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 process of 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, p- Aminophenol is represented as Formula I:

[0007] OH

[0008]

[0009] NH2

[0010] Formula I

[0011] 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.

[0012] 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.

[0013] OBJECTS

[0014] Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows: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.

[0015] Another object of the present disclosure is to provide an improved process for the preparation of / ?-aminophenol.

[0016] 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.

[0017] Still another object of the present disclosure is to provide a simple, efficient and cost-effective process for the preparation of / ?-aminophenol.

[0018] Yet another object of the present disclosure is to provide a robust and commercially scalable process for the preparation of / ?-aminophenol.

[0019] 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.

[0020] SUMMARY

[0021] The present disclosure relates to a process for the preparation of / ?-aminophenol, the process comprises the following steps:

[0022] i. nitrating benzene by using a nitrating agent under stirring at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising nitrobenzene; and

[0023] ii. reducing the nitrobenzene from the first reaction mixture by using a reducing agent in the presence of a catalyst and an acid in a fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-aminophenol.

[0024] In accordance with the present disclosure, the first reaction mixture is purified by the following sub -steps:

[0025] a) quenching the first reaction mixture in ice to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer;

[0026] b) separating the first organic layer followed by washing and treating with an aqueous alkali to obtain a crude oily nitrobenzene; andc) distilling the crude oily nitrobenzene to obtain a pure nitrobenzene.

[0027] In accordance with the present disclosure, the second reaction mixture is purified by the following sub-steps:

[0028] a) filtering the second reaction mixture followed by neutralizing to obtain a resultant mixture comprising a solid product of / ?-aminophenol and an oily fraction of aminobenzene; and

[0029] b) isolating the solid product from the resultant mixture followed by washing and drying to obtain the pure / ?-aminophenol.

[0030] In accordance with the present disclosure, the nitrating agent is a mixture of sulfuric acid and nitric acid, wherein a volume ratio of sulphuric acid to nitric acid in the nitrating agent is in the range of 1:0.7 to 1:1.

[0031] In accordance with the present disclosure, the first predetermined temperature is in the range of 40 °C to 80 °C.

[0032] In accordance with the present disclosure, the first predetermined time period is in the range of 20 minutes to 60 minutes.

[0033] In accordance with the present disclosure, a volume ratio of the benzene to the nitrating agent is in the range of 1:2 to 1:4.

[0034] In accordance with the present disclosure, the reducing agent is hydrogen gas and a pressure of hydrogen during reduction is in the range of 100 psi to 1000 psi.

[0035] In accordance with the present disclosure, the fluid medium is selected from water and ethanol.

[0036] In accordance with the present disclosure, the acid is selected from the group consisting of sulphuric acid, p-toluene sulphonic acid, acetic acid and formic acid.

[0037] In accordance with the present disclosure, the second predetermined temperature is in the range of 70 °C to 120 °C.

[0038] In accordance with the present disclosure, the second predetermined time period is in the range of 2 hours to 10 hours.In accordance with the present disclosure, a weight ratio of nitrobenzene to the catalyst is in the range of 1:0.05 to 1:0.5.

[0039] In accordance with the present disclosure, the aqueous alkali is selected from the group consisting of aqueous sodium bicarbonate, aqueous potassium bicarbonate, aqueous potassium carbonate, aqueous sodium carbonate and aqueous calcium carbonate.

[0040] In accordance with the present disclosure, the catalyst comprises an activated metal which is selected from the group consisting of activated platinum, activated nickel and activated palladium.

[0041] In accordance with the present disclosure, the catalyst is prepared by the following sub-steps:

[0042] • impregnating an aqueous catalyst precursor solution onto a support followed by drying at a third predetermined temperature for a third predetermined time period to obtain a supported catalyst; and

[0043] • calcining the supported catalyst at a fourth predetermined temperature for a fourth predetermined time period in air followed by activating the catalyst by using hydrogen in an inert gas stream at a fifth predetermined temperature for a fifth predetermined time period to obtain the catalyst.

