Direct oxidative conversion of benzylhalides, -amines, -alcohols, and arylaldehydes to nitriles with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane activated by NH4Br

Article abstract of DOI:10.1007/s13738-014-0461-3

A simple and efficient oxidative conversion of benzyl derivatives of halides, amines, alcohols, and aldehydes into corresponding nitriles is described using trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane in the presence of NH₄Br. The reactions proceeded smoothly at room temperature to afford the products in high-to-excellent yields. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-014-0461-3

J IRAN CHEM SOC
DOI 10.1007/s13738-014-0461-3
ORIGINAL PAPER
Direct oxidative conversion of benzylhalides, -amines, -alcohols,
and arylaldehydes to nitriles with trans-3,5-dihydroperoxy-3,5-
dimethyl-1,2-dioxolane activated by NH4Br
•
Davood Azarifar Zohreh Najminejad
Received: 15 December 2013 / Accepted: 29 April 2014
Ó Iranian Chemical Society 2014
Abstract A simple and efficient oxidative conversion of
benzyl derivatives of halides, amines, alcohols, and alde-
hydes into corresponding nitriles is described using trans-
3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane in the pre-
sence of NH4Br. The reactions proceeded smoothly at
room temperature to afford the products in high-to-excel-
lent yields.
corresponding aldoximes [28–32], or using reagents such
as trimethylsilyl azide [33], triazidochlorosilane [34],
sodium azide and aluminum chloride [35]. The transfor-
mation of aldehydes into their corresponding nitriles using
ammonium salts in combination with an appropriate oxi-
dant has emerged as an expedient method. Reagents
reported to effect this conversion are NH3/H2O2/CuCl [36],
NH3/O2/CuCl2.2H2O/MeONa [37], NH3/NBS/H2O [38],
NH3/I2 [39], NH3/Pb(OAc)4 [40], NH3/S8/NaNO2 [41], and
MeReO3/H2O2 [42]. Recently, the synthesis of nitriles has
been developed by treating aldehydes with hydroxylamine
hydrochloride in the presence of catalysts such as ZnO [43]
and KF/Al2O3 [44]. In addition, a few reports have been
published on one-pot oxidation of alcohols to nitriles [45–
47]. The most common approach for this conversion is
based on Mitsunobu’s reaction using HCN/Ph3P/diethyl
azadicarboxylate (DEAD) [48–50]. Other reagents used for
direct conversion of alcohols to nitriles include Ph3P/n-
Bu4NCN/2,3-dichloro-5,6-dicyanobenzoquinone (DDQ)
[51], CCl4/Ph3P/NaCN [52], n-Bu3P/CCl4/KCN/18-crown-
6 [53], Me3SiCl/NaI/NaCN [54, 55], and NH3/1,3-diiodo-
5,5-dimethyl hydantoin [56]. Huang et al. have recently
reported the use of ruthenium hydroxide in a highly
selective and green aerobic oxidation of amines to nitriles
in water [57]. Also, the use of a ruthenium(III) complex
bearing phenylpyridino as an efficient catalyst in an aerobic
dehydrogenation of benzylamines to the corresponding
benzonitriles has been reported [58]. However, most of the
reported methods are subject to certain drawbacks includ-
ing prolonged reaction times, low yield, use of highly toxic
reagents such as HCN or metal cyanides, necessity of using
costly and excess catalysts, and harsh reaction conditions.
Nevertheless, the development of alternative milder and
environmentally green approaches to aromatic and ali-
phatic nitriles appears as interesting challenge.
Keywords Trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-
dioxolane Á DHPDMDO Á Oxidation Á Nitrile Á Amine Á
Halide Á Alcohol Á Aldehyde
Introduction
Nitriles are known as important and versatile intermediates
in synthetic organic chemistry for conversion into various
functional groups such as amines, ketones, amides, ami-
dines, carboxylic acids, esters, N-heterocycles, etc. [1–6].
In addition, nitriles are industrially useful building blocks
of dyes, natural products, herbicides, and agrochemicals [7,
8]. Nitriles are also of pharmaceutical importance as HIV
protease inhibitors, 5-lipoxygenase inhibitors, and many
other bioactive molecules [9–12]. Several methods are
known for the preparation of nitriles that include (1)
nucleophilic displacement of various groups such as halo-
gens, sulfonates, alcohols, esters, ethers, nitro or amino,
and diazonium groups with inorganic cyanides [13–22]; (2)
dihydration of amides [23, 24] and aldoximes [25–27]; and
(3) direct conversion of aldehydes into nitriles via the
D. Azarifar (&) Á Z. Najminejad
Department of Chemistry, Bu-Ali Sina University,
65178 Hamedan, Iran
e-mail: dazarifar@gmail.com; azarifar@basu.ac.ir
123

