US3247247A

US3247247A - Preparation of naphthalene carboxylic acids from alkyl-substituted tetrahydronaphthalenes

Info

Publication number: US3247247A
Application number: US273838A
Authority: US
Inventors: Henry J Peterson; William D Vanderwerff; Archibald P Stuart
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1963-04-18
Filing date: 1963-04-18
Publication date: 1966-04-19
Anticipated expiration: 1983-04-19

Description

United States Patent Ofiice 3,247,247 Patented Apr. 19, 1956 This invention relates to the production of oxidation products of aromatic compounds, and more particularly relates to a novel method of preparing naphthalene carboxylic acids by the oxidation of the corresponding alkylsubstituted tetrahydronaphthalenes.

The oxidation of tetrahydronaphthalene and its alkyl derivatives is known in the prior art. Thus, for example, it is known to treat tetrahydronaphthal'e'ne with oxygen. Also, tetrahydronaphthalene has been oxidized with nitric acid. In each case, however, thea-carbon atom of the saturated ring has been attacked, thus resulting in the production of tetrahydronaphthalene hydroperoxide and its decomposition products, tetralone and tetralol. At times, ring rupture has also occurred, giving tetralic acid, phthalic acid and the like.

It has now been found in accordance with the present invention, that alkyl tetrahydronaphthalenes may be converted to the corresponding naphthalene carboxylic acids, with little or no conversion of the starting material to its less desirable decomposition products, by oxidizing these alkyl tetrahydronaphthalenes with N0 gas at elevated temperatures in the presence of Se0 and a solvent which is substantially inert to N0 By oxidizing these alkyl tetrahydronaphthalenes in this manner, it has been found that, most surprisingly and unexpectedly, a simultaneous dehydrogenation of the saturated ring together with oxidation of the alkyl groups to the corresponding carboxylic acid thus occurs.

This invention may be practiced on relatively pure alkyl tetrahydronaphthalene such as the monoalkyl, dialkyl, or trialkyl compounds, in which case the corresponding mono, di-, or tricarboxylic acid will be formed. Alkyl groups having from about l-6 carbon atoms are satisfactorily employed, as for example methyl, ethyl, n-propyl, isopropyl, n-butyl groups or the like, but in each case, regardless of the length of the alkyl side chain, only the naphthalene carboxylic acid having a -COOH group attached directly to the ring nucleus is formed. Preferably, a dialkyl tetrahydronaphthalene such as 2,6-dimethyl tetrahydronaphthalene, 1,5-dimethyl tetrahydronaphthalene or the like is employed as the starting material, but other alkyl tetrahydronaphthalenes as for example 2-ethyl tetrahydronaphthalene, or 6-npropyl tetrahydronaphthalene may likewise be utilized in the practice of this invention. In addition to practicing this invention with relatively pure starting materials, the aforesaid compounds may also be mixed with alkyl naphthalenes, as for example 2,6-dimethylnaphthalene; 1,6-dimethylnaphthalene; 1,3-diethylnaphthalene and like compounds, which when treated in accordance with the present process are also converted to the corresponding naphthalene carboxylic acids. These mixtures of alkylnaphthalenes and alkyltetrahydronaphthalene may occur when hydrosulfurization is practiced on alkylnaphthalene concentrates, in which case some of the concentrate may be converted to alkyltetrahydronaphthalenes. Alkyltetrahydronaphthalenes may also be formed during the isomerization of mixed dimethyltetrahydronaphthalenes.

The process of this invention is conveniently carried out by dissolving the alkyltetrahydronaphthalene starting material in a solvent which is inert to N0 at elevated temperatures utilized in this reaction and bubbling N0 through the reaction mixture until the oxidation and dehydrogenation are complete. It has been found that various chlorinated benzenes are quite suit-able as solvents and preferably those having from 1-4 chlorine atoms, particularly trichlorobenzene. However, depending upon the range of reaction conditions, other solvents such as higher or lower chlorinated benzenes, nitrobenzenes, ethers such as diphenyl-ether or chlorinated ethers and the like may also be employed.

