Chemistry Forum

How, if possible, can acidified potassium dichromate solution be utilised to differentiate between primary and secondary alcohols?

I already know that if you place a few drops of an unknown alcohol into acidified K₂Cr₂O₇, a colour change from orange to green will indicate it is not a tertiary alcohol. From that point onwards, what methods should be followed to determine whether primary or secondary?

Is it as simple as leaving the solution and waiting for another colour change or are there other steps to this and what would these be?

Use the Lucas test. Add conc. HCl and zinc chloride to the alcohol.
You can see a time milky reaction forming of alkylchloride in order tertiary
(immediately) > secondary (3 to 5 min.) > primary alcohol (oily layer if heated)

2 ROH + H₂]ZnCl₄] => 2 RCl + 2 H₂O + ZnCl₂

https://en.m.wikipedia.org/wiki/Lucas%27_reagent

Using alkaline Permaganate
Primary gives MnO₂ brown residiue
Secondary gives MnO₄ 2- Green
Tertiary no reaction

Also the obtained ketones can be checked with phenylurea, phenylhydrazine or semicarbazide.