FR2666333A1 - Process for the hydroxylation of phenols and phenol ethers - Google Patents

Abstract

The present invention relates to a process for the hydroxylation of phenols and phenol ethers by hydrogen peroxide. More precisely, it consists of a process for the hydroxylation of phenols and phenol ethers, and preferably of phenol, by hydrogen peroxide, characterised in that the reaction is carried out in the presence of an efficient amount of a zeolite of MFI structure based on silicon oxide and on tin oxide and having the general formula: in which x is between approximately 0.1 and 3.0, preferably between 0.1 and 2.0.

Description

PROCESS FOR HYDROXYLATION OF PHENOLS AND PHENOL ETHERS
The present invention relates to a process for the hydroxylation of phenols or phenol ethers with hydrogen peroxide.

 The hydroxylation of phenol or substituted phenols with hydrogen peroxide to prepare diphenols is a known reaction.

 According to FR-A 2 071 464 a process according to which the reaction is catalyzed by a strong acid, such as, for example, perchloric acid or sulfuric acid, is described.

 It is also described according to German Offenlegungsschrift 2,410,742 a process similar to the previous one, in which the hydrogen peroxide is used as a substantially anhydrous organic solution.

 These two methods are very interesting and the first method is implemented industrially.

However, in recent years, it has been sought to catalyze the hydroxylation reaction using undissolved solids in the medium, in order to simplify their separation from the reaction medium and their possible recycling and to avoid saline by-products, which form on the more often when removing dissolved acid catalysts
The present invention specifically relates to a process for the hydroxylation of phenols and phenol ethers by heterogeneous catalysis.

dans laquelle - R représente un atome d'hydrogène, un groupement méthyle, un groupement
éthyle ou un groupement phényle, - Rg représente un atome d'hydrogène, un radical alkyle ayant 1 à 4 atomes
de carbone, un radical alkoxy ayant I à 4 atomes de carbone, un radical
phényle ou cyclohexyle ; par réaction avec le peroxyde d'hydrogène, caractérisé par le fait que la réaction est conduite en présence d'une quantité efficace de zéolite de structure MFI à base d'oxyde de silicium et d'oxyde d'étain et ayant après calcination la formule suivante (II) :
(sig6-x Son,) 0192 (II) dans laquelle x est compris entre 0,1 et 3,0 environ, de préférence entre 0,1 et 2,0.The invention therefore consists in a process for the hydroxylation of phenols or phenol ethers of general formula (I)

in which - R represents a hydrogen atom, a methyl group, a grouping
ethyl or a phenyl group, - Rg represents a hydrogen atom, an alkyl radical having 1 to 4 atoms
of carbon, an alkoxy radical having 1 to 4 carbon atoms, a radical
phenyl or cyclohexyl; by reaction with hydrogen peroxide, characterized in that the reaction is carried out in the presence of an effective amount of zeolite of MFI structure based on silicon oxide and tin oxide and having after calcination the formula following (II):
(sig6-x Son,) 0192 (II) wherein x is from about 0.1 to 3.0, preferably from 0.1 to 2.0.

 The zeolites used in the process of the invention belong to the family of pentasils and are similar to zeolites of the MFI structural type. They are called stannozeosilites.

 According to another characteristic, the stannozeosilites used in the invention contain fluorine. The concentration of fluorine is generally between 0.01 and 1.3% by weight, before calcination. This fluorine can, however, be removed by hydrothermal treatment at pH> 7 without modifying the structure of the zeolite used.

Stannozeosilite as a catalyst in the process of the invention can be synthesized as follows
(i) the preparation of a reaction mixture in aqueous media
containing a silicon source with oxidation state + 4,
a source of tin with the degree of oxidation + 4, fluorescent ions
rure and a structuring agent; the pH of this reaction mixture
nel being between about 1.5 and about 12.0,
(ii) crystallization of this reaction mixture by heating and
recovery of the crystallized precipitate,
(iii) calcining it at a higher temperature
at 4500C for the removal of the structuring agent occluded in
canals.

 Advantageously, the pH of the reaction mixture is between 6.0 and 11.0.

