US2135062A

US2135062A - Preparation of aromatic dihydro dicarboxylic acids

Info

Publication number: US2135062A
Application number: US111676A
Authority: US
Inventors: Walker Joseph Frederic
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1936-11-19
Filing date: 1936-11-19
Publication date: 1938-11-01
Anticipated expiration: 1955-11-01

Description

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE Joseph Frederic Walker, Niagara Falls, N. Y., as-

signor to E. I. du Pont de Nemonrs & Company, Wilmington, Del., a corporation of Delaware N0 Drawing. Application November 19, 1936, Serial No. 111,676

16 Claims.

This invention relates to the preparation of organic acids and particularly to a method for preparing, separating, and isolating dicarboxylic acids of dihydroaromatic hydrocarbons containing two benzene nuclei per molecule.

Carboxyl derivatives of partially hydrogenated polycyclic aromatic hydrocarbons may be prepared by reacting an alkali metal with a polycyclic aromatic hydrocarbon in a suitable solvent medium to form an alkali metal hydrocarbon addition product and subsequently reacting said addition product with carbon dioxide to produce the alkali metal salts of the corresponding carboxyl derivatives. For example, if naphthalene is reacted with sodium in this manner, a disodium naphthalene addition compound having the empirical formula C'mHsNaz is formed. This addition product is soluble in the solvent medium in which it is formed, causing a green color therein. Similar alkali metal addition compounds of other polycyclic aromatic hydrocarbons may be formed by substantially the same method; all of these addition products are more or less soluble in the solvent mediums used and their presence is indicated by a distinct coloration of the solvent. If the colored solution of the alkali metal addition compound is treated with carbon dioxide the color is discharged and the sodium salts of the corresponding carboxyl derivatives are precipitated. For example, when disodium naphthalene is reacted with carbon dioxide, the product is a mixture of the sodium salts of isomeric acids having the formula C10Ha(COOH) 2. These acids,

N which may be termed .dihydronaphthalene dicarboxylic acids are the dicarboxyl derivatives of dihydronaphthalene. They probably occur in two isomeric forms which may be represented by the graphic formulas:

COOH

HVOOOH a m OUOOOH H COOH 1, 4-dihydronaphthalene l, 2-dihyd1'onapl1thalene 1, i-dicarboxylic acid is described by Schlenk and Bergmann, Liebigs Annalen, volume 463, pages 90 and 95. The methods of carrying out these reactions using certain ingredients as solvent media which facilitate the reaction of sodium and other alkali 5 metals with polycyclic aromatic hydrocarbons in general are described in U. S. Patent 2,027,000 issued January 7, 1936 to Norman D. Scott. Methods of preparing these carboxyl derivatives of partially hydrogenated polycyclic aromatic hydrocarbons are described and claimed in the above Scott patent and in my U. S. Patent 2,033,056 issued March 3, 1936.

As indicated above, salts of two isomeric dicarboxylic acids are formed when an alkali metal addition compound of a polycyclic aromatic hydrocarbon is treated with carbon dioxide. A general characteristic 'of those hydrocarbons, such as naphthalene and diphenyl, which have two benzene nuclei per molecule is that the acids 20 formed upon carboxylating the alkali metal addition compound of the hydrocarbon consists of a high melting and a low melting dihydro dicarboxylic acid. I

One object of the present invention is to pro- Vide an improved method of preparing dihydro dicarboxylic acids of polycyclic aromatic hydrocarbons having two benzene nuclei per molecule. Another object is to provide a method of isolating separately such acids. A further object is to provide a method for rearranging the so-called low melting dihydro dicarboxylic acid of polycyclic aromatic hydrocarbons having two benzene nuclei per molecule so as to form a product which may be easily and economically isolated in comparatively pure form, or as a mixture with the so-called high melting acid. Other objects will be hereinafter apparent.

