Preparation of phenols by direct N.sub.2 O hydroxylation of aromatic substrates

Phenol/substituted phenols are prepared by directly hydroxylating an aromatic substrate with nitrous oxide, in vapor phase, in the presence of a modified (acidified) ZSM-5 or ZSM-11 zeolite, containing such elements as Ga, Fe, B, In, Cr, Sc, Co, Ni, Be, Zn, Cu, Sb, As or V.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the preparation of phenol or a substituted 
phenol, and, more especially, to the preparation of phenol/substituted 
phenols, by the catalytic hydroxylation of aromatic substrates. 
2. Description of the Prior Art 
The hydroxylation of phenol, substituted phenols or phenol ethers using 
hydrogen peroxide to prepare diphenols, substituted diphenols or 
alkoxyphenols is a reaction that is known to this art. 
French Patent FR No. 2,071,464 describes a process in which the reaction is 
catalyzed by a strong acid, such as, for example, perchloric acid or 
sulfuric acid. 
German Patent No. 2,410,742 describes a process similar to the above, in 
which the hydrogen peroxide is used in the form of a virtually anhydrous 
organic solution. 
These two processes have considerable merit and the first is carried out 
industrially. 
However, for several years attempts have been made to catalyze the 
hydroxylation reaction with solids that are not dissolved in the reaction 
mixture, in order to simplify their separation therefrom, enable the 
optional recycling thereof and to avoid salt-type byproducts which most 
often form during the removal of the dissolved acid catalysts. 
Thus, French Patent FR No. 2,489,816 describes the use of titanium 
silicalite as a heterogeneous catalyst for the hydroxylation of aromatic 
compounds with hydrogen peroxide. 
In fact, such catalysis is extremely difficult to reproduce. Moreover, the 
fine size of the catalyst particles renders their separation from the 
reaction mixture very difficult and their recycling problematical. In this 
latter regard, it will be appreciated that it is essential to be able to 
recycle a costly catalyst in an industrial process. 
To overcome this problem of the separation of the catalyst, published 
European Patent Application No. 200,260 describes using agglomerates of 
these fine particles of titanium silicalite. 
The difficulty in controlling safety in plants where hydrogen peroxide is 
used and the relative mediocrity of the yields of the prior art processes 
have provided the impetus for those skilled in the art to attempt to 
introduce a hydroxyl group directly onto an aromatic nucleus in the 
absence of any peroxide derivative. Such attempts, however, have to date 
been unsuccessful. 
Moreover, the direct hydroxylation of an aromatic compound bearing no 
substituents or containing a deactivating substituent, such as benzene or 
the halogenobenzenes, is essentially absent from the scientific 
literature. 
Thus, the only publication thought to describe the direct introduction of a 
hydroxyl group onto a benzene ring is an article by Iwamoto in the Journal 
of Physical Chemistry, 87, 6 (1983). 
This reaction for the hydroxylation of benzene is carried out using nitrous 
oxide (N.sub.2 O) in the presence of a catalyst based on an oxide of a 
metal of Groups V or VI of the Periodic Table. 
Vanadium oxide is the preferred oxide from among the oxides of metals of 
Groups V and VI of the Periodic Table. It is preferable to use this oxide 
in the presence of a support based on silica, in an amount by weight 
ranging from 1% to 10% relative to the support. The support preferably is 
silica, as alumina causes the formation of a mixture of carbon oxides in 
the majority of cases. 
The Iwamoto process has attracted considerable interest, but the use of the 
catalysts described militates against conducting the process on an 
industrial scale. 
Hence, serious need continues to exist in this art for a hydroxylation 
process that is applicable to a wide variety of aromatic substrates and 
which does not require employing hydrogen peroxide. 
SUMMARY OF THE INVENTION 
Accordingly, a major object of the present invention is the provision of an 
improved process for the direct hydroxylation of aromatic substrates which 
conspicuously avoids those disadvantages and drawbacks to date 
characterizing the state of this art. 
