Usuari:Jaumellecha/proves
El permanganat de potassi és un compost inorgànic amb la fórmula química KMnO4 i compost per K+ i MnO−
4. És una sal cristal·lina de color negre porpra, que es dissol en aigua per donar solucions de color rosa intens o violeta.
El permanganat de potassi s'utilitza àmpliament a la indústria química i als laboratoris com a agent oxidant fort, i també com a medicament per a dermatitis, per netejar ferides i desinfecció general. Està a la llista model de medicaments essencials de l'OMS, els medicaments més segurs i eficaços necessaris en un sistema sanitari.[1] L'any 2000, la producció mundial es va estimar en 30.000 tones.[1]
Propietats
El permanganat de potassi és la sal de potassi del permanganat tetraèdric de metall de transició oxo complex, en el qual quatre lligands O2− estan units a un centre de manganès (VII).
Potassium permanganate is the potassium salt of the tetrahedral transition metal oxo complex permanganate, in which four O2− ligands are bound to a manganese(VII) center.
Estructura
El KMnO4 forma cristalls ortorròmbics amb constants: a = 910,5 pm, b = 572,0 pm, c = 742,5 pm. El motiu general és similar al del sulfat de bari, amb el qual forma solucions sòlides.
KMnO4 forms orthorhombic crystals with constants: a = 910.5 pm, b = 572.0 pm, c = 742.5 pm. The overall motif is similar to that for barium sulfate, with which it forms solid solutions.[2]
En el sòlid (com en la solució), cada centre de MnO−4 és tetraèdric. Les distàncies Mn–O són 1,62 Å
In the solid (as in solution), each MnO−4 centre is tetrahedral. The Mn–O distances are 1.62 Å.[3]
Color
El color negre porpra del permanganat de potassi sòlid, i el color intensament rosat a violeta de les seves solucions, és causat pel seu anió permanganat, que obté el seu color d'una forta banda d'absorció de transferència de càrrega causada per l'excitació dels electrons dels orbitals del lligand oxo a orbitals buits del centre del manganès (VII).
The purplish-black color of solid potassium permanganate, and the intensely pink to purple color of its solutions, is caused by its permanganate anion, which gets its color from a strong charge-transfer absorption band caused by excitation of electrons from oxo ligand orbitals to empty orbitals of the manganese(VII) center.[4]
Cristalls de permanganat de potassi
Difusió de permanganat de potassi en aigua
Solucions de permanganat de potassi amb diferents concentracions
Usos
Gairebé totes les aplicacions del permanganat de potassi exploten les seves propietats oxidants. Com a oxidant fort que no genera subproductes tòxics, el KMnO4 té molts usos nínxols.
Ús mèdic
El permanganat de potassi s'utilitza per a diverses afeccions de la pell. Això inclou infeccions per fongs del peu, impétigo, pèmfig, ferides superficials, dermatitis i úlceres tropicals. Està a la Llista de Medicaments Essencials de l'Organització Mundial de la Salut, els medicaments més segurs i eficaços necessaris en un sistema sanitari.
34- Potassium permanganate is used for a number of skin conditions.[5] This includes fungal infections of the foot, impetigo, pemphigus, superficial wounds, dermatitis, and tropical ulcers.[6][5] It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.[1]
Tractament de l'aigua
El permanganat de potassi s'utilitza àmpliament en la indústria del tractament d'aigües. S'utilitza com a producte químic de regeneració per eliminar el ferro i el sulfur d'hidrogen (olor d'ou podrit) de l'aigua del pou mitjançant un filtre "Sorra verda de manganès". "Pot-Perm" també es pot obtenir a les botigues de subministrament de piscines i s'utilitza addicionalment per tractar aigües residuals. Històricament s'utilitzava per desinfectar l'aigua potable i pot posar l'aigua de color rosa.
Actualment troba aplicació en el control d'organismes molestos com el musclo zebra en sistemes de recollida i tractament d'aigua dolça.
