Structure of Carboxylic Acids The carboxyl group is shown in red and may be written in the condensed form: -COOH. The term carboxylic is taken from the terms carbonyl and hydroxyl, the two structures that make up the carboxyl group.
Properties of Carboxylic Acids Very polar compounds Can hydrogen bond to one another and to water Boil at higher temperatures than aldehydes, ketones, or alcohols Smaller carboxylic acids are soluble in water Lower molecular weight acids have sharp, sour tastes and unpleasant aromas Longer chain carboxylic acids are called fatty acids and are important components of biological membranes
Naming Carboxylic Acids - IUPAC Determine the name of the parent compound, the longest continuous chain containing the carboxyl group. Replace the –e ending with the suffix –oic acid. If there are two carboxyl groups, the suffix is –dioic acid. Number the chain so the carboxyl carbon is number 1. Name and number substituents.
Naming carboxylic acids of cycloalkanes Add the suffix carboxylic acid to the name of the cycloalkane or substituted cycloalkane. The carboxyl group is always numbered 1. Other substituents are named and numbered as usual. Cyclopentanecarboxylic acid
Draw structures for the following. 2,3-dihydroxybutanoic acid 2-bromo-3-chloro-4-methylhexanoic acid 1,4-cyclohexanedicarboxylic acid 4-hydroxycyclohexanecarboxylic acid Formic acid Acetic acid
Naming Aromatic Carboxylic Acids These are usually named as derivatives of benzoic acid. Generally, the –oic acid or –ic acid suffix is attached to the appropriate prefix. o-bromobenzoic acid
Naming Aromatic Carboxylic Acids Often, the phenyl group is treated as a substituent. 2-phenylethanoic acid4-phenylpentanoic acid
Draw structures for the following. 2,4,6-tribromobenzoic acid 2,2,2-triphenylethanoic acid 3-phenylhexanoic acid 3-phenylcyclohexanecarboxylic acid
Preparation of Carboxylic Acids As discussed in Ch 14, carboxylic acids can be prepared from the oxidation of primary alcohols and/or aldehydes. 1º alcohol Aldehyde Carboxylic acid Examples: a)1-propanol b)2-methylbutanal
Carboxylic acid - ACID Carboxylic acids act as acids because they are proton (H+) donors. They are weak acids that dissociate to form a carboxylate ion and a hydrogen ion as shown: carboxylic acid carboxylate anion hydrogen ion
Acid/Base Reaction Since a carboxylic acid acts as an acid, it will neutralize a strong base like NaOH or KOH to form water and the salt of the carboxylic acid.
Examples Write a balanced equation and name the products that are formed. Acetic acid + sodium hydroxide Benzoic acid + potassium hydroxide
Structure of Esters Esters are carboxylic acid derivatives. They are formed from the reaction of a carboxylic acid with an alcohol.
Formation of an Ester Carboxylic acid alcoholEster Water EXAMPLE Ethanoic acidethanol (Acetic Acid) Ethyl ethanoate (Ethyl acetate) H+, heat
Properties of Esters Mildly polar Have pleasant aromas Found in natural foodstuffs (banana oil, pineapples, raspberries, etc.) Boil at approximately the same temperature as aldehydes or ketones of similar molecular weights Simpler ones are somewhat soluble in water
Naming Esters Use the alkyl portion of the alcohol as the first name. Remove the –ic acid ending of the carboxylic acid and replace it with –ate. The same naming rules apply if the common name of the carboxylic acid is used.