Briefly, the present invention features hydroxylation of an aromatic 
compound of formula (I): 
##STR1## 
in which R.sub.1 is an OH group, a bromine atom, a chlorine atom, a 
fluorine atom, a hydrogen atom, a straight or branched chain alkyl radical 
having from 1 to 6 carbon atoms, a straight or branched chain alkoxy 
radical having from 1 to 6 carbon atoms, and R.sub.2 is a hydrogen atom, a 
straight or branched chain alkyl radical having from 1 to 6 carbon atoms, 
or a straight or branched chain alkoxy radical having from 1 to 6 carbon 
atoms, comprising intimately conducting, at a temperature ranging from 
250.degree. C. to 500.degree. C., the aromatic compound of formula (I) 
with nitrous oxide, in the presence of a modified zeolite (a) or (b): 
(a) a modified zeolite of ZSM-5 type having the general formula (II), 
expressed in terms of the oxide ratios: 
EQU M.sub.2 O, X.sub.2 O.sub.n, mSiO.sub.2, pH.sub.2 O (II) 
in which M is a cation selected from among hydrogen and the alkali metals, 
at least some of the M cations being a hydrogen atom; X is Ga, Fe, B, In, 
Cr, Sc, Co, Ni, Be, Zn, Cu, Sb, As or V; D is 2, 3 or 5, depending on the 
valency of the element X; m is a number greater than or equal to 20; and p 
is a number ranging from 0 to 40; 
(b) a modified zeolite of ZSM-11 type having the general formula (III), 
expressed in terms of the oxide ratios: 
EQU M.sub.2 O, Z.sub.2 O.sub.n, mSiO.sub.2, xH.sub.2 O (III) 
in which M is a cation selected from among hydrogen and the alkali metals, 
at least some of the cations M being a hydrogen atom; Z is Al, Ga, Fe, B, 
In, Cr, Sc, Co, Ni, Be, Zn, Cu, Sb, As or V; n is 2, 3 or 5, depending on 
the valency of the element Z; m is a number greater than or equal to 20; 
and x is a number ranging from 6 to 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
More particularly according to the present invention, the modified zeolites 
of formula (II) or (III) may contain several of the elements represented 
by X or Z at the same time. 
The modified zeolites of the ZSM-5 and ZSM-11 type of formula (II) or (III) 
which are typically used in the process of the invention are those in 
which the symbol X or the symbol Z more particularly represents the 
trivalent elements (Al, Ga, Fe, B, In, Cr and Sc) or divalent elements 
(Co, Ni, Be, Zn and Cu) indicated above, either alone or in combination 
with one another or in combination with the pentavalent elements indicated 
above (Sb, As and V). 
The zeolites of the ZSM-5 type can be prepared by the process described in 
U.S. Pat. No. 3,702,888, replacing the aluminum compound by an inorganic 
gallium, iron, boron, indium, chromium, scandium, cobalt, nickel, 
beryllium, zinc, copper, antimony, arsenic or vanadium compound, or by a 
mixture of inorganic compounds of several of these elements. 
The procedure entails preparing a solution containing tetraalkylammonium 
hydroxide, such as tetrapropylammonium hydroxide for example; sodium 
oxide; gallium oxide, iron oxide, boron oxide, indium oxide, chromium 
oxide, scandium oxide, cobalt oxide, nickel oxide, beryllium oxide, zinc 
oxide, copper oxide, antimony oxide, arsenic oxide or vanadium oxide, or a 
mixture of several of these oxides; silica and water. The solution 
contains oxide ratios in the following ranges: 
(i) OH.sup.- /SiO.sub.2 from 0.07 to 10.0; 
(ii) tetraalkylammonium/tetraalkylammonium +Na.sup.+ : from 0.2 to 0.95; 
(iii) H.sub.2 O/OH.sup.- : from 10 to 300; 
(iv) SiO.sub.2 /X.sub.2 O.sub.n : greater than or equal to 20. 
It is possible to use excess tetraalkylammonium hydroxide, which increases 
the OH.sup.- /SiO.sub.2 ratio indicated above. However, the excess 
hydroxide does not participate in the reaction. 
The treatment to produce crystals of zeolites generally entails heating the 
above mixture at a temperature of 100.degree. C. to 200.degree. C. for a 
period of time of a few hours to 60 days under autogenous pressure. 
Preferably, the reaction conditions are ten hours to ten days at a 
temperature of 150.degree. C. to 200.degree. C. The crystals are then 
separated from the liquid by cooling it to ambient temperature, filtering 
off the crystals obtained and then washing them with water. 
The zeolite is then dried at about 100.degree. C., in general for several 
hours. The preparation of zeolites of the ZSM-5 type can be carried out 
using compounds which generate the necessary oxides. 
Thus, it is possible to use gallium, iron, boron, indium, chromium, 
scandium, cobalt, nickel, beryllium, zinc, copper, antimony, arsenic or 
vanadium nitrates, sodium silicate, silica gels, silicic acid, sodium 
hydroxide, or mixtures of these various compounds with the corresponding 
oxides. 
