CHEM 30B  Dr. R. Rinehart

Ch. 15  CARBOXYLIC ACIDS AND  ESTERS

 Welcome to the sweet-and-sour land of carboxylic acids, their salts, and their esters: three extremely important classes of compounds.  They play critical roles in industry, food, and biochemistry.  From the infamous “polyester” to flavors and odors to the fats in our diet [and our bodies] to the very core of our metabolism [the Krebs cycle uses 7 different acids]. this time they really are “all around us”.

I.   Carboxylic acids      
           
A.
Structure: contain the carboxyl [hydroxycarbonyl] group  -CO2H  
             B.
NOMENCLATURE:  
   
                     1.      Common names:  see tables below  
                        2. IUPAC names
: The carboxyl group is our highest-priority group.
                                   
a. Locate
longest chain containing the  -CO2H 
                                   
b. The
carboxyl carbon is automatically #1 in the chain
                                   
c. Drop the -e of the stem name and add
-oic  acid 
                                                thus HCO2H, formic acid, is methanoic acid 

                                                and  HO2CCO2H, oxalic acid, is ethanedioic acid                     

             C. Physical properties: See Tables 5.2, p136  & 5.3, p. 137  and  Fig. 5.4, p137

                        <C6  are water-soluble; all dissolve in 5% NaHCO3 ; sharp, penetrating odors.

                 D. CHEMICAL PROPERTIES e
                       
0. 
Preparation: via oxidation of an aldehyde [or primary alcohol]  
                        1.
ACIDITY [well, DUH!]  Yes, folks, they donate protons; much weaker than strong
                 
                 mineral acids  
   
                                             RCO2H + H2O à H3O+ + RCO2- 
                                                   
pKa for an isolated carboxyl group is ~4.7 .
                                        The pKa is strongly influenced by the presence of neighboring groups.
 
                        2.      [as a natural consequence of 1] React with BASES to form organic  SALTS

RCO2H + NaOH à  RCO2- Na+  +  H2O
                     a. Nomenclature:  e.g., sodium acetate

                                    b. properties:  electrolytes, water-soluble 
                                   
c. Long-chain (“
fatty”) acids form soaps

                                    To see an interactive Chime depiction of a lipid [unfortunately, not a soap]
                                    
micelle [assuming you have MDL Chime installed -- the Netscape version will
                                     work better here], go to: 
                                     http://info.bio.cmu.edu/courses/03231/micelles/micelle.htm

                         3. React with ALCOHOLS [an intermolecular dehydration or “condensation”]  to
 
                                    form ESTERS  [see diagram below]; Triglycerides are triple esters of glycerol with
                                     three molecules of long-chain ["fatty"] acids.

                see http://www.molecularmodels.ca/molecule/Esters.htm   
for Dave Woodcock's Chime structures of esters

                                    a. Nomenclature: alkyl alkanoate e.g., ethyl acetate;  
                                   
b. Properties: usually smell nice; water-insoluble; good solvents for other organics 
                                   
c. Reactions:
hydrolysis with acid or with base [saponification”]

                      4. [just in case life wasn’t complex enough]

                                        ALCOHOLS + HYDROXY INORGANIC ACIDS [boric, nitric, sulfuric, phosphoric]  yield INORGANIC ESTERS;  Especially important for PHOSPHORIC ACID H3PO4

           

                                  5. Activated Derivatives of carboxylic acids:

`                                   a. Anhydrides            

                                    b. Acyl chlorides        

                                    c. THIOESTERS: very important in living systems      

                                                

         Coenzyme A [usually abbreviated as "CoA"], shown above, is a crucial component in the metabolism of carboxylic acids. The  thiol [sulfhydryl] group, where the thioester link is formed, is the "business end" of the molecule seen here at its right side. The remainder of the molecule serves to specifically bind to the enzymes . Acetyl-CoA is the main entry point into the Krebs cycle for carbon from carbohydrates and fats. Succinyl-CoA is an intermediate of the Krebs cycle. Fatty acyl-CoA is the form in which fatty acids are actually broken down to give acetyl-CoA.  Malonyl-CoA is used in the biosynthesis of fatty acids.

