HClO4-SiO2 as an efficient and recyclable catalyst for the synthesis of amide derivatives

Article abstract of DOI:10.1080/00397911.2010.517414

An efficient and clean procedure for amide alkylation is reported by direct condensation of equimolar amounts of benzylic and allylic alcohols with primary amides in the presence of silica perchloric acid (HClO₄-SiO ₂). The direct co

Full text of DOI:10.1080/00397911.2010.517414

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HClO4-SiO2 as an Efficient and Recyclable
Catalyst for the Synthesis of Amide
Derivatives
Weibin Song a , Lei Ma a & Lihong Hu a b
a School of Pharmacy, East China University of Science and
Technology, Shanghai, China
b Shanghai Institute of Materia Medica, Chinese Academy of
Sciences, Shanghai, China
Version of record first published: 27 Jul 2011
To cite this article: Weibin Song, Lei Ma & Lihong Hu (2011): HClO4-SiO2 as an Efficient and
Recyclable Catalyst for the Synthesis of Amide Derivatives, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 41:21, 3186-3196
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Synthetic Communications1, 41: 3186–3196, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.517414
HClO4-SiO2 AS AN EFFICIENT AND RECYCLABLE
CATALYST FOR THE SYNTHESIS OF AMIDE
DERIVATIVES
Weibin Song,1 Lei Ma,1 and Lihong Hu1,2
1School of Pharmacy, East China University of Science and Technology,
Shanghai, China
2Shanghai Institute of Materia Medica, Chinese Academy of Sciences,
Shanghai, China
GRAPHICAL ABSTRACT
Abstract An efficient and clean procedure for amide alkylation is reported by direct conden-
sation of equimolar amounts of benzylic and allylic alcohols with primary amides in the
presence of silica perchloric acid (HClO4-SiO2). The direct condensation of secondary
benzylic and allylic alcohols with benzamide, sulfonamide, 2-furamide, cinnamamide, and
acrylamide has been achieved to afford the corresponding amide in excellent yields. The
convenient, recyclable, and excellent yields of products are attractive features of this
reaction.
Keywords Amide alkylation reactions; heterogeneous; recyclable; silica perchloric acid
(HClO4-SiO2)
INTRODUCTION
C–N bond formation is an important reaction in organic synthesis because of
the importance of nitrogen-containing compounds in the production of pharmaceu-
ticals and fine chemicals.[1] Traditionally, substitution reactions of alkyl halides,
alkyl acetates, or related compounds with amine nucleophiles are one of the most
useful types of C–N bond-forming reactions.[2] In contrast to traditional methods,
a good alternative approach is the nucleophilic substitution of the hydroxy groups
in alcohols with various amines, which is one of the most efficient and reliable
methods.[3] However, these methods produce stoichiometric amounts of salt waste
both in preactivation of the alcohols and the C–N bond-formation steps. Hence,
Received August 29, 2009.
Address correspondence to Weibin Song, School of Pharmacy, East China University of Science
and Technology, 130 Meilong Road, Shanghai 20023, China. E-mail: malei@ecust.edu.cn; simmhulh@
mail.shcnc.ac.cn
3186

HClO4-SiO2 CATALYST AMIDE SYNTHESIS
3187
in view of the demand for more atom-economical, ecofriendly, and convenient
processes, the direct catalytic substitution of alcohols with amines is desirable.
Over the years, a number of amide alkylation reactions by direct substitution
of alcohols with amines in the presence of transition metals with ligands, such as
Pd and Ru, have been reported.[4] However, the use of weak nitrogen nucleophiles
such as amides which are easily available, are extremely rare and require high
temperatures. Very recently, more and more groups have turned their attentions
to Lewis acid–catalyzed amidation reactions of alcohols with primary amides. A
series of Lewis acid such as NaAuCl4,[5a] MoCl5,[5b] H-montmorillonite,[5c] FeCl3,[5d]
12-phosphotungstic acid (PWA),[5e] a combination of Bi(OTf)3,[5f] with KPF6 as
additive, and water-soluble calix[4]resorcinarene sulfonic acid have been reported.[5g]
While these methodologies involved mild conditions and display increased func-
tional group tolerance, most of them suffer from unsatisfactory yields, expensive
require and detrimental metal precursors, and are also difficult to recycle, which lim-
its their use. Therefore, development of a more practical and atom-economical
method for direct substitution of primary amides with benzylic or allylic alcohols
has acquired relevance to current research.
Recently, HClO4-SiO2 has gained more and more attention because of its
outstanding qualities; new, heterogeneous, highly efficient, inexpensive, reusable,
and it is environmentally friendly. It has been utilized successfully in several organic
transformations to minimize undesirable waste causing environmental pollution,
including acylationreactions,[6a–6c] selective removal of anomeric o-acetate groups
in carbohydrates,[6d] the Ferrier rearrangement,[6e] the Hantzsch and Knoevenagel
condensations,[6f] the aza-Michael addition of amines to activated alkenes,[6g]
electrophilic substitution reaction,[6h] and synthesis of privileged heterocyclic com-
pounds through multicomponent reactions.[6i,6g] It is well known that perchlorates
can give rise to explosive reactions when heated at high temperatures in the presence
of combustible compounds.[7a] Therefore, the potential hazard connected with their
manufacture and use has prevented their extensive application in industrial proces-
ses,[6a] especially when large amounts of these compounds are involved. However,
recent reported methods indicate that low catalyst loading of HClO4-SiO2 can effec-
tively bring about the organic transformations and can be operated even at 90 ꢀC.[7b]
In this article, we report HClO4-SiO2 as an efficient catalyst for the synthesis of
amide derivatives by direct substitution of benzylic and allylic alcohols with various
carboxamides or sulfonamides (Scheme 1).
Scheme 1. HClO4-SiO2-catalyzed amidation of benzylic=allylic alcohols.

