Expert: Dr. Henry Boyter, Jr. - 1/13/2005

Question
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Followup To
Question -
I am studying chlorine dioxide for use in water purification in jungle situations and in African villages.

When chlorine dioxide ion CLO2 contacts a iron oxide particle in water or a pathogen an O2 oxygen ion is released from the chlorine.  The chlorine ion becomes a chloride.  The question is, is the O2 released as an O2 ion, or is it separated so as to be two O1 ions or do they remain together as O2?  In either case, are they nascent oxygen ions?

Thanks very much for your time.

Sincerely, Jim Humble
Answer -
I checked several web sites for confirmation.  A google search on ["chlorine dioxide" chemistry] will find them for you.  In all case, no O2 is produced in the reaction.  The oxygen atoms are present in the form of hydroxide anions (OH-).  The best site is

www.epa.gov/safewater/mdbp/pdf/alter/chapt_4.pdf

Follow up Question:

I appreciate your effort concerning chlorine dioxide chemistry.  I have been reading the various sites in google including the one you recommend, for a number of months now.  I've read most of those on the first few pages of Google.  They give the chemistry of what happens when chlorine dioxide reforms back to chlorite and chlorate, but what I am looking for is the chemistry of what happens when the chlorine dioxide chemical contacts a pathogen, a bacteria or virus or other contaminates.  There has to be another chemical reaction at this point as the mere reforming to chlorite and chlorate cannot do the job.  

The various sites usually state how the pathogens are killed, i.e. by loosening the viral envelope or it penetrates the bacteria shell and reacts with vital amino acides.  However, I have not been able to find one that gives the basic chemistry of the reaction.  

I believe that the contaminates that chlorine dioxide converts are oxidized in some manner, and it is the oxygen that is released that does it.  In the conversion process I don't see how an OH ion would be generated, but if that is so what is the intrim chemical process that happens that kills the pathogen as the OH cannot do it.  Actually, it would seem to me that the oxygen would do something to the organic material in the pathogen.  Further, it would seem that the chlorine ion would be converted to a chloride, since the oxygen would be used up in oxydizing the organics in the pathogen.  This may be a simplicity or generality, but is that basically what happens?

All the sites state that chlorine does not result from the chlorine dioxide process. Thus I assume that a chloride is the result of the chlorine dioxide reacting with a contaminate in the water, because as I mentioned above, the oxygen is used up.  

Thanks for your time.  I seem to have missed this basic data.  Normally, I guess, water chemists don't need to know the exact process so long as they know what contaminates chlorine dioxide neutalizes.  But in this case, this data is important to me.  Thanks again.

Sincerely, Jim Humble  

Answer
Read this site and you will see at best, all pathogens are probably slightly different and that biologists really don't know and that there may be many reactions taking place in each pathogen with hundreds of chemicals present in the pathogen.

http://www.who.int/entity/water_sanitation_health/dwq/en/watreatpath3.pdf

A few things, we can say.  There are two main possibilities, chlorination of cellular material (adding Cl atoms) and/or transfer of electrons in an oxidative mechanism (my vote is for this or both).  It will not be a reaction with oxygen (O2) since the bugs live on O2 and O2 is a terrible oxidant.  A more likely species is O2- since the ulimate reaction (shown below) is never really seen.  Oxygen is probably released as either O2 or OH- in the final reaction.

I would probably write it is something like this, knowing that there are probably many, many reactions going on.

ClO2- + 2H2O + pathogen = Cl- + 4OH - + pathogen(+4)

This would be the ultimate reaction.  When chlorates are formed not as many electrons would be transfered to the pathogen, so you would get ClO3- and pathogen(+1,+2,+3). I'll leave you to try to balance if you want.