A process for the preparation of p-aminophenol

Abstract

The present disclosure relates to a process for the preparation of p-aminophenol. The process of the present disclosure is simple, efficient, cost effective and commercially scalable. The present disclosure provides p-aminophenol having a comparatively high selectivity and high yield.

Description

[0001] A PROCESS FOR THE PREPARATION OF p- AMINOPHENOL

[0002] FIELD

[0003] The present disclosure relates to a process for the preparation of / ?-aminophenol.

[0004] BACKGROUND

[0005] The background information herein below relates to the present disclosure but is not necessarily prior art.

[0006] / / ra-Arninophenol ( / ?-aminophenol / 4-aminophenol) is a key intermediate in the synthesis of paracetamol (also known as acetaminophen) which is widely used as an analgesic and an antipyretic drug. It is also a key ingredient used in the preparation of dyes and pigments, hair dye formulations, polymer synthesis and electrochemical applications such as batteries as well as corrosion inhibitor and the like.

[0007] p- Aminophenol is represented as Formula I:

[0008]

[0009] Formula I

[0010] Conventional processes for the preparation of / ?-aminophenol are associated with the drawbacks such as use of toxic and expensive reagents / catalysts which make the process hazardous and uneconomical. Further, the conventional processes involve tedious work up steps as well as formation of impurities / byproducts that affects the selectivity and yield of the final product.

[0011] Therefore, there is felt a need to provide a process for the preparation of p- aminophenol that mitigates the aforestated drawbacks or at least provide an alternative solution.OBJECTS

[0012] Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

[0013] It is an object of the present disclosure to ameliorate one or more problems of the background or to at least provide a useful alternative.

[0014] Another object of the present disclosure is to provide an improved process for the preparation of / ?-aminophenol.

[0015] Yet another object of the present disclosure is to provide a process for the preparation of p-aminophenol with a comparatively high selectivity and high yield.

[0016] Still another object of the present disclosure is to provide a simple, efficient and cost-effective process for the preparation of / ?-aminophenol.

[0017] Yet another object of the present disclosure is to provide a robust and commercially scalable process for the preparation of / ?-aminophenol.

[0018] Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

[0019] SUMMARY

[0020] The present disclosure relates to a process for the preparation of / ?-aminophenol, the process comprises the following steps:

[0021] i. oxidizing benzene by using an oxidizing agent in the presence of a first catalyst in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising phenol; ii. nitrating phenol by using a nitrating agent in a second fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-nitrophenol; and

[0022] iii. hydrogenating / ?-nitrophenol by using a hydrogenating agent in the presence of a second catalyst in a third fluid medium under stirring at a predetermined stirring speed at a third predetermined temperature for a third predetermined time period to obtain a third reaction mixture comprising / ?-aminophenol,wherein the hydrogenating agent is hydrogen gas, and a pressure of hydrogen gas during hydrogenation is in the range of 150 psi to 800 psi.

[0023] In accordance with the present disclosure, the oxidizing agent is hydrogen peroxide.

[0024] In accordance with the present disclosure, the first fluid medium is at least one selected from the group consisting of sulfolane, acetic acid, dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO).

[0025] In accordance with the present disclosure, the first predetermined temperature is in the range of 60 °C to 100 °C.

[0026] In accordance with the present disclosure, the first predetermined time period is in the range of 4 hours to 8 hours.

[0027] In accordance with the present disclosure, the first catalyst is selected from the group consisting of Cu / TiCh, Co / TiCh, Co / ZSM-5, Ni / Ac, Cu / Ac, Ni / ZSM-5, Ti / ZSM-5, Fe / Al2O3, V-doped C3N4, Fe / TiCh, activated charcoal treated with nitric acid and copper chromium based catalyst.

[0028] In accordance with the present disclosure, the first catalyst is prepared by the following substeps:

[0029] a) dissolving a catalyst precursor in a fourth fluid medium under stirring to obtain a precursor solution;

[0030] b) separately, preparing a catalyst support in a fifth fluid medium under stirring to obtain a catalyst support slurry;

[0031] c) mixing slowly the precursor solution to the catalyst support slurry under stirring at a temperature in the range of 20 °C to 40 °C for 1 hour to 6 hours to obtain a supported catalyst;

[0032] d) distilling off the fourth fluid medium and fifth fluid medium from the supported catalyst at 55 °C to 120 °C to obtain a thick paste of supported catalyst; and e) drying the thick paste of the supported catalyst at a fourth predetermined temperature followed by calcining at a fifth predetermined temperature for a fourth predetermined time period followed by cooling in the range of 20 °C to 40 °C to obtain the first catalyst.In accordance with the present disclosure, the catalyst support slurry is mixed with a hydrazine solution and subjected to a hydrothermal treatment at a temperature in the range of 120 °C to 180 °C for time period in the range of 20 hours to 24 hours followed by washing to obtain a solid product which is subsequently filtered and subjected to drying and calcination.

