Ho do you distinguish between primary, secondary and tertiary alcohols?

Watch this thread
HEY_101
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 10 years ago
#1
I understand that they are different interms of the amnmount of carbons attacthed to the carbon with the halogen but what else?

Is their like colour, smell, properties?

please help, thanks
0
reply
thegodofgod
Badges: 19
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 10 years ago
#2
(Original post by HEY_101)
I understand that they are different interms of the amnmount of carbons attacthed to the carbon with the halogen but what else?

Is their like colour, smell, properties?

please help, thanks
You can distinguish between primary and secondary alcohols by oxidising them using Tollen's Reagent. If you get a precipitate of Ag+ ions formed in the test tube (silver mirror), that is an aldehyde (which is the product of a partial oxidation of a primary alcohol).

If you oxidise a tertiary alcohol with any other alcohol (primary or secondary) using potassium dichromate (a very strong oxidising agent), you will get a colour change from orange to green with the primary/secondary alcohols, but not with the tertiary alcohol, as they cannot be oxidised easily.

I think that's it
0
reply
illusionz
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report 10 years ago
#3
No idea if NMR is a valid answer at A level, but it's the best!
0
reply
charco
Badges: 18
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report 10 years ago
#4
Simple test is the Lucas test.

http://en.wikipedia.org/wiki/Lucas'_reagent
1
reply
HEY_101
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report Thread starter 10 years ago
#5
(Original post by thegodofgod)
You can distinguish between primary and secondary alcohols by oxidising them using Tollen's Reagent. If you get a precipitate of Ag+ ions formed in the test tube (silver mirror), that is an aldehyde (which is the product of a partial oxidation of a primary alcohol).

If you oxidise a tertiary alcohol with any other alcohol (primary or secondary) using potassium dichromate (a very strong oxidising agent), you will get a colour change from orange to green with the primary/secondary alcohols, but not with the tertiary alcohol, as they cannot be oxidised easily.

I think that's it

yay thanks! i remember the word 'tollens' from class
0
reply
HEY_101
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report Thread starter 10 years ago
#6
(Original post by charco)
Simple test is the Lucas test.
wow that is simple, thanks!
0
reply
HEY_101
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report Thread starter 10 years ago
#7
(Original post by illusionz)
No idea if NMR is a valid answer at A level, but it's the best!

NMR? never heard of that before, let me research it
0
reply
Sindy12
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#8
Report 7 years ago
#8
I am afraid that the above answer is not detailed enough and it might get you wrong.
While doing the oxidation of primary alcohol, the difference between heat under reflux and warm is significant.
If you warm a primary alcohol, you will get aldehydes which will react with Tollen's reagent to form silver/grey ppt
But if you heat a primary alcohol under reflux, it will undergo further oxidation and you will get carboxylic acid instead, which will NOT react with Tollen's reagent to form silver ppt
0
reply
Crydamoure
Badges: 11
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#9
Report 7 years ago
#9
Primary alcohols can be oxidised twice, first to an aldehyde, and then to a carboxylic acid.
Secondary alcohols can only be oxidised once, to a ketone.
Tertiary alcohols cannot be oxidised.
0
reply
Borek
Badges: 4
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#10
Report 7 years ago
#10
(Original post by HEY_101)
I understand that they are different interms of the amnmount of carbons attacthed to the carbon with the halogen but what else?
What halogen?
0
reply
charco
Badges: 18
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#11
Report 7 years ago
#11
This thread is actually fossilised ...
0
reply
RossK
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#12
Report 7 years ago
#12
(Original post by Borek)
What halogen?
I think they meant the hydroxyl group.
0
reply
Sindy12
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#13
Report 7 years ago
#13
I am afraid that the above answer is wrong.
To oxidise a secondary alcohol, you need to heat under reflux. While to partial oxidise a primary alcohol in order to get aldehydes, you just need to warm it. If you heat primary alcohol under reflux, you will get carboxylic acid, which will not react with Tollen's reagent.
Well, you can still do the above test, but test the end products with blue litmus paper or any tests that can identify a carboxylic acid.

Alternatively, warm the solutions with oxidising agent and test it with Tollen's reagent. The primary alcohol will form a silver precipitate but the secondary will form nothing as it didn't even get oxidised.
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#14
Report 7 years ago
#14
(Original post by Sindy12)
I am afraid that the above answer is wrong.
Well, you can still do the above test, but test the end products with blue litmus paper or any tests that can identify a carboxylic acid.
What are you planning to oxidise it with? Acidified potassium dichromate? Orange to green and all that? Do you see a problem here with your test?

You'd be better off adding some conc. sulfuric and an alcohol and seeing if you get a sweet smell
0
reply
Sindy12
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#15
Report 7 years ago
#15
(Original post by Pigster)
What are you planning to oxidise it with? Acidified potassium dichromate? Orange to green and all that? Do you see a problem here with your test?

You'd be better off adding some conc. sulfuric and an alcohol and seeing if you get a sweet smell
I don't see any problem with my test here, please do tell me if there is any problem.
0
reply
Pigster
Badges: 20
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#16
Report 7 years ago
#16
If you add acidified potassium dichromate to a secondary alcohol, it'll go orange to green, in the process you'll make a ketone.

If you dip in some blue litmus, you haven't made a carboxylic acid, but the litmus paper will turn red. Why?
0
reply
Sindy12
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#17
Report 7 years ago
#17
Ahh...now I see the problem. Thank you.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest

How are you feeling about your SQA results?

They're better than I expected (20)
32.79%
They're what I expected (19)
31.15%
They're worse than what I expected (22)
36.07%

Watched Threads

View All