[0044] In accordance with the present disclosure, the catalyst precursor is selected from the group consisting of chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O), platinum (II) chloride (PtCl₂), platinum (IV) chloride (PtCl₄), ammonium hexachloroplatinate (IV) ((NH₄)₂PtCl₆), potassium hexachloroplatinate (IV) (K₂PtCl₆), sodium hexachloroplatinate (IV) (Na₂PtCl₆), palladium nitrate (Pd(NO₃)₂), palladium acetate (Pd(OAc)₂), palladium acetylacetonate (Pd(acac)₂), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel acetate (Ni(CH₃COO)₂·4H₂O) and nickel chloride (NiCl₂·6H₂O).

[0045] In accordance with the present disclosure, the weight ratio of the catalyst precursor to water is in the range of 1:8 to 1: 15 in the aqueous catalyst precursor solution.

[0046] In accordance with the present disclosure, the support is selected from the group consisting of SiO₂–ZrO₂, TiO₂-ZrO₂, Al₂O₃-ZrO₂ and activated carbon.In accordance with the present disclosure, the catalyst is in the form of cylindrical shape extrudates having a diameter in the range of 0.5 mm to 2 mm and a length in the range of 1 mm to 5 mm.

[0047] In accordance with the present disclosure, the inert gas is selected from the group consisting of nitrogen, argon and helium.

[0048] In accordance with the present disclosure, the third predetermined temperature is in the range of 90 °C to 120 °C.

[0049] In accordance with the present disclosure, the fourth predetermined temperature is in the range of 275 °C to 325 °C.

[0050] In accordance with the present disclosure, the fifth predetermined temperature is in the range of 325 °C to 400 °C.

[0051] In accordance with the present disclosure, the third predetermined time period is in the range of 4 hours to 8 hours.

[0052] In accordance with the present disclosure, the fourth predetermined time period is in the range of 30 minutes to 150 minutes.

[0053] In accordance with the present disclosure, the fifth predetermined time period is in the range of 30 minutes to 150 minutes.

[0054] DETAILED DESCRIPTION

[0055] The present disclosure relates to a process for the preparation of -aminophenol.

[0056] 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.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.

[0057] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0058] 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.

[0059] 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 purity and yield of the final product.

[0060] The present disclosure provides a process for the preparation of / ?-aminophenol.

[0061] 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.

[0062] The present disclosure provides a process for the preparation of / ?-aminophenol. The process comprises the following steps:i. nitrating benzene by using a nitrating agent under stirring at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising nitrobenzene; and

[0063] ii. reducing the nitrobenzene from the first reaction mixture by using a reducing agent in the presence of a catalyst and an acid in a fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-aminophenol.

[0064] The process for the preparation of / ?-aminophenol is described in detail below.

[0065] In a first step, benzene is nitrated by using a nitrating agent under stirring at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising nitrobenzene.

[0066] In accordance with the present disclosure, benzene is added slowly in dropwise manner to a nitrating agent under stirring and maintaining the temperature below 55 °C.

[0067] In accordance with the present disclosure, the nitrating agent is a mixture of sulfuric acid and nitric acid.

[0068] In accordance with the present disclosure, a volume ratio of sulphuric acid to nitric acid in the nitrating agent is in the range of 1:0.7 to 1:1. In an exemplary embodiment, the volume ratio of sulphuric acid to nitric acid in the nitrating agent is 1:0.84.

[0069] The concentration of sulphuric acid is -98% w / w and nitric acid -65% w / w in the mixture of nitrating agent.

[0070] In accordance with the present disclosure, a volume ratio of the benzene to the nitrating agent is in the range of 1:2 to 1:4. In an exemplary embodiment, the volume ratio of benzene to the nitrating agent is 1:2.6.

