8_Carboxylic acids.pdf

Organic Chemistry 8: Carboxylic Acids 1 Chapter Outline 1 Carboxylic Acids 4 Classification of Carboxylic Acids 2 Nomenclature and Sources of Aliphatic Carboxylic Acids 5 Preparation of Carboxylic Acids 3 Physical Properties of Carboxylic Acids 6 Chemical Properties of Carboxylic Acids 2...

Organic Chemistry 8: Carboxylic Acids 1 Chapter Outline 1 Carboxylic Acids 4 Classification of Carboxylic Acids 2 Nomenclature and Sources of Aliphatic Carboxylic Acids 5 Preparation of Carboxylic Acids 3 Physical Properties of Carboxylic Acids 6 Chemical Properties of Carboxylic Acids 2 Carboxylic Acids 3 • The functional group of the carboxylic acid is called a carboxyl group and is represented in the following ways: O or -COOH or CO2H OH 4 Nomenclature and Sources of Aliphatic Carboxylic Acids 5 IUPAC Rules for Naming Carboxylic Acids 1. To establish the parent name, identify the longest carbon chain that includes the carboxyl group. 2. Drop the final –e from the corresponding hydrocarbon name. 3. Add the suffix –oic acid. HCOOH, methanoic acid CH3COOH ethanoic acid CH3CH2COOH propanoic acid 6 Naming Carboxylic Acids • Other groups bonded to the parent chain are numbered and named as we have done previously. 5 4 3 2 1 CH3CH2CHCH2COOH CH3 3-methylpentanoic acid 7 Nomenclature of Carboxylic Acids • Use of Greek letters: 5 4 3 2 1 CH3CH2CH2CH2COOH    CH3CH2CHCOOH OH -hydroxybutyric acid 2-hydroxybutanoic acid 9 Physical Properties of Carboxylic Acids 10 Physical Properties of Carboxylic Acids • Each aliphatic carboxylic acid molecule is polar and consists of a carboxylic acid group and a hydrocarbon group (-R). – Carbons 1-4 = water soluble – Carbons 5-8 = slightly water soluble – Carbons 8 and above = virtually insoluble in water 11 Physical Properties of Carboxylic Acids • The comparatively high boiling points for carboxylic acids are due to intermolecular attractions resulting from hydrogen bonding. O HO R C C OH R O 12 Physical Properties of Carboxylic Acids • Carboxylic acids are generally weak acids; they are only slightly ionized in water. O C H3C O + H2O OH acetic acid C hydronium ion + H3O+ - O H3C acetate ion 13 Classification of Carboxylic Acids 14 Classification of Carboxylic Acids • • • • • • saturated monocarboxylic acids unsaturated carboxylic acids aromatic carboxylic acids dicarboxylic acids hydroxy acids amino acids 15 Unsaturated Carboxylic Acids • An unsaturated acid contains one or more C=C. – Acrylic acid, CH2=CHCOOH, also called propenoic acid. • Even one C=C bond exerts an influence on the physical and chemical properties of the acid. Ex: stearic acid CH3(CH2)16COOH, mp = 70 C vs. oleic acid CH3(CH2)7CH=CH(CH2)7COOH, mp = 16 C 16 Aromatic Carboxylic Acids • In an aromatic carboxylic acid, the carbon of the carboxyl group (-COOH) is bonded directly to a carbon in an aromatic ring. COOH COOH CH3 benzoic acid o-toluic acid 17 18 Continue……. 19 20 Preparation of Carboxylic Acids 21 Preparation of Carboxylic Acids • oxidation of an aldehyde or primary alcohol • oxidation of alkyl groups attached to aromatic rings 22 Oxidation of an Aldehyde or a Primary Alcohol H R C O OH H primary (1o) [O] R C O H + H2O [O] R C OH [O] = Cr2O72- alcohol 23 Oxidation of Alkyl Groups Attached to Aromatic Rings - COO Na+ CH3 NaMnO4 NaOH heat toluene sodium benzoate CH2CH3 - COO Na+ NaMnO4 NaOH heat ethylbenzene + CO2 (g) sodium benzoate 24 Chemical Properties of Carboxylic Acids 25 Chemical Properties of Carboxylic Acids 1. Acid-Base reactions 2. Substitution reactions • • • • acid chlorides acid anhydrides esters amides 26 Acid-Base Reactions • Because of their ability to form hydrogen ions in solution, acids in general have the following properties: 1. Sour taste 2. Change blue litmus to red and affect other suitable indicators. 3. Form water solutions with pH values less than 7. 4. Undergo neutralization reactions with bases to form water and a salt. 27 Acidity of Carboxylic Acids O O C C H3C H3C OH + H2O - H3C O O O C C OH + NaOH H3C + H3O+ O-Na+ + H2O 28 Substitution Reactions • acid chlorides • acid anhydrides • esters • amides 29 Acid Chloride Formation • Thionyl chloride (SOCl2) reacts with carboxylic acids to form acid chlorides. O C R OH carboxylic acid O + SOCl2 thionyl chloride C R + SO2 + HCl Cl acid chloride 30 Acid Anhydride Formation •An organic anhydride is formed by the elimination of water from two molecules of carboxylic acid. O + C R OH HO O O O C C C R' R O + H2O R' anhydride Both acid chloride and acid anhydride react vigorously with alcohols to form esters. 31 Ester Formation • An ester is formed by the reaction of an acid with an alcohol or a phenol; water is also produced in the reaction: O O + C R OH carboxylic acid R' HO alcohol H+ C R R' + H2O O ester 32 33 34 Quiz 35 36