The Glauber reaction to manufacture potassium permanganate: An optimal balance between commercial efficiency and sustainability

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In this minireview, the efficiency of the Glauber reaction was evaluated by equilibrium determinations and comparatively viewed in light of today’s principle of sustainability. The manufacture of potassium permanganate through the method based on the Glauber reaction is taking a step in the direction of building a more sustainable world.

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Nội dung Text: The Glauber reaction to manufacture potassium permanganate: An optimal balance between commercial efficiency and sustainability

Cite this paper: Vietnam J. Chem., 2023, 61(S1), 86-88 Minireview DOI: 10.1002/vjch.202300140 The Glauber reaction to manufacture potassium permanganate: An optimal balance between commercial efficiency and sustainability Aliyar Mousavi Math & Sciences Department, Nashua Community College, 505 Amherst Street, Nashua, NH 03063, U.S.A. Submitted April 12, 2023; Revised May 10, 2023; Accepted May 15, 2023 Abstract The spontaneous oxidation of aqueous potassium manganate to aqueous potassium permanganate, first carried out by the German alchemist of the 17th century Johann Rudolf Glauber, was used for the manufacture of potassium permanganate until it was replaced with the electrolytic oxidation of potassium manganate, which is the current state of the art. The reason for the replacement was that the method that is based on the Glauber reaction is commercially less efficient. In this minireview, the efficiency of the Glauber reaction was evaluated by equilibrium determinations and comparatively viewed in light of today’s principle of sustainability. The manufacture of potassium permanganate through the method based on the Glauber reaction is taking a step in the direction of building a more sustainable world. Keywords. Disproportionation, Glauber, manganate, permanganate, sustainable development. Pyrolusite (manganese dioxide, MnO2) is the most disproportionation of the alkaline K2MnO4 induced common of the commercially more important by reducing the pH with carbon dioxide (CO2). deposits of manganese.[1] The German alchemist of However, the method has been replaced with the the 17th century Johann Rudolf Glauber[2] made that electrolytic oxidation of K2MnO4 according to the mineral undergo oxidation and prepared an aqueous reaction shown by Equation 2.[1] solution of potassium manganate (K2MnO4).[3] The 2K2MnO4(aq) + 2H2O(l) → 2KMnO4(aq) + green solution, however, changed color slowly,[3] as 2KOH(aq) + H2(g) (2) the very dark-green K2MnO4 was oxidized to the The method that is based on the Glauber reaction deep-purple potassium permanganate (KMnO4).[1] is a commercially “less-efficient method” compared This experiment done in the year 1659 is the first to the current method;[1] however, is it also less known synthesis of KMnO4.[3] The book “Vogel’s sustainable? This minireview aims to shed light on Qualitative Inorganic Analysis” by Svehla[4] refers to not only how commercially efficient the Glauber the hydrolysis of manganate (MnO42-) as an example reaction to manufacture KMnO4 is, but also how of “a disproportionation” and states about the sustainable it is. reaction that “manganese(VI) is partly oxidized to According to Silberberg and Amateis,[6] for any manganese(VII) and partly reduced to reaction, if the equilibrium constant is very large, the manganese(IV).” Manganates are stable in strongly reaction “goes to completion,” and if the equilibrium alkaline solution; however, they disproportionate constant is very small, there is “no reaction.” readily in neutral or acid solution.[1] The Glauber Therefore, the smaller the equilibrium constant, the reaction is shown by Equation 1 in the book less efficient the chemical process, unless a “Problems in General Chemistry” by Glinka.[5] nonspontaneous reaction is driven to completion by 3K2MnO4(aq) + 2H2O(l) → 2KMnO4(aq) + electrolysis (that is, the case of the reaction shown MnO2(s) + 4KOH(aq) (1) by Equation 2). What is the equilibrium constant of Several tens of thousands of tons of KMnO4 are the reaction shown by Equation 1 at room produced annually. It is important industrially (as an temperature (25 oC)? oxidizing agent in the production of saccharin and The net ionic equation for the reaction shown by benzoic acid) and medicinally (as a disinfectant).[1] Equation 1 is shown by Equation 3. Interestingly enough, as Johann Glauber is known as 3MnO42-(aq) + 2H2O(l) → 2MnO4-(aq) + MnO2(s) + a “manufacturer of chemicals on an industrial scale” 4OH-(aq) (3) himself,[2] the Glauber reaction used to be a method It is worth noting that if the reaction shown by to manufacture KMnO4 commercially, with the Equation 3 involves the partial oxidation and partial 86 Wiley Online Library © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
