PROCESS FOR THE PRODUCTION OF ARYL ALKYL ETHERS

Abstract: A method of preparing an aryl alkyl ether, comprises reacting a phenol (i.e. phenol itself or a substituted phenol) with a dialkyl carbonate in the vapour phase over an alumina, alumina-silica or zeolite catalyst. A further method of preparing an aryl alkyl ether, comprises feeding a phenol (i.e. phenol itself or substituted phenol) and a dialkyl carbonate to a reactor and reacting the phenol and the dialkyl carbonate therein to form the aryl alkyl ether.

Description: PROCESS FOR THE PRODUCTION OF ARYL ALKYL ETHERS This invention relates to a process for the production of aryl akyl ethers by reacting phenols with dialkyl carbonates in the vapour-phase in the presence of catalysts. By a "dialkyl carbonate" we mean a ccrπpound of the general formula where each R is an alkyl group and is the same as or different from the other R. Aryl alkyl ethers are iiτportant industrial chemicals and are extensively used in perfumery, because of their pleasant aroma, and as antioxidants for oils and greases, as stabilisers for plastics, as starting materials for the production of dyes and agrochemicals, and as general synthetic reagents. It is wall known that aryl alkyl ethers can be obtained by reacting phenols with alcohols, ethers or olefins in the presence of catalysts, for example potassium bisulphate, boron trifluoride, phosphorous compounds and β-naphthalene sulphonic acid. The main drawbacks of such a method are the low yields of ether and the formation of undesirable by-products. Another known method is a variation of the Williamson ether synthesis which involves reacting alkyl halides with sodium salts of phenols. Although high yields are obtained with these reagents, the main disadvantage is the relatively high cost of the alkyl halides and the use of sodium hydroxide in the preparation of the sodium salts, which adds to the price of the product. Dialkyl sulphates may be utilised as a substitute for the alkyl halides but their toxicity, particularly of dimethyl sulphate, causes problems. Another known method for preparing aryl methyl ethers involves the uncatalysed reaction between phenols and diazomethane. This gives high yields but the cost, toxicity and unstable nature of diazαrethane causes the method to be only applicable to small-scale reactions or high value products. It is also known that aryl alkyl ethers can be prepared by reacting dimethyl carbonate with phenols in the liquid phase and in the presence of catalysts, for example sodium hydroxide, sodium carbonate, sodium methoxide, tertiary amines, nitrogeneous hetercyclic ccmpounds and tri-n-butyl phosphine. The disadvantage of such a method is that pressure vessels are needed because of the high temperatures which are necessary. The present invention provides a process i r the preparation of an aryl alkyl ether, which process comprises reacting a phenol (i.e. phenol itself or a substituted phenol) with a dialkyl carbonate. According to a first aspect of the invention there is provided a method of preparing an aryl alkyl ether, cαrprising reacting a phenol (i.e. phenol itself or a substituted phenol) with a dialkyl carbonate in the vapour phase over an alumina, alumina-silica or zeolite catalyst. According to a second aspect of the invention, there is provided a method of preparing an aryl alkyl ether, comprising feeding a phenol (i.e. phenol itself or substituted phenol) and a dialkyl carbonate to a reactor and reacting the phenol and the dialkyl carbonate therein to form the aryl alkyl ether. In the process of the invention, contact time is not crucial to good yields but preferably may be up to 15 seconds. The reaction of the phenol and the dialkyl carbonate is preferably carried out at a terrperature of between 180°C and 500°C, more preferably between 200°C and 350°C. v - 3 - The dialkyl carbonate may be dimethyl carbonate. Advantageously from 0.1 to 5.0 moles, preferably from 1.0 to 2.0 moles, of dialkyl carbonate are used per mole of the phenol. Phenols suitable for use in the process according to the invention are mono- and polyhydroxy aromatic cc pounds optionally substituted by one or more substituents such as alkyl, cycloalkyl, alkoxy, formyl and carboxy groups and halogen atoms. Phenols, cresols, xylenols, polyalkyl substituted phenols, dihydroxy benzenes, chlorophenols and naphthols are particularly suitable phenols for use in the process of the invention. The process according to the present invention is preferably carried out by passing a mixture of the phenol and the dialkyl carbonate of known mole ratio, at a constant rate into an electrically heated stainless steel column, packed with inert material such as ceramic saddles and containing a catalyst bed of known volume. The teπperature of the catalyst bed, and therefore the temperature of the reaction, may be recorded by a movable thermocouple. The column eluent is cooled via an air condenser and by a cold water condenser and collected in a suitable vessel. The accompanying drawing shows diagrarπriatically equipment suitable for use in carrying out the process described in the preceding paragraph. The equipment shown in the drawing comprises a vertical main reactor 1, a product vessel 2, a preheater 3, a metering pump 4, a feed tank 5 and a water tank 6. The reactor 1 is in the form of an electrically heated stainless steel column. The product vessel 2 is provided with a water condenser 7 having a vent 7' and an air condenser 8. The air condenser 8 is connected to the lower end of the main reactor 1. The main reactor is filled, frαrt its lower end upwardly, with inert packing 9 having a depth or vertical extent of 9 cm, catalyst 10 having a depth of 12 cm and further inert packing 11 having a depth of 28 cm. At the upper end of the reactor 1 are provided a gas inlet 12 and a thermocouple 13. The upper end of the reactor is also connected through line 14 with the preheater 3, which is filled with inert packing 15. The preheater has a length of 29 cm and a depth or vertical extent of 3.2 cm. The preheater 3 is provided with a thermocouple 16. Lines 17 and 18 connect the feed tank 5 and the water tank 6 respectively through the metering pu p 4 to the preheater 3. The packing in the reactor 1 and the preheater 3 is constituted by ceramic saddles. In use of the equipment, in carrying out a process according to the invention, phenol and dialkyl carbonate are passed at a constant rate and at known mole ratio from the feed tank 5 through the preheater 6 into the reactor 1. Reaction product collects in the vessel 2. Separation of the reaction mixture is easily achieved via conventional techniques. Compared to previously known processes, the present invention gives aryl alkyl ethers more siitply and economically, in high yield and purity. Involved isolation and neutralisation steps are unnecessary. Ωe gas inlet 12 is a nitrogen purge line for cooling the reactor between runs. Except between runs, gas is not supplied through the inlet 12 in carrying out a process according to the invention. The water tank 6 is for providing a supply of water to be converted to steam for catalyst regeneration. Water is pumped from the tank 6 into the preheater 3 where steam is generated. The steam then passes into the reactor to regenerate the catalyst. The following examples are representative of the present invention. The examples were carried out using the equipment shown in the drawing and the reaction of the dialkyl ether with the phenol was effected at atmospheric pressure. The catalysts referred to were used as the catalyst 10. Exaπple 1 An equimolar vapour phase mixture of phenol and dimethyl carbonate was passed over an alumina catalyst at a terperature of 239°C and with a contact time of 10.83 seconds. Gas liquid chrcmatography (G.L.C.) analysis showed the product to have the following ccπposition: 73.8% anisole (methyl phenyl ether) 18.8% phenol 2.9% o-methylanisole 3.7% o-cresol 0.5% 2,6-xylenol 0.3% others Exaπple 2. An equimolar vapour phase mixture of phenol and dimethyl carbonate was passed over a zeolite catalyst at a temperature of 283°C and with a contact time of 5.14 seconds. G.L.C. analysis showed the product to have the following cαπposition: 81.8% anisole 12.7% phenol 2.0% o-methylanisole 0.6% o-cresol 0.2% 2,6-xylenol 2.6% others Exaπple 3. An equimolar vapour phase mixture of p-cresol and dimethyl carbonate was passed over a zeolite catalyst at a temperature of 242°C and with a contact time of 4.77 seconds. G.L.C. analysis showed the product to contain: 0.1% anisole 0.1% phenol 75.8% p-methylanisole 17.6% p-cresol 2.0% dimethyl anisole 4.0% xylenol 0.4% others Example 4. An equimolar vapour phase mixture of phenol and diethyl carbonate was passed over a zeolite catalyst at a teπprature of 237°C and with a contact time of 4.99 seconds. G.L.C. analysis showed the reaction mixture to contain: 0.6% anisole 28.0% phenol 56.1% phenetole 1.2% cresols 7.1% ethyl phenols 3.8% ethyl phenetoles 4.4% others Exaπple 5. A vapour phase mixture comprising 1 mole vanillin and 2 rroles dimethyl carbonate was passed over a zeolite catalyst at 320°C and with a contact time of 4.48 seconds. G.L.C. analysis showed the mixture to contain: 1.2% guaiacol 0.3% veratrole 50.3% vanillin 46.2% veratraldehyde 2.0% others

