IE58239B1 - Process for producing n-acyl-acyloxy aromatic amines - Google Patents

Description

It is known to produce N-acyl-acyloxy aromatic amines, e.g. 4-acetoxy-acetanilide, by preparing the sodium salt of the corresponding N-acylhydroxy aromatic amine, e.g.

N-acetyl-para-aminophenol (APAP), and reacting the sodium salt with the appropriate carboxylic acid anhydride.e.g. acetic anhydride. The N-acyl-hydroxy aromatic amine, e.g. APAP, used as the starting material for the foregoing reaction is in turn prepared by acylating the corresponding hydroxy aromatic amine, e.g. para-aminophenol, with an acylating agent such as an anhydride, e.g. acetic anhydride. However, the latter reaction may cause problems such as the difficulty of mono-acylating the hydroxy aromatic amine, oligomerization of the hydroxy aromatic amine, and color body formation.

Furthermore, when APAP is produced from para-aminophenol, nitro-benzene typically is catalytically hydrogenated and concomitantly rearranged in the presence of a platinum catalyst to produce the para-aminophenol, presenting the problem of recovering the dissolved platinum catalyst.

It is also known to prepare APAP by hydrogenating 4-nitro-chlorobenzene to a 4-cholroaniline which is then reacted with aqueous KOH to form para-aminophenol. This is then acetylated as , described previously to form the N-acetyl-para-aminophenol. This process is relatively complex requiring a fair number of reaction and purification steps. Moreover, the acetylation step in this process is believed to give rise to the same problems as occurs in the acetylation step of the nitrobenzene process described previously.

The preparation of hydroxy aromatic ketones by the Fries rearrangement of aromatic esters is well-known in the art. Thus, Lewis, U.S. Patent Specification No. 2,833,825 shows the rearrangement of phenyl or other aromatic esters to acylphenols or other hydroxy aromatic ketones using anhydrous fluoride as catalyst. The examples of this patent are limited to the rearrangment of esters of higher fatty -2acids with the yields ranging from 55% to 95%.

Simons et al, Journal of the America Chemical Society, 62, 485 and 486 (1940) show the use of hydrogen fluoride as a condensing agent for various rearrangements and at page 486 show the Fries rearrangement of phenyl acetate to obtain p-hydroxyacetophenone.

Dann and Mylius in a dissertation included as part of a series of Reports from the Institute for Applied Chemistry of the University of Erlangen, received for publication on January 7, 1954 and published in Annalen der Chemie 587 Band, pages 1 to 15 (1954), show the rearrangement of phenyl acetate in hydrogen fluoride to 4-hydroxyacetophenone, with a maximum yield of 81% after 24 hours of reaction time, and report a yield of 92% stated to be obtained by K.

Weichert as reported in Angewandte Chemie 56, 338 (1953). However, Dann and Mylius suggest that the difference in yields may be at least partly due to the previous ignoring by Weichert of the accompanying 2-hydroxyacetophenone.

Dann and Mylius also disclose the reaction phenol and glacial acetic acid in the presence of hydrogen fluoride to produce 4-hydroxyacetophenone at a yield of 61.6%. This reaction may be conventionally characterized as a Freidel-Crafts acetylation of phenol with acetic acid as the acetylating agent.

Simon et al, Journal of the American Chemical Society, 61, 1765 and 1796 (1939) teach the acylation of aromatic compounds using hydrogen fluoride as a condensing agent and in Table 1 on page 1796 show the acetylation of phenol with acetic acid to produce p-hydroxyacetophenone in 40% yield.

Meussdoerffer et al, German Offenlegungsschrift 26 16 986 published October 27, 1977 and assigned to Bayer AG, disclose the acylation of phenolic compounds such as phenol itself with an acyl halide such as acetyl choride to form hydroxy aromatic ketones.

Auwers et al, Chemische Berichte, 58, 36-51, (1925) show the Beckmann rearrangement of a large number of oximes of aromatic ketones -3most of which are substituted acetophenones. However, the only attempted rearrangement of the oxime of a ring-unsubstituted aromatic ketone was that of the oxime of o-hydroxyacetophenone, but amine was formecl, i.e. the attempted rearrangement was unsuccessful; see page 41.

I Ganboa et al, Synthetic Communications 13(11), 941-944 (1983) show the production of acetanilide from acetophenone be refluxing in a solution of hydroxylamine hydrochloride. There is however no suggestion of the synthesis of N-acylacyloxy aromatic amines such as 4-acetoxyacetani1ide (AAA) or of the synthesis of N-acylhydroxy aromatic amines such as N-acetyl-para-aminophenol (APAP).

