A general and practical oxidation of alcohols to primary amides under metal-free conditions

Article abstract of DOI:10.1039/c3gc40668g

A general procedure for oxidation of both benzyl alcohols and alkyl alcohols to primary amides under catalyst free conditions has been developed. 34 examples of primary amides were produced from their corresponding alcohols in moderate to excellent yields. This is a practical procedure for primary amides synthesis; water and tert-butanol are the only by-products. A commercial drug, Piracetam, was prepared in one step with 73% yield as well.

Full text of DOI:10.1039/c3gc40668g

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A general and practical oxidation of alcohols to primary
amides under metal-free conditions†‡
Cite this: DOI: 10.1039/c3gc40668g
Xiao-Feng Wu,*a,b Muhammad Sharif,b,c Jian-Bo Feng,a Helfried Neumann,b
Anahit Pews-Davtyan,b Peter Langerb,d and Matthias Beller*b
A general procedure for oxidation of both benzyl alcohols and alkyl alcohols to primary amides under
catalyst free conditions has been developed. 34 examples of primary amides were produced from their
corresponding alcohols in moderate to excellent yields. This is a practical procedure for primary amides
synthesis; water and tert-butanol are the only by-products. A commercial drug, Piracetam, was prepared
in one step with 73% yield as well.
Received 9th April 2013,
Accepted 30th April 2013
DOI: 10.1039/c3gc40668g
www.rsc.org/greenchem
Primary amides are an important class of compounds that are efficiency, high selectivity, free from hazard reagents and
used as starting materials for engineering plastics, detergents, using green solvent as the medium are the main targets.10
and lubricants.1 In organic synthesis, primary amides are
From the aspect of oxidation reaction, the development of
potent substrates for primary amines, nitriles, amino acid deri- selective and convenient processes is still challenging.11 Based
vates, and heterocycles preparation.2 Biologically, primary on our recent study on oxidation reactions,12 we wish to report
amides are present in numerous biologically active molecules.3 our new discovery for the oxidation of alcohols to primary
Based on their importance, several methodologies have been amides under metal-free conditions in aqueous solution. This
developed for their synthesis,4–8 such as the hydration of the is a general procedure that can oxidize both benzyl alcohols
corresponding nitriles4 and the reaction of benzoic acids or and alkyl alcohols under catalyst free conditions. 34 examples
acid chlorides with ammonia.5 Other synthetic strategies of primary amides were produced from their corresponding
involve the rearrangement of benzaldoximes,6 and palladium- alcohols in moderate to excellent yields. This is a practical pro-
catalyzed carbonylation of organo halides with ammonia.7 The cedure for primary amides synthesis; water and tert-butanol
direct oxidation of benzyl amines to the corresponding benz- are the only by-products. Notably, a commercial drug, Pirace-
amides was also developed.8 From the synthetic point of view, tam, was prepared in one step with 73% yield (Scheme 1).
the oxidation of alcohols with ammonia to primary amides is
As shown in Table 1, various aromatic amides were pro-
more interesting in view of the availability and price of starting duced in good yields. Electron donating groups at para-, meta-,
materials.9 The reported methodologies for this transform- and ortho-positions are all tolerable and gave the corres-
ation either needed a heterogeneous catalyst [OMS-2/O2(3 bar), ponding amides in 80–96% yields (Table 1, entries 1–6).
130 °C] or the combination of I2/H2O2, I2/TEMPO/FeCl3/K2CO3, 4-(Methylthio)benzamide was produced in 83% yield from the
and PhI(OAc)2/NaN3.
corresponding 4-methylthiobenzyl alcohol without the oxi-
Sustainable development has been accepted as a common dation of sulfur (Table 1, entry 7). Naphthyl can be tolerated as
knowledge by our society. From the aspect of organic syn- well and the desired amides were isolated in 64–70% yields
thesis, the development of green reactions, with high atom (Table 1, entries 8 and 9). The numbers of electron withdraw-
ing groups at different positions were tested as well; the benzyl
alcohols were oxidized into primary amides in good yields
without further optimization (Table 1, entries 10–19).
aDepartment of Chemistry, Zhejiang Sci-Tech University, Xiasha Campus, Hangzhou,
Zhejiang Province, People’s Republic of China, 310018.
