FR2491457A1 - PROCESS FOR THE PREPARATION OF PHENOLIC ETHERS - Google Patents

Abstract

THIS PROCESS FOR THE PREPARATION OF PHENOLIC ETHERS FROM MONO- OR POLYPHENOLS AND ALIPHATIC ALCOHOLS, WITH HIGH SELECTIVITY, IS CHARACTERIZED BY THE USE OF CATALYSTS CONTAINING (OR COMPOUNDS OF) "SUPERACID", AT A TEMPERATURE SITUATED BETWEEN 110 AND 170C, IN A PHENOL: ALCOHOL RATIO BETWEEN 2: 1 AND 6: 1.

Description

The present invention relates to a novel method for

  preparation of phenolic ethers from phenols and al-

aliphatic cools.

  The importance of phenolic ethers in large sectors of the chemical industry (especially in the pharmaceutical field and in the fields of dyes, antioxidants,

  cosmetics, etc.) is well known.

  Products like anisole, galacol, monomeric ether

  hydroquinone thyl, methyl naphthyl ethers or

  similar are widely used and find a large market.

  Many methods have been suggested and used up to

  now for the preparation of phenolic ethers.

  The most used processes for the preparation of phenolic ethers use the reaction of an alkyl sulfate

  or an alkyl chloride with an alkaline phenate.

  The main drawbacks associated with these scale processes

  the industrial are mainly due to the following two factors: 1. the alkylating agents are quite toxic and, in some cases, volatile, which leads to problems of pollution and environmental hygiene; 2. stoichiometric quantities of mineral salts (sulfates and alkali chlorides) are formed during the reaction,

  which poses difficult disposal problems.

  In order to overcome these disadvantages, several pro-

  ceded have been developed for the preparation of phenol ethers

  lics, directly from phenols and alcohols, according to the equation Ar-OH + R-OH -... Ar-OR + H20 (I) The characteristics of the catalyst play an essential role in this reaction. Hitherto two kinds of catalysts have been used: a) salts and metal oxides; b) acid ion exchange resins. The catalysts of type (a) (Japanese patents No. 8099-129 and 71-11494) do not give very satisfactory results,

  because they are not selective enough and it is therefore formed

  quent appreciable amounts of secondary products, and in particular of products containing alkyl groups on the benzene nucleus. Catalysts of type (b) (Nippon Kaishi 8, 1513 (1974); USSR patent 197613; French patent no. 2,373,506) allow good selectivities to be obtained only at very slow reaction rates (20 to 60 hours); if one

  try to increase the reaction rate by means of a

  temperature change, an opposite effect is obtained, because the reaction speed is further reduced and the selectivity

  is also lowered markedly; in addition, the cataly-

  seur deteriorates and it must no longer be recycled.

  However, it was discovered - and this is the subject of the pre-

  invention - a process for the preparation of phenolic ethers by direct reaction of phenols with aliphatic alcohols according to the equation: Ar (OH) n + ROH ArOR (OH) nl + H2O in which Ar = aryl radical, R = radical aliphatic at 1-6 C, n = 1, 2, this process being characterized by the use of "supersacids" as catalysts. This new process eliminates all the drawbacks mentioned above and makes it possible to produce phenolic ethers with high reaction rates and selectivities close to 100%, with good degrees of transformation of the phenol and almost yields.

theoretical aspects of the processed product.

  "Superacids" are compounds or catalytic systems

  ticks generally composed of particular acids or melanins

  Lewis acids with protic acids and their preparation and use are relatively recent (Bull. Soc.

  Chim. de France 1976, n2 11-12; 1979, no.2 5-6). All super

  acids are characterized by a Ho index lower than that of

  sulfuric acid, which is around -12.

  Superacids containing fluorinated sulfonic acids, such as trifluoromethane sulfonic acid and its counterparts

  higher, as well as perfluorosulfonic resins, including

  -those produced by Du Pont under the name of

  Nafion brand, are particularly interesting.

  The process of the present invention can be carried out in heterogeneous phase, using a solid insoluble catalyst

  and by mixing phenol and alcohol in com-

  taken between 2: 1 and 6: 1, at a temperature between 1102 and 1702C, at atmospheric pressure or under pressure,

  depending on the boiling point of the reaction mixture.