 The use of fluoride ions in the reaction medium, which act as a mobilizing agent, makes it possible to solubilize the T (Si and Sn) species in a synthesis medium having a pH of less than 10. Thus, it is It is possible to use NH4 + ions as compensation cations, which can be completely removed, if desired, during calcination. On the other hand, it is advisable to avoid the presence in the reaction medium of alkaline cations.

 In addition, the crystallization taking place in a medium at pH below 11, the nucleation rate is slower. Thus, it is possible to obtain zeolite crystals controlled by controlling the nucleation rate.

 Many sources of the +4 oxidation state silicon element can be used. By way of example, mention may be made of silicas in the form of hydrogels, aerogels, xerogels, colloidal suspensions, silicas resulting from precipitation from solutions of soluble silicates or hydrolysis of silicic esters. as Si (OCH3) 4, Si (OC2H5) 4, silicas prepared by extraction and activation treatments of crystalline or amorphous natural or synthetic compounds such as aluminum silicates, aluminosilicates, clays. It is also possible to use hydrolyzable tetravalent silicon compounds such as silicon halides or the like.

 Among the sources of tin oxide, there may be mentioned, by way of example, crystallized or amorphous tin oxides and hydroxides, the tetravalent tin compounds being able to be hydrolysed, such as halides (SnCl4), alcoholates, soluble salts of tin such as tin nitrate Sn (NO3) 4.

 It is also possible to use as sources of silica or tin oxide, compounds comprising Si and Sn elements such as, for example, glasses or gels based on the oxides of these two elements.

 The sources of silica and tin oxide may be engaged in soluble form or in pulverulent solids but also in the form of agglomerates such as, for example, pellets, extruded which can be converted into zeolite of desired structure without modification of form.

 The mobilizing agent F- is introduced in the form of acid and / or salt (s), not containing alkaline cations, and / or compounds releasing F- by hydrolysis. By way of example, mention may be made of hydrofluoric acid; hydrofluorines of amines; quaternary ammonium fluorides, for example NH (C 3 H 7) 3 F, N (C 3 H 7) 4 F; SiF4; SnF4; (NH4) 2SiF6.

 Ammonium fluoride or acidic ammonium fluoride are preferred salts. Indeed, these salts are very soluble and do not provide any undesirable element and, moreover, they are easily removed at the end of crystallization.

The structuring agents that are suitable for carrying out the invention are the tertiary amines of formula (III)

in which
R1, R2, R3 identical or different represent a group
alkyl, linear or branched having 1 to 6 carbon atoms,
preferably a propyl or butyl group.

the quaternary ammonium salts of formula (IV)

in which
R1, R2, R3, R4 identical or different represent a group
alkyl, linear or branched having 1 to 6 carbon atoms,
preferably propyl or butyl groups.

the compounds of formulas (III) and (IV) in which the nitrogen has
been replaced by a phosphorus atom.

 The structuring agents used preferentially are the compounds which can provide tetrapropylammonium or tripropylammonium cations.

 Advantageously, the structuring agent is introduced into the reaction mixture in the form of a quaternary ammonium salt of formula (IV) or of the amine of formula (III); the pH being optionally adjusted using a base. Preferably, this base will have weak structuring agent properties so as not to compete with the added structuring agent.

Thus, the bases suitable for the invention are, by way of example, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine and triethylamine.

The reaction mixture has the following composition, expressed in molar ratio
Sn / (Si + Sn) between 0.001 and 0.20, preferably between 0.005 and 0.1.

 Structuring agent / (Si + Sn) between 0.002 and 4, preferably between 0.04 and 1.

 F / (Si + Sn) between 0.02 and 6, preferably between 0.06 and 2.

H2O / (Si + Sn) between 4 and 400, preferably 10 and 200
When a base is used to adjust the pH, the molar ratio of base to (Sn + Si) is preferably less than 12, and preferably 0.1 to 8.

 The addition to this reaction mixture of crystalline seeds of determined structure, MFI, in a proportion that does not exceed a few percent by weight relative to the weight of SiO 2 + SnO 2 engaged, facilitates the crystallization of the zeolite. As crystallization seeds, it is possible to use any zeolite having the MFI structure, irrespective of its chemical composition.

It is preferable to use a zeosilite which is a zeolite equivalent to stannozéosilite, but containing only silicon in its framework. It is also possible to use stannozeosilite seeds originating from a previous manufacture.

