Highly selective conversion of glyceric acid to 3-iodopropionic acid by hydriodic acid mediated hydrogenation

Article abstract of DOI:10.1039/c9gc01084j

Glycerol, generated in abundance as the by-product in the process of biodiesel production and saponification, has seen attempts to convert it into value-added chemicals. However, due to the low selectivity of hydrogenolysis of the secondary hydroxyl group, valuable 1,3-substituted chemicals are difficult to obtain from glycerol by chemocatalysis. In this work, glyceric acid (GA), a renewable biomass from glycerol, was quantitatively converted to 3-iodopropionic acid (3-IPA) at 373 K in 3 h by hydroiodic acid mediated hydrogenation. As the reductant in this process, HI is oxidized to I₂ and then regenerated in situ by metal catalysts and H₂. The reaction pathway was proposed by intermediate identification and verified by a kinetics study and computational method. The catalytic system was shown to be stable and can be reused several times without loss in activity. As a 1,3-substituted chemical, 3-IPA is not only a potential monomer to form poly-3-hydroxypropionic acid, but also a good platform molecule to produce useful chemicals, e.g. 3-hydroxypropionic acid (3-HPA) and acrylic acid (AA), due to its highly reactive nature.

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DOI: 10.1039/C9GC01084J
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Highly Selective Conversion of Glyceric Acid to 3-Iodopropionic
Acid by Hydriodic Acid Mediated Hydrogenation
Teng Li,
†
a Shengqin Liu, a Bing Wang, b Jingen Long,a Jun Jiang,a Ping Jin,a Yao Fu,b Haizhu Yu *b and
†
Received 00th January 20xx,
Accepted 00th January 20xx
Weiran Yang *a
DOI: 10.1039/x0xx00000x
Glycerol, generated in abundance as the by-product in the process of biodiesel production and saponification, has been
attempted to convert into value-added chemicals. However, due to the low selectivity to the hydrogenolysis of secondary
hydroxyl group, valuble 1,3-substituted chemicals are difficult to be obtained from glycerol by chemocatalysis. In this work,
glyceric acid (GA), a renewable biomass from glycerol, was quantitatively converted to 3-iodopropionic acid (3-IPA) at 373 K
in 3 h by hydroiodic acid mediated hydrogenation. As the reductant in this process, HI is oxidized to be I2 and then
regenerated in situ by metal catalysts and H2. The reaction pathway was proposed by the intermediate identification and
verified by kinetic study and computational method. The catalytic system was shown to be stable and can be reused for
several times without loss in activity. As a 1,3-substituted chemical, 3-IPA is not only a potential monomer to form poly-3-
hydroxypropionic acid, but also a good platform molecule to produce useful chemicals, e. g. 3-hydroxypropionic acid (3-
HPA) and acrylic acid (AA) due to its highly reactive nature.
www.rsc.org/
a. T. Li, S. Liu, J. Long, J. Jiang, P. Jin, prof. W. Yang. School of Resources
Environmental and Chemical Engineering, Nanchang University, Nanchang
330031, Jiangxi, China. *E-mail: wyang16@ncu.edu.cn.
b. B. Wang, prof. Y. Fu, prof. H. Yu. Hefei National Laboratory for Physical Sciences
at the Microscale, iChEM, CAS Key Laboratory of Urban Pollutant Conversion,
Anhui Province Key Laboratory of Biomass Clean Energy, Department of
Chemistry, University of Science and Technology of China, Hefei 230026, Anhui,
China. *E-mail: yuhaizhu@ahu.edu.cn.
† T. Li and S. Liu contributed equally to this work.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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Hydroiodic acid is a good reductant aDnOdIi:o10d.i1d0e39c/aCn9GreCp01la0c8e4J
hydroxyl group efficiently34, 35, which makes it a highly
selective reagent toward reaction with polyols. Robinson et al.
converted D-sorbitol to iodohexane selectively by hydriodic
acid combining with H3PO3.36-41 In this process, HI was
regenerated in situ by H3PO3. Sen et al. improved this method
by using metal catalyzed hydrogenation (RhCl3 or Pd/C) to
regenerate HI in situ from I2.42-45 By this method, fructose was
converted selectively to 5-methylfurfural (yield 81%) at 413
K43 and glycerol was reduced to 2-iodopropane quantitatively
at 393 K45. HI has also been used to reduce saccharic acid46, 47
and tetrahydrofuran-2,5-dicarboxylic acid48, 49 to adipic acid in
organic acid solvent and the reaction mechanism of the metal-
free system was studied in detail48. Here, we would like to use
the high selectivity of HI mediated hydrogenation to
selectively produce valuable 1,3-substitued chemicals from
glycerol and its derivatives.
