Sciencemadness Discussion Board

Selenic Dioxide to Selenic Acid, possible exposure. Please advise

pax80 - 13-3-2015 at 14:25

Two Part Question:
Looking for a little information regarding Selenium dioxide. I was interested in creating mecke reagent. I'm sure most of you are aware that it is a combination of selenic acid and conc H2SO4. I thought it would be possible to simple combine selenic dioxide with 80% H2SO4 with the selenic dioxide reacting with the H20 to form selnic acid in situ. The experiment was a failure.

I am also aware of the toxicity of SE. Experiment was performed outside and I do not believe exposure would be an issue. The selenium dioxide is certainly not reaching a high temperature, which would (I believe) be necessary in order to form any toxic gases. Could anyone please confirm. My anxiety at the moment is getting the better of me.

woelen - 13-3-2015 at 15:30

Selenium oxide only is volatile at temperatures of boiling water or higher. If your solutions remained well below such temperatures, then you do not need to fear this. If indeed you have done the experiment as you describe, then I would not worry about excessive exposure to selenium dioxide.

Selenium dioxide does not react with water to make selenic acid. It makes selenous acid. For making selenic acid you need an oxidizer, e.g. H2O2 or Na2S2O8.

I want to give a general remark. If you do experiments with such toxic chemicals, and you do not feel comfortable at all with them, then I advice against doing these experiments. At least study the risks before you do the experiment.

As a guideline I can tell you that as long as you work with cold aqueous solutions and no gases (bubbles) are produced, then the risk is low. If there is vigorous bubbling during an experiment, even if the gas itself is non-toxic (e.g. CO2, H2), then the vigorous bubbling may take some of the solution with it into the air in the form of tiny droplets which can be inhaled. For such experiments, I cover the beaker or test tube with a paper tissue or a piece of wadding. Gas can escape from this, tiny droplets remain stuck and get absorbed. orking outside with a breeze from behind also reduces the risk of unwanted inhalation of toxic gases or droplets a lot.

battoussai114 - 13-3-2015 at 15:39

OMG RUN YOU'RE GONNA DIE!!!!!!

Just kidding... never worked with selenic acid before. But the method I know for synthesis is by oxidation of SeO2 with H2O2 in aqueous solution (though the H2O2 would give off water and yada yada). About exposure, I'm really not sure...

careysub - 13-3-2015 at 15:41

Quote: Originally posted by pax80  
Two Part Question:
Looking for a little information regarding Selenium dioxide. I was interested in creating mecke reagent. I'm sure most of you are aware that it is a combination of selenic acid and conc H2SO4.


That should be selenous acid (H3SeO3), not selenic (H3SeO4).
Quote:

I thought it would be possible to simple combine selenic dioxide with 80% H2SO4 with the selenic dioxide reacting with the H20 to form selnic acid in situ. The experiment was a failure.


My notes on preparing this reagent (I have some selenium dioxide on hand for it, but have not done it yet) is that the selenium dioxide must be converted to selenous acid first:

"Pure SeO2 is dissolved in a small amount of water. The solution is concentrated on a water bath with careful exclusion of dust particles (danger of reduction to Se) until crystallization starts. After cooling, the separated H2SeO3 is filtered and recrystallized from water. "
Quote:

I am also aware of the toxicity of SE. Experiment was performed outside and I do not believe exposure would be an issue. The selenium dioxide is certainly not reaching a high temperature, which would (I believe) be necessary in order to form any toxic gases. Could anyone please confirm. My anxiety at the moment is getting the better of me.


Literature reports have someone ingesting 2 g of selenium dioxide (+4 oxidation state) and surviving (that is, 20 mg/kg), and someone ingesting 10 g of selenium dioxide (100 mg/kg) and not surviving:
http://www.annclinlabsci.org/content/36/4/409.full

The selenic (+6) ion seems the most toxic, people have died from 5 mg/kg of this ion.

Looks you like you have to consume hundreds of milligrams of +4 Se at once to get a grossly observable acute toxic reaction.

The half-life in your body appears to be 12-18 hours or so, thus if no toxic effects are seen, their probably won't be any later.

pax80 - 13-3-2015 at 15:52

I appreciate the advice and will certainly heed your warning. I was foolish to attempt the reaction.