This invention relates to the production of a dieth- ylnaphthalene and more particularly concerns the highly selective production of 2,6-diethylnaphthalene by the transethylation of naphthalene or 2-ethylnaphthalene by 1,4-diethylbenzene, 1,2,4-triethylbenzene, at least one tetraethylbenzene or pentaethylbenzene.

Description of the Prior Art

Naphthalene dicarboxylic acids are monomers that are known to be useful for the preparation of a variety of polymers. For example, poly(ethylene 2,6-naphthalate) prepared from 2,6-naphthalene dicarboxylic acid and ethyl- ene glycol has better heat resistance and mechanical prop¬ erties than polyethylene terephthalate and is useful in the manufacture of films and fibers.

Diethylnaphthalenes are desirable feedstocks for oxi¬ dation to the corresponding naphthalene dicarboxylic acids. A known conventional process for producing a naphthalene dicarboxylic acid comprises the oxidation of a diethylnaphthalene with oxygen in the liquid phase in an acetic acid solvent at an elevated temperature and pres¬ sure and in the presence of a catalyst comprising cobalt, manganese and bromine components.

Diethylnaphthalenes can be found in low concentra¬ tions in refinery streams as mixtures of some or all of the ten possible diethylnaphthalene isomers. However, separation of these isomers is very difficult and expen- sive. Consequently, methods for producing specific dieth¬ ylnaphthalenes or mixtures of two or three specific diethylnaphthalenes in high purity and quality are highly desirable. One such method is disclosed in Japanese Kokai Patent Application Publication No. 61-83137 (April 26, 1986) and is a synthesis involving the transalkylation of naphthalene or a 2-methylnaphthalene in the presence of an aluminum chloride catalyst at 0-35°C in the liquid phase

SH£€1

to produce a 2,6-dialkylnaphthalene. Suitable alkylating agents are disclosed as including durene, diethylbenzene, triethylbenzene, triisopropylbenzene and isopropylxylene dibutylbenzene. The reported results indicate a rela- tively low degree of selectivity for the formation of specific dialkylnaphthalenes.

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. The Japanese patent discloses that reaction temperatures of less than 70°C delay the reaction rate.

The ring positions of the ethyl substituents in the ethyl- ated biphenyl products are not disclosed. Suitable ethyl- benzenes include ethylbenzene, diethylbenzene, triethylbenzene, tetraethylbenzene, other ethyl-substi¬ tuted benzenes, ethyltoluene,, diethyltoluene and other ethyl-substituted toluenes. Polyethylbenzenes containing relatively small amounts of monoethylbenzene, triethylben¬ zene and tetraethylbenzene can also be used advanta¬ geously.

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 ethylbenzene or ethylxylenes to form monoethylnaphthalenes in the presence of an aluminum chloride catalyst at 20-30°C. The rates of transethylation with ethylxylene isomers were reported to decrease in the order of l,2-dimethyl-4-ethylbenzene >, l,3-dimethyl-4-ethylbenzene >, 1,4-dimethyl-2-ethylbenzene > l,3-dimethyl-5-ethylbenzene.

Thus, no existing method is known for the highly selective production of 2,6-diethylnaphthalene or a mix- ture of 2,6- and 2,7-diethylnaphthalene by a transethyla¬ tion process.

OBJECTS OF THE INVENTION It is therefore a general object of the present invention to provide an improved method for the highly selective production of 2,6-diethylnaphthalene or a mix- ture of 2,6- and 2,7-diethylnaphthalene.

More specifically, it is an object of the present invention to provide an improved method for the highly selective production of 2,6-diethylnaphthalene or a mix¬ ture of 2,6- and 2,7-diethylnaphthalene by transethylating naphthalene or 2-ethylnaphthalene under highly regeospe- cific conditions.

