TECHNICAL FIELD OF THE INVENTION

The present invention relates to substituted phenethanol ethers and, more particularly, to a process for the preparation thereof. Still more particularly, the present invention discloses a process for preparing substituted phenethanol ethers (SPEE) by the etherification of corresponding substituted phenethyl alcohols.

BACKGROUND OF THE INVENTION

The compound 4(2'-methoxyethyl)phenol (MEP), a substituted phenethanol ether prepared in accordance with the present invention, is a known compound. It is used as an intermediate in the production of 1- [4-(2-methoxyethyl)phenoxy]-3-[l -(1 -methoxyethyl)aminol-2-propanol, a beta-adrenergic Mocker known as metoprolol tartrate and described in 2 Pharmaceutical Manufacturing Encyclopedia, 100-1010 (2nd ed. 1988). Several methods have been employed in the past to manufacture 4- (2'-methoxyethyl)phenol (MEP). A method is described in Baird et al., Neighboring Carbon and Hydrogen. LI. ¹ . Dienones from Ar, 0-3 Participation. Isolation and Behavior ofSpiro (2,5)octa-l ,4-diene-3-one, 85 Am. Chem. Soc'y 567, 575 (1963) and in Communication to the Editor from Baird et al., 79 Am. Chem. Soc'y 756-757 (1957). In that method, 4-(2'-methoxyethyl)phenol is synthesized from phenylacetic acid through a multi-step process.

French Patent 2,487,338 discloses the preparation of 4-(2'- methoxyethyl)- phenol utilizing brominated alkoxyphenol as a starting material. The method utilizes a multi-step process which includes a technically difficult Grignard reaction. Belgian patent 885,030 discloses another method for the preparation of 4-(2'-methoxyethyl)phenol. In that method, the starting material is 4-hydroxystyrene. Several steps are used to obtain the final product.

Still another method for the production of 4-2'- methoxyethyl)phenol is disclosed in Hallberg et al., A New Route to 4- (2'-methoxyethyl)phenol via Palladium-Catalyzed Arylation of Methyl Vinyl Ether, 15(13) Synthetic Com., 1131-6 (1985) wherein 4-(2'- methoxyethyl)phenol is prepared via palladium-catalyzed arylation of methyl vinyl ether. The palladium catalyzed reaction of methyl vinyl ether with 4-bromonitrobenzene, followed by hydrogenation and subsequent diazotization forms 4-(2'-methoxyethyl)phenol.

In U.S. 5,107,034, there is described a process for preparing MEP by brominating 4-hydroxyacetophenone to produce alpha-bromo-5- hydroxy-acetophenone, and then causing a methoxide-bromide exchange to thereby produce alpha-methoxy-4-hydroxyacetophenone; and then conducting a single step reduction of alpha-methoxy-4- hydroxyacetophenone with at least two (2) equivalents of hydrogen per equivalent of alpha-methoxy-4-hydroxyacetophenone in the presence of a hydrogenation catalyst to thereby directly produce MEP. In U.S. 5,124,489, there is disclosed a process for preparing substituted phenethanol ethers by the catalytic reduction of corresponding substituted phenylglyoxal acetals.

The above prior art references are disclosed in accordance with the terms of 37 CFR 1.56, 1.97, and 1.98. All of these references are incorporated herein by reference in their entirety.

One of the disadvantages of the above-referenced processes is that they include several, often complex, steps which give rise to economical and ecological problems. Furthermore, another disadvantage of some of the above-referenced processes was that they utilize expensive starting materials.

According to the present invention, a simple economical method is disclosed wherein 4-hydroxyphenethyl alcohol, a commercially available material, is subjected to etherification to prepare 4-(2'- methoxyethyl)phenol (MEP). The method is also employed to prepare other substituted phenethanol ethers which are believed to be useful as intermediates in pharmaceutical products by the etherification of corresponding substituted phenethyl alcohols.

These and other advantages and objects of the present invention will become apparent from the following description.

SUMMARY OF THE INVENTION

Substituted phenethanol ethers are produced by the etherification of the corresponding substituted phenethyl alcohols. According to the present invention, a phenethyl alcohol reacts with an aliphatic primary alcohol in the presence of an acid catalyst to prepare the corresponding phenethanol ether. The method is used for the production of a variety of substituted phenethanol ethers including, but not limited to, 4-(2'- methoxyethyl)phenol, 4-(2'-n-propoxyethyl)phenol, and 4-[2 '-3 "-methyl-

butoxy)ethyl]phenol. The acid catalyst is from the group protic acids and Lewis acids.

The reaction is preferably carried out in an enclosed reactor with the pressure of the reactor being about 100 psig to about 1000 psig and at a temperature in the range of about 100°C to about 150°C for about 0.5 to about twenty-four (24) hours. Upon completion of the reaction, the reaction mass may be treated by well-known separation techniques to recover the product and the acid catalyst.