A considerable range of temperatures may be used in this reaction. The minimum temperature for operation is about C., and preferably it ranges from about -200 0, although higher temperatures up to the decomposition points of reactants and end products may be employed. The selenium catalyst may be added to the reaction mixture as the dioxide, or as H SeO dissolved in water; alternatively, it may be. prepared. in situ in the reaction vesselby bubbling N0 gas through the solvent in the presence of selenium metal at an elevated temperature, either prior to the addition of the alkyl tetrahydronaphthalene or in small portions at equal intervals during the course of the reaction until the selenium is oxidized to the dioxide. The amount of selenium-needed to convert an alkyl tetrahydronaphthalene to the corresponding naphthalene carboxylic acid generally ranges from 0.5 to 10 parts by weight of selenium to convert 100 parts by weight of starting material. When a dimethyl tetrahydronaphthalene is converted to naphthalene dicarboxylic acid, for example, from two to six parts by weight of selenium to 100 parts by weight of dimethyl starting material is preferably employed.

In conducting this reaction, it is desirable that the amount of NO employed be as stoichiometric as possible in order to insure substantially complete reduction of the N0 to NO, thus making the recovery of the NO and reconversion to NO a simple and complete operation so that the N0 is recycled with practically no loss. The regulation of the amount of N0 thus employed is readily achieved by making certain that the off-gases produced by the reaction are essentially colorless; since brown off-gases will be a clear indication that unconsumed N0 is passing through. Generally rates of about 1.5 to 2.5 grams of N0 per minute are preferred. Alternatively, if necessary, when maximum yields in a onestage oxidation are desired, the reaction may be continued for a period of time after brown off-gases are noted to insure maximum oxidation and dehydrogenation of the starting material.

The naphthalene carboxylic acid reaction products are generally insoluble in the chlorobenzene solvent and may conveniently be recovered by filtering and drying the precipitated solids. Thus, for example, in the preparation of a naphthalene dicarboxylic acid, this product is readily recovered by filtering the solids, washing them with a suitable organic solvent such as hexane, heptane or the like, and drying the washed solids in an oven. The acid may, if desired, then be further purified by known crystallization methods, or alternatively, esteri'fied, as for example with a low molecular weight alcohol such as methanol or ethanol at an elevated temperature to form the corresponding ester or diester.

The following examples are given by way of illustration and are not to be regarded as limitations of this invention:

Example I 1200 ml. of trichlorobenzene is heated to C. in a reactor fitted with a gas inlet tube, a side arm with a condenser, .a thermometer, and a stirrer. One gram of selenium is added and N0 which has been preheated to 160 C. is bubbled through the flask at the rate of about dried in an oven.

tetrahydronaphthalene in 400 ml. of trichlorobenzene is' added in 25 ml. portions over a period of 4 hours. During this same period 3.75 grams of additional selenium is added to the reaction, the last grams of which is added at. the end of the fourth hour. The reaction is then continued for an additional hour. The temperature of the reaction varies between 190203 C., and 65 m1. of water is collected. The reaction mixture is cooled to room temperature, and the solids filtered, washed with hexane, and dried in an oven. The weight of the dry solids'is 171.5 grams. The solids have an acid number of 462 which corresponds to 76% of 2,6-naphthalene dicarboxylic acid. r

In accordance with the foregoing procedure, but starting with 2,7-'diethyl tetrahydronaphthalene, there is obtained the corresponding 2,7-naphthalene dicarboxylic acid.

In accordance with the foregoing procedure, but starting with 1,5-di-n-propyl tetrahydronaphthalene, there is obtained the corresponding 1,5-naphthalene dicarboxylic acid.

