Production of P-Amino Phenol - Report Example

Fine Chemical Production: p-Amino phenol Fine Chemical Production: p-Amino phenol Introduction p-Amino phenol (H2NC6H4OH) also known as para-aminophenol or 4-Aminophenol is an important organic compound that is normally available in its physical form as a white odourless powder or a colorless crystalline solid that turns brown on exposure to air. Generally, the compound is one of the three aminophenol isomers with the other two being 3-aminophenol and 2-aminophenol. Due to its slight hydrophilic properties, p-Amino phenol is moderately soluble in alcohols and can easily be dissolved in hot water. In the presence any base, p-amino phenol readily oxidises steadily to form both cation and anion. The N-methyl and N, N-dimethyl acquired from an oxidised p-Amino phenol are example of the commercial value derivatives. The chemical is also a strong reducing agent and is widely known to oxidize quickly when exposed to atmospheric oxygen (Mitchell and Waring, 2002, p. 34). Generally, para-aminophenol is a well known and critically useful industrial chemical that has a wide range of significant uses. For example, the chemical is widely used as an intermediate in the production of important pharmaceuticals such as acetaminophen, acetanilide, paracetamol and analgesics drug among others. The production of p-Amino phenol (PAP) via catalytic hydrogenation of Nitrobenzene is particularly deemed as a process of industrial significance considering that PAP is a useful pharmaceutical intermediate when manufacturing paracetamol. In addition, p-aminophenol and some of its derivatives such as glycine and metol are in photo development particularly as a concurrent developer in black-and-white films marketed broadly under the name Rodinal. Finally, the chemical also has an important application in the production of azo and suphur dyes. Although there are a number other well known production methods for p-aminophenol. p-Amino phenol (H2NC6H4OH) can effectively be produced for industrial purposes through the catalytic hydrogenation of nitrobenzene. The process particularly involves reducing of nitrobenzene in dilute sulphuric acid and in the presence of platinum catalyst. This is an endothermic reaction of that normally results into 4-aminophenol formation through phenyl-hydroxylamine. This paper presents a fine chemical production of p-Amino phenol using the route of catalytic hydrogenation of nitrobenzene with particular the chemistry of the fine chemical, its synthetic route selection, thermodynamics as well as kinetics and wastes issues. Fig. 1: Production of p-Amino phenol through Catalytic Hydrogenation of Nitrobenzene Synthetic Route Selection The fine chemical production route of catalytic hydrogenation of nitrobenzene is particularly preferred due to its relative cost effectiveness as well as the serious problem of affluent disposal that is facing many of the alternative reagent based production processes. According to Polat, Aksu and Pekel (2002, p.46), the catalytic route not only minimizes the problem of effluent disposal in the production of p-aminophenol but is also widely known to reduce the overall economics of the process as well as improve the quality of the product. For example, the conventional p-aminophenol synthesis methods like p-nitrophenol reduction normally causes serious affluent disposal issues due to their involvement of stoichiometric use of iron-acid which usually leads to the formation of Fe-FeO sludge, a process that is not can never be recycled. On the contrary, the catalytic hydrogenation process significantly minimizes the problems related to affluent disposal while at the same time improving the product quality and the overall process economics. Thermodynamic Calculations The overall hydrogenation reaction involved in the production of p-Amino phenol using the route of catalytic hydrogenation of nitrobenzene is a highly exothermic reaction that results in the release of a lot of energy in the form of heat. This is particularly attributed to the fact that metal catalyzed hydrogenation reactions often results in the addition of hydrogen atoms to the a double bond thereby leading to the dissociation or breaking up of the molecule(hydrogennolysis/destructive hydrogenation), and the subsequent release of energy in the form of heat. For example, the thermodynamic calculations of the process can be derived based on the balance chemical reaction as shown below: C6H5NO2 + 2 H2 → C6H5NHOH + H2O………………………………………………..…i C6H5NHOH → HOC6H4NH2 …………………………………………………………….ii The thermodynamic properties of each of the above reagents and products can be summarized as shown in the table below: Nitrobenzene H2 Water Phenylhydroxylamine (PHA) p-aminophenol ΔHf o (KJ/mol) 530 kJ/mol −20.63 kJ/mol 285.83 kJ/mol 106.67kj/mol -345.67kj/mol ΔGf o (KJ/mol) `109kj/mol 79.9 kJ/mol -237.129 kJ/mol 462.6kj/mol 190.6 kJ/mol cp (J/mol K) -44.5 KJ/mol 49 kj/mol 75.35 kJ/mol −109.7 kJ/mol  −131.2kJ/mol The initial thermodynamic calculation for the enthalpy change of reaction can be given as …………………………iii The above equation clearly demonstrates that the reaction is exothermic and is likely to result in the release of a lot of energy in the form of heat. The spontaneity of the overall reaction can be derived by calculation the reactions Gibbs free energy as follows: ………………………………….iv The negative Gibb’s free energy value is a likely indication that the reaction occurs at spontaneously at standard