Field of the Invention

This invention concerns the production of specific ethylated naphthalene compounds by selectively ethylating a 2-substituted naphthalene compound at the 6 position of the naphthalene nucleus. More particularly, this invention concerns the highly selective production of 2,6-methylethyl- naphthalene by the selective ethylation of 2-methylnaphthalene, and the highly selective production of 2-alkoxy-6-ethylnaphthalenes or 2-aryloxy-6- ethyl naphthalenes by the selective ethylation of a 2-alkoxy- or 2-aryloxy- naphthalene compound.

Description of the Prior Art

2,6-Naphthalene dicarboxylic acid is a monomer that is known to be useful for the preparation of a variety of polymers. For example, poly(ethylene

2,6-naphthalate) which has better heat resistance and mechanical properties than polyethylene terephthalate and is useful in the manufacture of films and fibers is prepared from 2,6-naphthalene dicarboxylic acid and ethylene glycol.

2,6-Dialkylnaphthaienes are desirable feedstocks for oxidation to 2,6- naphthalene dicarboxylic acid. A known conventional process for producing 2,6-naphthalene dicarboxylic acid comprises the oxidation of a 2,6-dialkyl- naphthaiene with oxygen in the liquid phase in an acetic acid solvent at an elevated temperature and pressure and in the presence of a catalyst com¬ prising cobalt, manganese and bromine components. Dialkylnaphthaleπes can be found in low concentrations in refinery streams as mixtures of some or all of the many possible dialkylnaphthalene isomers. However, separation of these isomers is very difficult and expensive. Consequently, methods for producing specific dialkylnaphthalenes or mixtures of two or three specific dimethylnaphthalenes in high purity and quality are highly desirable. Olah et al., "Alkylation of Naphthalene with Alkyl Halides," Journal of American Chemical Society, 98:7, pages 1839-1842 (March 31 , 1976) disclose that theretofore there was no clear understanding of directive effects and selectivities for the Friedel-Crafts alkylation of naphthalene.

Since then, Japanese Kokai Patent Application Publication No. 61- 83137 (April 26, 1986) discloses a synthesis involving the transalkylation of naphthalene or 2-methylnaphthalene in the presence of an aluminum chloride catalyst at 0-35°C in the liquid phase to produce a 2,6-dialkylnaphthalene. Suitable alkylating agents are disclosed as including durene, diethylbenzene,

triethylbenzene, triisopropylbenzene, isopropylxylene, and dibutyibenzene. The reported results indicate a relatively low degree of selectivity for the formation of specific dialkylnaphthalenes. Furthermore, it is specifically stated that the disclosed alkylation method must be performed at 0-35°C, preferably room temperature, and that the higher the reaction temperature, the lower the selectivity for the formation of beta-alkyl substituted naphthalene and especially 2,6-dialkylnaphthalene. In addition, although this published patent application specifically mentions durene (1,2,4,5-tetramethylbenzene) as an example of an alkylation agent, it contains actual examples that illustrate only the use as alkylating agents in the method disclosed therein of polyalkylben- zenes where the alkyl groups are larger than methyl groups, and indicates as follows that polyalkylbenzenes with alkyl groups other than methyl groups afford benefits in the method disclosed therein: "Polyalkylbenzenes with ethyl, propyl, or butyl groups with high-carbon alkyl groups have high reaction rates...." Moreover, this published Japanese patent application states that, when the naphthalene is solid at the reaction temperature, a solvent such as a paraffin or cydoparaffin should be employed. This published Japanese patent application also discusses the use of halogenated alkyls in the alkylation of naphthalenes as a prior art method which did not produce a beta-alkyl naph- thalenβ with the desired selectivity.

Japanese Kokai Patent Application Publication No. 62-252733 (November 4, 1987) discloses a process for the transethylation of biphenyl with an ethylbenzene to form monoethylbiphenyl and diethylbiphenyl in the presence of a Friedel-Crafts catalyst, such as aluminum chloride, at 70-150°C. This published Japanese patent application discloses that a reaction tempera¬ ture of less than 70°C delays the reaction rate. The ring positions of the ethyl substituents in the ethylated biphenyl products are not disclosed. Suitable ethylbenzenβs are disclosed as including ethylbenzene, diethylbenzene, tri¬ ethylbenzene, tetraethylbenzene, other ethyl-substituted benzenes, βthyl- toluene, diethyltoluene and other ethyl-substituted toluenes. Poiyethyl- benzenes containing relatively small amounts of monoethylbenzene, triethylbenzene and tetraethylbenzene can also be used advantageously.

