Carboxylic Acids and Derivatives Flashcards
(100 cards)
What are carboyxlic acids?
They contain the carboxyl group (-COOH)
What is the general formula for aliphatic carboxylic acids?
CnH2nO2
How to name carboxylic acids?
Replace ‘-e’ with ‘-oic acid’
How to name salts of carboxylic acids?
Replace ‘-oic acid’ with ‘-oate’
How does the boiling point of carboxylic acids change as the number of carbon atoms increases?
As the number of carbon atoms increases, the number of electrons in the molecule increases and more energy is required to overcome the stronger id-id between carboxylic acid molecules
What is glacial acid and why is it called that?
Anhydrous ethanoic acid as it freezes to an ‘ice-like’ solid at 17 degree celsius
How do carboxylic acids’ boiling point compared to alcohols of similar Mr and why?
Carboxylic acids have a higher boiling point compared to alcohols of similar Mr
- carboxylic acids have more extensive hydrogen bonds than alcohol as there are more sites for the formation of hydrogen bonds
- carboxylic acids form stronger hydrogen bonds than alcohol molecules as the O-H bond in -COOH is more polar due to the presence of electron-withdrawing carbonyl group
Are carboxylic acids soluble in water?
Lower carboxylic acid molecules are soluble in water because carboxylic acids can form hydrogen bonds with water molecules
What happens to the solubility of carboxylic acids as number of C increases?
As the length of non-polar hydrocarbon chain increases, solubility in water decreases while solubility in non-polar solvents increases
What happens when carboxylic acids in pure form and dissolved in non-polar solvents like benzene?
Carboxylic acids form dimers through the formation of hydrogen bonds between two acid molecules
What does the strength of acids depend on?
The stability of anion formed
What is the carboxylate anion stabilised by and what are the implications?
Carboxylate anion is stabilised by resonance, where the negative charge is delocalised over the -COO⁻, thus the two C-O bonds are equal in length
What affects the relative acidity of carboxylic acids?
- Electron-donating groups intensify the negative charge on the -COO⁻ group, thereby destabilising the anion and reducing acid strength
- Electron-withdrawing groups disperse the negative charge on the -COO⁻ group, thereby stabilising the anion and increasing acid strength
- benzoic acids are stronger acids than aliphatic acids due to delocalisation of negative charge on the benzoate anion into the ring, making the benzoate anion more stable
Why is the delocalisation of negative charge into the benzene ring possible?
It possible because the C atom of -COO⁻ group is sp² hybridised, similar to the sp² hybridised C atom in the benzene ring, allowing overlap of the unhybridised p orbitals
What is the strength of carboxylic acids in relation to other compounds?
Mineral acids > RCOOH > phenol > water > alcohol
What are the ways to prepare carboxylic acids?
- oxidation of primary alcohols and aldehydes
- oxidation of alkylbenzenes
- oxidation of alkenes with structure RCH=CHR’
- hydrolysis of nitriles
- hydrolysis of acyl chlorides and esters
What are the reagents and conditions for the oxidation of primary alcohols and aldehydes to prepare carboxylic acids?
acidified KMnO4 or acidified K2Cr2O7, heat under reflux
What are the reagents and conditions for the oxidation of alkylbenzenes to prepare carboxylic acids?
acidified KMnO4, heat under reflux
What are the reagents and conditions for the oxidation of alkenes with the structure RCH=CHR’ to prepare carboxylic acids?
acidified KMnO4, heat under reflux
How is vinegar produced?
Oxidation of ethanol by enzymes
What is the equation for vinegar production?
CH3CH2OH + O2 -(enzymes)-> CH3COOH + H2O
What are the reagents and conditions for the hydrolysis of nitriles?
- acid hydrolysis: dilute HCl (aq)/ dilute H2SO4, heat under reflux
- alkaline hydrolysis: NaOH (aq), heat under reflux, followed by acidification with dilute HCl (aq)/ H2SO4 (aq)
What is the equation for acid hydrolysis of nitriles?
RCN + 2H₂O + H⁺ → RCOOH + NH₄⁺
What is the equation for alkaline hydrolysis of nitriles?
RCN + H₂O + OH⁻ → RCOO⁻ + NH₃
(Upon addition of dilute HCl, RCOO⁻ becomes RCOOH)