PROCESS FOR THE PREPARATION OF ALKYLARYL ETHERS

Abstract: Alkylarylethers are produced in accordance with the in­ vention starting from phenols and ethers of aliphatic alcohols in the presence of amorphous BPO₄, calcined at a tem­ perature of from 150°C to 600°C.

Description: The present invention relates to a process for the preparation of alkylaryl ethers. More particularly the present invention relates to a process for the preparation of alkylaryl ethers starting from phenols and ethers of aliphatic alcohols. It is known the preparation of alkylaryl ethers starting from phenols and ethers of aliphatic alcohols in the presence of strongly acidic ion exchange resins (European Patent 13924). The use of ion exchange resins has, however, the drawback that it is not possible to operate at high temperatures for long periods because said resins tend to lose at said conditions, their physical and mechanical characteristics. Accordingly either it is necessary to operate at low temperature with the consequent strong lowering of the yields or, by working at high temperature, the resin needs to be frequently replaced. On the contrary it is known from German Patent 827803 a method for preparing methyl ether or methanol with phenols in the presence of BPO₄, which operates at high temperature with high yelds. In particular in the example 1 of this patent methanol is reacted with pyrocatechol in the presence of BPO₄ at a temperature of 250°C: the dimethyl ether is not added but it is obtained by the reaction and then it has gone out. It has been surprisingly found and this is the object of the present invention that it is possible as regards the method claimed in DE-827803 to reduce considerably the reaction time, on obtaining the same conversion and the same selectivity, by the use of a catalytic system constituted by an amorphous BPO₄ in amounts by weight in the range of from 0,5 to 50% based on the weight on the reagents and by the use as reagent of the dimethyl ether and not methanol. The process according to the present invention comprises the steps of contacting a phenol or a phenols mixture with an ether of aliphatic alcohols or a mixture of ethers of aliphatic alcohols, at a temperature of from 150 to 400°C, preferably from 200 to 300°C, in the presence of amorphous boron phosphate in amount by weight in the range of from 0,5 to 50% based on the weight of the reagents which has been calcined at a temperature of from 150 to 600°C. The alkylaryl ether obtained then are separated from the other reaction components, by fractionation or crystallization. A method for preparing boron phosphate, which method has not to be considered as restrictive of the invention, is disclosed in example 1. The reaction between phenol or phenols mixture and either the ether of aliphatic alcohols or the mixture of ethers of aliphatic alcohols can occurr in the presence of a solvent or in the absence of the same. As solvents, when they are used, use in made of hydrocarbons, preferably aromatic hydrocarbons, particularly toluene. Boron phosphate is utilized in amounts by weight in the range of from 0,5% to 50% based on the weight of the reagents. The process is carried out at atmospheric pressure or higher than the atmospheric pressure. The process can be batch or continuous. In the case of a continuous operation, the catalyst is placed in a fixed or fluid bed and the reagents are continuously fed through the same, while the reaction products are continuously withdrawn from the side opposite to that where the reagents are introduced. In the case of a batch operation the catalyst at the end of the reaction is removed by filtration or centrifugation, before separating the alkylaryl ether. Phenols can be chosen among: phenol, substituted phenols having C₁-C₄ alkyl groups, such as meta-, ortho-, para-cresol, xylenols and tert-butyl phenol, phenols substituted by halogen atoms (e.g. ortho-, metha-, para-chlorophenol), polyphenols such as hydroquinone and pyrocatechol, alpha- and beta-naphtol and hydroxyanthracene. The ethers are chosen among the ethers of aliphatic alcohols having a number of carbon atoms in the range of from 1 to 8, preferably from 1 to 4, particularly dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, diisobutyl ether and di tert-butil ether. Some examples will now be provided with the aim of a better illustration of the invention , being understood that the same has not be considered restricted to them or by them. Example No.1 In a pyrex glass beaker 1000g distilled water were heated to 70°C and there were added to them, under stirring, 92.7 g H₃BO₃. When all H₃BO₃ was dissolved, always under stirring, there were added g 172.8 H₃PO₄ (85% aqueous solution). Stirring was continued and water evaporated until a slurry was obtained. The solid was dried at 100°C and a portion thereof was calcined at 170°C and another portion thereof was calcined at 550°C for two hours. The calcined product was then washed 4 times, redispersing the same each time in one litre of distilled water kept boiling, filtering and drying. Example No.2 Into a 40 ml microreactor, heated by a sand bath and provided with an external system of mechanical stirring, there were charged 10.0 g of amorphous BPO₄, prepared as described in Example 1 and calcined at 550°C, 10.0 g of hydroquinone and 14.8 g of dimethyl ether at a weight ratio 1/1/1.48. The reagents were kept for two hours at the temperature of 280°C. The hydroquinone conversion was 44% by moles, the yield to methyl hydroquinone 33% by moles and the selectivity to methyl hydroquinone 75% by moles. The gascromatographic amolysis of the obtained products gave the following results: Example No.3 In the same microreactor with the previous procedures there were charged 8.0 g amorphous BPO₄ calcined at 170°C, 8.0 g hydroquinone and 7.9 g dimethyl ether, at a weight ratio 1/1/1. The hydroquinone conversion was 52% by moles, the yield to methyl hydroquinone 45% by moles and the selectivity to methyl hydroquinone 87% by moles. The gas-chromatographic analysis of the products gave the following result: Example No.4 Into a microreactor, heated by a sand bath and provided with a mechanical stirring system there were charged 10.3 g of amorphous BPO₄ prepared as in example 1 and calcined at 550°C, 10.2 g pyrocatechol and 10,3 g dimethyl ether at a weight ratio 1/1/1.3. The reagents were kept for two hours at the temperature of 280°C. The pyrocatechol conversion was 40%, the yield to guaiacol 37% and the selectivity to guaiacol 92%. The gas-chromatographyc analysis of the obtained products gave the following result:

Claims: A process for preparing alkylarylethers which comprises reacting a phenol or a mixture of phenols with an ether of aliphatic alcohol or a mixture of ethers of aliphatic alcohols in presence of a catalyst system constituted by amorphous BPO₄ at a reaction temperature of from 200 to 300°C characterized in that the amorphous BPO₄, which has been calcined at a temperature of from 150 to 600°C, is utilized in amounts by weight in the range of from 0,5 to 50% based on the weight of the reagents.

Inventors: BELLUSSI, GIUSEPPE, BRUNELLI, MAURIZIO
Applicants: ENIRICERCHE S.P.A.
Application year: 1987
Main classification: C07C43
IPC codes: C07C41