United States Patent US. Cl. 260-476 22v Claims ABSTRACT OF THE DISCLOSURE Process for preparing a carboxylic acid esters of a hydroxy aromatic, wherein the hydroxy group is on the aromatic nucleus, which involves heating an aromatic hydrocarbon, a halogenated aromatic hydrocarbon or an ester of an aromatic acid with iron, a noble metal or compounds of iron or noble metal in the presence of a nitrate ion and a carboxylic acid.

This invention relates to a process for preparing a carboxylic acid ester of a hydroxy aromatic, wherein said hydroxy group is on the aromatic nucleus, particularly to a process for preparing phenyl acetate.

It is difficult to place oxygen on a nuclear carbon atom of an aromatic ring. I have found that this can be done effectively under mild conditions, and a carboxylic acid ester of a hydroxy aromatic can be prepared, by the expedient of heating an aromatic compound with a substance selected from the group consisting of iron, noble metals, iron compounds and noble metal compounds in the presence of a substance selected from the group consisting of nitrate ions and species convertible to nitrate ions and a carboxylic acid. The present system must be essentially free of chloride or bromide ions. In the event an iron or noble metal chloride or bromide is employed herein, nuclear chlorination or bromination of the aromatic compound will occur, as set forth in my copending application Ser. No. 602,469 filed concurrently herewith. While this reaction is proceeding, the desired formation of the carboxylic acid ester of a hydroxy aromatic is not obtained. However, when the system becomes essentially free of chloride or bromide ions, as evidenced by the formation of corresponding amounts of halogenated aromatics, the desired reaction defined 'herein will then proceed.

The aromatic reactant employed herein can be an aromatic hydrocarbon, a halogenated (chloro, bromo, fiuoro, or iodo) aromatic hydrocarbon or an ester of an aromatic carboxylic acid wherein the alcoholic portion of the substituent thereof can be derived from methanol, ethanol and higher straight and branched chain alcohols. Of these, methanol and ethanol are preferred. Examples of aromatic compounds that can be employed herein include benzene, toluene, ethylbenzene, cumene, naphthalene, anthracene, biphenyl, phenanthrene, t-butylbenzene, u-phenylnaphthalene, para-xylene, polystyrene, terphenyl, 3-phenylheptane, 1,4-diphenylbutane, diphenylmethane, tetralin, propylium anion, etc.

As noted, the second reactant employed herein can be iron, a noble metal (platinum, palladium, iridium, rhodium, osmium and ruthenium), iron compounds and Patented Nov. 24, 1970 ice compounds of noble metals. Examples of iron compounds that can be employed include metallic iron, ferric acetate, ferric propionate, ferric hydroxy acetate, ferric chloride, ferric hydroxide, ferric nitate, ferric phosphate, ferric sulfate, ferrous acetate, ferrous nitrate, ferrous lactate, ferrous bromide, etc. Examples of noble metal compounds include palladium, rhodium, iridium, osmium, ruthenium, platinum, rhodium formate, palladium acetate, palladium propionate, iridium butyrate, palladium pivalate, palladium octanoate, osmium isooctanoate, palladium benzoate palladium laurate, ruthenium stearate, palladium isobutyrate, palladium para-toluate, platinum gammachlorobutyrate, ruthenium tetracontanoate, osmium phenylacetate, iridium cyclohexane carboxylate, rhodium crotonate, palladium furoate, palladium heptanoate, palladium eicosanoate, palladium chloride, palladium nitrate, palladium oxide, rhodium bromide, iridium sulfate, osmium cyanide, ruthenium perchlorate, rhodium iodide, platinum fluoride, platinum phosphate, platinum pyrophosphate, ruthenium oxide, platinic bromide, platinous bromide, platinum oxide, platinous cyanide, platinum hydroxide, rhodium sulfate, rhodium oxide, osmium tetroxide, ruthenium trichloride, iridium oxide, etc.

Of the noble metal compounds that are employed herein I prefer a carboxylic acid salt of a noble metal. Thus, the cationic portion of the salt can be one of the defined noble metals, preferably palladium, While the anionic portion thereof can be derived from the group of carboxylic acids, straight and branched chain, having from one to 40 carbon atoms, preferably from two to six carbon atoms. Examples of such carboxylic acids are formic, acetic, propionic, butyric, pivalic, octanoic, isooctanoic, benzoic, lauric, stearic, isobutyric, para-toluic, gamma-chlorobutyric, tetracontanoic, phenylacetic, cyclo hexane carboxylic, crotonic, furoic, heptanoic, eicosanoic, etc. Examples of carboxylic acid salts of noble metals that can be employed include rhodium formate, palladium acetate, palladium propionate, iridium butyrate, palladium pivalate, palladium octanoate, osmium isooctanoate, palladium benzoate, palladium laurate, ruthenium stearate, palladium isobutyrate, palladium para-toluate, platinum gamma-chlorobutyrate, ruthenium tetracontanoate, osmium phenylacetate, iridium cyclohexane carboxylate, rhodium crotonate, palladium furoate, palladium heptanoate, palladium eicosanoate, etc.