Pearson et al, Journal of the American Chemical Society 75 5905-5908 (Dec. 5, 1953) disclose the formation of hydrazones from ketones by reaction with hydrazine hydrate and the rearrangement of the hydrazone to the amide by reaction with sodium nitrite and concentrated sulfuric acid. Specifically, on page 5907 Pearson et al show the rearrangment of p-hydrozyacetanilide. i.e. APAP The present invention provides a process for preparing an N-acyl-p-aminophenol or a 4-acyloxy-N-acrylani1ide comprising contacting a 4-acylphenol, with hydroxyl amine, or a hydroxylamine salt, and a base to form the ketoxime of said ketone, and (i) contacting said ketoxime with a Beckmann rearrangement catalyst to form an N-acyl-para-aminophenol, or (ii) contacting said ketoxime with a carboxylic acid anhydride and Beckmann rearrangement catalyst to form a 4-acyloxy-N-acylanilide.

In one specfic embodiment, N-acetyl-para-aminophenol (APAP), also known as acetaminophen, is produced from phenyl acetate, or phenol and an acetylating agent such as acetic acid, by means of an integrated process including the steps of converting the phenyl acetate, or phenol and an acetylating agent, to a 4-hydroxyacetophenone (4-HAP) by a Fries rearrangement of Friedel-Crafts acetylation respectively, and converting the 4-hydroxyacetophenone to the corresponding ketoxime with hydroxylamine or a hydroxylamine salt. The ketoxime is then subjected to a Beckmann rearrangement in the presence of a catalyst to form the N-acetyl-para-aminophenol. -4In another specific embodiment, 4-acetoxyacetani1ide (AAA) is. produced from phenyl acetate, or phenol and an acetylating agent such as acetic acid, by means of an integrated process including the steps of converting the phenyl acetate, or phenol and an acetylating agent to 4-hydroxyacetophenone (4-HAP) by a Fries rearrangement of Friedel-Crafts acetylation respectively, and converting the 4-hydroxyacetophenone to the corresponding ketoxime with hydroxylamine or a hydroxylamine salt. The ketoxime is then subjected to a Beckmann rearrangement and accompanying acetylation by contacting the ketoxime with acetic anydride and a Beckmann rearrangement catalyst to form the 4-acetoxyacetani1ide.

When carrying out the process of this invention using phenyl acetate as the starting material, the initial Fries rearrangement to produce 4-hydroxyacetophenone (4-HAP) from phenyl acetate is defined by equation (I): If phenol and an aceylating agent are used as the starting material, the resulting acetylation reaction to form 4-HAP is indicated by equation (II) HX where X is the residue minus an acetyl group of compounds which are known acetylating agents. X may. be, for example, hydroxy, acetoxy, or halide, including fluoride, chloride, bromide, or iodine.

Acetylating agents which may be used are for example, acetic acid, acetic anhydride, acetyl fluoride, acetyl chloride and acetyl bromide. -5ihe ketoxiine formation of this invention proceeds as indicated in equation (III): HOAr -C=Q + ,,NH20H‘'->H0Arl-C=N0H + H?0 The formation of the ketone of 4-HAP, i.e. 4-HAP oxime, proceeds as in equation (IV): ',nh2oh·' base When N-acyl-hydroxy aromatic amines are the desired product, the Beckmann rearrangement of this invention proceeds as in equation (V): R HR HOA^-C'NOH-cata.llA*-> H0Arl-N-C=0 while the Beckmann rearrangement when APAP is the desired product proceeds as in equation (VI) When N-acyl-acyloxy aromatic amines are the desired product, the Beckmann rearrangement and accompanying acylation of this invention proceeds as in equation (VII): -6η Ο Η R κ 5 I I HOAr'-C=NOH » (RCO)jO "taVs 1 —, R-COAr1-N-CO - RCOOH while the Beckmann rearrangement and accompanying acylation when AAA is the desired product proceeds as in equation (VIII): γη OH CH, || | | J 10 ho7o>--oh + (CH3CO)2O cata1^ ch3-co-^n-c-o '—' +CH3COOH In equations (III),(V) and (VII), Ar^ is 1,4-phenylene.

