Indian Journal of Chemistry Vol. 38A. September 1999, pp.966-968 The reaction of barium manganate with fraction data were collected on a Phillips PW 3710 acids and their precursors diffractometer, with a Cu monochromator. Synthesis oj barium manganate (VI) Liszlo Kotai, Agnes Keszler, Janos Pato. Sandor Holly Chemical Research Center, Institute of Chemistry. KMn04 (15.8 g) was dissolved in 300 ml of water, Hungarian Academy of Sciences then BaCI2.2Hp (24.9 g dissolved in 100 ml of water), H-1025, Budapest, Pusztaseri u. 59-67, Hungary KOH (56 g dissolved in 100 ml of water) and KI (2.0 g and dissolved in 20 ml of water) were added with vigorous Kalyan K Banerji ' Department of Chemistry, J N V University, stirring. The mixture was boiled for 15 min, cooled, Jodhpur 342 005, India filtered, and washed. The permanganate-free product was dried at 105° C for I h, then the traces of water were Received 30 November 1998; revised 4 Mal' 1999 removed by azeotropic distillation with benzene (yield - 100%). Analysis (found/calc. fo r BaMn0 ): Ba 53.69/ 4 A simple and easy preparative route to obtain permangani c ac id 53.59%; Mn 21.40121.44%. and permanganate salts from barium manganate and sulphuric acid is described. Sulphuric acid reacts with bari um manganate to pro­ duce sparingly soluble bariulll sulphate and well-soluble permanga­ Synthesis ojpermanganic acid nic ac id or bariulll permanganate, these in turn can be usee! to pre­ To barium manganate (2.56 g, 0 .0 I mol) suspended pare ot her metal permanganates. in 50 ml of di stilled water, sulphuric acid ( 100 ml , 0 . 1 mol) was added with stirring. The stirring was contin­ ued for I h. The reaction mixture was filtered and per­ Permanganates are widely used in organic syntheses as manganic acid was titrated with NaOH potentiometri­ selective oxidizing agentsl . Barium permanganate is su it­ cally using a glass e lectrode (PH 5.5). The product, so­ able for selective oxidation itsclf2-6 and can be used as dium permanganate trihydrate, was crystall ized and iden­ starting materi al for the synthesis of several other metal tified by IR spectroscopy; yield - 100%. 7 X permanganates als0 . • The reaction of permallganic acid with oxides, hydroxides or carbonate' yields a lot of cIe­ SYllthesis of barium permanganate ri vati ves') . Bariu m manganate (2.56 g, 0.01 mol) was suspended Synthesis of barium pennanganate starts from barium in 100 ml of di stilled water. Then sulphuric acid (55 ml , manganate which itself is obtained in pure form from 0. 1 mol) was added over I h with slow stirring and then potassium permanganate and water soluble barium salts. refluxed for 15 min. The reaction mixture was filte red Reported methods for the conversion of barium manga­ and concentrated while barium permanganate crystal­ nate to the corresponding permanganare are compl icated lized (yield: 0.7 g), analysis [found/calc. for Ba(Mn04)2]: procedures. In this note, the synthesis of permanganic Ba 36.57/36.61% ; Mn 29.30129 .28%. acid and barium permanganate and their use in the syn­ thesis of several other metal permanganates are reported. Reaction of barium l1Iangana fe with sodium hydrogen carbonate Experimental Barium manganate (2.56 g, 0.0 I mol) was suspended Analytical grade reagents (Aldrich) and double-dis­ in 100 ml distilled water and calculated amounts of tilled water were used throughout. The IR spectra were NaHC01 (Ba:Na = I :0.75, I: I, I: 1.34 mol) was added. obtained in nujolmull with NICOLET 205 FT-IR spec­ The mixture was slowly stirred for I h a nd then refluxed trometer and by diffuse reflectance technique in KBr with for 30 min . The reaction mixture was filtered and crys­ NICOLET 170SX spectrometer in the range of 400-4000 talli zed. According to TR spectroscopy and X-ray l cm· . rcp measurements were made with Atomscan 25 diffractometry, the products contai ned Ba(Mn04)2' (Thermo Jarral Ash) spectrometer. X-ray powder dif- NaMn04 and Na2CO, in different ratios. NOTES 967 Reaction ofbarium manganate with ammonium sulphate To barium manganate (2.56 g, 0.01 mol), suspended Table 1- Comparison of effecti ve charge values and acidity of some in 100 mol distilled water, was added ammonium sul­ inorganic oxoacids '4 phate (1.24 g, 0.0 I mol). The reaction mixture was stirred Oxoacid 8 8,,1 8 <jl for I h and then refluxed for I h. The mixture turned 11 8, / x dark violet and intense odor of ammonia was obtained. H S0 +0.38 -0.46 -0.36 +0.88 1.125 The reaction mixture was filtered, concentrated and crys­ l 4 HMn04 +0.37 -0.53 -0.46 +1 .56 1.114 tallized. According to IR spectroscopy the water-soluble HlMnO.j· +0.37 -0.52 -0.42 +1.42 1.106 product was ammonium permanganate. Even if 2/3 HlCO +0.39 -0.50 -0.42 +0.67 0.965 amount of ammonium sulphate used, the only product J formed, under similar conditions, was ammonium per­ • Our calculation manganate. sulphuric acid. The ionic character of the hydroxy Is Results and discussion (8i8o) are nearly similar in manganic and permanganic Synthesis of barium manganate in alkaline medium acids but the polarizing effect of the central atom is higher from potassium permanganate and barium chloride in in permanganic acid. Consequently manganic acid is the presence of an alkali iodide is a well-known reaction easily formed from barium manganate and sulphuric acid (I). It results in the fornlation of insoluble barium man­ due to the hi'gh acidity of sulphuric acid as well as the ganate, which can be obtained in dry form after insolubility of barium sulphate. Carbonic acid being azeotropic distillation of water with benzene. weaker than manganic acid, the main driving force of the reaction is the formation of insoluble barium car­ ~ 6 KMnO, + 6BaCI 2 + 6 KOH + KI BaMn04 + 12 KCI bonate. However, it is an equilibrium process and disso­ + KIO, + 3 Hp .. .. (1) lution of barium carbonate in manganic acid takes place. Manganic acid disproportionates to permanganic acid Unstable manganic acid is formed when barium manga­ and manganese dioxide (3). This reaction (log K = 58) nate is treated with sulphuric or carbonic acid (2). It takes place completely in acidic, neutral or slightly al­ disproportionates to permanganic acid and manganese kaline media". dioxide (3). Due to these facts permanganic acid is formed quickly from barium manganate and SUlphuric acid via dispro­ ... (2) portionation of manganic acid (5). Thus this method is where X = S04 or CO, suitable for the preparation of permanganic acid. 3 BaMn0 + 3 H S0 ~ 2 HMn04 + 3 BaS0 + Mn02 + 2 Hp .. (3) 4 2 4 4 .. (5) Dissociation constant of manganic acid has not been determined so far. In order to explain the mechanism of Permanganic acid being a relatively strong acid re·­ these reactions, the relative strengths of the acids mu st acts easily with metal oxides, hydroxides or carbonates. be known. To estimate them, a method published earlier This method can be used to synthesize any permangan­ has been used l4 . Effective charges of the atoms of man­ ate. ganic acid and <p constants which characterize the acid The analogous reaction between barium manganate, water and carbon dioxide yield only very small amount .. strength IS were calculated using relation (4) . of manganic acid as expected from the relative strength .. (4) of the acids. Consequently longer time is required to obtain a significant amount of permanganic acid. Barium where <p means the acid strength, 8H' 8 and 8 mean the carbonate is soluble in permanganic acid (latter being a 0 x relative charges of the H,O, and X(S,C or Mn) atoms stronger acid) and this reaction has been reported as a respectively. The results are presented in Table I. method of preparation of barium permanganatelO. 12 but The data showed that manganic acid is a stronger acid this method is less favourable than the new method re­ than carbonic acid but is weaker than permanganic or ported here. 968 INDIAN J CHEM, SEC. A , SEPTEMBER 1999 To understand the reaction of barium manganate with While NaHCO, is a source of carbonic acid at slightly carbonic acid (2), it was considered essential to study its alkaline pH, ammonium sulphate behaves as a slightly reaction with sodium hydrogencarbonate. NaHCO, gen­ acidic sulphuric acid precursor (8). erates carbonic acid in boiling solutions which can form barium permanganate as per reaction (2) .. (8) ... (6) The reaction of sulphuric acid and BaMn04 results in the formation of permanganic acid. The end product of Sodium carbonate can be detected by IR spectroscopy. the reaction of permanganic acid and ammonium hydrox­ The reaction of barium permanganate and sodium car­ ide is ammonium permanganate. bonate yields barium carbonate and sodium permangan­ Equivalent amounts of ammonium sulphate and ate trihydrate. When the molar ratio of the reactants is barium manganate yield 2/3 mol ammonium permanga­ I : I , the main product is barium permanganate and a small nate while ammonia is evolved. Using 2/3 mol of am­ amount of sodium permanganate trihydrate is formed. monium sulphate, the ex pected product is barium per­ Similar results are obtained when an excess of barium manganate (in analogy with sulphuric acid) but in prac­ manganate is used. However, an excess of NaHCn, ti ce ammonium permanganate was the product. Prob­ ( I: 1.34) enhances the reaction between barium perman­ ably, manganic acid reacts rapidly with ammonia before ganate and sodium hydrogencarbonate and the main anything else can happen.