The zeolites of the ZSM-11 type can be prepared by the process described in 
U.S. Pat. No. 3,709,979, if necessary replacing the aluminum compound by 
an inorganic gallium, iron, boron, indium, chromium, scandium, cobalt, 
nickel, beryllium, zinc, copper, antimony, arsenic or vanadium compound, 
or by a mixture of inorganic compounds of several of these elements. 
It is thus possible to use the procedure described above for the zeolites 
of the ZSM-5 type, preparing a solution containing tetraalkylammonium 
oxide; sodium oxide; aluminum oxide, gallium oxide, iron oxide, boron 
oxide, indium oxide, chromium oxide, scandium oxide, cobalt oxide, nickel 
oxide, beryllium oxide, zinc oxide, copper oxide, antimony oxide, arsenic 
oxide or vanadium oxide or a mixture of several of these oxides; silica 
and water. The oxide ratios in this solution are in the following ranges: 
(i) Na.sub.2 O/SiO.sub.2 : from 0.05 to 0.7; 
(ii) tetraalkylammonium oxide/SiO.sub.2 : from 0.02 to 0.20; 
(iii) H.sub.2 O/Na.sub.2 O : from 50 to 800; 
(iv) SiO.sub.2 /Z.sub.2 O.sub.n : greater than or equal to 20. 
By the term "modified zeolite" are intended zeolites of the ZSM-5 and 
ZSM-11 type as defined above, in which at least some of the M cations are 
hydrogen and preferably the majority or all of the M cations are hydrogen. 
This can be accomplished by treating the zeolites of the ZSM-5 and ZSM-11 
type, in the formula of which the M cations are solely alkali metals or 
tetraalkylammonium ions, with an organic or inorganic acid. 
Exemplary inorganic acids which may be used to acidify the zeolites are 
hydrochloric acid, sulfuric acid, nitric acid, perchloric acid and 
phosphoric acid. 
Exemplary organic acids which may be used to acidify the zeolites are 
halosulfonic acids such as chlorosulfonic acid and fluorosulfonic acid, 
halomethanesulfonic acids such as trifluoromethanesulfonic acid, and 
halocarboxylic acids, such as trichloroacetic acid, dichloroacetic acid, 
monochloroacetic acid, trifluoroacetic acid, difluoroacetic acid, 
monofluoroacetic acid and monobromoacetic acid. 
In a preferred embodiment, the acidification of the zeolite of the ZSM-5 or 
ZSM-11 type is effected by charging therethrough 10 cc to 100 cc of acid, 
having a normality of 0.1 N to 2 N, per gram of zeolite. 
A throughput of this type can be carried out in a single step or, 
preferably, in several successive steps. 
In the formulae (II) and (III) of the modified zeolites of the ZSM-5 and 
ZSM-11 type, the cation M which possibly does not represent hydrogen is 
preferably sodium. 
Modified zeolites of the ZSM-5 and ZSM-11 types can also be obtained by 
exchanging all or some of the alkali metals using a solution of an 
inorganic ammonium salt, such as, for example, ammonium nitrate, ammonium 
fluoride or ammonium chloride, followed by a heat treatment for a few 
hours at temperatures of 300.degree. C. to 800.degree. C. in a stream of 
dry air in order to create H.sup.+ sites. 
According to the present invention, zeolites of the ZSM-5 types of formula 
(II) and of the ZSM-11 type of formula (III) in which the SiO.sub.2 
/X.sub.2 O.sub.n or SiO.sub.2 /Z.sub.2 O.sub.n ratio ranges from 20 to 500 
are preferred. 
More preferably, this SiO.sub.2 /X.sub.2 O.sub.n or SiO.sub.2 /Z.sub.2 
O.sub.n ratio in the formulae (II) and (III) ranges from 40 to 300. 
It is desirable to carry out a treatment of the modified zeolites of the 
ZSM-5 and ZSM-11 type in order to improve their catalytic activity in the 
reaction of the hydroxylation of aromatic compounds of formula (I), using 
nitrous oxide. 
This activation can entail, in particular, carrying out a heat treatment of 
the modified zeolites at a temperature of 300.degree. C. to 800.degree. 
C., and preferably of 400.degree. C. to 700.degree. C., for a few hours in 
a stream of dry inert gas such as nitrogen. If appropriate, the heat 
treatment can be continued for a few hours at a temperature in the ranges 
indicated above, but under a stream of dry air. 
The modified zeolites of the ZSM-5 and ZSM-11 type can be used in various 
forms in the process of the invention: powder, in particular in laboratory 
tests, or shaped articles, such as granules (for example cylinders or 
beads), beads, pellets or monoliths (blocks in honeycomb form), which are 
produced by extrusion, molding, compacting, or any other known process. 
