Carboxylic Acids All carboxylic acids are characterised by the presence of the carboxyl group as shown.

Naming Carboxylic Acids Names are derived from the number of carbons in the chain. The ‘e’ of an alkane is replaced by the suffix ‘oic acid’. The carboxyl carbon atom in the COOH functional group is ALWAYS numbered carbon 1. Branches on chains are always on the lowest number carbon possible, starting with the carboxyl carbon.

Structures of methanoic and ethanoic acids Week 4 Structures of methanoic and ethanoic acids © Pearson Education Ltd 2009 This document may have been altered from the original 3

Structure of 4-methylhexanoic acid Week 4 Structure of 4-methylhexanoic acid © Pearson Education Ltd 2009 This document may have been altered from the original 4

Naming Exercise Draw displayed structures and name the following: CH3CH2COOH C6H5COOH ClCH2COOH HOOCCH2COOH Propanoic acid Benzoic acid Chloroethanoic acid Propane-1,3-dioic acid

More naming practise Complete question 1a,b and c from p. 29 in OCR Chemistry Draw the following: 2-hydroxypropanoic acid 3-methylbenzoic acid. Benzene-1,4-dicarboxylic acid 3-methylbutanoic acid

Explain the water solubility of carboxylic acids. Week 4 Explain the water solubility of carboxylic acids. Describe the reactions of carboxylic acids with metals, carbonates and bases. © Pearson Education Ltd 2009 This document may have been altered from the original 7

Physical Properties of Carboxylic Acids All carboxylic acids are either liquids or solids. MP and BP increase with increasing chain length. The first 4 carboxylic acids are soluble in water but solubility decreases with increasing chain length. Why? Hydrogen bonding explains it all.

More naming practise Boiling Points of first 4 carboxylic acids. Acid Formula BP/oC Methanoic acid HCOOH 110.5 Ethanoic acid CH3COOH 118 Propanoic acid CH3CH2COOH 141 Butanoic acid CH3CH2CH2COOH 163

Hydrogen Bonding Each acid is capable of forming 2 hydrogen bonds per molecule. (Shown as thin lines) These increase intermolecular forces so that more energy than expected is needed to separate the molecules than if simple Van der Waal’s forces only were present.

Hydrogen bonds, strong dipole–dipole interactions Week 4 Hydrogen bonds, strong dipole–dipole interactions © Pearson Education Ltd 2009 This document may have been altered from the original 11

Solubility Hydrogen bonding also accounts for the solubility of carboxylic acids. As the chain length increases the solubility decreases as a result of the increasing non polar chain which cannot interact with water molecules and doesn’t disrupt the hydrogen bonds between water molecules.

Reactions of Carboxylic Acids Carboxylic acids are WEAK compared with the mineral acids, nitric sulphuric etc. Why are they weak acids? They do however behave as typical acids reacting with metals, metal oxides, metal hydroxides and metal carbonates to from salts containing the carboxylate anion.

Week 4 Carboxylate ion 14 © Pearson Education Ltd 2009 This document may have been altered from the original 14

Weak Acids? Mineral acids are strong acids – they ionise completely in water. HCl + H2O → H3O+ + Cl- Carboxylic acids only partly dissociate in water: CH3COOH + H2O D CH3COO- + H3O+ This is because the carboxylate anion is a strong base, strengthened by the +I effect of the chain, increasing electron density on the O of the OH group, strengthening the OH bond and making the ethanoate ion more likely to attract an H+ ion back, should it be lost.

Reactions of Carboxylic Acids: Complete the Spider Diagram Salt + water Salt + Hydrogen Acid Salt + water Salt ,water + carbon dioxide