Ananthakrishnanadar, P.

Murugesan, R.

Shanmugasundaram, A.

English

NOPR

INDIAN J. CHEM., VOL. 14A, FEBRUARY 1976Oxidation of Acetonaphthones byHexacyanoferrate(III)P. ANANTHAKRISHNANADAR, A. SHANMUGASUNDARAM&R. MURUGESANDepartment of P.G. Chemistry, V.H.N.S.N. CollegeVirudhunagar 626002Received 2 December 1974; accepted 7 March 1975Kinetics of oxidation of a number of 4-substitutedl-acetonaphthones and of 2-acetonaphthone by hexa-cyanoferrate(III) in aq. ethanol at 35° have been studied.An increase in ethanol content of the solvent decreasesthe kinetic rate while increase in concentration of eitheralkali or a neutral salt increases the rate. This mayprovide evidence for the oxidation to proceed throu~hthe enolate anion intermediate. Hammett equation ISfound to be valid in the presently studied system.ALTHOUGH far more attention has been paidto correlate the reactivities of meta- and para-substituted benzene derivatives in a larg~ num~erof reactions", relatively very few systematic studiesof similar type are available in naphthalene system--",The kinetics of oxidation of a number of 4-SUbS~l-tuted 1-acetonaphthones by hexacyanoferratelIII) maq. ethanol at constant ionic strength and constanttemperature have been investigated and the resultsare reported in this note. .All the ketones used were prepared by the. hte~a-ture methods. The procedure for the determinationof rate constants was similar to that followed foracetophenones''. Rate constants have .been deter-mined using second order rate eq,:atIOn for .thereactants present in equal concentration. The kine-tic data are given in Tables 1-3. It has been shown4,5that the oxidation of acetophenones by hexacyano-ferrate(III) proceeds through the enolate amon.TABLE1 - EFFECTOFVARYING[KCI] ONTHEREACTIONRATE{[1-Acetonaphthone] = [K3Fe(CN).]=1·014 x 10-8 M; ° INaOH]=0·05M; solvent=15% ethanol; temp.=35 C}[KCI] v'~ k, litreM mole!min "0·2500·18750·12500·07640·03710·55330·49350·42550·36410·30543·222·632·481·811·36TABLE 2 - EFFECT OF VARYINGSOLVENTCOMPOSITIONAND[NaOH] ON THE REACTIONRATE([I-Acetonaphthone] = [K3Fe(CN).] = 1·014 x 10-3M; [KCI]=0·25M; temp. = 35°C}k, litre [NaOH]mole'? Mmin!Ethanol% (v/v)k, litremole-!min ?[NaOH]=0·05M15 3·2220 2·3925 2·19Ethanol, 15%0·0100·0250·0500·075(v/v)0·881·803·225·12146TABLE 3 - SECOND ORDER RATE CONSTANTS FOR THEOXIDATIONOFKETONESIN 15% (v/v) ETHANOLAT35°{[Ketone] = [K3Fe(CN).l =0·OO1014M; [KCI] =0·25M; [NaOH}=O·OSM}Ketones klitre mole'?min ?Acetophenone2-Acetonaphthone1-Acetonaphthon e4- FIuoro- 1-acetona ph tho ne4-Chloro- 1-acetonaphthone4-Bromo- 1-acetonaphthore4-Methyl- 1-acetonaphthon e4-l\fethoxy-l-acetoll<l.phthone1·543·073·223·427·519·532·601·52With a view to finding whether a similar mechanismholds good for acetonaphthones, the oxidation ofl-acetonaphthone was carried out at differentionic strengths. The rate (Table 1) was found toincrease with increasing ionic strength. A plot oflog k versus V~ ws s linear. Also the rate was foundto decrease with increasing ethanol content of thesolvent medium (Table 2). Thec;e determinationspoint out to an ion-ion type of reaction which pro-ceeds through the formation of enolate anion.It is seen from the data in Table 3 that electronattracting groups in the naphthalene ring facilitateoxidation whereas electron releasing groups retardthe oxidation. If the oxidation proceeds throughthe enolate anion, the rate of oxidation will dependon the stability and percentage of the enol content.In the presence of electron attracting groups theketo form will be more unstable than the enolic form.The results on the effect of various substituents andthose in Table 2 of varying [alkali] provide evidencein favour of the oxidation taking place throughthe enolate anion. However, it is difficult to decideabout the exact nature of enolate in the absence ofany product analysis.A plot of log k/ko against the (J constants of the4-substituents is linear at 35° (P = 1·3; r = 0·942)showing that the Hammett equation applies satis-factorilv in the oxidation of 4-substituted l-aceto-naphthones.It is evident that I-acetonaphthone reacts fasterthan acetophenone. This is due to the electronattracting nature of the 2,3-benzo substituent whichhas a (J value" of 0·5. Oxidation of 2-acetonaph-thone proceeds at a slower rate than l-acetonaph-thone. This mav be due to the lower (J value(0·04) of the 3,4-benzo substituent+ compared tothat of the 2,3-benzo substituent.References1. JAFFE, H. H., Chem, Reu., 53 (1953), 19t.2. BALlAH, V. & ANANTHAKRISHNA""ADAR, P., Indian J.Chem.,9 (1971), 671, 1241, 1339; 11 (1973),886.3. BALIAH, V., ANANTHAKRISHNANADAR, P. & SIVAPRA-KASAM,R., Indian J. Chem., 9 (1971), 1337.4. RADHAKRISlINAMURTI,P. S. & SUSHlLA DEVI, Indian J.Chem., 10 (1972), 496.5. SINGH, V. N., SINGH, M. P. & SAXENA, B. B. L., IndianJ. Chem., 8 (1970), 529. .6. BARLlN, G. B. & PERRIN, D. D., Q. Rev., 20 (1966), 75.

Oxidation of Acetonaphthones by Hexacyanoferrate(III)

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Oxidation of Acetonaphthones by Hexacyanoferrate(III)

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