E-mail: xiao-feng.wu@catalysis.de; Tel: (+49)381-1281-343
bLeibniz-Institut für Katalyse an der Universität Rostock e.V. Albert-Einstein-Str. 29a,
18059 Rostock, Germany. E-mail: matthias.beller@catalysis.de
cDepartment of Chemistry, COMSATS Institute of Information Technology,
Abbottabad, Pakistan
dInstitut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock,
Germany
†Dedicated to Professor Irina Beletskaya.
‡Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3gc40668g
Scheme 1 Synthesis of Piracetam.
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Table 1 Aromatic primary amides synthesisa
Table 1 (Contd.)
Entry Benzyl alcohol
13
Product
Yieldb[%]
89
Entry Benzyl alcohol
1
Product
Yieldb[%]
80
14
15
16
95
58
85
2
3
4
5
87
96
89
96
17
18
19
89
90
67
6
80
7
8
83
64
a Benzyl alcohols (1 mmol), NH3 (25 wt% in H2O; 1 mL), TBHP (70% in
H2O; 8 mmol), 100 °C, 16 h (reaction time was not optimized).
b Isolated yields.
9
70
72
Additionally, 6 examples of heterocyclic amides were pro-
duced to prove the generality of this methodology (Table 2).
Not only pyridines and thiophenes, but also benzothiophene
can be tolerated. The solubility of the amide in water is respon-
sible for the decreased yield in some cases.
10
Remarkably, various aliphatic primary amides were pro-
duced in a one step manner as well (Table 3). Even cinnam-
amide and 3-phenylpropiolamide can be produced from the
corresponding alcohols in 41–65% yields (Table 3, entries 7
and 8).
Moreover, Piracetam, a nootropic drug, with trade names
such as Breinox, Dinagen, Lucetam, Nootropil, Nootropyl,
Oikamid and many others, with the ability to increase the
performance in a variety of cognitive tasks among dyslexic
11
12
68
91
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Table 2 Heteroaromatic primary amides synthesisa
Table 3 Aliphatic primary amides synthesisa
Entry
1
Benzyl alcohol
Product
Yieldb[%]
76
Entry
1
Benzyl alcohol
Product
Yieldb[%]
70
2
3
4
5
6
85
86
69
80
79
2
3
82
95
4
5
61
71
7
8
65
41
6
60
a Alcohols (1 mmol), NH3 (25 wt% in H2O; 1 mL), TBHP (70% in H2O;
8 mmol), 100 °C, 16 h (reaction time was not optimized). b Isolated
yields.
a Alcohols (1 mmol), NH3 (25 wt% in H2O; 1 mL), TBHP (70% in H2O;
8 mmol), 100 °C, 16 h (reaction time was not optimized). b Isolated
yields.
children and also inhibit brain damage caused by a variety
of factors including hypoxia and excessive alcohol con-
sumption, was prepared in a one-step manner in 73%
yield.13
As to the reaction mechanism, it is not clear yet. However,
some control experiments were also carried out. If ammonia
was replaced with N-butylamine, amide was not formed under
the same conditions. Several zinc salts [ZnCl2, ZnBr2, Zn(OAc)2
and Zn(OTf)2] were tested as an additional catalyst for the oxi-
dative amidation of benzyl alcohol, but the yield of benzamide
was decreased. A possible reaction mechanism has been pro-
posed (Scheme 2). More detailed mechanistic studies are
ongoing in our group.
Scheme 2 Proposed reaction mechanism.
Experimental section
Typical reaction procedure for the oxidation of benzyl alcohol
to benzamide
In a 25 mL pressure tube equipped with a stirring bar, benzyl
In conclusion, a general and practical methodology for the alcohol (1 mmol), an aqueous ammonia solution (25 wt% in
oxidation of alcohols to primary amides in aqueous solution H2O; 1 mL) and tert-butyl peroxide (70% in H2O; 8 mmol) were
under metal free conditions has been developed. 34 different injected by a syringe. Then the tube was closed and heated up
kinds of primary amides were produced in good yields. A com- to 100 °C for 16 hours. When the reaction was completed, the
mercial drug, Piracetam, was prepared in one step with 73% reaction mixture was cooled to room temperature. The pure
yield as well. The mechanism of this transformation is under product was isolated after a simple filtration. When necessary,
investigation in our group based on DFT calculation, in situ IR the crude product was purified by chromatography using ethyl
and related tools.
acetate and hexane as the eluent.