Shimada et al., "Ethylation and Transethylation of Naphthalene," Bulletin of the Chemical Society of Japan, Vol. 48 (II), pages 3306-3308 (November, 1975), disclose the transethylation of naphthalene by ethyl¬ benzene or ethylxylenes to form monoethyinaphthalenes in the presence of an aluminum chloride catalyst at 20-30°C. The rates of transethylation with et ylxylene isomers were reported to decrease in the order of 1 ,2-dimethyl-4-

ethylbenzene ≥ 1 ,3-dimethyl-4-ethylbenzene > 1 ,4-dimethyl-2-ethylbenzene > 1 ,3-dimethyl-5-ethylbenzene.

Japanese Patent Application 35/391/48, published on October 18, 1989, discloses a method for the preparation of ethyldiphenylethane or 5 diethyldiphenylethane by the transethylation of diphenylethane with poly- ethylbenzene(s) in the presence of a Fried el Crafts catalyst at ϋ-150°C. Preferred catalysts are aluminum chloride, aluminum bromide and boron trifluoride. Transethylation of 1 ,1 -diphenylethane by this method produces either 1 -phenyl- 1-ethylphenylethane, 1 -phenyl- 1-diethylphenylethane or 1 ,1-

10 bis(ethylphenyl)ethane. The ring positions of the ethyl substituents in the ethylated products are not disclosed.

Thus, until recently, no existing method was known for the highly selective production of 2,6-dialkylnaphthalene or of a mixture of 2,6- and 2,7- dialkylnaphthalenes by a transalkylation process. Then Hagen et al., U.S.

15 Patent No. 4,873,386, which issued on October 10, 1989, disclosed a method for producing 2,6-diethylnaphthalene, which comprises: reacting in the liquid phase at least one of naphthalene or 2-ethylnaphthalene as the feed with at least one of 1 ,4-diethylbenzene, 1 ,2,4-triethylbenzene, at least one tetra¬ ethylbenzene or pentaethylbenzene as the ethylating agent per mole of the

20 feed by weight, in the presence of a Lewis acid catalyst selected from the group consisting of aluminum chloride, aluminum bromide, tantalum pen- tachloride, antimony pentafluoride, and red oil, at a level of from about 0.01 to about 1 mole of the catalyst per mole of the feed (for red oil, based on the aluminum chloride content of the red oil) by weight and at a temperature in the

25 range of from about -10°C° to about 100°C. In particular, Hagen et al., disclose that 1 ,2,3,4- and 1 ,2,3,5-tetraethylbenzenes, as well as 1 ,2,4,5- tetraethylbenzene, are useful ethylating agents, but that hexaethylbenzene is not. Hagen et al. further disclose that 2,6-diethylnaphthalene is formed at a , higher selectivity and yield when 2-ethylnaphthalene is transethylated and that

^*" 30 pentaethylbenzene and any tetraethylbenzene are the preferred ethylating agents.

Furthermore, it has been discovered that the oxidation of 2,6-dialkyl¬ naphthalene proceeds with substantially less by-product formation when the alkyl groups are ethyl groups than when the alkyl groups are methyl groups,

35 and thus that the crude 2,6-naphthalene dicarboxylic acid formed by the oxidation of 2,6-diethylnaphthalene can be purified to polymer grade purity more readily than can crude 2,6-naphthalene dicarboxylic acid formed by the

oxidation of 2,6-dimethyinaphthalene. For this reason, the aforesaid trans¬ ethylation method of Hagen et al. is especially desirable.

