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YI~EDERICKR. DUKE.4su TRICEW. HASS
Yol. 65
THE HOMOGENEOUS BASE-CATALYZED DECOMPOSITION OF HYDROGEN PEROXIDE BY FREDERICK R. DUKEAND TRICE W. HAAS ,rnst&te for Atomzc Research and Department os Chenzsstr?l,Iowa State Unzversity, ilrnes, Ioica Recezued Auyust 1 , 1960
The dt.compoeition of hydrogen peroxide in alkaline aqueous solution u as found to be homogeneous in polyethylene vessels when the reactants were sufficiently pure. The rate equation found is rate = IZ, [HzOz][HOL-] over a vide range of concentrstions of reactants.
Introduction Results The study of the base-catalyzed decomposition Evidence that harmful impurities were absent of hydrogen peroxide has been the subject of many was inferred from two things. First in early work investigations.2 Erdey and Inczedy3 have estab- on this project disodium dihydrogen ethylenelished the kinetics for this decomposition in glass diaminetetraacetate (EDTA) was added as an invessels where the reaction is found to be heterogene- hibitor. This results in the complexing of all heavy ous. The kinetics for the homogeneous base-cata- metal ions present which are catalysts for this lyzed decomposition of hydrogen peroxide, however, reaction ; the EDTA greatly diminished their activappear not to have been successfully completed for ity, although it was found that they were still two reasons. First the vessels used must be shown slightly active. The rate was independent of the to have inactive surfaces and second there must be amount of EDTA present above a small minimum. assurance that foreign ions are not catalyzing the When EDTA was added to the purified reagents in decomposition. It is felt that both of these diE- the filial work no detectable effect was noted. culties are overcome in this work. Secondly, many of the runs were made using comExperimental mercial Hz02 and purified KOH, Its03 and water. Adequate purification of the KOH used in this work was a It was known that a small amount of iron arid posmajor problem. Various methods were tried and finally a sibly copper was added from the peroxide. Redismethod using a s adsorbing agents Fe(OH), and Mg(0H)z tillation of the peroxide removed the last traces of was adopted. Last traces of iron were removed by complexing with phenyl-2-pyridyl ketoxime and extraction into iso- these ions (analyses were sensitive to 1 part per amyl alcohol according to the method of Trusell and DiehlS4 billion; they were below this level). This last The KNO, arid hTa2SO4used to adjust the ionic strength lowering of the impurity concentrations had no were reagent grade materials recrystallized tw-o times from effect on the rate, hence the level of impurity conredistilled water. Water and hydrogen peroxide used in this work were redistilled a t least once. All other chemical- centrations from the peroxide must have already been low enough so as not to be harmful. Some used were reagent grade materials. Analyses for peroxide were carried out by titration with catalytic decomposition due to other impurities standard Ce(1V ) solution. Analyses for traces of heavy must have occurred, but it is felt that this term in metal impurities in the reagents used were carried out by the rate equation was small compared with the various spectrophotometric methods. Sixteen 02. polyethylene bottles were used for the reaction uncatalyzed rate (see Fig. 1). vessels. These were submerged in a constant temperature Nost of the work was done a t an ionic strength bath held t o +0.05”. Samples of the decomposing solutions were withdrawn of 2.0. I n the majority of cases this was adjusted periodically with 10-ml. pipets and quenched in dilute HJ- by adding the proper amount of a KN03 solution. SO4. Samples were then ready for titration. This quench- I t was felt necessary to show that the NO3- ion was ing technique was found to be effective. The polyethylene bottles used as reaction vessels were not entering into the reaction. To this end a series tested for surface activity in the following manner;, One of of solutions were made using KazS04 instead of the bottles of the kind actually used was “frozen in Dry ICN03 to adjust the ionic strength. KOdifference Ice and ground into fine particles using an ordinary wood file. was found, hence it was concluded that nitrate ions The polyethylene was then cleaned to remove dirt, etc. This was added to a solution and the change in the rate were not entering into the reaction. Since Na2S04 Btudied. I t is estimated that the surface area was increased instead of KzS04 was used, and since ionization is by a factor of a t least 50. No effect due to the added poly- essentially complete for these tn7o electrolytes, it ethylene was ever found. This experiment was carried out was also concluded that KaOH would give the same under various conditions such as various hydroxyl and initial result as KOH, that is the I