[0033] In accordance with the present disclosure, the catalyst precursor is at least one selected from the group consisting of Copper(II) acetate monohydrate (Cu(OAc)2 ILO), Cobalt(II) acetate (CO(OAC)2), Copper(II) acetate (Cu(OAc)2), Nickel(II) acetate (Ni(OAc)2), Nickel(II) nitrate (Ni(NOs)2), Titanium isopropoxide (Ti[OCH(CH3)2]4), Iron(III) chloride (FeCh), Ammonium metavanadate (NH4VO3) and Copper(II) nitrate trihydrate (Cu(NOs)2 3H2O).

[0034] In accordance with the present disclosure, the catalyst support is selected from the group consisting of Titanium dioxide (TiCh), Zeolite ZSM-5 (ZSM-5), Activated carbon (C), Aluminum oxide / Alumina (AI2O3), Chromium(III) nitrate nonahydrate (Cr(NOs)3 9H2O) and Graphitic carbon nitride (g-CsN4).

[0035] In accordance with the present disclosure, the fourth fluid medium is selected from the group consisting of water, acetone and isopropanol.

[0036] In accordance with the present disclosure, the fifth fluid medium is selected from the group consisting of isopropanol, acetone and water.

[0037] In accordance with the present disclosure, the fourth predetermined temperature is in the range of 25 °C to 110 °C.

[0038] In accordance with the present disclosure, the fifth predetermined temperature is in the range of 150 °C to 650 °C.

[0039] In accordance with the present disclosure, the fourth predetermined time period is in the range of 1 hour to 6 hours.

[0040] In accordance with the present disclosure, the nitrating agent is nitric acid in the presence of metal chloride, wherein the metal chloride is selected from the group consisting of zinc chloride, copper chloride, manganese chloride, iron chloride, cobalt chloride, titanium chloride, chromium chloride, aluminium chloride, gallium chloride and indium chloride.In accordance with the present disclosure, the second fluid medium is selected from the group consisting of ethyl acetate, dichloromethane, ethylene dichloride, acetonitrile, chloroform and diethyl ether.

[0041] In accordance with the present disclosure, the second predetermined temperature is in the range of 30 °C to 60 °C.

[0042] In accordance with the present disclosure, the second predetermined time period is in the range of 30 minutes to 120 minutes.

[0043] In accordance with the present disclosure, a weight ratio of phenol to the metal chloride is in the range of 1:1.3 to 1:1.5.

[0044] In accordance with the present disclosure, the third fluid medium is at least one selected from the group consisting of ethanol, water and methanol.

[0045] In accordance with the present disclosure, the third predetermined temperature is in the range of 25 °C to 80 °C.

[0046] In accordance with the present disclosure, the third predetermined time period is in the range of 120 minutes to 180 minutes.

[0047] In accordance with the present disclosure, the predetermined stirring speed is in the range of 600 rpm to 1000 rpm.

[0048] In accordance with the present disclosure, the second catalyst is selected from non-noble metal catalyst and Raney nickel, wherein the non-noble metal catalyst comprises oxides and / or metallic forms of one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), aluminium (Al), copper (Cu), chromium (Cr), titanium (Ti), zirconium (Zr), and vanadium (V), optionally supported on a support material selected from silica, alumina, zeolite, zirconia, and activated carbon.

[0049] In accordance with the present disclosure, a weight ratio of / ?-nitrophenol to the second catalyst is in the range of 1 :0.2 to 1 : 0.6.

[0050] In accordance with the present disclosure, the yield of / ?-aminophenol is in the range of 70 % to 99 %.DETAILED DESCRIPTION

[0051] The present disclosure relates to a process for the preparation of -aminophenol.

[0052] Embodiments of the present disclosure will now be described herein. Embodiments are provided so as to thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth, relating to specific components and methods, to provide a complete understanding of embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

[0053] The terminology used in the present disclosure is only for the purpose of explaining a particular embodiment, and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well, unless the context clearly suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units and / or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The particular order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

[0054] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0055] The terms first, second, third, etc., should not be construed to limit the scope of the present disclosure as the aforementioned terms may be only used to distinguish one element, component, region, layer or section from another component, region, layer or section. Terms such as first, second, third, etc., when used herein, do not imply a specific sequence or order unless clearly suggested by the present disclosure.

[0056] Conventional processes for the preparation of / ?-aminophenol are associated with the drawbacks such as use of toxic and expensive reagents / catalysts which make the processhazardous and uneconomical. Further, the conventional processes involve tedious work up steps as well as formation of impurities / byproducts that affects the selectivity and yield of the final product.

[0057] The present disclosure provides a process for the preparation of / ?-aminophenol.

[0058] The process of the present disclosure provides / ?-aminophenol with a comparatively high selectivity and high yield. Further, the process of the present disclosure is simple, efficient, cost-effective and commercially scalable.

