Carboxylic acids, esters and derivatives
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Acidity
Acidity
React with bases to form salt (carboxylates) plus water
What do you get when ethanoic acid reacts with sodium hydroxide ,Sodium ethanoate and water
Position lies to the left
Carboxylic acids are stronger acids than alcohols
Strength of acidity is Carboxylic acids>phenol>water>ethanol
All are weak acids
Reason
Reason
The O-H bond is weakened in carboxylic group by the carbonyl group, C=O so the charge density on the CO- will decrease and more H+ ions will form.
The carboxylate ion is stabilised by the delocalisation of electrons around the COO- group spreading out the negative charge making it less likely to bond with H+ ions
Electron withdrawing groups
Electron withdrawing groups
Chlorine is an electron withdrawing group which will make the acid stronger by decreasing the negative charge of the COO- group
Oxidation of two carboxylic acids
Oxidation of two carboxylic acids
Only methanoic acid and ethanedioc acid can be oxidised into CO2 and H2O because they are strong reducing agents
Fehling solution: CU2+ ions will be reduced and form CU+ which is red in colour from blue
Tollens reagent: Ag+ will be reduced and form Ag which causes the mirror effect
Methanoic acid
Methanoic acid
Under warmed with Fehling’s or Tollens’ reagent
Acidified KMnO4 or K2Cr2O7
Ethanedioc acid
Ethanedioc acid
Acidified KMnO4 or K2Cr2O7
Acyl chlorides
Acyl chlorides
Reactions of Acyl chloride
Reactions of Acyl chloride
Carboxylic acids are quite unreactive
The best way to do synthetic reactions are to first convert carboxylic acids into acyl chlorides
Acyl chlorides are more reactive than carboxylic acids
• Carbonyl carbon has electrons drawn away by Cl atom and O atom as both of them are strongly electronegative
Carbonyl carbon has a relative large partial positive charge and open for nucleophilic attack
General formula is ROCl + HZ= ROZ +HCl
HZ can be water, alcohol,ammonia or amine
Mechanism of hydrolysis of acyl chlorides with water
Mechanism of hydrolysis of acyl chlorides with water
Hydrolysis
Hydrolysis
For acyl chlorides, neutral water is sufficient at room temperature
Hydrolysis of chloroalkanes needs a strong alkali, aq NaOH , refluxed with chloroalkanes to hydrolyse it
Aryl chlorides, such as chlorobenzene will not undergo hydrolysis because the carbon atom bonded to the chlorine atom is part of the delocalised pie bonding system. The P orbitals from the Cl ion tend to overlap with the delocalized electron in benzene. This causes the C-Cl bond to have a double bond character making it stronger so hydrolysis does not occur
Reactions with alcohol
Reactions with alcohol
Reagent : Alcohol
Reagent : Alcohol
Condition : Room temperature
Condition : Room temperature
Product : Ester and HZ
Product : Ester and HZ
Reaction with phenol
Reaction with phenol
Reagent : Phenol
Reagent : Phenol
Condition : warm, with NaOH
Condition : warm, with NaOH
Product : Phenyl esters
Product : Phenyl esters
Must be warmed
No reaction between phenol with carboxylic acids so conversion first
Acyl chloride must be used to make phenyl esters
must have base (NaOH)
Phenol and the base creates phenoxide ion, acts as nucleophile to attack the acyl chloride
Reactions with ammonia
Reactions with ammonia
Reagent : Ammonia
Reagent : Ammonia
Condition : Room temperature
Condition : Room temperature
Product : Amide + hydrogen chloride
Product : Amide + hydrogen chloride
Reactions with amines
Reactions with amines
Reagent : Amines
Reagent : Amines
Condition : Room temperature, anhydrous
Condition : Room temperature, anhydrous
Product : amide and hydrogen chloride
Product : amide and hydrogen chloride
Amine with hydrogen and a different group is called a substituted amine
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