  The amount of catalyst in the reaction mixture is

  -locates between 1 and 30% (by weight) of the weight of the substances

cipant to the reaction.

  --- On the other hand, it is possible to operate - in homogeneous phase, ---

  using a soluble superacid and a solvent for the two substances participating in the reaction, inert under the conditions

  of the reaction, such as for example a hydrocarbon, a hydrocarbon

  halogenated bure or dioxane; reaction conditions

are the same.

  The method can be applied for the etherification of any commercial phenol, such as for example phenol, cresol, xylenols, pyrocatechol, hydroquinone, resorcinol, naphthols, etc. It is particularly interesting that,

  In the case of polyphenols, the new process gives the mono-

  ether with high selectivity. As aliphati- alcohol

  that any 1-6 alcohol can be used. Nevertheless, the use of methanol or ethanol is particularly advantageous, having regard to the fact that the methyl ethers and

ethyl are very important.

  The unreacted excess phenol is separated from the phenolic ether and recycled. Any suitable separation process

  can be applied, depending on the products considered: ordi-

  The separation is generally carried out by distillation.

  If the reaction is carried out in a heterogeneous phase, the cataly-

  This can be separated from the reaction mixture by decantation, filtration or centrifugation and used in the following operations, since it does not lose its activity under the conditions

of the reaction.

  In addition, it has been discovered that the "super"

  acids ", which characterize the process according to the present in-

  vention, can also be used in admixture with known catalysts for direct etherification, consisting

  by acid ion exchange resins. -

  In this case, the reaction speed increases with the

  centering of the superacid and we can therefore reach reaction times which are 2 to 4 times shorter than those which we

  obtained with known catalysts.

  The quantities of the two catalysts used in the reaction

  between 1 and 30-% (by weight) of the weight of the mixture--

reactive.

  The advantage of using a mixture of catalysts lies in the remarkable reduction in reaction times compared to known methods, while using smaller amounts of superacid, which means that the use of these mixtures is preferable in cases where the superacid

is relatively expensive.

  The possibility of using "superacids" and, in particular

  In particular, Nafion-type resins as catalysts for the direct etherification (with a selectivity close to 100%) of phenols with aliphatic alcohols was completely unpredictable, having regard to the fact that, as is known (J. Org. Chem. Vol 43, n-16, 1978; J. of Catalysis 61, 96-102, 1980), Nafion-type catalysts catalyze the methylation of the nucleus and the formation of dimethyl ether in a mixture of phenols and methanol . There was nothing to suggest that the process could follow an entirely different path, to the point of achieving almost complete selectivity for the process

  mono-etherification, under different reaction conditions

  rents, in particular as regards the relationships between the substances participating in the reaction and the temperature. Some examples are given below to allow

  more easily reproduce the process which is the subject of the pre-

  invention; but it is understood that these examples are offered only by way of illustration and that the invention is not there

obviously not limit.

Example 1

  g (1.155 mol) of pyrocatechol, 14.5 g (0.454 mol) of methanol and 30.6 g (0.03063 equiv.) of perfluorosulfonic acid (Nafion 501 - Du Pont) are placed in a flask fitted with a stirrer, thermometer and reflux condenser. The mixture is heated at 120-C for 5 hours. At the end of this reaction period, the composition of the mixture turns out to be the following: --- unreacted pyrocatechol - --- 87% - guaiacol 12.8% - compounds with methyl groups on the nucleus 0 , 1% - veratrole 0.1% galacol yield, based on pyrocatechol

  transformed, can be considered almost quantitative.

  By operating exactly as described above, but using as an catalyst an ion exchange resin composed of polystyrene-sulfonic acid crosslinked with divinylbenzene (Amberlist 15), in an amount corresponding to

  0.03063 equiv. acid, a mixture is obtained after 5 hours

  reaction reaction having the following composition: - unreacted pyrocatechol 98.8% - guaiacol 1.0% - compounds with methyl groups on the nucleus 0.1% - veratrole 0.1%

Example 2

  250 g of pyrocatechol (2.27 mol), 36.3 g of methanol (1.135

  mol) and 61.2 g of Nafion 501, which corresponds to 0.0612 equiv.

  acid, are placed in the same flask as in Example 1. The mixture is heated to 150-155C20 for 5 hours. At the end of this reaction time, the composition of the reaction mixture is as follows: unreacted pyrocatechol 80% - guaiacol 18.5% - methyl compounds 1.0% - veratrole 0.5%

Example 3

  107 g of phenol (1.135 mol), 14.5 g of methanol (0.454 mol) and 30.6 g of Nafion 501 (0.03063 equiv.) Are placed in

  the same balloon as in Example 1.