Introduction
As a sustainable material derived from living organisms,
biomass can serve as a partial replacement for petroleum to
produce chemicals and fuels1, 2. Glycerol, reported as one of
the “top 10” platform molecules by DOE of the USA3, is
generated in abundance as the by-product in the process of
biodiesel production4 and saponification5. With the expansion
of the biodiesel market, glycerol is available in cheap price and
desirable to produce value-added products. Many useful
chemicals, such as 1,3-propanediol6-8, 1,2-propanediol9-11
,
Lactic acid12, 13, 3-hdyropropionic acid (3-HPA)7, 8, glyceric acid
(GA)14-16, acrolein17-19, allyl alcohol20, 21 and epichlorohydrin22,
23, can be produced from glycerol by various catalytic reactions,
such as oxidation, hydrodeoxygenation, dehydration,
acetalization, esterification and etherification4, 24
.
1,3-substituted chemicals, such as 3-HPA and 1,3-
propanediol, are very important and valuable. However, due
to the low selectivity to the hydrogenolysis of secondary
hydroxyl group, valuable 1,3-substituted chemicals are
difficult to be obtained from glycerol by chemocatalysis, which
can be explained by the mechanical calculation that the active
energy for the cleavage of the secondary hydroxyl group is 9.6
kJ/mol higher than that for the terminal hydroxyl group25.
Currently, 3-HPA is usually produced from expensive or toxic
starting material, such as β-propiolactone, acrylic acid, or 3-
hydroxypropionitrile. Renewable 3-HPA produced from
glycerol or sugar is more desirable. Chemical catalysis method
is not usually used here partly due to the low selectivity.5, 26
Biological catalytic method has made some important process
for 3-HPA production recently.5 Tian et al. obtained 83.8 g/L 3-
HPA from glycerol in 72 h with IPTG-inducible tac promoter
and the recombinant K. pneumoniae strain;27 another work by
Jung reported the highest yield of 0.97 g 3-HPA/g glycerol can
be obtained in a fed-batch experiment.28 However, the
intrinsic efficiency, 3-HPA tolerance, and separation problems
in the fermentation process are difficult to address.29 On the
contrary, it is hopeful for chemocatalysis to solve these
problems. 1,3-propanediol is another useful 1,3-substituted
chemical, whose production from glycerol also suffers from
the low selectivity.5, 26 Recently, researchers have made some
progress by using Pt-W6-8, 30 and Ir-Re31, 32 as the catalyst to
improve the selectivity. Zhang et al. reported a 42.0% yield of
1,3-propanediol from glycerol by a high dispersed Au and Pt
catalyst on WOx at 413 K under 1 MPa H2;30 Zong et al. used
Pt/W–SBA-15 as the hydrodeoxy-genation catalyst, and the
highest yield of 1,3-propanediol obtained is 61.5% at 423 K;7
Racha et al. found that a 69% 1,3-propanediol was yielded by
Pt/WOx/AlOOH at 453 K.33 In all, no more than 70% yield of
1,3-propanediol was obtained from glycerol during 413~533 K
in water. Because of the low efficiency and high reaction
temperature, this process is still unsatisfactory for the
industrial production. Hence, it is necessary to develop an
efficient and highly selective hydrogenolysis method for the
selective reduction of the secondary hydroxyl group of
glycerol or its derivatives.
Scheme 1. Proposed mechanism of the reaction from glycerol to 2-iodopropane [21]
The mechanism for the glycerol reduction by HI to produce
2-iodopropane was proposed that glycerol was first converted
to 1,2,3-triiodopropane by the substitution reaction of
hydroxyl groups, and 3-iodopropene was formed by
elimination of iodine; then the addition of HI to 3-iodopropene
makes 1,2-diiodopropane following Markovnikov rule as
hydroxymethyl is electron-donating group; repeating the
previous process (substitution-elimination-addition), 2-
iodopropane was selectively obtained (Scheme 1).50 Based on
this reaction mechanism, a new method to produce 1,3-
substitued chemicals from glycerol was designed in this work.
Using glycerol derivatives with an electron-withdrawing group
on their terminal as the reactant, the anti-Markovnikov
addition will happen during the reaction process, and iodide
will be added on the 3rd carbon, so more useful 1,3-
substituted chemicals can be obtained (Scheme 2).