3188
W. SONG, L. MA, AND L. HU
RESULTS AND DISCUSSION
Our initial efforts were directed to the optimization of the reaction conditions,
which were examined in the reaction between benzyl amide 1a and diphenyl methanol
2a in the presence of 5 mol% HClO4-SiO2 under reflux condition (Table 1). Initially,
we tested a series of solvents, such as H2O, CH3CN, tetrahydrohuran (THF), CH2Cl2,
and 1,4-dioxane. It was found that the reaction took place in CH3CN, giving the
desired product in 72% yield (entry 2), while no products were detected in H2O even
after 6 h (entry 1). Besides, the reactions that occurred in CH2Cl2 and THF did not
furnish satisfactory results after 4 h (entries 3 and 4). To our satisfaction, when this
reaction was performed in 1,4-dioxane, the product was obtained in excellent yield
of 93% after only 3 h (entry 5). Therefore, 1,4-dioxane was chosen as a solvent for
further reaction optimization with respect to reaction time and the maximum yield
of the products. In the study of catalyst loading, 0%, 2%, and 10 mol% of HClO4-
SiO2 were tested. No product was obtained after 6 h in the presence of silica gel alone
(entry 6); the reaction with 10 mol% catalyst gave 95% yield (entry 8) in 3 h, whereas
2 mol% catalyst loading only gave 77% yield (entry 7). These results suggested that the
optimal amount of HClO4-SiO2 was 5 mol%, and that greater amounts of the catalyst
did not increase the yield noticeably.
Because reducing the amount of catalyst and making it reusable are two impor-
tant aspects of green chemistry, we tested the activity of the recovered catalyst
HClO4-SiO2. After each reaction, the reaction mixture was filtered. The catalyst
was washed with CHCl3 (2 ꢁ 5 mL), EtOH (2 ꢁ 5 mL), and Et2O (2 ꢁ 5 mL) and sub-
sequently dried at 80 ꢀC for reuse directly in the next cycle. Activity of catalyst was
retained after being recycled multiple times. Even after recycling the catalyst four
times, the yields were practically identical to those observed when fresh catalyst
was used (Table 1, entry 5).
a
Table 1. Solvent effect on the synthesis catalyzed by HClO4-SiO2
Entry
Solvent
H2O
CH3CN
Catalyst (mol%)
Time (h)
Yield (%)b
1
2
3
4
5c
6
7
8
5
5
6
4
4
4
3
6
3
3
—
72
THF
CH2Cl2
5
16
Trace
93, 91, 88, 92, 91
5
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
5
0
—
77
95
2
10
aUnless otherwise specified, all reactions were performed with 1a (1 mmol), 2a (1 mmol), and HClO4-
SiO2 in solvent (2 mL) under reflux conditions.
bIsolated yield.
cThe yields corresponded to the recycling reusability of catalyst.