Detailed Description of the Invention

According to the present invention, a substituted phenethanol ether is prepared by the etherification of a corresponding substituted phenethyl alcohol and, more particularly, by the reaction of such phenethyl alcohol with an aliphatic primary alcohol in the presence of a suitable acid catalyst. The substituted phenethanol ethers prepared in accordance with the present invention are of the formula:

which is hereinafter referred to as Formula I. The corresponding

reactant substituted phenethyl alcohol is of the formula:

which is hereinafter referred to as Formula EL

In Formulas I and π, Rj is a primary alkyl group containing preferably one (1) to twenty (20) carbon atoms and most preferably, one (1) to six (6) carbon atoms. Furthermore, in Formulas I and π, R ₂ , R ₃ , 1 ₄ , R ₅ , and R^, are independently hydrogen, an alkyl group, a substituted or an unsubstituted aryl group, a hydroxy group, an alkoxy group, a substituted or an unsubstituted aryloxy group, a halogen, a carboxylic acid group, a carboxylic acid derivative group, an acyloxy group, an aroyloxy group, an amino group, an alkyl substituted amino group, or a substituted or an unsubstituted aryl substituted amino group. When R ₂ , R ₃ , R ₄ , R ₅ , or R ₆ , is an alkyl group, said group contains preferably one (1) to twenty (20) carbon atoms and, most preferably one (1) to six (6) carbon atoms. When R ₂ , R ₃ , R ₄ , R ₅ , or R*, is a substituted or unsubstituted aryl group, said group is preferably a phenyl group. It should be understood that, unless stated otherwise, the above definitions of R„ R ₂ , R ₃ , R ₄ , R ₅ , and R« shall be applicable hereinafter.

In accordance with the present invention, the etherification step or reaction to prepare the phenethanol ethers of Formula I from the corresponding phenethyl alcohol of Formula II is represented stoichiometrically as follows (Reaction 1):

Examples of substituted phenethanol ethers prepared in accordance with the present reaction include, but are not limited to, 4-(2'- methoxyethyl)phenol (Formula HI); 4-(2'-n-propoxyethyl)phenol (Formula IV); and 4-[2'-(3"- methylbutoxy)ethyl]phenol (Formula V). These compounds are shown below:

It is believed that the acid catalyst promotes the conversion of the H H

I I C — OH group of the phenethyl alcohol to a — C— OR _j

I I

H H

group. It is totally unexpected to achieve the production of a specific ether compound in such high yields when reacting two primary alcohols together. Accordingly, suitable acid catalysts that promote this step are used to carry out the reaction. A suitable amount of catalyst is in the range of about 0.1 to about twenty (20) weight percent, and preferably in the range of about 0.5 to about fifteen (15) weight percent with respect to phenylethyl alcohol reactant on a dry catalyst basis. Any acid catalyst which can promote Reaction I (above) may be used. Acid catalysts which function in the capacity to achieve the desired end result, i.e. the promotion of Reaction I above, are soluble acids and insoluble acids. Typical soluble acids include, without limitation, hydrochloric acid, sulfuric acid, methane sulfonic acid, and p- toluenesulfonic acid. Typical insoluble acids include, without limitation, zeolites and H ⁺ ion exchange resins such as Dowex brand catalysts,

Amberlyst brand catalysts, and the like. Insoluble acid catalysts such as sulfonated copolymer of styrene and divinyl benzene (e.g. "Amberlyst 15" manufactured by Rohm & Haas Corporation of Philadelphia, PA), or an acid clay such as an activated clay adsorbent such as "Filtrol 105" are suitable materials that can be used. The acid catalysts are either soluble or insoluble in the overall reaction mass. The preferred acid catalyst is one which is insoluble.

Although a small amount of the acid catalyst, e.g. one (1) percent by weight of the total weight of the reaction mass, is sufficient to promote Reaction I of the present invention, it is preferred to use from about five (5) to about fifty (50) percent by weight; more preferably from

about five (5) to about ten (10) percent by weight, based on the total weight of the reaction mass.

While Reaction I above discloses the stoichiometrically balanced equation, it is to be understood that the substituted phenethyl alcohol (SPEA) can be used in an amount of from about five (5) percent to about seventy (70) percent by weight, based on the total weight of the reaction mass. Also, the primary aliphatic alcohol (PAA) can be used in an amount of from about thirty (30) percent to about ninety-five (95) percent by weight, based on the total weight of the reaction mass. PAA includes, without limitation, methanol, n-butyl alcohol, and isoamyl alcohol.