33- Potassium permanganate is used extensively in the water treatment industry. It is used as a regeneration chemical to remove iron and hydrogen sulfide (rotten egg smell) from well water via a "Manganese Greensand" Filter. "Pot-Perm" is also obtainable at pool supply stores and is used additionally to treat waste water. Historically it was used to disinfect drinking water[7][8] and can turn the water pink.[9]
It currently finds application in the control of nuisance organisms such as zebra mussels in fresh water collection and treatment systems.[10]
Síntesi i compostos orgànics
Una aplicació important del KMnO4 és com a reactiu per a la síntesi de compostos orgànics. Es necessiten quantitats importants per a la síntesi d'àcid ascòrbic, cloramfenicol, sacarina, àcid isonicotínic i àcid pirazinoic.
32- A major application of KMnO4 is as a reagent for the synthesis of organic compounds.[11] Significant amounts are required for the synthesis of ascorbic acid, chloramphenicol, saccharin, isonicotinic acid, and pyrazinoic acid.
El KMnO4 s'utilitza en l'anàlisi orgànica qualitativa per comprovar la presència d'insaturació. De vegades es coneix com el reactiu de Baeyer en honor al químic orgànic alemany Adolf von Baeyer. El reactiu és una solució alcalina de permanganat de potassi. La reacció amb enllaços dobles o triples (-C=C- o -C≡C-) fa que el color s'esvaeixi de rosa porpra a marró. Els aldehids i l'àcid fòrmic (i els formiats) també donen una prova positiva. La prova és antiquat.
31- KMnO4 is used in qualitative organic analysis to test for the presence of unsaturation. It is sometimes referred to as Baeyer's reagent after the German organic chemist Adolf von Baeyer . The reagent is an alkaline solution of potassium permanganate. Reaction with double or triple bonds (-C=C- or -C≡C-) causes the color to fade from purplish-pink to brown. Aldehydes and formic acid (and formates) also give a positive test.[12] The test is antiquated.
Ús analític
El permanganat de potassi es pot utilitzar per determinar quantitativament el material orgànic oxidable total en una mostra aquosa. El valor determinat es coneix com a valor de permanganat. En química analítica, de vegades s'utilitza una solució aquosa estandarditzada de KMnO4 com a valorant oxidant per a valoracions redox (permanganometria). A mesura que es titula el permanganat de potassi, la solució es converteix en una ombra clara de magenta, que s'enfosquit a mesura que s'afegeix un excés de valorant a la solució. D'una manera relacionada, s'utilitza com a reactiu per determinar el nombre Kappa de polpa de fusta. Per a l'estandardització de solucions de KMnO4, s'utilitza sovint la reducció per àcid oxàlic.
30- Potassium permanganate can be used to quantitatively determine the total oxidizable organic material in an aqueous sample. The value determined is known as the permanganate value. In analytical chemistry, a standardized aqueous solution of KMnO4 is sometimes used as an oxidizing titrant for redox titrations (permanganometry). As potassium permanganate is titrated, the solution becomes a light shade of magenta, which darkens as excess of the titrant is added to the solution. In a related way, it is used as a reagent to determine the Kappa number of wood pulp. For the standardization of KMnO4 solutions, reduction by oxalic acid is often used.[13]
Les solucions aquoses i àcides de KMnO4 s'utilitzen per recollir mercuri gasós als gasos de combustió durant les proves d'emissions de fonts estacionàries.
28- En histologia es va utilitzar permanganat de potassi com a blanquejador.
29- Aqueous, acidic solutions of KMnO4 are used to collect gaseous mercury in flue gas during stationary source emissions testing.[14]
28- In histology, potassium permanganate was used as a bleaching agent.[15][16]
Conservació de la fruita
27- Ethylene absorbents extend storage time of bananas even at high temperatures. This effect can be exploited by packing bananas in polyethylene together with potassium permanganate. By removing ethylene by oxidation, the permanganate delays the ripening, increasing the fruit's shelf life up to 4 weeks without the need for refrigeration.[17][18][19]
Survival kits
26- Potassium permanganate is sometimes included in survival kits: as a hypergolic fire starter (when mixed with glycerol antifreeze from a car radiator;[20][21][22] as a water sterilizer - and for creating distress signals on snow.[23]
Fire service
25- Potassium permanganate is added to "plastic sphere dispensers" to create backfires, burnouts, and controlled burns. Polymer spheres resembling ping-pong balls containing small amounts of permanganate are injected with ethylene glycol and projected towards the area where ignition is desired, where they spontaneously ignite seconds later.[24]Both handheld and helicopter or boat-mounted plastic sphere dispensers are used.
