The Decomposition of Hypochlorous Acid

Lister, M. W.

doi:10.1139/v52-107

Cited by 64 publications

(43 citation statements)

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“…The methods were the same as those outlined by the author in a previous paper (4 The general procedure in almost all runs was as follows. A quantity of the stock hypochlorite solution was poured into the reaction flask, the amount added being weighed to the nearest 0.1 gm.…”

Section: Methodsmentioning

confidence: 99%

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Decomposition of Sodium Hypochlorite: The Uncatalyzed Reaction

Lister¹

1956

Can. J. Chem.

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'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

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Section: Methodsmentioning

confidence: 99%

“…At very low sodium hydroxide concentrations hydrolysis t o hypochlorous acid and its decomposition become important; but the rate of this reaction has been measured (4), and it call be calculated that the sodium hydroxide would have to be close to 0.001 M before this reaction made much difference to the total rate. Can.…”

Section: 62mentioning

confidence: 99%

Decomposition of Sodium Hypochlorite: The Uncatalyzed Reaction

Lister¹

1956

Can. J. Chem.

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“…The apparatus was the same as described in the first paper on the uncatalyzed reaction (9). The analytical methods have been described in another previous paper (7).…”

Section: Experimen'i'al Methodsmentioning

confidence: 99%

Decomposition of Sodium Hypochlorite: The Catalyzed Reaction

Lister¹

1956

Can. J. Chem.

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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.

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“…Gray et al (1977) found an inverse dependence of Cu-catalyzed decomposition rates on [OH-] at very high Cuand OH-levels, i.e., 27 ppm and 1.3-7.0 M, respectively. All work reported herein was carried out at [OH-] = 0.03-0.05 M (typical of commercial hypochlorite solutions), which also avoided complications from the rapid decomposition of appreciable amounts of free HClO as would be found near neutrality (Lister, 1952;Adam et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the uncatalyzed and copper(II)-catalyzed decomposition of sodium hypochlorite

Church¹

1994

Ind. Eng. Chem. Res.

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Rate equations for the decomposition of aqueous alkaline NaClO were integrated with inclusion and exclusion of the effects of first-order Cu(I1) catalysis, yielding new time-dependent expressions for [ClO-I, evolved oxygen, and [C103-1. Using a gravimetric technique, uncatalyzed and Cu(I1)-catalyzed rate constants for oxygen evolution and C10-loss were measured and consolidated with previous results. Activation parameters of the uncatalyzed rate-limiting reactions to CIOz-and oxygen could be approximated as linear functions of ionic strength k , allowing estimation of the respective rate constants kl and k, a t 40-70 "C in the p range 2-5. For Cu(I1) catalysis a t 40-70 OC in the p range 4.2-4.7, E,, AH*, and AS* values of 83 300 J g-mol-', 80 550 J g-mol-', and -14.6 J K-l g-mol-l, respectively, were derived from previous and current results, allowing kcu also to be estimated and used in the system of integrated equations.

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The Decomposition of Hypochlorous Acid

Cited by 64 publications

References 1 publication

Decomposition of Sodium Hypochlorite: The Uncatalyzed Reaction

Decomposition of Sodium Hypochlorite: The Uncatalyzed Reaction

Decomposition of Sodium Hypochlorite: The Catalyzed Reaction

Kinetics of the uncatalyzed and copper(II)-catalyzed decomposition of sodium hypochlorite

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