CSJ acting as a versatile highly efficient greener resource for organic transformations

Article abstract of DOI:10.1039/c6ra01760f

Simple, new, greener and efficient alternatives to the existing protocols have been developed for the reduction of aromatic aldehydes to their corresponding alcohols, decarboxylation of substituted benzoic acids (C₆-C₁) and substituted cinnamic acids (C₆-C₃) with a hydroxyl group at the para position with respect to the acid group to corresponding phenolic compounds and vinyl phenols respectively by using a natural feedstock, cucumber juice (CSJ), which acts as a greener solvent system, performing a substrate-selective reaction. Additionally, the hydrolysis of the acetyl as well as the benzoyl group of aromatic compounds has been carried out to afford excellent yield by CSJ.

Full text of DOI:10.1039/c6ra01760f

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CSJ acting as a versatile highly efficient greener
resource for organic transformations†
Cite this: RSC Adv., 2016, 6, 24446
*
Himadri Sekhar Maity, Kaushik Misra, Tanushree Mahata and Ahindra Nag
Received 20th January 2016
Accepted 19th February 2016
DOI: 10.1039/c6ra01760f
www.rsc.org/advances
Simple, new, greener and efficient alternatives to the existing proto- a highly abundant naturally occurring phenolic compound, is
cols have been developed for the reduction of aromatic aldehydes to a precursor of 4-VG, the commercial cost of which nearly 40
their corresponding alcohols, decarboxylation of substituted benzoic times more than that of ferulic acid.4a 4-VG has been chemically
acids (C6–C1) and substituted cinnamic acids (C6–C3) with a hydroxyl transformed into more biodegradable, oxygenated polystyrenes
group at the para position with respect to the acid group to corre- which demonstrate superior mechanical strengths over other
sponding phenolic compounds and vinyl phenols respectively by using polystyrenes.4b Moreover, catechol and pyrogallol obtained from
a natural feedstock, cucumber juice (CSJ), which acts as a greener protocatechuic acid and gallic acid are oen introduced into
solvent system, performing a substrate-selective reaction. Addition- synthesis of biologically active molecules such as avonoids,
ally, the hydrolysis of the acetyl as well as the benzoyl group of the anti-biotic trimethoprim, and muscle relaxant gallamine
aromatic compounds has been carried out to afford excellent yield triethiodide.5 A burgeoning global demand, several research
by CSJ.
groups have been involved for the synthesis of the above dis-
cussed compounds to replace the chemical methods by using
the green and safer technologies such as ionic liquids, micro-
wave and bio-catalysis.6 However, the development of a simple
and efficient synthetic methodology has been a tedious task
because of the requirement for harsh reaction conditions (such
as high temperature, high pressure), protection–deprotection
steps, low yield, toxic reagents, besides the susceptibility of the
hydroxyl functional group towards several side reactions,
including polymerization.3,6
Deprotection of functional groups is one of the most
important and widely carried out synthetic transformations in
preparative organic chemistry. Phenols are protected as acetates
and benzoates.7 The methods available for deprotection of aryl
acetates involve the treatment with activated Zn in MeOH,8
NaHTe in reuxing EtOH,9 n-BuNH2 in benzene,10 Al2O3 under
microwave irradiation,11 cyclodextrine in aqueous DMSO,12
Yb(OTf)3,13 K2CO3 in N-methyl-2-pyrrolidone,7 amberlyst-15,14
metal complexes,15 metalloenzymes,16 and natural kaolinitic
clay.17 However, these methods suffer from the disadvantages of
harsh reaction conditions, use of costly reagents, and not always
being effective for multifunctional substrates.7,18
Hydroxycinnamic acids in plants are known to be precursors of
aromatic compounds such as styrenes, polymers, epoxides,
alkylbenzenes, stilbenes etc.1 Vinyl phenol (hydroxy styrene)
derivatives, like 4-vinylphenol (4-VP), 4-vinylcatechol (4-VC), 4-
vinylguaiacol (4-VG) and 4-vinylsyringol (4-VS) obtained from p-
coumaric acid, caffeic acid, ferulic acid and sinapic acid
subsequently, are considered as avouring agents in perfumery,
food, and beverage industries being recognized as FEMA GRAS
(Flavour and Extract Manufacturer's Association; General
Regarded as for the Safe).2 4-VP and p-acetoxystyrene (pAS)
derivatives are active starting materials for the synthesis of bio-
active compounds and act as versatile intermediates in the
preparation of ion-exchange resins, additives in elastomers,
adhesives, agents for control of germination, coatings, auto-
motive nishes, ink, semiconductor manufacturing, UV-
absorbers, photoresists, photolithography and cancer preven-
tive agents.2,3 In addition, these compounds have attracted
considerable attention due to their various biological and