Altres usos
24- Potassium permanganate is one of the principal chemicals used in the film and television industries to "age" props and set dressings. Its ready conversion to brown MnO2 creates "hundred-year-old" or "ancient" looks on Hessian cloth (burlap), ropes, timber, and glass.[25]
23- Potassium permanganate can be used to oxidize cocaine paste to purify it and increase its stability. This led to the Drug Enforcement Administration launching Operation Purple in 2000, with the goal of monitoring the world supply of potassium permanganate; however, potassium permanganate derivatives and substitutes were soon used thereafter to avoid the operation.[26]
22- In agricultural chemistry, it is used for estimation of available nitrogen in soil.
Història
21- In 1659, Johann Rudolf Glauber fused a mixture of the mineral pyrolusite (manganese dioxide, MnO2) and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution (potassium manganate) which slowly shifted to violet and then finally red.[27] This report represents the first description of the production of potassium permanganate.[28] Just under 200 years later, London chemist Henry Bollmann Condy had an interest in disinfectants; he found that fusing pyrolusite with sodium hydroxide (NaOH) and dissolving it in water produced a solution with disinfectant properties. He patented this solution, and marketed it as 'Condy's Fluid'. Although effective, the solution was not very stable. This was overcome by using potassium hydroxide (KOH) rather than NaOH. This was more stable, and had the advantage of easy conversion to the equally effective potassium permanganate crystals. This crystalline material was known as 'Condy's crystals' or 'Condy's powder'. Potassium permanganate was comparatively easy to manufacture, so Condy was subsequently forced to spend considerable time in litigation to stop competitors from marketing similar products.[29]
20- Early photographers used it as a component of flash powder. It is now replaced with other oxidizers, due to the instability of permanganate mixtures.
Preparació
19- Potassium permanganate is produced industrially from manganese dioxide, which also occurs as the mineral pyrolusite. In 2000, worldwide production was estimated at 30,000 tonnes.[30]The MnO2 is fused with potassium hydroxide and heated in air or with another source of oxygen, like potassium nitrate or potassium chlorate.[30] This process gives potassium manganate:
- MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O
18- With sodium hydroxide, the end product is not sodium manganate but an Mn(V) compound, which is one reason the potassium permanganate is more commonly used than sodium permanganate. Furthermore, the potassium salt crystallizes better.[30]
17- The potassium manganate is then converted into permanganate by electrolytic oxidation in alkaline media:
- K2MnO4 + 2 H2O → 2 KMnO4 + 2 KOH + H2
Altres mètodes
16- Although of no commercial importance, potassium manganate can be oxidized by chlorine or by disproportionation under acid conditions.[31] The chlorine oxidation reaction is
- K2MnO4 + Cl2 → 2 KMnO4 + 2 KCl
15- And the acid-induced disproportionation reaction may be written as
- K2MnO4 + 4 HCl → 2 KMnO4 + MnO2 + 2 H2O + 4 KCl
14- A weak acid such as carbonic acid is sufficient for this reaction:
- K2MnO4 + 2 CO2 → 2 KMnO4 + 2 K2CO3 + MnO2
13- Permanganate salts may also be generated by treating a solution of Mn2+ ions with strong oxidants such as lead dioxide (PbO2), sodium bismuthate (NaBiO3), or peroxydisulfate. Tests for the presence of manganese exploit the vivid violet color of permanganate produced by these reagents.
Estructura
12- KMnO4 forms orthorhombic crystals with constants: a = 910.5 pm, b = 572.0 pm, c = 742.5 pm. The overall motif is similar to that for barium sulfate, with which it forms solid solutions.[32] In the solid (as in solution), each MnO4− centres are tetrahedral. The Mn–O distances are 1.62 Å.[33]
Reaccions
Química orgànica
11- Dilute solutions of KMnO4 convert alkenes into diols (glycols). This behaviour is also used as a qualitative test for the presence of double or triple bonds in a molecule, since the reaction decolorizes the initially purple permanganate solution and generates a brown precipitate (MnO2). In this context, it is sometimes called Baeyer's reagent. However, bromine serves better in measuring unsaturation (double or triple bonds) quantitatively, since KMnO4, being a very strong oxidizing agent, can react with a variety of groups.