In carrying out the reaction, the SPEA, PAA, and the acid catalyst are charged to a corrosion-resistant reactor. The reactor is purged with an inert gas such as nitrogen. The inert gas can also be used to pressurize the reactor during the reaction if desirable. Accordingly, it is desirable to operate the reaction under pressure in order to conduct the reaction in liquid phase. The pressure therein should be at least fifty (50) psig, preferably in the range of about 100 psig to about 1000 psig, and more preferably, in the range of about 100 psig to about 750 psig. The reaction is carried out at a temperature above 75°C, and preferably in the range of about 100°C to about 300°C, and most preferably, in the range of about 100°C to about 150°C. The rate of the reaction depends on the amount of acid catalyst, the pressure, and the reaction temperature. The amount of the catalyst used is within the lower portion of the aforesaid ranges with the temperature and the pressure being in the upper portion of the aforesaid ranges. High yields, however, are also observed

when the amount of catalyst is in the upper portion of the aforesaid ranges and the reaction temperature and the pressure are in the lower portion of their respective aforesaid ranges.

The reaction mass is continuously stirred by well-known stirring means. The reaction is carried out for a sufficient period of time to obtain a satisfactory conversion of the SPEA to the SPEE product. Depending on the amount of the catalyst, the reaction temperature and the pressure, the time period may be in the range of about 0.50 hours to about twenty-four (24) hours or longer. Preferably, the reaction is carried out for a time period in the range of about one (1) hour to about twelve (12) hours. The reaction is relatively slow and can be carried out in a batch mode, a semi-batch mode, or a continuous mode.

Upon the completion of the reaction, the SPEE product may be separated from the reaction mass by well-known techniques such as distillation, crystallization, and filtration. For example, the acid catalyst can be recovered by filtration of the reaction mass. The acid catalyst may be reformulated and recirculated to the reactor for further utilization. The unreacted SPEA can be separated from SPEE by distillation or crystallization and recycled. The following examples further illustrates the invention but are not to be construed as limitations on the scope of the invention contemplated herein.

Example 1 4-f2'-Methoxyethy1.Phenol A solution of twenty (20) grams 4-hydroxyphenethyl alcohol in

150 ml methanol containing 36.75 grams sulfuric acid (catalyst) were

loaded into a 300 cc autoclave. The autoclave was then sealed and purged with nitrogen and pressurized with nitrogen gas to 500 psig. The autoclave was then heated to 100°C with stirring at 300 ipm. The reaction was allowed to take place for approximately twenty-four (24) hours. The autoclave was then purged with nitrogen, cooled to 5°C, and vented slowly. The resultant material was 90 ml of a dark, greenish- black solution. An aliquot was treated with base and analyzed by gas chromatography (GC). A 40% yield of 4-(2'-methoxyethyl)ρhenol was obtained.

Example 2

4-.2'-MethoxyethyttPhenol

A mixture of 20.0 grams 4-hydroxyphenethyl alcohol, 150 ml methanol, and 10.5 grams Zeolite ZS FM-5 catalyst (solid) was loaded into a 300 cc autoclave. The autoclave was then sealed and purged with nitrogen and pressurized with nitrogen gas to 210 psig. The autoclave was then heated up to 125°C over a four (4) hour period with stirring at 250 rpm. The pressure rose from 210 psig to 400 psig. The reaction was allowed to take place for approximately twelve (12) hours. The autoclave was then purged with nitrogen and cooled to room temperature. The catalyst was filtered off, providing 19.5 grams of a gray solid. A 58% yield of 4-(2'-methoxyethyl)phenol was obtained.

Example 3 4-.2'-Methoxyethyl.Phenol

A mixture of 20.0 grams 4-hydroxyphenethyl alcohol, 100 ml methanol, and 10.0 grams Dowex 50 (H+ form) catalyst were loaded into an autoclave. The autoclave was then sealed and purged with

nitrogen and pressurized with nitrogen gas to 200 psig. The autoclave was then vented of excess pressure, sealed, and heated to 118°C over a sixteen (16) hour period with stirring at 300 rpm. The pressure rose from 200 psig to 440 psig. The reaction was allowed to take place for approximately sixteen (16) hours. The autoclave was then purged with nitrogen and cooled to 17.2°C (230 psig) and then vented. The solid catalyst was filtered off, providing 15.5 grams of oil which solidified. A 31 % yield of 4-(2'-methoxyethyl)phenol was obtained.

Examples 4-9 The procedure set forth in Example 3 is repeated six (6) separate times but using the substituted phenethyl alcohols shown in Table I where R„ R ₂ , R ₃ , R ₄ , R ₅ , and Re are defined. The respective ethers are formed with yields ranging from eighteen (18) percent to thirty-four (34) percent.

Table J

Acid Catalyst

R4 ♦ Ri-OH

While the invention is described with respect to specific embodiments, modifications thereof can be made by one skilled in the art without departing from the spirit of the invention. The details of said embodiments are not to be construed a limitation except to the extent indicated in the following claims.