In practice, on an industrial scale, it is the granule, bead and monolith 
forms which are the most advantageous, both with regard to effectiveness 
and with regard to convenience in handling. 
As the process of the invention is carried out in vapor phase, the problem 
of the recovery of the catalyst is thus resolved. 
Exemplary of the compounds of formula (I), particularly representative are 
fluorobenzene, phenol, benzene, toluene, orthocresol, metacresol, 
paracresol, anisole, bromobenzene, chlorobenzene, orthochlorophenol and 
parachlorophenol. 
Phenol, fluorobenzene and benzene are compounds of formula (I) which are 
especially suited for hydroxylation by the process of the invention. 
The nitrous oxide is used in the pure form, or as a mixture with an inert 
gas which does not contain oxygen, such as nitrogen. 
The compound of formula (I) is preferably introduced as a mixture with the 
nitrous oxide, in a molar ratio of nitrous oxide relative to the compound 
of formula (I) of from 1 to 10. 
In a preferred embodiment of the invention, the compound (I) is vaporized, 
mixed with nitrous oxide in the previously defined proportions and the 
mixture is circulated over the zeolites of formula (II) or (III). The 
reaction preferably is carried out at a temperature of from 300.degree. to 
500.degree. C. 
The gases produced from the reaction and containing, where appropriate, a 
mixture of isomers, are condensed and separated by any technique known to 
this art. 
When it is applied to phenol, the process of the invention is particularly 
valuable since it permits the three dihydroxybenzenes, pyrocatechol, 
hydroquinone and resorcinol to be produced, while the known processes for 
the hydroxylation of phenol produce almost exclusively a 
pyrooateohol/hydro-quinone mixture. The process, therefore, provides an 
original route to resorcinol. 
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 
Preparation of a gallium-containing zeolite of the ZSM-5 type 
A solution of 5.94 g of gallium nitrate hydrate (Ga(NO.sub.3).sub.3 
.multidot.6H.sub.2 O) and 16 g of H.sub.2 SO.sub.4 (96%) in 200 g of water 
was poured into a solution of 200 g of sodium silicate (SiO.sub.2 
/Na.sub.2 O=3.22) in 200 g of water. 
24 g of tetrapropylammonium bromide in 100 g of water were added to the gel 
thus obtained. 
The mixture was stirred for several minutes and the mixture was then placed 
in a stirred 1-liter autoclave, under autogenous pressure, for 4 days at 
170.degree. C. 
The white solid thus obtained was filtered off, washed with water and dried 
at 100.degree. C. 
Analysis of the powder by X-ray diffraction confirmed the formation of a 
gallium-containing zeolite of the ZSM-5 type. 
The SiO.sub.2 /Ga.sub.2 O.sub.3 molar ratio was 80. 
The activation of this gallium-containing zeolite entailed subjecting it to 
a heat treatment at 550.degree. C. for 18 hours under a stream of dry 
nitrogen, then for 5 hours at 550.degree. C. under a stream of dry air. 
After cooling, the zeolite was subjected to ion exchange with a 1 M 
solution of NH.sub.4 NO.sub.3 and to a heat treatment for 10 hours in a 
stream of dry air, in order to form H.sup.+ sites. 
EXAMPLE 2 
Preparation of an iron-containing zeolite of the ZSM-5 type 
A solution of 50 g of sodium metasilicate (Na.sub.2 SiO.sub.3 
.multidot.5H.sub.2 O) in 50 g of water was poured into a solution 
containing 2.1 g of ferric nitrate (Fe(NO.sub.3).sub.3 .multidot.9H.sub.2 
O) in 50 g of water. 
The pH was adjusted to a highly acid value using 5.0 g of 96% H.sub.2 
SO.sub.4. 
6.5 g of tetrapropylammonium bromide in 10 g of water were added to the gel 
obtained, which was pale lemon in color. 
After vigorous stirring, the mixture was placed in a stainless steel 
autoclave, the autoclave was closed and the mixture was heated under 
autogenous pressure and with stirring for 5 days at 170.degree. C. 
The white solid obtained was filtered off, washed with water and dried at 
100.degree. C. 
Analysis of the powder by X-ray diffraction confirmed the formation of an 
iron-containing zeolite of the ZSM-5 type. 
The SiO.sub.2 /Fe.sub.2 O.sub.3 molar ratio was 90. 
