Iodine catalyzed oxidation of alcohols and aldehydes to carboxylic acids in water: A metal-free route to the synthesis of furandicarboxylic acid and terephthalic acid

Article abstract of DOI:10.1039/c7gc02802d

A metal-free iodine/NaOH-catalyzed oxidation of alcohols and aldehydes has been developed for the practical synthesis of a wide range of carboxylic acids using water as the solvent. This transformation involves dehydrogenation of an alcohol, followed by a fast attack of water on an aldehyde. This method is mostly free from chromatographic purification, which makes it suitable for large-scale synthesis. The iodine species formed during the reaction as the active oxidation catalyst has been deduced as IO₂^- by control experiments. We also demonstrate a 10 gram scale synthesis of furandicarboxylic acid (FDCA) from HMF in good yield using our method.

Full text of DOI:10.1039/c7gc02802d

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DOI: 10.1039/C7GC02802D
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COMMUNICATION
Iodine Catalyzed Oxidation of Alcohols and Aldehydes to
Carboxylic Acids in Water: A Metal-Free Route to Synthesis of
Furandicarboxylic Acid and Terephthalic Acid
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Susanta Hazra, Mayukh Deb and Anil J. Elias*
www.rsc.org/chemcomm
A metal-free iodine/NaOH-catalyzed oxidation of alcohols and fine chemicals and pharmaceuticals has encouraged the
aldehydes has been developed for the practical synthesis of a development of mild, safe, and highly chemoselective
wide range of carboxylic acids using water as the solvent. This oxidizers. Iodine based reagents are now increasingly being
transformation involves dehydrogenation of alcohol, followed by used in organic synthesis as an alternative to transition metal
10
a fast attack of water on the aldehyde. This method is mostly free based reagents.
from chromatographic purification, which makes it suitable for
large-scale synthesis. The iodine species formed during the
reaction as the active oxidation catalyst has been deduced as IO2
by control experiments. We also demonstrate a 10 gram scale
synthesis of furandicarboxylic acid (FDCA) from HMF in good yield
by our method.
Selective oxidation of alcohols is an essential step in organic
synthesis as it can be used to produce aldehydes, acids,
1-5
amides, acetals and esters.
Among all the oxidized
feedstocks, carboxylic acids are needed as bulk chemicals in
large amounts in various fields including fine chemicals,
6
polymers and many commercial products. The global
production of aryl carboxylic acids was estimated as 480
7a
kilotons in 2014 and is likely to exceed 620 kilotons by 2023.
Scheme 1: Methods for the preparation of carboxylic acid from alcohols and
aldehydes.
Terephthalic acid (TPA), the monomer for the polyester PET,
used extensively for the manufacture of mineral water and
6
7
beverage bottles has a worldwide demand of 12.6×10 tons.
, 5- Furandicarboxylic acid (FDCA) has been identified by the During the last decade hypervalent iodine(V) reagents, namely
2
US Department of Energy as one of the twelve priority Dess-Martin periodinane (DMP), 2-iodoxybenzoic acid (IBX)
chemicals for establishing the “green” chemistry industry of and iodosobenzene have emerged as highly selective reagents
8
the future. However, large-scale syntheses of these carboxylic for the stoichiometric oxidation of alcohols to carbonyl
acids are still being carried out by oxidizing aldehydes and compounds and for many synthetically useful oxidative
10,11
alcohols with stoichiometric amounts of routine oxidants, such transformations.
In spite of the utility and popularity of
as permanganate and chromate. Often these reactions take DMP and IBX which are relatively expensive, a serious
place in unsafe organic solvents, generating copious amount of disadvantage is their explosive nature restricting their usage in
9
10f-g
used solvents and harmful side products. The recent demand larger quantities.
Thus, a facile and efficient use of the
for highly efficient and environmentally benign syntheses of readily available and relatively stable molecular iodine I
, in
2
place of iodine(V) reagents has been long desired. Recently, I2 /
aqueous tertiary-butyl hydrogen peroxide (TBHP) system has
become a powerful methodology to construct new C-C, C-N
a.