The acids produced from those hydrocarbons having more than two benzene nuclei per molecule generally are readily isolated as a mixture from their salts since both acids whose salts are primarily formed upon carboxylating the alkali metal addition compound are sparingly soluble in water. 0n the other hand, I have discovered that the acids produced from those hydrocarbons having only two benzene nuclei per molecule, e. g., naphthalene and diphenyl and their substituted derivatives, are not easily isolated as a mixture from their salts. For example, in the 5 case of the naphthalene derivatives, I have found that whereas the 1,4-dicarboxylic acid is only slightly soluble in and crystallizes readily from water, the 1,2-dicarboxylic acid is rather soluble in and crystallizes with difiiculty from water.

The above differences in the properties of the two acids derived from those hydrocarbons having two benzene nuclei per molecule afford a method for isolating the two acids separately from their salts. Accordingly, one modification of my invention comprises an improved method for preparing these acids in isolated form. The isolation may be accomplished by dissolving in water the salts of the acids which are formed by carboxylating the alkali metal addition compound of the hydrocarbon and acidifying the resulting solution with a suitable strong acid, e. g., hydrochloric or sulfuric acid. By this treatment the insoluble high melting acid is precipitated while the low melting acid remains in solution. The former acid may be removed by filtration and freed from traces of the low melting acid by thorough washing with warm water. The low melting acid may be isolated from the combined filtrate and washings by any of several methods, for example, by extraction with a suitable solvent, e. g., ether, or by the formation of an insoluble salt such as the calcium salt from which the acid may be isolated in the usual manner. A further method for isolating the acid from the filtrate is to salt it out with sodium chloride. This method is illustrated in the following example.

Example I the 1,2-dicarboxylic acid. The isolated acid was then washed thoroughly with cold water. The solubilities of the two products in water ar approximately as follows:

Grams of acid per 100 cc. of solution At 25 C. At 95-100 C.

1, 4-dicarboxy1ic acid. 0. 14 1.7 1, 2-dicarboxylic acid. 2. 48

The above illustrated method affords a suitable manner for isolating separately the individual acids primarily formed by carboxylating the alkali metal addition compound. However, it is frequently desired to isolate dihydro dicarboxylic acids either in the form of a mixture or separately as comparatively pure acids by a more direct and less involved method. Accordingly, an important modification of my invention relates to such a method.

It is known that dihydro dicarboxylic acids of certain aromatic monocyclic hydrocarbons undergo a molecular rearrangement when they are heated in an alkaline medium. For example, it is known that 1,4-dihydroterephthalic acid may be heated in an alkaline solution so as to cause a molecular rearrangement to occur. The resultant product of the rearrangement is 3,6- dihydroterephthalic acid. I have discovered that rearrangements, which may be somewhat sim lar to the above referred to rearrangement, also occur when the so-called low melting dicarboxylic acids of dihydro polycyclic aromatic hydrocarbons having two benzene nuclei per molecule are treated with alkaline solutions. For example, the low melting dihydro dicarboxylic acids of diphenyl and naphthalene or their substituted derivatives undergo rearrangements when they are heated in caustic soda solution so that products having different properties from the original acids are produced. I have further discovered that the rearrangement is accompanied by marked changes in certain properties of the acid, e. g., its solubility in water is markedly reduced and its melting point is appreciably raised.

The above objects which relate to the rearrangement of the so-called low melting acid are accomplished in accordance with the present invention by treating the salt of the low melting acid, or a mixture of the salts of the low and high melting acids, with an alkaline aqueous solution. This is carried out preferably by warming or boiling the solution of the salt or salts in the presence of free alkali. Rearrangement of the low melting acid occurs during the alkali treatment to produce a product having a higher melting point and a markedly lower solubility in water.

It is believed that the acids primarily formed in carboxylating sodium naphthalene, for example, are 1,4-dihydro 1,4-dicarboxylic and 1,2- dihydronaphthalene 1,2-dicarboxylic acids and that rearrangement of the latter acid occurs in the manner indicated by the following equation:

n coon coon H ooon coon H Although it is believed that the above equation indicates the type of rearrangement that occurs in the case of the so-called low melting acids during the alkali treatment, it is to be understood that the present invention is not limited by the above suggested mechanism of the rearrangement.

The following example illustrates the rearrangement of the low melting dihydronaphthalene 1,2-dicarboxylic. acid.

