JOURNAL OF CATALYSIS 160, 134–136 (1996)
ARTICLE NO. 0131
NOTE
Catalytic Methylation of 1-Naphthol over Iron Oxide
Selective ring alkylation of naphthols is difficult because
The reaction was carried out in an electrically heated,
these are typical multireactive substrates. They react with a steel flow reactor with a length of 70 cm and an inner
variety of electrophilic reagents giving mixtures of mono- diameter of 22 mm. Due to a coaxially positioned thermo-
and polysubstituted isomers. Usually the alkylation of aro- couple it was possible to measure temperature along the
matic substrates is a process of low selectivity because an length of the reactor. A volume of 25 cm3 of catalyst with a
alkylated ring is more susceptible to a subsequent elec- grain size of 2–4 mm was placed in the middle of the reac-
trophilic attack than a nonalkylated one.
tor. The space over and below the catalyst was filled with an
It seems that the only systematic data published so far inert material. The reactants (substrates) at molar ratio of
that concern the gas phase alkylation of naphthols with 1-naphthol : CH3OH (1 : 10) were introduced through the
methanol in the presence of Al2O3 are those of Klemm top of the reactor using metering pumps. The experiments
et al. (1, 2). Their results confirm the above observations, were carried out continuously, beginning with the reduc-
as besides numerous ring alkylated products the reaction tion of the catalyst with methanol or reactant mixture at
mixtures also contained products of O-alkylation and dehy- 473 K. Then the reaction was carried out for 1–2 h under
droxylation as well as methylnaphthalenes. For 1-naphthol, steady conditions, the products being collected after con-
2-methyl-1-naphthol was obtained with a maximum yield densation. They were analyzed by gas chromatography. The
of 37%. In the crude mixture nearly 20 other ring alkylated compounds resulting from the reaction of 1-naphthol with
products could be found and in addition about 30% of this methanol are presented in Scheme I.
mixture consisted of undefinable compounds. Therefore,
this reaction has not found an industrial application.
Compounds 1 and 3 and the remaining 1-naphthol were
also isolated from the product mixture by medium pressure
Some of the present authors have developed an oxide column chromatography on silica gel as adsorbent. The re-
catalyst that contains iron, chromium, silicon, and potas- sultsobtainedbypreparativecolumnchromatographywere
sium (3). It was active in the alkylation of phenol with consistent with those obtained by gas chromatography, in
methanol or higher alcohols as well as in the alkylation reasonable approximation. Compound 1 was identified by
1
of other hydroxyarenes with good selectivity (4, 5).
comparison of its spectral (IR, H NMR) and other phys-
In this Note are presented experimental results of the re- ical properties with those described in the literature (1).
action of 1-naphthol with methanol in the presence of an Compound 3 was synthesized by a known method (6). Both
iron oxide catalyst that contains additives, namely, Cr- and samples of compound 3, the synthetic one and that isolated
Si-oxides to prevent sintering and K2O as an activator. The from the reaction mixture, were shown to be identical by
catalyst was obtained at room temperature by coprecipita- comparison of their physical properties (mp, IR, 1H NMR
tion, until pH 7 was reached, from aqueous solutions of Fe and MS spectra). Compounds 2 and 4, being present in the
and Cr nitrates and sodium silicate with aqueous ammo- reaction mixture in small amounts, were not isolated. They
nia solutions (1 : 1). After filtering the precipitate, nitrate were identified by comparison of their gas chromatographic
ions were removed by washing and potassium carbonate retention times with the retention times of original samples
was added. The dried precipitate was then powdered and synthesized in our laboratory. The other compounds exist-
pelletized with 3% addition of graphite. The solid mixture ing in trace amounts were not identified.
was next calcined at 743 K for 5 h. The resulting catalyst
The methanol alkylation of 1-naphthol was investigated
was composed of Fe, Cr, Si, and K oxides in a molar ratio of as a function of temperature and space velocity (LHSV).
100 : 2 : 1 : 0.1. X-ray diffraction showed that the fresh cata- Figure 1 shows the dependence on temperature of the con-
lyst was amorphous. Its specific surface area (nitrogen BET version of 1-naphthol and the yield of the main product 1
method) was 107 m2/g. After use the structure of the cat- and of the two derivatives 2 and 3. At 550 K the selectivity
alyst changed to magnetite (Fe3O4) with a specific surface of reaction is nearly 100%. The quantity of the collected
area of 40 m2/g. From the broadening of the (104) X-ray liquid products was 95–98% which indicates that there is
line, the average size of the crystallites was calculated to be practically no methanol degradation. In the temperature
about 30 nm.
range of 563–613 K 1-naphthol conversion increases with a
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