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New
Delhi-110016, India, Email: eliasanil@gmail.com, Fax: +91-11-26581102; Tel: +91-
1
1
and C-O bonds. However, almost all of these reactions were
carried out in organic solvents. With its abundance and
inherent greener characteristics, water has been the most
1
1-26591504.
†
Electronic Supplementary Information (ESI) available: For full experimental
techniques, X-ray data, UV-visible spectroscopic studies, see
DOI: 10.1039/x0xx00000x
12
desirable and ideal solvent for chemists. Biological oxidations
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Journal Name
in water using enzymes or microorganisms are well known. In After optimizing the reaction conditions, we eVixepwlAorrtieclde Ontlhinee
000, Sheldon and co-workers established an aqueous-phase substrate scope for the reaction (FigureDO1I):.1T0.h10is39r/eCa7cGtCio0n28w02aDs
homogeneous catalytic aerobic oxidation of alcohols, thus extended to compounds having electron donating as well as
2
1g
mimicking the nature. Following this pioneering work, electron withdrawing substituents on the aryl ring of alcohols
several groups have reported oxidation of alcohols to and aldehydes. Both gave > 85% yields of carboxylic acids.
1
,2
carboxylic acids in water (Scheme 1). Recently, research Under identical conditions, aliphatic alcohols showed lower
group of Li and Wei independently reported aerobic oxidation percentage of conversion (50-57%). Therefore, with a view to
of aldehydes to carboxylic acids using water as the solvent increase the yield by promoting homogeneity, a small amount
13
(
Scheme 1). Yet, all these methods require transition metals of CH CN as a co-solvent was added. Unfortunately, there was
3
or their salts as catalysts and in some cases high pressure and no improvement in yields even after using a water and
large excess of additives. So, the development of a transition acetonitrile (1:1) mixture and yield further decreased when we
metal free methodology to oxidize alcohols and aldehydes to used pure acetonitrile as the solvent.
their corresponding carboxylic acids using a greener oxidant in
water medium is highly desirable. Here, we report a highly
efficient, I /NaOH catalyzed oxidation of a wide range of
2
alcohols and aldehydes using only water as the solvent with
TBHP as the co-oxidant.
2f
As demonstrated by Bera and co-workers , one pot conversion
of alcohols to carboxylic acids can be accomplished by two
consecutive reactions: (1) acceptorless dehydrogenation (AD)
of alcohol to aldehyde, and (2) subsequent “aldehyde−water
shift” (AWS) reaction (Scheme 2).
Scheme 2: Alcohol dehydrogenation (AD) followed by an aldehyde−water
shift (AWS) reaction.
Figure 1: Substrate scope for the oxidation of alcohols and aldehydes to
carboxylic acids. (% yields in parenthesis are for alcohol substrates).
An ideal catalyst system should facilitate both the reactions
simultaneously. Although, molecular iodine has been used for
the dehydrogenation of alcohols to aldehydes and CDC
Reaction Conditions: Alcohols or aldehydes (5 mmol), I (0.5 mmol), NaOH (1
2
o
a
mmol), TBHP (70% in water; 20 mmol), H
2
O (2 mL), 70 C, 10-16h. For
compound 19 and 20, I (20 mol%), NaOH (0.5 equiv.), TBHP (70% in H O; 8
2
2
equiv.) were used.
1
0,11
coupling reactions,
similar iodine catalyzed “aldehyde-
water shift” reactions have not been explored. We were keen
to study whether water could play the role of both an oxygen
donor and reaction medium in a catalytic coupling between
alcohols and water under mild reaction conditions. We began
our investigation by examining the oxidation of 4-
methoxybenzylalcohol in water medium using iodine and
sodium hydroxide. We observed 12% conversion to the
desired carboxylic acid in presence of 4 equiv. of NaOH.