10- Under acidic conditions, the alkene double bond is cleaved to give the appropriate carboxylic acid:[34]
- CH3(CH2)17CH=CH2 + 2 KMnO4 + 3 H2SO4 → CH3(CH2)17COOH + CO2 + 4 H2O + K2SO4 + 2 MnSO4
9- Potassium permanganate oxidizes aldehydes to carboxylic acids, such as the conversion of n-heptanal to heptanoic acid:[35]
- C6H13CHO + 2 KMnO4 + 3 H2SO4 → 5 C6H13COOH + 3 H2O + K2SO4 + 2 MnSO4
8- Even an alkyl group (with a benzylic hydrogen) on an aromatic ring is oxidized, e.g. toluene to benzoic acid.[36]
- C6H5CH3 + 6 KMnO4 + 9 H2SO4 → 5 C6H5COOH + 14 H2O + 3 K2SO4 + 6 MnSO4
7- Glycols and polyols are highly reactive toward KMnO4. For example, addition of potassium permanganate to an aqueous solution of sugar and sodium hydroxide produces the chemical chameleon reaction, which involves dramatic color changes associated with the various oxidation states of manganese. A related vigorous reaction is exploited as a fire starter in survival kits. For example, a mixture of potassium permanganate and glycerol or pulverized glucose ignites readily.[20] Its sterilizing properties are another reason for inclusion of KMnO4 in a survival kit.
6- By itself, potassium permanganate does not dissolve in many organic solvents. If an organic solution of permanganate is desired, "purple benzene" may be prepared, either by treating a two phase mixture of aqueous potassium permanganate and benzene with a quaternary ammonium salt,[37] or by sequestering the potassium cation with a crown ether.[38]
Reacció amb els àcids
5- The reaction of permanganate with concentrated hydrochloric acid gives chlorine. The Mn-containing products from redox reactions depend on the pH. Acidic solutions of permanganate are reduced to the faintly pink manganese(II) ion (Mn2+) and water. In neutral solution, permanganate is only reduced by three electrons to give manganese dioxide (MnO2), wherein manganese is in a +4 oxidation state. This is the material that stains one's skin when handling KMnO4. KMnO4 spontaneously reduces in an alkaline solution to green K2MnO4, wherein manganese is in the +6 oxidation state.
4- A curious reaction occurs upon addition of concentrated sulfuric acid to potassium permanganate. Concentrated sulfuric acid reacts with KMnO4 to give Mn2O7, which can be explosive.[39] Although no reaction may be apparent, the vapor over the mixture will ignite paper impregnated with alcohol. Potassium permanganate and sulfuric acid react to produce some ozone, which has a high oxidizing power and rapidly oxidizes the alcohol, causing it to combust. As the reaction also produces explosive Mn2O7, this should only be attempted with great care.[40][41]
Descomposició termal
3- Solid potassium permanganate decomposes when heated:
- KMnO4 → K2MnO4 + MnO2(s) + O2
2- Here, the oxidation state of manganese changes as the potassium permanganate (oxidation state +7) decomposes to potassium manganate (oxidation state +6) and manganese dioxide (oxidation state +4). Oxygen gas is also liberated.
Safety and handling
1- Potassium permanganate poses risks as an oxidizer.[42] Contact with skin will result in a long lasting brown stain.[43]
Referències
Bibliografia
- Barthel, H; Duvinage, B «Clemens Winkler. His Experiments with Ozone in 1892» (en anglès). Praxis der Naturwissenschaften, Chemie, 49, 2000.
- Brauer, E. Handbook of Preparative Inorganic Chemistry (en anglès). New York: Academic, 1963.
- Bretherick, L; Urben, P. G; Pitt, Martin John. Bretherick's Handbook of Reactive Chemical Hazards (en anglès). 1. Elsevier Academic Press, 2007. ISBN 978-0-12-373945-2.
- Brody, Ester «Victor DeLor contractor profile» (en anglès). PaintPRO, 2(1), febrer 2000. «Una de les tècniques per les quals DeLor és conegut entre dissenyadors i clients són els efectes especials que crea amb diverses solucions químiques. Quan s'apliquen a superfícies de fusta, aquests productes químics donen un aspecte resistent a la intempèrie a la fusta nova. ... Per aconseguir l'estètica a les superfícies interiors, DeLor utilitza sovint una barreja d'aigua i permanganat de potassi, una pols química seca».