The R groups in the foregoing equations may be the same or different and are each a monovalent organic radical containing, for example, 1 to 18 carbon atoms, preferably 1 to 4 carbon atoms. R may be, for example, alkyl, alkenyl, alkoxy, acyl or acyloxy containing 1 to 18 carbon atoms, either unsubstituted or substituted with radicals such as halogen, e.g. chlorine, bromine, or iodine; hydroxy; amino; or sulfhydryl; or any aryl radicals, Ar, which may be a monovalent radical resulting from the removal of one ring hydrogen atom from benzene, naphthalene, or biphenyl, either unsubstituted or with ring hydrogens substituted with radicals such as alkyl, alkenyl, alkynyl, alkoxy or acyloxy containing 1 to 18 carbons atoms, aralkyl containing 7 to 18 carbon atoms; halogen, e.g. chlorine, bromine, or iodine; hydroxy; amino; or sulfhydryl. Ar is preferably phenyl, 2 naphthyl, 3- phenyl-phenyl or 3 methyl-phenyl. Preferably, R is the same in all occurrences in equations (III), (V), and (VII) and is methyl, ethyl, propyl, of n-butyl and most preferably methyl corresponding to the use of acetate esters and ketones in the latter equations. The preferred specfic hydroxy aromatic ketone used to form the oxime is 4- hydroxyacetophenone (4-HAP) and the preferred products are 4-acetoxyacetani1ide (AAA) and N-acetyl-para-aminophenol (APAP).

The hydroxy aromatic ketone used to form the oxime may be prepared by any method known in the art. For example, it may be -7prepared by the Fries rearrangement of the corresponding aromatic ester as indicated by the following equation, which is a generalized for of equation (I), where ArJ and R have the defintions given above: H· ! I } HO-Ar -CR Alternatively, a phenolic compound and an acylating agent may be reacted in a Friedel-Crafts acylation to form the hydroxy aromatic ketone, in accordance with the following equation, which is a generalized form of equation (II) • 0 II where Ar'- and R have the meanings given previously and X is the residue minus the acyl group, R-CO-,of the compounds which are known acylating agents, such as hydroxy, acyloxy, e.g. acetoxy, and halide, e.g. flouride, chloride, bromide, and iodide. The phenolic compound which may be employed is phenol.

Acylating agents which may be used are for example alkanoic acids, e.g. acetic and propionic acids, alkanoic acid anhydrides, e.g. acetic and propionic anhydrides, and acyl halides, e.g. acetyl and propionyl fluorides, chlorides, and bromides. Note that although the reaction of a phenolic compound and an acylating agent is characterized herein as a Friedel-Crafts acylation, no opinion as to the mechanism of reaction should be implied by this characterization.

The catalyst for both of the foregoing reactions is preferably hydrogen fluoride but any other catalyst known in the art to be effective for the Fries and Friedel-Crafts reactions may be used, e.g. aluminum chloride, zinc chloride, or boron trifluoride.

In carrying out the reaction, the aromatic ester or phenolic -8compound and acylating agent, catalyst and if desired when an aromatic ester is the starting material, an additive for the reaction such as acetic anhydride or acetic acid, may be charged to corrosion-resistant reactor and the mixture maintained at a temperature, for example, of about 20 to 100°C for a period , for example, of about a half to about 4 hours, at a pressure, for example, of about 50 to about 500 psi (3.4 to 34 bar). If HF is used as the catalyst it may be charged as a liquid or a gas using technologies of handling well-known to those skilled in the art. In carrying out the reaction, an inert gas such as nitrogen may be used to keep the reaction space under the desired pressure and sufficient HF in contact with the reacting liquid. An excess of HF is generally used, for example, about 7 to about 75 moles per mole aromatic ester or phenolic compound initially present in the reaction zone. If AAA or APAP is the desired product of the reaction, the starting material if a Fries rearrangement is employed will be phenyl acetate while phenol and an aceylating agent such as acetic acid is the starting material if a Friedel-Crafts acylation is utilized. In both cases, the starting material is converted to 4-HAP which is in turn converted by the process of this invention to AAA or APAP.

The conversion of hydroxy aromatic ketones, e.g. 4-HAP, into N-acylacyloxy aromatic amines, e.g., AAA or into N-acy1-hydroxy aromatic amines e.g. APAP, is accomplished by first forming the ketoxime from the hydroxy aromatic ketone as indicated by equations (III) and (IV), by contacting the ketone with hydroxylamine or a hydroxylamine salt, e.g. hydroxylamine hydrochloride, hydroxylamine sulfate, hydroxylamine bisulfate, or hydroxylamine phosphate, and a base e.g. ammonium hydroxylide, potassium hydroxide, sodium hydroxide, or lithium hydroxide in an amount, for example, of 1 to 3 moles per mole or hydroxylamine, at a temperature, for example, of 0 to 60°C for a period, for example, of 1 to 4 hours. Any pressure may be used, e.g. 80 mm of mercury to 10 atmospheres absolute (0.1 bar to 10.1 bar). The reaction is preferably carried out in an aqueous or alcoholic medium, i.e. in the presence of water and/or an alcohol such as methanol, ethanol, or isopropanol.