[0059] The present disclosure provides a process for the preparation of / ?-aminophenol. The process comprises the following steps:

[0060] i. oxidizing benzene by using an oxidizing agent in the presence of a first catalyst in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising phenol; ii. nitrating phenol by using a nitrating agent in a second fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-nitrophenol; and

[0061] iii. hydrogenating / ?-nitrophenol by using a hydrogenating agent in the presence of a second catalyst in a third fluid medium under stirring at a predetermined stirring speed at a third predetermined temperature for a third predetermined time period to obtain a third reaction mixture comprising / ?-aminophenol,

[0062] wherein the hydrogenating agent is hydrogen gas, and a pressure of hydrogen gas during hydrogenation is in the range of 150 psi to 800 psi.

[0063] The process for the preparation of / ?-aminophenol is described in detail below.

[0064] In a first step, benzene is oxidized by using an oxidizing agent in the presence of a first catalyst in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising phenol.

[0065] The so-obtained first reaction mixture is distilled to obtain pure phenol.

[0066] In accordance with the present disclosure, the oxidizing agent is hydrogen peroxide.

[0067] In accordance with the present disclosure, the first catalyst is selected from the group consisting of Cu / TiCh, Co / TiCh, Co / ZSM-5, Ni / Ac, Cu / Ac, Ni / ZSM-5, Ti / ZSM-5, Fe / Al2O3, V-dopedC3N4, Fe / TiCh, activated charcoal treated with nitric acid and copper chromium based catalyst. In an exemplary embodiment, the first catalyst is Cu / TiCh.

[0068] In accordance with the present disclosure, the first fluid medium is at least one selected from the group consisting of sulfolane, acetic acid, dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO). In an exemplary embodiment, the first fluid medium is mixture of sulfolane and acetic acid.

[0069] In accordance with the present disclosure, the first predetermined temperature is in the range of 60 °C to 100 °C. In an exemplary embodiment, the first predetermined temperature is 80 °C.

[0070] In accordance with the present disclosure, the first predetermined time period is in the range of 4 hours to 8 hours. In an exemplary embodiment, the first predetermined time period is 6 hours.

[0071] In accordance with the present disclosure, the first catalyst is prepared by the following substeps:

[0072] a) dissolving a catalyst precursor in a fourth fluid medium under stirring to obtain a precursor solution;

[0073] b) separately, preparing a catalyst support in a fifth fluid medium under stirring to obtain a catalyst support slurry;

[0074] c) mixing slowly the precursor solution to the catalyst support slurry under stirring at a temperature in the range of 20 °C to 40 °C for 1 hour to 6 hours to obtain a supported catalyst;

[0075] d) distilling off the fourth fluid medium and fifth fluid medium from the supported catalyst at 55 °C to 120 °C to obtain a thick paste of supported catalyst; and e) drying the thick paste of the supported catalyst at a fourth predetermined temperature followed by calcining at a fifth predetermined temperature for a fourth predetermined time period followed by cooling in the range of 20 °C to 40 °C to obtain the first catalyst.

[0076] The process for the preparation of first catalyst is described in detail below.

[0077] A catalyst precursor is dissolved in a fourth fluid medium under stirring to obtain a precursor solution.In accordance with the present disclosure, the catalyst precursor is at least one selected from the group consisting of Copper(II) acetate monohydrate (Cu(0Ac)2 H2O), Cobalt acetate, Cu acetate, Nickel acetate, Nickel nitrate, titanium isopropoxide, Iron chloride, ammonium metavanadate (NH4VO3) and Cu (NCh)? 3H2O.

[0078] In accordance with the present disclosure, the fourth fluid medium is selected from the group consisting of water, acetone and isopropanol.

[0079] Separately, preparing a catalyst support in a fifth fluid medium under stirring to obtain a support slurry.

[0080] In accordance with the present disclosure, the catalyst support is selected from the group consisting of Titanium dioxide (TiCh), Zeolite ZSM-5 (ZSM-5), Activated carbon (C), Aluminium oxide / Alumina (AI2O3), Chromium(III) nitrate nonahydrate (Cr(NOs)3 9H2O) and Graphitic carbon nitride (g-CsN^.

[0081] The precursor solution is mixed slowly to the catalyst support slurry under stirring at a temperature in the range of 20 °C to 40 °C for 1 hour to 6 hours to obtain a supported catalyst. In an exemplary embodiment, the precursor solution is mixed slowly to the support slurry under stirring at a temperature in the range of 27 °C for 2 hours to obtain a supported catalyst.

[0082] The fourth fluid medium and the fifth fluid medium from the supported catalyst is distilled off at 55 °C to 120 °C to obtain a thick paste of supported catalyst.