[0071] In accordance with the present disclosure, the first predetermined temperature is in the range of 40 °C to 80 °C. In an exemplary embodiment, the first predetermined temperature is 60 °C.

[0072] In accordance with the present disclosure, the first predetermined time period is in the range of 20 minutes to 60 minutes. In an exemplary embodiment, the first predetermined time period is 45 minutes.In accordance with the present disclosure, the first rection mixture is purified by the following sub -steps:

[0073] a) quenching the first reaction mixture in ice to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer;

[0074] b) separating the first organic layer from the first aqueous layer followed by washing and treating with an aqueous alkali to obtain a crude oily nitrobenzene; and

[0075] c) distilling the crude oily nitrobenzene to obtain a pure nitrobenzene.

[0076] The process for the purification of the first rection mixture is described in detail below.

[0077] During the purification stage, the so-obtained first reaction mixture is quenched in ice to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer.

[0078] The first organic layer is separated from the first aqueous layer followed by washing and treating with an aqueous alkali to obtain a crude oily nitrobenzene.

[0079] In accordance with the present disclosure, the aqueous alkali is selected from the group consisting of aqueous sodium bicarbonate, aqueous potassium bicarbonate, aqueous potassium carbonate, aqueous sodium carbonate and aqueous calcium carbonate. In an exemplary embodiment, the aqueous alkali is aqueous sodium bicarbonate.

[0080] The crude oily nitrobenzene is distilled to obtain the pure nitrobenzene.

[0081] In a second step, nitrobenzene from the first reaction mixture is reduced by using a reducing agent in the presence of a catalyst and an acid in a fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-aminophenol.

[0082] In accordance with the present disclosure, the reducing agent is hydrogen gas.

[0083] In accordance with the present disclosure, the pressure of hydrogen during reduction is in the range of 100 psi to 1000 psi. In an exemplary embodiment, the pressure of hydrogen during reduction is 400 psi.

[0084] In accordance with the present disclosure, the catalyst comprises an activated metal which is selected from the group consisting of activated platinum, activated nickel and activated palladium. In an exemplary embodiment, the catalyst comprises an activated metal which isactivated platinum. In another exemplary embodiment, the catalyst comprises an activated metal which is activated palladium. In yet another exemplary embodiment, the catalyst comprises an activated metal which is activated nickel.

[0085] In accordance with the present disclosure, the acid is selected from the group consisting of sulphuric acid, p-toluene sulphonic acid, acetic acid and formic acid. In an exemplary embodiment, the acid is sulphuric acid.

[0086] An acid is used to provide the acidic environment for selective reduction.

[0087] In accordance with the present disclosure, the fluid medium is selected from water and ethanol. In an exemplary embodiment, the fluid medium is water.

[0088] In accordance with the present disclosure, a weight ratio of the nitrobenzene to the catalyst is in the range of 1:0.05 to 1:0.5. In an exemplary embodiment, the weight ratio of the nitrobenzene to the catalyst is 1:0.13.

[0089] In accordance with the present disclosure, the second predetermined temperature is in the range of 70 °C to 120 °C. In an exemplary embodiment, the second predetermined temperature is 80 °C.

[0090] In accordance with the present disclosure, the second predetermined time period is in the range of 2 hours to 10 hours. In an exemplary embodiment, the second predetermined time period is 4 hours.

[0091] In accordance with the present disclosure, the second reaction mixture is purified by the following sub-steps:

[0092] a) filtering the second reaction mixture followed by neutralizing to obtain a resultant mixture comprising a solid product of / ?-aminophenol and an oily fraction of aminobenzene; and

[0093] b) isolating the solid product from the resultant mixture followed by washing and drying to obtain a pure / ?-aminophenol.

[0094] The process for the purification of the second reaction mixture is described in detail below.The so-obtained second reaction mixture is filtered followed by neutralizing to obtain a resultant mixture comprising a solid product of / ?-aminophenol and an oily fraction of aminobenzene.