However, because of the relative unavailability of 2-ethylnaphthalene compared to the greater availability of 2-methyinaphthalene for use as the preferred feedstock for the aforesaid method of Hagen et al., and because of the benefit in efficiency in oxidizing the 2,6-dialkylnaphthalene of the lowest possible molecular weight to 2,6-naphthalene dicarboxylic acid, it is highly desirable to devise a method for the Friedel-Crafts transethylation of 2-methyl¬ naphthalene to 2,6-methylethylnaphthalene. 2,6-Methylethylnaphthalene is a compromise oxidation feedstock which would afford the benefits of a 2,6- dialkylnaphthalene both having the next to the lowest molecular weight of any dialkylnaphthalene and having one ethyl substituent for oxidation with substantially less by-product formation. Thus, it is highly desirable to provide a method for producing 2,6-methylethylnaphthalene by transethylation of a more relatively available feedstock than 2-ethylnaphthalene.

It is also highly desirable to be able to prepare other ethylated naphtha¬ lene compounds such as, for example, 2-alkoxy- or 2-aryloxy-6-ethyl- naphthalenes, and specifically 2-methoxy-6-ethylnaphthaJene, by the selective ethylation of a 2-alkoxy- or 2-aryloxynaphthalene compound. 2-Methoxy-6- ethylnaphthalene is an intermediate useful for the synthesis of pharmaceutical compounds such as (S)-6-methoxy-a-methyl-2-naphthaleneacetic acid, also known as d-2-(6-methoxy-2-naphthyl) propionic acid, and commonly referred to as Naproxen. Naproxen is an analgesic and anti-inflammatory agent.

Q&jgctsQfThg Inv ntion

It is therefore a general object of the present invention to provide an improved method for the highly selective ethylation of methyl-, alkoxy-, and aryloxy-substituted naphthalene compounds using a transethylation reaction.

More specifically, it is an object of the present invention to provide an improved method for the highly selective production of 2,6-methylethyl¬ naphthalene or a mixture of 2,6- and 2,7-methylethylnaphthalenes by transethylating 2-methylnaphthalene under highly regiospeάfic conditions.

It is another object of the present invention to provide an improved method for the highly selective production of 2-alkoxy- or 2-aryloxy-6-ethyl- naphthalene compounds by transethylating a 2-alkoxynaphthalene or a 2- aryloxynaphthalene compound under regiospecific conditions, and particularly wherein the 2-alkoxynaphthalene is 2-methoxynaphthalene.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims.

Summary Qf The invention The present invention is a method for ethylating 2-methylnaphthalene, a

2-alkoxynaphthalene, or a 2-aryloxynaphthaiene as a feed compound, which comprises reacting the feed compound in the liquid phase with an ethylating agent comprising 1 ,2,4-triethylbenzβne, a tetraethylbenzene, pentaethylbenzene, or a mixture thereof at a level of from about 0.5 to about 10 moles of the ethylating agent per mole of the feed, in the presence of a catalyst comprising a Lewis acid or a Bronsted acid alkylation catalyst or mixture thereof, at a level of from about 0.01 to about 1 mole of the catalyst per mole of the feed, and at a temperature in the range of from about -10°C to about 100°C.

Detailed Description Of The Preferred Embodiments The feed compounds for the method of this invention are 2-methyl¬ naphthalene, 2-alkoxynaphthalenes and 2-aryloxynaphthanenes. The hydrocarbon portion of the alkoxy-moiety of the 2-alkoxynaphthalene contains 1 to about 20 carbon atoms and the hydrocarbon portion of the aryloxy-moiety of the 2-aryloxynaphthalene contains 6 to about twenty carbon atoms. For example, the hydrocarbon portion can be methyl, ethyl, isopropyl, phenyl, tolyl, etc. The two most preferred feed compounds for the method of this invention are, however, 2-methylnaphthalene and 2-methoxynaphthalene. When 2- methylnaphthalene is transethylated according to the method of this invention, 2,6-methylethylnaphthalene is produced. When 2-methoxynaphthalene is transethylated according to the method of this invention, 2-methoxy-6- ethylnaphthalene is produced.

