CA1154790A - Process for the production of 6-hydroxy-2-naphthoic acid - Google Patents

Abstract

28,678 Canada PROCESS FOR THE PRODUCTION OF

ABSTRACT OF THE DISCLOSURE
The production of 6-hydroxy-2-naphthoic acid from anhydrous potassium 2-naphthoxide and carbon dioxide is improved by forming a mixture of 0.8 - 1.45 moles of 2-hydroxynaphthalene per equivalent of potassium base, de-hydrating the mixture, adding carbon dioxide at about 20 to 90 psi at about 255-280°C and agitating and heating at said pressure and temperature.

Description

~5~9(~

PR~CESS FOR THE PRODUCTION OF
6-H~DROXY-2-NAPHTHOIC ACID

The present invention relates to a process for the preparation of 6-hydroxy-2-naph~hoic a id, more par-ticularly, by the carboxylation of the potassium salt of

2-hydroxynaphthalene with carbon dioxide. Still more par-ticularly, the invention relates to an Lmproved process for the preparation o 6-hydroxy 2-naphthoic acid in which said potassium salt is reacted with carbon dioxide u~der ~0 specific conditions of temperature, pressure, and ratios of reactants which results in increased yield o~ the de-sired product.
The production o~ 6-hydroxy-2-naphthoic acid, an intermediate useful for the prepartion of synthetic fibers, and s~ructural plastics, by the reaction of the potassium salt of 2-hydroxynaphthalene and carbon dioxide at an ele-vated temperature, is disclos d by Andre in U.S. Patent 1,593,816. Andre, however, does not disclose the criti-cality of temperature, pressure, or ratios of reactan~s.
Moreover, upon repeating Andre's work, the actual yield of 6-hydroxy-2 naphthoic acid obtained was ound to be only about one-third of the yield reported by Andre. ~See Example 6 below).
The carboxylation of alkali metal sal~s o~
phenols with carbon dioxide to foxm acids containing phenolic substituents, the well-known Rolbe-Schmitt re-action, is alsa disclosed in U.S. Patents 3,816,521 and '~' ; ;. . . .

~ 79

3,405,169.
In the carboxylation of the potassium salt o~ 2-hydroxynaphthalene, the initial product form is 3-hydroxy-2-naphthoic acid which subsequently rearranges i~ situ to form 6-hydroxy-2-naphthoic acid. It has been found tha~ the conditions which favor the formation of 3-hydroxy-2-naph-thoic acid in the Kolbe-Schmitt reaction hinder the rear-rangement reaction.
There is a need, therefore, ~or an improved pro-cess for the preparation of 6-hydroxy-2-naphthoic acid which will optimize the yield of 6-hydroxy-2-1~aphthoic acid in the reaction product.
Summary of the Invention In accordance wi~h the present invention, there is provided an improved process for preparing 6-hydroxy-2-naphthoic acid by reacting essentially anhydrous potassium 2-naphthoxide ~ith carbon dioxide at an elevated tempera-ture, and recovering 6-hydroxy-2-naphthoic acid therefrom, the improvement comprising forming a mixture of 2-hydroxy-naphthalene and a potassium base9 using about 0.8 to 1.45 moles of 2-hydroxynaphthalene per equivalent of potassium base; dehydrating said mixture, introducing carbon dioxide into said dehydrated mixture at about 20 to 9() psi at about 255`C to 2~0C, while agitating said mixture in a pressure reactor; and heating said stirred mixture al: said temper-ature and under said pressure. PreferabLy the heating co~tinues until the ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid in the reaction mixture is at a suffieiently high level to increase the yield of the 6-hydroxy-2-naphthoic acid.
In the preferred embodiment, the reaction mix-ture of potassium 2-naphthoxide and carbon dioxide also contains a non-polar organic flux. I~ the especially preferred embodiment, the flux is a mixture of isopropyl-naphthalenes. .
The improved process of the present invention affords the following advan~ages:

i4~9(~

1. A higher yield of 5-hydroxy-2-naphthoic acid is obtained.
2. The presence oE a ~ioh ratio of 6-~ydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid abtained will `5 improve the recovery, yield and purity of the product, but it is not mandatory.
3. The use of a flux improves heat and mass trans-fer rates thus reducing time cycles and improving the yield.
In carrying out the Lmproved process of the pre-sent invention, 2-hydroxynaphthalene and a potassium base are mixed in amounts sufficient to provide a ratio of about 0.8 to 1.45 moles of 2-hydroxy-naphthalene per equivalent of potassium base, and the reaction mixture is dehydrated by distillation, or by passing it through a dehydration ~ppa-ratus.
. Suitable potassium bases inciude potassium hydroxide, potassium carbonate, potassium hydride, potas-sium amide, and the like, as well as mixt~re~s thereof. The preerred potassium base is potassium hydxoxide with or without potassium c~ konate.
. Pre~erably, the potassium base and 2-hydroxy~
naphthalene are mixed in ~he presence of a non-polar organic flux to form the potassium 2-naphth~xide and the reaction mixture is dehydra~ed by distillation under nitrogen until essentially all of the water is removed.
Preferably~ tn foxming the reaction mixture about 1.0 to 1.1 moles of 2-hydroxynaph~halene, and m~st prefer-ably, about 1.02 to 1.04 moles, are used per mole of yotas sium base. A large excess of 2-hydroxynaphthalene, for example, a~out 1.5 moles per mole of potassium hydroxide, has ~een found to produce a large decrease in the yield of the final product.
It has been found that higher yields may be Ob-tained when a fIux is used. As used herein, th~ term '7flux"
defined as any non-polar organic material which is not a .

~ '7 solvent for the reactants and which is a liquid under the reaction conditions employed. Suitable materials which may be used as a flux include the following:
l-isopropylnaphthalene, 2-isopropylnaphthalene, naphthalene, kerosene, and the like T~e preferred ~lux is a mixture of i-, and 2-isopropylnaphthalene. Preferably, the dehydrated mixture contains about one part by weight of potassium 2-naphthoxide per part by weight of the mixed isopropylnaphthalenes.
The dehydrated mixture is charged to a pressure xeactor, preferably with additional flux and purged with carbon dioxide~ The reactor is then se~led and heated at akout 255C to 285~C, preferably about 260C to 280C, more preferably abaut 260C to 270JC, under a carbon dioxide pressure of about 20 psi to 90 psi, preferabl~ about 30 psi to 80 psi, more preferably about 40 psi to 60 p9i, while stirring the reaction mixture vigorously, until analysis of an aliquot of the reaction mixture shows a molecular ratio o 6-hydroxy-2-naphthoic acid ~o 3-hydroxy-2-naphthoic acid of the desired level, preferably more than ~, more preferably more than 3, and most preferably more than 6. The agitation must be sufficient to ensure the uniform mixing of the carbon dioxide into the reaction mixture~ otherwise the carboxylation ~eaction stops.
At temperatures belo~ 255C, the reaction product is found to bè mainly 3-hydroxy-2-naphthoic acid. Only about a 20% yield of the desired 6-hydroxy-2-~aphthoic acid was ob-tained below ~55C.
At pressures below 40 psi, the yield of 6-hydroxy-2-naphthoic acid decreases. At pressures above 60 psi, the ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic .. . . . . .
acid decreases.
At temperatures of 280C, or higher, ~he reaction time can be critical because of ~he formation of tars. In carrying out the reaction at 2~0C and 60 psi, the reac~ion ~ 7 time should be limited to maximize the produc~ion of the desired product.
When the ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid reaches the desired level, with the higher ratio being better, the reactor is vented to the atmosphPre and the reaction mixture is cooled under a nitro-gen atmosphere to about 120C. The reaction mixture is then either diluted with water and/or discharged into water containing enough sulfuric acid to bring the pH of ~he re-sulting mixture to 7, or above, preferably about 7.1 + 0.2.
The aqueous phase of the resulting two pbase liq-uid mixture is split off from the organic phase at a temperature of about 85-98C, preferably about 95C, and back-extracted twice with an equal volume of an organic flux (even if the flux was not present during the reaction) at the same temperature as the aqueous phase. A buffer, preferably about 0.1 gram of acetic acid per gram of 6-hydroxy-2-naphthoic acid expected, is added to the ex-tracted aqueous phase, and then enough dilute sulfuric acid is added to adjust the pH to about 4.8 to 5.2 to precipitate the 6-hydroxy-2-naphthoic acid. The precipitate may then be recovered by conventional means and dried to obtain the desired 6-hydroxy-2-naphthoic acid in a yield of about 40-60% of theoretical.
The mother liquor obtained on recovery of the product may be treated with additional sulfuric acid to adjust the pH to about 2-4 and precipitate 3-hydroxy-2-naphthoic acid, which may be recovered by filtration.
In the examples which follow, all parts are by 3~ weight unless otherwise indicated. All yields are based on potassium base charged. A theoretical yield is defined as one mole of 6-hydroxy-2-naphthoic acid produced for every 2 moles of potassium 2-naphthoxide.