 The crystallization of the zeolite can be obtained by heating the reaction mixture at a temperature between about 400C and about 2400C, preferably between 600C and 2200C for the time required for crystallization, according to a standard procedure of zeolite synthesis and known to the skilled person. As an indication, the heating time can be between 6 hours and 500 hours.

 This heating and crystallization are preferably carried out in a vessel or autoclave coated with a layer such as, for example, polytetrafluoroethane.

 The reaction mixture can be stirred or not.

 After crystallization, the precipitate obtained is collected according to standard solid / liquid separation techniques, in particular by filtration or centrifugation.

The precipitate obtained, referred to as "zeolite precursor", is a crystalline product of zeolite type based on silica and tin oxide having the following formula (V)
(Sig6 ~ xSnx) O1g2,4 + 1 (S + F-) (V) in said formula
x is between 0.1 and 3.0, preferably between 0.1 and 2.0.

 S + symbolizes the cation coming from the structuring agent.

 It more particularly represents a cation resulting from the amine of formula (III), a cation of quaternary ammonium type of formula (IV), or those same compounds in which the nitrogen is replaced by a phosphorus atom.

The crystalline precipitate is advantageously washed to remove the impurities and in particular the cations or anions not hooked or incorporated into the structure
This product is easily handled and is subjected to a calcination operation thus leading to the production of stannozéosilite.

 The calcination consists in heating said precipitate after a possible drying, at a temperature greater than 4500.degree. C., preferably greater than 5000.degree. C., in order to decompose by calcination or thermal decomposition the organic species contained in the precipitate, such as, for example, the agent structuring.

 The stannozeosilite of the invention of structure MFI is thus obtained.

 The identification of the stannozéosilite MFI structure can be achieved in particular by the establishment of the diffraction pattern of the precursor which gives rise to it.

 Said zeolite precursor has an orthorhombic crystalline system and an X-ray diffraction pattern defined in Table I.

 In this table, the extreme values of the different lattice equidistances dhkl are given and correspond to the limit concentrations of tin incorporated into the framework of the zeolite before calcination, or more precisely to the ratio Sn / (Si r Sn).

This diffraction pattern can be obtained using a diffractometer using the conventional powder method with copper Ka radiation. From the position of the diffraction peaks represented by the angle 2A one calculates, by the relation of
Bragg, the characteristic dhkl reticular equidistances of the sample. The estimation of the measurement error Y (dhkl) on dhkl is calculated as a function of the absolute error y (2A) assigned to the measurement of 2A by the Bragg relation. An absolute error y (2A) equal to + 0.20 is currently accepted. The relative intensity I / Io assigned to each value of dhkl is estimated from the height of the corresponding diffraction peak. A scale of symbols is often used to characterize this intensity: FF = very strong, F = strong, mF = average at high, m = average, mf = medium to low, f = low, ff = very low.

 The volume value VO of the crystallographic mesh of the zeolite before calcination is a function of the substitution of silicon by tin.

