, J = 7.4 Hz, 6H); 13C NMR (126 MHz,
CDCl3) δ 172.70, 77.59, 77.33, 77.08, 66.58, 29.44, 22.20, 10.64.
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D. Lu et al.
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Biomass-derived dibasic acids to diesters with inorganic…
Fig. 6 1H NMR spectra of the dipropyl succinate
Fig. 7 13C NMR spectra of the dipropyl succinate
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D. Lu et al.
Dibutyl succinate, 1H NMR (501 MHz, CDCl3) δ 4.09 (t, J = 6.7 Hz, 1H), 2.62
(s, 1H), 1.65–1.54 (m, 1H), 1.37 (dd, J = 15.0, 7.5 Hz, 1H), 0.93 (t, J = 7.4 Hz,
1H).; 13C NMR (126 MHz, CDCl3) δ 172.70, 77.58, 77.33, 77.08, 64.88, 30.88,
29.46, 19.38, 13.99.
1
Dipentyl succinate, H NMR (501 MHz, CDCl3) δ 4.03 (t, J = 6.7 Hz, 4H),
2.58 (d, J = 10.6 Hz, 4H), 1.58 (p, J = 6.8 Hz, 4H), 1.32–1.25 (m, 8H), 0.86 (t,
J = 6.7 Hz, 6H); 13C NMR (126 MHz, CDCl3) δ 172.70, 77.59, 77.33, 77.08,
66.58, 29.44, 22.20, 10.64.
Diheptyl succinate, 1H NMR (501 MHz, CDCl3) δ 4.09 (t, J = 6.7 Hz, 4H), 2.63
(s, 4H), 1.67–1.55 (m, 4H), 1.30 (dd, J = 13.1, 5.6 Hz, 16H), 0.89 (t, J = 6.7 Hz,
6H); 13C NMR (126 MHz, CDCl3) δ 172.73, 77.58, 77.33, 77.07,65.21, 32.00,
29.47, 29.20, 26.12, 22.87, 14.36.
Dioctyl succinate, 1H NMR (501 MHz, CDCl3) δ 4.08 (t, J = 6.8 Hz, 4H), 2.62
(s, 4H), 1.62 (s, 4H), 1.31–1.24 (m, 20H), 0.88 (d, J = 7.1 Hz, 6H); 13C NMR
(126 MHz, CDCl3) δ 172.67, 77.57, 77.32, 77.07, 65.18, 32.08, 32.05, 29.67,
29.55, 29.47, 29.44, 28.84, 26.15, 26.02, 22.90, 14.34.
1
Dimethyl adipate, H NMR (501 MHz, CDCl3) δ 3.66 (s, 6H), 2.32 (s, 4H),
1.65 (s, 4H); 13C NMR (126 MHz, CDCl3) δ 174.11, 77.59, 77.33, 77.08, 51.82,
33.91, 24.60.
1
Diethyl adipate, H NMR (501 MHz, CDCl3) δ 4.17–4.05 (m, 4H), 2.31 (s,
4H), 1.65 (d, J = 2.7 Hz, 4H), 1.24 (t, J = 7.1 Hz, 6H); 13C NMR (126 MHz,
CDCl3) δ 173.69, 77.61, 77.35, 77.10, 60.57, 34.18, 24.62, 14.44.
1
Dipropyl adipate, H NMR (501 MHz, CDCl3) δ 4.02 (t, J = 6.7 Hz, 4H),
2.32 (t, J = 6.3 Hz, 4H), 1.70–1.58 (m, 8H), 0.93 (t, J = 7.4 Hz, 6H); 13C NMR
(126 MHz, CDCl3) δ 173.78, 77.59, 77.33, 77.08, 66.24, 34.20, 24.69, 22.22,
10.63.
1
Dibutyl adipate, H NMR (501 MHz, CDCl3) δ 4.08 (t, J=6.7 Hz, 4H), 2.34 (s,
4H), 1.67 (s, 4H), 1.62 (s, 4H), 1.39 (d, J=7.5 Hz, 4H), 0.95 (t, J=7.4 Hz, 6H); 13
C
NMR (126 MHz, CDCl3) δ 173.79, 77.55, 77.30, 77.05, 64.55, 34.25, 30.94, 24.73,
19.42, 13.99.
Dipentyl adipate, 1H NMR (501 MHz, CDCl3) δ 4.06 (t, J=6.8 Hz, 4H), 2.32 (t,
J=6.5 Hz, 4H), 1.71–1.57 (m, 8H), 1.38–1.28 (m, 8H), 0.90 (t, J=6.9 Hz, 6H); 13
C
NMR (126 MHz, CDCl3) δ 173.71, 77.57, 77.32, 77.06, 64.79, 34.22, 28.58, 28.33,
24.71, 22.57, 14.21.
Diheptyl adipate, 1H NMR (501 MHz, CDCl3) δ 4.05 (t, J=6.8 Hz, 4H), 2.31 (t,
J=6.4 Hz, 4H), 1.63 (dd, J=23.6, 10.4, 5.3 Hz, 8H), 1.34–1.24 (m, 16H), 0.87 (t,
J=6.8 Hz, 6H); 13C NMR (126 MHz, CDCl3) δ 173.64, 77.58, 77.33, 77.08, 64.76,
34.19, 31.96, 29.15, 28.88, 26.12, 24.69, 22.81, 14.28.
