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Departmen1 cf C ~ L C I ~ I T11c I I ~ IColle~e . ~ , of General Education, University of Tokyo, ~lfeegzrro-kzr,Tokyo, Japajt Received December 28, 19G1 ABSTRACT &Ianganese(llI) ethylcnediamir~etetraaceticacid co~npleshas bee11 prepared by various methods. The solid having a co~npositionof ICMnY.2.514?0 is obtained as deep red crystals when the rnallgallese dioxide suspel~sionreacts with free ethylenediaminetetraacetic acid (HAY).The manganese \\,as sho\vn to be trivalent from its redos equivalent in its reaction with acidified iodide s o l u t i o ~ ancl ~ , its ~nagneticmornelit, which was 4.89 Bohr magnetons, corresponding to four ~ ~ n p a i r eelectroll d spins. The complex ion has a n absorptio~lmaximum a t 500 mp (log e = 2.67) in a slightly acidic medium. 'The variation of the visible spectra with pH has been studied by the spectrophotornetric method, the value pIC 5.3 being obtained between the red and the yellow species. Observatio~~s have been made o n the type of bond between the ~ n e t a land carbosylate groups by the ir~fraredspectral method. From its ion-exchange ancl pH titratio11 I~chavior a f o r ~ ~ ~ u I~II(OHI)EDTA].I.~H~O, la, was suggested.



The for~natio~l of rllangai~ese(II1)-EDTA complex in solution was utilized blr I'iibil et al. for the photometr~.and redox titration of mang:unese ( 1 , 2, 3). They oxidized divalent manganese to the trivalent state by means of lead dioxide, sodium bismuthate, etc. in the presence of excess EDTA. However, since the manganese(II1)-EDTA coinplex solution thus obtained contains reaction products of the oxidizing agents, their methods for the formation of the mai~ganese(II1)-EDTA complex was found to be unsuitable for studying the nature of the complex. 111 the course of study on the stabilization of less familiar oxidation states of metals by coordination (1,5), the present authors have t'o~iindthat the manganese(1 I I)-EDTA complexes could be forined by the reaction of EDTA with manganese compounds of higher oxidation states, such as manganese dioxide or potassiuill permanganate. The critical examination of stoichiometry of the complex formation reaction revealed that the manganese dioxide or permanganate ion was reduced by EDTA itself, giving a reddish-purple solutioil of the manganese(II1)EDTA complex. After a i~umberof attempts, we have been able to prepare a crystalliile solid. The present paper describes the preparation and properties of the complex of this sort. ESI'ERIhIENTAL ilfatcrials I n o r g a ~ ~ salts, ic acids, and bases were all the JIS3 special-class grade. Free acid (HqY) and disodium salt ( N a ? H ? Y . 2 H 2 0 )of ethylenediami~tetetraaceticacid were also the J I S special-class grade. Fe(II1)E D T A chelate, NaFe(CloHlrN?08).2H@, p ~ ~ r c h a s efrom d Daiichi Pure Chemicals Co., \\,as of reagent grade. Co(II1)-EDTA chelate, ICCo(CloH12hT?Oe)2H?O, was prepared according to the method of Dwyer et al. (6). Organic solvents of the J I S first-class grade were used after distillation. As ion-exchange resins, strongly acidic cation-exchange resin Diaiolt SIC-1 of 100-200 mesh (sulphonated polystyrene-divinyl-be~i~e~~e copolymer, purchased from Mitsubishi ICasei Co., Tokyo) and s t r o ~ ~ g basic ly anion-exchange resin, Dowex 1-X8, 100-200 mesh, were employed in a colu~nnnlethod.

'Presented in part at the 14th ilnnrlal Conference of the Che7nical Society of J a p a n in Tokyo in A p r i l , 1961. Preliminary paper was plrblished in tlte Bzrll. Cltem. Soc. J a p a n , 34, 1194 (1961). 2Present address: Government Chevlical Industrial Research Institzlte, Tokyo. 3Japanese Indfrstrial Standard. Canadian Journal of Cliemistry. Volume 40 (1962)






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Magnetic ~ n e a s ~ ~ r e n l ewere n t s made on the solid comples using a Goiiy apparatus of conventional type. A11 X-ray dilfractometer, "Geigerflex" of Rigaku Denlii Co., was used for examining powder diffraction patterns of the chelate using Cu I(,, ray. For thermal analysis, the "Tolcoshi type" thermobalance was used. The infrared spectra were recordcd with a recording spectrophotometer of Nihon Bu11lio Co., type DS-301, equipped with a sodium chloride prism. As the sample, which was handled a s a potassium bromide pellet, decolnposed gradually, a Nujol mull technique was employed. Visible and ultraviolet spectra were measured with the E P S I1 recording spectrophotometer and the E P U I1 spectrophotometer, both from Hitachi Co. The p H of the solution was measured by a glass electrode pH-meter of Iio Denki Co., model 43. PREPARATION O F COMPLEXES