TABLE I
X-ray diffraction pattern

<tb> Extreme <SEP> values <SEP> I / Io <SEP> Extreme <SEP> values <SEP> I / Io
<tb><SEP> dhkl <SEP> (nm) <SEP> of <SEP> dhkl <SEP> (nm)
<tb><SEP> 1,114-1,133 <SEP> F <SEP> 0,368-0,374 <SEP> mF
<tb><SEP> 0.988-1.008 <SE> F <SEP> 0.361-0.367 <SEP> mF
<tb> 0.969-0.983 <SEP> mF <SEP> 0.340-0.346 <SEP> m
<tb><SEP> 0.886-0.897 <SEP> f <SEP> 0.330-0.336 <SEP> m
<tb><SEP> 0.734-0.744 <SEP> m <SEP> 0.327-0.332 <SEP> m
<tb><SEP> 0.699-0.709 <SEP> f <SEP> 0.321-0.327 <SEP> mf
<tb><SEP> 0.660-0.670 <SEP> f <SEP> 0.314-0.319 <SEP> ff
<tb><SEP> 0.627-0.637 <SEP> m <SEP> 0.310-0.315 <SEP> ff
<tb><SEP> 0.597-0.607 <SEP> m <SEP> 0.300-0.305 <SEP> m
<tb><SEP> 0.591-0.601 <SEP> m <SEP> 0.294-0.299 <SEP> m
<tb><SEP> 0.564-0.574 <SEP> m <SEP> 0.291-0.296 <SEP> mf
<tb><SEP> 0.548-0.557 <SEP> m <SEP> 0.282-0.287 <SEP> ff
<tb><SEP> 0.530-0.539 <SEP> ff <SEP> 0.276-0.280 <SEP> ff
<tb><SEP> 0.510-0.5t9 <SEP> ff <SEP> 0.270-0.274 <SEP> ff
<tb><SEP> 0.492-0.301 <SEP> mf <SEP> 0.257-0.261 <SEP> f
<tb><SEP> 0.454-0.462 <SEP> mf <SEP> 0.253-0.257 <SEP> f
<tb><SEP> 0.438-0.446 <SEP> ff <SEP> 0.248-0.252 <SEP> f
<tb><SEP> 0.432-0.440 <SEP> mf <SEP> 0.247-0.251 <SEP> f
<tb><SEP> 0.420-0.427 <SEP> m <SEP> 0.238-0.242 <SEP> f
<tb><SEP> 0.394-0.401 <SEP> mf <SEP> 0.203-0.206 <SEP> ff
<tb><SEP> 0.379-0.386 <SEP> FF <SEP> 0.198-0.202 <SEP> mf
<tb><SEP> 0.372-0.379 <SEP> mF <SEP> 0.197-0.201 <SEP> m
<Tb>
According to the process of the invention, the phenol or phenol ether of formula (I) is reacted in the presence of stannozeosilite.

 Hydrogen peroxide can be used in the form of an aqueous solution generally having a hydrogen peroxide concentration greater than 20% by weight. Hydrogen peroxide can also be used in the form of a solution in an organic solvent. As organic solvents that can be used for the implementation of hydrogen peroxide, it is possible to use esters such as in particular the alkyl or cycloalkyl esters of saturated aliphatic carboxylic acids; alkyl acetates and propionates having a total of 4 to 8 carbon atoms or mixtures of such esters are preferably used. It is also possible to use solutions of hydrogen peroxide in an ether such as, for example, dioxane, diisopropyl ether or methyl tert-butyl ether.

 The molar ratio of compound of formula (1) / hydrogen peroxide is generally from 25/1 to 3/1 and preferably from 20/1 to 4/1.

 The amount of stannozeosilite defined above which can be used in the present process can vary within very wide limits.

 When the process is carried out batchwise, the catalyst may represent by weight relative to the weight of the compound of formula (I) engaged from 0.1% to 20%. Preferably, this weight ratio will be between 0.5% and 10%. However, if the process is carried out continuously, for example by reacting a mixture of compound (I) and hydrogen peroxide solution on a fixed bed of catalyst, these catalyst / compound (I) ratios are no longer of meaning and, at a given moment, one may have a weight excess of catalyst relative to the compound (I).

 It is also possible to carry out the hydroxylation reaction of the compound (I) in a solvent of the compound (I), which is preferably miscible or partially miscible with water.

As non-limiting examples of such solvents, mention may be made of water; alcohols such as methanol, t-butanol, isopropanol or ethanol; ketones such as acetone or methyl isobutyl ketone; nitriles such as acetonitrile; carboxylic acids such as acetic acid; esters such as propyl acetate; ethers such as methyl-tert-butyl ether polar aprotic solvents such as tetrahydrothiophene dioxide (sulfolane), ethylene glycol carbonate, propylene glycol carbonate,
N-methylpyrrolidone.

 The temperature at which the reaction is conducted is generally between 450 and 1600 ° C. under atmospheric pressure.

It is also possible to operate at a higher temperature and under a pressure greater than atmospheric pressure.

 The phenols and phenol ethers which are preferably used in the process of the invention are the compounds of formula (I) in which R represents a hydrogen atom, a methyl group or an ethyl group, and Rg represents a hydrogen atom. hydrogen, a methyl, ethyl or tert-butyl group, a methoxy or ethoxy group.

 By way of non-limiting examples, mention may be made of phenol, anisole, orthocresol, metacresol, paracresol, 4-tert-butylphenol, 2-methoxyphenol and 4-methoxyphenol.

