1 / 44

Chapter 3

Chapter 3. Carboxylic Acids. Carboxylic Acids. 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.

lucio
Download Presentation

Chapter 3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 3 Carboxylic Acids

  2. Carboxylic Acids • 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. => Chapter 20

  3. Carboxylic Acids Carboxylic acid, compounds of the type RCOOH such as Acetic acid ( present in vinegar), Malonic acid and Benzoic Acid.

  4. Common Names 1-Carboxylic Acid Nomenclature • Many aliphatic acids have historical names. • Positions of substituents on the chain are labeled with Greek letters.

  5. special names

  6. trans-3-phenyl-2-propenoic acid (cinnamic acid) => IUPAC Names • Remove -e from alkane (or alkene) name, add -oic acid. • The carbon of the carboxyl group is #1. 2-chlorobutanoic acid Chapter 20

  7. parent chain = longest, continuous carbon chain that contains the carboxyl group  alkane, drop –e, add –oic acid HCOOH methanoic acid CH3CO2H ethanoic acid CH3CH2CO2H propanoic acid CH3 CH3CHCOOH 2-methylpropanoic acid Br CH3CH2CHCO2H 2-bromobutanoic acid

  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. dicarboxylic acids: HOOC-COOH oxalic acid HO2C-CH2-CO2H malonic acid HO2C-CH2CH2-CO2H succinic acid HO2C-CH2CH2CH2-CO2H glutaric acid HOOC-(CH2)4-COOH adipic acid HOOC-(CH2)5-COOH pimelic acid

  10. Naming Cyclic Acids • Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids. • Aromatic acids are named as benzoic acids. o-hydroxybenzoicacid (salicylic acid) => 2-isopropylcyclopentanecarboxylicacid Chapter 20

  11. 2-Physical properties 1- Boiling point Intermolecular forces, especially hydrogen bonding, are stronger in carboxylic acids than in other compounds of similar shape and molecular weight.

  12. Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.

  13. H O O H H3CC H O H O H 2-Solubility in Water • Carboxylic acids are similar to alcohols in respect to their solubility in water • Form hydrogen bonds to water

  14. 3-Acidity of carboxylic acids • Most carboxylic acids have a pKa close to 5. • Carboxylic acids are weak acids but carboxylic acids are far more acidic than alcohols.

  15. The greater difference in ionization energy (∆ G) of ethanol and acetic acid reflects a greater stabilization of acetate ion relative to ethoxide ion.

  16. Greater acidity of carboxylic acids is attributedstabilization of carboxylate ion by inductive effect of carbonyl group And by resonance stabilization of carboxylate ion.

  17. Salts of Carboxylic Acids

  18. salts of carboxylic acids: name of cation + name of acid: drop –ic acid, add –ate CH3CO2Na sodium acetate or sodium ethanoate CH3CH2CH2CO2NH4 ammonium butyrate ammonium butanoate (CH3CH2COO)2Mg magnesium propionate magnesium propanoate

  19. 4-Substituent and acid strength Alkyl substituents have negligible effect

  20. Electronegative substituents increase acidity

  21. Electronegative substituents withdraw electrons from carboxyl group; increase K for loss of H+

  22. Effect of substituent decreases the acidity as number of bonds between X and carboxyl group increases.

  23. Substituent Effects on Acidity pKa = 4.46 pKa = 3.47 pKa = 3.41 pKa = 2.16 pKa = 4.19

  24. Ionization of Substituted Benzoic Acids Hybridization Effect sp2-hybridized carbon is more electron-withdrawing than sp3, and sp is more electron-withdrawing than sp2

  25. Effect is small unless X is electronegative; effect is largest for ortho substituent

  26. 5-Synthesis of carboxylic acids 1- Oxidation of alkylbenzene

  27. 2- Oxidation of primary alcohols

  28. 3- Oxidation of aldehydes

  29. 4-Carboxylation of Grignard reagents

  30. 5- Hydroylsis of nitriles

  31. 6- Reactions of Carboxylic acids 1- Formation of Acyl chlorides

  32. 2-Lithium aluminium hydride reduction

  33. 3-Esterification

  34. Mechanism of Esterification

  35. Intramolecular ester formation (Lactones)

  36. 4-α-Halogenation This reaction of α- bormination of carboxylic acid is called Hell- Volhard- Zelinasky reaction

  37. 5- Decarboxylation of carboxylic acids

More Related