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Benzamide. Ethyl acetate–hexane (2 : 1); H NMR (300 MHz, d6): δ = 127.9 (d, J = 13.5 Hz), 129.7, 130.6, 130.9 (CH), 138.0
DMSO-d6): δ = 7.40 (s, 1H), 7.47–7.59 (m, 3H), 7.92–7.95 (m, (C), 169.3 (CO).
2H), 8.10 (s, 1H); 13C NMR (DMSO-d6): δ = 127.9 (2CH2), 128.6
(2CH2), 131.7 (CH), 134.7 (C), 168.4 (CO).
3-Chlorobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR
(300 MHz, DMSO-d6): δ = 7.50–7.55 (m, 1H), 7.57 (s, 1H, NH2),
2-Methylbenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR 7.60–7.64 (m, 1H), 7.85–7.89 (m, 1H), 7.94–7.96 (m, 1H), 8.12
(300 MHz, DMSO-d6): δ = 2.67 (s, 3H), 7.32–7.52 (m, 2H), (s, 1H, NH2); 13C NMR (DMSO-d6): δ = 127.0 (CH), 128.1 (CH),
7.64–7.65 (m, 2H), 8.32–8.44 (m, 2H); 13C NMR (DMSO-d6): δ = 131.1 (CH), 131.9 (CH), 134.0 (C), 137.1 (C), 167.3 (CO).
22.2 (CH3), 126.6, 131.5, 131.7, 132.2 (CH), 133.6, 135.8 (C),
169.6 (CO).
4-Chlorobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR
(300 MHz, DMSO-d6): δ = 7.49 (s, 1H, NH2), 7.54–7.58 (m, 2H),
3-Methylbenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR 7.91–7.95 (m, 2H), 8.08 (s, 1H, NH2); 13C NMR (DMSO-d6): δ =
(300 MHz, DMSO-d6): δ = 2.37 (s, 3H), 7.32–7.39 (m, 2H), 129.2 (2CH), 130.3 (2CH), 133.9 (C), 137.0 (C), 167.7 (CO).
7.67–7.73 (m, 2H), 7.95 (s, 1H), 8.00–8.05 (m, 1H); 13C NMR
4-Bromobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR
(DMSO-d6): δ = 22.2 (CH3), 126.6, 131.5, 131.7, 132.2 (CH), (300 MHz, DMSO-d6): δ = 7.53 (s, 1H, NH2), 7.66–7.71 (m, 2H),
133.6, 135.8 (C), 169.6 (CO).
7.83–7.89 (m, 2H), 8.10 (s, 1H, NH2); 13C NMR (DMSO-d6): δ =
4-Methylbenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR 126.0 (C), 130.5 (2CH), 132.2 (2CH), 134.3 (C), 167.9 (CO).
(300 MHz, DMSO-d6): δ = 2.36 (s, 3H), 7.27 (d, J = 8.23 Hz, 2H),
4-(Trifluoromethyl)benzamide. Ethyl acetate–hexane (2 : 1);
7.34 (s, 1H, NH2), 7.83 (d, J = 8.23 Hz, 2H), 7.96 (s, 1H); 13C 1H NMR (300 MHz, DMSO-d6): δ = 7.69 (s, 1H, NH2), 7.85–7.89
NMR (DMSO-d6): δ = 21.9 (CH3), 128.5 (2CH), 129.7 (2CH), (m, 2H), 8.10–8.13 (m, 2H), 8.26 (s, 1H, NH2); 13C NMR
132.2 (C), 142.0 (C), 168.9 (CO).
(DMSO-d6): δ = 124.7 (d, JCF3 = 273.1 Hz, CF3), 126.2 (2CH),
4-Methoybenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR 129.3 (2CH), 132.1 (d, J = 31.5 Hz, C), 139.1 (C), 167.7 (CO).
