'The decomposition of sodiu~n hypochlorite has been re-examined. The results show that Foerster and Dolch's mechanism of the decomposition to chlorate and chloride is correct; they postulated a slow bimolecular reaction to chlorite and chloride, followed by a faster reaction of chlorite with more hypochlorite. Values of the rate constants of both steps are reported; they make the activation energies 24.8 l;cal./g~n-molec~~le for the first step and 20.8 kcal./gm-molecule for the second. The rates are such that a t 40" C. a solution of sodium hypochlorite will contain about lyo as much chlorite as hypochlorite. The rate is strongly affected by changing ionic strength; a t low ionic strengths it is nearly constant or falls slightly; above about 0.8, the rate rises and a t high ionic strengths the rise is quite rapid. No signs of specific catalytic effects of sodium chloride, hydroxide, or carbonate could be observed, and it seems probable that earlier reports of this were due to variations in ionic strength. The decomposition to chloride and oxygen has been measured and is a unimolecular reaction, which is possibly, but not certainly, uncatalyzed. Values of its rate constant are reported; they also are much altered by changing the ionic strength.Although this reaction was first investigated a considerable number of years ago, there are several matters connected with it that are still not entirely clear. Briefly, the position seems to be this. The best early work on the subject was that of Foerster and his co-worlters, particularly Foerster and Dolch (2). They found it to be a second order reaction, and consequently deduced that the mechanism was: 2NaOC1 + NaClOz + NaCl NaOCl + NaCIO? + NaC103 + NaC1 .The first step is the slower. They showed by an independent experiment that the second step was indeed faster, and their rate constants gave activation energies of 224 and 20% kcal./gm-molecule for the first and second step respectively. In addition to the reactions given above it has long been known that decomposition to sodium chloride and oxygen also occurs. Foerster and Dolch's rates are the total reaction rates, though they knew that the reaction to chlorate was very much the more important. They also found that the rate increased as they added sodium hydroxide. Later Giordani (3) investigated the reaction, and concluded that it was a combinatiori of a termolecular reaction giving chlorate, and a bimolecular reaction giving oxygen. He also found a marked effect of sodium hydroxide, but in the opposite direction from that fou~lci by Foerster; and, a t least from about 0.5 to 1.0 M sodium hydroxide, obtained rate constants proportional to (Na0H)-?. H e therefore assumed that hypochlorous acid was essential to the reaction, and that it went in one step, as follows:OCI-+ 2HOC1+ C103-+ 2HC1 He proposed that the reaction to oxygen was 20C1--, 2C1-+ 0,. 'Manuscript

T h e catalyzed decomposition of sodium hypochlorite has been examined; the catalysts tried were manganese, iron, cobalt, nickel, and copper oxides. I t was shown that in no case was the decomposition to chlorate and chloride accelerated, only the reaction to chloride and oxygen. Manganese and iron did not catalyze even the latter reaction, or only t o a very small extent; this was in fairly concentrated sodium hypochlorite containing some sodium hydroxide. T h e manganese and iron are largely oxidized to permanganate and ferrate under these conditions. I t was found that copper could catalyze the formation of perrnanganate and ferrate, and niclcel the formation of permanganate. Cobalt catalyzed the reaction going to oxygen, and the rate was proportional to the cobalt added, but little dependent on the hypochlorite concentration; the same is true of nicltel. Copper (as reported earlier) gives a catalyzed reaction not far from first order in hypochlorite. The activation energies were measured, and were consistent with the relative catalytic activity of these metals. The mechanism of the reaction is briefly discussed.

Various reactions of cyanic acid and the cyanate ion have been examined. Cyanic acid, in the presence of added hydrochloric or nitric acid, decomposes quantitatively according t o the equation: HNCO+H30f -+ C02+NH.if. The rate constant for this reaction was measured over a range of temperature and ionic strength, and was found t o be 0.86 mole liter-' min.-I a t unit ionic strength and 1.5"C. The activation energy is 144 kcal. The effect of ionic strength on the reaction with hydrochloric acid closely parallels that on the activity coefficients of the acid itself. Without added acid cyanic acid decomposes by a first order reaction: HNC0+2H20-+NH.,HCOs, followed by a rapid second stage: NH.~HCOP+HNCO-+ NHaNCO+H2C03. This reaction has a rate constant of 0.011 min.-I a t O°C., and a n activation energy of 16 Itcal. There is also a few per cent of some side reaction. Cyanate ions in alkaline solution decompose thus: OCN-+2HzO-+ NH.if +Cox--. This reaction was examined over a range of temperature and ionic strength: it is first order with k = 3.0 X min.-I a t IOO°C. (0.3 ionic strength) and 23: kcal. activation energy. T h e rate is somewhat dependent on hydroxide concentration, when this is fairly low. The reaction is catalyzed by carbonate, but not by a number of other anions that were examined. The rate of the catalyzed reaction is proportional t o the carbonate concentration, but independent of cyanate, a t least over a considerable range. The ionization constant of cyanic acid has been measured by a method t h a t avoids errors from hydrolysis; the value obtained was 2.0 X The oxidation of cyanate by hypochlorite and by chlorine was examined more briefly.