As discussed above, in accordance with one embodiment of the invention, the ketoxime may be converted into the corresponding -9N-acyl-hydroxy aromatic amine by a Beckmann rearrangement as shown in equations (V) and (VI), by contacting the ketoxime with a catalyst for the reaction at a temperature, for example of -70°C to 118°C for a period for example of ten minutes to 4 hours. The pressure is not critical and may be, for example, in the range of 80 mm of mercury to 10 atmospheres absolute (0.1 bar to 10.1 bar). Preferably, the rearrangement is conducted at a temperature of from about - 70°C to about 40°C and at a molar ratio of ketoxime to catalyst from about 1:0.001 to about 1:0.1, for a reaction time of about ten minutes to about two hours. Any Beckmann rearrangement catalyst may be used, as for example, an acid, e.g. mineral acid such as sulfuric or hydrochloric acid, an organic acid such as trifluoroacetic acid, para-toluenesulfonic acid, benzenesulfonic acid or methanesulfonic acid, an acidic ion-exchange resin such as Amberlyst (trade mark) 15 or Nafion (trade mark) 501 which are sulfonic acid ion-exchange resins, or thionyl chloride in liquid sulfur dioxide, diethyl ether, ethylacetate, acetone, tetrahydrofuran, or methylene chloride. Preferably the Beckmann rearrangement is conducted with thionyl chloride in liquid sulfur dioxide. The reaction may be advantageously carried out in the presence of the glacial carboxylic acid corresponding to the N-acyl group of the desired product which will ordinarily yield the hydroxy derivative. The total amount of glacial carboxylic acid is not critical but is usually present such that the ketoxime concentration is in the range of 2 to 50% by weight at the start of the reaction.

In accordance with another embodiment of the invention, the ketoxime may be converted into the corresponding N-acyl-acyloxy aromatic amine by a Beckmann rearrangement and accompanying acylation as shown in equations (VII) and (VIII), by contacting the ketoxime with the appropriate carboxylic acid anhydride and a Beckmann rearrangement catalyst at a temperature, for example, of 0 to 118°C for a period for example of 1 to 4 hours. As defined in the foregoing equations, any of a broad class of anhydrides may be used but the anhydride is preferably that of an alkanoic acid containing 2 to 4 carbon atoms, e.g. acetic anhydride, propionic anhydride, or n-butyric anhydride.

The pressure is not critical and may be, for example, in the range of 80 mm of mercury to 10 atmospheres absolute (0.1 to 10.1 bar). Again, any Beckmann rearrangement catalyst may be used, as discussed above. -10The reaction may be advantageously carried out in the presence of the glacial carboxylic acid corresponding to the anhydride employed in the reaction in an amount, for example up to 50% by weight of the anhydride. The total amount of glacial carboxylic acid is not critical but the total amount of anhydride or anhydride/acid mixture is such that the ketoxime concentration is in most cases in the range of about 2 to 50 % by weight at the start of the reaction.

The following examples further illustrates the invention.

Example 1 This example illustrates the preparation of 4-hydroxyacetophenone by the Fries rearrangement of phenyl acetate using hydrogen fluoride as catalyst.

I To a 300 cc Hastelloy C autoclave was charged 40.8g (0.3 mol) of phenyl acetate. The autoclave was sealed, immersed in a Dry Ice/isopropanol bath and cooled internally to -45°C, and evacuated to ca. 100 Torr (0.13 bar). Addition of 120g (6.0 mol) of anhydrous hydrogen fluoride was performed in a manner such as that the internal temperature of the autoclave did not exceed 0°C. The internal pressure of the reactor was then adjusted to 0 psig (1.1 bar) with nitrogen. The contents of the autoclave were stirred and heated to 75°C for 1 h. The hydrogen flouride was vented over a 45 min period at ca. 45°C. The mixture was poured onto 25g of ice and neutralized with 45% of potassium hydroxide solution. The aqueous mixture was extracted with ethyl acetate. The organic fraction was then dried over anhydrous magnesium sulfate, filtered, and the solvent was removed on a rotary evaporator to yield 44.Og of a dark green solid corresponding to 99.9% conversion of phenyl acetate and 94.3% selectivity of 4-hydroxyacetophenone.

Example 2 This example illustrates the preparation of 4-hydroxyacetophenone by the Fries rearrangement of phenyl acetate using hydrogen fluoride as -11catalyst with acetic anhydride as additive.

