4.5 Carboxylic Acids And Their Derivatives Flashcards
(40 cards)
What is an acid
A compound that is a proton donor
What is a strong acid
An acid that dissociates fully when dissolved in water
What is a weak acid
An acid that partially dissociates when dissolved in water
Are carboxylic acids strong or weak acids?
Weak
Explain the relative acidity of a carboxylic acid
• the hydrogen from the carboxyl can be donated
• the negative charge can be shared over the carbon and oxygen of the carbonyl group
• this delocalisation of charge stabilises the carboxylate ion
Rate the acidity of the following
Water, carboxylic acid, phenol, ethanol
- Carboxylic acid
- Phenol
- Water
- Ethanol
Why are the ions formed from carboxylic acids more stable than those formed from ethanol and water
The negative charge is delocalised across 2 oxygen atoms
Why is the phenoxide ion formed from phenol more stable than the ions formed from ethanol and water
The negative charge is delocalised around the pi-electron ring system of benzene
Test to distinguish between carboxylic acids and phenols
• carboxylic acids react with carbonate compounds and form bubbles of CO2
• phenol doesn’t react with carbonates as it is insufficiently acidic and so no effervescence is seen
Why dont ethanol molecules ionise
The ethoxide ion isn’t stabilised by the delocalisation of electrons
How to form a carboxylic acid from an aldehyde or primary alcohol
Oxidation
• use excess oxidising agent such as acidified potassium dichromate or acidified potassium manganate
• heat under reflux
• distil carboxylic acid from reaction mixture and purfiy
Why is heated under reflux important when oxidising to carboxylic acid
As distillation will form the aldehyde - must have further warming for further oxidation to occur
Why might it be difficult to see oxidation has occurred using excess acidified potassium manganate
The solution turns from purple to colourless but if theres excess when the solution is purple it will be hard to see when the reaction would be colourless
Can NaBH4 reduce a carboxylic acid? Explain
No
Carboxylic acid is a stable compound and this is not a strong enough reducing agent
Which reducing agent to use when trying to reduce carboxylic acid
Lithium tetrahydridoaluminate (III) dissolved jn ethoxyethane
What is formed when a carboxylic acid is reduced?
A primary alcohol and water is produced
What is an aromatic carboxylic acid?
-COOH group is attached to benzene ring
How to form an aromatic carboxylic acid
• oxidation of methyl side-chain
• reflux an alkylbenzene with an alkaline potassium manganate (VII) solution
• purple solution of potassium manganate (VII) is reduced to brown manganase (IV) oxide
• the potassium or sodium salt of the benzenecarboxylic acid is formed
• mixture is acidified with a dilute acid (HCl (aq)) to reprotonate the salt to produce white crystals of benzenecarboxylic acid
What is decarboxylation
Loss of a carboxyl group
• descends the homologous series
When will a carboxylic acid be decarboxylated
The carboxylic acid (or its sodium salt which is generally more effective) is strongly heated with an alkali such as solid NaOH or preferably sodalime
What is produced when a carboxylic acid is decarboxylated
An alkane and a carbonate
How is sodalime prepared
Heating together sodium hydroxide and calcium oxide
Is it represented by NaOh
Can decarboxylation occur without the use of sodalime
Yes
CO2 will be removed if calcium salt of an acid is heated
A ketone will be produced
This will increase the chain length
How is a carboxylic acid converted to an ester
• react carboxylic acid with 1• or 2• alcohol
• conc sulfuric acid used as catalyst
• mixture is refluxed using a water bath or electrical heater
• the OH bond is broken
• the remaining acid is neutralised by NaHCO3(aq)
• the 2 layers are separated using a separating funnel
• the ester-containing layer is dried and distilled
• the ester is collected at boiling temperature
• esterification reaction
• condensation reaction