(300 MHz, DMSO-d6): δ = 3.38 (s, 1H), 3.87 (s, 3H), 7.04 (d, J =
4-(Trifluoromethoxy)benzamide. Ethyl
acetate–hexane
9.18 Hz, 2H), 7.92 (d, J = 9.18 Hz, 2H), 12.6 (s, 1H); 13C NMR (2 : 1); 1H NMR (300 MHz, DMSO-d6): δ = 7.43–7.49 (m, 2H),
(DMSO-d6): δ = 56.3 (OCH3), 114.6 (2CH), 123.8 (C), 132.2 7.58 (s, 1H), 8.03–8.08 (m, 2H), 8.16 (s, 1H); 13C NMR (DMSO-
(2CH), 163.7 (C), 167.8 (CO).
d6): δ = 121.1 (d, JCF3 = 253.9 Hz, OCF3), 121.3 (2CH), 130.6
3,4-Dimethoybenzamide. Ethyl acetate–hexane (2 : 1); 1H (2CH), 132.4, 134.2, 151.2 (C), 167.5 (CO).
NMR (300 MHz, DMSO-d6): δ = 3.82 (s, 3H), 3.84 (s, 3H),
4-(Thiomethyl)benzamide. Ethyl acetate–hexane (2 : 1); 1H
6.99–7.05 (m, 2H), 7.23 (s, 1H), 7.47–7.56 (m, 2H), 7.90 (s, 1H); NMR (300 MHz, DMSO-d6): δ = 3.31 (s, 3H), 7.70 (s, 1H),
13C NMR (DMSO-d6): δ = 56.4, 56.5 (2OCH3), 111.6, 121.6, 8.01–8.09 (m, 2H), 8.10–8.16 (m, 2H), 8.25 (s, 1H); 13C NMR
127.5 (CH), 149.1, 152.2 (C), 168.4 (CO).
(DMSO-d6): δ = 44.2 (CH3), 127.9 (2CH), 129.3 (2CH), 139.7,
Picolinamide. Ethyl acetate–hexane (2 : 1); 1H NMR 143.8 (C), 167.5 (CO).
(300 MHz, DMSO-d6): δ = 7.58–7.62 (m, 1H), 7.71 (s, 1H, NH2),
4-Acetamidobenzamide. Ethyl acetate–hexane (2 : 1); 1H
7.98–8.03 (m, 1H), 8.07 (s, 1H, NH2), 8.07–8.09 (m, 1H), NMR (300 MHz, DMSO-d6): δ = 2.11 (s, 3H), 7.26 (s, 1H),
8.17 (s, 1H, NH2), 8.64–8.66 (m, 1H); 13C NMR (DMSO-d6): δ = 7.65–7.68 (m, 2H), 7.83–7.89 (m, 3H), 10.2 (s, 1H); 13C NMR
122.7 (CH), 127.3 (CH), 138.5 (CH), 149.3 (CH), 151.1 (C), (DMSO-d6): δ = 124.2 (2CH), 129.6 (2CH), 140.7, 149.8 (C),
166.9 (CO).
166.9 (CO).
Nicotinamide. Ethyl acetate–hexane (2 : 1); 1H NMR
Thiophene-2-carboxamide. Ethyl acetate–hexane (2 : 1); 1H
(300 MHz, DMSO-d6): δ = 7.48–7.53 (m, 1H), 7.69 (s, 1H, NH2), NMR (300 MHz, DMSO-d6): δ = 7.15–7.17 (m, 3H), 7.40 (s, 1H),
8.24–8.30 (m, 2H), 8.71–8.76 (m, 2H); 13C NMR (DMSO-d6): δ = 7.76–7.79 (m, 2H), 7.99 (s, 1H); 13C NMR (DMSO-d6): δ = 128.8,
124.4, 130.6, 136.2, 149.7 (CH), 152.9 (C), 167.6 (CO).
129.6, 131.9 (CH), 141.3 (C), 163.8 (CO).