Example II Dihydronaphthalene 1,2-dicarboxylic acid, 21.8 grams, which melted in the range of 172 to 183 C., was dissolved in 100 cc. of water containing 16 grams of caustic soda. The resultant solution was refluxed for 5 hours and, after cooling, was treated with an amount of hydrochloric acid equivalent to the quantity of caustic soda previously used. The acid which separated from the solution was recrystallized from alcohol to give a product which melted at 240 C. Its solubility in water was 0.02 and 0.3 gram per 100 cc. of solution at 25 C. and 95-100 C., respectively. The resultant high melting product had the same neutralizing equivalent as the original low melting acid and upon oxidation with potassium ferricyanide by the method described in U. S. Patent 2,054,100, issued September 15, 1936 to Norman D. Scott and Joseph Frederic Walker, beta naphthoic acid was obtained.

The separation of dihydronaphthalene 1,4=dicarboxylic acid from dihydronaphthalene 1,2-

dicarboxylic" acid is illustrated by thefollowing example.

Example III A mixture of the sodium salts of the above acids was obtained by. carboxylating the sodium addition product of naphthalene. The mixed sodium salts were acidified with hydrochloric acid which caused a precipitate of the 1,4-dicarboxylic acid to form, while the 1,2-dicarboxylic acid remained in solution due to its greater solubility in water. The precipitate was washed thoroughly with water at 40 C. after which it Was digested with a small amount of water at C. and filtered while hot in order to remove last traces of the 1,2 -dicarboxylic acid. The filtrate containing the soluble 1,2-dicarboxylic acid was treated with a slight excess of caustic soda solution and boiled for 1 hour, after which the solution was cooled and acidified with hydrochloricacid. The mixture was filtered and the separated rearranged acid was washed with hot water.

The melting point of the precipitated 1,4-dicurboxylic acid was 219-227 C. and thecrude rearranged dicarboxylic acid melted at ZOE-215 G. Since the solubility of the 1,2-dicarboxylic acid is markedly changed as a result of the alkaline treatment, this change in its solubility makes possible a simple and easy method for isolating the acid from the reaction mixture in which it is prepared.

The following example illustrates the separation of mixed acids from a reaction mixture in which they were prepared.

Example IV Naphthalene, 32 grams, was reacted with 16 grams of sodium in 300 cc. of dimethyl glycol ether and the mixture carboxylated by the method disclosed in my U. S.-Patent 2,033,056. The

unreacted sodium then was removed and weighed a and thesodium salts were filtered off and dissolved in water.- To this solution was added a 1% caustic soda solution and the mixture was then heated to distill oiT any dimethyl glycol ether that had not been removed when the salts were filtered. After the ether was removed, the alkaline solution was refluxed for 1 hour and then cooled and filtered to remove unreacted naphthalene. The filtrate containing the sodium salts of the reaction products was acidified with hydrochloric acid and the precipitated mixture of acids was filtered off and dried. 26.6 grams of mixed dicarboxylic acids were obtained which corresponded to a yield of 69.5% of thetheory based upon the quantity of sodium consumed in the first reaction. 'The mixed acids sintered at 200 C. and melted at 205 to 214 C.

The most suitable alkalies for the present purpose are the alkali metal hydroxides. However, any alkali may be employed. since it is only necessary that the rearranging medium be alkaline in reaction. If the medium is only sl ghtly alkaline a longer time is required to efiect the rearrangement than if a more strongly alkaline medium is employed. In order that the time required may not be unduly long, for example, longer than about 1 to-5 hours, I prefer to use an amount of alkali equivalent to at least 2 grams of caustic soda .for every 100, grams of sodium salt of the dicarboxylic acid. My preferred quantities of alkali range from 2-10 grams, calculated asca'ustic soda, for every grams of sodium salt being arrangement is not objectionable. Similarly, larger amounts of alkali may be employed but in general there is no advantage in using more than 10 grams caIcuIated as caustic soda, for every 100 grams of salt.

The following experiment serves to illustrate the effect of, alkali concentration upon the extent to which rearrangement occurs during refluxing periods of hour and 3 hours.

