3.3.9 carboxylic acid and derivatives Flashcards
Carboxylic acid functional group
COOH
The carbon atom on the functional group is counted as part of the carbon chain
benzenecarboxylic acid (This is still often called benzoic acid).
Physical properties of carboxylic acids
Can form hydrogen bonds
Up to 5C soluble in water
Higher bp and mp than alkanes
Way of identifying carboxylic acids by melting point
Other carboxylic acids facts
Can be identified by specific smells (ethanoic acid as vinegar)
hexanoic and octanoic acids are caproic and capryllic acid respectively - used in goat fat - unpleasant smell
Measuring a carboxylic acid melting points
put a section of a sample in a cappilary tube
Ester functional group
RCOOR
- replace the H on the carboxylic acid with a r group
Derived from carboxylic acids
Hydrogen replaced by a hydrocarbon group (alkyl or aryl)
Short chains - volatile - have a fruity smell - used in flavourings and perfume ( and as solvents and plasticisers)
Fats and oils are ester with long carbon chains
Ester naming
Based of the name of the parent acid
Name begins with alkyl group
Reactivity of carboxylic acids
the c and the h is a delta pos the o are delta neg
C is open to attacked by nucleophiles
O may be attacked by a pos charged species
H+ may be lost - behaving as an acid
carboxylate ion is a carboxylic acid without a proton
Neg charge shared over the whole carboxylate group - delocalisation makes the resulting ions more stable
Weak acid - eq to left
Distinguished as react with NaHCO3 - release CO2
Reactions of acids
Carboxylic acids are proton donors
Form ionic salts with more reactive metals
Salts general name is carboxylates
Formation of esters
Carboxylic acids react with alcohols to form esters
Catalysed by a strong acid catalysts
Hydrolysis of esters (acid catalyst)
Water acting as a weak nucleophile
With acid catalyst
reversible reaction
Does Not go to completion
Creates an equilibrium mixture containing the ester, water , acid, and alcohol
Room temp
Hydrolysis of esters ( base catalyst)
Salt produced rather than the acid
Removes the acid form the mixture - meaning no eq meaning goes to completion
reversible reaction
to a full on reaction with naOH
Uses of esters
Animal and vegetable oils - esters of propane 1,2,3 triol
- fats and oils can be hydrolyzed in acidic conditions - to give glycerol and fatty acids
- can be hydrolyzed by boiling with NaOH - produces glycerol and sodium salts of the acids
the sodium salts formed are ionic and dissociate to form Na+ and RCOO- = allows them to work as cleaning agents
propane -1,2,3-triol (glycerol)
Can form hydrogen bonds and is very soluble in water
Used ub pharmaceuticals and cosmetic preparation
Used as a solvent in medicine
Solvent in the food industry
Used as a plasticiser
What is acylation
Where an acyl group is introduced into another molecule
the acyl group is a carbon with a double bond and an r group
Acid derivatives
Have the acyl group in their structure
ester
acyl chloride
acid anhydride
Nucleophilic acyl substitution
Reaction takes place because of the polarisation leaving the carbon susceptible to nucleophilic attack
The z group is replaced therefor the nucleophile has been acylated
Factors that effect
1. The magnitude of the charge on the carbon group which depends on the electron releasing or attacking power of z
2. How easily z is lost
3. How good the nucleophile is
Order of reactivity for nucleophiles in acylation
The nucleophiles are neutral so they must loose a hydrogen ion during the reaction
water more than alochol more than ammonia more than primary amine
Polarisation of acid derivatives
Acid chlorides and acid anhydrides withdraw electrons
Meaning they are both good acylating agents as the z is easily lost
Products of addition elimination reactions
ammonia - amide
amine - n-substituted amide
alcohol - ester
water - carboxylic acid
Mechanism for nucleophilic addition elimination reactions
the nucleophile attcks the pos carbon eith the = o attached
arrow breaks the double bond electrons move to o - o- lone pair
then the o lone pair move back in to the bond
the nucleophile is attached with a pos charge
then the carbon with halogen attched bond collapes and cl- removed
then the h colappses into the pos part of nucleophile
Ethnic anhydride vs ethanoyl chloride
Its is cheaper
It is less corrosive
It does not readily react with water
Its is safer as no HCl byproduct
Important in the production of aspirin
