Sunlight assisted solvent free synthesis of tert-butylperesters

Article abstract of DOI:10.1080/00397911.2020.1783560

A green and efficient methodology has been developed for the direct conversion of aryl aldehydes to the corresponding tert-butyl peresters. The reaction has been carried out in absence of any solvent and the sunlight is used as the green source of energy. In this reaction tetrabutylammonium iodide (TBAI) acts as the mild organo catalyst and tert-butyl hydroperoxide (TBHP) serve as the source of tert-butyl group.

Full text of DOI:10.1080/00397911.2020.1783560

Synthetic Communications
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Chemistry
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Sunlight assisted solvent free synthesis of tert-
butylperesters
Raju Singha & Prasenjit Shit
To cite this article: Raju Singha & Prasenjit Shit (2020): Sunlight assisted solvent free synthesis of
tert-butylperesters, Synthetic Communications, DOI: 10.1080/00397911.2020.1783560
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https://doi.org/10.1080/00397911.2020.1783560
Sunlight assisted solvent free synthesis of
tert-butylperesters
Raju Singha and Prasenjit Shit
Department of Chemistry, Panskura Banamali College (Autonomous), Panskura R. S, India
ABSTRACT
ARTICLE HISTORY
Received 20 May 2020
A green and efficient methodology has been developed for the dir-
ect conversion of aryl aldehydes to the corresponding tert-butyl
peresters. The reaction has been carried out in absence of any solv-
ent and the sunlight is used as the green source of energy. In this
reaction tetrabutylammonium iodide (TBAI) acts as the mild organo
catalyst and tert-butyl hydroperoxide (TBHP) serve as the source of
tert-butyl group.
KEYWORDS
Sunlight; Solvent free
reaction; TBHP; TBAI; tert-
butylperester
GRAPHICAL ABSTRACT
O
O
O
O
H
R
R
O
TBAI
H
O
R = F, Cl, Br, OMe, NO2
19 examples
Solvent free
mild condition
up to 92% yield
Introduction
In this twenty first century, the interests are gradually growing on the use of obsolete
source of energy and among the different sources; the solar energy is the pioneer in this
field.[1,2] The solar energy is the most green and endless source of energy and thus its
application is gradually dominates from day to day.[3] In last few decades, chemists are
employed to use the solar energy into chemical energy and this trend is even more
focused after the development of the concept of sustainable chemistry.[4] Herein, we
have used sunlight as the initiator for the synthesis of tert-butylperesters.
tert-Butylperesters are an important class of organic compound because they can eas-
ily undergo a homolytic cleavage to give a tert-butyloxy radical and a hydroxy radical
which are used to initiate different radical reactions, in presence of different transition
metal catalysts.[5] Traditionally the tert-butylperesters are synthesized by the condensa-
tion reaction between a carboxylic acid derivative with tert-butyl hydroperoxide.[6]
CONTACT Raju Singha
rajusingha70@gmail.com
Department of Chemistry, Panskura Banamali College
(Autonomous), Panskura R. S, West Bengal, India.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
R. SINGHA AND P. SHIT
Table 1. Screening of the reaction conditions.a
O
O
O
Ph
H
Ph
O
1a
TBHP, catalyst
2a
Ã
Entry
TBHP
Catalyst
Time (h)
Yield
1
2
3
4
5
6
7
8
1.5
2.0
2.5
3.0
4.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
TBAI
TBAI
TBAI
TBAI
TBAI
KI
NaI
–
TBAI
TBAId
TBAIe
TBAI
5
5
5
2
2
5
5
5
24
2
36
43
81
83
72b
56
45
13
21
84
76
31
9c
10
11
12f
5
2
aThe reaction condition: 1a (1 mmol), TBHP (mmol), catalyst (10 mol %), time (h) and all the reactions were started at
10 am at roof top.
bFormation of trace amount of benzoic acid was observed.
cThe reaction was carried out at dark.
d20 mol% TBAI,
e5 mol% TBAI,
fBenzyl alcohol was used instead of benzaldehyde.
Ã
Isolated yield.
Recently few reports are there in literature for the synthesis of tert-butylperesters via
cross-dehydrogenative coupling (CDC) approaches.[7] Wan group have synthesized tert-
butylperester from aldehyde using heating conditions in presence of TBAI/TBHP.[7a]
Nikam group have synthesized using TBHP and Copper acetate catalyst starting from
benzyl nitrile.[8] Recently, Guo and coworkers have synthesized from methyl arenes in a
microfluidic chip reactor.[9] Herein, we are reporting a sunlight assisted solvent free
methodology for the synthesis of tert-butylperesters; a short, green and efficient
methodology.
Results and discussion
Our experiment was initiated by reacting the model substrate benzaldehyde (1a) with
tert-butyl hydroperoxide (1.5 equiv.), tetrabutylammonium iodide (10 mol %) under
sunlight, and the desired product tert-butyl perbenzoate was isolated in 36% yield
(Table 1). On increasing the amount of TBHP, the yields were gradually increased and
the maximum yield was observed with three equivalents of TBHP within 2 h (Table 1,
entries 1–4). The yield was decreased and formation of trace amount of benzoic acid
was observed when we used four equivalents of TBHP. The other iodide sources such
as KI and NaI were also able to promote the reaction but gave lower yields. In absence
of any iodide catalyst, the product 2a was formed only in 13% and this result indicates
the importance of iodide catalyst. When the reaction was carried out at dark, it gives
only 21% of the product after 24 h. Thus the sunlight takes part an important role in