3189

3190

3191

3192
W. SONG, L. MA, AND L. HU
Encouraged by the results obtained for benzyl amide 1a and diphenyl methanol
2a, we investigated a number of alcohol substrates and various types of nitrogen
nucleophiles to probe their behaviors under the current catalytic conditions
(Table 2). In general, the reactions proceeded efficiently with various substituted
secondary benzyl alcohols and unsaturated primary amides in excellent yields within
short period of time. Obviously, secondary benzylic alcohols afforded the corre-
sponding product with greater yields than secondary allylic alcohols (entries 1, 2,
and 4–6), but no corresponding products were detected when using benzyl alcohol
under these conditions, even after prolonged heating (entry 3). The present method
was equally effective for benzyl amide with electron-donating groups such as
p-methyl-benzamide (entries 10 and 11), which gaves lightly greater yields (84–
95%) than electron-donating groups of p-nitro-benzamide (78–88%) (entries 7 and
8). In contrast, p-methyl-benzamide favored the formation of product with greater
yield and needed less time than o-methyl-benzamide (entries 12 and 13); the steric
effects of o-methyl should be responsible for this. Furthermore, this reaction was
also applied to p-toluenesulfonamide 1e, acrylamide 1f, 2-furamide 1g, cinnamamide
1h, and 4-chloro cinnamamide 1i. All of them underwent smooth amidation with
diphenyl methanol 2a or 1-phenylethanol 2b and gave the desired products in yields
of 68–96% (entries 14–19). Although this reaction was highly efficient for these types
of amides, acetamide 1j itself did not react under these conditions even with
prolonged heating (entry 20).
Although many people have probed the Lewis acid-catalyzed reaction
mechanism of the amide alkylation reactions, the exact reaction mechanism is not
quite clear at the moment. For example, Wang et al. have recently reported that
(R)-1-phenylethanol [99% ee] and p-toluenesulfonamide were activated by the Lewis
acid to produce the final product in excellent yield as a racemic mixture and
proposed the SN1 mechanism for the reaction.[5e] Jana et al. have reported that
the benzylic alcohols were first converted to the corresponding dimeric ether and
then activated by the Lewis acid to produce the final product by nucleophilic substi-
tution with the amide,[5d] but this mechanism has not been proved by corresponding
experiment.
To further verify the Lewis acid–catalyzed amide alkylation reaction mech-
anism, we designed the following experiment (Scheme 2). First, 1-phenylethanol
2b was converted to the corresponding dimeric ether 5 (0.5 equiv) and then treated
with benzyl amide 1a and HClO4-SiO2 under the typical reaction conditions. After
3h, the final product 3ab was isolated in 87% yield, which was almost equal to the
previous yield of 83% (entry 1). In light of these results, we think that the reaction
proceeds through the catalytic cycle described in Scheme 3. The reaction occurs in
the catalyst surface,[8] in which the interaction between 2b and Z-H (HClO4-SiO2)
generates the intermediate 4. This, reacting with 1a, gives rise to the key intermediate
Scheme 2. Amide alkylation reactions of la with 2b.

HClO4-SiO2 CATALYST AMIDE SYNTHESIS
3193
Scheme 3. Catalytic cycle mechanism.
6, which releases the product 3ab with regeneration the catalyst of Z-H. Then, Z-H is
ready to start another catalytic cycle. It is worthy of note that this process is the main
mechanism of the amide alkylation reactions. Additionally, the intermediate 4 reacts
with 2a to furnish 5, which could be regenerated as 4 in the presence of HClO4-SiO2
to participate in the next cycle of reaction.
CONCLUSIONS
In summary, we have developed a novel and facile method for the synthesis of
amide derivatives in the presence of solid-supported HClO4-SiO2 as a heterogeneous
catalyst. The present methodology offers very attractive features such as ease of
recovery, reuse of the catalyst, benign reaction, excellent yields, and a waste-free
chemical process.
EXPERIMENTAL
1
Characterization of all compounds was done with H NMR and mass spec-
1
trometry. H NMR spectra were recorded on a Bruker Avance 500 spectrometer
(500 MHz). Electrospray ionization (ESI) mass spectra were obtained on a Mariner
System 5303 mass spectrometer. Melting points were measured with an SGWX-4
apparatus and are uncorrected.
Preparation of the Catalyst
HClO4 (1.25 g, 12.5 mmol, as a 70% aqueous solution) was added to the
suspension of silica gel (23.75 g, 230–400 mesh) in diethyl ether (75 mL). The mixture
was concentrated, and the residue was dried under vaccum at 100 ꢀC for 72 h to
afford HClO4–SiO2 (0.5 mmol gꢂ1) as a free-flowing powder.[7c]