Relative to the diβthylbenzenes and 1,2,3- and 1,3,5-triethylbenzenes, polyethylated benzenes having from 3 up to 5 ethyl substituents on the benzene ring, two of which are para to one another, afford substantially improved yields of the desired ethylated naphthalene in the method of this invention. Thus, 1 ,2,4-triethylbenzene, any tetraethylbenzene, pen¬ taethylbenzene, and mixtures thereof are the only suitable ethylating agents in the method of this invention. Since all tetraethylbenzenes have at least one pair of ethyl substituents that are in ring positions that are located para to each other, all tetraethylbenzenes are suitable ethylating agents in the method of this invention, and therefore, mixtures of tetraethylbenzene isomers need not

be separated and can be used as such as the ethylating agent in the method of this invention. Hexaethylbenzene forms an irreversible addition complex with the acid catalyst, and therefore, is not an effective ethylating agent. Preferably, a tetraethylbenzene, and more preferably 1 ,2,4,5-tetraethyl- benzene, is the ethylating agent in the method of this invention. The mole ratio of the ethylating agent to 2-methyl-, 2-alkoxy-, or 2-aryloxy-feβd compound is in the range of from about 0.5:1 , preferably from about 2:1, to about 10:1, preferable to about 5:1 , in the method of this invention.

As described hereinabove, the ethylating agent used in the transethy- lation reaction of this invention can be 1 ,2,4-triethylbenzene, any tetraethyl¬ benzene, pentaethylbenzene, or mixtures thereof. It is most convenient, however, to use a mixture of these polyethylated benzene compounds as the ethylating agent. A mixture is easily prepared and a separation step is not required. The mixture of polyethylated benzenes is suitably prepared by ethylating benzene or, preferably, a partially ethylated benzene compound such as ethylbenzene, diethylbenzene or triethylbenzene. Benzene or the partially ethylated benzene compound is ethylated with ethylene in the presence of a Lewis acid catalyst and, preferably, a promoter such as hydrogen chloride, hydrogen bromide, ethyl bromide or chloride. The ethylene is added until the desired mixture of polyethylated benzene compounds is produced. It is most desirable to continue the ethylation until the concentration of tetraethylbenzene is maximized. For example, a suitable mixture of polyethylated benzenes contains about 20 weight percent triethylbenzene, about 70 weight percent tetraethylbenzene and about 5 weight percent pentaethylbenzene. The polyethylated benzene mixture is preferably at least 70 weight percent tetra- and pentaethylbenzene, and it is most preferred for the tetraethylbenzene to be at least 50 weight percent of the polyethylated benzene mixture.

The transethylation reaction of the present invention is conducted in the liquid phase in the presence or absence of a solvent. Any liquid that is inert under the reaction conditions employed and serves as an effective solvent for the reactants and products is suitable for use in the method of this invention. Suitable solvents include haiocarbons, such as methylene chloride, chlorobenzene, 1,1-dichioroethane, 1 ,2-dichloroethane, and chloroform, or carbon disulfide, benzene, cyclohexane, and n-octane. Solvents which are basic and bind irreversibly with the catalyst are not suitable. Such unsuitable solvents include ketones, aldehydes, ethers, esters and alcohols. Preferably, the solvent is methylene chloride. If a solvent is employed, the weight ratio of

solvent-to-feed compound is in the range of from about 1 :1 , preferably from about 2:1 , to about 15:1 , preferably to about 8:1.

Lewis acids and Bronstβd acids or mixtures thereof that are conventionally used as alkylation catalysts are suitable for use as the catalyst in the method of this invention. Suitable Lewis acid catalysts include aluminum chloride, aluminum bromide, tantalum pentachloride, antimony pentafluoride, boron trichloride, ferric bromide, ferric chloride, sulfonated zirconia, trifluoromethanesulfonic acid, titanium chloride, antimony chloride, tin chloride, and "red oil," a complex polar liquid catalyst phase which is synthe- sized for example by the addition of ethyl chloride or bromide or hydrogen chloride or bromide to a slurry of aluminum chloride or some other aforesaid suitable Lewis Acid in an aromatic solvent such as benzene, methylbenzene, ethylbenzene, mixed dimethylbenzenes, mixed diethylbenzenes, mixed tetramethylbenzenes, mixed tetraethylbenzenes or mixed polyethylated benzenes and which forms a separate liquid phase below the phase containing the feed. Preferably, aluminum chloride or red oil containing aluminum chloride is the catalyst. For the ethylation of 2-methylnaphthalene according to the method of this invention, it is preferable that the alkylation catalyst be more acidic than ferric chloride and preferably at least as acidic as ferric bromide. For example, antimony chloride, bismuth chloride, ferric chloride, tin chloride, titanium chloride and zinc chloride are not such effective catalysts for the ethylation of 2-methylnaphthalene.

