A third method to convert chlorates to perchlorates is by chemical oxidation. A sufficiently strong oxidiser added to a chlorate can oxidise a chlorate to a perchlorate. Suitable oxidisers are persulfates and lead dioxide in concentrated sulfuric acid. Hydrogen peroxide does not seem to work. I must admit my experience with this method is limited and I have not been able to obtain much literature about it. It is mentioned in literature however, and it is definately a possible method that can be used with good results. If anyone has some experience with it, I would be most interested to hear about it. The experiments I have conducted involved sodium persulfate as the oxidiser. I will give an account of the general method I used, the ideas behind it and the results obtained with it. Anyone with comments, results, ideas, anything is very welcome to comment on it. I can currently not do any further experiments untill july/august this year. Soon after that, this text should be updated. If you wish to try this method in the meantime this may be used as a starting point:
Persulfates are strong oxidisers. They are reduced according to the following half-reaction:
[ REACTION ]
The H+ generated in this reaction will prevent it from taking place below a certain pH. When a base is added to neutralise the acid generated the reaction may go to completion. All persulfate may be consumed in the reaction. Persulfate being a stronger oxidiser than perchlorate may be used to convert chlorates to perchlorates according to the following half reaction:
[ REACTION ]
Neither persulfates, chlorates or perchlorates are destroyed at a significant rate at the temperature of boiling water, so the reaction rate may be increased by boiling a solution containing the reactants.
Oxidation of KClO3 by persulfate
The general procedure I tried:
A solution of 30 g/l sodium persulfate was prepared and the pH raised to 14 by the addition of a concentrated sodium hydroxide solution. The sodium persulfate was obtained from an electronics supply store, where it was sold for etching printed circuit boards. A foggy solution was obtained, which was filtered. 5 ml of the clear solution obtained after filtering was added to a test tube. Approximately 1 gram of potassium chlorate was added to the same tube, and solution heated. The solution was boiled vigorously for 15 minutes during which time water was added occasionally to make up for what had evaporated. The solution was then allowed to cool. Upon cooling white crystals formed. These were filtered, washed with ice cold water and recrystallised. The crystal shape during recrystallization was observed and found to resemble that of potassium perchlorate best. As described in the analysis page, crystal shape is not a reliable way to determine the identity of a product however. The crystals obtained after recrystallisation were tested qualitatively for chlorate with phenylanthranilic acid (as described in the analysis page). Chlorate was shown to be present. It seems most likely that the chlorate was only partially converted to perchlorate. Maybe the addition of more persulfate or allowing a longer reaction time will convert more chlorate to perchlorate. Destruction of the chlorate followed by recrystallization should afford a chlorate free product.
Что хим общественность скажет про это? Хлорат натрия можно готовить кипячением гипохлорита, который в свою очередь очень дешевый реактив.