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3
Table 2. Scope of the reaction of aldehydes with TBHP.a
O
O
H
O
O
Ar
R
Ar
R
O
TBAI
H
O
R = F, Cl, Br, OMe, NO2
Ar = Aromatic, Heterocyclic
O
O
O
O
O
O
O
O
O
O
O
O
Cl
MeO
OMe
2a, Y = 83%
2b, Y = 82%
2c, Y = 85%
2d, Y = 89%
O
O
O
O
MeO
MeO
O
O
O
O
O
O
O
O
MeO
Br
F
OMe
OMe
2g, Y = 82%
2e, Y = 91%
2f, Y = 88%
2h, Y = 84%
O
O
O
O
O
O
O
F
O
O
O
Ph
O
O
O2N
Br
2l, Y = 75%
2k, Y = 82%
2i, Y = 81%
2j, Y = 87%
O
O
O
O
O
O
O
S
O
O
O
O
N
O
O
N
2m, Y = 80%
2n, Y = 83%
2o, Y = 77%
2p, Y = 79%
O
O
O
O
O
O
O
O
O
MeO
2q, Y = 92%
2s, Y = 91%
2r, Y = 87%
aThe standard reaction condition: 1a-s (1 mmol), TBHP (3.0 mmol), TBAI (10 mol %), stirred under direct sunlight for 2 h.
this reaction. The yield was almost unchanged on increasing the amount of catalyst to
20 mol% however, it decreased on lowering the catalyst amount (entry 10 & 11). When
we used benzyl alcohol as the substrate instead of benzaldehyde then about 31% of tert-
butylperoxy benzoate was formed (entry-12). This probably occurs via oxidation of ben-
zyl alcohol to benzaldehyde and then per esterification through cross dehydrogenative
coupling pathway. The results of the Table 1 indicate that entry 4 represents the
screened reaction conditions.

4
R. SINGHA AND P. SHIT
O
OH
Ph
H
1a
+
O
OOH
H2O
HO
n-Bu4N
n-Bu4N
+
+
1/2 I2
n-Bu4NI
O
O
+
OO
HOO
Ph
+ HO
A
O
Ph
Scheme 1. Plausible reaction mechanism
O
2a
Once we got the optimized reaction conditions, we employed it on different sub-
strates to examine its versatility and the results are summarized in Table 2.
At first, different benzaldehyde derivatives were employed for the peresterification
and the corresponding tert-butylper benzoate derivatives were obtained in good to
excellent yields regardless of the electron donating or withdrawing groups in the
benzene ring (Table 2, entries 2a-2k). It was observed that electronic or steric effect
is not so prominent but the substrates having electron donating group in benzene
ring were little superior to those having electron withdrawing group. The substituted
groups in the ortho-position to aldehyde afforded the desired product in quite lower
yield and this is probably due to the steric hindrance with the bulky tert-butyl
group (Table 2, entries 2c, 2 g and 2i). The aliphatic substrate cinnamaldehyde gave
the corresponding tert-butyl perester in 75% yield. Heterocyclic substrates also
underwent a smooth reaction to give the desired product in good yields (Table 2,
entries 2 m-2p). 2-naphthaldehyde derivatives were gave higher yield than 1-naphthal-
dehyde and this is due to the presence of more steric crowding in 1-naphthaldehyde
(Table 2, entries 2q-2s).
On the basis of our experimental results and literature survey,[7–11] we proposed a
plausible reaction mechanism as shown in Scheme 1. Initially, the tert-butoxyl and
tert-butylperoxy radicals were formed by the decomposition of TBHP in TBHP-TBAI
system. As the rate of reaction is very slow (21% yield in 24 h, Table 1, entry 9) in
absence of sunlight, so we can say that the rate of decomposition of TBHP in TBAI
catalytic cycle is enhanced by sunlight. Then the aldehydic H atom was abstracted
by the tert-butoxyl radical to form the radical intermediate A, which was coupled
with the tert-butylperoxy radical to give the desired product tert-butylperoxy benzo-
ate (2a).
In absence of iodide catalyst, the product also formed in 13% and this occurs due to
the formation of corresponding radicals, initiated by the cleavage of peroxide bond in
TBHP under sunlight.

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5
Conclusions
In conclusion, we have successfully developed a green and efficient methodology for the
synthesis of tert-butyl peresters from the corresponding aliphatic, aromatic and hetero-
cyclic carboxaldehydes. The reaction was carried out under mild conditions where
TBHP acts as the source of tert-butyperoxy group and TBAI acts as the catalyst and the
rate of reaction is accelerated by sunlight. This catalytic protocol is suitable for a long
range of substrates with good to excellent yield.
General reaction procedure
The substrate aldehyde (1 mmol) and tetrabutylammonium iodide (37 mg, 10 mol %)
were taken in a beaker and then TBHP (0.3 mL, 3.0 equiv., ꢀ80% in di-tert-butyl perox-
ide/water) was added. The reaction mixture was stirred under sunlight at top roof for
2 h. After completion of the reaction, the mixture was diluted with aqueous Na2S2O3
solution and then extracted with ethyl acetate (3 x 20 mL). The combined organic layer
was washed with brine solution, dried over anhydrous Na2SO4 and evaporated under
reduced pressure. The crude product was purified by column chromatography using sil-
ica gel (60–120 mesh) and hexane/EtOAc as eluent.
Funding
I would like to thank DST-SERB, Government of India for financial support of this project [File
No.: ECR/2017/000396] and DST-FIST, Government of India for sponsoring departmental
research facilities.
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