pharmacological activities such as antioxidant, antibacterial,
antifungal, hypolipidemic and antimutagenic.3a Ferulic acid,
Biotransformation, a simple, environmentally friendly and
useful alternative to the chemical route, is rapidly drawing
interest owing to the possibility of producing compounds with
high stereo-specicity and selectivity under mild reaction con-
ditions.6a Nowadays, much attention has been paid to biocon-
version of organic compounds by using plants, animal or
Department of Chemistry, Indian Institute of Technology Kharagpur, Kharagpur,
India-721302. E-mail: ahinnag@chem.iitkgp.ernet.in; Fax: +91-3222-255303; Tel:
+91-3222-281900
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra01760f
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microbial cells or puried enzymes as catalyst.19 The bio-
catalytic decarboxylation of substituted para-hydroxycinnamic
acids were performed by para-hydroxycinnamic acid decarbox-
ylase (PDC) in biphasic reaction medium,20 Sporotrichum ther-
mophile,1 Bacillus pumilus,4b Klebsiella oxytoca,21 plant cell
culture (e.g. Camellia sinensis),22 Saccharomyces cerevisial23 etc.
The development of green, safe and sustainable protocols for
the use of natural feedstocks in chemical synthesis alternative
to hazardous organic chemicals is extensively acknowledged.24
Some plants were reported as natural resources of reductase
activity with alcohol dehydrogenase systems such as Daucus
carota, Manihot species and Saccharum officinarum.25 Water
Extract of Banana (WEB) at room temperature was very efficient
catalyst system for Dakin reaction.24a Suzuki–Miyaura cross-
coupling reaction was also developed by Water Extract of Rice
Straw Ash (WERSA) as well as WEB at room temperature.24b-c The
two fruits of Cucurbita pepo L. (marrow) and Cucurbita maxima
L. (pumpkin) showed reducing properties towards ketones.26
Nag et al. reported that the decarboxylation of the para-
hydroxycinnamic acids to styrene and the reduction of some
aromatic aldehydes to alcohols have been performed by the juice
of Cocos nucifera L. and Borassus abellifer L.2b Being concerned
about environmental impact, we focused our attention on
cucumber juice (CSJ), a highly abundant natural feedstock.
Cucumber (Cucumis sativus L), belongs to cucurbitaceae family
which is agriculturally and economically important crop used as
a fruit in worldwide and cheap, easily available throughout the
year. But two fruits (Cocos nucifera L. and Borassus abellifer L.)
are expensive and collections of juices are tedious. Our present
method for choosing cucumber juice over two specied juices
and vegetables is more appropriate on the basis of availability,
price, collection of juice, simplicity in reaction procedure and
versatility. To the best of our knowledge, we rst report the
biotransformation of cucumber juice for the selective reduction
Scheme 2 Decarboxylation of substituted benzoic acid.
Scheme 3 Decarboxylation of substituted cinnamic acids.
Scheme 4 (a) De-acetylation and de-benzoylation of substituted
aromatic compounds. (b) Deprotection of substituted benzyl acetates.
of aromatic aldehydes to alcohols, decarboxylation of ground under the mixture grinder. Then it was ltered through
substituted aromatic acids, deacetylation and debenzoylation of Buchner funnel in vacuum using ordinary lter paper as soon as
substituted aromatic compounds without using any catalyst, possible for the maximum elimination of residue and the
base, hazardous reagent and organic solvent. In this communi- ltrate was abbreviated as CSJ here. Literature reports reveal
cation, we report on the use of cucumber juice as an all-in-one that CSJ is composed mostly of water more than 95% along with
mixture of solvent and greener alternatives.
proteins, ions, fats, vitamin B1 and C, pectin, sugars, erepsin,
In CSJ catalysed reduction, decarboxylation and depro- proteolytic enzyme, rutin, oxidase, succinic and maleic dehy-
tection (hydrolysis) were discussed according to Schemes 1–4 drogenases and so on.27 In each experiment for biotransfor-
where all experiments were investigated at 30–35 ꢀC under mation by CSJ, substrate (1 g) separately was added to the
argon atmosphere. During our study, 40 to 50 ml fruit juice was freshly prepared cucumber juice (200 ml). The reaction mixture
ꢀ
obtained from 100 g of cucumber fruit. Fresh green cucumbers was stirred at 30–35 C temperature maximum for 72 h under
collected from the local market were washed with distilled water argon atmosphere (Schemes 1–4). Each individual suspension
and cut into small pieces by a metallic sharp knife. Then it was was ltered, and the residue was washed with water, as well as
with ethyl acetate. The ltrate was then extracted with ethyl
acetate (3 Â 100 ml), and the organic phase was dried over
sodium sulphate and evaporated under reduced pressure.
