4.5 Carboxylic acids and their derivatives Flashcards
(21 cards)
Are carboxylic acids strong or weak?
Weak but stronger than most phenols
How can the difference in acidity between carboxylic acids and phenols be shown/proven?
By their reaction with sodium hydrogencarbonate solution. Only carboxylic acids are strong enough acids to produce carbon dioxide bubbles. Also replacing any of the hydrogens in either phenols or carboxylic acids does result in stronger acids and greater dissociations of the acids into ions.
How can carboxylic acids be produced and what reagents can be used? discuss colour changes
By the oxidation of alcohols. Primary alcohols are first oxidised to aldehydes and then on further oxidation to carboxylic acids.
Acidified pottasium dichromatecan be used and this turns from orange [Cr2o7]2- ions to green Cr3+ ions as the oxidation of the alcohol proceeds.
Also alkaline pottasium manganate can be used and this turns from purple containing MnO4- ions to a brown black sludge of manganese oxide.
What conditions and reagents are needed for the reduction of carboxylic acids?
LiAlH4 is needed as it is stronger than NaBH4 . But LiAlH4 reacts violently with water thus ethoxyethane is used as the solvent for this reaction. Ultimately carboxylic acids are reduced to primary alcohols.
What is true about all aromatic carboxylic acids?
The acid group must be directly bonded to the benzene ring.
What happens in the decarboxylation of a carboxylic acid and what is used?
The removal of a carbon dioxide group happens.
The compound used is soda lime. As Co2 is acidic it reacts with a base.
This is a method of reducing the size of the carbon chain as the resulting compound has one less carbon.
CH3COOH + Ca(OH)2 -> CH4 + CaCO3 + H2O is an example
What happens in the decarboxylation of a carboxylic acid if soda lime is not used?
A ketone is formed (carbon chain increased)
What happens when you react carboxylic acids with alcohol?
Esterification - reversible reaction where esters are made by heating carboxylic acids with alcohols in the presence of a little sulfuric acid. The acids OH group is lost in this reaction not the alcohols.
What occurs during the hydrolysis of esters?
A carboxylic acid is made and this can happen under basic or acidic conditions. The ester is heated to reflux with aqueous sodium hydroxide and the mixture is then acidified (e.g using HCL) to produce the carboxylic acid.
What reagents can be used to make acid chlorides from carboxylic acids and which is preferred?
PCl3
PCl5
SOCl2
the last reagent is preferred as the first has a low yield, the second produces a waste product that must be separated thus the third is preferred.
Why are acid chlorides more reactive than carboxylic acids?
The carbonyl carbon atom is electron deficient as it is bonded to the more electronegative chlorine and oxygen atoms thus making it more susceptible to nucleophilic attack.
What occurs in the reaction between carboxylic acids and ammonia?
The reaction gives the ammonium salt of the acid. When this salt is heated, water is lost and the amide is produced.
What is the dehydrating agent used to dehydrate amine to a nitrile?
Phosphorus oxide
What is the full process of getting a nitrile from a carboxylic acid?
Carboxylic acid + ammonia -> the ammonium salt of the acid
the ammonium salt + heat -> an amine
Amine + phosphorus oxide -> Nitrile
How can nitriles be produced from halogenoalkanes?
By reacting the halogenoalkane with potassium cyanide (KCN) using an alcohol-water mixture as solvent.
This is a nucleophilic substitution where the cyanide ion reacts as a nucleophile.
How can cyanide be a nucleophile and how do you draw it?
Cyanide is C triple bond N meaning carbon has only got three bonds, this means its missing the bond so has a lone pair of electrons, hence you put the minus sign on the carbon atom.
How can a hydroxynitrile be formed?
an aldehyde and some ketones will react with hydrogen cyanide in the presence of sodium or potassium cyanide.
What happens during the hydrolysis of nitriles?
When heated under reflux with a dilute acid 9such as H2SO4, a nitrile is hydrolysed, giving a carboxylic acid.
What happens during the hydrolysis of amides?
When an amide is heated under reflux with a base such as aqueous sodium hydroxide, the amide is hydrolysed as the carbon to nitrogen bond is broken, producing ammonia gas.
What happens during the reduction of different nitriles?
- Warming a nitrile with a solution of LiAlH4 in ethoxyethane will reduce a nitrile to a primary amine