To a 300 cc Hastelloy C autoclave were added 30.6 grams (0.3 mole) of acetic anhydride. The autoclave was cooled to -50°C and evacuated to 5 Torr (0.007 bar) whereupon 120g (6.0 mole) of anhydrous hydrogen fluoride was transferred from a cylinder to the autoclave. After the transfer of hydrogen fluoride was completed, the internal temperature and the internal pressure of the autoclave was adjusted to -50°C and 1.1 bar using nitrogen, respectively. To the stirred autoclave was added 81.6g (0.6 mol) of phenyl acetate at such a rate that the temperature of the mixture did not exceed -23°C. Upon completion of phenyl acetate addition, the contents were warmed to 50°C and stirred for 3 h during which time a pressure of ca. 40 psig (3.9 bar) was generated. At the end of the run, the hydrogen fluoride was vented through a caustic scrubber and the contents of the autoclave were poured onto ca. 30 g of ice. The pH of the mixture was adjusted to 6.5 using 45% potassium hydroxide and the mixture was then extracted with 75ml of ethyl acetate (3x). The organic solution was dried over anhydrous magnesium sulfate, filtered, and the solvent was removed using a rotary evaporator.

The reaction proceeded with 98.1% conversion of phenyl acetate and with the following select!vities: phenol 1%, 4-hydroxyacetophenone (4-HAP) 82.3%; 2-hydroxyacetophenone (2-HAP) 4.3%; 3-hydroxyacetophenone (3-HAP) 0.1%; 4-acetoxyacetophenone (4-AAP) 3.8%; and 4-(41-hydroxyphenyl)acetophenone (HPAP) 0.4%.

Example 3 This example describes the formation of 4-hydroxyacetophenone by the Fries rearrangement of phenyl acetate using hydrogen fluoride as catalyst and acetic acid as additive.

The procedure for Example 2 was repeated except that 18 grams (0.3 mole) of acetic acid rather than acetic anhydride were charged to the reactor before it was cooled and charged with the hydrogen fluoride. A conversion of 99.0% of phenyl acetate was obtained with the following selectives: phenol 3.3%; acetic acid 0.8%; 4-HAP 80.8%; -123- HAP 0; 2-HAP 5.8%; 4-AAP 0.3%; and HPAP 0.3%.

Example 4 This example illustrates the preparation of 4-hydroxyacetophenone (4HAP) by the Friedel-Crafts acetylation of phenol with acetic acid as the acetylating agent.

Phenol (9.4g, 0.1 moles) and acetic acid (12.Og, 0.2 moles) were charged to a 300ml Hastelloy C autoclave at room temperature. The reactor was evacuated and cooled to -20°C. HF (lOOg, 5 moles) was then transferred into the reactor. The reactor was heated to 80°C and maintained for 1 hour at reaction temperature. At the end of the reaction the reactor was cooled to 20°C and the excess HF was vented to a KOH scrubber. Ethyl acetate was added to the contents of the reactor. The mixture was then neutralized with 45% aqueous KOH. The resulting organic phase was separated, dried over MgSO^ and evaporated to afford a yellow solid which contained 13.lg (0.096 moles) of 4-HAP.

Example 5 This example illustrates the formation of 4-hydroxyacetophenone oxime from 4-hydroxyacetophenone and hydroxylamine hydrochloride.

A solution was prepared by adding 13.6g (0.1 mol) of 4- hydroxyacetophenone 7.6g (0.11 mol) of hydroxylamine hydrochloride, and lOg of water to 40ml of ethanol. To the solution was added 5.0g of 30% ammonium hydroxide which was then heated at reflux for 2 hours.

The ethanol was removed on a rotary evaporator to yield a yellow oil.

An extractive work-up afforded 15.lg (99%) of 4-hydroxyacetophenone oxime.

Example 6 This example illustrates the formation of 4-hydroxyacetophenone oxime from 4-hydroxyacetophenone and hydroxylamine sulfate. -13A solution was prepared by adding 20.4g (0.15 mol) of 4-hydroxyacetophenone and 13.Og (0.08 mol) of hydroxylamine sulfate to 100ml of water at 70°C. To the solution was added 16.3ml of 30% ammonium hydroxide which was then heated at reflux for 0.5h. White crystals formed upon cooling yielding 21.Og (92.6%) of 4-hydroxyacetophenone oxime.

Example 7 This example illustrates the formation of 4-hydroxyacetophenone oxime from 4-hydroxyacetophenone and hydroxylamine phosphate.

A solution was prepared by adding 20.4g (0.15 mol) of 4-hydroxyacetophenone and 12.9g (65.6 mmol) of hydroxylamine phosphate to 100ml of water at 70°C. To the solution was added 16.3 ml of 30% ammonium hydroxide which was then heated at reflux for 0.5h. White crystals formed upon cooling yielding 21.Og (92.6%) of 4-hydroxyacetophenone oxime.

Example 8 This example illustrates the formation of 4-acetoxyacetanilide (AAA) by the Beckmann rearrangement and accompanying acetylation of 4-hydroxyacetophenone oxime using an acidic ion-exchange resin as catalyst.