 The process according to the invention is particularly applicable to phenol for the preparation of hydroquinone and pyrocatechol.

 Other objects, features and details of the invention will become more clearly apparent from the following examples given for illustrative and illustrative purposes only.

 Example 1 which follows relates to the preparation of stannozéosilite which is implemented in Example 2 of the invention which relates to a hydroxylation process of phenol.

Example 1
Preparation of stannozeosilitis
This example describes a synthesis of an acidic zeolite using F- ions as a mobilizing agent.

0.26 g of SnCl4 tin chloride is added dropwise with vigorous stirring to a solution containing
13.2 g of tetrapropylammonium bromide (TPA-Br),
- It g of ammonium fluoride NH4F,
- 120 g of water,
- 6 g of silica AEROSIL 130 sold by DEGUSSA.

After homogenization of the gel, 0.12 g of a zeolite of MFI structure, namely a zeolite, are added as crystallization seeds.
The pH of the reaction mixture is 8.5.

The molar ratios in the reaction mixture are as follows
Sn / Si = 0.01; F / Si = 3.0; TPA + / Si = 0.5; H20 / Si = 70.

 The reaction mixture is transferred to an autoclave whose walls are sheathed with polytetrafluoroethane.

 It is heated for 1 day at 2000C.

 The pH of the medium at the opening of the autoclave is 9.0.

 After filtration, washing with water and drying at 800 ° C., 6.6 g of stannozéosilite precursor of pure MFI type are obtained, the X-ray diffraction pattern of which is in accordance with that given in Table I.

The crystals obtained are rods of dimensions 5 × 1 μm
The chemical analysis of the product gives a fluorine content of 1.0%.

 The previously obtained precursor is calcined at 5500C for 6 hours, which makes it possible to eliminate the structuring agent and to restore the porosity of the stannozéosilite obtained.

Example 2
Phenol hydroxylation process
In a 30 cm3 pyrex glass reactor, provided with a central stir bar stirrer, a refrigerant connected to a gasometer, a controlled heating system and an injection system, it is charged after having previously purged the apparatus with nitrogen
9.4 g of phenol (0.10 mol)
0.25 g of stannozeosilite prepared in Example 1.

 The mixture is heated to 800 ° C. with stirring, and then an aqueous solution of H 2 O 2 at 70% by weight by volume is injected. (0.005 mol H 2 O 2).

 It is then allowed to react for 2 hours 30 minutes.

 After filtration of the catalyst, untransformed H 2 O 2 is measured by iodometry and the diphenols by high performance liquid chromatography (HPLC).

We obtain the following results
- conversion rate (TT) of H202: 61.0%
- yield of pyrocatechin
at H202 transformed (RT): 23.0%
- yield of hydroquinone compared
at H202 transformed (RT): 4.5%
- total yield of diphenols: 27.5%

Claims (23)

 (sig6-x Son,) 0192 (II) wherein x is from about 0.1 to 3.0, preferably from 0.1 to 2.0.  phenyl or cyclohexyl; by reaction with hydrogen peroxide, characterized in that the reaction is conducted in the presence of an effective amount of zeolite of MFI structure based on silicon oxide and tin and having after calcination the following formula (II ):  of carbon, an alkoxy radical having 1 to 4 carbon atoms, a radical  ethyl or a phenyl group, - Rg represents a hydrogen atom, an alkyl radical having 1 to 4 atoms  in which - R represents a hydrogen atom, a methyl group, a grouping