Maximum cases, column chromatography was not required for
product purication due to excellent yield. Some cases, reaction
mixtures were puried by column chromatography using ethyl
acetate and n-hexane as eluents to afford the products. The
structure of the products were conrmed by NMR spectroscopy.
In Scheme 1, the activity of CSJ on aromatic aldehydes and
Scheme 1 Reduction of subsisted aromatic aldehydes.
ketones were shown.
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Table 2 Decarboxylation of substituted benzoic acids by CSJa
From Table 1, it was seen that the reducing activity and yield
of the products depended on substituents with respect to
aldehyde group in benzene ring. These results indicated that
the electron donating groups present either at meta or para
position of aromatic aldehydes showed activity in the presence
of CSJ, but ortho substituted aromatic aldehydes did not
produce any alcohol. The methoxy group present at para rather
than meta position of the phenyl ring, enhanced the rate as well
as the yield of the product. That is why; it was isolated with
better yield from vanillin (1i) to isovanillin (1k) to vera-
traldehyde (1j). CSJ did not show any activity towards chloro,
nitro substituted benzaldehyde, acetophenone and benzophe-
none during 72 h.
Subsequently, in Tables 2 and 3 it was observed that p-
hydroxybenzoic acids and p-hydroxycinnamic acids produced
decarboxylated products rather than reduced products within
24 h. From Table 2, it was observed that benzoic acids con-
taining phenolic –OH group at para position rather than ortho
and meta position with respect to acid group, decarboxylated
products were obtained. When more –OH groups are present at
R2 or R4 position together with phenolic –OH group at R3
position, the yield of decarboxylated products were increased. It
was also observed that when bulky groups such as methoxy
group present at R2 or R4 position along with phenolic –OH
group at R3 position the, the yield of decarboxylated products
were decreased in presence of CSJ due to steric effect.
Reaction
time (h)
Reactant
R1
R2
R3
R4
Yieldb (%)
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
H
H
H
OH
H
H
H
H
H
H
H
H
H
H
H
H
OH
H
H
H
H
H
OH
OMe
OH
COOH
OH
OMe
H
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
OH
OMe
72
48
72
72
72
72
72
72
48
48
72
72
48
48
0
75
0
0
0
0
0
0
85
80
0
0
98
25
H
OMe
NO2
NH2
SH
OH
OH
OMe
H
OH
OH
a
Reaction conditions: 1 g substrate in 200 ml CSJ stirred at 30–35 ꢀC
b
maximum for 72 h under argon atmosphere. Isolated yield.
Table 3 Decarboxylation of substituted cinnamic acids by CSJa
Reaction
time (h)
Reactant R1
R2
R3
R4
R5
Yieldb (%)
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
H
H
H
H
H
H
H
H
H
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OH
OMe
H
H
H
H
H
H
H
H
H
H
H
H
72
24
72
24
24
72
72
24
72
72
72
72
0
94
0
98
92
0
0
30
0
0
0
OH
OMe
OH
OH
OMe OH
OMe OMe
For this reason, the increasing yield was observed from
syringic acid (3n) to protocatechuic acid (3i) to gallic acid (3m)
with the increase of hydroxyl groups rather than methoxy
groups. In case of hydroxycinnamic acids to hydroxystyrenes
were formed by the removal of the carboxyl group from the C-3
side chain. The same trend of increasing yield was observed for
4-VC (6d) from caffeic acid (5d). But the isolated yield of 4-VS
OMe OH
OMe
OH
H
H
H
H
H
H
H
H
H
H
H
H
NH2
NO2
OH
OH
OH
0
H
Me 24
15
10
0
OMe Me 24
OMe Ph 72
Table 1 Reduction of substituted aromatic carbonyl compounds
by CSJa
a
Reaction conditions: 1 g substrate in 200 ml CSJ stirred at 30–35 ꢀC
b
maximum for 72 h under argon atmosphere. Isolated yield.