In order to obtain the desired reaction herein with substantial production of the desired carboxylic acid ester of a hydroxy aromatic it is imperative that the above reactants be brought into contact with each other in the presence of a substance selected from the group consisting of nitrate ions and species convertible to nitrate ions. By nitrate ions I mean N0 1 a singly charged anion containing one nitrogen atom and three oxygen atoms. By species convertible to nitrate ions I mean to include compounds, ions or radicals containing nitrogen and oxygen which by ionization, oxidation or disproportionation under conditions defined for this process give NO Species convertible to nitrate ions that can be employed herein include nitric acid, nitric oxide, nitrous anhydride, nitrate ion, nitrous acid, nitrogen dioxide, nitrogen tetroxide, nitric anhydride, etc.

Also required in the reaction system is a carboxylic acid, examples of which have been defined above. The

amount of carboxylic acid employed, relative to the iron or noble metal catalyst, on a weight basis, can be from about 10 :1 to 1:1, preferably from about 10 :1 to 100:1.

Preferably, the aromatic compound, the iron or noble metal species, the carboxylic acid and the nitrate ion are heated in the presence of a solvent which will not ad versely affect the course of the reaction and will not react with the reactants and/ or the products produced herein. Examples of such solvents are ethers, amides, s'ulfoxides, ketones, such as meta dioxane, dimethylacetamide, dimethylformamide, dimethylsulfoxide, acetone, etc. In a preferred embodiment, however, the solvent can be the carboxylic acid, straight and branched chain having from one to 40 carbon atoms, preferably from two to six carbon atoms, specific examples of which have been set forth above.

The reaction defined herein is simply effected by bringing the materials defined above into contact with each other under specified conditions. The amount of aromatic to iron, noble metal or compounds thereof, as metal, on a molar basis, employed can range from about 1:1 to about 10 :1, preferably from about 10:1 to about 10 :1. The amount of nitrate ion employed, on a molar basis, relative to the aromatic compound, can be from about 1:1 to about 1:10, preferably from about '1:3 to about 1:10 The amount of solvent employed can be from about 0.1 to about 1000 mols, preferably from about 1 to about 50 mols, per mol of aromatic compound. The temperature employed during the process can range from about 40 to about 200 C., preferably from about 60 to about 150 C., the pressure from about 0.1 to about 10,000 pounds per square inch gauge, preferably from about to about 1000 pounds per square inch gauge, and the contact time from about 0.1 to about 100, preferably from about one to about 10 hours.

At the end of the reaction period, iron or noble metal may precipitate out of solution and can be recovered thereof in any convenient manner, for example, by distillation and removal of the organic portions of the product. During the distillation unreacted hydrocarbon, carboxylic acid and solvent will come off before the product and can be isolated in a pure form thereby and recycled and will be followed in the distillation by the carboxylic acid ester of the hydroxy aromatic. The temperature, pressure and reflux ratio necessary to carry out the distillation will depend on the components involved and are readily determinable by those skilled in the art. If desired to reemploy the metal so recovered in the form of a compound, for example, the salt thereof, the metal can be heated wtih a carboxylic acid, such as defined hereinabove, in a molecular oxygen atmosphere to convert the metal to a metal carboxylate. This is believed to require the use of one mol of metal, two mols of carboxylic acid and one-half mol of molecular oxygen, resulting in the production of one mol of the metal carboxylate and one mol of water. This oxidation procedure can involve a temperature of about 80 to about 180 C., a pressure of about 50 to about 3000 pounds per square inch gauge and a reaction time of about 0.1 to about 100 hours. Compounds resulting from the process defined herein include phenyl acetate, phenyl furoate, a-naphthyl acetate, fl-naphthyl propionate, Z-anthracyl butyrate, para-phenylpheuyl isoctanoate, 9-phenanthryl tetracontanoate, para-t-butylphenyl laurate, para-pivaloxychlorobenzene, methyl metaacetoxybenzoate, 4-chloro-4'-phenylacetoxybiphenyl, 1-phenyl-4-para-toluoxynaphthalene, Z-(meta-acetoxyphenyl)thiophene, S-acetoxy benzofuran, para-tolyl acetate, meta tolyl acetate, ortho tolyl acetate, para-ethylphenyl acetate, 3-(para-butyroxyphenyl)heptane, 1-(para-acetoxyphenyl-4-phenylbutane, 5-actoxy- 1,2,3,4-tetrahydronaphthalene, etc.

