Preparation of methylhydroquinone

Methylhydroquinone (MeHQ) or methyl ether derivative thereof is prepared by contacting paramethoxyphenol or para-dimethoxybenzene with an acid catalyst, preferably a solid acid catalyst, at a temperature ranging from 100.degree. to 300.degree. C.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the preparation of methylhydroquinone. 
2. Description of the Prior Art 
Methylhydroquinone is a known compound that is a very useful intermediate 
in a wide variety of organic syntheses. 
SUMMARY OF THE INVENTION 
Briefly, the present invention features the preparation of 
methylhydroquinone (MeHQ) by contacting paramethoxyphenol or 
para-dimethoxybenzene with an acid catalyst, notably a solid acid 
catalyst, at a temperature ranging from 100.degree. to 300.degree. C. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
More particularly according to the present invention, while a liquid acid 
such as sulfuric acid is a useful such acid catalyst, it is preferred to 
use a solid catalyst comprising acid functions within the definitions of 
Lewis or Bronsted acid. Such solid catalysts are defined as any solids 
having a cation-exchange capacity which has been partially or completely 
exchanged by H.sup.+ and/or a Lewis acid (M.sup.n+ where n&gt;3). Exemplary 
of these solids, the following are particularly representative: 
(a) clays that have been treated with a strong acid; 
(b) zeolites that have also been exchanged; 
(c) crosslinked sulfonated resins of the styrene/divinylbenzene type and 
Nafion.RTM. (a perfluorinated and sulfonated resin marketed by Dupont de 
Nemours); 
(d) acid or amphoteric oxides, the reactivity of which has been increased 
by treatment with an acid; and 
(e) heteropolyacids, such as the phosphomolybdic acids and the 
phosphotungstic acids. 
The reaction temperatures according to the invention can vary widely over 
the broad range of from about 100.degree. to about 300.degree. C. Best 
results are obtained using a temperature ranging from 150.degree. to 
250.degree. C. 
The reaction can thus be represented: 
##STR1## 
wherein R is CH.sub.3 or H. 
The compound (1) is methylhydroquinone, the desired final product, and 
compounds (2) and (3) are methylated derivatives (of the OH radical or 
radicals) of methylhydroquinone. The compounds (2) and (3) are readily 
converted into methylhydroquinone, and thus are useful "precursors" of 
methylhydroquinone. 
When para-methoxyphenol is used as the starting material, 
methylhydroquinone will be produced in a high yield and with relatively 
few of the "precursors" described above. 
When para-dimethoxybenzene is used as the starting material, larger 
proportions of such "precursors" will be produced. However, it will be 
appreciated that paradimethoxybenzene is a particularly attractive 
starting material because it is a by-product from the polyphenol chemical 
industry. Thus, its value is enhanced. 
While the subject reaction mechanism appears to be relatively simple when 
para-methoxyphenol is used as the starting material (while not wishing to 
be bound to any particular theory, it is probably a dealkylation reaction 
followed by an alkylation reaction on an adjacent carbon atom of the ring, 
or an intramolecular reaction), the mechanism becomes very complex, and is 
still largely hypothetical and therefore unknown, when 
para-dimethoxybenzene is used as the starting material. 
In order to further illustrate the present invention and the advantages 
thereof, the following specific examples are given, it being understood 
that same are intended only as illustrative and in nowise limitative.

EXAMPLE 1 
(liquid phase) 
5.7 g (46 mmoles) of para-methoxyphenol and 1 g of ultrastabilized 
commercial zeolite of the faujasite type (US-Y marketed by Toyo-Soda) were 
introduced into a 50 cm.sup.3 glass tube. The tube was sealed and inserted 
into a metallic sheath. The assembly was placed in a balancing furnace 
known as a "Carius" furnace and heated to 200.degree. C. for 2.5 hours. 
The solid catalyst was recovered by filtration on fritted glass and washed 
with ethyl acetate. The solution was analyzed by gas phase chromatography, 
and the nature of the final products was confirmed by a complete 
spectroscopic analysis (infrared, nuclear magnetic resonance, mass 
spectrometry). 
The results obtained evidenced that: 
(i) the degree of conversion of the paramethoxyphenol was 54%; 
(ii) the yield of methylhydroquinone and "precursors" from the reaction was 
11%. 
EXAMPLE 2 
(liquid phase) 
The procedure of Example 1 was repeated, but using para-dimethoxybenzene as 
the starting material. 
The degree of conversion was 57% and the yield 52%. 
EXAMPLE 3 
(liquid phase) 
The procedure of Example 2 was repeated, but using a commercial acid clay 
(KSF montmorillonite marketed by SudChemie) in place of the zeolite. 
The degree of conversion was 58% and the yield 45%. 
EXAMPLE 4 
(vapor phase) 
1 g of an ultrastabilized commercial zeolite of the faujasite type (US-Y 
marketed by Toyo-Soda) and 6 g of quartz particles, 1 mm in diameter, were 
introduced into a quartz tube. This catalytic bed was heated to 
400.degree. C. for 10 hours. The bed was then cooled to 200.degree. C. 
A current of nitrogen and para-dimethoxybenzene was introduced into a tube, 
and a gaseous flowstream comprising 1 1 per hour nitrogen and 9 mmoles per 
hour paradimethoxybenzene was passed over the catalytic bed. The contact 
time was 2 3 seconds. 
At the outlet of the reactor, the reaction products were trapped and then 
analyzed 
The mean degree of conversion (during the duration of the experiment, which 
was 3 hours) was 23% and the yield 31%. 
EXAMPLE 5 
(vapor phase) 
The procedure of Example 4 was repeated, but employing a reaction 
temperature of 240.degree. C. 
The mean degree of conversion (duration of the experiment, 1.8 hours) was 
19% and the yield 22%. 
While the invention has been described in terms of various preferred 
embodiments, the skilled artisan will appreciate that various 
modifications, substitutions, omissions, and changes may be made without 
departing from the spirit thereof. Accordingly, it is intended that the 
scope of the present invention be limited solely by the scope of the 
following claims, including equivalents thereof.