 1. A process for hydroxylation of phenols or phenol ethers of general formula (I) 2. Method according to claim 1, characterized in that it is applied to the phenols and phenol ethers of formula (I) wherein R represents a hydrogen atom, a methyl group or an ethyl group, and Rg represents a hydrogen atom, a methyl, ethyl or tert-butyl group, a methoxy or ethoxy group. 3. Method according to one of claims 1 or 2, characterized in that it is applied to phenols and phenol ethers selected from phenol, anisole, orthocresol, metacresol, paracresol, tert-butyl- 4 phenol, 2-methoxyphenol, 4-methoxyphenol. 4. Method according to one of claims 1 to 3, characterized in that the stannozéosilite contains between 0.01 and 1.3% fluorine by weight after calcination. 5. Method according to one of claims 1 to 4, characterized in that the stannozéosilite used is obtained by a process comprising the following steps  (i) the preparation of a reaction mixture in aqueous media  containing a silicon source with oxidation state + 4,  a source of tin at the oxidation state + 4, ions  fluoride and a structuring agent with molar ratios  Sn / (Si + Sn) between 0.001 and 0.20, F / (Si + Sn) between  0.02 and 6, structuring agent / (Si + Sn) between 0.002 and 4; the  pH of this reaction mixture being between 1.5  about 12.0, preferably between 6.0 and 11.0,  (ii) crystallization of the reaction mixture,  (iii) Recovery and calcination of the crystalline precipitate at a  temperature above 4500C. 6. Process according to claim 5, characterized in that during the preparation of stannozéosilite, the Sn / (Si + Sn) molar ratio is between 0.005 and 0.1. 7. Method according to one of claims 5 and 6, characterized in that during the preparation of stannozéosilite, the molar ratio F / (Si + Sn) is between 0.06 and 2. 8. Method according to one of claims 5 to 7, characterized in that during the preparation of stannozéosilite, the molar ratio structuring agent / (Si + Sn) is between 0.04 and 1. 9. Method according to one of claims 5 to 8, characterized in that during the preparation of stannozéosilite, the molar ratio H 2 O / (Si + Sn)) in the reaction medium is between 4 and 400, preferably between 10 and 200. 10. Method according to one of claims 5 to 9, characterized in that during the preparation of stannozéosilite, the pH of the reaction medium is controlled by the addition of a base containing no alkaline ions 11. The method of claim 10, characterized in that during the preparation of stannozéosilite, the molar ratio base / (Sn + Si) in the reaction medium is less than 12, preferably between 0.1 and 8. 12. Method according to one of claims 5 to 11, characterized in that during the preparation of stannozéosilite, silicon oxide and tin oxide have a common source. 13. Method according to one of claims 5 to 12, characterized in that during the preparation of stannozéosilite, the source of silicon oxide is selected from the group comprising hydrogels, aero or xerogels, colloidal silica suspensions silicic esters, water-soluble silicates, silicas extracted from natural or synthetic crystalline compounds, hydrolyzable tetravalent silicon compounds such as silicon halides. 14. Method according to one of claims 5 to 11 and 13, characterized in that during the preparation of stannozéosilite, the source of tin is selected from the group comprising crystallized or amorphous tin oxides and hydroxides , halogens, alcoholates, soluble salts of tin. 15. Method according to one of claims 5 to 4, characterized in that during the preparation of stannozéosilite, the fluoride ions are added to the reaction mixture in the form of hydrofluoric acid, amine hydrofluorides or dichloromethane. quaternary ammonium, hydrolysable compounds releasing fluoride anions. 16. The method of claim 15, characterized in that during the preparation of stannozéosilite, the hydrolyzable compounds are fluorinated salts containing silicon or tin selected from the group consisting of tin fluorides and fluorides of silicon. 17. Method according to one of claims 1 to 16, characterized in that the molar ratio phenol / hydrogen peroxide is 25/1 to 3/1 and preferably 20/1 to 4/1. 18. Process according to one of Claims 1 to 17, carried out in a discontinuous manner, characterized in that the catalyst represents, by weight relative to the weight of the compound of formula (I) employed, from 0.1% to 20% and preferably from 0.5% to 10%. 19. Method according to one of claims 1 to 17, characterized in that the process is carried out continuously on a fixed bed of catalyst. 20. Process according to one of claims 1 to 19, characterized in that the hydrogen peroxide is used in the form of an aqueous solution. 21. Method according to one of claims 1 to 19, characterized in that the hydrogen peroxide is used in the form of an organic solution. 22. Process according to one of Claims 1 to 21, characterized in that the hydroxylation reaction is carried out in a solvent of the compound of formula (I) which is preferably miscible or partially miscible with water, such as water, an alcohol, a ketone, a nitrile, a carboxylic acid, an ester, an ether or a polar aprotic solvent. 23. Method according to one of claims 1 to 22, characterized in that the hydroxylation reaction is conducted at a temperature between 450C and 1600C.