[0095] Further, the solid product is isolated from the resultant mixture followed by washing and drying to obtain the pure / ?-aminophenol.

[0096] In accordance with the present disclosure, the reaction conditions are precisely controlled to minimize the undesired formation of aminobenzene during the reduction of nitrobenzene.

[0097] In accordance with the present disclosure, the catalyst is prepared by the following sub-steps:

[0098] • impregnating an aqueous catalyst precursor solution onto a support followed by drying at a third predetermined temperature for a third predetermined time period to obtain a supported catalyst; and

[0099] • calcining the supported catalyst at a fourth predetermined temperature for a fourth predetermined time period in air followed by activating the catalyst by using hydrogen in an inert gas stream at a fifth predetermined temperature for a fifth predetermined time period to obtain the catalyst.

[0100] The process for the preparation of catalyst is described in detail below.

[0101] An aqueous catalyst precursor solution is impregnated onto a support followed by drying at a third predetermined temperature for a third predetermined time period to obtain a supported catalyst.

[0102] In accordance with the present disclosure, the catalyst precursor is selected from the group consisting of chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O), platinum (II) chloride (PtCl₂), platinum (IV) chloride (PtCl₄), ammonium hexachloroplatinate (IV) ((NH₄)₂PtCl₆), potassium hexachloroplatinate (IV) (K₂PtCl₆), sodium hexachloroplatinate (IV) (Na₂PtCl₆), palladium nitrate (Pd(NO₃)₂), palladium acetate (Pd(OAc)₂), palladium acetylacetonate (Pd(acac)₂), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel acetate (Ni(CH₃COO)₂·4H₂O) and nickel chloride (NiCl₂·6H₂O). In an exemplary embodiment, the catalyst precursor is chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O).

[0103] In accordance with the present disclosure, a weight ratio of the catalyst precursor to water is in the range of 1:8 to 1:15 in the aqueous catalyst precursor solution. In an exemplaryembodiment, the weight ratio of the catalyst precursor to water is 1: 10 in the aqueous catalyst precursor solution.

[0104] In accordance with the present disclosure, the support is selected from the group consisting of SiO₂–ZrO₂, TiO₂-ZrO₂, Al₂O₃-ZrO₂ and activated carbon. In an exemplary embodiment, the support is SiO₂–ZrO₂.

[0105] In accordance with the present disclosure, the catalyst is in the form of cylindrical shape extrudates having a diameter in the range of 0.5 mm to 2 mm and a length in the range of 1 mm to 5 mm. In an exemplary embodiment, the support is in the form of cylindrical shape extrudates having particle diameter of 1 mm and length in the range of 2 mm to 3 mm.

[0106] The catalyst of the present disclosure in the form of extrudates facilitates easy separation after the reaction and to scale-up the process using more economical fixed-bed reactor configurations.

[0107] Conventionally known nano-form catalysts cannot be separated completely after the reaction, thereby leading to material / catalyst loss. Such nano-form catalysts are expensive. Moreover, the inability to achieve complete recovery renders the conventional processes uneconomical.

[0108] In accordance with the present disclosure, the third predetermined temperature is in the range of 90 °C to 120 °C. In an exemplary embodiment, the third predetermined temperature is 110 °C.

[0109] In accordance with the present disclosure, the third predetermined time period is in the range of 4 hours to 8 hours. In an exemplary embodiment, the third predetermined time period is 6 hours.

[0110] The supported catalyst is calcined at a fourth predetermined temperature for a fourth predetermined time period in air followed by activating the catalyst in an inert gas stream at a fifth predetermined temperature for a fifth predetermined time period to obtain the activated metal.

[0111] In accordance with the present disclosure, the fourth predetermined temperature is in the range of 275 °C to 325 °C. In an exemplary embodiment, the fourth predetermined temperature is 300 °C.In accordance with the present disclosure, the fourth predetermined time period is in the range of 30 minutes to 150 minutes. In an exemplary embodiment, the fourth predetermined time period is 120 minutes.

