4.5 carboxylic acids and their derivitives Flashcards
What is the relative acidity of carboxylic acids, phenols, alcohols and water
Carboxylic acids> phenols > water/alcohols
How can you show the relative acidity difference between these groups?
Can be shown by the reaction with Sodium Hydrogen carbonate solution. Only carboxylic acids are strong enough to produce co2 bubbles
What are the physical properties of carboxylic acid
Polar, have hydrogen bonding and higher boiling points compared to other compounds with similar molecular mass.
acidic as theyre able to donate h+ ions
Why are carboxylic acids acidic
able to donate h+ from carboxyl group (COOH) to form a carboxylate ion (COO-) stabilising the negative charge via resonance
How do you form carboxylic acids
Primary alcohols can be oxided to aldehydes then further oxidisation to a carboxylic acid.
Using Acidified potassium dichromate Orange to green. Also just potassium manganate Purple - brown/black.
How to reduce a carboxylic acids
Carboxylic acids can be reduced back to alcohols or aldehyde.
Need powerful reducing agent like LiAlH4 which reacts violently with water so reaction carried out using ethoxyethane. NaBH4 is too weak.
What is an aromatic carboxylic acid
Carboxylic acid bonded directly to a benzene ring
How to produce aromatic carboxylic acid
Oxidise an aromatic alcohol or aldehyde using potassium dichromate OR Oxidise a methyl side chain by heating the compound with alkaline potassium manganate solution
How to produce aromatic carboxylic acid using a methyl chain
Oxidise a methyl side chain by heating the compound with alkaline potassium manganate solution
The initial product is a potassium salt which is then acidified producing the acid itself.
What is decarboxylation?
Carboxylic group is removed as co2. Leaving a hydrocarbon.
What are the decarboxylation reagents
NaOH or Sodalime
Describe the decarboxylation reaction of carboxylic acids
Decarboxylation is the removal of the carboxylic group (COOH) usually by heating the carboxylate salt with soda lime.
This is a method to reduce a carbon chain length.
how do you shorten a carbon chain
decarboxylation.
heat with sodalime
How do you represent soda lime in a reaction
NaOH CaOH2 CaO
How do you convert carboxylic acids to ester
Via esterification Heat the acid with an alcohol In the presence of conc H2SO4 catalyst
What is the role of concentrated sulphuric acid in the process of esterfication
A catalyst
What are properties of esters
Volatile Fruity smell Low boiling point and make good solvents for other polar molecules.
Why is HCl a sometimes preferred catalyst for esterfication
HCl as a gaseous catalyst provides better yield since no Alkenes side products are formed.
Give the 3 possible reagents which can be used to produce an acyl chloride from a carboxylic acid
PCl5 - phosphorus 5 chloride PCl3 - Phosphorous 3 chloride SoCl2 - thionyl chloride
Why is SOCl2 the preferred reagent when making acid chlorides?
Because only gaseous co-products are formed and isolation of the acid chloride is more difficult when using Pcl3 or PCl5
Esters + acid chlorides form carboxylic acids in a what reaction?
In a Hydrolysis reaction
What’s an acid hydrolysis
Ester must be refluxed with dilute acid eg HCl OR H2SO4
What’s a base hydrolysis
Ester must be refluxed with dilute alkali eg NaOH
How does the hydrolysis of acid chlorides compare with the hydrolysis of esters
The hydrolysis of acid chlorides is much more rapid than the hydrolysis of esters. Acid chlorides will react vigorously with cold water.
How is an amide made from a carboxylic acid
- ammonium carbonate is added to an excess of the carboxylic acid until the ammonium salt is formed.
- Then the ammonium salt is heated to undergo dehydration and produce an amide.
How is a nitrile formed by an amide
A nitrile will be produced if the amide undergoes dehydration by heating it with phosphorus oxide (P4O10)
How are nitriles formed from haloalkanes?
By the reaction with potassium cyanide using an alcohol water mixture solvent. Via nucleophilic substitution.
How are hydoxynitriles formed from aldehydes and ketones
Potassium or sodium cyanide is added to sulphuric acid to produce hydrogen cyanide Temperature of 20*C
Why is HCN not added directly to aldehyde or ketone
Hydrogen cyanide is a very poisonous gas.
Describe the stages in the hydrolysis of nitriles.
When heated under reflux, a nitrile is hydrolysed giving a carboxylic acid
- Nitriles react with water to produce amides
- Amide undergo further hydrolysis and react with water to form a carboxylic acid or a carboxylate salt.
What is the reducing agent used in the reduction of nitriles to primary amines
LiAlH4 IN ethoxyethane.