7~

Exam~le 1 A mixture of 2-hydroxynaphthalene (84 grams; 0.58 mole), 45% potassium hydroxide (70O5 grams; 0.56 mole), and 100 mls of a mixture of 1-, and 2-isopropylnaphthalenes is stirred and heated under a nitrogen abmosphere until 100 mLs total of water and isopropylnaphthalane are distilled off, At that point, 100 mls of isopropylnaphthalene is added and the mixture is fur~her heated to distil off an addi~ional 50 mls of isopropylnaphthalene, and obtain a dehydrated mixture.
The dehydrated reaction mixture is cooled to 265C, charged to a pressure reactor, and purged with car-bon dioxide. The reactor is then sealed and pressurized with carbon dioxide to 40 psi while stirring slowly. The rate of stirring is then increased to 1500 rpm and the mix-ture is stirred at 265C under 40 psi of carbon dioxide for 16 hours. The reaction mixture is then cooled to 260C, vented to atmospheric pressure, and cooled under a nitrogen atmosphere to 120C. Water is then added to dilute the re-action mixture~
The diluted reaction mixture ls discharged into a flask containing 7.5 grams of sulfuric acid in 100 mls of water. The pH of the resulting mixture is then adjusted to 7.0 ~ 1 with sulfuric acid, and the two--phase liquid mix-ture is heated to 95C while stirring. The mixtur~ is allowed to set~le, the layers are split apart, and the aqueous phase is washed twice with 100-rnl portions of isopropylnaphthalene. The isopropylnaphthalene-wash~d aqueous phase is then stirred at 65-75t and 20 grams of a 3~ 15~ by weight solution o acetic acid in water is added thereto. Sulfuric acid (15 grlms of sulfuric acid per 100 mls of solution) is then added over a period of 15 to 30 minutes until the pH of the resulting sl~rry is 4.8 to 5.2.
The slurry is then cooled to 25-35C and filtered. The re~
- sulting filter cake is then washed with water and dried to obtain 27.4 grams ~54% of theoretical) of 6-hydroxy-2-naphthoic acid.

~ 3~

The aqueous mother liquor is adjusted to pH 2.5 with dilute sulfuric acid and the resulting precipitate is collected by filtration, washed, and dried to afford a mix-ture containing 1.6 grams of 6-hydro~y-2-naphthoic acid and 2.9 grams of 3-hydroxy-2-naphthoic acid.
The com~ined organic phases contain 50.2 grams of 2--hydroxynaphthalene, which can be recovered and recycled.
In the manner described above, carrying out the reaction at 80 psi, and 100 psi, the yields of 6-hydroxy~2-naphthoic acid obtained are 49.7~, and 26.8%, respectively.
The above example illustrates the present inven-tion as well as the effect of increased pressure on the yield of 6-hydroxy-2-naphthoic acid.
Example 2 The procedure of Example 1 is followed in every detail except that a mixture of 2 hydroxynaphthalene (83 grams; 0.576 mole), 45% potassium hydroxide (69.7 grams;
0.559 mole), and potassium carbonate (20 grams; 0.145 mole) is employed initially, the dehydrated reaction mixture is ~0 heated under 60 psi of carbon dioxide fox 10 hours, and the aqueous phase is washed twice with 100-ml portions of iso-propylnaphthalene at 85-95C. There is obtained 25.5 grams of 6-hydroxy-2-naphthoic acid (48.1~ of theoretical), and

4.6 grams of 3-hydroxy-2-naphthoic acid.
~5 Example 3 The procedure of Example 2 is followed in every detail except that no potassium carbonate is used. There is obtained 23.? grams (44.5~ of theoretical) of 6-hydroxy-2-naphthoic acid, and 4.8 grams of 3-hydroxy-2-naphthoic acid.
Example 4 The procedure of Example 1 is followed in every detail except that the reaction mixture is heated at 265C
in a pressure reactor for 16 hours under a pressure of 60 psi.
There is obtained 36.6 grams t49.5~ of the~retical) of 6-hydroxy-2-naphthoic acid. The yield of 3-hydroxy-2-naph-thoic acid is 7.5%. The ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naph~hoic acid is 6.6 to 1.
Carrying Out the reaction described above, at 250C for 16 hours under a pressure of 60 psi, af~ords only ll.S grams ~15.5~ of theoretical) of 6-hydroxy-2-naphthoic acid. The yield of 3-hydroxy-2-naphthoic acid is 53.6~.
The above example illustrates the decreases in the yield of 6-hydroxy-2-naphthoic acid of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid obtained when the temperature is reduced helow 255C.
Examp_e 5 A mixture of 2-hydroxynaphthalene (116 gxams;
0.80 mole), and 45% potassium hydroxide (97.8 grams; 0.78 mole), is stirred and heated under nitrogen until distil-lation stops and the temperature rises to 275~C. The mix-ture is then cooled to 270C and held under a fast stream of nitrogen for 30 minutes. The mixture is then further cooled to 265C and purged with carbon dioxide while stirring rapidly.
The reaction mixture is placed in a pressure reactor, and the reactor is sealed and pressurized with carbon dioxide ~o 60 psi. The reaction mixture is then stirred at 600 rpm and 265C for 11 hours under a pres~ure of 60 psi. The reactor is then vented to atmospheric pressure, and cooled under a nitrogen atmosphere to 120C.
The reaction mixture is then processed as described in Example 2. There is obtained 29.0 grams (39.3% of theo-retical) of 6-hydroxy-2-naphthoic acid and 6.0 grams (8.2%
of theoretical) of 3-hydroxy-2-naphthoic acid.
The above example illustrates the process of the present invention carried out without a flux.
Example 6 The procedure o~ Example 5 is followed in every detail except that the reaction mixture is heated at 230C
t 5C for 18 . 5 hours . The yield of 6-hydroxy 2-naphthoic acid obtained is only 19.5~ of theoretical, whereas the ~ 79~