- Cotton, F. A; Wilkinson, G; Murillo, C. A; Bochmann, M. Advanced Inorganic Chemistry (en anglès). Wiley-VCH, 1999. ISBN 0-471-19957-5.
- Doheny, Anthony J., Jr; Ganem, Bruce «Purple benzene revisited» (en anglès). J. Chem. Educ., 57(4), 1980. Bibcode: 1980JChEd..57..308D. DOI: 10.1021/ed057p308.1.
- Dzhabiev, T. S; Denisov, N. N; Moiseev, D. N; Shilov, A. E «Formation of Ozone During the Reduction of Potassium Permanganate in Sulfuric Acid Solutions» (en anglès). Russian Journal of Physical Chemistry, 79, 2005.
- Fatiadi, A «The Classical Permanganate Ion: Still a Novel Oxidant in Organic Chemistry» (en anglès). Synthesis, 1987(2), 1987. DOI: 10.1055/s-1987-27859.
- Gardner, K. A; Mayer, J. M «Understanding C-H Bond Oxidations: H· and H- Transfer in the Oxidation of Toluene by Permanganate» (en anglès). Science, 269, 1995. Bibcode: 1995Sci...269.1849G. DOI: 10.1126/science.7569922. PMID: 7569922(5232.
- Herriott, Arthur W «Purple benzene: Solubilization of anions in organic solvents» (en anglès). J. Chem. Educ., 54(4), 1977. Bibcode: 1977JChEd..54Q.229H. DOI: 10.1021/ed054p229.1.
- Kovacs, K. A; Grof, P; Burai, L; Riedel, M «Revising the Mechanism of the Permanganate/Oxalate Reaction» (en anglès). J. Phys. Chem. A, 108(50), 2004, pàg. 11026. Bibcode: 2004JPCA..10811026K. DOI: 10.1021/jp047061u.
- Lee, Donald G; Lamb, Shannon E; Chang, Victor S «Carboxylic Acids from the Oxidation of Terminal Alkenes by Permanganate: Nonadecanoic Acid» (en anglès). OrgSynth, 7, 1990. cv7p0397
- Murphy, C. L; Eulitz, M; Hrncic, R; Sletten, K; et al. «Chemical typing of amyloid protein contained in formalin-fixed paraffin-embedded biopsy specimens» (en anglès). Am. J. Clin. Pathol., 116(1), 2001, pàg. 135-142. DOI: 10.1309/TWBM-8L4E-VK22-FRH5. PMID: 11447744.
- Palenik, Gus J «Crystal structure of potassium permanganate» (en anglès). Inorg. Chem., 6(3), 1967. DOI: 10.1021/ic50049a015.
- Picken, M. M «Amyloidosis-where are we now and where are we heading?» (en anglès). Arch Pathol Lab Med, 134(4), abril 2010. DOI: 10.5858/134.4.545. PMID: 20367306.
- Reidies, Arno H «Manganese Compounds» (en anglès). Ullmann, 2002. DOI: 10.1002/14356007.a16_123.
- Scott, K. J; McGlasson, W. B; Roberts, E. A «Potassium Permanganate as an Ethylene Absorbent in Polyethylene Bags to Delay the Ripening of Bananas During Storage» (en anglès). Australian Journal of Experimental Agriculture and Animal Husbandry, 10(43), 1970. DOI: 10.1071/EA9700237.
- Scott, K. J; Blake, J. R; Stracha, G; Tugwell, B. L; McGlasson, W. B «Transport of Bananas at Ambient Temperatures using Polyethylene Bags» (en anglès). Tropical Agriculture (Trinidad), 48, 1971.
- Scott, K. J; Gandanegara, S «Effect of Temperature on the Storage Life of bananas Held in Polyethylene Bags with an Ethylene Absorbent» (en anglès). Tropical Agriculture (Trinidad), 51, 1974.
- Walton, H. F. Inorganic Preparations (en anglès), 1948.
- Weeks, Mary Elvira; Leicester, Henry M. Discovery of the Elements (en anglès). Easton, Pennsylvania: Journal of Chemical Education, 1956.
Enllaços externs
- «Potassium permanganate» (en anglès). Drug Information Portal (U.S. National Library of Medicine ).
- «Manganese and compounds Fact Sheet» (en anglès). National Pollutant Inventory.
- «The use of potassium permanganate in fish ponds» (en anglès).