Carboxylic Acids and Esters

CA functional group

COOH

What is the carbonyl and hydroxyl group

Carbonyl C=O, hydroxyl O-H

What type of acid is a CA and why

Weak acid- H from. Hydroxyl group can donate a H+

Dissociation equation

RCOOH → ← RCOO- + H+

What is the RCOO-

Carboxylate ion

What is the shape and bond angle of the carbonyl group (COOH)

Planar, 120

Ethanoic acid + magnesium

2CH3COOH + Mg → H2 + (CH3COO)2MG

(CH3COO)2Mg

Magnesium ethanoate

Carboxylic acid in a neutralisation reaction

NaOH + CH3COOH → H2O + CH3COO-Na+

Carboxylic acid with a carbonate

2CH3COOH + Na2CO3 → 2CH3COO-Na+ + H2O + CO2

Carboxylic acid + alcohol (esterification)

CH3COOH + CH3CH2OH → ← CH3COOCH2CH3 (ethyl ethanoate) + H2O

Relative solubility of CAs in organic solvents

Very soluble

Why are CAs soluble in water

They can form hydrogen bonds

How does solubility change with chain lengths

Smaller chain dissolve in cold water but as mass/ chain length solubility decreases as the proportion of the non polar part of the molecule increases

Solubility of benzoic acid

Fairly soluble in cold water, soluble in hot water

How do CAs dissolve in organic solvents

Organic solvents interact with the organic part of the CA and form LDF induced dipole dipole bonds

What happens to CAs in non polar solvents

They dimerise due to intermolecular bonding (2 CA molecules join together)

What do you have to remember when drawing hydrogen bonding

Lone pair of electrons on oxygen atom

Compare relative BP of alkanes, aldehydes, alcoholic ad CAs

Allánales lowest as have only LDFs, aldehydes next as have perm and induced dipole dipole from polar c=o bonds, then alcohols as have hydrogen bonding from OH group, ten CAs the highest as have more hydrogen bonding

Esters

Derivatives of CAs

Functional group of esters

COO

What is the hydroxyl group of a CA for an ester

An alkyl group eg methyl

General formula for esters

RCOOR

Features of esterification reaction

Condensaiton (H2O is formed), reversible

Reagents needed for esterification

alcohol, CA

Conditions fro esterification

Reflux, concentrated H2SO4 catalsyt

What is the function of the conc h2so4 catalyst

Acts as a dehydrating agent- removes water so shift equilibrium right increasing yield of ester, provides alternate reaction pathway to reduce Ea

Example of esterification

Propano is acid + methanol → methyl propanoate + water

Uses of esters

Artificial flavourings, perfumes, solvents (can dissolve organic solvents), plasticizers

hydrolysis

Breaking up using water

Ester + water →

Carboxylic acid + alcohol

Why do you need a dilute acid or alkali to hydrolyse an ester

Water is not a strong enough Nucleophile

Conditions needed fro acid hydrolysis

Dilute acid eg HCl

Features of acid hydrolysis

Reversible reaction, weather is in excess to shift PoE right and favour hydrolysis products

Conditions needed for alkaline hydrolysis

Weak alkali in excess, reflux

Products of alkaline hydrolysis

Initial hydrolysis makes alt of carboxylic acid and alcohol → ester + water gives alcohol + CA as in acid hydrolysis, the NaOH reacts with carb acid to make salt and water

How can carboxylic acids be made from hydrolysis of esters

React te carboxylate salt formed with an acid

Which bond is broken in both acid and alkaline hydrolysis

C-O bond in COO functional group