Isonicotinamide. 1H NMR (300 MHz, DMSO-d6):
δ
=
Thiophene-3-carboxamide. Ethyl acetate–hexane (2 : 1); 1H
7.79–7.84 (m, 3H), 8.72–8.75 (s, 3H); 13C NMR (DMSO-d6): δ = NMR (300 MHz, DMSO-d6): δ = 7.27 (s, 1H), 7.51–7.53 (m, 1H),
122.5 (2CH), 123.9 (C), 142.3 (C), 151.2 (2CH), 167.5 (CO).
3-Fluorobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR (DMSO-d6): δ = 127.4, 128.0, 129.9 (CH), 138.9 (C), 164.6 (CO).
(300 MHz, DMSO-d6): δ = 7.38–7.42 (m, 1H), 7.51–7.57 (m, 2H), Benzo[b]thiophene-2-carboxamide. Ethyl acetate–hexane
7.58–7.59 (m, 1H), 7.82 (s, 1H), 8.18–8.17 (m, 1H); 13C NMR
7.67–7.71 (m, 1H), 7.74–7.77 (m, 1H), 8.09 (s, 1H, NH2); 13C (2 : 1); 1H NMR (300 MHz, DMSO-d6): δ = 7.43–7.54 (m, 2H),
NMR (DMSO-d6): δ = 114.0 (d, J3CF = 24.4 Hz, CH), 118.1 (d, 7.67 (s, 1H), 7.93–7.98 (m, 1H), 8.02–8.07 (m, 1H), 8.09–8.12
J3CF = 22.2 Hz, CH), 123.6 (d, J4CF = 3.01 Hz, CH), 130.3 (d, J3CF (m, 1H), 8.28 (m, 1H); 13C NMR (DMSO-d6): δ = 123.7, 125.7,
= 8.15 Hz, CH), 136.7 (d, J3CF = 6.91 Hz, C), 161.9 (d, JCF = 244.1 125.9, 126.1, 127.0 (CH), 140.1, 141.2, 141.3 (C), 164.2 (CO).
Hz, CF), 166.4 (CO).
1-Naphthamide. Ethyl acetate–hexane (2 : 1); 1H NMR
4-Fluorobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR (300 MHz, DMSO-d6): δ = 7.54–7.70 (m, 5H), 7.98–8.07 (m, 3H),
(300 MHz, DMSO-d6): δ = 7.29–7.35 (m, 2H), 7.43 (s, 1H), 8.33–8.38 (m, 1H); 13C NMR (DMSO-d6): δ = 125.7, 125.9,
7.96–8.00 (m, 2H), 8.03 (s, 1H, NH2); 13C NMR (DMSO-d6): δ = 126.4, 126.9, 127.3, 128.9, 130.4 (CH), 130.5, 133.7, 133.9,
115.8 (d, J = 23.8 Hz, 2CH), 130.9 (d, J = 9.40 Hz, 2H), 131.6 135.4 (C), 171.2 (CO).
(C), 164.7 (d, J = 248.8 Hz, CF), 167.6 (CO).
2-Naphthamide. Ethyl acetate–hexane (2 : 1); 1H NMR
2-Chlorobenzamide. Ethyl acetate–hexane (2 : 1); 1H NMR (300 MHz, DMSO-d6): δ = 7.60–7.77 (m, 3H), 7.79–8.04 (m, 4H),
(300 MHz, DMSO-d6): δ = 6.83–8.13 (m, 6H); 13C NMR (DMSO- 8.13–8.17 (m, 1H), 8.64 (s, 1H); 13C NMR (DMSO-d6): δ = 126.2,
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127.8, 128.7, 129.1, 129.3, 129.4, 130.5 (CH), 131.4, 133.2,
135.9 (C), 168.6 (CO).
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Formamide. Ethyl acetate–hexane (2 : 1); 1H NMR (300 MHz,
DMSO-d6): δ = 5.52 (s, 2H), 7.37 (m, 1H); 13C NMR (DMSO-d6):
δ = 160.6 (CO).
1
Acetamide. Ethyl acetate–hexane (2 : 1); H NMR (300 MHz,
DMSO-d6): δ = 1.79 (s, 3H), 6.71 (s, 1H), 7.31 (s, 1H); 13C NMR
(DMSO-d6): δ = 23.4 (CH3), 160.6 (CO).
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