Example V 7 100 cc. portions of the solution of mixed sodium salts were treated with '1 and. 10 grams of caustic soda, respectively. The samples were refluxed for 3 hours after which the solutions were acidifled-and the mixed acids, which were precipitated, were separated and their melting points determined. The extent of the rearrangement that occurred in each treatment is indicated by the weight of product obtained as well as by the melting point of the product. The results are shown in the following table:

, Refluxed for hour Refluxed for 3 hours Grams of caustic soda per 100 cc. sample Grams of Melting Gram: .A'eltmg product point of product point of product product 0. o. (J 5. 3 198-203 J. 14. 3 203-2l9 17. 6 209-219 10 15. 6 205-212 15. 4 2 1- 218 Although it is generally desirable toeffect rearrangement by refluxing the alkaline solution of the salt or salts in order to shorten the time required to produce complete rearrangement, rearrangement may be effected at temperatures below the boiling temperature of the solution, for example, the solution may merely be warmed. Generally, when lower temperatures are used, a more alkaline solution is desirable in order to shorten, as much as possible, the time required for complete rearrangement.

The rearrangement of dihydronaphthalene dicarboxylicacids, illustrated by the above examples, is also characteristic of the dihydro dicarboxylic acids of other polycyclic aromatic hydrocarbons which have two benzene nuclei per molecule. For example, when the alkali metal addition product of diphenyl is reacted with carbon dioxide, it produces alkali metal salts of high and low melting dihydro dicarboxylic acids, similar to the high and low melting dihydro dicarboxylic'acids of naphthalene. As in the case o-f the low melting naphthalene derivative, the low melting dihydro dicarboxylic acid of diphenyl may be isolated only with difiiculty unless it is rearranged to form an insoluble acid. l

Therearrangement of the acids under consideration is "believed to involve a shift of a double bond andnot solely a stereo rearrangement.

But regardless of what actuallyoceurs during the rearrangement, its effect is generally a lowering of the solubility of the acids in water and a raising of their melting points. The decrease of the solubility in water makes possible the separation in a practical direct manner of individual acids from the products produced by carboxylating an alkali metal addition product of a polycyclic aromatic hydrocarbon having two benzene nuclei per molecule, and also makes possible an easy and practical method for separating mixed acids.

The exact structure of the rearranged acids has not been definitely established. Such an accomplishment is exceedingly difficult due, not only to the possibility of several structural isomers existing, but also, to the probable existence of stereo isomers. Stereo isomerism may occur both in the acids originally obtained by carboxylating the alkali metal hydrocarbon addition product as well as in the rearranged acids. However, it may be said that all indications so far obtained, relative to the structure of the dihydronaphthalene 1,2-dicarboxylic acids, indicate that the rearrangement occurs in the manner shown in the equation presented above.

My invention is not limited to dihydro dicarboxylic acids of naphthalene and diphenyl but includes any such acids of polycyclic aromatic hydrocarbons which have two benzene nuclei per molecule. This includes dihydro dicarboxylic acids of substituted derivatives of these hydrocarbons, e. g., alkyl naphthalenes and alkyl diphenyls. Accordingly, I use the terms naphthalene, diphenyl and polycyclic aromatic hydrocarbons having two benzene nuclei per molecule in the appended claims to include the substituted derivatives of such hydrocarbons.

It would be obvious to any one skilled in the art that various modifications of my invention may be practiced without departing from the spirit and scope thereof. It is therefore understood that the scope of my invention is not to be limited by the accompanying examples but only by the scope of the appended claims.

I claim:

1. The process comprising heating a salt of a dihydrodicarboxy derivative of a polycyclic aromatic hydrocarbon having two benzene nuclei per molecule in an aqueous medium containing a quantity of alkali equivalent to approximately 2-10 grams of caustic soda for every 100 grams of said salt being treated.

2. The process comprising heating a salt of a dihydrodicarboxy derivative of a polycyclic aromatic hydrocarbon having twobenzene nuclei permolecule in an aqueous medium containing approximately 2-10 grams of caustic soda for every 100 grams of said salt being treated.

3. The process comprising heating a. salt of a dihydrodicarboxy derivative of naphthalene with an alkaline aqueous medium.

