Sciencemadness Discussion Board

Proposed Reaction by Wolcott and Franks

AJKOER - 27-7-2018 at 16:34

The below reaction system with aqueous N2O under irradiation (a source of hydroxyl radicals), chloride ions and some acid is a starting point of my discussion:

•OH + Cl- --> •ClOH- k = 4.3x10^9 (Source: Supplement Table S1 at: http://www.mdpi.com/1420-3049/22/10/1684 and click on Supplement F1 Fto download)
•ClOH- --> •OH + Cl- k = 6.1x10^9 (Source: Supplement Table S1)
•ClOH- + H+ --> •Cl + H2O k = 2.1×10^10 (Source: Supplement Table S1)

The main question of this thread is the validity of a proposed reaction from a paper (see ‘Bactericidal Potency of Hydroxyl Radical in Physiological Environments’, by Robert G. Wolcott, Benjamin S. Franks, Diane M. Hannum, and James K. Hurst in THE JOURNAL OF BIOLOGICAL CHEMISTRY, Vol. 269, No. 13, pp. 9721-9728, 1994 available at http://www.jbc.org/content/269/13/9721.full.pdf ), with respect to the following proposed Reaction 11 by Wolcott and Franks, et al:

•ClOH- + H+ + N2O --> HOCl + N2 + •OH (Reaction 11)

My suggested path consistent with this possible reaction is that irradiated •ClOH- + H+ behaves like HOCl + •H in acidic conditions per the hypothetical sequence :

•ClOH- + Photon (from radiation, light,..) --> HOCl + e-

H+ + e- (aq) = •H (see Buxton Eq. (3), “The hydrogen atom is the conjugate acid of e- aq, and it is the major reducing species in acidic solution” at https://pdfs.semanticscholar.org/d696/b35956e38351dd2eae6706... )

where the net of the last two reaction:

•ClOH- + H+ + Photon --> HOCl + •H

(Note: •HClOH --> H+ + •ClOH- k = 1.0x10^8)

Now, the interaction of hypochlorous acid and the hydrogen atom radical could suggestively further react as follows:

•H + HOCl = •Cl + H2O

which is consistent with the known half cell reaction:

H+ + e- + HOCl --> ½ Cl2 + H2O

and •Cl + •Cl = Cl2

[ Note: •ClOH- + H+ --> •Cl + H2O (k = 2.1×10^10 ) is a documented fast reaction.]

So, for the proposed reaction by Wolcott and Franks, the pair of •ClOH- + H+ , which I suspect may functionally behave as HOCl + •H ,likely acts on N2O as follows:

HOCl + •H + N2O = HOCl + •OH + N2

with the products as proposed being in line with various reports of the hydrogen atom radical (like https://aip.scitation.org/doi/10.1063/1.479074 ) and also from H2 at high temperatures (forming •H see http://pubs.rsc.org/en/content/articlelanding/1975/f1/f19757...), or H2 adsorped on a metal surface (again creating •H like in the case of Mg, Al or Pd, and on the latter see https://www.ideals.illinois.edu/bitstream/handle/2142/18324/... ), or photolysis of H2, where the resulting hydrogen atom radical acting on N2O results in •OH and N2 ).
---------------------------------

It is interesting to consider, as a possible validity test, adding a transition metal ion to the hypothetically created HOCl + e- from •ClOH- under irradiation:

•ClOH- + Photon (irradiation) + Cu(ll) --> HOCl + e- + Cu(ll) --> HOCl + Cu(l) --> Cu(ll) + •ClOH-

Which is consistent with my prior comments on SM:
Quote: Originally posted by AJKOER  
Background:
.....

Note, as to the underlying mechanics of Cupric oxide formation, I speculate that the NaOCl/HOCl first acts electrochemically on Cu to form Cu2O. The latter cuprous forms a soluble complex with say chloride followed by a Fenton-type redox creating cupric. My take:

Cu(l) + HOCl --> Cu(II) + ClOH•-

Followed by either of the following reactions, depending on pH or presence of bicarbonate:

ClOH•- --> Cl- + OH• k = 6.1×10^9

ClOH•- + H+ --> Cl• + H2O k = 2.1×10^10
......
[Edited on 14-6-2018 by AJKOER]

-------------------------------------------------------------------

Interestingly, another test would be to add a hydroxyl radical to both sides of the reaction, •H + HOCl = •Cl + H2O:

•OH + (•H + HOCl) = •OH + ( •Cl + H2O)

But, •OH + •H = H2O + Photon

H2O + Photon + HOCl = H2O + •OH + •Cl

which agrees with the photolysis products of aqueous HOCl, namely:

HOCl + hv --> •OH + •Cl
-----------------------------------

Others with suggested paths are welcome to comment.

