[Compound + Compound = Compound] Reactions: A question

[Dong Aleta]

Hi!

I noticed that almost all of the [Compound + Compound = Compound] reactions that I have encountered do not involve any transfer of electrons, or are not oxidation-reduction (redox) reactions. Can it be generalized that all [Compound + Compound = Compound] reactions are not redox reactions?

Thanks so much!

 

[Bystander]

"Compound," like carbon plus "compound" like oxygen (or perhaps ozone) = carbon suboxide, plus oxygen = carbon monoxide, plus oxygen = carbon dioxide?

 

[Almeisan]

Maybe you don't see that the oxidation state is changing because they are bonded and the electorns are 'shared'.

 

[Radhakrishnam]

Chemical reactions represented by the equation: ∑ν_iX_i=0, where ν_i is the stoichiometric coefficient of the species X<sub>i are broadly classified into two categories.
1. Acid-Base reactions
2. Redox reactions.

In the first category reactions there is no change in the oxidation state of any species. In the second category reactions the is change in the oxidation state of two or more species.

Therefore, we cannot generalize to state that all reactions are not redox reactions.

Radhakrishnamurty P</sub>

 

[lavoisier]

Hi Dong Aleta.
Your reaction looks like an addition. I can't think of another reaction that fits that pattern (guys, correct me if I'm wrong).
So I suppose the real question is, can an addition reaction involve changes in the oxidation states of the atoms involved?

If you consider the addition of Br₂ to ethylene (H₂C=CH₂) to yield 1,2-dibromoethane, I think we can say that the oxidation state of Br goes from 0 to -1, and the oxidation state of each ethylene carbon goes from -2 to -1 (formally - maybe other people will use different numbers).
This is also reflected in the change in reactivity of the compounds involved. Br₂ is an electrophile --> Br becomes a relatively electron-rich centre in the product. The carbon goes from a relatively electron-rich centre in ethylene, that can be protonated by strong acids, to an electron-poor centre that can undergo nucleophilic substitution.

On the other hand, the addition of H2O to an epoxide doesn't change the oxidation state of any of the atoms involved. Maybe you can try to write the molecules down and do the maths.

 

[Borek]

Bystander already gave an example of the reaction that fits the equation as given and involves change of the oxidation states.

 

[Dong Aleta]

"Compound," like carbon plus "compound" like oxygen (or perhaps ozone) = carbon suboxide, plus oxygen = carbon monoxide, plus oxygen = carbon dioxide?

What I meant by "compounds" are those non-monoatomic ones. Like, CaO(s) + H₂O(l) -> Ca(OH)₂, where calcium retains its +2 oxidation state, hydrogen its +1, and oxygen its -2. Or CaO(s) + CO₂(g) -> CaCO₃ where calcium still retains +2, carbon +4, and oxygen -2.

 

[Bystander]

Diamond, graphite --- ozone --- you'll be able to make all sorts of generalizations if you start picking and choosing what chemical species are and are not "compounds." Take a look at iron oxides, or sulfur oxides.

 

[Dong Aleta]

Diamond, graphite --- ozone --- you'll be able to make all sorts of generalizations if you start picking and choosing what chemical species are and are not "compounds." Take a look at iron oxides, or sulfur oxides.

I see. Thanks a lot for the input! I really appreciate it. :)

 

[lavoisier]

Bystander already gave an example of the reaction that fits the equation as given and involves change of the oxidation states.

Indeed Borek, he/she did.
Is it forbidden to add more examples? If so, apologies.

 

[Borek]

Is it forbidden to add more examples?

No. But it always suggests whoever repeats what was already posted didn't bother to read the thread.

 

[lavoisier]

OK...
Well, I had read the thread, which as a rule I do.
The most concise correct answer to the OP's question would be 'no'; he never asked for examples.
Still, more than one person took the time to mention examples. So I joined in, and I think my post added something to the discussion, e.g. pointing out that not all types of reaction fitted the bill, and exemplifying the answer in the context of organic chemistry rather than inorganic.
Even if that's not the case, I think my participating in this discussion didn't harm anyone. Nevertheless, if someone felt that it did, as I said, I apologise.

In fact, on a more scientific note, I think the OP raised an interesting point. I was taught that organic reactions can be categorised in: Additions, Eliminations, Substitutions, Transpositions and Redox. This discussion highlights the fact that an addition can actually be a redox reaction; perhaps some eliminations are, too; etc.
I don't know, I find it quite interesting, in my own little, naive way.