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

SUMMARY OF THE INVENTION These objects are achieved by an improved method for producing 2,6-diethylnaphthalene, comprising: reacting in the liquid phase at least one of naphthalene or 2-ethyl¬ naphthalene as the feed with at least one of 1,4-diethyl- benzene, 1,2,4-triethylbenzene, at least one tetraethylbenzene or pentaethylbenzene as the ethylating agent at a level of from about 1 to about 10 moles of the ethylating agent per mole of the feed by weight, in the presence of a Lewis acid catalyst selected from the group consisting of aluminum chloride, aluminum bromide, tanta¬ lum chloride, antimony fluoride, 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 content of aluminum chloride content of the red oil) by weight and at a temperature in the range of from about -10°C to about 100°C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Naphthalene or 2-ethylnaphthalene or mixtures thereof are suitable for use as the feed in the method of this invention. Preferably the feed comprises 2-ethylnaphthal¬ ene. As illustrated in the examples hereinbelow, relative to 1,2- and 1,3-diethylbenzenes, 1,2,3- and 1,3,5-triethylbenzenes, and hexaethylbenzene, polyethy- lated benzenes having from 2, preferably from 3, up to 5 ethyl substituents on the benzene ring, two of which are para to one another afford substantially improved yields of 2,6- and 2,7-diethylnaphthalenes in the method of this invention. Thus, 1,4-diethylbenzene, 1,2,4-triethyl- benzene, any tetraethylbenzene, pentaethylbenzeney- and mixtures thereof are the only suitable ethylating agents in the method of this invention. Since all tetraethylben- zenes 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 addi¬ tion complex with the acid catalyst and therefore does not work in the preferred method of this invention.

The mole ratio of the ethylating agent-to-naphthalene and/or 2-ethylnaphthalene feed is in the range of from about 1:1, preferably from about 2:1, to about 10:1, pref¬ erably to about 5:1, in the method of this invention. 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 halocarbons, such as methylene chloride, chloro- benzene, 1,1-dichloroethane, 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 sol¬ vents include ketones, aldehydes, ethers, esters and alco- hols. Preferably the solvent is methylene chloride. If a solvent is employed, the weight of solvent-to-feed com¬ pound is in the range of from about 1:1, preferably from about 2:1, to about 15:1, preferably to about 8:1.

Certain specific Lewis acids are suitable for use as the catalyst of the method of this invention. Suitable Lewis acid catalysts include aluminum chloride, aluminum bromide, tantalum pentachloride, antimony pentafluoride, boron trichloride, and "red oil," a complex polar liquid catalyst phase which is synthesized by addition of ethyl chloride or bromide to a slurry of aluminum chloride or some other aforesaid suitable Lewis Acid in an aromatic solvent such as benzene, ethylbenzene, or mixed diethyl- benzenes or mixed tetraethylbenzenes. Preferably aluminum chloride is the catalyst. The catalyst can be employed either dissolved in a suitable solvent or in an immiscible phase in a hydrocarbon medium.

Other conventional Lewis acids such as antimony chlo¬ ride, bismuth chloride, ferric chloride, tin chloride, titanium chloride, zinc chloride and zirconium chloride are not effective catalysts in the preferred method of the present invention. Ethyl bromide and ethyl chloride are useful promoters.

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 0.2 mole per mole of the total of naphthalene and 2-ethylnaphthalene employed.

If the reaction is performed continuously or batch- wise, the residence time is from about 0.1, preferably from about 1, to about 10, preferably to about 5 hours. The reaction temperature is in the range of from about -10°C, preferably from about -5°C, to about 100°C,

preferably to about 20°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 gauge.

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

Examples 1-34

Except as indicated hereinbelow, each of Examples 1-34 was performed using a 250 milliliter, 3-neck round bottom flask equipped with a magnetic stirrer, purged with nitrogen and cooled in an ice bath. The components of the reaction mixture that are identified in Tables 1, 3 and 5 were introduced in the amounts specified in Tables 1, 3 and 5. In each case, the catalyst was introduced last, at which point the transethylation reaction commenced imme¬ diately, and essentially identical reaction conditions were employed in each example. 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 combined weight percent of naphthalene (identified as Np in Tables 2, 4 and 6), and 2-ethylnaphthalene (identified as 2-ENp in Tables 2, 4, and 6) that is converted, the combined weight percent of naphthalene and 2-ethylnaphthalene that is converted selectively to 2,6- and 2,7-diethylnaphthalenes (identi- fied as 2,6-DENp and 2,7-DENp, respectively, in Tables 2, 4, and 6) combined, and the relative concentrations of each of 2,6-diethylnaphthalene and 2,7-diethylnaphthalene in the combined amounts of 2,6-diethylnaphthalene and 2,7-diethylnaphthalene produced in each example.

