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DOI: 10.1002/adsc.200505495
Sodium Nitrite-Catalyzed Oxybromination of Aromatic
Compounds and Aryl Ketones with a Combination of
Hydrobromic Acid and Molecular Oxygen under Mild
Conditions
Guofu Zhang,a, b Renhua Liua,* Qing Xu,a Lixin Ma,a Xinmiao Lianga,*
a
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, Peopleꢀs Republic of China
Fax: (þ86)þ411-8437-9539, e-mail: liangxm@dicp.ac.cn; renhua@dicp.ac.cn
b
Graduate School of the Chinese Academy of Sciences, Beijing 100039, Peopleꢀs Republic of China
Received: December 29, 2005; Accepted: March 7, 2006
Abstract: A novel andefficient catalytic system for
the oxybromination of aromatic compounds and
aryl ketones utilizing a combination of aqueous hy-
drobromic acid and molecular oxygen in the pres-
ence of sodium nitrite under mild conditions has
been developed. The newly developed catalytic sys-
tem utilizes cheap andreadily available reactants, ex-
hibits high bromine atom economy andreleases only
innocuous water as the by-product.
goal of non-toxic andwaste-free chemistry. In large-
scale operations this is not only an economic problem
but also an environmental one. Recently, an intriguing
solution, namely the oxidation and recycling of the bro-
mination by-product, HBr, using an in situ oxidizing
agent, is emerging as a versatile strategy to reach this
goal. Typically, oxybrominations of aromatic com-
pounds are carried out with a combination of a bromina-
tion reagent anda variety of oxidizing reagents. [3–18] Al-
though these systems have nicely embodied the bromine
atom economy, many such systems require stoichiomet-
ric oxidizing agents. The use of stoichiometric oxidizing
agents to perform the transformation is not an ideal
process as the concurrent formation of undesirable
wastes is inherently unavoidable.[5,7–9] H2O2-basedoxy-
bromination systems,[10–17] however, seem to be green
Keywords: arenes; aryl ketones; atom economy; oxy-
bromination; oxygen; sodium nitrite
The central importance of bromination reactions is a andmany of them are synthetically useful. Even so, sev-
widely accepted fact in synthetic organic chemistry.[1] eral drawbacks remain including the relatively higher
Bromocarbon products are useful chemical intermedi- cost of hydrogen peroxide and its undesirable decompo-
ates, serving as branch points in the synthesis of numer- sition during a reaction at elevated temperatures and/or
ous functionalizedcompounds such as antitumor, anti-
in the presence of metal catalysts. In addition, most re-
as well as specialty ports involve the oxybromination of aromatic com-
chemicals, agrochemicals andpharmaceuticals. For pounds and only rare examples involve the oxybromina-
over 100 years, bromination processes using molecular tion of ketones.[6a,18,19]
[2]
bacterial, andantioxidant agents
bromine as the bromination reagent have been a class
of the most significant andwidely usedsynthetic meth-
On the other hand, molecular oxygen is the most
abundant, and atom economical oxidant known today.
ods for bromocarbon products because molecular bro- Thus, it is surprising that oxybromination methods using
mine is known to be a cheap andreadily available bromi-
nation reagent (Scheme 1).
molecular oxygen for the oxidation and recycling of the
concurrent product, HBr, have until now been compara-
However, these classical bromination methods suffer tively less common and underdeveloped. Only two ex-
from the inherent disadvantage that the efficiency of amples involving aerobic oxybrominations of aromatic
bromine use allows for only 50% atom economy with compounds have been reported. Neumann et al. have
one equivalent of HBr being produced. It is certain described an efficient aerobic oxybromination method
that such bromination processes do not advance the for active aromatic compounds with H5PMo10V2O40 as
the catalyst andHBr gas as the brominating reagent. [19]
More recently, Raja et al. have developed a heterogene-
ous copper phthalocyanine catalyst for the aerobic oxy-
bromination of aromatic compounds. Under relatively
Scheme 1.
mildconditions the authors were able to achieve a
862
ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2006, 348, 862 – 866