The catalyst can be employed as a separate immiscible layer such as the aforementioned red oil, or it can be dissolved with the reactants and products in an organic solvent such as methylene chloride or chiorobenzene. Thus, depending upon the selection of solvent for the catalyst, the feed, ethylating agent and catalyst can be present in a single liquid phase, or the feed and catalyst can be present in separate liquid phases. In the alternative, the catalyst can be in the form of a solid, for example, aluminum chloride deposited or intercalated with graphite. The catalyst is employed in the method of this invention at a level in the range of from about 0.01 , preferably from about 0.05, to about 1.0, preferably to about 0.3 mole per mole of 2- methy-, 2-alkoxy-, or 2-aryloxynaphthalene feed compound.

If the reaction is performed continuously or batchwise, the residence time is from 0.1, preferably from about 1 , to about 20, preferably to about 5 hours. The reaction temperature for the ethylation of 2-methylnaphthalene is in the range of from about -10°C, preferably from about -5°C, to about 100°C, prefer¬ ably to about 50°C. This reaction temperature for the ethylation of the 2-

alkoxy- and 2-arylσxynaphthalene compounds is in the range of about -10°C, preferably from about 10°C to about 100°C, preferably to about 80°C. The reaction pressure must be sufficiently high to maintain the reactants and products in the liquid phase at the particular reaction temperature employed and generally is in the range of from about 0.5, preferably from about 0.8, to about 10, preferably to about 5, atmospheres absolute.

Preferably, when a polar solvent is not used, a hydrogen haiide, such as hydrogen chloride, or an alkyl, alkylene or alkyiidene haiide is employed as a promoter in the method of the present invention. Typically, such alkyl, alkylene, or alkyiidene halides include a methyl haiide, such as methyl chloride, or a methylene, ethylene, or ethylidene haiide. The promoter is employed at a level of from about 0.1, preferably from about 0.5, up to about 100, preferably up to at least about 2 moles per mole of catalyst (for red oil, based on the aluminum chloride content of the red oil). When the solvent is an alkyl or alkylene haiide, it also serves as a promoter in the method of the invention.

The 2-methoxynaphthalene feed for the method of this invention can be prepared by methyiating 2-naphthol by any one of a number of techniques known in the art such as, for example, the reaction of the alkali or other metal salt of 2-naphthol with a methyiating agent such as methyl iodide or dimethyl sulfate and using a suitable solvent. Alternatively 2-methoxynaphthalene can be purchased from, for example, the Aldrich Chemical Company, Milwaukee, Wisconsin.

The 2,6-methylethylnaphthalene and 2-methoxy-6-ethylnaphthalene prepared by the method of this invention are suitably isolated from the reaction mixture by first quenching the alkylation catalyst with, for example, water, optionally containing a caustic component, or with an alcohol such as methanol. Optionally, the catalyst layer can be first separated from the reaction mixture and recycled. However, for the ethylation of 2-methoxy- naphthalene we have found that the catalyst layer incorporates a substantial portion of the desired 2-methoxy-6-ethylnaphthalene product and, consequently it is desirable to quench the catalyst layer in order to recover the 2-methyoxy-6-ethylnaphthalene contained therein.

