Chem 102 1st Edition Lecture 16 Outline of Last Lecture I. Chapter 16: Lessons 5.1-5.4 : Structure of Carboxylic Acids and Their Derivatives, IUPAC Nomenclature for Carboxylic Acids, Common Names for Carboxylic Acids, Polyfunctional Carboxylic AcidsOutline of Current Lecture II. 5.5 - Physical properties of Carboxylic AcidsIII. 5.6 - Preparation of Carboxylic AcidsIV. 5.7 - Acidity of Carboxylic AcidsV. 5.8 – Uses of Carboxylic Acid SaltsVI. 5.9 – Structure of EstersVII. 5.10 – Preparation of EstersVIII. 5.11 - IUPAC Nomenclature of estersCurrent Lecture5.5 - Physical properties of Carboxylic Acids• Carboxylic acids are most polar organic compounds (both carbonyl (C=O) and hydroxyl (-OH) groups arepolar) • At room temperature and pressure: – Straight chain carboxylic acids with 1-9 carbon atoms are liquids and have strong odors – Straight chain carboxylic acids with >10 C atoms are waxy solids with no odor. • Aromatic and dicarboxylic acids: Odorless solids Melting and Boiling Points • Most polar organic compounds because of the presence of polar C=O and polar -OH groups form H-bonding interactions • Therefore have highest melting and boiling points compared to those of other types of compounds with comparable number of carbon atoms. Hydrogen bonding in carboxylic acids explains the high B.P • A given carboxylic acid molecule can form two hydrogen bonds to another carboxylic acid molecule, producing a “dimer”, a complex with a mass twice that of a single molecule.5.6 - Preparation of Carboxylic Acids• Non-aromatic carboxylic acids: Oxidation of primary alcohols or aldehydes, using an oxidizing agent such as K2Cr2O7 • Aromatic carboxylic acids: Oxidation of a carbon side chain (alkyl group) on a benzene derivative 5.7 - Acidity of Carboxylic Acids• Carboxylic acids are weak acids • In water they dissociate to release protons (H+) and form carboxylate ion (RCOO-) -- in equilibrium situations the equilibrium lies towards the left indicating that small amount of acid is ionized • Monocarboxylic acids release one H+ to form carboxylate ion with one negative charge • Dicarboxylic acids release two H+ ions to form carboxylate ion with two negative charges and so on • Carboxylic acids react with bases to form “Caboxylic Acid Salts” and water – R-COOH + NaOH  R-COO-Na + + H2O • Naming carboxylic acid salts : – Positive ion name (Na+, K+ etc) followed by anion (RCOO-) name (drop “-ic acid” and replace with “-ate”) – Names of anion and cation are written as separate words – Example 1: CH3COO-Na+ -- Sodium acetate – Example 2: C6H5COO-K+ -- Potassium benzoate • Carboxylic acid salts are more soluble in water than their parent acids – Example: Benzoic acid = 3.4 g/L; sodium benzoate = 550g/L 5.8 - Uses of Carboxylic Acid Salts• Good antimicrobial and antifungal agents – Benzoate salts: Effective (0.1%, m/m) against yeast and mold in beverages, jams and jellies, etc. – Potassium sorbate: Inhibits mold and yeast in dairy products, dried fruits, some meat and fish products – Propionate: Used in preservation of baked goods – Benzoate and sorbate can’t be used in yeast leavened baked goods as they inhibit mold and yeast5.9 - Structure of Esters• An ester is a carboxylic acid derivative in which the — OH portion of the carboxyl group has been replaced with an —OR group • The simplest aromatic ester is derived from benzoic acid 5.10 Preparation of Esters• Esters are produced by an esterification reaction • Esterification reaction: Reaction of a carboxylic acid with an alcohol (or phenol) to produce an ester • Esterification reaction require a strong acid catalyst such as H2SO4 • Hydroxy acids contain both a hydroxyl and a carboxyl group and such compounds have the capacity to undergo intramolecular esterification to form cyclic esters • Takes place in situations where a five- or six-membered ring can be formed • Cyclic esters are called lactones 5.11 - IUPAC Nomenclature of estersRule 1: The name for the alkyl (alcohol) part of the ester appears first and is followed by a separate word giving the name for the acyl (acid) part of the ester. Rule 2: The name for the alkyl (alcohol) part of the ester is simply the name of the R group (alkyl, cycloalkyl, or aryl). Rule 3 The name for the acyl (acid) part of the ester is obtained by dropping the “-ic” acid ending for the acid’s name and adding the suffix “-ate.” • IUPAC names for lactones are generated by replacing the “-oic” ending of the parent hydroxycarboxylic acid name with “-olide” and identifying the hydroxyl-bearing carbon by