pressure and temperature. On the other hand, based on the provided Gibb’s free energy, the reversibility of the reaction can effectively be determined using the following equilibrium constant: ………………………………………………………………....v The high equilibrium indicated above is a likely suggestion that the irreversibility of the reaction. Type of Catalyst Used The preferred catalyst for the reaction is Platinum on Carbon (popularly abbreviated as Pt/C). Although a number of metal catalysts may effectively be used for the process, Pt/C catalyst is often favor favored during the production of p-Amino phenol using the route of catalytic hydrogenation of nitrobenzene due to highest selectivity and activity towards the formation of p-Amino phenol. In addition, the catalyst can also be effectively recovered with ease and efficiently recycled before being reused again in the process. However, numerous patents report on the need to add surfactants with the intention of increasing the contact area featuring between water and nitrobenzene. In this type of reactions, water serves the role of a solvent. Often times, this hydrogenation process will be run through the use of pt/C catalyst in addition to aqueous sulphuric acid plus a surfactant intended to assist in the dispersal of the NB all through a reaction tool. The PAP yield bears a close association with the reaction parameters that facilitate the initial step of partial hydrogenation plus the second acid-triggered rearrangement prior to the conversation of the resulting intermediary product to aniline. Kinetics and Mechanism The process of the production of p-Amino phenol using the route of catalytic hydrogenation of nitrobenzene involves two major steps being carried out usually in a single reactor. The initial reaction entails an electrolytic conversion of nitrobenzene compound under stable temperature to phenyl-hydroxylamine. Phenyl-hydroxylamine chemically spontaneously rearranges to form a 4-aminophenol. P-Amino phenol is a building block chemical compound structure once synthesised through a nitrobenzene reaction. C6H5NO2 + 2 H2 → C6H5NHOH + H2O………………………………………………..…i C6H5NHOH → HOC6H4NH2 …………………………………………………………….ii The industrial process entails nitrobenzene first going through a partial hydrogenation in order to form phenylhydroxylamine (PHA) on Pt. Following this initial step is the PHA going through the Bamberger rearrangement in order to form PAP, though this requires the presence of sulphuric acid. Nadgeri (2011) presents a study that involved the use of the palladium catalyst in the hydrogenation process. The process, he states, lead to the production of 4,4-diaminodiphenyl ether, p-Aminophenol and aniline that were established through reversed phase high performance liquid chromatography. The final or intermediate industrial synthetic routes in this chemical reaction overly rely on the synthesis of paracetamol. Treating synthetically the p-Aminophenol with an acetic anhydride chemically produces paracetamol. Metol synthesis additionally was a modest synthetic route used initially to produce 4-aminophenol. Metol is essentially the N-methyl derivative of p-aminophenol. In the year 1891, metol derivatively replaced p-aminophenol as a faster developing agent for black and white photography. The crystal orthorhombic structure of p-Amino phenol is oxidised in the laboratory to produce and oxidant of a 4-amino phenol thermo-chemically (Sheldon, 2001, p.88). Generally, the thermodynamics of p-amino phenol represents stability constants of complexes. The thermodynamics of this substance irreversibly changes at a constant ionic strength of (0.1 M KCL) which is determined potentiomentrically spontaneous at 30 degrees, 35 degrees, 40 degrees and 45 degrees through the use of Irving-Rossotti pH-titration technique. P-amino phenol composition complexes reflect its endothermic and exothermic chemical reactions in cases where an estimation of thermodynamics is used in a ductometric and photometric titrations. In the endothermic cum irreversible chemical reaction of p-Amino phenol, a digit conductivity meter of 05 solution analyser oxides in the final product. In order to concomitantly understand the exothermic and endothermic thermodynamic reactions of p-amino phenol an interactional reaction between metal ions and ligands must first be understood. The proton-ligand and metal-ligand are the additional key elements of analysis through the use of log K constants in the thermodynamic Irving-Rossotti formulas. The thermodynamic data of complexes at 303 amino phenol by order include; Mn complex, Fe complex, Co complex, Ni complex and Cu complex respectively. The amino phenol thermodynamics present unique temperature characteristics of both a solvent and an insolvent molality. This indicates that the non-electrostatic forces in this chemic bond are stronger than the electrostatic ones. Reactor Selection Every step in this type of reaction is regulated by kinetics. Other than the use of water as a solvent, a bi-functional catalyst constituting of a mechanical mixture of zirconium sulphate and Pt catalyst always helps in the conversion of nitrobenzene to p-aminophenol. According to Nadgeri (2011), the performance level associated with this approach never depends on the support leveraged for Pt, or different supports like sulphated or pure zirconia and titania. Waste Identification Waste identification in aminophenol may be done through the identification of chlorophenols, chloroguaiacols, and