After the reaction mixture is quenched, the reaction product is typically subjected to a distillation procedure, preferably fractional distillation, to isolate the desired product-containing fraction. Un reacted feed material and un reacted ethylating agent can be recycled. For example, recovered ethylbenzene, diethylbenzenes and triethylbenzenes can be re-ethylated to

form tetra- and pentaethylbenzene. The product-containing fraction may contain other isomers in addition to the desired 2,6-isomer. For example, the distillation of the product produced by the ethylation of 2-methoxynaphthalene according to the method of this invention produces a product fraction containing a major amount of 2-methoxy-6-ethylnaphthalene and a minor amount of 2-methoxy-3-ethylnaphthalene. The desired 2,6-isomer in the product-containing fraction, e.g., 2,6-methylethylnaphthalene or 2-methoxy-6- ethyl naphthalene, is isolated in pure form using a recrystallization procedure.

Low molecular weight mono-hydric alcohols having 1-6 carbon atoms, and preferably methanol, ethanol or isopropanol, are suitable recrystallization solvents. Methanol is the most preferred recrystallization solvent. Recrystallization from a low molecular weight alcohol such as methanol provides for the desired 2,6-isomer in pure form, for example, a purity of about 99.5% or greater can be obtained. The 2-methoxy-6-ethylnaphthaiene produced by the transethylation of 2- methoxynaphthalene according to the method of this invention can be dehydrogenated to prepare 2-methoxy-6-vinylnaphthalene. In a preferred method for this dehydrogenation reaction, 2-methoxy-6-ethylnaphthalene is reacted with N-bromosucciπimide in a non-polar solvent such as carbon tetra- chloride to form a brominated intermediate (2-methoxy-6-(1-bromoethyl) naphthalene). This brominated intermediate is either thermally or catalytically dθhydrobrominated to produce the vinyl compound, 2-methoxy-6-vinylnaph- thalene. The dehydrobromination can be , conducted using the isolated brominated intermediate by reacting the brominated intermediate with a base catalyst such as pyridine, or by simply heating the brominated intermediate to eliminate hydrogen bromide.

2-Methoxy-6-vinylnaphthalene is a compound of considerable importance. 2-Methoxy-6-vinylnaphthalene may be converted to 6-methoxy-α- methyl-2-naphthalene acetic acid (also known as 2-(6-methoxy-2-naphthyl) propronic acid). One method effective for such conversion utilizes the reaction of carbon monoxide with 2-methoxy-6-vinylnaphthalene either catalyzed by a transition metal catalyst or strong acid, or both. The reaction of carbon monoxide with produces racemic 6-methoxy-α- methyl-2-naphthaiene acetic acid. Racemic 6-methoxy-α-methyl-2- naphthalene acetic acid is used to prepare Naproxen.

The present invention will be more clearly understood from the following specific examples:

Examples 1-3

Except as indicated hereinbelow, each of Examples 1 -3 was performed using a 250 miililiter, 3-neck, round-bottom flask equippeα with a magnetic stirrer, purged with nitrogen and cooled in an ice bath. The components of the reaction mixture that are identified in Table 1 were introduced in the amounts and under the reaction conditions specified in Table 1. In each case, the catalyst was introduced last, at which point the transethylation reaction commenced immediately. Twenty-four hours after the catalyst was introduced, methanol, in a volume that was approximately twice the volume of the reaction medium, was introduced to quench the reaction. The product mixture was then analyzed to determine the weight percent of benzene, toluene, or 2- methylnaphthalene (identified as 2-MN, in Table 2) that is converted ("Conversion of 2-MN"), the "Yield" or mole percent of 2-methylnaphthalene that is converted selectively to each of 2,6-methylethylnaphthalene (identified as 2,6-MEN) and 2,7-methyiethylnaphthalene (identified as 2,7-MEN), and the "Selectivity" or relative mole percent of 2,6-methylethylnaphthaiene and 2,7- methlethyinaphthalene in the combined amounts of products produced in each example. The Yield is also the quotient obtained by dividing 100 into the product of the Conversion multiplied by the Selectivity. In Table 1 , TeEB means a mixture of tetraethylbenzene isomers.