1
Dioctyl adipate, H NMR (501 MHz, CDCl3) δ 4.03 (t, J=6.7 Hz, 4H), 2.30 (s,
4H), 1.60 (dd, J=18.9, 11.9 Hz, 8H), 1.33–1.21 (m, 20H), 0.85 (t, J=6.6 Hz, 6H);
13C NMR (126 MHz, CDCl3) δ 173.69, 173.67, 77.61, 77.36, 77.10, 64.77, 34.17,
32.02, 29.44, 28.86, 26.17, 22.90, 14.22.
Dimethyl sebacate, 1H NMR (501 MHz, CDCl3) δ 3.67 (s, 6H), 2.31 (s, 4H), 1.62
(s, 4H), 1.31 (s, 8H); 13C NMR (126 MHz, CDCl3) δ 174.57, 77.56, 77.31, 77.06,
51.72, 34.34, 29.31, 25.17.
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Biomass-derived dibasic acids to diesters with inorganic…
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Diethyl Sebacate, H NMR (501 MHz, CDCl3) δ 4.09 (q, J=7.1 Hz, 4H), 2.25
(t, J=7.5 Hz, 4H), 1.64–1.53 (m, 4H), 1.32–1.22 (m, 12H); 13C NMR (126 MHz,
CDCl3) δ 174.15, 77.58, 77.33, 77.08, 60.44, 34.61, 29.32, 25.20, 14.53.
Dipropyl sebacate, 1H NMR (501 MHz, CDCl3) δ 4.01 (t, J=6.7 Hz, 4H), 2.28 (t,
J=7.5 Hz, 4H), 1.62 (dt, J=12.0, 7.0 Hz, 8H), 1.29 (s, 8H), 0.93 (t, J=7.4 Hz, 6H);
13C NMR (126 MHz, CDCl3) δ 174.31, 77.55, 77.30, 77.04,66.14, 34.64, 29.35,
25.25, 22.28, 10.68.
Dibutyl sebacate, 1H NMR (501 MHz, CDCl3) δ 4.07 (t, J=6.7 Hz, 4H), 2.29 (t,
J=7.5 Hz, 4H), 1.67–1.56 (m, 8H), 1.42–1.28 (m, 12H), 0.94 (t, J=7.4 Hz, 6H);
13C NMR (126 MHz, CDCl3) δ 174.23, 77.37, 77.05, 76.55, 64.37, 34.63, 30.97,
29.34, 25.23, 19.41, 13.97.
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Dipentyl sebacate, H NMR (501 MHz, CDCl3) δ 4.06 (t, J=6.7 Hz, 4H), 2.29
(t, J=7.5 Hz, 4H), 1.62 (dd, J=13.0, 6.4 Hz, 8H), 1.35–1.28 (m, 16H), 0.91 (t,
J=6.8 Hz, 6H).; 13C NMR (126 MHz, CDCl3) δ 174.28, 77.58, 77.33, 77.08,64.68,
34.64, 29.37, 28.61, 28.36, 25.25, 22.61, 14.27.
Diheptyl sebacate, 1H NMR (501 MHz, CDCl3) δ 4.07 (t, J=6.7 Hz, 4H), 2.30 (t,
J=7.5 Hz, 4H), 1.66–1.59 (m, 8H), 1.32 (d, J=10.5 Hz, 24H), 0.90 (d, J=6.3 Hz,
6H); 13C NMR (126 MHz, CDCl3) δ 174.25, 77.56, 77.31, 77.05, 64.69, 34.65,
32.10, 32.00, 29.36, 29.19, 28.92, 26.17, 25.25, 22.85, 14.34.
Dioctyl sebacate, 1H NMR (501 MHz, CDCl3) δ 4.06 (s, 4H), 2.29 (d, J=7.6 Hz,
4H), 1.62 (s, 8H), 1.31 (s, 28H), 0.88 (d, J=7.0 Hz, 8H); 13C NMR (126 MHz,
CDCl3) δ 174.24, 77.58, 77.33, 77.07, 64.68, 34.62, 32.04, 29.34, 28.90, 26.19,
25.23, 22.89, 14.33.
Conclusion
The use of [AlMo6] catalyst mentioned in this paper showed advantages in environ-
ment and economy for it’s warm reaction conditions and convenient post-treatment.
In this investigation, the efects of experimental factors on succinic acid diester
yield were investigated by RSM-BBD approach (4 factors, three level designs).
The second-order polynomial regression model (R2 =93.04%) was validated to be
appropriate in the design of a similar reaction system. Furthermore, RSM integrated
with desirability function approach was employed to fnd out the global solution
for the best response. The results showed the maximum dipropyl succinate yield
of 77 2.5% with the optimum conditions. The optimum conditions identifed are
1.19 mol.% catalyst concentration (compared with succinic acid), 4.9:1 propanol to
succinic acid molar ratio, 9.6 h reaction time, and 113 °C reaction temperature. The
catalytic activity remained almost constant even after 6 cycles of esterifcation by
simple recycling methods. In addition, this work suggests that the growth of the car-
bon chain of the carboxylic acid and alcohol of the substrate can also obtain satisfac-
tory results.
Supplementary Information The online version contains supplementary material available at https://doi.
org/10.1007/s11164-021-04570-z.
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D. Lu et al.
Acknowledgements This work was supported from the National Natural Science Foundation of China
[Grant Number 22008155, 22075183, 21878188 and 21975161]; Chenguang Program of Shanghai
Education Development Foundation and Shanghai Municipal Education Commission [Grant Number
19CG69]; and Shanghai Gaofeng and Gaoyuan Project for University Academic Program Development.
Declarations
Confict of interest The authors declare that there is no confict of interest.
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