Example 2 To 1000 ml. of trichlorobenzene preheated to 190 C. in a reaction vessel identical to the one used in Example 1 is added 3 grams of selenium. Nitrogen dioxide, preheated to 160 C. is bubbled through the flask at the rate of about 1.5 grams per minute. A solution of 100 grams of a mixture of 2,6-dimethyl tetrahydronaphthalene and 2,6-dimethy1 naphthalene in a ratio of about 1:9 by weight dissolved in 500 ml. of trichlorobenzene is added in 25 ml. portions over a period of 4 hours. During this same period 2 grams of additional selenium is added to the reaction, the last gram of which is added at the end of the third hour. The temperature varies between 185-2O0 C. The'reaction mixture is cooled to room temperature, the solids filtered, washed with hexane and The solids have an acid member of 478 which corresponds to 83% of 2,6-naphthalene dicarboxylic acid.

In accordance with the foregoing procedure, but starting with a mixture of 1,5-dimethyl tetrahydronaphthalene and 1,5-dimethyl naphthalene there is recovered the corresponding 1,5-naphthalene dicarboxylic acid.

Example 3 To a reaction vessel fitted the same as in Example-1 is added 1200 ml. of tn'chlorobenzene which is then heated rate of 2 gms./min. A solution of grams of 6-methyl tetrahydronaphthalene in 400 ml. of trichlorobenzene is added in 25 ml. of portions over a period of four hours. During this same period 3.75 grams of additional selenium is added to the reaction, the last gram of which is added at the end of the fourth hour. The reaction is then continued for an additional hour. The temperature of the reaction varies between 190-203 C., and 50 ml. of water is collected. The reaction mixture is cooled to room temperature, the solids filtered, washed with benzene, and dried in an oven to yield Z-naphthoic acid.

In accordance with the foregoing procedure, the starting with 2-methyl tetrahydronaphthalene, there is obtained the corresponding 2-naphthoic acid.

In accordance with the foregoing procedure, but starting with 5 n-propyl tetrahydronaphthalene, there is obtained the corresponding lnaphthoic acid.

The invention claimed is:

1. The process which comprises reacting a lower alkyl tetrahydronaphthalene with N0 in the presence of selenium dioxide and a solvent which is inert to N0 to produce the corresponding naphthalene carboxylic acid, said reaction being conducted at a temperature in the range of from about 145 C. to the decomposition temperature of said products.

2. The process according to claim 1 wherein the start ing material is a dialkyl tetrahydronaphthalene.

3. The process according to claim 2 wherein the starting material is 2,6-d-imethyl tetrahydronaphthalene.

4. The process according to claim 1 wherein the starting material is a mixture of dialkyl tetrahydronaphthalenes and dialkyl naphthalenes.

5. The process according to claim 4 wherein the starting material is a mixture of 2,6-dimethyl tetrahydronaphthalene and 2,6-dimethyl naphthalene.

6. The process according to claim 1 wherein the starting material is a monoalkyl tetrahydronaphthalene.

7. The process according to claim 1 wherein the starting material is 2-methyl tetrahydronaphthalene.

8. The process according to claim 1 wherein the reaction is carried out at a temperature of from about C. to 200 C.

References Cited by the Examiner UNITED STATES PATENTS 2,428,590 10/ 1947 Shokal et a1. 252-439 X 2,860,162 11/ 1958 Ekenstam 260-524 LORRAINE A. WEINBERGER, Primary Examiner. V DANIEL D. HORWITZ,.Examiner.

Claims

1. THE PROCESS WHICH COMPRISES REACTING A LOWER ALKYL TETRAHYDRONAPHTHALENE WITH NO2 IN THE PRESENCE OF SELENIUM DIOXIDE AND A SOLVENT WHICH IS INERT TO NO2 TO PRODUCE THE CORRESPONDING NAPHTHALENE CARBOXYLIC ACID, SAID REACTION BEING CONDUCTED AT A TEMPERATURE IN THE RANGE OF FROM ABOUT 145*C. TO THE DECOMPOSITION TEMPERATURE OF SAID PRODUCTS.