Modern organic synthesis uses oxidants which are highly
selective, efficient, and environmental friendly. Therefore, we
explored the effect of external oxidants for the reaction and
after several reactions it was found that aq. TBHP improved
the yields of the desired carboxylic acids (See SI Table-S4). This
finding prompted us to explore the scope of the reaction by
using catalytic amounts of iodine and base. We carried out the
reaction by varying reaction parameters and after detailed
exploration (see SI Table S2, S3 and S4), it was found that 10
mol% of iodine, 20 mol% of NaOH and 4 equiv. of aq. TBHP are
best suited for the reaction (Scheme 3).
This methodology is highly selective towards primary alcohol
and aldehyde groups for oxidation. To probe the selectivity, we
used 4-methyl benzylalcohol and 2, 4,
6 –trimethyl
benzylalcohol as substrates and these were separately treated
with aq. KMnO as oxidant as well as employing I /NaOH
4
2
Scheme 4: Selectivity towards primary alcohol and aldehyde groups for
a
4
oxidation. Reaction Conditions: Alcohols or aldehydes (5 mmol), KMnO (
o
b
1
2.5 mmol), H
2
O (5 mL), 70 C, 10h. Alcohols or aldehydes (5 mmol), I
2
( 0.5
o
mmol), NaOH ( 1 mmol), TBHP (70% in H
2
O: 20 mmol), H O (2 mL), 70 C, 10h.
2
Scheme 3: Oxidation of alcohols and aldehydes using I
| J. Name., 2012, 00, 1-3
2
/NaOH/TBHP.
2
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catalytic system. Terephthalic acid 19 was obtained in 55%
yield when aq. KMnO was used as oxidant but 4-toluic acid
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DOI: 10.1039/C7GC02802D
5
4
was obtained in 90% yield when I /TBHP was used. We also
2
obtained 2, 4, 6-trimethyl benzoic acid 13 in 82% yield using
our methodology but a mixture of partially oxidized products
was obtained when aq. KMnO was used (Scheme 4). Similar
4
results were obtained when substituted aldehydes were used
as substrates (Scheme 4).
To illustrate a potential application, we used our methodology
to convert fructose from biomass into FDCA, a highly desired
bio-based
feedstock
with
numerous
applications.
Simultaneous or successive oxidation of both the functional
groups (-CH OH and -CHO) of hydroxymethylfurfural (HMF) has
2
been a challenge for deriving polyester building-block
chemicals of commercial importance. Enormous efforts are
being undertaken for the production of FDCA by an
economically acceptable way that could be scaled up at the
industrial level. Partenheimer et. al. described the synthesis of
Scheme 6: Control experiments carried out for mechanistic studies.
reaction in the absence of a base. These results rule out the
intermediacy of esters during acid synthesis. Neither equal nor
excess amounts of I could catalyze this oxidation reaction in
2
2
,5-furandicarboxylic acid by catalytic air-oxidation of 5-
the absence of base, oxidant and water. As previously
reported, iodine species with different oxidation states (IO¯,
IO ¯, IO ¯) could be generated in situ from iodine and hydroxyl
hydroxymethylfurfural with Co/Mn/Br in acetic acid at
temperatures ranging from 50 to 125° C, commonly known as
the Amoco process. Using this catalyst, FDCA was obtained
2
3
14b
anion in presence of TBHP (eqn.(1), Scheme 7). Hypoiodite
IO¯) can be easily generated by reacting iodine with equimolar
8d
with a maximum yield of 35.2 %.
(
amounts of base in water. However, stoichiometric amount of
I2 and NaOH were unable to oxidize alcohol or aldehyde to the
corresponding carboxylic acid (Scheme 6c). This result
indicates that hypoiodite (IO¯) is not the active catalyst for this
transformation. Since, iodate (IO ¯) can also be formed in the
3
reaction medium (eqn(1) Scheme 7), we carried out separate
reactions of alcohol and aldehyde by using excess (2 equiv.) of
KIO (Scheme 6d). Excess amount of KIO was also unable to
3
3
oxidize the alcohols or aldehydes to carboxylic acids. This
result ruled out the possibility of iodate (IO ¯) as the possible
active catalyst for this transformation. Our controlled
3
Scheme 5: Synthesis of FDCA from Biomass.
experiments suggest that in-situ formed iodite (IO ¯) is the
2
active catalyst for this oxidation reaction. It is noteworthy that
Kita and co-workers have successfully used excess of an
There are few reports on the oxidation of HMF to FDCA using
transition metal based heterogeneous catalysts in aqueous
medium. However, a major limitation of these reported
11f
8
organoiodine (III) reagent, PhIO for a similar oxidation.
