126
Published on the web January 16, 2010
Hydroxyalkylation of p-Cresol to 2,2¤-Methylenebis(4-methylphenol)
Using Sn/Si-MCM-41 Catalysts
Ajit C. Garade,1 Prashant S. Niphadkar,2 Praphulla N. Joshi,*2 and Chandrashekhar V. Rode*1
1Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411008, India
2Catalysis Division, National Chemical Laboratory, Pune 411008, India
(Received November 13, 2009; CL-091002; E-mail: cv.rode@ncl.res.in, pn.joshi@ncl.res.in)
Sn/Si-MCM-41 has exhibited an excellent catalytic activity
SiO2/SnO2 ratio of 110, a third catalyst possessing nearly
identical composition was prepared differently by wet impreg-
nation using Si-MCM-41 as a substrate having molar ratio of
SiO2/SnO2 = 110. After drying for 2 h at 373 K, it was then
calcined at 673 K for 6 h and labeled as Sn/Si-MCM-41(B).
The characteristics of the prepared material matched very well
with those reported.12 The specific BET surface areas and the
concentration of acid sites (mmol NH3 desorbed/g) measured
using NH3-TPD profiles were obtained from a Quantachrome
CHEMBET 3000 instrument.3
The hydroxyalkylation of p-cresol with formaldehyde was
carried out in a magnetically stirred glass reactor (Capacity
50 mL) fitted with a reflux condenser and an arrangement for
temperature control. In a typical experiment, p-cresol (42 mmol),
formaldehyde (8.4 mmol), toluene (108 mmol), and catalyst
(0.04 g cm¹3) were added to the reactor, then heated to 363 K
for 2 h. The product yield and DAM selectivity were determined
using a HP6890 series GC System (Hewlett Packard) coupled
with FID detector and HP-1 capillary column (30 m length ©
0.32 mm i.d.). The products were identified by 1H NMR,
13C NMR, and by GC-MS.
[70% product yield with 88% selectivity to 2,2¤-methylenebis(4-
methylphenol)] for the selective hydroxyalkylation of p-cresol.
At equal level of Sn loading, Sn/Si-MCM-41 prepared by direct
hydrothermal synthesis showed higher activity than Sn-impreg-
nated Si-MCM-41 catalyst.
Developing eco-friendly and efficient catalysts are highly
desirable for an industrially important hydroxyalkylation reac-
tion of phenols to give bisphenols.1 Hydroxyalkylation based
on the use of conventional catalysts like HCl, H3PO4, and
oxalic acid in the stoichiometric amount leads to serious
environmental and operational problems.2 In order to overcome
these drawbacks, several solid acid catalysts were reported for
the hydroxyalkylation of phenols.3-8 Among such solid acid
catalysts, zeolites were found to give better activity for the
hydroxyalkylation of phenols, however they suffer from a
serious problem of fast deactivation due to pore blockage by
trimers and oligomers formed during the reaction.8 Although
larger surface areas and variety of unique structures make
mesoporous materials useful in various catalytic reactions
involving larger molecules, tuning of their acidity and hydro-
thermal stability is necessary for their application to a specific
reaction. By virtue of higher electronegativity, atomic size and
stronger acidity, the incorporation of tetrahedral Sn(IV) in silica-
based mesoporous materials not only enhances the overall
acidity but also the structural stablility.9 Sn-containing meso-
porous materials have exhibited excellent catalytic activity in
hydroxylation of phenol and 1-naphthol, epoxidation of norbor-
nene, Mukaiyama-type aldol condensation, Baeyer-Villiger and
Meerwein-Ponndorf-Verley reactions.10-14
Although Sn/Si-MCM-41(A) and Si-MCM-41 were pre-
pared by following the same hydrothermal synthesis route,
Sn/Si-MCM-41(A) exhibited higher specific BET surface area
(1215 m2 g¹1) compared to Si-MCM-41 (1070 m2 g¹1). This may
be attributed to the changes in synthesis periods, unit cell
parameters and wall thicknesses caused by the difference in the
initial gel composition. Sn/Si-MCM-41(B) has shown specific
¹1
BET surface area of magnitude 955 m2 g which is marginally
lower than Si-MCM-41 indicating no structural damage due to
the post-synthesis treatments such as impregnation/calcination.
Figure 1 shows the typical UV-vis diffuse reflectance
spectra of these three samples. Si-MCM-41 did not show
any absorption band relevant to charge transitions from O2¹
to Sn4+ in tetrahedral coordination. Sn/Si-MCM-41(B) exhib-
ited a broad absorption at 280 nm which may be assigned to
Here we report for the first time a very high product yield
with 88-90% selectivity to 2,2¤-methylenebis(4-methylphenol)
(DAM) for the hydroxyalkylation of p-cresol (Scheme 1) using
Sn/Si-MCM-41 catalyst prepared by two methods viz. direct
hydrothermal synthesis and post-synthesis modification by
impregnation of Sn on Si-MCM-41.
Sn/Si-MCM-41(B)
Sn-free MCM-41 and Sn-containing MCM-41 were pre-
pared hydrothermally by following a reported procedure and
designated them as Si-MCM-41 and Sn/Si-MCM-41(A) respec-
tively.12 Since calcined Sn/Si-MCM-41(A) has shown molar
OH
OH
OH
Sn/Si-MCM-41(A)
Si-MCM-41
O
Sn/Si-MCM-41
2
H
H
200
250
300
350
400
450
Wavelength/nm
DAM
Figure 1. Diffuse reflectance UV-vis spectra of Si-MCM-41,
Sn/Si-MCM-41(A), and Sn/Si-MCM-41(B).
Scheme 1. Hydroxyalkylation of p-cresol to DAM.
Chem. Lett. 2010, 39, 126-127
© 2010 The Chemical Society of Japan