Table 1 Et ytatjnota rt Catataβ Promoter

Exp. riBQCfon

No Feed Compound Amount ¹ Compound Amount ¹ Temp(*C) Solvent Compound Amount ²

1 2-MN TβS 2 AlClj 0.26 40 None EtBr 0.26/11.357

2 2-MN TeEB 2 AICI3 0.25 90-60 None EtBr 0.25/11.868

3 2-MN TeEB 2 AICI3 0.26 50-35 None EtBr 0.26/11.354

¹ moles per mole of 2-MN ² moles per actual number Of moles of 2-MN used

The results in Table 2 illustrate that, regardless of the differences in the resulting reaction rates, the use of different reaction temperatures affords similarly high yields of 2,6-methylethylnaphthalene provided that the reaction is permitted to proceed for sufficiently long times. In addition, the use of relatively lower reaction temperatures affords the highest and most favorable

ratios of the amount of 2,6-methylethylnaphthalene produced-to-the amount of 2,7-methylethylnaphthalene produced.

The following is a procedure for preparing 2-methoxy-6-ethylnaphtha- lene by the transethylation of 2-methoxynaphthalene.

To a 250 ml., 3-neck, round-bottom flask equipped with a magnetic stirrer and a sparge tube were added 70 g of mixed diethylbenzenes obtained from the Aldrich Chemical Company, Milwaukee, Wisconsin. After cooling the reaction mixture with an ice bath hydrogen chloride gas was added for three minutes and thereupon 14.48 grams of aluminum chloride were slowly added. Hydrogen chloride gas was again added for three minutes. The reaction flask was then placed in a hot water bath to raise the temperature of the reaction mixture to 85-90°C. At this point ethylene gas was sparged into the reaction mixture until the level of tetraethylbenzene in the reaction mixture was

maximized. The composition of the mixture was monitored by gas chromatog- raphy. After the ethylene addition was stopped, the reaction mixture was stirred for an additional 30 minutes at 90°C.

To the above reaction mixture at 15°C was added a mixture of 29.02 grams of 2-methoxynaphthalene dissolved in 50 ml of dichloromethane. The reaction mixture was permitted to warm to room temperature and after 900 minutes it was heated to 32°C using a water bath. After 15 hours total reaction time the yield of 2-methoxy-6-ethylnaphthalene was 71.5% as measured by gas chromatography. This example shows the high yield of 2-methyoxy-6-ethylnaphthalene that can be achieved by the method of this invention.

Example 5 Polyethylbenzene was prepared as follows: To a 12 liter flask fitted with a nitrogen purge, stirrer and sparge tube was charged with 3634 grams of 95% mixed diethylbenzenes (from Aldrich Chemical Company, Milwaukee, Wl.) and 540 grams of anhydrous aluminum chloride. Into this mixture was sparged anhydrous hydrogen chloride until the aluminum chloride was saturated with hydrogen chloride. During this addition of hydrogen chloride the temperature of the mixture increased to about 38°C. This reaction mixture was then sparged with ethylene until the amount of tetraethylbenzene in the reaction mixture reached about 58-60 weight percent. During this period the temperature of the reaction mixture increased to about 85°C and it was maintained at this temperature during the addition of the ethylene using a water bath. After the addition of ethylene the mixture was maintained at approximately 90°C for one hour. When the stirrer was stopped the product mixture formed a lower, "red oil" layer weighing 1371 grams and an upper, polyethylbenzene layer weighing 4197 grams. Analysis by gas chromatography indicated that the polyethylbenzene layer was 0.2 weight percent diethylbenzene (DEB), 22.0 weight percent triethylbenzene (TrEB), 73.2 weight percent tetraethylbenzenes (TeEB) and 4.6 weight percent pentaethylbenzene (PEB). This mixture of polyethylbenzene was used in ethylation reactions described below.

Example 6

2-Methoxynaphthalene was ethylated using the mixture of polyethyl- benzene prepared according to Example 5. The reaction was conducted in a

500 ml flask equipped with a stirrer and nitrogen gas inlet tube. The flask was charged with 250 grams of the polyethylbenzene mixture (183 grams of tetraethylbenzene) and 25.7 grams of anhydrous aluminum chloride, and the

mixture was sparged with gaseous hydrogen chloride. To this mixture, with stirring, was added 76 grams of 2-methyoxynaphthalene. The temperature was maintained at 40°C. The reaction mixture was sparged at 1 hour intervals with hydrogen chloride. At the end of the reaction the reaction mixture was quenched with water and the product layer analyzed by gas chromatography using a 12.5 meter capillary chromatography column having a crosslinked dimethylsilicone stationary phase. By-products were identified using gas chromatography/mass spectroscopy. When the stirring was stopped either during or at the end of the rection, the reaction mixture separated into an upper, organic layer and a lower, catalyst-containing layer.