Scheme 2. Proposed reaction path from glycerol derivatives to 2- or 1,3-substituted
chemicals
In this work, by experimental design, we are able to
convert glyceric acid (GA), which can be produced readily and
efficiently from glycerol by either the fermentation51, 52 or the
chemical catalytic process15, 16, 53, 54, to 3-iodopropionic acid (3-
IPA) selectively by hydroiodic acid that is regenerated in situ
by metal catalyzed hydrogenation (Scheme 3). Consequently,
we realized the highly selective hydrogenolysis of the
secondary hydroxyl group of glycerol derivative and obtained
1,3-substituted chemical (3-IPA) quantitatively. 3-IPA can be
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further converted to 3-HPA and acrylic acid completely. Due Further, SEM-EDS elemental mapping alsDoOsIh: o10w.1e0d39t/hCa9tGmC0e1t0a8l4sJ
to 3-HPA’s broad transformation ways and abundant dispersed well on the supports. In addition, the surface area
subsequent products, it is promising to be a good platform of Ni/C, Pd/C, Pt/C and Rh/C is 1237.5, 822.4, 872.2 and 868.0
molecule. Moreover, the reaction pathway and mechanism m2/g and the loading is 3.7%, 3.7%, 3.9% and 4.9% measured
are elucidated by intermediates identification, the reaction by ICP-AES. It was found that the results obtained over Ni/C
kinetics study and computational calculation.
and Pd/C catalysts are similar to the blank (compare entries
8&9 to entry 7). Pt/C showed better reactivity than Ni/C and
Pd/C, but lower than Rh/C (Table 1, entry 10). Using RhCl3 as
the catalyst, the conversion was 80% and the yield of 3-IPA
was 75%, which was better compared to the results by Rh/C
(compare entry 11 with entry 1) with the same loading. That is
because the homogeneous catalyst, e.g. RhCl3 usually
dispersed better in the reaction system than heterogeneous
catalyst, e.g. Rh/C.
To further confirm that the metal catalyst used during this
process is to regenerate HI form I2 and test their performance,
Ni/C, Pd/C, Pt/C and Rh/C are used to catalyze the formation
of HI from I2 under H2, respectively (Figure 1). The yield of HI
from I2 at 353 k in 1 h is following the order of blank < Ni/C <
Pd/C < Pt/C < Rh/C (Figure 1, Left), which is consistent with the
order for the 3-IPA formation. Further, the formation rates of
HI by blank, Ni/C, Pd/C, Pt/C and Rh/C were calculated to be
1.4×10-5, 2.7×10-5, 1.4×10-4, 3.1×10-4 and 1.1×10-3 mol∙L-
1∙s-1 (Figure 1, Right). Therefore, Rh/C shows the highest
catalytic activity for the reaction from I2 to HI and for GA
conversion, thus is chosen for the GA reaction.
Temperature effect to the reaction rate was also studied
(Table 1, entries 12~14). No GA conversion was observed with
57wt% hydroiodic acid at 333 K in 1 h (Table 1, entry 12). The
conversion of GA increased to 29% and the yield of DIPA and
3-IPA were 13% and 17% respectively at 353 K under the same
reaction condition (Table 1, entry 13). At 373 K, the conversion
and 3-IPA yield increased to 69% and 52%, respectively, while
the yield of DIPA was constant(Table 1, entry 1). When the
reaction temperature was 393 K, GA was observed to be fully
converted, and 96% yield of 3-IPA was obtained without DIPA
detected (Table 1, entry 14). Therefore, the reaction rate
increased dramatically with reaction temperature.
Finally, under the optimal condition, the reactant was
converted completely and the yield of 3-IPA was nearly 100%
at 373 K in 3 h (Table 1, entries 15&16). By using 57wt% HI (the
highest concentration we can obtain commercially) as the
reagent, usually excess amount of HI is applied (we need to
dissolve the reactant, and no external water can be added due
to lower activity, which will be discussed in the following
section). To overcome the drawback, acetic acid and methyl
glycerate (MG) were used as the solvent and the reactant,
respectively. Instead of HI, 1.3 mmol I2 was used in this system,
quantitative 3-IPA can be obtained from MG in 3 h (Table 1,
entry 17). Further reducing the amount of I2 and H2 to 1 mmol
and 100 psi, respectively, 94% yield of 3-IPA can still be
obtained at 393 K for 3 h (Table 1, entry 18).
Scheme 3. Conversion of glycerol and glyceric acid reduced by H2 or HI
Results and Discussion
Reduction of glyceric acid by hydroiodic acid
The results of the catalytic reduction of glyceric acid (GA)
under different reaction conditions (Scheme 4) were
summarized in Table 1. To start with, GA was reacted with
57wt% hydroiodic acid (about 7.5 M HI) and hydrogen over
Rh/C (5wt%) at 373 K for 1 h. As expected, 3-iodopropionic
acid (3-IPA) was obtained with high selectivity (Table 1, entry
1). Besides 3-IPA, 2,3-diiodopropionic acid (DIPA) was
detected, which is proved to be one of intermediates (see
more discussions in the next section).