[0112] In accordance with the present disclosure, the inert gas is selected from the group consisting of nitrogen, argon and helium. In an exemplary embodiment, the inert gas is nitrogen.

[0113] In accordance with the present disclosure, the fifth predetermined temperature is in the range of 325 °C to 400 °C. In an exemplary embodiment, the fifth predetermined temperature is 350 °C.

[0114] In accordance with the present disclosure, the fifth predetermined time period is in the range of 30 minutes to 150 minutes. In an exemplary embodiment, the fifth predetermined time period is 120 minutes.

[0115] In accordance with the present disclosure, the catalyst comprises an activated metal which is selected from the group consisting of activated platinum, activated nickel and activated palladium.

[0116] 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 the / ?-aminophenol.

[0117] In accordance with the present disclosure, the schematic representation for the preparation of / ?-aminophenol is illustrated as Scheme A below:

[0118]

[0119] Aminobenzene

[0120] Scheme-AThe present disclosure provides a simple, efficient and cost effective process for the preparation of / ?-aminophenol with a comparatively high yield and high selectivity.

[0121] The present disclosure provides a robust, scalable, and industrially viable synthetic pathway for producing / ?-aminophenol directly from benzene.

[0122] 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.

[0123] 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.

[0124] EXPERIMENTAL DETAILS

[0125] Experiment 1: Preparation of / i-aminophenol in accordance with the present disclosure

[0126] Step 1: Synthesis of nitrobenzene in accordance with the present disclosure

[0127] In a 250 mL round-bottom flask, 25 mL of concentrated sulphuric acid was mixed with 21 mL of concentrated nitric acid to obtain a nitrating agent.

[0128] 17.5 mL of benzene was added slowly in dropwise manner to the nitrating agent under continuous stirring to obtain a mixture. During the addition of benzene, the reaction temperature was maintained below 55 °C using external cooling. After the complete addition of benzene, the mixture was heated to 60 °C (first predetermined temperature) for 45 minutes (first predetermined time period) to obtain a first reaction mixture comprising nitrobenzene.

[0129] The first reaction mixture was quenched in 150 g of crushed ice to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer. The first organic layer was separated using a separating funnel followed by washing thoroughly with water to remove residual acids and treated with 50 mL of aqueous sodium bicarbonate (aqueous alkali) to neutralize any remaining strong acids to obtain a crude oily nitrobenzene. The so-obtainedcrude oily nitrobenzene was purified by distillation and the fraction collected in the boiling range of 206 °C to 211 °C was obtained as pure nitrobenzene.

[0130] The amount of nitrobenzene obtained was 23 g with a yield of 83% yield.

[0131] Step 2: Synthesis of p-aminophenol from nitrobenzene in accordance with the present disclosure

[0132] Preparation of the catalyst (activated metal catalyst) (Cl):

[0133] 1 g of H₂PtCl₆·6H₂O (chloroplatinic acid hexahydrate) (catalyst precursor) was dissolved in 10 ml demineralized water to obtain an aqueous catalyst precursor solution. The aqueous catalyst precursor solution was added slowly in a dropwise manner to SiO₂–ZrO₂ (support), until the surface appeared uniformly wetted, ensuring complete absorption / impregnation of the solution into the pore structure followed by drying at 110 °C (third predetermined temperature) for 6 hours (third predetermined time period) to remove residual moisture to obtain a supported catalyst. The so obtained supported catalyst was calcined at 300 °C (fourth predetermined temperature) for 2 hours (fourth predetermined time period) in air followed by activating the catalyst under 5% to 10% of H2 in nitrogen (inert gas) stream at 350 °C (fifth predetermined temperature) for 2 hours (fifth predetermined time period) to obtain the activated platinum (convert platinum oxide (PtOx) to the active metallic platinum (Pt° form).