TABLE 1

Amounts of Components Employed in Reaction Mixture

2-Ethyl- 1,4- Example Naphtha- naphtha- Aluminum Methylene Diethyl-

No. lene lene Chloride Chloride benzene

In millimoles, except in milliliters for methylene chloride

SUBSTITUTE

TABLE 1 (Cont'd.) Amounts of Components Employed in Reaction Mixture

1,2- 1,3- 1,2- 1,2,4- Dimethyl-

Example Diethyl- Ethyl- Triethyl- 4-ethyl No. benzene benzene benzene benzene

1 2

3

4 50.94

5 50.94

6 38.20 7 , 39.48

8 9

10

11 12

13

14

15

16

Footnotes

In millimoles, except in milliliters for methylene chloride

1

2

1 In millimoles, except in milliliters for methylene chloride

2 A mixture of 72 weight percent of tetraethylbenzenes 0 and 21 weight percent of pentaethylbenzene.

5

SUBSTITU

converted to 2,6- or 2,7-DENp

Product of conversion and selectivity to 2,6- or

2,7-DENp

TABLE 2 (Cont'd)

converted to 2,6- or 2,7-DENp

Product of conversion and selectivity to 2,6- or

2,7-DENp

TABLE 2 (Cont'd.)

converted to 2,6- or 2,7-DENp

Product of conversion and selectivity to 2,6- or

2,7-DENp

TABLE 3

Amounts of Components Employed in Reaction Mixture

2-Ethyl- 1,4-Di Tetra- Example Naphtha- naphtha- ethyl- ethyl- Methylene

No. lene lene benzene benzene Chloride

1 In millimoles, except in milliliters for methylene chloride

2 Carbon disulfide instead of methylene chloride

3 Benzene instead of methylene chloride

UBS I U E SHEET

TABLE 3 (Cont'd.) Amounts of Components Employed in Reaction Mixture

Example Aluminum Tantalum Zinc Stannic Titanium .5 No. Bromide Chloride Chloride Chloride Chloride

17 2.54

18 6.37

19 2.54

10 20 2.54

21 2.54

22 2.54 23

24 15 25 26 27 28 29 „ 20 30 31

Footnotes

1 In millimoles, except in milliliters for methylene 25 chloride

2 Carbon disulfide instead of methylene chloride

3 Benzene instead of methylene chloride

4 Contains additionally 2.54 - 3.81 millimoles of ethyl bromide as a promoter

30

35

TABLE 3 (Cont'd.) Amounts of Components Employed in Reaction Mixture ς Example Antimony Antimony Ferric Bismuth Zirconium Red No. Chloride Fluoride Chloride Chloride Chloride Oil

17 18 19 20 21 22

23 2.54

24 3.57 ^~ -_^r7- 25 8.27

26 12.73

27 2.54

28 1.27

29 2.54 ⁴ 30 2.54 ⁴

31 2.54 ⁴

Footnotes

1 In millimoles, except in milliliters for methylene chloride

2 Carbon disulfide instead of methylene chloride

3 Benzene instead of methylene chloride

4 Contains additionally 2.54 - 3.81 millimoles of ethyl bromide as a promoter 5 Millimoles of aluminum chloride in red oil

SDBsrrruTE SHEET

TABLE 4

Conversion

Reaction of Selectivity to Yield of

1 Time ^"1" Np + 2-Np 2,6-DENp 2,7-DENp 2,6-DENp 2,7-DENp Example 17

70.5 29.5 3.67 1.53 63.9 36.1 11.18 6.32 53.2 44.4 20.48 17 .09 40.1 40.7 23.18 23 .52

45.8 42.4 6.64 6 .14 42.6 45.0 8.86 9 .36 33.4 47.5 12.06 17.15

42.9 25.2 10.77 6.33

41.6 27.0 14.89 9.67 42.6 31.7 19.30 14.36

Footnotes 1 Minutes

2 Weight percent of feed compound converted

3 Weight percent of feed compound converted that is converted to 2,6- or 2,7-DENp

4 Product of conversion and selectivity to 2,6- or 2,7-DENp

TABLE 4 ( Cont ' d . )

Conversion'

