1. C HAPTER 14: C ARBOXYLIC A CIDS

2. 2 I NTRODUCTION 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. Fatty acids are long-chain aliphatic acids Aromatic acids have an aryl group bonded to - COOH.

3. 3 C OMMON N AMES Many aliphatic acids have historical names. Positions of substituents on the chain are labeled with Greek letters.  -chlorobutyric acid  -phenylcaproic acid

4. N OMENCLATURE Common names you need to know: Formic acid (methanoic acid) Acetic Acid (ethanoic acid) Benzoic Acid

5. Propionic Acid (propanoic acid) Butyric acid (butanoic acid) Valeric acid (pentanoic acid)

7. 7 IUPAC N AMES Remove - e from alkane (or alkene) name, add - oic acid. The carbon of the carboxyl group is #1. 2-chlorobutanoic acid trans-3-phenyl-2-propenoic acid

8. Nomenclature For acyclic acid chlorides: change the suffix –ic acid of the parent carboxylic acid to the suffix –yl chloride; or When the –COCl group is bonded to a ring: change the suffix – carboxylic acid to –carbonyl chloride.

9. 9 N AMING C YCLIC A CIDS Cycloalkanes bonded to -COOH are named as cycloalkanecarboxylic acids. Aromatic acids are named as benzoic acids. 2- isopropylcyclopentanecarboxylic acid o- hydroxybenzoic acid

10. 10 D ICARBOXYLIC A CIDS Aliphatic diacids are usually called by their common names. 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 (common)

11. S TRUCTURE OF C ARBOXYL 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.

12. 12 B OILING P OINTS Higher boiling points than similar alcohols, due to dimer formation. Acetic acid, b.p. 118  C

13. P HYSICAL P ROPERTIES

14. 14 M ELTING P OINTS 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

15. S OLUBILITY 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.

16. A CIDITY They are weak acids. The Ka value for most unsubsituted aliphatic and aromatic carboxylic acids fall within the range from 10 -4 to 10 -5. Recall small pKa stronger acid large pKa waker acid Ka are related as such pKa= -log(Ka) pka+pKb=14

17. A CIDITY

18. Substitution of the alpha-carbon of an atom or a group of atoms of higher electronegativity than carbon increases the acidity of carboxylic acid. The inductive effect of an electronegative atom

22. 22 S UBSTITUENT E FFECTS ON A CIDITY =>

23. 23 S UBSTITUENT E FFECTS ON A CIDITY pK a = 4.46pK a = 4.19pK a = 3.47pK a = 3.41pK a = 2.16 =>

24. Cha pter 20 24 S ALTS OF C ARBOXYLIC A CIDS Sodium hydroxide removes a proton to form the salt. Adding a strong acid, like HCl, regenerates the carboxylic acid. =>

25. S ALTS

26. 26 N AMING A CID S ALTS Name the cation. Then name the anion by replacing the -ic acid with -ate. potassium  -chlorovalerate (common) potassium 3-chloropentanoate (IUPAC)

27. C OMPLETE R EACTIONS AND N AME THE SALTS A) Butanoic Acid + Sodium Hydroxide B) 2-hydroxypropanoic (lactic acid) acid + sodium bicarbonate

28. A) B) COOH + NaOH COONa +H 2 O Butanoic Sodium Sodium Water Acid Hydroxide Butanoate COOH + NaHCO 3 + H 2 O +CO 2 OH COONa 2-Hydroxypropanoic Sodium Sodium 2-hydroxypropanoate Acid Bicarbonate(sodium lactate, common) (Lactic Acid COMMON)

29. R EDUCTION OF C ARBOXYL GROUP TO 1  A LCOHOLS Use strong reducing agent, LiAlH 4 (Lithium Aluminum Hydride) And either diethyl ether or Tetrahydrofuran (THF) as solvents; it reduces carboxylic acid to alcohol, but does not reduce it to a ketone.

30. F ISCHER E STERIFICATION After the German Chemist Emil Fischer Carboxylic Acid (strong acid as a catalyst) + alcohol yields ester + water. All steps are reversible. Reaction reaches equilibrium.

31. A CID C HLORIDES The functional group of an acid halide is a carbonyl bonded to a halogen atom Acid chlorides are the most frequently used in lab and in industrial organic chemistry. The most common way to synthesize acid chlorides is to treat a carboxylic acid with thionyl chloride (SOCl 2 ) or oxalyl chloride with the acid. (Oxalyl Chloride)