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oxidation of alcohols
somebody please help me answer these questions. it is revision for my retake of unit 2 for chemistry.
the reactions of alcohols with an acidified dichromate(v1) solution vary according to the alcohol used, and the way in which the reaction is carried out. describe the results of the following reactions, giving the names of the products where appropriate.
(a) propan-1-ol is boiled under reflux with excess acidified sodium dichromate (V1).
(B) PROPAN-2-OL is boiled under reflux with excess acidified sodium dichromate(V1)
(c) butan-1-ol is heated whilst acidified sodium dichromate(V1) is added slowly, the product being distilled out as it is formed.
(d) methylpropan-2-ol is boiled under reflux with excess acidfied sodium dichromate(v1)
(e) with reference to (a) explain why sodium dichromate(V1) is added to butan-1-ol (rather the other way round) and why it is possible to distil out the product as it is formed.
why Na2Cro7 is added to butan-1-ol
why the product can be distilled out.............
THANK YOU SOOOO MUCH
the reactions of alcohols with an acidified dichromate(v1) solution vary according to the alcohol used, and the way in which the reaction is carried out. describe the results of the following reactions, giving the names of the products where appropriate.
(a) propan-1-ol is boiled under reflux with excess acidified sodium dichromate (V1).
(B) PROPAN-2-OL is boiled under reflux with excess acidified sodium dichromate(V1)
(c) butan-1-ol is heated whilst acidified sodium dichromate(V1) is added slowly, the product being distilled out as it is formed.
(d) methylpropan-2-ol is boiled under reflux with excess acidfied sodium dichromate(v1)
(e) with reference to (a) explain why sodium dichromate(V1) is added to butan-1-ol (rather the other way round) and why it is possible to distil out the product as it is formed.
why Na2Cro7 is added to butan-1-ol
why the product can be distilled out.............
THANK YOU SOOOO MUCH
(a) propan-1-ol is boiled under reflux with excess acidified sodium dichromate (V1).
propal-1-ol is a primary alcohol and so can be oxidised all the way to carboxilic acid, first to an aldehyde by removing the OH hydrogen and another hydrogen so that the carbon can form a double bond with the remaining oxygen. secondly by fitting an oxygen between the remaining carbon attached to the end hydroigen and that hydrogen. this second stage can only happen to primary alcohols because when secondary alcohols are oxidised to ketones there is no final hydrogen attached to the carbon as it is double bonded to the oxygen and then has two carbon-carbon bonds either side (as it is in the centre of the chain). the second stage requires heating under reflux as well. both stages require an oxidising agent which is what the dichromate ion does (it is reduced and therefore causes oxidation).
propal-1-ol is a primary alcohol and so can be oxidised all the way to carboxilic acid, first to an aldehyde by removing the OH hydrogen and another hydrogen so that the carbon can form a double bond with the remaining oxygen. secondly by fitting an oxygen between the remaining carbon attached to the end hydroigen and that hydrogen. this second stage can only happen to primary alcohols because when secondary alcohols are oxidised to ketones there is no final hydrogen attached to the carbon as it is double bonded to the oxygen and then has two carbon-carbon bonds either side (as it is in the centre of the chain). the second stage requires heating under reflux as well. both stages require an oxidising agent which is what the dichromate ion does (it is reduced and therefore causes oxidation).
G_S
the reactions of alcohols with an acidified dichromate(v1) solution vary according to the alcohol used, and the way in which the reaction is carried out. describe the results of the following reactions, giving the names of the products where appropriate.
(a) propan-1-ol is boiled under reflux with excess acidified sodium dichromate (V1).
Propan-1-ol, as it is a primary alcohol, is fully oxidised by the oxidising agent of acidified sodium dichromate to Propanoic Acid, a carboxylic acid.
G_S
(B) PROPAN-2-OL is boiled under reflux with excess acidified sodium dichromate(V1)
Propan-2-ol, as it is a secondary alcohol, is oxidised by the oxidising agent to propanone, a ketone.
Ketones, despite having teh same chemical formula as Aldehydes, can not be oxidised further.
G_S
(c) butan-1-ol is heated whilst acidified sodium dichromate(V1) is added slowly, the product being distilled out as it is formed.
Butan-1-ol, despite being a primary alcohol, is only partially oxidised by the acidified sodium dichromate to Butanal, an aldehyde.
Heatin the Aldehyde by Reflux with acidified sodium dichromate wud cause it to be further oxidised to a Carboxylic acid.
G_S
(d) methylpropan-2-ol is boiled under reflux with excess acidfied sodium dichromate(v1)
(2-)methylpropan-2-ol is a tertiary alcohol, It cannot be oxidised, hence there is no change to the alcohol.
instead of telling you all the anbswers, i think it's better that you learn the stuff and then get to try is on the questions. so here's all you need to know about the oxidation of alcohols:
You get three types of alcohol, primary secondary and tertiary. the difference is the place of the OH group on the organic molecule. When I say "OH carbon"< I mean the carbon atom that is bonded to the oxygen which is bonded to the hydrogen forming the OH grou (making it an alcohol).
In primary alcohols, the OH carbon is on the end of a carbon chain. eg. methanol, ethanol, porpan-1-ol, 3,4-dimethylhexan-1-ol. in all of these, the OH grou is on the end of the chain.
Oxidation of these is the most complex. They can be oxidised TWICE.
OXIDISATION 1: They are mixed with an oxidising agent, and they lose tweo hydrogens. First, the OH hydrogen is removed, and the CH (ONE of the hydrogens attached to the OH carbon) hydrogen is removed. This makes hydrogen gas, and leaves an aldehyde (draw it out in a dot and cross diagram to make sure you understand the mechanism - it will be very helpful).