  The mixture is heated at 120-O for 5 hours.

  At the end of this period, the composition of the reaction mixture

is as follows:

  - unreacted phenol - 85% _--

  - anisole 14.9% - alkylated products 0.1%

Example 4

  250 g of pyrocatechol (2.27 mol), 3.63 g of methanol (0.1135 mol) and 61.2 g of perfluorosulfonic acid (0.0612

  equiv. acid) are placed in the same flask as in example

  ple 1. The mixture is heated to 150-15520 for 1 hour, and then another 3.63 g of methanol is added thereto. The mixture is again heated to 1501552C for 1 hour, after which an additional 3.63 g of methanol is added while continuing to heat to

150-1552 C.

  After 3 hours after the start of the reaction, the mixture has the following composition: - unreacted pyrocatechol 88.6% - galacol 11.4%

Example 5

  g of hydroquinone (1.135 mol), 14.5 g of methanol (0.454 mol) and 30.6 g (0.03063 acid equiv.) of Nafion 501 DuPont are placed in the same flask as in Example 1. The mixture is heated to 12020 for 5 hours. At the end of this period, the reaction mixture has the following composition: unreacted hydroquinone 90.5% - monomethyl ether of hydroquinone 9.4% - products with alkylation of the nucleus 0.1%

Example 6

  g of pyrocatechol (1.135 mol), 21 g of ethanol (0.455 mol) and 30.6 g (0.03063 acid equiv.) of Nafion 501 are placed

  in the same balloon as in Example 1.

  The mixture is heated at 1200C for 5 hours. At the end of this time, the composition of the mixture is as follows: - unreacted pyrocatechol 85% -guetol 14.5% - other products 0.5%

Example 7 _._ -

  162 g of -naphthol (1.135 mol), 14.5 g of methanol (0.454 mol) and 30.6 g (0.03063 equiv.) Of Nafion 501 are placed in the same flask as in Example 1. The mixture is heated to 12520 for 5 hours. At the end of this time, the composition of the mixture turned out as follows: - unreacted naphthol 86% - monomethyl ether -naphthol 13.7% other products 0.3%

Example 8

  g of pyrocatechol (1.135 mol), 14.5 g of methanol

  (0.454 = mol), 0.01 equivalents of Nafion 501 and 0.02 equiv.

  of Amberlist 15 are placed in the same balloon as in example-

  ple 1. The mixture is heated to 12520 for 5 hours.

  At the end of this time, the mixture has the following composition: - unreacted pyrocatechol 89% - gatacol 10.9% - other products 0.1% VE3NDICkTIO0NS 1. Process for the preparation of phenolic monoethers with

  from mono- or polyvalent phenols and aliphatic alcohols

  according to the equation Ar (OH) n + ROH ---- w ArOR (OH) _1 + H20 in which Ar = aryl radical, R = aliphatic radical at- 1-6

  0, n = 1, 2, characterized in that a mixture of phenol and al-

  cool aliphatic is reacted in the presence of an "super

  acid "as a catalyst, at a temperature between 110 and 1702 C, in a phenol: alcohol ratio between

2: 1 and 6: 1.

  2. Method according to claim 1, characterized in that the

  "superacid" is used in admixture with -exchange resins

its acid ions.

  15. The method of claim 1, characterized in that the "superacid" is selected from the group consisting of

  fluorinated sulfonic acids and perfluorosulfonic resins.

  4. Method according to claim 1, characterized in that the catalyst is used in a proportion of 1 to 30% by weight

  relative to the weight of the substances participating in the reaction.

  5. Method according to claim 1, characterized in that a solvent of phenol and alcohol is used which is inert in

the reaction conditions.