[0083] The thick paste of the supported catalyst is dried at a fourth predetermined temperature followed by calcining at a fifth predetermined temperature for a fourth predetermined time period followed by cooling in the range of 20 °C to 40 °C to obtain the first catalyst.

[0084] In accordance with the present disclosure, the fourth predetermined temperature is in the range of 25 °C to 110 °C.

[0085] In accordance with the present disclosure, the fifth predetermined temperature is in the range of 150 °C to 650 °C.

[0086] In accordance with the present disclosure, the fifth predetermined time period is in the range of 1 hour to 6 hours.In a second step, phenol is nitrated by using a nitrating agent in a second fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising -nitrophenol.

[0087] The so-obtained second reaction mixture is distilled to obtain the / ?-nitrophenol.

[0088] In accordance with the present disclosure, the nitrating agent is nitric acid in the presence of metal chloride, wherein the metal chloride is selected from the group consisting of zinc chloride, copper chloride, manganese chloride, iron chloride, cobalt chloride, titanium chloride, chromium chloride, aluminium chloride, gallium chloride and indium chloride. In an exemplary embodiment, the nitrating agent is nitric acid in the presence of zinc chloride. In accordance with the present disclosure, the weight ratio of phenol to the metal chloride is in the range of 1 : 1.3 to 1 : 1.5. In an exemplary embodiment, the weight ratio of phenol to the metal chloride is 1:1.45.

[0089] In accordance with the present disclosure, the second fluid medium is selected from the group consisting of ethyl acetate, dichloromethane, ethylene dichloride, acetonitrile, chloroform and diethyl ether. In an exemplary embodiment, the second fluid medium is ethyl acetate.

[0090] In accordance with the present disclosure, the second predetermined temperature is in the range of 30 °C to 60 °C. In an exemplary embodiment, the second predetermined temperature is 45 °C.

[0091] In accordance with the present disclosure, the second predetermined time period is in the range of 30 minutes to 120 minutes. In an exemplary embodiment, the second predetermined time period is 60 minutes.

[0092] In a third step, -nitrophenol is hydrogenated by using a hydrogenating agent in the presence of a second catalyst in a third fluid medium under stirring at a predetermined stirring speed at a third predetermined temperature for a third predetermined time period to obtain a third reaction mixture comprising / ?-aminophenol, wherein the hydrogenating agent is hydrogen gas, and a pressure of hydrogen gas during hydrogenation is in the range of 150 psi to 800 psi. After the H2 consumption is stopped, the reaction is terminated. The reactor comprising the third reaction mixture is cooled and vented off followed by filtering to obtain a crude product. The so-obtained crude product is neutralized with sodium m-bisulphite and treated with activated carbon to obtain pure -ami nophenol.Hydrogen gas in the presence of the second catalyst facilitates the addition of hydrogen across the nitro group, reducing it to the amino group.

[0093] In accordance with the present disclosure, the second catalyst is selected from non-noble metal catalyst and Raney nickel, wherein the non-noble metal catalyst comprises oxides and / or metallic forms of one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), aluminium (Al), copper (Cu), chromium (Cr), titanium (Ti), zirconium (Zr), and vanadium (V), optionally supported on a support material selected from silica, alumina, zeolite, zirconia, and activated carbon. In an exemplary embodiment, the second catalyst is Raney nickel.

[0094] In accordance with the present disclosure, the weight ratio of / ?-nitrophenol to the second catalyst is in the range of 1:0.2 to 1: 0.6. In an exemplary embodiment, the weight ratio of p-nitrophenol to the second catalyst is 1:0.4.

[0095] In accordance with the present disclosure, the third fluid medium is at least one selected from the group consisting of ethanol, water and methanol. In an exemplary embodiment, the third fluid medium is a mixture of ethanol and water.

[0096] In accordance with the present disclosure, the predetermined stirring speed is in the range of 600 rpm to 1000 rpm. In an exemplary embodiment, the predetermined stirring speed is 800 rpm.

[0097] In accordance with the present disclosure, the third predetermined temperature is in the range of 25 °C to 80 °C. In an exemplary embodiment, the third predetermined temperature is 60 °C. In another exemplary embodiment, the third predetermined temperature is 70 °C.

[0098] In accordance with the present disclosure, the third predetermined time period is in the range of 120 minutes to 180 minutes. In an exemplary embodiment, the third predetermined time period is 150 minutes.

[0099] In accordance with the present disclosure, the yield of / ?-aminophenol is in the range of 70 % to 99 %. In an exemplary embodiment, the yield of / ?-aminophenol is 89.2 %.

[0100] The present disclosure systematically optimized reaction parameters such as temperature, hydrogen pressure, catalyst loading, and acidity to enhance conversion, minimize undesired side reactions, and achieve superior selectivity towards / ?-aminophenol.In accordance with the present disclosure, the schematic representation for the preparation of / ?-aminophenol is illustrated as Scheme A below:

[0101] B

[0102]

[0103] Scheme-A

[0104] The present disclosure provides a simple, efficient and cost effective process for the preparation of / ?-aminophenol with a comparatively high yield and high selectivity.