OXIDISATION 2: They are mixed with an oxidising agent (this is the aldehyde now), and heated under reflux. this heating bring about further oxidation where the bond between REAMINING hydrogen bonded to the OH carbon is split and there is an oxygen put in the middle. this makes a carboxilic acid.
Secondary alcohols are ones where the OH carbon is attached to two more carbons and one hydrogen. eg. propan-2-ol, pentan-3-ol, 2-methylbutan-3-ol. They can only be oxidised once:
OXIDISATION 1: This happens in exactly the same way as with primary alcohols: The OH hydrogen and the only remaining hydrogen attached to the OH carbon are lost to hydrogen gas, and this forms a ketone. This is done with an oxidising agent.
THey can carry out NO MORE oxidation because there are no remaining OH carbon hydrogens. Ketones are much harder to oxidise than aldehydes because of this and so we say this is as far as they can be oxidised. (in A" you will use this fact (that aldehydes can easily be oxidised and ketones cannot) to distinguish between the two, using oxidising agents.
Tertiary alcohols: these are alcohols where the OH carbon is attached to 3 other carbons, os it in the middle of a branched chain. Eg. methlypropan-2-ol, 4-ethyloctan-4-ol.
Since there are no hydrogens even to start with that can be lost to make that hydrogen gas (except the OH hydrogen, which cannot be oxidised on its own because that would leave an O with a lone pair! very unstable), so this cannot be oxidised at all.
Hope this helps! Was good revision for me at least
Mike.
You get three types of alcohol, primary secondary and tertiary. the difference is the place of the OH group on the organic molecule. When I say "OH carbon"< I mean the carbon atom that is bonded to the oxygen which is bonded to the hydrogen forming the OH grou (making it an alcohol).
In primary alcohols, the OH carbon is on the end of a carbon chain. eg. methanol, ethanol, porpan-1-ol, 3,4-dimethylhexan-1-ol. in all of these, the OH grou is on the end of the chain.
Oxidation of these is the most complex. They can be oxidised TWICE.
OXIDISATION 1: They are mixed with an oxidising agent, and they lose tweo hydrogens. First, the OH hydrogen is removed, and the CH (ONE of the hydrogens attached to the OH carbon) hydrogen is removed. This makes hydrogen gas, and leaves an aldehyde (draw it out in a dot and cross diagram to make sure you understand the mechanism - it will be very helpful).
OXIDISATION 2: They are mixed with an oxidising agent (this is the aldehyde now), and heated under reflux. this heating bring about further oxidation where the bond between REAMINING hydrogen bonded to the OH carbon is split and there is an oxygen put in the middle. this makes a carboxilic acid.
Secondary alcohols are ones where the OH carbon is attached to two more carbons and one hydrogen. eg. propan-2-ol, pentan-3-ol, 2-methylbutan-3-ol. They can only be oxidised once:
OXIDISATION 1: This happens in exactly the same way as with primary alcohols: The OH hydrogen and the only remaining hydrogen attached to the OH carbon are lost to hydrogen gas, and this forms a ketone. This is done with an oxidising agent.
THey can carry out NO MORE oxidation because there are no remaining OH carbon hydrogens. Ketones are much harder to oxidise than aldehydes because of this and so we say this is as far as they can be oxidised. (in A" you will use this fact (that aldehydes can easily be oxidised and ketones cannot) to distinguish between the two, using oxidising agents.
Tertiary alcohols: these are alcohols where the OH carbon is attached to 3 other carbons, os it in the middle of a branched chain. Eg. methlypropan-2-ol, 4-ethyloctan-4-ol.
Since there are no hydrogens even to start with that can be lost to make that hydrogen gas (except the OH hydrogen, which cannot be oxidised on its own because that would leave an O with a lone pair! very unstable), so this cannot be oxidised at all.
Hope this helps! Was good revision for me at least
Mike.
mc_watson87
Propan-1-ol, as it is a primary alcohol, is fully oxidised by the oxidising agent of acidified sodium dichromate to Propanoic Acid, a carboxylic acid.
Propan-2-ol, as it is a secondary alcohol, is oxidised by the oxidising agent to propanone, a ketone.
Butan-1-ol is partially oxidised by the acidified sodium dichromate to Butanal, an aldehyde.
Is methylpropan-2-ol not the same as Butan-2-ol?
I think It wud be oxidised to a ketone. Hence Forming Methylpropanone.
Propan-2-ol, as it is a secondary alcohol, is oxidised by the oxidising agent to propanone, a ketone.
Butan-1-ol is partially oxidised by the acidified sodium dichromate to Butanal, an aldehyde.
Is methylpropan-2-ol not the same as Butan-2-ol?
I think It wud be oxidised to a ketone. Hence Forming Methylpropanone.
methylpropan-2-ol is a tertiary alcohol where butal-2-ol is a secondary alcohol.
it cannot be oxidised. look at methylpropanone... the middle carbon has 5 bonds! not allowed!
mik1a
methylpropan-2-ol is a tertiary alcohol where butal-2-ol is a secondary alcohol.
it cannot be oxidised. look at methylpropanone... the middle carbon has 5 bonds! not allowed!
it cannot be oxidised. look at methylpropanone... the middle carbon has 5 bonds! not allowed!
Lol ah yes.
Though methylpropan-2-ol doesn't tell u the position of the methyl group.
1-Methylpropan-2-ol (aka Butan-2-ol) cud be oxidised.
mik1a
lol
you're allowed to shorted 2-methylpropane to methylpropane because otherwise it would be called butane
you're allowed to shorted 2-methylpropane to methylpropane because otherwise it would be called butane
Ah ok, I never knew that.
Though it makes sense now.
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