3194
W. SONG, L. MA, AND L. HU
General Procedure for the Preparation of 3aa
To a stirred solution of benzamide 1a (128 mg, 1 mmol) and diphenyl methanol
2a (220 mg, 1.2 mmol) in dry 1,4-dioxane (2 mL) was added HClO4–SiO2 (100 mg,
0.05 mmol). The resulting reaction mixture was refluxed for 3h. The reaction mixture
was then concentrated under reduced pressure and loaded onto a silica-gel column
and chromatographed with petroleum etherl=ethyl acetate (4:1) to obtain a white
solid (93%).
Selected Spectroscopic Data
N-(1-Phenylethyl)benzamide (3ab). White solid, mp 120–122 ꢀC. 1H NMR
(CDCl3, 500 Hz) dH (ppm): 1.62 (d, J ¼ 6.9 Hz, 3H), 5.34 (m, 1H), 6.28 (d, J ¼ 3.8 Hz,
1H), 7.29 (m, 2 H), 7.34–7.46 (m, 6 H), 7.48–7.51 (m, 2H), 7.78 (d, J ¼ 7.3 Hz, 2H).
ESI-MS: m=z 225.1 [M þ H]þ.
N-(Diphenylmethyl)-4-nitro-benzamide (3ba). White solid, mp 216–218 ꢀC.
1H NMR (CDCl3, 500 Hz) dH (ppm): 6.47 (d, J ¼ 8.0 Hz, 1 H), 7.28–7.38 (m, 1H),
8.23–8.30 (m, 4H), 9.72 (d, J ¼ 8.0 Hz, 1H). ESI-MS: m=z 332.1 [M þ H]þ.
N-(4-Methylbenzoyl)-a-methylbenzylamine (3cb). White solid, mp 127–
128 ꢀC. 1H NMR (CDCl3, 500 Hz) dH (ppm): 1.58 (d, J ¼ 6.9 Hz, 3H), 2.36 (s,
1H), 5.28–5.47 (m, 1H), 6.40 (br s, 1H), 7.12–7.16 (d, J ¼ 7.8 Hz, 2H), 7.32–7.43
(m, 5 H), 7.67 (d, J ¼ 7.8 Hz, 2H). ESI-MS: m=z 239.0 [M þ H]þ.
1
N-(Diphenylmethyl-)-2-toluamide (3da). White solid, mp 159–160 ꢀC. H
NMR (CDCl3, 500 Hz) dH (ppm): 2.48 (s, 3H), 6.48 (br d, 1H), 6.43 (br d, 1H,
J ¼ 7.8 Hz), 6.62–6.76 (m, 1H), 7.23–7.42 (m, 10H), 7.60–7.67 (m, 4H). ESI-MS:
m=z 301.2 [M þ H]þ.
N-Benzhydryl-4-toluenesulfonamide (3ea). White solid, mp 155–156 ꢀC.
1H NMR (CDCl3, 500 Hz) dH (ppm): 2.38 (s, 3H), 5.02 (d, 1H, J ¼ 6.6 Hz), 5.57
(d, 1H, J ¼ 6.9 Hz), 7.08–7.11 (m, 4H), 7.12–7.16 (d, 2H, J ¼ 6.9 Hz), 7.18–7.12 (m,
6H), 7.53–7.58 (d, 2H, J ¼ 8.0 Hz). ESI-MS: m=z 337.1 [M þ H]þ.
N-(1-Phenylethyl)-4-methylbenzenesulfonamide (3eb). White solid, mp
1
78–79 ꢀC. H NMR (CDCl3, 500 Hz) dH (ppm): 1.51 (d, 3 H, J ¼ 6.8 Hz), 2.37 (s,
3H), 4.45 (m, 1H), 4.92 (d, 1H, J ¼ 6.8 Hz), 7.08–7.11 (m, 2H), 7.17–7.22 (m, 5H),
7.62 (d, 2H, J ¼ 8.2 Hz). ESI-MS: m=z 275.1 [M þ H]þ.
N-(Diphenylmethyl)propenamide (3fa). White solid, mp 177–179 ꢀC. 1H
NMR (CDCl3, 500 Hz) dH (ppm): 5.69 (d, 1 H, J ¼ 10.2 Hz), 6.14 (br s, 1H), 6.16–
6.20 (dd, 2H, J ¼ 17.0, 10.2 Hz), 6.33 (s, 1H), 6.36 (d, 2H, J ¼ 17.0 Hz), 7.25–7.29
(m, 6H), 7.32–7.35 (m, 4H). ESI-MS: m=z 237.2 [M þ H]þ.
N-(1-Methylbenzyl)-3-(p-chlorophenyl)propenamide (3ib). White solid,
mp 142–144 ꢀC; 1H NMR (CDCl3, 500 Hz) dH (ppm): 1.50 (d, J ¼ 7.0 Hz, 3H),
4.90–5.04 (dd, J ¼ 7.0 Hz, 1H), 6.11 (br s, 1H), 6.48 (d, J ¼ 16.0 Hz, 1H), 7.27–7.47
(m, 9H), 7.62 (d, J ¼ 16.0 Hz, 1H). ESI-MS: m=z 285.1 [M þ H]þ.

HClO4-SiO2 CATALYST AMIDE SYNTHESIS
3195
ACKNOWLEDGMENTS
Financial support for this work was provided by the Chinese National
High-Tech Research Development Program (2007AA02Z147) and China 111 Project
(B07023).
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