GA was not consumed without hydroiodic acid (Table 1,
entries 2&3), indicating that HI is essential for GA reduction
under this reaction condition36-45 and Rh/C is inactive for the
hydrodeoxygenation of hydroxyl group at such low
temperature. Using equivalent of HCl or NaI to replace HI, GA
cannot be converted, implying that both H+ and I– are
necessary for this reaction (Table 1, entries 4-6). Without
metal catalyst or H2 or both, HI itself can still reduce GA but
with lower reactivity (compare entries 6&7 with entry 1).
Besides, lots of I2 was formed at the same time due to the
oxidation of HI, confirming that GA was reduced by HI directly.
Considering the fact that few I2 was detected in entry 1, we
concluded that metal catalyzed the regeneration of HI from I2
and H2, which was reported in previous papers42-45 and would
be studied in details below. In absent of metal catalysts, when
the reaction was performed under H2 instead of N2, the 3-IPA
yield was increased from 28% to 31% (compare entry 7 with
entry 6), which could be that a little of HI was regenerated
from I2 by H2 even without metal catalysts in this process. It
was proved by the blank experiment in Figure 1.
To study the influence of different metal catalysts on this
reaction, different commercial metal hydrogenation catalysts
were characterized (Figure S1 & S2) and used as the catalysts
(Table 1, entries 8~10). It was found that only some very small
peaks assigned to metals in XRD (details shown in Figure S1),
so most of metals on the active carbon were amorphous.
Scheme 4. Conversion of GA to 3-IPA catalyzed by HI-Rh/C-H2
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DOI: 10.1039/C9GC01084J
Table 1. Conversion of GA under different reaction conditions[a]
Intermediates identification
Entry
Acid
Metal
t (h)
Conv.
(%)
Yield of
DIPA (%)
Yield of 3-
IPA (%)
During the reaction process, it was found that the yield of 3-
IPA was less than the GA conversion during the reaction, so
there must be some intermediates in this process. The 1H NMR
spectrum of the reaction liquids at different reaction times
was performed (Figure S3). It clearly showed that with
increasing reaction time, the peak of GA decreased and the 3-
IPA peak increased. Besides, a group of unknown peaks (2.50
ppm, 2.54 ppm and 3.59 ppm) increased first, then decreased,
and finally disappeared, which must correspond to the
intermediate. To make the structure of this intermediate clear,
this unknown compound was separated by a chromatographic
column and then confirmed to be 2,3-diiodopropionic acid
(DIPA) by 1H NMR spectrum and MS spectrum (Figure S4 and
1
HI
-
Rh/C
-
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3
3
3
3
69
0
14
52
2[b]
3[b]
4[b, c]
5[b, c]
6[d]
7
N. D.
N. D.
N. D.
N. D.
12
N. D.
N. D.
N. D.
N. D.
28
-
Rh/C
Rh/C
Rh/C
-
0
HCl
NaI
HI
HI
HI
HI
HI
HI
HI
HI
HI
HI
HI
HI
HI
0
0
40
45
42
45
55
80
N. D
29
99
100
100
100
100
-
15
31
8
Ni/C
Pd/C
Pt/C
RhCl3
Rh/C
Rh/C
Rh/C
Rh/C
RhCl3
Rh/C
Rh/C
9
32
1
experimental section). DIPA was quantified by H NMR and
HPLC.
9
15
32
10
15
42
11
6
75
12[e]
13[f]
14[g]
15
N. D
13
N. D
17
1
96
N. D.
N. D.
N. D.
N. D.
>99
>99
>99
94
16
17[h]
18[i]
Figure 2. Left: Kinetic curve of conversion of GA reduced by HI. Right: Influence of the
HI concentration. Reaction condition: 0.56 g 20wt% GA aqueous solution (0.84 mmol
GA), 4.5 mL 57wt% hydroiodic acid, I2 0.65 g, 5wt% Rh/C 0.05 g, 373 K, reaction time 1
h, initial H2 pressure 400 psi, 400 rpm.
[a] Reaction condition: 0.56 g 20wt% GA aqueous solution (0.84 mmol GA), 4.5
mL 57wt% hydroiodic acid, I2 0.65 g (If I2 added into the system is reduced to HI
totally, the concentration of HI in the reaction liquid is about 7.5 M, namely
57wt%), metal catalyst 15 μmol, 373 K, initial H2 pressure 400 psi, 400 rpm. [b]
No HI or I2. [c] 7.5 M HCl or NaI. [d] Initial N2 pressure 400 psi. [e] 333 k. [f] 353
k. [g] 393 k. [h] Methyl glycerate 0.84 mmol, I2 1.3 mmol, CH3COOH 5 mL, initial
H2 pressure 400 psi. [i] Methyl glycerate 0.84 mmol, I2 1.0 mmol, CH3COOH 2 mL,
393 K, initial H2 pressure 100 psi. GA: Glyceric aid; DIPA: 2,3-diiodopropionic acid;
3-IPA: 3-iodopropionic acid.