J IRAN CHEM SOC
Experimental
Material and instruments
Chemicals were purchased from the Merck company and
used without further purification. 1H and 13C NMR spectra
were obtained on a Bruker 500 MHz Avance spectrometer
with CDCl3 as solvent. FT-IR spectra on were recorded a
Bruker 500 scientific spectrometer in KBr pellets. Trans-
3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane was pre-
pared following our previously reported procedure [59–
62].
Scheme 1 Oxidative conversion of benzyl derivatives into nitriles
with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane
Table 1 Effect of various oxidants on the NH4Br-activated conver-
sion of benzyl alcohol (1a) into benzonitrile (2a) in aqueous ammonia
Entry
Oxidant
Time (min)
Yield (%)a
Caution Although we did not encounter any problem
with trans-3,5-dihydroperoxy-3,5-dimethyl-1,2 dioxolane,
it is potentially explosive and should be handled with
precautions; all reactions should be carried out behind a
safety shield inside a fume hood and transition metal salts
or heating should be avoided.
1
2
3
4
5
6
7
H2O2
300
300
300
100
300
300
300
–
TBHP
NaOCl
DHPDMDO
Al2O3
CuO
29
–
95
25
15
–
Preparation of trans-3,5-dihydroperoxy-3,5-dimethyl-
–
1,2-dioxolane
Conditions: PhCH2OH (1 mmol), aqueous NH3 (3 mL, 45 mmol),
NH4Br (1.1 mmol), oxidant (1 mmol), rt
a
To a stirred solution of acetylacetone (100 mg, 1 mmol) in
CH3CN (5 mL) was added SnCl2Á2H2O (45 mg, 0.2 mmol)
and the resulting mixture was stirred for 5 min at room
temperature. Then, aqueous 30 % H2O2 (5 mmol) was
added to the reaction mixture and stirred for 12 h at room
temperature. After completion of the reaction as monitored
by TLC, water (15 mL) was added and the product was
extracted with ethylacetate (2 9 10 mL). The combined
organic layer was dried over anhydrous MgSO4 and
evaporated under reduced pressure to give almost pure
white crystalline product in 85 % yield (140 mg); mp
98–100 °C.
Isolated yield
product. Physical and spectroscopic (IR, 1H NMR, and 13
NMR) data of all the products matched those reported.
C
Results and discussion
In continuation of our efforts in the synthesis of gem-di-
hydroperoxides [59–62], and their applications in various
organictransformations[63–66], herein, wewishtoreportfor
the first time the versatile oxidative capability of trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2-dioxolane(DHPDMDO)as
a non-toxic oxidant with high atom-efficiency in direct oxi-
dative conversion of various benzyl derivatives including
alcohols, amines, halides as well as aldehydes to their cor-
responding nitriles in the presence of aqueous ammonia and
NH4Br at room temperature (Scheme 1).
General experimental procedure for the conversion
of benzyl derivatives of alcohols, amines, halides,
and aryl aldehydes into corresponding nitriles
To a mixture of benzyl substrate or aryl aldehyde
(1 mmol), aqueous ammonia (3.0 mL, 45 mmol) and
NH4Br (0.11 g, 1.1 mmol) was added trans-3,5-dihydrop-
eroxy-3,5-dimethyl-1,2-dioxolane (166 mg, 1 mmol). The
reaction mixture was stirred at room temperature for an
appropriate time (Tables 3, 4, 5). After completion of the
reaction as monitored by TLC, the mixture was treated
with aqueous Na2SO3 solution (3 mL) with stirring for
10 min to neutralize the remaining peroxide. The resulting
mixture was diluted with distilled water (15 mL) and then
the product was extracted with Et2O (2 9 10 mL). The
combined organic layer was dried over anhydrous MgSO4
and evaporated under reduced pressure to leave the pure
To establish the reaction conditions, we initially exam-
ined the oxidative conversion of benzyl alcohol (1a) to
benzonitrile (2a) as the model reaction. To screen the effect
of the oxidant in this reaction, various oxidants including
H2O2, t-butyl hydrogen peroxide (TBHP), NaOCl, Al2O3,
CuO as well as trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-
dioxolane (DHPDMDO) were examined in the presence of
NH4Br as the promoter in aqueous ammonia at room
temperature. The results are summarized in Table 1.
As shown in Table 1, trans-3,5-dihydroperoxy-3,5-
dimethyl-1,2-dioxolane (DHPDMDO) appeared as the
most efficient oxidant when activated by NH4Br to afford
123