[0105] The present disclosure provides a robust, scalable, and industrially viable synthetic pathway for producing / ?-aminophenol directly from benzene.

[0106] The foregoing description of the embodiments has been provided for purposes of illustration and is not intended to limit the scope of the present disclosure. Individual components of a particular embodiment are generally not limited to that particular embodiment but are interchangeable. Such variations are not to be regarded as a departure from the present disclosure, and all such modifications are considered to be within the scope of the present disclosure.

[0107] The present disclosure is further described in light of the following experiments, which are set forth for illustration purposes only and not to be construed for limiting the scope of the disclosure. The following experiments are scalable to industrial / commercial processes.

[0108] EXPERIMENTAL DETAILS

[0109] Experiment 1: Preparation of / i-aminophenol in accordance with the present disclosure:

[0110] Preparation of first catalyst

[0111] General procedure:A predetermined amount of a catalyst precursor was dissolved in a predetermined amount of fourth fluid medium under stirring to obtain a precursor solution. Separately, a predetermined amount of a catalyst support was added in a predetermined amount of fifth fluid medium under stirring to obtain a catalyst support slurry. The precursor solution was slowly mixed to the catalyst support slurry under stirring at a temperature in the range of 20 °C to 40 °C for 1 hour to 6 hours to obtain a supported catalyst. The fourth fluid medium and fifth fluid medium from the supported catalyst was distilled off at 55 °C to 120 °C to obtain a thick paste of supported catalyst. The thick paste of the supported catalyst was dried at a fourth predetermined temperature followed by calcining at a fifth predetermined temperature for a fourth predetermined time period followed by cooling in the range of 20 °C to 40 °C to obtain the first catalyst.

[0112] Cl: Copper doped Tioz catalyst

[0113] 2 g of Cu(OAc)2 LO (catalyst precursor) was dissolved in 75 mL of deionized water (fourth fluid medium) under stirring to obtain a copper acetate solution. Separately, 5 g of TiCL powder (catalyst support) was added in 30 mL isopropanol (fifth fluid medium) under stirring / sonication to obtain a catalyst support slurry. The copper acetate solution was mixed slowly with the catalyst support slurry under stirring at 27 °C (room temperature) for 3 hours to obtain a supported catalyst. Water and IPA was evaporated (distilled off) from the supported catalyst at 55 °C to 120 °C to obtain a thick paste of supported catalyst. The so-obtained thick paste of the supported catalyst was dried in an oven at 80 °C to 110 °C (fourth predetermined temperature) to remove residual moisture to obtain a dried supported catalyst. The dried supported catalyst was calcined in the muffle furnace at 500 °C (fifth predetermined temperature) with a ramp rate of 5 °C / min and maintained for 2 hours (fourth predetermined time period) followed by cooling to 27 °C (room temperature) to obtain a copper doped TiCh catalyst (first catalyst). Copper concentration further increased from 5% to 40%.

[0114] Similarly, C2 to Cll catalysts were prepared by using the above general procedure as shown in Table 1:

[0115] Table 1: Catalysts preparation (C2 to Cll)

[0116]

[0117]

[0118] C12: Copper chromium based catalysts

[0119] Cu-Cr mixed oxides were synthesized via a soft-templated gel route using copper nitrate, chromium nitrate, cetyltrimethylammonium bromide (CTAB), and hydrazine. The precursor gel was prepared using a molar ratio of Cu: CTAB: hydrazine: H2O = 1 : 0.75: 1 : 300.40 g of Cr(NOs)3-9H2O was dissolved in 40 ml water followed by the addition of 2.95 g of Cu(NOs)2 3H2O to obtain a mixture. 3.9 g of cetyltrimethylammonium bromide (CTAB) was added in 5 ml of water to obtain a CTAB solution. The so obtained CTAB solution was added drop wise to the mixture to obtain a homogeneous mixture. Hydrazine solution (0.5 g of hydrazine in 2 g of water) was added drop wise to the homogeneous mixture to obtain a gel. The so obtained gel was stirred for 3 hours and subjected to hydrothermal treatment at 150 °C for 24 hours in a Teflon-lined stainless-steel autoclave under autogenous pressure to obtain a solid product. The so obtained solid product was washed with water and ethanol followed by drying at 27 °C (room temperature) for 10 hours and calcined in air at 550 °C to obtain the copper chromium based catalyst.

[0120] Step 1: Synthesis of phenol in accordance with the present disclosure

[0121] 7 ml of benzene, 18 ml of sulfolane, 1ml acetic acid (first fluid medium) and 1.2 g 40% Cu-TiO2 (first catalyst) were mixed to obtain a mixture. 18 mL of hydrogen peroxide (oxidizing agent) was added dropwise to the mixture followed by heating at 80 °C (first, predetermined temperature) and maintained for 6 hours (first predetermined time period) to obtain a first reaction mixture comprising phenol.