Reaction kinetic curve and reaction pathway
To study the reaction pathway, the kinetic curve was drawn
(Figure 2, Left). It was shown that the yield of DIPA increased
from 6% to 18% and then decreased to 13% in 2 h, and GA was
converted to 3-IPA completely in 3 h (Figure 2, Left). Therefore,
this reaction pathway is GA → DIPA → 3-IPA. As initially
designed in Scheme 3, the reaction mechanism of GA
conversion with HI is proposed to go through the following
pathway55: first, hydroxyls on GA were substituted by I- to
form DIPA; then acrylic acid was obtained by the elimination
of I2 from DIPA; finally, 3-IPA was formed by the addition of HI
to acrylic acid following the anti-Markovnikov rule (Scheme 6).
To confirm other intermediates, 7.3 M NaI and 0.2 M HI
were used to replace 7.5 M HI to slow down the reaction, and
a 2.1% yield of acrylic acid was detected besides DIPA and 3-
IPA after the reaction (Scheme 5). To further confirm the
pathway, the possible intermediate, acrylic acid, was used as
reactants to carry out this reaction under the same reaction
conditions and the yield of 3-IPA (>99%) is higher than that
from GA (Table 2, compare entry 2 with entry 1), which is
consistent with our proposed pathway. Another aspect
remaining unclear is the substitution order of the 2, and 3,-
Figure 1. Reduction of I2 to HI over different metal catalysts. Left: Yield of HI at 353 K
in 1 h. Right: Formation rate of HI for different metal catalysts at 353 K. Reaction
condition: I2 5 mmol, metal catalyst 12 μmol, 36wt% hydroiodic acid 2 mL, initial H2
pressure 400 psi, 400 rpm. (Hydroiodic acid was added into the system to improve the
solubility of I2 in water)
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hydroxyl group by I-, which was not covered in the previous the GA conversion and the 3-IPA yield wDitOhI:t1h0e.10in3c9r/Cea9GseC0o1f0H84IJ
mechanistic study of glycerol reaction with HI either. To shed concentration. It is proposed that the decrease of mass
light on this, 3-HPA and lactic acid were used as model fraction of HI (ω(HI)), including added HI and HI formed from
reactants for the iodination reaction, respectively (Table 2, I2, reduced the reactivity of the substitution of hydroxyl with
entries 3&4). 62% of 3-HPA was converted to yield 54% of 3- iodide 38, 40. It is also implied that the substitution reaction may
IPA by 57wt% hydroiodic acid at 373 K in 5 min, while the be the rate-determing step (RDS). No 3-IPA from GA is
conversion of lactic acid was only 16.0% and the yield of 2- detected when ω(HI) is below 40wt%. Furthermore, 3-IPA can
iodopropionic acid and propionic acid (PA) were 0.5% and 11% be hydrolyzed to form 3-HPA efficiently at 373 K in 22wt%
respectively under the same reaction condition. PA was most hydroiodic acid (Table S1, entry 1). Therefore, water in
probably obtained through 2-iodopropionic acid reduction48, hydroiodic acid can hydrolyze iodide and prevent the
49. Therefore, it was obvious that the primary hydroxyl group iodization of the hydroxyl group (Scheme 7). To confirm this
was substituted more quickly and easily than the secondary conclusion, the iodization reaction of 3-HPA in water and
hydroxyl group here, which implies that 2-hydroxy-3- cyclohexane was carried out (Table S1, entries 2-3). It is found
iodopropionic acid was formed from GA first rather than 3- that 3-IPA can be produced in cyclohexane rather than water
hydroxy-2-iodopropionic acid (Scheme 6). Therefore, it is at lower concentration of HI (about 9wt%)34, 35. Therefore,
confirmed that the “substitution-elimination-addition” water amount has a crucial effect to the reaction.
process shown in Scheme 6 is the most possible pathway.
