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Esters

Hi all,

Having a bit of trouble with this question:
"Ethane-1,2-diol is heated under reflux with ethanoic acid and a small amount of H2SO4 catalyst. Compound A is formed with the molecular formula C6H10O4.

Draw the structure of compound A."

Firstly I know compound A must be an ester because an alcohol and carboxylic acid are reacting together. However, I don't understand how there can be six carbons in compound A, when only four carbons come from the ethanoic acid and ethane-1,2-diol.

I've tried drawing out the ester, and the "alkyl" group still has an O-H bond and a 'O' bond, too. Whether I'm doing this right or the question is wrong, I'm not entirely sure.

Any help appreciated!
Reply 1
as ethane-1,2-diol has two alcohol groups on it, when you react with ethanoic acid, it will form a ester link betweens both molecules, because carboxylic acid reacts with alchol to form ester bonds, if you dont understand me just ask and ill explain it better
(edited 10 years ago)
Reply 2
a hint, the structural would be CH3COOCH2CH2OOCCH3 ill let you work out the displayed


little diagram scan0001.jpg
(edited 10 years ago)
Reply 3
Original post by mattcandy3
a hint, the structural would be CH3COOCH2CH2OOCCH3 ill let you work out the displayed


little diagram scan0001.jpg


Thanks, but I still don't really understand where the two extra carbons come from?
Reply 4
i cant explain it in words so ill draw a nice diagram :biggrin:
Reply 5
So in the normal esterification process with just 1 OH group you will receive an ester ( ethyl ethanoate) which has 4 carbons, this is because, 2 carbons in the alcohol and 2 in the acid, so 4 altogether,

However with the ethane 1,2 diol there are 2 OH groups, therefore it will react with the acid twice , so you will have ester bonds on both sides of the molecule so 2 carbons from the original alcohol and 4 come from the acid that has reacted with the OH groups on either side of the alcohol
Reply 6
Original post by mattcandy3
So in the normal esterification process with just 1 OH group you will receive an ester ( ethyl ethanoate) which has 4 carbons, this is because, 2 carbons in the alcohol and 2 in the acid, so 4 altogether,

However with the ethane 1,2 diol there are 2 OH groups, therefore it will react with the acid twice , so you will have ester bonds on both sides of the molecule so 2 carbons from the original alcohol and 4 come from the acid that has reacted with the OH groups on either side of the alcohol


I see! That makes much more sense now :smile:
Reply 7
scan0001.jpg yeah so 2 from each, however as it has 2 OH groups it will react again with ethanoic acid, creating another ester link, therefore it will gain another 2C from the acid , GLAD i could help, if you have any other problems just ask
(edited 10 years ago)
Reply 8
Original post by mattcandy3
So in the normal esterification process with just 1 OH group you will receive an ester ( ethyl ethanoate) which has 4 carbons, this is because, 2 carbons in the alcohol and 2 in the acid, so 4 altogether,

However with the ethane 1,2 diol there are 2 OH groups, therefore it will react with the acid twice , so you will have ester bonds on both sides of the molecule so 2 carbons from the original alcohol and 4 come from the acid that has reacted with the OH groups on either side of the alcohol


Out of curiosity do you happen to know the nomenclature? Can the Oxygen double bond be a ketone? (Sorry if I'm asking a lot of questions - we've just covered esters but nothing to this sort of level).
Reply 9
NO, if they gave this molecule and asked you to name the function groups and you put ketone, you would be wrong, whenever you see double bond oxygen then an oxygen it is an ester group
(edited 10 years ago)
Reply 10
Original post by mattcandy3
I dont really get what you are trying to ask, but NO, if they gave this molecule and asked you to name the function groups and you put ketone, you would be wrong, whenever you see double bond oxygen then an oxygen it is an ester group


By "nomenclature" I meant the name of the compound (if that's what you didn't understand). Also I'm talking about the other double bond, not the COO bond which defines it as an ester.
No you wouldnt need to need the ketone, (one) in there, i believe the name would be ethane-1,2-diyl diethanoate, (but i gather you are AS) so you will probably not be required to name any esters which have more then one ester bond ( like this one )
(edited 10 years ago)
Reply 12
Original post by mattcandy3
No you wouldnt need to need the ketone, (one) in there, i believe the name would be ethane-1,2-diyl diethanoate, (but i gather you are AS) so you will probably not be required to name any esters which have more then one ester bond ( like this one )


I see. Thanks for the help, again!
No probs
Original post by mattcandy3
So in the normal esterification process with just 1 OH group you will receive an ester ( ethyl ethanoate) which has 4 carbons, this is because, 2 carbons in the alcohol and 2 in the acid, so 4 altogether,

However with the ethane 1,2 diol there are 2 OH groups, therefore it will react with the acid twice , so you will have ester bonds on both sides of the molecule so 2 carbons from the original alcohol and 4 come from the acid that has reacted with the OH groups on either side of the alcohol

THANK YOU, I was struggling to understand too