An efficient and inexpensive catalyst system for friedel-crafts alkylation of aromatic compounds with benzyl and allyl alcohols

Article abstract of DOI:10.1081/SCC-200028600

An new strategy that uses Ce₂(SO₄)₃ as an effective catalyst for Friedel-Crafts alkylation of aromatic compounds with benzyl and allyl alcohols is presented. In the presence of 1 to 10 mol% of Ce₂(SO₄)₃, Friedel-Crafts alkylation with both benzyl alcohols, including primary and secondary benzyl alcohols, and allyl alcohol were carried out smoothly and efficiently. Moreover, the catalyst was recovered and reused three times without significant loss of activity.

Full text of DOI:10.1081/SCC-200028600

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An Efficient and Inexpensive
Catalyst System for
Friedel‐Crafts Alkylation of
Aromatic Compounds with
Benzyl and Allyl Alcohols
Jin‐Heng Li a , Wen‐Jie Liu a & Du‐Lin Yin a
a Institute of Fine Catalysis and Synthesis, College
of Chemistry and Chemical Engineering, Hunan
Normal University, Changsha, 410081, China
Version of record first published: 10 Jan 2011.
To cite this article: Jin‐Heng Li , Wen‐Jie Liu & Du‐Lin Yin (2004): An Efficient and
Inexpensive Catalyst System for Friedel‐Crafts Alkylation of Aromatic Compounds
with Benzyl and Allyl Alcohols, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 34:17, 3161-3165
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 17, pp. 3161–3165, 2004
An Efficient and Inexpensive Catalyst
System for Friedel-Crafts Alkylation
of Aromatic Compounds with Benzyl
and Allyl Alcohols
*
Jin-Heng Li, Wen-Jie Liu, and Du-Lin Yin
Institute of Fine Catalysis and Synthesis, College of Chemistry and
Chemical Engineering, Hunan Normal University, Changsha, China
ABSTRACT
An new strategy that uses Ce2(SO4)3 as an effective catalyst for Friedel-
Crafts alkylation of aromatic compounds with benzyl and allyl alcohols is
presented. In the presence of 1 to 10 mol% of Ce2(SO4)3, Friedel-Crafts
alkylation with both benzyl alcohols, including primary and secondary
benzyl alcohols, and allyl alcohol were carried out smoothly and effi-
ciently. Moreover, the catalyst was recovered and reused three times
without significant loss of activity.
Key Words: Allyl alcohol; Aromatic compound; Benzyl alcohol;
Ce2(SO)3; Friedel-Crafts alkylation reaction.
*
Correspondence: Jin-Heng Li, Institute of Fine Catalysis and Synthesis, College of
Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081,
China; E-mail: jhli@hunnu.edu.
3161
DOI: 10.1081/SCC-200028600
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3162
Li, Liu, and Yin
Lewis acid-mediated Friedel-Crafts alkylation reaction, (for reviews, see
Ref. [1]; Refs. [2,3]; and for lanthanide(III) chlorides-catalyzed benzylation
reaction benzyl halides, see Ref. [4]) including alkylation of aromatic com-
pounds with alcohols,[3] is one of the most important methods for constructing
carbon–carbon bonds resulting in introducing alkyl substituents to an aromatic
ring. As the other Friedel-Crafts alkylation reactions, alkylation of aromatic
compounds with alcohols generally requires large amounts of Lewis and
Brønsted acids, such as AlCl3, ZnCl2, BF3, and HF.[3] Furthermore, the Lewis
and Brønsted acids-mediated alkylation not only must be carried out under
strictly anhydrous conditions but it also releases large amounts of environ-
mentally hazardous wastes. Most important, the catalysts are difficult to be
recycled. In recent years, much attentions has been paid in development of
water-resistant and environmentally benign Lewis acid, such as rare earth
salts,[2–4] to catalyze the alkylation. Of rare earth salts, attention is mostly
focused on RE(OTf)3-catalyzed Friedel-Crafts alkylation of aromatic com-
pounds with alcohols due to their mildness and efficiency. All RE(OTf)3
salts are commercially available but expensive. Therefore, we considered
using cheap, readily available, and environmentally benign common rare
earth salts such as RECl3 and RE2(SO4)3 instead of RE(OTf)3 to catalyze
the alkylation. To the best of our knowledge, only ScCl3 and YbCl3
were tried by Fukuzawa and coworkers to catalyze the alkylation with
alcohols.[4] After a series of attempts, we found that the Friedel-Crafts alkyla-
tion reactions of aromatic compounds with benzyl and allyl alcohols could
proceed efficiently in the presence of catalytic amounts of Ce2(SO4)3. Here
we report the details of those reactions (Schs. 1 and 2 and Table 1).
Scheme 1.