chlorocatechols. These sub-structural elements of aminophenol should be continuously treated in an up flow anaerobic sludge type of a blanket reactor in the presence of highly concentrated biodegradable organic compounds. Whereas the traditional platinum catalysts are better placed to prepare substantial amounts of PAP, they feature the ability to further hydrogenate the PAP to some alicyclic compounds that are uncalled for by products. Hydrogenation processes that are underlain by the use of increased volumes of platinum catalyst are better reflections of this. Moreover, in reactions revolving around the use of platinum catalyst, it is difficult hydrogenating nitrobenzene in entirety without over hydrogenation occurring. It is for this reason that the traditional hydrogenation processes have to be halted before completion in order to evade the formation of unnecessary alicyclic compounds, a move that requires an extra step of using steam distillation to reinstate unused nitrobenzene. Recycling and Waste Treatment Chlorination is the first treatment process for these aminophenol chemical substances. The chlorinated compounds additionally should not be ideally fully mineralised, though are converted directly to lesser chlorinated compounds by biologically modified reductive chlorination reactors. Chlorinated velatroles as supposedly chemically converted into chloroguaiacols and then into chlorocatechols before these substances are finally reductively de-chlorinated. Reductive de-chlorination operational methods of treatment reactors are dependently reliant on chlorine’s reactant position with removal preference of chlorine from adjacent positions to hydroxyl groups. Through an acclimation process, the meta-chlorines are also done away with in the treatment of p-Amino phenol. Anaerobic process perfects the art of p-amino phenol identification and treatment. The Enso-Fenox process may act as an additional treatment process in the removal of chlorinated phenolic compounds from pulp-based bleaching effluents. The Enso-Fenox is a more verified treatment method treatment and it easily identifies p-amino phenol wastes. This is a two-stage process minimally consisting of an anaerobic fluidised reducing agent-bed reactor followed by a dripping filter. Even though the Enso-Fenox anaerobically treats p-amino phenol anaerobically, the whole process is not prone to yielding methane. This treatment process therefore result in chlorophenols removal efficiently between the ranges of 65-100%. The protection of phenols and alcohols is one of the commonest synthetic strategies aimed at unmasking hydroxyl functionalities especially during the multi-step synthetic procedures occurrence. O-acetylation procedures play a major role in the recycling, protection and purification of various synthetic or natural products having carbohydrate substructures. Apart from O-acetylation recycling process, B/R instrument may offer an out of world solvent and insolvent recycling activities. This instrument offers variety of equipment for the recycling processes of alcohol, xylene, formalin as well as other p-amino phenol substitutes both solvent and insolvent. Procedurally, these instruments are loaded with the solvent/insolvent compounds, started and finally bring out the recycled solvent within the shortest time possible. The recycled solvents ready to use by the B/R instruments are normally observed as follows; xylene is 99.9% in purity while concentration is 99.9%. Formalin is 99.9% in purity while 10% in concentration. Lastly, alcohol is 99.9% in purity and 95% or higher in concentration. Finally, after every nitrobenzene is charged and consumed, the hydrogen sparge used in the production process is halted then the reaction mixture will be covered using nitrogen after which the sparge is cooled to a temperature of 50 C. The resulting mixture then goes through filtration, and the hot water is used to wash catalyst-can hot mixture then preserved for the subsequent cycles. Process Block Diagram: Fine Chemical Production: p-Amino phenol References Gelder, E. A. (2005). The hydrogenation of nitrobenzene over metal catalysts. Glasgow: University of Glasgow. Mitchell, S.C. & Waring, R.H. 2002. Aminophenols. In Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. Nadgeri, J. M. (2011). Studies on mono bimetallic and nano catalysts of nickel palladium and platinum metals and their applications in selective hydrogenation of acetylenic compounds and nitroaromatics of industrial relevance. Polat, K; Aksu, M.L.; Pekel, A.T. 2002. Electroreduction of nitrobenzene to p-aminophenol using voltammetric and semipilot scale preparative electrolysis techniques. Journal of Applied Electrochemistry 32(3): pp.217–223. Sheldon R. A. 2001. Fine chemicals though heterogeneous catalysis processes. Weinheim: Wiley-VCH. Tanielyan, S.K, Nair, J.J, Marin, N., Alvez, G. McNair, R.J., Wang, D.J; Augustine, R.L. (2007). Hydrogenation of nitrobenzene to 4-aminophenol over supported platinum catalysts. Org. Process Res. Dev.11, 4, 681-688. Visentin F. (2005.) Kinetic Study of Hydrogenation Reactions of Aromatic Nitro Compounds Using a New Pressure Resistant Reaction Calorimeter Combined with a FTIR-ATR Device. Diss. ETH, Zurich. Visentin F., Gianoli S. I.; Kut O. M., Hungerbühler K. (2004). A Pressure-Resistant Small-Scale Reaction Calorimeter That Combines the Principles of Power Compensation and Heat Balance (CRC.v4). Organic Process Research & Development. 2004, 8, 725-737. Read More