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574 Analyst, May, 1981, Vol. 106, $9. 574-583 Evaluation of NN’-Di(2-naphthyl)phenylene-l,4- diamine as a Reagent for the Spectrophotometric Determination of Organic Peroxides V. L. Ferracini” and C. G. de Lima? Departamento de Quimica, Universidade de Brasilia, Brasilia, D.F. 70910, Brazil The effects of cobalt(I1) naphthenate (and other metal naphthenates), temperature, time, some possible interferents, excess of reagent, light and oxygen on the application of NN’-di( 2-naphthy1)phenylene- 1,4-diamine as a reagent for the determination of organic peroxides were investigated. Of twelve peroxides with different reactivities, three (di-tert-butyl peroxide, cumyl peroxide and succinic peroxide) did not react under the conditions examined. Keywords : Organic peroxide determination ; NN’-di( 2-naphthy1)Phenylene- 1,4-diamine reagent ; spectrophotometry ; metal naphthenates For different reasons (such as quality control, fire, explosion or toxicity hazards or the organoleptic properties of some foods), methods based on spectrophotometry in the ultraviolet and visible ranges have been proposed in the last 10 years for the determination of organic peroxides.1-5 Most of these spectrophotometric methods are based on the reduction of the organic peroxide.According to Johnson and Siddiqi,l these methods are usually very sensitive, although non-specific, being susceptible in most instances to interference by other compounds capable of oxidation or reduction reactions, by atmospheric oxygen and light. Spectrophotometry based on the reduction of a peroxide by iodide to give iodine appears to be the method that has been most widely The molar absorptivity at the wave- length of maximum absorption (Amax. 362 nm) is 23000 1 mol-1 cm-’.However, when an instrument with glass optics is employed, the molar absorptivity of the 1-/13- method is reduced to 7 900 1 mol-l cm-l as the absorbance is determined at 400 nm.6 The methods with the highest sensitivities are those which use as reagents the leuco base of methylene blue (E = 77200 & 3 900 1 mol-1 cm-1)’ or its N-benzoyl derivative ( E = 155 000 1 mol-1 cm-1) .as9 In the former instance light should be avoided during the determination. Of the various peroxides, lauroyl peroxide and tert-butyl hydroperoxide react slowly, taking 1 h or more for complete reaction.2 With the method that employs the N-benzoyl derivative, tert-butyl hydroperoxide takes 30 min to complete the reaction, but with benzoyl peroxide 30 h are necessary.2 Some derivatives of phenylene-1 ,kdiamine, such as NN-dimethyl-, NN’-diphenyl-, NN’- dimethyl- and NNN’N’-tetramethylphenylene-1,4-diamine, have also been studied as reagents for the determination of organic peroxides by Dugan,loJ1 Dugan and O’Neill2 and Ryland.2 Of the phenylene-l,4-diamine derivatives studied by Ryland,2 NN’-diphenyl- phenylene-l,4-diamine (DPPD) proved to be the most stable.The molar absorptivities ranged from 10500 to 54500 1 mol cm-l and were dependent on the solvent mixture used and on the peroxide tested. Recently, Kasahara et al.13 studied five NN-disubstituted phenylene-l,4-diamine derivatives alone and in conjunction with 1-phenyl-5-pyrazolone derivatives as redox colour reagents for the determination of cumyl hydroperoxide, tert-butyl hydroperoxide and ethyl oleate hydroperoxide.In this work an evaluation of NN’-di-(2-naphthyl)phenylene-l,4-diamine as a reagent for the spectrophotometric determination of organic peroxides was carried out. * Present address : Centro de Pesquisas e AnQlises Tecnolbgicas, Conselho Nacional de Petrbleo, Brasilia, t To whom correspondence should be addressed. D.F., Brazil.FERRACINI AND DE LIMA 575 Experimental Reagents NN'-Di(2-naphthy1)phenylene- 1,4-diamine (DNPD) was of technical grade (Eastman Organic Chemicals, Rochester, N.Y., USA) and was purified using an adaptation of the method suggested by Ryland14 for the purification of DPPD.After purification the DNPD had a melting-point of 234-235 "C. A 0.05 g per 100 ml solution of DNPD in

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