Reaction
time (h)
Reactant R1
R2
R3
R4
R5
Yieldb (%)
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1q
H
H
H
OH
H
H
OMe
H
H
H
H
H
H
H
H
H
H
H
H
OH
H
H
OMe
H
OH
OMe OH
OMe OMe
OH
OMe OH
OMe OMe OMe
H
H
H
H
H
OH
H
H
OMe
H
H
H
H
H
H
H
H
H
H
H
H
OMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
50
65
60
0
68
63
0
70
74
81
78
82
86
0
(6h) from sinapic acid (5h) was low due to presence of methoxy
groups at R2 and R4 position with respect to acid group. Both o-
coumaric acid (5j) and m-coumaric acid (5i) did not undergo
decarboxylation reaction in presence of CSJ. But when nitro and
amino group (also contain proton source) present at the para
position of the cinnamic acid, no decarboxylated products were
obtained. So, the observation indicating that the para hydroxy
group was essential for decarboxylation reaction both for
substituted benzoic acid and substituted cinnamic acids.
H
OH
OMe
˜
In 2010, Mancheno et al. also exhibited that PDC catalyse the
non-oxidative decarboxylation of hydroxycinnamic acids to
corresponding vinyl derivatives where hydrogen atom of p-OH
group attains a signicant role.28 Here, it was also examined
that, cinnamic acid and benzoic acid in the absence of p-OH
group with respect to carboxylic acid group, decarboxylation
was not achieved up to 72 h due to non-participation of
NO2
Cl
H
H
H
H
H
0
0
0
CH3 72
Ph 72
H
a
Reaction conditions: 1 g substrate in 200 ml CSJ stirred at 30–35 ꢀC
b
maximum for 72 h under argon atmosphere. Isolated yield.
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Table 4 Hydrolysis of aromatic acetates or benzoates by CSJa
Reactant
R1
R2
R3
Reaction time (h)
Yieldb (%)
7a
7b
7c
7d
7e
7f
7g
7h
7i
CHO
CHO
CHO
CHO
CH]CH2
CH]CH2
CH]CH2
CH]CH–COOH
CH]CH–COOH
H
Me
Me
Me
Ph
Me
Me
Me
Me
Me
6
6
6
6
6
6
6
6
6
90
94
98
85
92
95
98
80
84
OMe
OAc
H
H
OMe
OAc
H
OAc
7j
OMe
Me
6
78
a
b
Reaction conditions: 1 g substrate in 200 ml CSJ stirred at 30–35 ꢀC maximum for 6 h under argon atmosphere. Isolated yield.
Table 5 Hydrolysis of substituted benzyl acetate by CSJa
selectivity and constitutes a useful environmentally benign
alternative to commonly accepted procedures of reduction,
Reactant
R1
R2
Reaction time (h)
Yieldb (%)
decarboxylation, deacetylation and debenzoylation. The devel-
oped method allows the new industrial scale synthesis of
vinylphenols in good yield and excellent selectivity than other
conventional chemical methods. Our investigation is
continuing to understand the proper mechanistic pathway by
which CSJ is responsible for reduction, decarboxylation and
hydrolysis reactions.
7k
7l
7m
H
OMe
NO2
OMe
OMe
H
6
6
6
90
92
90
a
Reaction conditions: 1 g substrate in 200 ml CSJ stirred at 30–35 ꢀC
b
maximum for 6 h under argon atmosphere. Isolated yield.
hydrogen atom of phenolic OH group in reaction mechanism.
This result indicates that mechanism of decarboxylation may be
followed via enzymatic route.
In Scheme 4a and b, it was discussed about the hydrolysis of
acetyl as well as benzoyl group of aromatic compounds. With
the increase of the electron donating group and bulky group
present with respect to acetate and benzoate group, the yield as
well as rate of hydrolysis also increased.
From Table 4, it was seen that the rate of hydrolysis of 2-
methoxy-4-vinylphenyl acetate (8f) with respect to 4-vinylphenyl
acetate (8e) increased due to addition of an extra methoxy group
acting as electron donor as well as sterically hindered with
respect to acetoxy group in benzene ring.
The practical utility of using CSJ was deprotection of acetyl
and benzoyl group of aromatic compounds in the presence of
several other functional groups, such as aldehyde, vinyl, acrylic
acid etc. Which were remain unaffected under this reaction
condition (Table 4 and 5).
Acknowledgements
The author Himadri Sekhar Maity is indebted to CSIR Delhi, for
the award of SRF and for the nancial support of this research.
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