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Question

Posted on: March 6 2013

How to prepare oxygen water now that phenacetine is no longer available?

Phenacetine is not to be given in bulk anymore. We always used this to stabilize oxygen water. I have found that this can also be with phosphoric acid, benzoeic acid, salicylic acid and acetanilide. Benzoeic acid would not allow stabilisation within the acceptable deadlines and therefore does not seem to be suitable. Salicylic acid is perhaps the easiest (because in every pharmacy in stock), but also good? Phosphoric acid I have found a concentration of 5 G on 1000 g of oxygen water of a 10% diluted solution. What do I use best and in what concentration?

Answer

Phosphoric acid is a possibility. Another mentioned is Napyrophosphate, which is not mentioned in the product list of the distributors of pharmaceutical raw materials in Belgium. But we can assume that napyrosphate, dissolved in water, hydrolyzes to 2 molecules of disodium hydrogen phosphate. So there is the possibility to use this salt that is available. The concentration, which is used for napyrophosphate is 0.05%. This concentration corresponds to this of phosphoric acid. For disodium hydrogen phosphate, this is 0.05% x 284/266 = 0.054% I suspect there will be a difference in acidity between the 2 possibilities. I would prefer that solution, which is the least acidic.