[Edited on 28-7-2018 by AJKOER]

AJKOER - 29-7-2018 at 17:49

Some added research results, first, •ClOH- has a name, the Chlorine hydroxide radical (see https://books.google.com/books?id=FrHcZmwj7JQC&pg=PA739&... ).

Also, from Table 1: Inorganic Standard Electrode Potentials at https://www.bnl.gov/isd/documents/92710.pdf :

ClOH•– (aq) + e– + H+ ⇌ Cl– + H2O +2.74
HO• + e− + H+ ⇌ H2O +2.730
ClOH•– (aq) + e– ⇌ Cl– + OH– +1.912
Tl2+ + e– ⇌ Tl+ +2.225
Tl3+(aq) + e– ⇌ Tl2+(aq) +0.34
HOCl(aq) + e– ⇌ ClOH•– +0.25
O2(aq) + H+ + e− ⇌ HO2• +0.10
O2(g) + e− ⇌ O2•– -0.35

Of note is the very high Standard Electrode Potential for ClOH•– in acidic conditions suggesting reactivity at least equal to the hydroxyl radical. Also, the low value for my professed equivalent between ClOH•– and HOCl(aq) + e– where the decomposition of ClOH•– to HOCl with the release of an electron is akin to the creation of gaseous superoxide from oxygen plus an electron. Another more interesting case is the derivation of the spontaneity of the Fenton type reaction between Tl+(aq) (and also Tl2+(aq) ) with HOCl:

Tl+(aq) ⇌ Tl2+(aq) + e– -2.225
HOCl(aq) + e– ⇌ ClOH•– +0.250
------------------------------------------------
Tl2+(aq) + HOCl --> Tl3+(aq) + ClOH•– -1.975

Tl2+(aq) ⇌ Tl3+(aq) + e– -0.34
HOCl(aq) + e– ⇌ ClOH•– +0.25
------------------------------------------------
Tl2+(aq) + HOCl --> Tl3+(aq) + ClOH•– -0.09

More research found a reaction involving •ClOH- cited by ‘Oxidative degradation of malachite green by Fenton generated hydroxyl radicals in aqueous acidic media’ by Dutta K, Bhattacharjee S, Chaudhuri B, Mukhopadhyay S., ln J Environ Sci Health A Tox Hazard Subst Environ Eng. 2003 Jul;38(7):1311-26., link:
https://www.ncbi.nlm.nih.gov/pubmed/12916854 namely:

•ClOH- + Fe2+ --> Cl- + HO- + Fe3+

Again, substituting HOCl + e- for •ClOH- implies first, via a Fenton-type reaction::

Fe2+ + HOCl (+ e- )→ Fe3+ + .OH + Cl- ( + e-)

where the hydroxyl radical is a product assuming the pH is above 4 (see discussion paralleling my prior comments at https://books.google.com/books?id=64DNE6QKD6IC&pg=PA284&... .

This is followed by:

•OH + e- = OH-

Reducing to, as claimed:

(HOCl + e-) + Fe2+ = •ClOH- + Fe2+ --> + Fe3+ + OH- + Cl-

However, a similar reaction can also happen in the classic Fenton system by the reaction:

•OH + Fe2+ = OH- + Fe3+ (where recent research suggests this reaction could be a reversible source of hydroxyl radicals in living organisms!)

Interestingly, the classic Fenton system also suffers from the interaction of excess H2O2 with •OH via:

H2O2 + •OH → •HO2 + H2O

So the authors speculation of the importance of the possible parasitic reaction remains speculative in my opinion.

Also found a source (actually just a page) discussing optical absorbance of •ClOH- , see https://books.google.com/books?id=gNLFCgAAQBAJ&pg=PA145&... .

[Edited on 30-7-2018 by AJKOER]

[Edited on 30-7-2018 by AJKOER]