A solution of lOg (22.0 mmol) of 4-hydroxyacetophenone oxime, 3.0 of Amberlyst (trade mark) 15 (a sulfonic acid ion-exchange resin made by Rohm & Haas), and 75 ml of a mixture of glacial acid and acetic anhydride (1:1) was heated at reflux under nitrogen for 4 h. The ion-exchange resin was then removed and the aceic acid/acetic anhydride was distilled in vacuo to yield yellow-white crystals. The crystals were dissolved in ethyl acetate and treated with activated carbon and anhydrous magnesium sulfate. The mixture was filtered and the solvent was removed on a rotary evaporator to yield 3.4g (80.4%) of yellow crystals of 4-acetoxyacetanilide (AAA). -14Example 9 This example illustrates the formation of 4-acetoxyacetanilide (AAA) by the Beckmann rearrangement and accompanying acetylation of 4-hydroxyacetophenone oxime using methanesulfonic acid as catalyst.

A solution of lOg (66.2 mmol) of 4-hydroxyacetophenone oxime, 1.6 of 70% methanesulfonic acid, 50g of acetic anhydride and lOOg of glacial acetic acid was heated at reflux under under nitrogen for 2 h. Rotary evaporation of the solution yielded 17.Og of light brown crystals. Recrystallization from water yielded 6.7g (52.4%) of 4-acetoxyacetanilide (AAA). The mother liquor contained 32.0% of AAA for a total yield of 84.4%.

Example 10 This example illustrates the formation of 4-acetoxyacetanilide (AAA) by the Beckmann rearrangement and accompanying acetylation of 4-hydroxyacetophenone oxime using phosphoric acid (H^PO^) as catalyst.

To a mixture of lOOg of glacial acetic acid, 50g of acetic anhydride, and 3.6g of 85% H^PO^, sparged with nitrogen for 30 minutes, was added lOg of 4-hydroxyacetophenone oxime. The mixture was heated at reflux for 1 hour under a nitrogen atmosphere, then cooled to room temperature and neutralized with 13% Νβ2Ε0β. The mixture was evaporated to dryness using a rotary evaporator and the solid was dissolved in 200g of boiling water. After hot filtration, the solution was allowed to cool and stand overnight. The ensuing white crystals were collected, washed with 20ml of water, and dried in a vacuum oven (60°C/100mm Hg (0.13 bar)) for 2 hours. Upon drying, 9.4g (73.9%) of white crystalline plates of 4-acetoxyacetanilide having a melting point of 148-150°C was obtained. An additional 0.8g of AAA and 1.5 of N-acetyl-paraaminophenol (APAP) were reclaimed from the mother liquor.

Example 10A The procedures of Examples 8 to 10 may also be used to prepare -15N-propionyl-(4-propionoxyphenyl) amine from phenyl propionate or phenol and propionic acid, and propionic anhydride; and N-n-butyryl(4-n-butyroxyphenyl) amine from phenyl n-butyrate or phenol and n-butyric acid, and n-butyric anhydride, in the first and second reactions respectively.

The N-aceyl-aceyloxy aromatic amines, e.g. AAA, of this invention may be utilized as monomers in the preparation of poly(ester-amide)s capable of forming an anisotropic melt phase and suitable for being formed into shaped articles such as molded articles, fibers and films, as shown, for example in U.S. Patent Specification Nos. 4,330,457; 4,339,375; 4,341,688; 4,351,918; and 4,355,132.

The N-acyl-acyloxy aromatic amines of this invention, e.g. AAA, may also be hydrolyzed to form the corresponding N-acyl-hydroxy aromatic amine, e.g. N-acetyl-para-aminophenyl (APAP) which is one of most widely used over-the-counter analgesics. The following example illustrates this process: Example 11 A mixture of 5g (25.9 mmol) of 4-acetoxyacetanilide (AAA), 1.4g of 70% methanesulfonic acid, and 50g of water was heated at reflux for lh. Upon cooling, white crystals formed. Analysis (GLC) of the crystals as well as the aqueous solution indicated 90% conversion of the AAA to N-acetyl-para-aminophenol (APAP).

Example 12 This example illustrates the formation of N-acetyl-para-aminophenol by the Beckmann rearrangement of 4-hydroxyacetophenone oxime using an acidic ion-exchange resin as catalyst.

A mixture of 3.0g of Amberlyst (trade mark) 15 (a sulfonic acid ion-exchange resin made by Rohm & Haas), 3.0g (22.0 mmol) of 4-hydroxyacetophenone oxime, and 50ml of acetic acid was heated at reflux under nitrogen for 2h. The ion exchange resin was then removed -16and the acetic acid was distilled in vacuo to afford an orange residue. The residue was dissolved in ethanol and treated with activated carbon and anhydrous magnesium sulfate. Removal of the ethanol using a rotary evaporator produced 2.9g of a yellow oil, which upon drying afforded 2.0g (66.7%) of N-acetyl-para-aminophenol.