The process of the invention can further be illustrated by the following.

EXAMPLE I There was refluxed at atmospheric pressure and a reflux temperature of 115 C. over a period of 23 hours a mixture of 20 millimols of an aromatic compound, 1.0 millimol of palladium acetate, 10 millimols of sodium acetate, 0.5 millimol of percent aqueous nitric acid and 25 milliliters of acetic acid. At the end of the reaction period the reaction mixture was analyzed by gaslbiqluid chromatography. The results obtained are analyzed e ow.

and Z-naphthyl acetate.

The results from Runs Nos. 1, 2, 3 and 5 show that aromatic compounds not encompassed within the definition of aromatic compounds defined herein cannot be employed herein to obtain the defined products.

EXAMPLE II In a series of similar runs various Group VIII metals were examined as to their ability to catalyze the desired acetoxylation of benzene. In these runs a mixture of 1.0 milligram atom of each metal was stirred in 25 milliliters of acetic acid containing 20 millimols of benzene and 70 percent aqueous nitric acid at atmospheric pressure and reflux temperature. The reaction product was analyzed by gas-liquid chromatography. As the results in Table II show the noble metals and irons were eflective but nickel was an ineflective catalyst.

TABLE II Nitric Phenyl Time, acid acetate, Run number hours Metal mlllimols millimol 7 6 Platinum- 1. 0 O. 13 22 ,.do l. 0 0.42 8 6 Palladium 1. 0 1. 43 22 .do 1.0 1.42 9 6 Iridium.-- 1.0 0.42 22 do 1. 0 1.30 10 6 Ruthenium.-. 1. 0 0. 50 22 -do 1.0 1.37 1. 0 0. 69 1. 0 1. 23 3. 0 0. 7 3. 0 2. 0 3. 0 0 Ruthenium--. 3. 0 l. 5

EXAMPLE III An additional series of runs were made in which 50 milliliters of a solution containing 50 percent by weight of benzene and 50 percent by weight of acetic acid, various amounts of nitric acid and various amounts of palladium were refluxed at atmospheric pressure and C., stirred and analyzed by gas-liquid chromatography. It can be seen from Table III below that up to 290 mols of phenyl acetate are formed per mol of palladium, indicating that palladium serves as a catalyst herein.

TABLEIIII 6 palladium acetate and five millimols of salt. After reiluxing for 24 hours at atmospheric pressure and a temperature of 85 C. each system was analyzed by gas chro- Palladium Time, hours Run number Type Nitric acid, Millimols millimols Mols phenyl acetate formed per mo palladium EXAMPLE IV That a nitrate ion or a species convertible to a nitrate ion is required is illustrated by the following. There was refluxed at atmospheric pressure and at a temperature of 115 C. 20 millimols of benzene, palladium acetate and matography, five millimols of nitric acid was added and after an additional 68 hours of reflux analyzed again. A comparison of the product before and after nitric acid addition shows a significant improvement in the amount of phenyl acetate obtained. The results are tabulated below in Table V.

TABLE V After 24 hours of reflux .but before nitric acid addition 68 hours of reflux after addition of nitric acid Phenyl acetate, Biphenyl, Phenyl acetate, Biphenyl, Nitro benzene, Run number Salt weight percent weight percent weight percent weight percent weight percent 33 NazSO; 0. 14 0.22 1. 29 0. 30 0. 20 34. 3F 0. 03 0.15 0. 43 0. 25 35- KCN 0 0 1. 50 0 0 36 LiClO4 0.02 0. 23 0.46 0.50 0.15 37 NaI 0 0 0.54 0 0 3s NaHPOi 0.01 0. 08 0.28 0.18 0

25 millimols of acetic acid. The reaction product was analyzed by gas-liquid chromatography. The results are tabulated below in Table IV.

EXAMPLE VII A mixture of 1.15 grams of palladium nitrate, five millimols of toluene and 20 milliliters of acetic acid were TABLE IV Results based on palladium, yield of- Run acetate, Benzene, time, Phenyl number Additive Millimols millimols millimols hours acetate Biphenyl Silver acetate 5 24 4 16 23 Dimethylacetamid 140 5 57 64 4 1. 5 24 Sulfuric acid. 10 5 86 88 0 58 25--. Magnesium perchlorate 2 2 8 2O 0 20 26 Ammonium acetate 5 20 20 0 0 27 Triphenyl phosphine. 10 5 20 20 0 1 28 Triphenylamine 10 5 20 20 0 0 29 Water 12 5 2 201 4 8 30.. Ammonium sulfate 20 5 20 20 0 0 31 None. 5 2O 20 6 10 32 Nitric acid 5 20 20 48 4 EXAMPLE V refluxed for 20 hours at atmospheric pressure and 116 C.