To look into the effect of H+ and I- respectively on this
Based on the similar mechanism reported in some previous reaction, the reactions with different concentration of H+ and
papers 46-49, another possible reaction pathway from DIPA to I- were performed and the results are shown in Figure 3. With
3-IPA is that secondary iodine on DIPA is reduced by HI and H2 7.5 M hydrochloric acid, no GA conversion was observed due
directly to form 3-IPA, but it has not been proved here.
to the weak nucleophilicity of Cl- 55. No GA was converted
either with 7.5 M NaI, mostly because proton was necessary
to the iodization of hydroxyl here56. Compared to the reaction
in 57wt% hydroiodic acid, the GA conversion reduced to 8%
and 21% as the concentration of H+ and I- reduced to half,
respectively. It is indicated that both H+ and I- are important to
the substitution of hydroxyl group by iodide here. Therefore,
the iodization of hydroxyl group is based on the synergistic
effect of H+ and I- (Scheme 7).
Table 2. The reduction of glycerol and its derivatives by hydroiodic acid[a]
Entry
Reactant
Conv. (%)
Major
Yield (%)
products
1[b]
2
GA
69
3-IPA
3-IPA
3-IPA
PA
52
Acrylic acid
3-HPA
100
62
>99
54
3[c]
4[c]
Lactic acid
16
11
[a] Reaction conditions: 0.84 mmol reactant, 5 mL 57wt% hydroiodic acid,
5wt% Rh/C 0.05 g, 373 K, 1 h, initial H2 pressure 400 psi, 400 rpm. [b] 0.56
g 20wt% GA aqueous solution (0.84 mmol GA), 4.5 mL 57wt% hydroiodic acid, I2
0.65 g. [c] 4.2 mmol reactant, reaction time 5 min.
Scheme 5. Conversion of GA in NaI-HI. Reaction conditions: 0.84 mmol GA, 5 mL H2O,
7.3 M NaI, 0.2 M HI, 5wt% Rh/C 0.05 g, 363 K, 1 h, initial H2 pressure 400 psi, 400 rpm
Scheme 7. Iodization of alcohol and hydrolysis of iodoalkane (Left)
Figure 3. Influence of concentration of H+ and I- (Right). Reaction condition: 0.84 mmol
GA, 5 mL water, 5wt% Rh/C 0.05 g, 373 K, reaction time 1 h, initial H2 pressure 400 psi,
400 rpm (Using NaI and HCl to modify the loading of H+ and I- in hydroiodic acid).
Reaction kinetic study
Scheme 6. Reaction pathway of the reduction of GA in hydroiodic acid
It was proposed above that the substitution of hydroxyl group
with iodide is the rate-determining step (RDS). To prove this,
GA and DIPA were reacted in hydroiodic acid-H2-Rh/C system
at 353 K and the reaction rates were calculated (Table 3). It
was found that 12% yield of DIPA and 3% yield of 3-IPA were
obtained from GA in 1 h, then the reaction rate from GA to
DIPA/3-IPA was figured out to be 1.8×10-6 mol∙L-1∙s-1. Under
the same condition, DIPA produced 3-IPA and GA and their
yields were 13% and 2%, respectively, in 0.5 h. Thus, the rate
for the reaction from DIPA to 3-IPA is 3.2 × 10-6 mol∙L-1∙s-1
Effect of HI and water on the iodization of GA
It is observed that the concentration of HI has a dramatic
influence on the reaction rate, which is studied in details here
(Figure 2, Right). The conversion of GA is sluggish at lower
concentration of HI (10 ~ 40wt%), but escalated significantly
(18% to 100%) when the concentration of HI increased from
46wt% to 62wt%. At the same time, the yield of 3-IPA soared
to 99% from 11%. Thus, it is synchronous for the increase of
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Scheme 8. Free energy profile for the formation of 3-IPA from GA and hydroiodic acid
Table 3. Conversion of GA and DIPA at 353 K in hydroiodic acid [a]
which is obviously higher than that of GA. Therefore, the step
from DIPA to 3-IPA is faster than that from GA to DIPA,
confirming that the process from GA to DIPA is the rate-
determining step. Considering the substitution reaction from
GA to 2-hydroxy-3-iodopropionic acid (RDS) is SN2-type
reaction and the concentration of HI is too high to change
much during the reaction, this reaction can be seen as pseudo
first order reaction. The kinetic study was performed to
confirm this. The ln r-ln([GA]0) curve gives a 1.1 order for this
reaction (Figure 4, Left), which is consistent with the
experimental observation and the following computational
result. The overall activation energy (Ea=103 kJ/mol) was
calculated from the initial reaction rates of the conversion of
GA in hydroiodic acid in a temperature range of 343 K to 373
K (Figure 4, Right), which coincides with the computational
energy in the next section.
Yield (%)
DIPA
Conv.
