Liquidphase tert-butylation of cresols catalysed
by 12-tungstophosphoricacid and 12-tungstosilicicacid
supported onto neutral alumina
Nikunj Bhatt and Anjali Patel*
Chemistry Department, Faculty of Science, M.S. University of Baroda, Vadodara 390002, India
Received 5 November 2006; accepted 21 December 2006
A comparative study on tert-butylation of cresols such as o-cresol, m-cresol and p-cresol with tert-butyl alcohol was carried out
over 30% 12-tungstophosphoricacid and 12-tungstosilicicacid supported onto neutral alumina in liquid phase under mild
conditions. The catalysts show high activity in terms of % conversion and % selectivity for the products, p-tert butyl o-cresol, o-tert
butyl m-cresol, o-tert butyl p-cresol, under mild conditions.
KEY WORDS: tert-butylation; cresols; 12-tungstophosphoricacid; 12-tungstosilicicacid; neutral alumina.
1. Introduction
The tertiary butylation of cresols with tertiary butyl
alcohol is an industrially important since the reaction
gives a variety of corresponding value added products.
Among these, tert-butylation of p-cresol is most
important as the obtained products, o-tert-butyl-p-
cresol, o-di-tert-butyl-p-cresol, are widely used in the
production of varnish, resins, as antioxidants [1] and
polymerization inhibitors [2]. In general, this reaction
is carried out using Friedel-Crafts catalysts such as
AlCl
3
,BF
3
,FeCl
3
and ZnCl
2
. Due to the known
disadvantages of the homogeneous catalysts, the use
of solids as catalytic materials in liquid-phase reac-
tions has recently been a major goal in catalytic
research. Liquid acids are being replaced with solid
acids.
A literature survey shows that, even though tert-
butylation of cresols is equally important as that of
tert-butylation of phenol, not much work has been
carried out for the same. Solid acids such as cation
exchange resins [3, 4], sulfated zirconia [5], zirconia
supported heteropolyacids and tungsten oxide [6, 7],
modified K-10 [8] are being evaluated for the
tert-butylation of cresols. Most of the reported heter-
ogeneous catalysts are active in vapour phase
tert-butylation reactions.
Heteropolyacids (HPAs) are promising solid acid
catalysts due to their stronger Bronsted acidity and
supported heteropolyacids have been gaining impor-
tance as alkylating and acylating catalysts. Among
them, the keggin type, 12-tungstophosphoricacid (TPA)
has been widely studied [9, 10] as it is most stable and
strongest acid in the series. TPA supported onto dif-
ferent supports has been used for the alkylation of
various substrates [6, 11, 12]. It was also observed that
all used supports are acidic in nature. It is well known
that basic support cannot be used for supporting HPAs,
since it gets decomposed on the same. So, in the present
paper we have made use of neutral alumina as the
support. It is available in 3 different pH ranges: basic,
acidic and neutral. Neutral alumina at pH of 6–8 is best
as a support. To the best of our knowledge, no study
has been carried out on tert-butylation of cresols using
TPA supported on to neutral alumina. It was also found
that no study was carried out using supported 12-
tungsotsilicicacid (TSA), next stronger acid in the HPA
series for the same. From our earlier studies [13, 14] it
was found that 30% TPA and TSA supported onto
neutral alumina is best as acid catalyst for esterification
reactions. So, in the present paper, we have made effort
to explore the use of same catalyst for alkylation reac-
tion, one of the most important industrial reaction. We
report the detailed study of the tert-butylation of cresols
using TPA and TSA supported onto neutral alumina
under mild conditions. Tert-butylation of p- cresol was
carried out by varying different parameters such as
temperature, mole ratio of cresol to tert-butyl alcohol
(t-BA), amount of the catalyst and reaction time to
optimize the conditions for maximum % conversion as
well as % selectivity for o-isomer. The tert-butylation of
o-cresol and m-cresol was carried out under optimized
conditions.
*To whom correspondence should be addressed.
E-mail: aupatel_chem@yahoo.com
Catalysis Letters, Vol. 113, Nos. 3–4, February 2007 (Ó 2007) 99
DOI: 10.1007/s10562-007-9024-x
1011-372X/07/0200–0099/0
Ó
2007 Springer Science+Business Media, LLC