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Test for primary, secondary and tertiary alcohol

Could anyone suggest a test to distinguish between primary, secondary and tertiary alcohol? Using Lucas Reagent?
What is the standard text of the observation of this test in Edexcel Chem?

Reply 1

john !!

Firstly you can distinguish between primary and secondary, and tertiary becaise tertiary alcohols cannot be oxidised. So add some of an oxidising agent acidified with sulphuric acis, if it reacts (first oxidation producing hydrogen gas), it is not tertiary.

I'm not sure about the difference between primary and secondary. I know primary alcahols can be oxidised further by heating under reflux, but don't know about the corect test for carboxilic acids. :redface:

Reply 2

Ben.S.

keisiuho

Could anyone suggest a test to distinguish between primary, secondary and tertiary alcohol? Using Lucas Reagent?
What is the standard text of the observation of this test in Edexcel Chem?

Couldn't you use potassium dichromate thing and the silver-mirror test in combination? I have no idea what Lucas reagent is.

Ben

Reply 3

qqqwwweee

good idea!
thx everyone

Reply 4

Understate

I think Potassium Dichromate (VI) will turn from Green to Orange. That means its either 1st or 2nd Alcohol.

Fehlings will result in a silver mirror when added to a Prim. Alcohol.

Reply 5

Ben.S.

Understate

I think Potassium Dichromate (VI) will turn from Green to Orange. That means its either 1st or 2nd Alcohol.

Fehlings will result in a silver mirror when added to a Prim. Alcohol.

Orange to green for the dichromate (I think). Yeah - Fehling's is it's name!

Ben

Reply 6

qqqwwweee

Ben.S.

Orange to green for the dichromate (I think). Yeah - Fehling's is it's name!

Ben

Is Fehling's a blue solution?

Reply 7

z!D4N

Understate

I think Potassium Dichromate (VI) will turn from Green to Orange. That means its either 1st or 2nd Alcohol.

Fehlings will result in a silver mirror when added to a Prim. Alcohol.

orange to green dude.

Reply 8

The Best

Couldn't u just oxidise the 3 samples, using K2Cr2O7 / H+

the one that stays orange is tertiary

add 2,4 DNP to the products of the remaining 2, the one that forms orange ppte is secondary

then the last one must be primary. double check by adding sodium carbonate (test for -COOH) a +ve result, CO2 gas released?

Reply 9

kriztinae

keisiuho

Is Fehling's a blue solution?

yes fehlings solution is blue, it consists of CU2+ ions which are blue! easy to rememeber?

Reply 10

supreme

I thought this attachment could be of some help.

oxidation and distinguishing.jpg101.8KB

Reply 11

spali

look, things are getting a bit confused.
ive never heard of lucus, prob another exam board.
Fehlings does not make a silver mirror, thats Tollens Reagent. this is made up of a silver ion with ammonia ligands. when oxidised= silver ions = silver mirror. but this is a test for distinguishing between aldehydes and ketones. aldehydes make the mirror, ketones don't.
Fehlings shows the same thing but turns from blue to red in the presence of an aldehyde.
you tell different alcohols with potassium dichromate. primary and secondary alcohols turn it from orange to green. tertiary alcohols have no effect on the colour.
There, Done!!

Reply 12

jag_jatt

seriously - how can such an easy topic get so confusing!!!!

Warm solutions with acidified potassium dichromate

primary - ol = orange solution slowly turns green
seconday - ol = orange solution slowly turns green
tertiary -ol = no change

primary -ol = oxidised to aldehyde then to carboxylic acid
seconday - ol = ketones

add 2,4 -DNPH

orange solution to yellow/orane ppt (shows carbonyl compound)

if primary -ol not oxidised through to -COOH then both solutions will give a positive test to 24, -DNPH test. if only one solution gives positive result - ketone - 2nd ol

To distinguish between aldehyde and ketone - warm with ammoniacal silver nitrate solution.

silver mirror deposit indicates an aldehyde (therefore primary -ol)
no change = ketone

Reply 13

hitchhiker_13

You should be able to smell the difference between primary and secondary alcohols after heating with acidified potassium dichromate.

Seconday alcohols have a "ketone" smell kind of like pearl drops.
Primary will first smell sweet (aldehyde) then like an acid - you could also react it with a carbonate and see if CO2 is released or something.

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