[0122] The so-obtained first reaction mixture was distilled to obtain pure phenol.

[0123] The so obtained amount of phenol was 2.2g with a yield of 30.7%. The pure phenol was collected at the boiling point of 181 °C.

[0124] Preparation of phenol through air oxidation route in a tubular flow reactor:

[0125] The catalytic oxidation of benzene to phenol was carried out in a fixed-bed, down-flow high-pressure reactor charged with 1.2 g of 40% Cu-TiCb (catalyst) followed by addition of benzene at a flow rate O.lml / min (Liquid Hourly Space Velocity (LHSV) preferably in the range of 30 hour'1) at a temperature in the range of 350 °C for 6 hour and an air pressure 4 MPa maintained by the air (oxidant) to obtain a reaction mixture.

[0126] The so-obtained reaction mixture was purified by distillation to obtain pure phenol. The pure phenol was collected at the boiling point of 181 °C.

[0127] Step 2: Synthesis of / ?-nitrophenol in accordance with the present disclosure

[0128] 10 g of Phenol, 1000 ml of ethyl acetate (second fluid medium) and 14.5 g of zinc chloride (metal chloride) was mixed to obtain a mixture. 10 ml of concentrated nitric acid (nitratingagent) was added dropwise to the mixture followed by heating at a temperature of 45 °C (second predetermined temperature) and maintained for 1 hour (second predetermined time period) to obtain a second reaction mixture comprisin p-nitrophenol.

[0129] The second reaction mixture was distilled to obtain pure -nitrophenol. The pure p-nitrophenol was collected at the boiling point of 279 °C.

[0130] The amount of p-nitrophenol obtained was 11 g with a yield of 74.8% and having melting point of 113 °C.

[0131] Step 3: Synthesis of p-aminophenol in accordance with the present disclosure Preparation of a second catalyst [Raney nickel (in-situ)J in accordance with the present disclosure

[0132] A. Preparation of Ni-Al alloy powder:

[0133] 5.87 g of Nickel metal (0.10 mol) and 2.70 g of aluminium metal (0.10 mol) were accurately weighed, thoroughly cleaned to remove surface oxides, and intimately mixed to obtain a metal mixture. The metal mixture was transferred to a clean ceramic crucible and heated in a muffle furnace at 600 °C to 700 °C. Upon heating, aluminium melted at approximately 660 °C and dissolved the nickel, to obtain a homogeneous molten alloy. Heating of the homogeneous molten alloy was continued for 30 minutes to ensure complete fusion. The crucible was then allowed to cool slowly to room temperature. The resulting alloy was removed from the crucible and crushed into a coarse powder, which was used as the precursor for the preparation of Raney nickel via alkali leaching.

[0134] B. Preparation of active catalyst:

[0135] The crushed Ni-Al alloy (precursor of Raney nickel) (approximately 8.6 g) was added slowly, with constant stirring, to 100 mL of 8% (w / v) sodium hydroxide solution contained in a beaker fitted with a reflux condenser at 27 °C (room temperature) and stirring at 300 rpm. During this process, aluminium selectively dissolved as sodium aluminate, accompanied by vigorous evolution of hydrogen gas. Stirring was continued until hydrogen evolution nearly ceased (60 minutes), indicating the removal of most of the aluminium to obtain an alkaline slurry. The alkaline slurry was then carefully decanted, and the remaining finely divided nickel was washed repeatedly with hot distilled water until the washings became neutral to pH paper. Finally, the catalyst was washed with distilled water followed by ethanol and stored underalcohol to prevent oxidation. The resulting wet, highly porous nickel constitutes Raney nickel (second catalyst).

[0136] Reduction of p-nitrophenol by using the so prepared Raney nickel (second catalyst) of the present disclosure:

[0137] 10 g of -nitrophenol and 4 g of wet Raney nickel (second catalyst) were mixed in a solvent which is blend of 50 ml of ethanol and 50 ml of water (third fluid medium) to obtain a mixture. The so-obtained mixture was sealed in the reactor and pressurized with hydrogen gas (hydrogenating agent) at 580 psi (pressure) followed by heating to 60 °C (third predetermined temperature) for 150 minutes (third predetermined time period) and maintained under vigorous stirring at 800 rpm to obtain a third reaction mixture comprising p-aminophenol.

[0138] After the H2 consumption was stopped, the reaction was terminated. The reactor comprising the third reaction mixture was cooled and the pressure vented off followed by filtration to remove catalyst to obtain a filtrate. The so-obtained filtrate was neutralised with sodium m- bisulphite and treated with activated carbon to obtain pure p-aminophenol (white crystals). The amount of p-aminophenol obtained was 7 g, with a yield of 89.2%, had a melting point of 189 °C.