EXAMPLE VI Into SO-milliliter flasks were placed 25 milliliters of a solution consisting of 50 percent by weight of benzene and 50 percent by weight of acetlc acid, one millimol of Analysis by gas chromatography of the product in this run (Run No. 39) showed the yield of acetoxylated toluene was 60 percent and this consisted of 11.9 percent meta tolyl acetate, 14.4 percent para tolyl acetate, 15.4 percent ortho tolyl acetate and 58.3 percent benzyl acetate. Small amounts of p,p'-dimethylbiphenyl and other toluene dimers were also formed.

EXAMPLE VIII In this run (Run N0. 40) a mixture of 1.58 grams of benzene, 0.2317 grams of palladium acetate, 25 milliliters of propionic acid and one millimol of nitric acid was refluxed for 20 hours. Analysis of the product by gas chromatography disclosed 0.76 millimols of phenyl propionate.

EXAMPLE IX The present run (Run No. 41) involved heating at atmospheric pressure and 115 C. over a period of 68 hours a mixture of 25 milliliters of acetic acid, 20 millimols of benzene, one millimol of sodium nitrate and one millimol of palladium acetate. Analysis by gas chromatography showed the presence in the mixture of 0.1 percent by weight of phenol and 0.1 percent by Weight of phenyl acetate. The phenol resulted from hydrolysis of phenyl acetate.

EXAMPLE X The present run (Run No. 42) discloses that cobalt and nickel is inoperative herein. A 25 milliliter solution of 20 millimols of benzene in acetic acid, three millimols of nitric acid and one millimol of cobalt metal was refluxed for 68 hours at atmospheric pressure and 115 C. No phenyl acetate was found. An additional experiment similar to the above was conducted in which one millimol of nickel metal was employed in place of cobalt. Again no phenyl acetate was found.

Obviously, many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In a process for preparing a carboxylic acid ester of a hydroxy aromatic, said hydroxy group being on the aromatic nucleus, wherein an aromatic compound selected from the group consisting of an aromatic hydrocarbon having from six to 16 carbon atoms and at least one hydrogen on a ring thereof, a halogenated aromatic hydrocarbon having from six to 16 carbon atoms and at least one hydrogen on a ring thereof and an alkyl ester of an aromatic hydrocarbon carboxylic acid having from six to 16 carbon atoms and at least one hydrogen on a ring thereof, wherein the carboxylic acid group of said ester is on a ring thereof and the alkyl portion of said ester is derived from a lower alcohol, is heated with a lower carboxylic acid and a metalic compound selected from the group consisting of iron, a noble metal selected from the group consisting of platinum, palladium, iridium, rhodium, osmium and ruthenium and compounds of iron and said noble metals, the improvement which comprises additionally having present a substance selected from the group consisting of nitrate ions and species convertible to nitrate ions.

2. The process of claim 1 wherein the reactant aromatic compound is said aromatic hydrocarbon.

3. The process of claim 1 wherein reactant aromatic compound is said halogenated aromatic hydrocarbon.

4. The process of claim 1 wherein the reactant aromatic compound is said ester of an aromatic hydrocarbon carboxylic acid.

5. The process of claim 1 wherein the reactant aromatic compound is benzene.

6. The process of claim 1 wherein the reactant aromatic compound is naphthalene.

7. The process of claim 1 wherein the reactant aromatic compound is methyl benzoate.

8. The process of claim 1 wherein said metallic compound is a salt of a noble metal.

9. The process of claim 1 wherein said metallic compound is a carboxylic acid salt of a noble metal.

10. The process of claim 1 wherein said metallic compound is iron.

11. The process of claim 1 wherein said metallic compound is platinum.

12. The process of claim 1 wherein said metallic compound is palladium.

13. The process of claim 1 wherein said metallic compound is iridium.

14. The process of claim 1 wherein said metallic compound is ruthenium.

15. The process of claim 1 wherein said metallic compound is rhodium.

16. The process of claim 1 wherein said metallic compound is palladium acetate.

17. The process of claim 1 wherein said metallic compound is palladium chloride.

18. The process of claim 1 wherein said metallic compound is palladium nitrate.

19. The process of claim 1 wherein the reaction is carried out in the presence of a species convertible to nitrate ions.

20. The process of claim 1 wherein the reaction is carried out in the presence of nitric acid.

21. The process of claim 1 wherein the reaction is carried out in an inert solvent.

22. The process of claim 1 wherein the reaction is carried out at a temperature of about 40 to about 200 C., a pressure of about 0.1 to about 10,000 pounds per square inch gauge and a contact time of about 0.1 to about hours.

References Cited UNITED STATES PATENTS 3,418,361 12/1968 Kaeding et al. 260473 JAMES A. PATTEN, Primary Examiner D. E. STENZEL, Assistant Examiner US. Cl. X.R.