Claims: CLAIMS 1. A method of preparing an aryl alkyl ether, comprising reacting a phenol (i.e. phenol itself or a substituted phenol) with a dialkyl carbonate in the vapour phase over an alumina, alumina-silica or zeolite catalyst. 2. A method according to claim 1, wherein the phenol is phenol itself. 3. A method according to claim 1, wherein the phenol has one or more substituents selected frcm alkyl, cylcoalkyl, alkoxy, formyl and carboxy groups and halogen atoms. 4. A method according to claim 1 or 2, wherein the dialkyl carbonate is dimethyl carbonate or diethyl carbonate. 5. A method according to any of claims 1 to 4, wherein the reaction is carried out at 0.75 to 2 atmospheres. 6. A method according to any of claims 1 to 4 , wherein the reaction is carried out at a temperature of 180°C to 500°C. 7. A method of preparing an aryl alkyl ether, ccπprising feeding a phenol (i.e. phenol itself or substituted phenol) and a dialkyl carbonate to a reactor and reacting the phenol and the dialkyl carbonate therein to form the aryl alkyl ether. 8. A method according to claim 7, vvherein the reaction is carried out in the vapour phase. 9. A method according to claim 8, when carried out under the conditions specified in any of claims 1, 5 and 6. 10. A method according to claim 8 or 9, when carried out using a reactant as specified in any of claims 1, 2, 3 and 4. 11. A method of preparing aryl alkyl ether, substantially as described herein in any of the examples.

Inventors: NIGHTINGALE PETER, RHODES ROBERT, NIGHTINGALE, PETER, RHODES, ROBERT
Applicants: COALITE GROUP PLC
Application year: 1985
Main classification: C07C43
IPC codes: C07C41, C07C45