[0139] The optimization of the process for preparation of p-aminophenol is carried out using various reaction parameters such as temperature, amount of catalyst, amount of acid and hydrogen pressure.

[0140] The optimized reaction conditions maximized the yield of p- aminophenol while minimizing the formation of undesired side product.

[0141] Catalyst regeneration:

[0142] Spent catalyst (10 g) was added to 100 mL of a 4% (w / v) sodium hydroxide solution in a reaction vessel and stirred at 300 rpm for 60 minutes under an inert atmosphere. During this treatment, most of the surface impurities were removed, resulting in reactivation of the catalyst. After 60 minutes, the alkaline solution was carefully decanted, and the remaining catalyst was washed repeatedly with hot distilled water until the washings were neutral to pH paper. The catalyst was then washed with distilled water followed by ethanol and stored under alcohol to prevent oxidation. Approximately 90% of the catalyst was recovered after regeneration. Theregenerated catalyst was reused in the reduction reaction and exhibited a conversion comparable to that of the first cycle, indicating effective regeneration of the catalyst.

[0143] The optimization of the process for the preparation of / ?-aminophenol was carried out using different reaction parameters as shown in Table 2:

[0144] 5

[0145] Table 2: Optimization of the process for the preparation of / ?-aminophenol

[0146]

[0147] Based on the experimental data for the hydrogenation of p-nitrophenol using Raney Nickel, several variations are observed.

[0148] Increasing the catalyst amount generally improves the yield, though excessive catalyst does not 10 always result in proportional gains.

[0149] Moderate reaction temperatures favor high selectivity toward p-aminophenol, whereas very high temperatures can lead to over-hydrogenation of the aromatic ring, producing by-products.

[0150] Sufficient hydrogen pressure is necessary for effective reduction, and extending reaction time increases yield at lower temperatures but promotes side reactions at higher temperatures. The 15 highest yields were achieved with moderate catalyst loading, moderate temperature, and controlled reaction time, indicating these as near-optimal conditions for selective formation of / ?-aminophenol. Overall, control of catalyst loading, temperature, solvent ratio, and reaction time is critical to maximizing yield and selectivity.

[0151] From Table 2, it is observed that the formation of p-aminophenol in this reaction is strongly dependent on effective catalytic hydrogenation conditions. Specifically, the reaction yield increases with the amount of catalyst, indicating that the active catalytic sites directly influence the reaction rate and overall conversion.

[0152] Additionally, maintaining a hydrogen pressure of approximately 580 psi is crucial for achieving a high product yield, while low or absence of hydrogen pressure drastically reduces or eliminates product formation, demonstrating that molecular hydrogen is essential to the process. The optimal temperature range of 60 °C to 75 °C indicates that the reaction has a specific thermal window in which the desired steps for formation of / ?-aminophenol are both kinetically and thermodynamically favoured. Altogether, these observations suggest that efficient hydrogen activation on the catalyst surface under optimal pressure and temperature conditions is important for maximizing p-aminophenol yield.

[0153] From Table 2, it is observed that variations in the type of catalyst, the amount of catalyst / acid / starting material, and the reaction pressure and temperature significantly influence the product selectivity towards the p-aminophenol.

[0154] As temperature increases, the yield of the side product also increases due to enhanced reaction rates. However, the high yield of the desired product is obtained at an optimum temperature, where the reaction proceeds efficiently with minimal formation of unwanted by-products. TECHNICAL ADVANCEMENT

[0155] The present disclosure described hereinabove has several technical advantages including, but not limited to, the realization of a process for the preparation of / ?-aminophenol that

[0156] • is simple, efficient and cost effective; and

[0157] • provides / ?-aminophenol with a comparatively high selectivity and high yield.

[0158] The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merelyto facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0159] The foregoing description of the specific embodiments so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

[0160] The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.

[0161] Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

[0162] The numerical values given for various physical parameters, dimensions, and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

CLAIMS:

1. A process for the preparation of / ?-aminophenol, said process comprising the following steps:i. oxidizing benzene by using an oxidizing agent in the presence of a first catalyst in a first fluid medium at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising phenol; ii. nitrating phenol by using a nitrating agent in a second fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-nitrophenol; andiii. hydrogenating / ?-nitrophenol by using a hydrogenating agent in the presence of a second catalyst in a third fluid medium under stirring at a predetermined stirring speed at a third predetermined temperature for a third predetermined time period to obtain a third reaction mixture comprising / ?-aminophenol, wherein said hydrogenating agent is hydrogen gas, and a pressure of hydrogen gas during hydrogenation is in the range of 150 psi to 800 psi.

2. The process as claimed in claim 1, wherein• said oxidizing agent is hydrogen peroxide;• said first fluid medium is at least one selected from the group consisting of sulfolane, acetic acid, dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO);• said first predetermined temperature is in the range of 60 °C to 100 °C;and• said first predetermined time period is in the range of 4 hours to 8 hours.