Efficient and Inexpensive Catalyst System for Friedel-Crafts Alkylation
3163
Scheme 2.
In the presence of a catalytic amount of Ce2(SO4)3, Friedel-Crafts alkyl-
ation reactions of various aromatic compounds 1a–1e with benzyl alcohol
2a–2c was carried out smoothly to afford the corresponding products 3a–3i
in moderate to good yields, and the results are summarized in Table 1. We
first examined the activity of Ce2(SO4)3 as the catalyst for the Friedel-
Crafts benzylation of benzene 1a with benzyl alcohol 2a (entries 1–4,
Table 1). The results show that the reaction temperature plays a curial role
Table 1. Ce2(SO4)3-catalyzed Friedel-Crafts alkylation of aromatics with benzyl
alcohols.a
Entry
Aromatics
Alcohol
Product
Yield (%)b
–
1c
2d
3
4e
5
1a
1a
1a
1a
1b
1c
1d
1e
1f
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2c
2c
3a
3a
3a
3a
3b
3c
3d
3e
3f
30
85
55
93 (p/o ¼ 3/2)
56 (p/o ¼ 3/2)
84
6
7
8
87 (p/o ¼ 3.56/1)
9
,5
10
11
12
1a
1a
1d
3g
3h
3i
81
61
50
aReaction conditions: 1 (5 mL), 2 (1 mmol), Ce2(SO4)3 (10 mol%, hydrate) in a sealed
tube at 1258C–1308C overnight.
bIsolated yield. Ratios of p/o-isomer given in parentheses were determined by
1H NMR.
cAt room temperature.
dAt reflux.
eCe2(SO4)3 (1 mol%) for 72 hr.

3164
Li, Liu, and Yin
in the Ce2(SO4)3-catalyzed benzylation. In the presence of 10 mol% of
Ce2(SO4)3, no reaction occurred at room temperature overnight, whereas
30% yield of 2a was obtained at reflux (entries 1 and 2). The yield of 2a
was increased dramatically to 85% by raising the reaction temperature to
1258C (entry 3). Interestingly, the activity of Ce2(SO4)3 was maintained
when employed for the same reaction after recovered and reused three
times. The 2a was obtained in 84%, 81%, and 82% yields in three runs,
respectively. Although a prolonged reaction time was required and yield of
2a decreased to some extent, benzylation of 1a with 2a took place smoothly
in the presence of 1 mol% of Ce2(SO4)3 (entry 4). In the presence of
10 mol% of Ce2(SO4)3, benzylation of 1b–1e with 2a was also carried out
smoothly to afford the corresponding products 3b–3e in 93%, 56%, 84%,
and 87% yields, respectively, at 1258C overnight (entries 5–8). Benzylation
of 1f with 2a failed (entry 9).
Benzylation with 2b and 2i was then evaluated in the presence of
10 mol% of Ce2(SO4)3. The results showed that benzylation of 1a and 1d
with both primary benzyl alcohol 2b and secondary benzyl alcohol 2c pro-
ceeds smoothly to afford the corresponding products 3g–3i in 81%, 61%,
and 50% yields, respectively (entries 10–12).
Friedel-Crafts alkylation reaction of aromatic compounds with allyl alco-
hols were also investigated, and the results are summarized in Sch. 2. In the
presence of 10 mol% of Ce2(SO4)3, alkylations of aromatic compounds 1a
and 1b with allyl alcohol 2d proceeded smoothly to afford the corresponding
products 3j and 3k in 81% and 99% yields, respectively, at 1258C overnight.
In conclusion, we have developed an efficient and inexpensive protocol
by use of 1 to 10 mol% of Ce2(SO4)3 for Friedel-Crafts alkylation of aromatic
compounds with benzyl and allyl alcohols. We are currently working toward
expanding the scope of this process.
EXPERIMENTAL
All 1H and 13C nuclear magnetic resonance (NMR) spectra were recorded
on a Bruck-400 spectrometer with CDCl3 as solvent. All reagents were used
directly as obtained commercially.
A Typical Experimental Procedure for Ce2(SO4)3-Catalyzed
Friedel-Crafts Alkylation of Aromatics with Alcohols
A mixture of 1 (5 mL), 2 (1 mmol), and cerium sulfate (10 mol%) was
placed in a sealed tube, and stirred at 1258C overnight. After usual work-

Efficient and Inexpensive Catalyst System for Friedel-Crafts Alkylation
3165
up, the residue was purified by flash column chromatography to give 3
(hexane/ethyl acetate).
ACKNOWLEDGMENTS
We thank the National Natural Science Foundation of China (No.
20202002) and Hunan Normal University for financial support.
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Received in Japan February 23, 2004