( i ) Formation of ilhnganese(III)-EDTA Complex in Sol~ition In prelirniilary attempts, various methods for the preparation of the manganese(III)EDTA complex in solution were tried. ( a ) Freshly prepared manganese dioxide suspended in water was lnixed with solid EDTA (H4Y) under vigorous stirring. The resultant reddish purple coinplex in the filtrate was determined b57 both spectropl~otometryand iodoinetric titration. The relation between the inole ratio EDTA to Mi102 and that of produced Mn(II1)-EDTA coillplex was shown in Fig. 1. During the reaction the evolution of carbon dioxide was observed

FIG. 1. Relation between the mole ratio of E D T A to manganese dioxide and the mole ratio of produced ~\IIII(III)Yto manganese dioside (i\iIr~Op:2.69X10-3 mole). and a little of EDTA was lost; this 111a57 be due to the oxidation of EDTA by manganese dioxide. However, the mole ratio of Mn(II1) to EDTA in the complex was found to be close to 1:l. (b) In the above-mentioned case, H4Y could be replaced by a mixed solution of NazHzY and acetic acid (pH 2.5-3). In this case, however, the yield, i.e., the ratio of NIn(II1)-EDTA to RlnOn, showed a ~naximum a t EDTA/MnOn z 1, and then gradually decreased as the ratio EDTA/Mn02 was increased. This is presuinably ascribed to the partial deco~npositionof NIn(II1)-EDTA by the excess of EDTA in the solution. (c) I t was also found that potassiuin permanganate could be used in place of manganese dioxide. The inaxiinunl yield was obtained a t the point where the mole ratio EDTA/Mn04- was a little larger than 1, although the reaction sometimes did not proceed smoothly, depending upon the conditions employed, and the yield and the purity of the products were not always high. (d) The nlanganese(II1)-EDTA co~nplexwas also forlned by oxidizing manganese(I1)EDTA coinplex with ilianganese dioxide. The relation between the obtained Mn(II1)EDTA and the used Mn(I1)-EDTA is illustrated in Fig. 2. For a fixed amount of Mn02, the amount of Mn(II1)-EDTA increased until Mn(I1)-EDTA/MnO? reached ca. 1.7,

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FIG. 2. Relati011between the mole ratio of M n ( I I ) Y to manganese dioxide and the n ~ o l ratio e of produced i\/In(II I)Y to manganese dioxide (IvlnO?: 2.69X mole).

and then the yield reinailled nearly coilstant (MI~(III)-EDTA/~M~IO~ 1 :1.5). I t seeins that the EDTA chelated to bIn(I1) is easily decoinposed by oxidation, but, in the above case, the main reaction may be (ii) Preparation of Solid Complex After a n~lrnberof atteinpts, it was found that an extension of the method clcscribecl above in (a) was inost suitable for preparing a solid complex. One of the typical niethocls of preparation of potassiuin salt is as follows: Six grams of finely powdered potassiuin perinanganate were added to a inixed solution of 40 ml of water and 10 in1 of ethanol. The mixture was shaken and then carefully warmed. After the vigorous reaction had ended, the mixture was warmed repeatedly in order to expel1 the excess ethanol and aldehyde. T o the mixture of inanganese dioxide and potassium hydroxide so obtained, 10 g of EDTA (H4Y) was added. With vigorous stirring, a reaction took place, evolving carbon dioxide, and a deep cherry-red solutioil was obtained. After the excess manganese dioxide was filtered off with a glass filter, an equal volume of cold ethanol was added to the filtrate. The mixture was allowed to stand for 3-4 hours in a cold, dark place. The precipitated crystals were then filtered off with a glass filter and washed with goy0, then absolute ethanol and ether. Finally they were dried in the air in a cold, dark place. The yield based on the used EDTA (H4Y) was 45-60%. When more diluted solution of inanganese(II1)-EDTA was mised with an equal volume of ethanol, large, needle-like crystals were obtained after standing of the solutioil for 1 or 2 days in a refrigerator. (iii) -4nalysis The manganese was separated as hydroxides by the addition of sodiuin hydroxide and hydrogen peroxide to the coinplex solutioil. After the hydroxides were dissolved in dilute sulph~~ric acid with the aid of sodiunl sulphite, the nlanganese was weighed as manganese sulphate, or back-titrated with EDTA and zinc chloride solutions a t pH 10 using Eriochrome Blacli T as indicator. A checli on the manganese content was niade by iodoinetric titration: the sample was added to acidified potassium iodide solution, and then liberated iodine was titrated with thiosulphate solution. The results of these separate determinations were in good agreement, and this ineans that the


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manganese in the complex is in a trivalent state. T o determine potassium, the solid sainple was ignited a t red heat and the residue was dissolved in h~~drochloric acid. From the solution so obtainecl, potassium was determined gravimetrically by its weight as potassium sulphate after separation from other constituents. Carbon and 111-drogen were tletermined through microchemical analysis, with special care being taken for the presence of potassium by the additioil of tungsten trioxicle to the sanlple. The nitrogen analysis was made by micro-Duinas nlethod. 'The results of a typical analysis follow: Found: K, 9.41%; Mn, 12.7070; C , 28.73y0; H , 3.83y0; N, 6.6'i70. Calculated for I