3. The process as claimed in claim 1, wherein said first catalyst is selected from the group consisting of Cu / TiCh, Co / TiCh, Co / ZSM-5, Ni / Ac, Cu / Ac, Ni / ZSM-5, Ti / ZSM-5, Fe / AhCh, V-doped C3N4, Fe / TiCh, activated charcoal treated with nitric acid and copper chromium based catalyst.

4. The process as claimed in claim 1, wherein said first catalyst is prepared by the following sub-steps:a) dissolving a catalyst precursor in a fourth fluid medium under stirring to obtain a precursor solution;b) separately, preparing a catalyst support in a fifth fluid medium under stirring to obtain a catalyst support slurry;c) mixing slowly said precursor solution to said catalyst support slurry under stirring at a temperature in the range of 20 °C to 40 °C for 1 hour to 6 hours to obtain a supported catalyst;d) distilling off said fourth fluid medium and fifth fluid medium from said supported catalyst at 55 °C to 120 °C to obtain a thick paste of supported catalyst; ande) drying said thick paste of said supported catalyst at a fourth predetermined temperature followed by calcining at a fifth predetermined temperature for a fourth predetermined time period followed by cooling in the range of 20 °C to 40 °C to obtain said first catalyst.

5. The process as claimed in claim 4, wherein said catalyst support slurry is mixed with a hydrazine solution and subjected to a hydrothermal treatment at a temperature in the range of 120 °C to 180 °C for time period in the range of 20 hours to 24 hours followed by washing to obtain a solid product which is subsequently filtered and subjected to drying and calcination.

6. The process as claimed in claim 4, wherein• said catalyst precursor is at least one selected from the group consisting of Copper(II) acetate monohydrate (Cu(OAc)2 LO), Cobalt(II) acetate (CO(OAC)2), Copper(II) acetate (Cu(OAc)2), Nickel(II) acetate (Ni(OAc)2), Nickel(II) nitrate (Ni(NOs)2), Titanium isopropoxide (Ti[OCH(CHs)2]4), Iron(III) chloride (FeCh), Ammonium metavanadate (NH4VO3) and Copper(II) nitrate trihydrate (Cu(NOs)2 3H2O); and• said catalyst support is selected from the group consisting of Titanium dioxide (TiCh), Zeolite ZSM-5 (ZSM-5), Activated carbon (C), Aluminum oxide / Alumina (AI2O3), Chromium(III) nitrate nonahydrate (Cr(NOs)3 9H2O) and Graphitic carbon nitride (g-CsN4).

7. The process as claimed in claim 4, wherein• said fourth fluid medium is selected from the group consisting of water, acetone and isopropanol;• said fifth fluid medium is selected from the group consisting of isopropanol, acetone and water;• said fourth predetermined temperature is in the range of 25 °C to 110 °C;• said fifth predetermined temperature is in the range of 150 °C to 650 °C; and• said fourth predetermined time period is in the range of 1 hour to 6 hours.

8. The process as claimed in claim 1, wherein• said nitrating agent is nitric acid in the presence of metal chloride, wherein said metal chloride is selected from the group consisting of zinc chloride, copper chloride, manganese chloride, iron chloride, cobalt chloride, titanium chloride, chromium chloride, aluminium chloride, gallium chloride and indium chloride;• said second fluid medium is selected from the group consisting of ethyl acetate, dichloromethane, ethylene dichloride, acetonitrile, chloroform and diethyl ether;• said second predetermined temperature is in the range of 30 °C to 60 °C;• said second predetermined time period is in the range of 30 minutes to 120 minutes; and• a weight ratio of phenol to said metal chloride of said nitrating agent is in the range of 1:1.3 to 1:1.

59. The process as claimed in claim 1, wherein• said third fluid medium is at least one selected from the group consisting of ethanol, water and methanol;• said third predetermined temperature is in the range of 25 °C to 80 °C;• said third predetermined time period is in the range of 120 minutes to 180 minutes; and• said predetermined stirring speed is in the range of 600 rpm to 1000 rpm.

10. The process as claimed in claim 1, wherein said second catalyst is selected from nonnoble metal catalyst and Raney nickel, wherein said non-noble metal catalyst comprises oxides and / or metallic forms of one or more metals selected from iron (Fe), cobalt (Co), nickel (Ni), aluminum (Al), copper (Cu), chromium (Cr), titanium (Ti), zirconium (Zr), and vanadium (V), optionally supported on a support material selected from silica, alumina, zeolite, zirconia, and activated carbon.

11. The process as claimed in claim 1, wherein a weight ratio of / ?-nitrophenol to said second catalyst is in the range of 1 :0.2 to 1 : 0.6.

12. The process as claimed in claim 1, wherein the yield of / ?-aminophenol is in the range of 70 % to 99%.

Images