4:. The process comprising heating a salt of a dihydrodicarboxy derivative of naphthalene in an aqueous medium containing a quantity of alkali equivalent to approximately 2-10 grams of caustic soda for every 100 grams of said salt being treated.

5. The process comprising heating a salt of a dihydrodicarboxy derivative of diphenyl with an alkaline aqueous medium.

' 6. The process comprising heating a salt of a dihydrodicarboxy derivative of diphenyl in an aqueous medium containing a quantity of alkali equivalent to approximately 2-10 grams of caustic soda for every 100 grams of said salt being treated.

'7. The method of preparing a high melting substantially water insoluble dihydronaphthalene dicarboxylic acid comprising heating a salt of a low melting, water soluble dihydronaphthalene dicarboxylic acid in an aqueous medium containing approximately 2-10 grams of caustic soda for every 100 grams of said salt being treated and thereafter isolating said high melting substantially water insoluble acid from said aqueous medium.

8. The method of preparing mixed dihydronaphthalene dicarboxylic acids comprising reacting naphthalene with an alkali metal and carboxylating the resulting alkali metal naphthalene addition compound, heating the resulting mixture of alkali metal salts of dihydronaphthalene dicarboxylic acids thus formed with an alkaline aqueous medium and thereafter acidifying the mixture to precipitate mixed dihydronaphthalene dicarboxylic acids.

9. The method of preparing mixed dihydronaphthalene dicarboxylic acids comprising reacting naphthalene with sodium and carboxylating the resulting sodium naphthalene addition compound, heating the mixture of sodium salts of dihydronaphthalene dicarboxylic acids thus formed with an aqueous medium containing 2-10 grams of caustic soda for every 100 grams of said sodium salts, and thereafter acidifying the mixture to precipitate mixed dihydronaphthalene dicarboxylic acids.

10. The method of separating high and low melting acids from the reaction mixture obtained by carboxylating an alkali metal addition compound of a polycyclic aromatic hydrocarbon having two benzene nuclei per molecule comprising acidifying said reaction mixture and separating the high. melting dihydro dicarboxylic acid of said hydrocarbon, heating the aqueous solution obtained upon separation of said high melting acid in the presence of free alkali, and thereafter acidifying said solution to precipitate a dihydro dicarboxylic acid.

11. The method of separating high and low melting acids from the reaction mixture obtained by carboxylating an alkali metal addition compound of naphthalene comprising acidifying said reaction mixture and separating the high melting dihydronaphthalene dicarboxylio' acid, heating the aqueous solution obtained upon separation of said high melting acid in the presence of free alkali, and thereafter acidifying said solution to precipitate a dihydronaphthalene dicarboxylic acid.

12. A method for separating high and low melting acids from the reaction mixture obtained by carboxylating a sodium addition compound of naphthalene comprising acidifying said reaction mixture and separating the high melting dihydronaphthalene dicarboxylic acid, heating the aqueous solution obtained upon separation of said high melting acid in the presence of free caustic soda and thereafter acidifying said solution to precipitate a dihydronaphthalene dicarboxylic acid.

13. In a process for preparing dihydro dicarboxylic acids of polycyclic aromatic hydrocarbons having two benzene nuclei per molecule, the step which comprises rearranging a dihydro dicarboxylic acid by heating with an alkaline aqueous medium.

14. As a new composition of matter, the mixture of dihydronaphthalene dicarboxylic acids prepared by heating a mixture of the dihydronaphthalene LZ-dicarboxylicanddihydronaphthalene 1,4-dicarboxylic acids primarily formed by carboxylating a sodium addition compound of naphthalene in the presence of an alkaline aqueous medium.

15. As a new compound, the dihydronaphthalene dicarboxylic acid prepared by heating the dihydronaphthalene 1,2-dicarboxylic acid pri- 10 marily formed by carboxylating a sodium addition compound of naphthalene in the presence of an alkaline aqueous medium.

16. As a new compound, 3,4-dihydronaphthalene 1,2-dicarboxylic acid, which compound has a melting point of approximately 240 C., is substantially insoluble in water and which is oxidized by potassium ferricyam'de to beta naphthoic acid.

JOSEPH FREDERIC WALKER.