Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chem 2642 Chapter 19 I. Carboxylic Acids Structure of carboxylic acids A. R – CO- OH B. The carbon of the carbonyl is electron-poor. C. The oxygen of the carbonyl is electron-rich. II. Nomenclature A. IUPAC system 1. The parent name comes by replacing the ending of the longest chain with –oic acid. 2. C-1 is the carbonyl carbon. 3. Examples O Methanoic acid H OH O Hexanoic acid OH 4. If the COOH group is bonded to a ring, the words carboxylic acid are added to the parent ring name. The carbon where the COOH is bonded is C-1. 5. Examples COOH 2-methylcyclohexancarboxylic acid 2 COOH 3,3-dimethylcyclopentanecarboxylic acid B. Common naming system COOH Benzoic acid Formic acid H-COOH Acetic acid CH3-COOH Propionic acid CH3-CH2-COOH Butyric acid CH3-CH2-CH2-COOH Valeric acid CH3-CH2-CH2-CH2-COOH Caproic acid CH3-CH2-CH2-CH2-CH2-COOH 1. The carbon next to the COOH is called the -carbon. 2. Substituents are located using the greek letters , , , , , etc. 3. Examples O ,-dimethylbutyric acid OH O -bromobutyric acid Br OH 3 C. Diacids 1. IUPAC system – replace the ending of the longest chain with –dioic acid 2. Common naming system Oxalic acid HOOC-COOH Malonic acid HOOC-CH2-COOH Succinic acid HOOC-CH2-CH2-COOH Maleic acid HOOC COOH COOH Fumaric acid HOOC D. Carboxylates 1. The structure is R-CO-O- M+ where the metal ion is commonly sodium or potassium 2. The metal name comes first, followed by the carboxylate name 3. The carboxylate name is named by replacing –ic acid with –ate. 4. Examples COO-Na+ Sodium benzoate Sodium acetate CH3COO-Na+ 4 III. Preparation of carboxylic acids A. Oxidation of 1o alcohols with Na2Cr2O7 or CrO3 B. Oxidation of alkyl benzenes that have a benzylic carbon, with KMnO4 COOH KMnO4 heat C. Oxidative cleavage of alkynes using ozone followed by H2O R-CC-R + ozone then H2O 2 R-COOH D. Acid hydrolysis of a nitrile R-CN IV. + H+/H2O R-COOH Reactions of carboxylic acids A. with the bases NaOH, hydride, or methoxide RCOO-Na+ R-COOH + NaOH B. with the acids HCl, H2SO4 or HNO3 OH+ R-COOH + HCl R OH 5 V. Acidity of carboxylic acids A. They are weak acids with pKa ‘s about 5 1. acetic acid has pKa 4.7 2. benzoic acid has pKa 4.2 3. carboxylic acids can be deprotonated using a base that has a conjugate acid with a pKa greater than 5, such as NaOH or NaHCO3 B. Electron withdrawing groups near the COOH group will weaken the OH bond, making the compound more acidic (lower pKa). 1. This is an inductive effect, through the sigma bond system. 2. Inductive effects weaken with distance. 3. Electron withdrawing groups include X, CO, CN, NO2 C. Electron donor groups near the COOH group will strengthen the OH bond, making he compound less acidic (higher pKa). 1. also an inductive effect 2. also weakens with distance 3. groups include R and Z: D. For benzoic acids 1. If put an electronegative group on the meta or para carbon, the compound will be more acidic than benzoic acid 2. If put an electron donor group on the meta or para carbon, the compound will be less acidic than benzoic acid. 3. If put any group on the ortho carbon, the compound will be more acidic than benzoic acid (ortho effect)