J IRAN CHEM SOC
the highest yield (95 %) in a short reaction time (100 min)
in aqueous ammonia (entry 4). It was noticed that, no
reaction occurs when conducted in the absence of the
oxidant (entry 7).
yield to promote the reaction (entry 6). It was also noticed
that, the yield was increasingly enhanced by increasing
the amount of NH4Br in the reaction (entries 4–6) until
the maximum yield (95 %) was reached (entry 6).
Moreover, not only the yield was not improved by further
increasing the amount of NH4Br, but considerable dimi-
nution of the yield was observed after longer reaction
times (entries 7, 8). The significance of the catalyst
NH4Br in the reaction was approved by conducting the
reaction in the absence of the catalyst that resulted in no
detectable amount of the product after a long reaction
time (entry 9).
In the later step, we studied the activating role of the
salt on the model reaction using DHPDMDO with
examining the catalytic potency of several inorganic salts
such as KF, KI, NH4Br and NH4I under different loadings
(Table 2). The results summarized in Table 2 demonstrate
that, among different salts examined in this reaction,
NH4Br with a loading of 1.1 mmol was found to be the
most efficient salt in terms of the reaction rate and the
To explore the generality of this method, we applied the
optimized conditions, i.e., NH4Br (1.1 mmol), DHPDMDO
(1 mmol), aqueous NH3 (45 mmol), room temperature, to a
series of differently substituted benzyl alcohols 1a–j into
their corresponding nitriles 2a–j as summarized in Table 3.
As seen in Table 3, the electron-withdrawing groups
attached to the phenyl ring generally reduce the yields,
whereas the electron-releasing groups cause slight
improvement of the yields. It is noticed that, both the
hydroxymethyl groups present in 1,4-di(hydroxy-
methyl)benzene 1d undergo conversion into nitrile groups
in this reaction (entry d). However, other groups attached
to the phenyl ring such as halogens, nitro and aldehyde
groups remained intact and only the hydroxymethyl group
was selectively converted to nitrile group. Nevertheless, all
the reactions proceeded smoothly under mild conditions to
afford the respective products in high-to-excellent yields
(98–84 %).
Table 2 Effect of various catalysts on the conversion of benzyl
alcohol into benzonitrile with DHPDMDO in aqueous ammonia
Entry
Catalyst (mmol)
Time (min)
Yield (%)a
1
2
3
4
5
6
7
8
9
KI (0.1)
100
100
100
100
100
100
150
150
150
50
35
65
70
80
95
50
50
–
KF (0.1)
NH4I (0.1)
NH4Br (0.1)
NH4Br (0.5)
NH4Br (1.1)
NH4Br (1.5)
NH4Br (2.2)
–
Conditions: PhCH2OH (1 mmol), aqueous NH3 (3 mL, 45 mmol),
oxidant (1 mmol), rt
a
Isolated yield
Table 3 Direct conversion of benzyl alcohols 1a–j to benzyl nitriles 2a–j with DHPDMDO using NH4Br in aqueous NH3
Entry
Ar
Product 2
Time (min)
Yield (%)a
a
b
c
d
e
f
C6H5
C6H5CN
100
100
90
95
96
95
98
86
88
87
84
84
86
2-MeC6H4
4-MeOC6H4
4-HOCH2C6H4
4-NO2C6H4
3-BrC6H4
2-MeC6H4CN
4-MeOC6H4CN
4-CNC6H4CN
4-NO2C6H4CN
3-BrC6H4CN
4-IC6H4CN
90
80
80
g
h
i
4-IC6H4
90
4-CNC6H4
4-CHOC6H4
2-Cl-4-NO2C6H3
4-CNC6H4CN
4-CHOC6H4CN
2-Cl-4-NO2C6H3CN
100
100
100
j
Conditions: ArCH2OH (1 mmol), aqueous NH3 (3 mL, 45 mmol), NH4Br (1.1 mmol), DHPDMDO (1 mmol), rt
a
Isolated yield
123