Reaction ooff Selectivity to Yield of

Time ¹ Np + 2-Np 2,6-DENp 2,7-DENp 2,6-DENp 2,7-DENp

1 Minutes

2 Weight percent of feed compound converted

3 Weight percent of feed compound converted that is converted to 2,6- or 2,7-DENp

4 Product of conversion and selectivity to 2,6- or 2,7-DENp

TABLE 4 (Cont'd.)

converted to 2,6- or 2,7-DENp

Product of conversion and selectivity to 2,6- or

2,7-DENp

TABLE 5 Amounts of Components Employed in Reaction Mixture

2-Ethyl- 1,4-Di- Tetra- Example Naphtha- naphtha- ethyl- ethyl- Aluminum No. lene lene benzene benzene Chloride

1.27 1.27

38.20 1.27

1 In millimoles, except n milliliters for methylene chloride

lUBSTJTUTE

TABLE 5 ( Cont ' d . ) Amounts 1 of Components Employed in Reaction Mixture

Carbon 1,2-Di- Example Aluminum Disul- Chloro- chloro- No. Bromide fide Benzene benzene ethane

25

25

25 25

10

1 In millimoles, except in milliliters for methylene chloride

US

TABLE 6

Conversion

Reaction of Selectivity to Yield of Time Np + 2-Np 2,6-DENp 2,7-DENp 2,6-DENp 2,7-DENp

48.3 18.2 31.15 18.26

Footnotes

1 Minutes 2 Wt. % of feed compound conv.

3 Wt. % of feed compound conv. that is converted to 2,6- or 2,7-DENp

4 Product of conv. & select, to 2,6- or 2,7-DENp

SUBSTITUTE: SHEET

Comparison of the results from Examples 1-16, 32 and 33 illustrates that the superiority of tetra- and pentae- thylbenzenes as selective ethylating agents and the supe¬ riority within the same compound class of p-substituted isomers over their non-parasubstituted isomers. Compar¬ ison of the results from Examples 1-3 illustrates that the effect of the ratio of ethylating agent-to-feedstock com¬ pounds on activity, with higher such ratios affording higher activity and reaction rates. Comparison of the results from Examples 9-12 illustrates (1) higher cata¬ lytic activity at higher catalyst loadings but with little change in selectivity and (2) higher selectivity and yield with 2-ethylnaphthalene present in the feed. Comparison of the results from Examples 13-14 illustrates that a mix- ture of tetraethylbenzenes prepared by the ethylation of a lower ethylbenzene with ethylene is a suitable ethylating agent for the selective production of 2,6-diethylnaphthalene.

Example 15 illustrates that pentaethylbenzene, like - tetraethylbenzenes, is a highly selective ethylating agent in the method of the present invention. Comparison of the results from Examples 17-31 illustrates that Lewis acids that are at least as acidic as aluminum chloride exhibit significant activity for the production of 2,6-diethylnaphthalene. Comparison of the results from Examples 17-18 illustrates that soluble catalysts in non- polar solvents are ^' effective in the method of this invention for the production of 2,6-diethylnaphthalene. The results of Examples 19 and 24 illustrate that tanta- lum, pentachloride and antimony pentafluoride, although less active than aluminum chloride, are more selective than aluminum chloride and afford high ratios of 2,6- to 2,7-diethylnaphthalene.

Comparison of the results from Examples 25-28 illus- trates that ferric chloride, bismuth chloride and zirco¬ nium chloride are inactive under the reaction conditions employed. Comparison of the results from Examples 29-31

illustrates that "red oil"—complexes of aluminum chloride with an alkyl halide (or with hydrogen chloride and an olefin) and an aromatic compound are highly selective cat¬ alysts in the present invention. Examples 17, 18, 29-31 and 32-35 illustrate that the method of the present invention can be carried out as either (1) a homogeneous catalytic reaction in a solvent in which both the catalyst and reactants are dissolved or (2) a heterogeneous catalytic reaction with either a non- polar solvent or no solvent, in which case the catalyst comprises a polar liquid phase—for example red oil—which exhibits little or no solubility for the reactants.

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, alter¬ native embodiments and various modifications will be apparent from the above description to those skilled in the art. These alternatives are considered equivalents and within the spirit and scope of the present invention. Having described the invention, what is claimed is:

SU&STΓΓUTE SHEE