[0134] The catalyst is in the form of cylindrical shape extrudates having a diameter in the range of 0.5 mm to 2 mm and a length in the range of 1 mm to 5 mm.

[0135] Similarly, C2 to C6 were prepared by using same procedure at different metal ratios.

[0136] Table 1: Activated metal catalyst used in the preparation of p-aminophenol

[0137] Sr. Activated metal Metal Amount of Metal p-Aminophenol Aminobenze No. Catalyst of the Used Acid used content in yield, % ne yield, % present during the Catalyst

[0138] disclosure reduction of matrix, %

[0139] nitrobenzene (stochiometr

[0140] topic amounts)

[0141] aminophenol

[0142]

[0143] Cl Platinum 8 ml H₂SO₄ 5 28.8 48.5 C2 Platinum 8 ml H₂SO₄ 10 42.5 32.6 C3 Platinum 8 ml H₂SO₄ 15 60.6 17 C4 Palladium 8 ml H₂SO₄ 5 25.5 50.8 C5 Palladium 8 ml H₂SO₄ 10 38.5 38.6 C6 Palladium 8 ml H₂SO₄ 15 49.3 23.6

[0144]

[0145] Table 1 demonstrates that the catalytic performance of the acid resistant catalyst C3 in directing the selective reduction of nitrobenzene to / ?-ami nophenol which highlights the importance of controlled reaction conditions to suppress unwanted formation of by-product (aminobenzene).

[0146] The yield is comparatively lower with the Pd catalyst due to its higher activity, which promotes complete reduction of the nitro group to the corresponding amine. This leads to increased formation of aniline, resulting in a lower isolated yield of the desired intermediate.

[0147] Synthesis of p-aminophenol from nitrobenzene

[0148] 15 g of nitrobenzene was reduced by using 2 g of an activated platinum catalyst (as mentioned above) in 130 mL of water (fluid medium) and 8 mL. of concentrated sulfuric acid (acid) to obtain a mixture. The mixture was charged into a high-pressure reactor, sealed, and purged before pressurized with the hydrogen gas to 400 psi (pressure) followed by heating to 80 °C (second predetermined temperature) for 4 hours (second predetermined time period) and vigorous stirring to obtain a second reaction mixture comprisin p-aminophenol.

[0149] Hydrogen uptake was continuously monitored, and the reaction was terminated once the pressure was stabilized that indicates completion of the reduction process.

[0150] After cooling the reactor to ambient temperature and safely venting the system, the second reaction mixture was filtered to remove the catalyst followed by neutralizing a filtrate to obtain a resultant mixture comprising a solid product of / ?-aminophenol and an oily fraction of aminobenzene.

[0151] The solid product ~ami nophenol (white crystalline) was separated from the resultant mixture followed by washing and drying to obtain / ?-aminophenol. The amount of / ?-aminophenol obtained was 8 g with a yield of 60.6% with a melting point of 189 °C, that confirmed its purity.Additionally, an oily fraction of aminobenzene was obtained as 2 g having yield of 17%, that represented the minor side product formed during the rearrangement and reduction step.

[0152] The optimization of the process for preparation of / ?-aminophenol is carried out through various reaction parameters such as temperature, amount of catalyst, amount of acid and hydrogen pressure, and it is observed the results are re-producible within the temperature range and within the range of the amount of the catalyst.

