Naftalinin seryum (IV) ile oksidasyon kinetiği ve mekanizması

Abstract

Bu çalışmada Naftalinin seryum(IV) tuzu ile preparatif oksidasyonu ve kinetiği incelenmiştir. Preparatif oksidasyonda seryum (IV) amonyum nitrat ile seryum (İV/) amonyum sülfat kullanılmıştır. Oksidasyon sonucu 1.4 naftakinon elde edilmiştir. 1,4.naftakinon özellikle boyar madde üretiminde, parfümeride vs. alanlarda kullanılmakta dır. Seryum tuzlarının geniş ölçüde kullanımı vardır. Fa kat daha çok ürün tanınması ve stokimetri belirlenmesinde kullanılmıştır. Kinetik çalışmalarda kullanımı fazla olmamıştır. Bu çalışmadaki kinetik denemeler nitrik asit, nitrik asit-perklorik asit ve nitrik asit-sodyum nitrat ortamlarında değişik sıcaklıklarda spektrofotometrik olarak incelenmeler yapılmıştır. Kinetik çalışmaların sonu cunda sözü edilen ortamlarda reaksiyon hız sabitleri ve aktivasyon parametreleri ile stokiometrik katsayısı elde edilmiştir.

Cerium, salts have been used in many organic oxida tion reactions. The common valances of cerium salts are three and four, in which the most probable unhybridized electronic configurations are, 5S2 5PS 4d1D 4f1 and 5S2 5PS 4d1D respectively. Monomeric cerium (IV) will then be a one-electron oxidant. The oxidation potential of the cerium (IV)-(III) couple is ligand dependent. For example, oxidation potentials of cerium salts are -1.7 D to -1.71, -1.61, -1.44 and -1.28 volts in 1N perchloric, nitric, sulfuric and hydrochloric acids, respetively. In sulfuric acid solutions, cerium(IU) is appeared as. CeSD£, Ce(5D,)_ and Ce(S0,)2~ comp lexes in perchloric acid solutions hydrolysis of cerium(IU) -Ce(DH), Ce(DH)_ and dimerization of the hydrolysis products CeOCe, (H0CeDCe0H)4+. Cerium salts have been used in oxidation of hydrocarbons widely. Especially, They have been used in aromatic hydrocarbuns to determine stDcyometry and identification products. Aromatic substitustion remains one of the most fundamental transformation in organic chemistry. By for the most common mechanism involwes direct electrophilic attack on the aromatic nucleus to form the ^-complex intermediate. However many electrophiles are also known to be election acceptors. Some of the most important electron acceptors are Tl(III), H3CII), Pb(IV), Co(III), Fe(III), Ce (IV). Thus it is not always easy tD make on unequivocal mechanistic distinction between such a concerted activa tion process and involving prior electron transfer. There VI are many Examples of aromatic compound undergoing one- electron oxidation by different electron acceptors, E, -* E. (1) BincE some electron acceptors also partricapet in aromatic substitution, the redox system offers qn opportinity to evauiate the relevance of electron transfer to aromatic donors. In order to establish the mechasim of electron transr-. fer from aromatic compounds, the oxidation of various methylarenes by series of tris iron (III). Complexes which are constrained to effect single electron transfer. Morever, Methylarenes ArCH, are useful aromatic donars for these kinetic studies since they are know to endergo substitution via the arene cation radical formed by either electrochemical or chemical oxidation. The kinetic scheme is outlined by equation (2 and 3) ArCH, <- k-1 ArCH! [*] (2) ArCH" -» products + f_e] Other kind of oxidation of hydrocarbons is anodic oxidation There are two mechanism in anodic oxidation. In first mechanism, where l\lu represents a nucleophile and B a base, the initially, cation radical forms and reacts by a nucleophile, and ring substitutions is the ultimate result. -e ArH ?* ArH< Nu / > Ar. - Nu Nu / \H "e -* Ar+ L» ArNu++B.H+ \ (3) In second mechanism, cation radical forms, then, -it transfer a proton tD a base and the ultimate result is side Chain substitution. ArCH2R - If ^ArGHgR* % ArCHR + BH "e »ArCH-R - j. Nu I ArCHR (4) Vll BDth of these mechanism are Smilar, and the essential difference in two mechanism is in the relative timing of the proton transfer and the attack by the nucleophile. In this work, preparative oxidation of naphthalene was made by eerie ammonium sulphate and eerie ammonium nitrate. - Oxidation of naphthalene by Ceric ammonium sulphate (CAS) 1 mmril napthalene is dissolved in acetonitrile and 4W H"SD, (40ml acetonitrile/10ml İ-L50,). And then 6mmol CAS is dissolved in 4I\IH"S0, (50ml ) then the solution of CAS is Poured into the solution of napthalene. Reac- o tiûn mixture is stirred at 50 C, & hours. Ce(III) salt is precipitated. After S hours, reaction mixture was decanted to separete Ce(III) salt. Then this mixture was diluted by distilled water, and extracted by ether to separate organic phgse. Then organic phase dried Under the vacum, And then product was recrystallized by CC1,. - Oxidation of Naphthalene by ceric ammonium nitrate (CAN) U.k gr CAN was added to 1 mmol naphthalene in 5D ml acetonitrile. Reaction mixture was stirred at 30 C, 30 minute. Then reaction mixture was diluted by distilled water. And precipitate was formed. This precipitate was separated by filtration. and liquid phase was extracted with ether, tD seperate organic products. Then organic phase was evoporated by vacum at the same time, Resinous material which might be a dimer, and it seperated from naphtaquinone by CC1,. Kinetic measurements were studied spectrophotometrically Schimadu 160 A type' Spectrophotometry was used in this work. These measurements were made in HND,, HNO,, HC10, and HMo - NaNO, at various temperature and constant ionic strength (1= 0.5m) Re suits of reaction rate constants in hND, were shown in Table 1. Vlll (Napth)xlO I -11 üseuda first order K,, Sn K r obs' Dbs 10" 1.25 2.5D 3.125 3.75 6.25 B.75 1.14 1.70 1.86 2. 3D 3.86 4.82,-3 [Ce(IV)] = 2.5.1D"JM, 1= 0.5M, >s = 430nm, Results of reaction rate constants in HND--HC1D, at dif f ererittemperatures mere shDuin in Table 2. [Ce(IV)] = 2.5.1D,3M, [Napht] =1.25. 1D~2M, 1=0. 5M, >=430mm. Results meters table 3 of reaction rate constants and activation para^. in HN0, -NaNO, at different temperatures were sho\Ain,-3, -2 [Ce(IV)]o= 2.5.10 M, [l\lapht]=3.125.10, 1=0. 5M, A=430.nm. IX From the above results for the oxidation mech Reaction rate decrease concentration and with tion. High intercept obtained from 1/,, v tion state for trie o Negative entrDphy chan Small changes ( AB) i f Dİloujingconclusions can be drawn anism of napthalene by cerium( IV) s uithan increase Df nitrate ion a decrease hydrogen ion concentra- values of straight lines which are ersus 1/[Napth] indicates a transi- xidatiDn of napthalene by cerium(IV) ges ( AS) obtanied in this work. ndicates to more ordered conditions. similar activation parameters obtained in both HMD - HC1D. and H!\!D3- mechanism for both media.