yield of 3-hydroxy-2~naphthoic acid is 37.6~ of theoretical.
The above example represents the process of Andre carxied out under conditions which should have maximized the yield of 6-hydroxy-2-naphthoic acid. It is obvious from these results that the process of Andre neither af~ords a high yield of 6-hydroxy-2-naphthoic acid, nor a high ratio of 6-hydroxy-2-naphthoic acid to 3-hydroxy-2-naphthoic acid.
A comparison of Example 5 with Example 6 again illustrates the beneficial effect of tempexatures above 255C on the yield of 6 hydroxy-2-naphthoic acid.

.

Claims (10)

WHAT IS CLAIMED IS:

1. In a process for preparing 6-hydroxy-2-naph-thoic acid by reacting essentially anhydrous potassium 2-naphthoxide with carbon dioxide at an elevated temperature, and recovering 6-hydroxy-2-naphthoic acid therefrom, the improvement which comprises forming a mixture of 2-hydroxy-naphthalene and a potassium base, using about 0.8 to 1.45 moles of 2-hydroxynaphthalene per equivalent of potassium base; dehydrating said mixture; introducing carbon dioxide into said dehydrated mixture at about 20 psi to 90 psi at about 255°C to 280°C, while agitating said mixture in a pressure reactor; and heating said agitated mixture at said temperature and under said pressure before recovering said 6-hydroxy-2-naphthoic acid.

2. The process of Claim 1 wherein said potassium base is potassium hydroxide.

3. The process of Claim 2 wherein potassium car-bonate is used in addition to potassium hydroxide.

4. The process of Claim 1 wherein said reaction mixture of 2-hydroxynaphthalene and potassium base also contains a non-polar organic flux.

5. The process of Claim 4 wherein said flux is a mixture of isopropylnaphthalenes.

6. The process of Claim 1 wherein about 1.0 to 1.1 moles of 2-hydroxynaphthalene are used per mole of potas-sium hydroxide; and, the carbon dioxide is introduced into said reaction mixture at about 260°C to 280°C to obtain a carbon dioxide pressure of about 30 psi to 80 psi.

7. The process of Claim 6 wherein the carbon dioxide is introduced into the raaction mixture at about 260°C to 270°C to obtain a carbon dioxide pressure of about 40 psi to 60 psi.

8. In a process for preparing 6-hydroxy-2-naph-thoic acid by reacting essentially anhydrous potassium 2-naphthoxide with carbon dioxide at an elevated temperature, and recovering 6-hydroxy-2-naphthoic acid therefrom, the improvement which comprises forming a mixture of 2-hydroxy-naphthalene and a potassium base, using about 0.8 to 1.45 moles of 2-hydroxynaphthalene per equivalent of potassium base; dehydrating said mixture; introducing carbon dioxide into said dehydrated mixture at about 20 psi to 90 psi at about 255°C to 280°C, while agitating said mixture in a pressure reactor; heating said agitated mixture at said temperature and under said pressure; either diluting said reaction mixture with or discharging said reaction mixture into water containing sufficient sulfuric acid to bring the pH to at least 7, thereby forming a two-phase mixture;
separating the aqueous phase from the organic phase; con-tacting said aqueous phase with 0.1 gram of acetic acid per gram of expected 6-hydroxy- 2-naphthoic acid and additional sulfuric acid to bring the pH to about 4.8 - 5.2 and recovering said 6-hydroxy-2- naphthoic acid.

9. A process according to Claim 8 wherein said aqueous phase is extracted with an organic flux and the resultant extracted aqueous phase is recovered and then contacted with said acetic acid.

10. A process according to Claim 8 wherein the mother liquor resulting from the recovery of said 6-hydroxy-2-naphthoic acid is contacted with additional sulfuric acid to bring the pH to about 2-4 and recovering 3-hydroxy-2-naphthoic acid therefrom.