Why doesn't the oxidation of cellulose oxidise all the alcohol groups, and how does it cause discolouration? In cellulose, there are several alcohol groups - the two on the ring being secondary alcohols, and the one on the branch being a primary alcohol. I would expect all of these to be oxidised in the presence of any oxidising agent, such as heating under reflux with acidified potassium dichromate - this would give an aldehyde, and then a carboxyl group on the branch, whilst the two on the ring would be oxidised to ketones. However, as you can see in the diagram below (ignoring the sulfonation step which is irrelevant to the question), this is not the case with cellulose.


Why is the branched alcohol not also oxidised? Is it to do with it being a primary alcohol?

Further to this, the oxidation of these groups in paper causes discolouration. Is this because the double bonded oxygen atom then joins the delocalised system, increasing the size of the chromophore and hence bringing the frequency at which the material absorbs into the visible region? Or is there a different reason?
Well Noah,
Primary alcohols, in general can be oxidised more easily, if we are using suitable reagents like acidified dichromate/permanganate etc.

By looking at the reaction it looks like there has been some reagent used like lead teraacetate (LTA) or NaIO4, which attack syn, vicinal diols/(alpha)-hydroxy aldehydes/glyoxal to cleave the C-C bond and produce the oxidized product:


It has been mentioned elsewhere, that cellulose can be oxidised by NaIO4 into some carbonyl derivatives:

This reaction has been responsible for yellowing [at times referred to as discolouration] of paper:

These carbonyl groups arranged in some definite fashion give rise to yellow colour, sometimes called chromophore, which are any group responsible for proving colour to an otherwise colourless compound.