Based on our observations and related studies from other
methods is the requirement of dilute conditions to avoid
1
0,11,14
8
g
groups,
a possible catalytic cycle has been proposed
polymerization or degradation of intermediates. Hence, most
of the reactions were carried out only in milli-gram scale. The
(Scheme 7). The first step involves the formation of hypoiodite
(
IO¯) initiated by the reaction of I and OH¯ (eqn (1), Scheme
2
use of I /NaOH catalyst in our system enables efficient
2
7
). Next, TBHP oxidises hypoiodite (IO¯) to the active catalyst
oxidation of HMF to FDCA in gram scale synthesis (Scheme 5).
To understand the reaction mechanism and to identify the
active iodine species for these transformations, several control
experiments were carried out (Scheme 6). The addition of
TEMPO (2, 2, 6, 6-tetramethylpiperidine-N-oxyl) and BHT
(butylated hydroxytoluene) had no effect on the yield of the
reaction (Scheme 6 ), suggesting that the free radical
a-b
pathway is not involved in the present oxidation reaction.
Recently, Wan and co-workers have reported synthesis of an
ester from aldehyde by employing n-Bu NI/TBHP catalyst
4
11l
system in water.
One can consider that esters as
intermediates susceptible to hydrolysis in the presence of base
to carboxylic acid. However, no ester was detected under our
reaction conditions and it was also observed that there was no
Scheme 7: Possible catalytic cycle and generation of active catalyst for the
oxidation of alcohols to carboxylic acids in water.
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Khusnutdinova, G. M. Leitus, D. Milstein, J. AmV.ieCwhAertmicle. OSnolicn.e,
iodite (IO ¯) (eqn (1), Scheme 7). The iodite (IO ¯) species
2
2
2
015, 137, 4851; (d) S. L. Zultanski, J. Zhao, S. S. Stahl, J. Am.
DOI: 10.1039/C7GC02802D
oxidizes the primary alcohol to aldehyde and gets itself
reduced to IO¯. Next, water molecule attacks the carbonyl
centre under this reaction condition i.e. AWS reaction and
results in the formation of a tetrahedral intermediate IM1
Chem. Soc., 2016, 138, 6416; (e) C. Chen, F. Verpoort, Q. Wu,
RSC Adv., 2016, , 55599; (f) R. M. de Figueiredo, J. –S.
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5
(
Scheme 7). Following this, IO ¯ oxidises IM1 to the
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corresponding carboxylic acid and regenerates IO¯ and water.
It may be noted that a reaction of 4-methoxybenzyl alcohol
with anhydrous TBHP in anhydrous CH CN as solvent resulted
3
only the formation of 4-methoxybenzaldehyde supporting the
AWS reaction.
Conclusion
In conclusion, we have for the first time developed an efficient,
metal free, I / NaOH catalyzed synthesis of carboxylic acids
2
from alcohols and aldehydes in water as the solvent. Our
studies indicate that IO ¯ is the most likely active catalyst
2
6
(a) G. J. Hollingworth, in Comprehensive Organic Functional
Group Transformations, ed. A. R. Katritzky, O. Meth-Cohn, C.
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Operational simplicity, broad substrate scope and ease of
scaling up are additional features of this green oxidation
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Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgement
2
017, 82, 3781.
The authors thank DST, India for financial assistance in the
form of research grant to A. J. E [DST EMR/2015/000285]. S.
H., M. D thank UGC, India, for research fellowship. We thank
DST-FIST and IIT D for funding the single crystal X-ray
diffraction and HRMS facilities at IIT Delhi.
7
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