Using the same operating method, iron-containing zeolites having SiO.sub.2 
/Fe.sub.2 O.sub.3 molar ratios of 120 and 150, respectively, were prepared 
by modifying the proportion of sodium metasilicate/ferric nitrate and 
adjusting the hydroxide content. 
The activation of these iron-containing zeolites was carried out in the 
manner described in Example 1 to form the H.sup.+ sites. 
EXAMPLE 3 
Preparation of a cobalt-containing zeolite of the ZSM-5 type 
First, a solution A of 0.27 g of Co(NO.sub.3).sub.2 .multidot.6H.sub.2 O 
and 0.6 g of H.sub.2 SO.sub.4 in 15 g of water was prepared. 
Then a solution B of 10 g of silica (marketed under the trademark Q-Brand) 
in lo g of water and then a solution C of 1 g of tetrapropylammonium 
bromide in 10 g of water were prepared. 
The solutions A and B were first mixed rapidly and stirred until a gel was 
obtained. 
Solution C was then added to this gel, with gentle stirring. 
The gel thus obtained was placed in a stirred autoclave for 3 days at 
170.degree. C. 
The white solid obtained was filtered off, washed with water and dried at 
100.degree. C. 
Analysis of the powder by X-ray diffraction confirmed the formation of a 
cobalt-containing zeolite of the ZSM-5 type. 
The SiO.sub.2 /2CoO molar ratio was 80. 
The activation of this cobalt-containing zeolite was carried out in the 
manner described in Example 1 to form the H.sup.+ sites. 
EXAMPLE 4 
Preparation of an aluminum-containing zeolite of the ZSM-11 type 
A solution A containing 55 g of sodium silicate (SiO.sub.2 /Na.sub.2 
O=3.22) and 1.3 g of 1,8-diaminooctane in 38 g of water was prepared. 
A solution B containing 0.7 g of sodium aluminate in 40 g of water was 
prepared. 
The two solutions A and B were mixed. 
The pH of the gel thus obtained was adjusted to 1 using sulfuric acid. 
The gel was placed in an autoclave, stirred for 3 days at 220.degree. C. 
The white solid obtained was filtered off, washed with water and dried at 
100.degree. C. 
Analysis of the powder by X-ray diffraction confirmed the formation of 
aluminum-containing zeolite of the ZSM-11 type. 
The SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio was 40. 
The activation of this aluminum-containing zeolite was carried out in the 
manner described in Example 1 to form the H.sup.+ sites. 
EXAMPLES 5 to 10 
Hydroxylation of fluorobenzene to fluorophenols 
Experimental conditions 
(i) Vapor phase: continuous; 
(ii) Catalyst: modified zeolite of the ZSM-5 or ZSM-11 type prepared in 
Examples 1, 2, 3 and 4 (see Table below); 
(iii) Temperature: 400.degree. C.; 
(iv) Liquid space velocity/hour (weight of substrate/weight of 
catalyst/hour): 1.5 h.sup.-1 ; 
(v) Fluorobenzene/N.sub.2 /N.sub.2 O molar ratios: 2/5/8. 
2 cc of modified zeolite (about 1 g) in powder form, dispersed in 4 cc of 
quartz in the form of grains (smaller than 0.8 mm) were introduced into a 
tubular reactor made of quartz and having a length of 16 cm and an 
internal diameter of 1.8 cm. 
A bed of 10 cc of glass beads was then introduced into the reactor, 
enabling the gaseous mixture to homogenize. 
The reactor thus charged was conditioned for 2 hours at 400.degree. C. 
under nitrogen in a tubular oven. 
The reaction was carried out continuously, introducing 1.5 cm.sup.3 /h of 
fluorobenzene, 1.44 1/h of N.sub.2 O and 0.9 1/h of nitrogen. 
The results are reported in the Table below: 
TABLE 
______________________________________ 
SiO.sub.2 /X.sub.2 O.sub.n 
% DC of % Yld of 
Modified or SiO.sub.2 /Z.sub.2 O.sub.n 
fluoro- fluoro- 
Examples zeolite molar ratio 
benzene phenols 
______________________________________ 
Example 5 
ZSM-5 Ga 80 4.1 75 
Example 6 
ZSM-5 Co 80 1.3 89 
Example 7 
ZSM-5 Fe 90 16.0 90 
Example 8 
ZSM-5 Fe 120 9.8 93 
Example 9 
ZSM-5 Fe 150 8.4 94 
Example 10 
ZSM-11 Al 40 1.2 69 
______________________________________ 
% DC = degree of conversion 
% Yld = yield relative to fluorobenzene converted 
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.