(%)
Reaction rate
Entry
Reactant
t (h)
(mol∙L-1·s-1
)
GA
3-IPA
1.8×10-6
1
2
GA
1.0
0.5
15
15
/
12
/
3
DIPA
2
13
3.2×10-6*
[a] Reaction condition: 0.22 mmol reactant, 4.5 ml 57wt% hydroiodic acid, 0.1 g
5wt% Rh/C, 353 K, initial H2 pressure 400 psi, 400 rpm. *: Rate of the reaction
from DIPA to 3-IPA.
Computational study on the reaction mechanism
To get a clearer picture of the mechanism of the reaction from
GA to 3-IPA, a detailed mechanism study was performed by
DFT calculations and the energy profile was given as shown in
Scheme 8. It starts from the protonation and substitution of
one OH group of GA via the SN2-type transition state TS1,
leading to the terminal iodinated product I3. The iodination of
the internal OH group was also considered (TS1’) but found to
be disfavored. It is consistent with the experimental
observation that 3-HPA was iodinated more quickly than lactic
acid (Table 3). Then the substitution of the other OH group
proceeds with the assistance of the neighboring iodine atom,
and DIPA (I5) is generated as
a considerable stable
intermediate. The formation of this complex has been
confirmed experimentally as mentioned before. The
subsequent elimination of I2 occurs in a concerted manner.
One of the iodine atom binds to I- to facilitate the formation of
the alkene I6. Finally, the electrophilic addition of HI (with the
assistance of H2O) to the alkene gives the product I7. It is
found that anti-Markovnikov addition (via TS4) is preferred
over Markovnikov addition (via TS4’), which tallies with the
regioselectivity observed in experiments. Further analysis
shows that the internal carbon of the alkene is more
negatively charged. Such biased distribution of the electron
Figure 4. Kinetic study on the GA reaction in hydroiodic acid. Reaction condition: 0.56
g 20wt% GA aqueous solution (0.84 mmol GA), 4.5 ml 57wt% hydroiodic acid, 5wt%
Rh/C 0.05 g, initial H2 pressure 400 psi, 400 rpm. Left: Effect of initial concentration of
GA at 353 K after 4 h on the GA conversion rate. Right: Effect of reaction temperature
on the reaction rate constant.
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pathway was elucidated to be GA → DIPA → acrylic acid → 3-
IPA by contrast experiments, kinetic study and computational
calculation, which is consistent with our initial reaction design.
Kinetic study confirmed that the substitution reaction from GA
to DIPA is the rate-determining step and the overall activation
energy is 103 kJ/mol. This catalyst system is stable and can be
reused. As a good platform chemical, 3-IPA can produce
varieties of terminal substituted products. Our process opens
a new gate to obtain 1,3-substituent products from glycerol.
density on the C=C bond results in the anti-Markovnikov
selectivity herein. Thus, the complete reaction mechanism is
proved to be the pathway shown in Scheme 6 again.
Stability study of the catalysts
To test the stability of the catalyst, the recycling experiments
were carried out in the autoclave using HI and RhCl3 as the
catalyst at 373 K for 1 h. The yield of 3-IPA was kept at 92% for
cycles 1~3 (Figure S5). Therefore, the reaction system can be
reused to produce 3-IPA stably and efficiently.
Conversion of 3-IPA to the important chemicals
Experimental Section
3-IPA is a renewable platform molecule that can produce
varieties of useful chemicals readily, such as hydrolyzed to
obtain 3-HPA57, eliminated to get acrylic acid 58, carboxylated
to form succinic acid, cyanided to obtain 3-cyanopropionic
acid59, and coupled to form adipic acid38, 40, etc. which are all
important terminal substituent chemicals (Scheme 9). We
showed in this publication that 3-IPA can be converted to 3-
HPA and acrylic acid efficiently. Quantitative yield of acrylic
acid was obtained from 3-IPA catalyzed by 1.0 M NaOH at
313 K in 2 h. While 3-IPA was converted to 3-HPA completely
in 6.7×10-4 M hydrochloric acid at 373 K in 4 h (Figure 5).
Materials: all chemicals and materials, glyceric acid (20%,
Tokyo Chemical Industry), 3-iodopropionic acid (99%, Alfa
Aesar), hydroiodic acid (55~58wt%, Aladdin), iodine (99.8%,
Innochem), Rh/C (5wt%, Alfa Aesar), Pd/C (5wt%, Aladdin),
Pt/C (5wt%, Tokyo Chemical Industry), RhCl3 (38.5~45.5wt%,
Alfa Aesar), lactic acid (80wt%, Acros Organic), 3-
hdyroxypropionic acid (≥97%, Damas-beta), Acrylic acid
(99.5%, Innochem), HCCl3 (≥99%, Xilong Scientific), hexane
(97.0%, Tianjin Damao), cyclohexane (99.5%, Innochem), CCl4
(≥99.0%, Aladdin), ether (≥99.0%, Alfa Aesar), hexanol (≥99.0%,
Sigma-Aldrich), tributyl phosphate (≥99.0%, Aladdin), NaOH
(≥96%, Xilong Scientific), D2O (99.9%, Innochem) and maleic
acid(≥99.0%, Aladdin), were commercially available and
directly used without further treatment.