Example 13 This example illustrates the formation of N-acetyl-para-aminophenol by the Beckmann rearrangememt of 4-hydroxyacetophenone oxime using trifluoroaeetic acid as catalyst.

A solution of lOg (66.2 mmol) of 4-hydroxyacetophenone oxime and 75g of trifluoroaeetic acid was heated at reflux under a nitrogen atmosphere. The trifluoroaeetic acid was then removed in a rotary evaporator to afford 14.7g of oil which was dissolved in 100 ml of water. Upon cooling to 0°C for 0.5h, crystallization occurred. Filtration and drying of the crystals yielded 7.1g (71%) of N-acetyl-para-aminophenol.

Example 14 This example illustrates the formation of N-acetyl-para-aminophenol by the Beckmann rearrangememt of 4-hydroxyacetophenone oxime using thionyl chloride in liquid sulfur dioxide as catalyst.

A pressure bottle (cooled in a C02/acetone bath) was charged with 50 ml of S02, 0.05 ml of SOC12, and 15g of 4-hydroxyacetophenone oxime. The COg/acetone bath was removed and the contents of the pressure bottle stirred for 1.5 h at room temperature. The S02 was then vented and the crystals washed from the pressure bottle with 50 ml of warm water. The pH of the aqueous slurry was adjusted to 6.5 by dropwise addition of 30% NH^OH. The slurry was cooled in an ice bath and then filtered. -17The filtered crystals were washed with 10 mL of ice water and dried overnight in a vacuum oven (60°C/100 mm Hg (0.13 bar)) yielding 13.3g (88.7%) of white crystals of N-acetyl-para-aminophenol having a melting poinl of 166.5-170°C.

Example 15 The procedures of Examples 12 through 14 may also be used to prepare N-propionyl-para-aminophenol from phenyl propionate or phenol and propionic acid; and N-n-butyryl-para-aminophenol from phenyl n-butyrate of phenol and n-butyric acid.

Example 16 A 250 ml pressure bottle was first cooled in a Dry Ice/acetone bath and was then charged with 50 ml of S0£ (via vacuum transfer), 0.05 ml of S0CT2* anc* 15g of 4-hydroxyacetophenone oxime. The Dry Ice/acetone bath was removed and the contents of the pressure bottle stirred for 1.5 h at room temperature. The SO2 was then vented and the crystals washed from the pressure bottle with 50 ml of warm water. The pH of the aqueous slurry was adjusted to 6.5 by the dropwise addition of concentrated ammonium hydroxide. The slurry was cooled in an ice bath and then filtered. The filtered crystals were washed with 10 ml of ice water and dried overnight in a vacuum oven at 60°C, yielding 13.3g of white N-acetyl-para-aminophenol crystals with a melting point of 166.5-170°C.

Example 17 The same general procedure as Example 16 was employed except that tap water (24°C) was used to wash the crystals from the pressure bottle. Also, the amount of SOC^ was increased to 0.1 ml and the reaction time was decreased to 25 minutes. Off-white crystals of N-acetyl-para-aminophenol (13.7g) were recovered with a melting point of 165-169°C. -18Example 18 This example illustrates the preparation of N-acetyl-para-aminophenol by the Beckmann rearrangement of 4-hydroxyacetophenone using thionyl chloride as catalyst in diethyl ether.

A 250 ml round-bottom flask equipped with a reflux condenser and addition funnel was charged with 5g of 4-hydroxyacetophenone oxime dissolved in 50ml of anhydrous diethyl ether. A solution of 0.5 ml of thionyl chloride in 15 ml of ether was added dropwise from the addition funnel. The contents of the flask were stirred during the addition and for an additional 30 minutes after completion of the addition. The ether was then removed on a rotovap. The solid residue was then dissolve in 25ml of hot water. The pH of the solution was adjusted to about 6.5 with ammonium hydroxide and subsequently the solution was cooled in an ice bath. The crystals which were formed were filtered and washed with approximately 10 ml of ice water and then dried in a vacuum oven at 65°C overnight. Brown crystals of N-acetyl-para-aminophenol (l.lg) were obtained with a melting point of 161-2°C.

Example 19 This example illustrates the preparation of N-acetyl-para-aminophenol from 4-hydroxyacetophenone, using thionyl chloride as the catalyst in ethyl acetate.

The same procedure as Example 18 was employed except that ethyl acetate was used as the solvent instead of diethyl ether. Light brown crystals of N-acetyl-para-aminophenol (1.9g) with a melting point of 158-161°C were recovered.

