[danceislife]

Hello,

So for a culminating assignment we were told to choose a topic we are interested in and explain the chemistry behind it. It is going to be a presentation in the style of a TEDtalk as those presentations find creative ways to educate people on a topic they are passionate about.
Anyways, my presentation is going to be on the chemical reactions involved in permanent box hair dye.
These are the steps (said to be a two step process but there is much more to it):

Step 1: Bleaching
-The cuticle is opened by the ammonia
-The coupler enters the cuticle before the H202 as it is a rxn modifier and will slow down the release of oxygen
-H202 enters and oxidizes the melanin releasing sulphur (classic smell of hair dye) and de-colorizing the melanin

Step 2: Colouring:
-The primary intermediate is oxidized by the H202
-The oxidized intermediate joins the coupler in "electrophilic aromatic substitution"
-The product of this (oxidized intermediate-coupler polymer) is oxidized to create the final hair dye

and then there is conditioning which counts as step three but that just closes the cuticle and moisturizes the hair so its nothing complex

The main question I have here is about the color of the dye itself. The molecules start off colourless of course, and its the redox rxn between the strong oxidizing agent (H2O2) and the primary intermediate that allows that product to join with the coupler and then oxidize again to form color. Does this happen in the bottle?
With bleaching it is quite straight forward as the mixture (developer+tint) enters the hair and breaks down the melanin. But the redox rxns involved in forming the color? I know that the second step in colouring is called the indo dye. But the oxidation of the primary intermediate... does that happen inside the bottle? Because when you mix the components together it becomes coloured in the bottle so if the color develops in the hair, why does it become coloured in the bottle prior to application? I guess to sum it all up, Which steps in the colouring step happen inside the bottle, and which steps happen in the hair?

And my second question I think is more of double checking but for "Step 1: Bleaching" is this what is really meant by "hydrogen peroxide oxidizes the melanin"

H2O2 ---> H2O + O

O + melanin ---> oxymelanin

Why does hydrogen peroxide release oxygen or "peroxide"? I understand H2O2 is used to bleach the hair but technically its the release of oxygen that is reacting with the melanin to remove the natural color?

[Arkcon]

Please don't cross post

http://www.chemicalforums.com/index.php?topic=83828.msg303831#msg303831

[Borek]

Technically these are different (although strongly related) questions.