25728288, 2023, S1, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300140 by Readcube (Labtiva Inc.), Wiley Online Library on [02/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Aliyar Mousavi reduction of manganese(VI), the half-reactions mol × (-500.7 kJ/mol)) + (2 mol × (-237.1 kJ/mol))] shown by Equations 4 and 5 may be written to = -12 kJ (per mole of the reaction) describe its intermediate steps. Therefore, using R = 8.314 J/(mol reaction.K), K 2MnO42-(aq) → 2MnO4-(aq) + 2e- (4) may be calculated based on Equation 6 and is equal MnO4 (aq) + 2H2O(l) + 2e → 2- - to 1.3×102. MnO2(s) + 4OH-(aq) (5) ΔGorxn = -RT ln K (6) The equilibrium constant for the reaction shown With examples of very large and very small by Equation (3) (K) at 25 oC (298.15 K) may be equilibrium constants being 2.2×1022 and 1×10-30, determined thermodynamically by calculating the respectively (6), K = 1.3×102 is to be considered standard free energy of the reaction (ΔGorxn) from intermediate. This means that the extent of the the standard free energy of formation (ΔGof) of the reaction shown by Equation 1 is not ample. reactants and the products in “Equation 3”. The CRC However, in light of the hydrolysis reaction shown Handbook of Chemistry and Physics[7] lists -500.7 by Equation 3 (with neither MnO4- nor OH- initially kJ/mol, -237.1 kJ/mol, -447.2 kJ/mol, -465.1 kJ/mol, present), if we use K to calculate the ratio of the and -157.2 kJ/mol as ΔGof of MnO42-(aq), H2O(l), molar concentration of MnO4- ([MnO4-]) to the MnO4-(aq), MnO2(s), and OH-(aq), respectively. molar concentration of MnO42- ([MnO42-]) when the ΔGorxn = [(2 mol × (-447.2 kJ/mol)) + (1 mol × reaction shown by Equation 1 is at equilibrium, the (-465.1 kJ/mol)) + (4 mol × (-157.2 kJ/mol)] – [(3 results shown in table 1 are observed. Table 1: Numerous equilibrium concentrations (M) of MnO42- and MnO4- and their ratios in the Glauber reaction to produce potassium permanganate at 25 oC [MnO42-] (M) [MnO4-] (M) [MnO4-]/[MnO42-] 2.0 2.0 1.0 1.0 1.4 1.4 1.0×10-1 4.5×10-1 4.5 1.0×10-2 1.4×10-1 1.4×10 1.0×10-3 4.5×10-2 4.5×10 1.0×10-4 1.4×10-2 1.4×102 1.0×10-5 4.5×10-3 4.5×102 1.0×10-6 1.4×10-3 1.4×103 The results shown in table 1 show that at higher However, the production of the electrical energy on equilibrium concentrations of MnO42-, equal or which electrolysis is based from the combustion of quantitatively similar (that is, having the same the primary energy source, coal, by power plants orders of magnitude) equilibrium concentrations of creates many environmental problems.[8] On the MnO4- are present; however, at lower equilibrium other hand, although the method based on the concentrations of MnO42-, the present equilibrium Glauber reaction is commercially less efficient than concentrations of MnO4- are several orders of the other, it is not environmentally hazardous at all. magnitude higher than those of MnO42-. This shows Even the manganese byproduct in Equation 1 that the Glauber reaction has high theoretical yields (MnO2) is always applied in the non-metallurgical of MnO4- if the starting solutions have low industries where manganese is used, which are concentrations of MnO42-. important and widespread, such as the manufacture The current method of the electrolytic oxidation of dry-cell batteries and the brick industry.[1] of K2MnO4 according to the reaction shown by The Glauber reaction to manufacture KMnO4 is Equation 2 is commercially more efficient than the an optimal balance between commercial efficiency method based on the Glauber reaction because it and sustainability, especially if the production of “goes to completion” and all the manganese in the millimolar concentrations of aqueous KMnO4 is reactant K2MnO4 is used in the product KMnO4. desired (see table 1). This minireview does not © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 87
25728288, 2023, S1, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300140 by Readcube (Labtiva Inc.), Wiley Online Library on [02/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry The Glauber reaction to manufacture potassium… suggest the replacement of the electrolysis-based Chemistry of Alchemy: From Dragon’s Blood to method for the manufacture of KMnO4 with the Donkey Dung, How Chemistry Was Forged, 1st ed., method based on the Glauber reaction. It does, Prometheus Books, Amherst, NY, 2014. however, call for the revival of the latter in light of 3. Organic Industries Pvt Ltd. Potassium Permanganate, what “sustainability” was first defined as, by the http://www.organicgroup.co.in/potassium_permangan United Nations Brundtland Commission, in 1987,[9] ate.html (accessed 25 February 2023). which is “meeting the needs of the present without 4. G. Svehla. Vogel’s Qualitative Inorganic Analysis, 7th compromising the ability of future generations to ed., Longman, Essex, UK, 1996. meet their own needs.” It is most noteworthy that in 5. N. L. Glinka. Problems in General Chemistry, 1st ed., the words of the United Nations,[9] “sustainable Mir, Moscow, 1973. development requires an integrated approach that takes 6. M. S. Silberberg, P. Amateis. Chemistry: The into consideration environmental concerns along with Molecular Nature of Matter and Change, 9th ed., economic development”. The manufacture of McGraw-Hill Education, New York, 2021. KMnO4 through the method based on the Glauber 7. J. R. Rumble, Ed., CRC Handbook of Chemistry and reaction is taking a step in the direction of building a Physics, 103rd ed., CRC Press/Taylor & Francis, Boca more sustainable world. Raton, FL, 2022 (Internet Version). 8. P. Buell, J. Girard. Chemistry Fundamentals: An REFERENCES Environmental Perspective, 2nd ed., Jones and Bartlett Publishers, Sudbury, MA, 2003. 1. N. N. Greenwood, A. Earnshaw. Chemistry of the 9. United Nations Sustainability, Elements, 1st ed., Pergamon Press, Tarrytown, NY, https://www.un.org/en/academic-impact/sustainability 1994. (accessed 25 February 2023). 2. C. Cobb, M. L. Fetterolf, H. Goldwhite. The Corresponding author: Aliyar Mousavi Math & Sciences Department Nashua Community College, 505 Amherst Street, Nashua, NH 03063, U.S.A. E-mail: amousavi@ccsnh.edu. © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 88