C HAPTER 14: C ARBOXYLIC A CIDS

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 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

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

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

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

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 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 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)

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

P HYSICAL P ROPERTIES

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

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.

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

A CIDITY

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 S UBSTITUENT E FFECTS ON A CIDITY =>

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

Cha pter 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. =>

S ALTS

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)

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

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)

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.

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.

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)