Example 20 This example illustrates the preparation of N-aceylated-para-aminophenol from 4-hydroxyacetophenone using thionyl chloride as catalyst in acetone. -19The same procedure as Example 18 was employed except that acetone was used as the solvent instead of diethyl ether. Brown crystals of N-acetyl-para-aminophenol (3.7g) with a melting point of 159-161°C were recovered.

Example 21 This example illustrates the preparation of N-acetyl-para-aminophenol from 4-hydroxyacetophenone oxime using thionyl chloride as catalyst in tetahydrofuran.

The same procedure as Example 18 was employed except that tetrahydrofuran was used as solvent instead of diethyl ether. Tan crystals of N-acetyl-para-aminophenol (2.5g) with a melting point of 156-8°C were recovered .

Example 22 This example illustrates the preparation of N-acetyl-para-aminophemol from 4-hydroxyacetophenone oxime using thionyl chloride as the catalyst in methylene chloride.

The same procedure as Example 18 was employed but methylene chloride was used as the solvent instead of diethyl ether. Dark brown crystals of N-acetyl-para-aminophenyl (2.7g) with a melting point of 152-156°C were obtained.

Example 23 This example illustrates the preparation of N-aceytl-para-aminophenol from 4-hydroxyacetophenone oxime using thionyl chloride as catalyst in acetone, under vacuum conditions.

The same procedure as Example 18 was employed except that acetone was used as the solvent instead of diethyl ether and the system was run under vacuum (360 mm Hg (0.48 bar)). Tan crystals of N-acetyl-para-aminophenol (3.6g) with a melting point of 162-164°C were obtained. -20Example 24 This example illustrates the fact that the process of the present invention is capable of producing nearly quantitative yields of the desired N-acy1-hydroxy aromatic amine.

The same general procedure as Example 17 was employed except that the filtrate was also analysed for N-acetyl-para-aminophenol to determine the actual product yield. The recovered solid weight 13.7g and the filtrate contained an additional 0.7g of N-acetyl-para-aminophenol. Therefore, a yield of 97 percent was realized.

Claims (14)

1. A process for preparing an N-acyl-p-aminophenol or a 4-acyloxy-N-acyl-ani1ide comprising contacting 4-acylphenol with hydroxylamine, or a hydroxyimine salt, and a base to form the ketoxime of said 4-acylphenol, and (i) contacting said ketoxime with a Beckmann rearrangement catalyst to form N-acyl-para-aminophenol, or (ii) contacting said ketoxime with a carboxylic acid anhydride and a Beckmann rearrangement catalyst to form 4-acyloxy-N-acyl-ani1ide.

2. The process of claim 1 wherein said 4-acylphenol is 4-hydroxyacetophenone, said ketoxime is 4-hydroxyacetophenone oxime, and said N-acyl-para-aminophenol is N-acetyl-para-aminophenol.

3. The process of claim 2 wherein the ketoxime is contacted with a catalytic amount of thionyl chloride in a solvent selected from liquid sulfur dioxide, diethyl ether, ethylacetate, acetone, tetrahydrofuran, and methylene chloride.

4. The process of claim 3 wherein the solvent is sulfur dioxide and the rearrangement is conducted at temperature of from -70°C to 40°C and at pressure of from 0.1 bar to 10 bar.

5. The process of claim 1 wherein said 4-acylphenol is 4-hydroxyacetophenone, said ketoxime is 4-hydroxyacetophenone oxime, said anhydride is acetic anhydride, and said 4-acyloxy-N-acyl-ani1ide is 4-acetoxyacetanilide.

6. The process of claim 5 wherein said 4-acetoxyacetanilide is hydrolyzed to form N-acetyl-para-aminophenol.

7. The process of any of claims 1 to 6 also comprising contacting an ester of phenols and a carboxylic acid with a Fries arrangement catalyst to form said 4-acylphenol.

8. The process of claim 7 wherein said Fries rearrangement catalyst is hydrogen fluoride.

9. The process of claim 7 or 8 wherein the ester is phenyl acetate.

10. The process of any of claims 1 to 6 also comprising contacting phenol and an acylating agent with a Friedel-Crafts catalyst to form said 4-acylphenol.

11. The process of claim 10 wherein said Friedel-Crafts catalyst is hydrogen fluoride.

12. The process of claim 10 or 11 wherein the acylating agent is acetic acid.

13. A process for preparing an N-acyl-p-aminophenol or a 4-acyloxy-N-acyl-anilide as claimed in claim 1 substantially as hereinbefore described with reference to the Examples.

14. An N-acyl-p-aminophenol or a 4-acyloxy-N-acyl-anilide whenever prepared by a process as claimed in any of claims 1 to 13.