[0153] Table 2: Comparative data for the process for the preparation of / ?-aminophenol

[0154] Wt. of H Aminobenz Sr. Conventional2

[0155] Temperatu P- Catalyst Acid (mL) Pressur aminophen ene No. Catalyst re (°C)

[0156] (g) e (psi) ol Yield (g) (Aniline)

[0157] Yield (g) i. 5%Pt / C 0.1 7.2 ml H₂SO₄ 400 90 3.5 6

[0158] 8 ml of

[0159] ii. 10%Ni / C 1 400 120 2.5 4 H2SO4

[0160] 8 ml of

[0161] iii. 5%Pt / C 0.1 400 90 3.5 6 H2SO4

[0162] 8 ml of

[0163] iv. 10%Ni / C 1 1000 120 2.5 3 H2SO4

[0164] 20 ml of

[0165] v. Raney Ni 2 140 60 to70 3 - 10%H2SO4

[0166] 6 ml of

[0167] vi. Pd / C 0.05 300 70 6 - H2SO4

[0168] 10%

[0169] 8 ml of

[0170] vii. Ni / alumina 2 400 130 3.3 2 H2SO4

[0171] catalyst

[0172] 10%

[0173] 8 ml of

[0174] viii. Ni / alumina 2 400 100 2.5 2 H2SO4

[0175] catalyst

[0176] 6 ml of

[0177] ix. 10% Ni / ZSM5 1 600 120 0.3 5 H2SO4

[0178] Activated

[0179] platinum

[0180] 8 ml of

[0181] catalyst 2 400 80 8 2 H2SO4

[0182] of the present

[0183]

[0184] disclosure

[0185] From Table 2, it is observed that variations in the type of catalyst, the amount of catalyst / acid, reaction pressure and temperature significantly influence the product selectivity towards p- aminophenol and aniline.

[0186] 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.The results clearly show that the type of catalyst plays a decisive role in determining both the activity and selectivity of the reaction toward -ami nophenol. Noble metal catalysts such as platinum and palladium supported on carbon exhibit better performance compared to nickel-based catalysts. Palladium / platinum-supported catalysts demonstrate the highest selectivity toward -aminophenol, with minimal formation of aniline, indicating that noble metals favour the desired hydrogenation pathway while suppressing side reactions. Platinum-supported catalysts show good activity; however, however the conventional palladium / platinum catalyst tend to promote the formation of aniline alongside -aminophenol, suggesting comparatively lower selectivity.

[0187] Raney nickel exhibits better selectivity toward / ?-aminophenol compared to other conventional catalysts, with reduced aniline formation, particularly under milder reaction conditions. Overall, the study indicates that noble metal catalysts and lower reaction severity favour selective / ?-aminophenol formation, while nickel-based catalysts, especially those with acidic supports, tend to promote undesired aniline formation. Thus, catalyst selection is the key factor governing reaction selectivity in this system.

[0188] TECHNICAL ADVANCEMENT

[0189] 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

[0190] • is simple, efficient and cost effective; and

[0191] • provides / ?-aminophenol with a comparatively high selectivity and high yield.

[0192] 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 merely to 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.

[0193] 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 genericconcept, 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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. nitrating benzene by using a nitrating agent under stirring at a first predetermined temperature for a first predetermined time period to obtain a first reaction mixture comprising nitrobenzene; andii. reducing said nitrobenzene from said first reaction mixture by using a reducing agent in the presence of a catalyst and an acid in a fluid medium at a second predetermined temperature for a second predetermined time period to obtain a second reaction mixture comprising / ?-aminophenol.

2. The process as claimed in claim 1, wherein said first reaction mixture is purified by the following sub-steps:a) quenching said first reaction mixture in ice to obtain a first biphasic mixture comprising a first organic layer and a first aqueous layer;b) separating said first organic layer followed by washing and treating with an aqueous alkali to obtain a crude oily nitrobenzene; andc) distilling said crude oily nitrobenzene to obtain a pure nitrobenzene.

3. The process as claimed in claim 1, wherein said second reaction mixture is purified by the following sub-steps:a) filtering said second reaction mixture followed by neutralizing to obtain a resultant mixture comprising a solid product of / ?-aminophenol and an oily fraction of aminobenzene; andb) isolating said solid product from said resultant mixture followed by washing and drying to obtain a pure / ?-aminophenol.