J IRAN CHEM SOC
Table 4 Conversion of benzyl amines 3a–i and benzyl halides 3j–
r into corresponding nitriles with DHPDMDO/NH4Br
Table 5 Direct conversion of aryl aldehydes 5a–h to benzonitriles
6a–h with DHPDMDO using NH4Br in aqueous ammonia
Entry Ar
X
Product 4
Time Yield
(min) (%)a
Entry
Ar
Product 6
Time
(min)
Yield
(%)a
a
b
c
d
e
f
C6H5
NH2
NH2
NH2
NH2
NH2
NH2
NH2
C6H5CN
120
90
78
95
83
82
98
96
86
a
b
c
d
e
f
C6H5
C6H5CN
50
50
45
45
40
40
50
50
94
95
83
83
78
82
78
78
4-NO2C6H4
3-BrC6H4
4-IC6H4
4-NO2C6H4CN
3-BrC6H4CN
4-IC6H4CN
2-MeC6H4
4-NO2C6H4
3-BrC6H4
4-IC6H4
2-MeC6H4CN
4-NO2C6H4CN
3-BrC6H4CN
4-IC6H4CN
100
120
90
4-CNC6H4
4-CHOC6H4
4-CNC6H4CN
4-CHOC6H4CN
90
4-CNC6H4
4-CHOC6H4
2-Cl-4-NO2C6H3
4-CNC6H4CN
4-CHOC6H4CN
2-Cl-4-NO2C6H3CN
g
2-Cl-4-
NO2C6H3
2-Cl-4-
NO2C6H3CN
100
g
h
h
i
C6H5
NH(CH3) C6H5CN
N(CH3)2 C6H5CN
150
200
140
100
90
83
83
75
83
78
78
88
78
80
80
C6H5
Conditions: ArCH2OH (1 mmol), aqueous NH3 (3 mL, 45 mmol),
NH4Br (1.1 mmol), DHPDMDO (1 mmol), rt
j
C6H5
Cl
Br
Cl
Cl
Cl
Cl
Cl
Cl
C6H5CN
a
Isolated yield
k
l
C6H5
C6H5CN
4-NO2C6H4
3-BrC6H4
4-IC6H4
4-CNC6H4
4-CHOC6H4
4-NO2C6H4CN
3-BrC6H4CN
4-IC6H4CN
4-CNC6H4CN
4-CHOC6H4CN
m
n
o
p
q
120
100
90
benzyl amines 3a–i bearing different groups in the aro-
matic ring. According to the results summarized in
Table 4, all the reactions proceeded smoothly to furnish the
respective nitriles 4a–i in high-to-excellent yields
(78–98 %). Similarly, this method was found equally
convenient for conversion of different benzyl halides 3j–
r into corresponding nitriles 4j–r in high yields (75–88 %)
as summarized in Table 4 (entries j–r). As seen in this
table, these reactions also occur selectively while the other
groups attached to the phenyl ring remain resistant.
Alternatively, this method can conveniently provide a
direct and environmentally more benign approach to aro-
matic nitriles in comparison with other previously reported
methods such as the Sandmeyer reaction of diazonium
compounds with toxic CuCN or dehydration of aromatic
amides with dehydrating agents.
90
2-Cl-4-
NO2C6H3
2-Cl-4-
NO2C6H3CN
120
r
2-Cl-4-
NO2C6H3
Br
2-Cl-4-
NO2C6H3CN
90
85
Conditions: ArCH2X (1 mmol), aqueous NH3 (3 mL, 45 mmol),
NH4Br (1.1 mmol), DHPDMDO (1 mmol), rt
a
Isolated yield
The successful accomplishment of the oxidation of
benzyl alcohols into corresponding nitriles with trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2-dioxolane encouraged us
to explore the suitability of this reagent for oxidative
conversion of other benzyl-bearing functionalities includ-
ing amines, halides as well as aldehydes. We preliminarily
studied the oxidative conversion of benzyl amine 3a as the
test compound into the corresponding benzonitrile with
trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane. The
reaction was conducted under the aforementioned opti-
mized conditions which led to the formation of the desired
product 4a in high yield (78 %). The crucial roles played
by both the oxidant DHPDMDO and NH4Br in this reac-
tion were evaluated by carrying out the reaction in the
absence of either the oxidant or NH4Br and no expected
transformation was observed in either case. The generality
of this reaction was examined by extending it to a series of
Finally, in order to further generalize the present method
and extend it to conversion of other functional groups, we
were encouraged to continue our research with direct
transformation of aryl aldehydes into corresponding nitriles
by treatment with trans-3,5-dihydroperoxy-3,5-dimethyl-
1,2-dioxolane under the promotion of NH4Br in aqueous
NH3 at room temperature. Several aryl aldehydes 5a–
h were readily converted into the corresponding nitriles
6a–h in high yields as summarized in Table 5. As seen in
this table, all these reactions proceeded in shorter reaction
times in comparison with the aforementioned reactions. It
is interesting to note that, from two aldehyde groups
123

J IRAN CHEM SOC
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Conclusions
In summary, different benzyl derivatives of amines, alco-
hols, halides and also aryl aldehydes have been effectively
converted to their corresponding nitriles with trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2-dioxolane as an effective
and high potent oxidant under the promotion of NH4Br in
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