1. Chemistry

2. Carboxylic Acids Session - 2

3. Session Objectives 1.Introduction to carboxylic acids 2.Physical properties and structure 3.General method of preparation By oxidation Carbonation of grignard reagent Hydrolysis of acid derivatives From nitriles 4.Reactions of the carboxylic acids

4. Introduction The functional group of carboxylic acids consists of a C=O with -OH bonded to the same carbon. Carboxyl group is usually written -COOH. Aliphatic acids have an alkyl group bonded to -COOH. Aromatic acids have an aryl group. Fatty acids are long-chain aliphatic acids.

5. Common Names -chlorobutyric acid-phenylcaproic acid => Many aliphatic acids have historical names. Positions of substituents on the chain are labeled with Greek letters.

6. IUPAC Names 2-chlorobutanoic acid trans-3-phenyl-2-propenoic acid (cinnamic acid) Remove -e from alkane (or alkene) name, add -oic acid. The carbon of the carboxyl group is #1.

7. Naming Cyclic Acids 2-isopropylcyclopentanecarboxylic acid o-hydroxybenzoic acid (salicylic acid) Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids. Aromatic acids are named as benzoic acids.

8. Dicarboxylic Acids Aliphatic diacids are usually called by their common names (to be memorized). For IUPAC name, number the chain from the end closest to a substituent. Two carboxyl groups on a benzene ring indicate a phthalic acid. 3-bromohexanedioic acid -bromoadipic acid

9. Structure of Carboxyl Carbon is sp 2 hybridized. Bond angles are close to 120. O-H eclipsed with C=O, to get overlap of  orbital with orbital of lone pair on oxygen.

10. Boiling Points Acetic acid, b.p. 118  C Higher boiling points than similar alcohols, due to dimer formation.

11. Melting Points Aliphatic acids with more than 8 carbons are solids at room temperature. Double bonds (especially cis) lower the melting point. Note these 18-C acids: Stearic acid (saturated): 72C Oleic acid (one cis double bond): 16C Linoleic acid (two cis double bonds): -5C

12. Solubility  Water solubility decreases with the length of the carbon chain.  Up to 4 carbons, acid is miscible in water.  More soluble in alcohol.  Also soluble in relatively nonpolar solvents like chloroform because it dissolves as a dimer.

13. Acidity

14. Resonance Stabilization

15. Substituent Effects on Acidity pK a = 4.46pK a = 4.19pK a = 3.47pK a = 3.41pK a = 2.16

16.  Oxidation of Primary Alcohols  Oxidation of Aldehydes  Oxidation of Substituted Aromatics  Carbonation of Grignard reagents  Hydrolysis of Acid derivatives and Nitriles  Haloform reaction  Periodic acid Cleavage of Vicinal Dials/Diketones  Oxidative Cleavage of Alkenes/Alkynes Preparation Reactions

17. Carboxylic Acids via Oxidation From Primary Alcohols From Aldehydes From Substituted Aromatics

18. Oxidative Cleavage Reactions  Alkene Cleavage  Hot Potassium Permanganate  Alkyne Cleavage  Hot Potassium Permanganate  Ozonolysis

19. Grignard Synthesis Grignard reagent + CO 2 yields a carboxylate salt.

20. Hydrolysis of acid derivatives

21. Hydrolysis of Nitriles Basic or acidic hydrolysis of a nitrile produces a carboxylic acid.

22. Haloform Reaction Cleavage of methyl carbinols Cleavage of methyl carbonyls

23. Periodic Acid Cleavage of Vicinal Dials/Diketones

24. Reduction of Carboxylic Acids  Lithium Aluminum Hydride reduction  Diborane reduction

25. Conversion to acid derivatives The group bonded to the acyl carbon determines the class of compound: -OH, carboxylic acid -Cl, acid chloride -OR’, ester -NH 2, amide These interconvert via nucleophilic acyl substitution.

26. Fischer Esterification Acid + alcohol yields ester + water. Acid catalyzed for weak nucleophile. All steps are reversible. Reaction reaches equilibrium.

27. Conversion to Acid Chlorides An activated form of the carboxylic acid. Chloride is a good leaving group, so undergoes acyl substitution easily. To synthesize acid chlorides use thionyl chloride or oxalyl chloride with the acid.

28. Conversion to Amides Amine (base) removes a proton from the carboxylic acid to form a salt. Heating the salt above 100C drives off steam and forms the amide.

29. Reduction to 1 Alcohols Use strong reducing agent, LiAlH 4. Borane, BH 3 in THF, reduces carboxylic acid to alcohol, but does not reduce ketone.

30. Decarboxylation of RCOOH  Thermolysis of beta-diacids  Thermolysis of beta-keto acids

31. Substitution in the hydrocarbon part Acids having an -hydrogen are halogenated at the -position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give -halocarboxylic acids. Hell-Volhard-Zelinsky reaction

32. Ring substitution in aromatic acids —COOH group is deactivating and meta directing. Aromatic carboxylic acids do not undergo Friedel-Crafts reaction. Nitration Bromination

33. Some commercially important carboxylic acids Methanoic acid; (HCOOH) It is colourles, pungent smelling liquid. It is powerful reducing agent. It reduces Tollen’s reagent and Fehling solution. Used in rubber, textile, dyeing, leather and electroplating industries.

34. Ethanoic acid(acitic acid, CH 3 COOH) Main constituent of vinegar and is obtained by fermentation of molasses in presence of air. Industrially, it is obtained in pure form by oxidation of ethanal with air in the presence of cobalt acetate catalyst or by carbonylation of methanol in the presence of rhodium catalyst. CH 3 CHO + CO  CH 3 COOH CH 3 OH + CO  CH 3 COOH Colourless liquid with pungent odour. Freezes at 289 K forming ice like crystal. Water free acetic acid, obtained by melting of the crystals is called glacial acetic acid.

35. Thank you