4. The process as claimed in claim 1, wherein• said nitrating agent is a mixture of sulfuric acid and nitric acid, wherein a volume ratio of sulfuric acid to nitric acid in said nitrating agent is in the range of 1:0.7 to 1:1;• said first predetermined temperature is in the range of 40 °C to 80 °C;• said first predetermined time period is in the range of 20 minutes to 60 minutes; and• a volume ratio of the benzene to said nitrating agent is in the range of 1:2 to 1:4.

5. The process as claimed in claim 1, wherein• said reducing agent is hydrogen gas and a pressure of hydrogen during reduction is in the range of 100 psi to 1000 psi;• said fluid medium is selected from water and ethanol;• said acid is selected from the group consisting of sulphuric acid, p-toluene sulphonic acid, acetic acid and formic acid;• said second predetermined temperature is in the range of 70 °C to 120 °C;• said second predetermined time period is in the range of 2 hours to 10 hours;and• a weight ratio of said nitrobenzene to said catalyst is in the range of 1:0.05 to 1:0.5.

6. The process as claimed in claim 2, wherein said aqueous alkali is selected from the group consisting of aqueous sodium bicarbonate, aqueous potassium bicarbonate, aqueous potassium carbonate, aqueous sodium carbonate and aqueous calcium carbonate.

7. The process as claimed in claim 1, wherein said catalyst comprises an activated metal which is selected from the group consisting of activated platinum, activated nickel and activated palladium.

8. The process as claimed in claim 7, wherein said catalyst is prepared by the following sub -steps:• impregnating an aqueous catalyst precursor solution onto a support followed by drying at a third predetermined temperature for a third predetermined time period to obtain a supported catalyst; and• calcining said supported catalyst at a fourth predetermined temperature for a fourth predetermined time period in air followed by activating said catalyst by using hydrogen in an inert gas stream at a fifth predetermined temperature for a fifth predetermined time period to obtain said catalyst.

9. The process as claimed in claim 8, wherein said catalyst precursor is selected from the group consisting of chloroplatinic acid hexahydrate (H₂PtCl₆·6H₂O), platinum (II) chloride (PtCl₂), platinum (IV) chloride (PtCl₄), ammonium hexachloroplatinate (IV) ((NH₄)₂PtCl₆), potassium hexachloroplatinate (IV) (K₂PtCl₆), sodiumhexachloroplatinate (IV) (Na2PtCl6), palladium nitrate (Pd(NO3)2), palladium acetate (Pd(OAc)2), palladium acetylacetonate (Pd(acac)2), nickel nitrate hexahydrate (Ni(NO3)2·6H2O), nickel acetate (Ni(CH3COO)2·4H2O) and nickel chloride (NiCl2·6H2O).

10. The process as claimed in claim 8, wherein a weight ratio of said catalyst precursor to water is in the range of 1:8 to 1: 15 in said aqueous catalyst precursor solution.

11. The process as claimed in claim 8, wherein said support is selected from the group consisting of SiO2–ZrO2, TiO2-ZrO2, Al2O3-ZrO2and activated carbon.

12. The process as claimed in claim 8, wherein said catalyst is in the form of cylindrical shape extrudates having a diameter in the range of 0.5 mm to 2 mm and a length in the range of 1 mm to 5 mm.

13. The process as claimed in claim 8, wherein said inert gas is selected from the group consisting of nitrogen, argon and helium.

14. The process as claimed in claim 8, wherein• said third predetermined temperature is in the range of 90 °C to 120 °C. • said fourth predetermined temperature is in the range of 275 °C to 325 °C;• said fifth predetermined temperature is in the range of 325 °C to 400 °C; • said third predetermined time period is in the range of 4 hours to 8 hours;• said fourth predetermined time period is in the range of 30 minutes to 150 minutes; and• said fifth predetermined time period is in the range of 30 minutes to 150 minutes.

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