Questions for the water chemistry show

[skipper]

*** WARNING - MAJOR GEEK CONTENT ***

OK, there was an attempt made to answer my "free chlorine" vs Chloride ion question during the Bitter Sweet show, however I found it somewhat unsatisfying. To summarise the discussion, ionic Chlorine (Chloride or Cl-) does not form Chlorophenols, but "free" Chlorine (whatever that is) in the form of chlorination or Chloramines does.

Question is why and how?

Here is my ASCII art attempt at a Phenol molecule.

Code: Select all

      OH
       |
     /  \\   
    ||    |
     \  //


Here is my equally pathetic attempt at a Chlorophenol molecule.

Code: Select all

     OH
       |   Cl
     /  \\/   
    ||    |
     \  //


Apparently Phenol dissolves in water to form Hydrogen ions (H+) and Phenoxide (C6H5O-). Clearly this is Phenoxide is unlikely to combine with Chlorine ionically (they are both negative ions), so I get the reason why Chloride is not a problem.

If we look at standard water chlorination, we effectively end up with Hypochlorite (Cl0-) ions in the water. With Chloramine, we end up with NH2Cl (what does this ionise to?).

So how and why is the Chlorine swapped with the Hydrogen in the Benzine ring? Is this the mechanism Electrophylic halogenation? If so, I guess that is why the chlorine needs to be bonded rather than ionic. Can any organic chemistry types out there confirm and expand (back to the text books, Doc!!)? Is anyone still reading this?

[Geegs]

I think the mechinism is electrophilic halogenation (or technically electrophilich aromatic substitution). In my old organic chemistry book it shows the reaction with Benzene and Cl2. Cl2 can form the Cl+ ion (chloronium ion) in the presence of a lewis acid. This ion can attack at a double bond in the ring making it a single bond with a + charge on of the Carbon atoms and the Cl and H on the other. The H transfers to the extra Cl (which was bonded to the lewis acid) forming HCl and the double bond is reformed. If you have an -OH in the ring (like in the phenol) this can be done without the lewis acid. It seems like this could happen with NH2Cl or ClO- where it forms NH3 or OH- instead of HCl. Of course I'm just guessing. If you google Electrophilic Aromatic Substitution you can find out more...if you care.

[J.Brew]

Glorp?

[Speyedr]

:shock:

Glorp?