I have a few questions about organic chem,
By means of a simple chemical test, distinguish the following pairs of compounds:
1) butanol and 2-methylpropan-2-ol
2) phenylmethanol and phenol
3) pentan-3-one and pentan-3-ol
Originally posted by lolerchild:I have a few questions about organic chem,
By means of a simple chemical test, distinguish the following pairs of compounds:
1) butanol and 2-methylpropan-2-ol
2) phenylmethanol and phenol
3) pentan-3-one and pentan-3-ol
Pretty straightforward question. Anyway, now that the forum these days have a lot more helpful post-'A' level pple (you know who you are, feel free to help out on this forum), I'll let them guide you (you = current 'A' level students). I'll 'moderate' only when I have comments to add.
Eh, let's see.
1. 2-methylpropan-2-ol is a 3 degree alcohol. So it can't be oxidised.
2. Phenylmethanol has a carbon attached to the phenyl ring thus can be oxidised. Phenol can't be.
3. One is ketone and the other one alcohol. I believe there's a test to distinguish between carbonyl group and alcohol. Tollen's reagent or Fehling's solution.
Haha, that's as much as I can remember.
1. Yep, 2-methylpropan-2-ol is 3 degree alcohol. can't be oxidised. For butanol, u can oxidise it to form carboxylic acid and test with ca(oh)2, white ppt formed
2. pretty much wad destiny said, but i was wondering if we could use 2,4 NDPH (Please confirm)
3. Use Tollen reagent, only alcohol forms the silver mirror.
A couple of minor issues, but overall, good attempt, d3sT1nY and Eyelessz.
2,4 NDPH is to be used for distinguishing question (3) pentan-3-one and pentan-3-ol. Only the ketone will give a positive result.
Tollen's reagent or Fehling's solution, both give positive results only with aldehydes (because they oxidize aldehydes to carboxylic acids), hence does not help to distinguish a ketone from an alcohol. Ketones can't be oxidized by Tollen's or Fehling's, or by KMnO4 or K2Cr2O7 for that matter. Primary and secondary alcohols can be oxidized, but require a stronger oxidizing agent like KMnO4 or K2Cr2O7. Note that pentan-3-ol is a secondary alcohol.
The solution to question (3), is to use 2,4 NDPH, and not Tollen's reagent or Fehling's solution.
>>> Q2) i was wondering if we could use 2,4 NDPH (Please confirm) <<<
No you can't. 2,4 NDPH only distinguishes aldehydes/ketones from non-aldehydes/ketones, and phenylmethanol and phenol (question 2) are both non-aldehydes/ketones.
1) Oxidation or Lucas' Test
2) Oxidation or Neutral aq FeCl3 solution or SOCl2/PCl5 or Bromine (aq)
3) Oxidation or Brady's reagent (2,4-dinitrophenylhydrazine)
Very good, basmoth. Additional valid alternative methods offered.
With neutral FeCl3(aq), a purple colouration indicates presence of phenol.
With SOCl2 or PCl5, steamy fumes of HCl evolved indicates presence of (non-phenolic) alcoholic hydroxy group.
I can think of one more, that so far no one has suggested.
2) phenylmethanol and phenol
Notice that these 2 compounds are both, in neutral or acidic conditions, rather insoluble in water (due to the large, non-polar benzene ring).
Adding NaOH(aq), would result in deprotonation of phenol, forming the phenoxide ion, which is able to form ion-dipole interactions with water, and is thus highly soluble.
Phenylmethanol would not be deprotonated by sodium hydroxide, and thus remains insoluble.