The results are reported in Table III. In this table, and in the following tables, "2-MON" is 2-methoxynaphthalene, "N" is naphthol, "2,6-EMON" is 2- methoxy-6-ethylnaphthalene, "2,3-EMON" is 2-methoxy-3-ethylnaphthene, "EN" is ethylnaphthol, "MEMON" is methylethylmethoxynaphthalene, "DEMON" is diethylmethoxynaphthalene and "CD" is a by-product mixture believed to be mainly the product formed by the condensation of a polyethylbenzene, particularly a tetraethylbenzene, with 2-methoxynaphthalene. The reported conversion (Conver.) is the weight percent 2-methoxynaphthalene consumed. The "Selectivity" is the weight percent of the 2-methoxynaphthalene consumed that is converted to the listed products.

Iabls ll

Reaction Temperature: 40°C

Molar Feed Ratio: TeEB/2-MON/AICI ₃ = 2/1/0.4

at room temperature wt out st r ng. n er t ese con t ons there was a phase separation with the lower layer "red oil" containing the catalyst. The reaction rate was very low under these conditions.

Example 7 The procedure of Example 6 was repeated except the reaction temper¬ ature was 80°C. The results are reported in Table IV.

A comparison of the data in Table III with the data in Table IV demonstrates that at a temperature of 40°C the reaction time is longer but a higher selectivity to 2-methyoxy-6-ethylnaphthalene (2,6-EMON) is obtained at equivalent conversion of 2-MON.

Table IV

Reaction Temperature: 80°C

Molar Feed Ratio: TeEB/2-MON/AICI ₃ = 2/1/0.4

at room temperature wt out st r ng. n er t ese con tons t ere was a phase separation with the lower layer "red oil" containing the catalyst. The reaction rate was very low under these conditions. c) Analysis of the combined upper and lower layers.

Example 8

Table V provides the data derived from a series of reactions conducted similarly to that described in Examples 6 and 7 except that the amount of aluminum chloride catalyst was varied from 0.1 to 0.4 moles per mole of 2- methoxynaphthalene. The reaction temperature was 80°C. The data in Table V demonstrate that reduced catalyst loading increases the time required to achieve 50% conversion. At a ratio of 0.1 moles of catalyst per mole of 2-methoxynaphthalene, a conversion of only 33% was achieved after 40 hours reaction time. Suitable reaction rates were achieved when the ratio of catalyst to 2-methoxynaphthalene was in the range of 0.2 to 0.4.

2/1/0.4 1.1 55.5 66.3

2/1/0.2 2.0 50.6 66.0

2/1/0.1 40.2 32.6 57.0

Example 9 Table VI provides the data derived from a series of reactions conducted similarly to that described in Examples 6 and 7 except the amount of tetraethylbenzene ethylating agent was varied from 0.5 mole to 4.0 moles per mole of 2-methoxynaphthalene. The reaction temperature was 60°C.

These data demonstrate that higher ratios of ethylating agent (i.e., tetraethylbenzene) to 2-methoxynaphthalene result in improved selectivity to 2-methoxy-6-ethylnaphthalene (2,6-EMON).

Table VI

Molar Feed Ratio Selectivitva % eEB/2-MQN/AICI ₃ ) 2.6-EMQN 2,3-EMQN tL QZMQh Q_

0.5/1/0.2 56.5 8.2 3.4 5.6 26.2

1/1/0.2 66.2 6.7 5.7 7.9 13.5

2/1/0.2 70.3 5.9 7.4 6.6 9.6

4/1/0.2 74.1 5.0 4.5 8.3 8.1

a) These data are at a 2-MON conversion of about 50%.

From the above description, it is apparent that the objects of the present invention have been achieved. While only certain embodiments have been set forth, alternative embodiments and various modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of the present invention.