3.9 Carboxylic Acids And Esters Flashcards
What functional groups do carboxylic acids have?
The carbonyl group and hydroxyl group seen in alcohols
Are carboxylic acids soluble in water
The carboxylic group can form hydrogen bonds with water, as a result, short chain acids are soluble in water.
What is formed when a carboxylic acid loses a proton?
If they hydrogen of the O-H is lost a negative carboxylate ion is formed. The negative charge is shared over the whole carboxylate group.
Describe how you name esters.
Names based upon the parent acid with the name beginning with the alkyl group that replaced the hydrogen of the acid.
Describe how esters are formed.
Carboxylic acids react with alcohols to form esters, catalysed with H+ (eg sulfuric acid)
Describe ester hydrolysis, and what does it need?
The carbonyl atom of an ester has a delta+ charge and can therefore be attacked by water, breaking them back into carboxylic acids and alcohols.
What are animal+vegetable fats and oils esters of?
Propan-1,2,3-triol (glycerol)
In what reaction are biodiesels formed, and what are the reagents + catalyst.
- Transesterification
- rape seed oil and methanol, with a strong alkali catalyst.
How are acyl chlorides formed?
By reacting a carboxylic acid with PCl5
Eg. CH3COOH + PCl5 -> CH3COCl + POCl3 + HCl
What is the mechanism to form a carboxylic acid from an acyl chloride, and what is the reagent?
Nucleophilic addition elimination, using the poor nucleophile water.
Describe the nucleophilic addition elimination of water and acyl chloride to form a carboxylic acid
- An arrow is drawn from the lone pair on water to the delta+ carbon, and an arrow is drawn from the double bond between C=O to the oxygen. This forms an intermediate with a C-O bond (with the oxygen having a negative charge and lone pair), and with a H2O attached to the carbon (with the Oxygen having a positive charge).
- An arrow is drawn from the lone pair on the oxygen to the C-O bond, an arrow is drawn from the C-Cl bond to the Cl, and an arrow is drawn from the O-H bond to the positive O.
- This forms a carboxylic acid + HCl
Name what reagents can be used (and what they form) with acyl chlorides
H2O -> carboxylic acid
Alcohol -> Ester
Ammonia -> amide
Amine -> N-substituted amide.
How are acid anhydrides formed ?
By reacting two carboxylic acids with a phosphorus pentoxide catalyst.
Eg 2CH3COOH —-P4O10 > (CH3CO)2O
What are the benefits of using Acid anhydrides rather than acyl chlorides for nucleophilic addition elimination?
- They produce carboxylic acids rather than HCl which is much less corrosive
- They are cheaper than acyl chlorides.