The rates of oxygen evolution from carefully purified solutions of sodium hypochlorite have been measured. Methods of purification are described, and it is found that substantially the same rate is observed regardless of the method of purification. The rate of oxygen evolution is proportional to the square of the concentration of hypochlorite ions. The effect of temperature and ionic strength are examined. The rate constant is 7.5X1OP6 (g-rn~l/l.)-~(min)-I a t 60" C and an ionic strength of 3.5; the activation energy is 26.6 kcal/g-mol. These results are compared with the corresponding quantities for the reaction of hypochlorite ions t o form chlorite and chloride ions, and some tentative explanations are offered.In an earlier paper ( I ) , one of the present authors exa~nined the decomposition of aqueous sodium hypochlorite solutions, particularly the rate of deconlpositioil to sodiuin chlorate and chloride. The accompanying reaction giving sodiuin chloride and oxygen was exanlined more superficially. Rates of oxygen evolution were observed on a nu~nber of solutions a t that time, but it was never proved that the oxygen evolutio~l could not be ascribed to the presence of traces of catalyst. The reasons for this uilcertainty were as follows. Firstly, measurements on the catalyzed reaction (2) showed that the observed rates could be accounted for by the presence ol copper in co~lce~ltrations of the order of a pg/l. Secondly, the rates were somewhat variable. Thirdly, it was fouild that the observed rates were r o u g h l~~ proportional to the co~lcentratio~l of hypochlorite, and it is difficult to suggest a simple first-order ~nechailis~n for the u~lcatalyzed reaction. However, relatively low orders of dependence on l~ypocl~lorite concentration are observed for the catalyzed reaction, which suggests that these earlier solutioils contained traces of catalyst. Finally, and perhaps the most convincing reason for believing some catalyst to be present, it was found that the apparent activation energy for oxygen evolution was 21 l;cal/g-11101, less than the 24.8 l;cal/g-mol found for the reaction giving chlorate and chloride; yet the latter is the predominant reaction.Other worlters have also examined this deconiposition, though they usually did not separate the rates of the two reactions. Giordani (3) found a second-order gas evolution; but his conclusio~~s about the reaction to chlorate had not been confirmed, so it seemed worth while to investigate the reaction in inore detail. EXPERIMENTAL P A R TThe main proble~n was to obtain sodiuin hypochlorite free from traces of catalyst. At present-only cobalt, niclcel, and copper are known t o catalyze this deco~~~position, so that the methods of purification were directed towards the removal or coinplexing of these metals. I t seemed much more promising to purify the sodium hypochlorite solution as opposed t o the chlorine and sodium hydroxide solution from which it was made. The following general methods of purification, or a t least of removal of catalyst, were e...

The rate of decomposition of hypochloro~~s acid has been measured i n aqueous solution in the presence of much sodium hypochlorite. The rate is ilearly independent of the hypochlorite concentration, and proportional to the square of the hypochloro~~s acid concentration. Hence the mechanism proposed is 2HOC1+ HCI + HCIO? (both ionized), HOCl + C102-+ C1-+ HClOj (ionized).The first step is the slower. The reaction HOCl + CIO--+ C1-+ HClOn (ionized) also occurs, but is much slower. Oxygen is also evolved, by a hrst order reactio~~. Values for the rate constants a t different ternpcratures of all these reactions are given. Meas~~rements are also reportcd on certain equilibria present in these solutions: the ionization of hypochlorous and chlorous acids, and the reaction HOCl + H30++ C1-= C1?+ 2H20.Details of modified analytical methods for hypochlorite and chlorate in the presence of chlorite are given.