X-Ray Diffraction. Powder X-ray diffraction (XRD) patterns
were performed with a Rigaku D/Max-200 diffractometer
using Cu Kα1 radiation (incident wavelength λ = 0.15406 nm)
operated at 40 kV and 100 mA with a scanning speed of 1°min-
1 and a step-size of 0.04°.
Scanning electron microscopy-energy dispersive X-ray
spectrometry (SEM-EDS) elemental mapping. SEM-EDS was
measured with a Quanta 200FEG field emission scanning
electron microscope (FEG-SEM) equipped with an Oxford
AZtec X-Max 80 EDS.
Scheme 9. The proposed subsequent conversion of 3-IPA
Inductively Coupled Plasma-Atomic Emission Spectrum (ICP-
AES). The concentration of Metal/C was measured by
inductively coupled plasma atomic emission spectrum (ICP-
AES, VARO EL). Before measurement, samples (~30 mg) were
digested at 120oC in 12 h in an acid solution (5 mL 65% HNO3
and 15 mL 37% HCl).
Brunauer–Emmett–Teller (BET). The Brunauer–Emmett–Teller
Figure 5. Conversion of 3-IPA to acrylic acid and 3-HPA
(BET) surface area (SBET
) was measured by nitrogen
adsorption–desorption isotherms, which was operated at -
196°C on a Micromeritics-TriStar II (Surface Area and Porosity)
instrument. The samples were outgassed at 150°C for 5 h
before the measurements.
Catalytic reaction and product analysis. These reactions were
carried out in an autoclave with a glass liner (the volume is
about 30 mL). Typically, reactants, catalysts and solvents were
put into the liner and the reaction started at desired
temperature under vigorous agitation in presence of H2. The
reaction was then quenched in a cold bath. Chemicals in water
were analyzed by HPLC (Agilent, LC-1200) using an organic acid
column (Alltech OA1000-Organic Acid column: 6.5 mm ID ×
300 mm).
Conclusions
In summary, a new method was developed to convert GA to
3-IPA selectively and efficiently at mild reaction condition. Due
to the high reducibility and strong nucleophilicity of HI, a 99%
yield of 3-IPA was obtained from GA catalyzed with Rh/C in
57wt% hydroiodic acid at 373 K in 3 h. And the reactivity to
regenerate HI from I2 is following the order of Rh/C > Pt/C >
Pd/C > Ni/C, indicating that rhodium (e. g. Rh/C and RhCl3) is
the best catalyst for this reaction. High concentration of HI
with less water are in favor of this reaction. DIPA was
identified to be the intermediate of the reaction. The reaction
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7.
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Y. Fan, S. Cheng, H. Wang, D. Ye, S. Xie, Y. Pei, H. Hu, W. Hua, Z. H.
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Identification of 2,3-diiodopropionic acid (DIPA). DIPA was
prepared from GA in hydroiodic acid under suitable reaction
conditions. Typically, DIPA was separated from concentrated
reaction liquid by chromatographic column (Dowex 50WX8
200-400(H), Alfa Aesar) and measured with 400 M NMR
(Bruker) and HRMS (Agilent). DIPA 1H NMR (400 MHz, CDCl3)
δ ppm: 3.38 (m, 1H, CH2–I), 3.45 (m, 1H, CH2–I), 4.31 (t, 1H,
CH–I, J = 8.6 Hz).
Stability test. The recycling experiments were carried out in
the autoclave using HI and RhCl3 (because Rh/C can be
extracted by CHCl3, RhCl3 was used here instead of Rh/C) as
the catalyst at 373 K for 1 h. Under this reaction conditions,
the GA was converted to 3-IPA completely. After the reaction,
the product was extracted by CHCl3, which is the most suitable
extraction liquid (Table S2). After that, GA and I2 were added
into the reaction system for the second cycle under the same
reaction condition. The third cycle was performed with the
same method.
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This work was supported by the funds from financial support
of the National Natural Science Foundation of China (Grant
No.21808100), “Thousand Young Talents” Program of China,
and “Thousand Talents”Entrepreneurship Program of Jiangxi
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Dr. Jun Wang and the analysis support from Comprehensive
Laboratory center, the College of Chemistry and Center of
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Keywords: glyceric acid • 3-iodopropionic acid • hydroiodic
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