Tables of carboxylic acids are below:

You can see Dave Woodcock’s Chime structures of carboxylic acids at:
http://www.molecularmodels.ca/molecule/Acids_(organic).htm
 
PowerPoint-type presentation of oxygen-containing functional groups [aldehydes, ketones, carboxylic acids, esters, etc.]
by Warren Gallagher at U Wisconsin Eau Claire are viewable [with Acrobat Reader] at:
http://www.chem.uwec.edu/Chem150_S06/Pages/lecture-materials.html  > Lecture 5 
and bookmark the site for future reference

# of C

formula

IUPAC name

Common name

source

1

HCO2H

methanoic acid

formic acid

ants

2

CH3CO2H

ethanoic acid

acetic acid

vinegar

3

CH3CH2CO2H

propanoic acid

propionic acid

cheese

4

CH3(CH2)2CO2H

butanoic acid

butyric acid

butter

5

CH3(CH2)3CO2H

pentanoic acid

valeric acid

?

6

CH3(CH2)4CO2H

hexanoic acid

caproic acid

goats

7

CH3(CH2)5CO2H

heptanoic acid

enanthic acid

wine

8

CH3(CH2)6CO2H

octanoic acid

caprylic acid

goats

9

CH3(CH2)7CO2H

nonanoic acid

pelargonic acid

geranium oil

10

CH3(CH2)8CO2H

decanoic acid

capric acid

goats

12

CH3(CH2)10CO2H

dodecanoic acid

lauric acid

coconut oil

14

CH3(CH2)12CO2H

tetradecanoic acid

myristic acid

nutmeg

16

CH3(CH2)14CO2H

hexadecanoic acid

palmitic acid

palm oil

18

CH3(CH2)16CO2H

octadecanoic acid

stearic acid

beef tallow

20

CH3(CH2)18CO2H

eicosanoic acid

arachidic acid

peanut oil

7

C6H5CO2H

benzenecarboxylic acid

benzoic acid

Na salt is preservative

11

C10H7CO2H

naphthalenecarboxylic acid

xxx

xx

# of C

Unsaturated acids

IUPAC name

Common name

Source/use

16

cis-D9 C15H29CO2H

cis-9-hexadecenoic acid

palmitoleic acid

 

18

cis-D9 C17H33CO2H

cis-9-octadecenoic acid

oleic acid

olives, pigs, man

18

D9,12 C17H31CO2H

You name it!

linoleic acid

linseed oil

18

D9,12,15 C17H29CO2H

You name it!

g-linolenic acid

linseed oil

20

D5,8,11,14C19H31CO2H

You name it!

arachidonic acid

make PG’s, TX’s, LT’s

20

D5,8,11,14,17

eicosapentaenoic acid

EPA

(w-3) fatty acid

22

D5,8,11,14,17,19

docosahexenoic acid

DHA

(w-3) fatty acid

# of C

Dicarboxylic acids

IUPAC name

Common name

Source/use

2

HO2CCO2H

ethanedioic acid

oxalic acid

rhubarb; removes rust

3

HO2CCH2CO2H

propanedioic acid

malonic acid

in synthesis

4

HO2C(CH2)2CO2H

butanedioic acid

succinic acid

Krebs cycle

5

HO2C(CH2)3CO2H

pentanedioic acid

glutaric acid

 

6

HO2C(CH2)4CO2H

hexanedioic acid

adipic acid

make Nylon  6-6

7

HO2C(CH2)5CO2H

heptanedioic acid

pimelic acid

 

8

HO2C(CH2)6CO2H

octanedioic acid

suberic acid

 

9

HO2C(CH2)7CO2H

nonanedioic acid

azelaic acid

treat skin problems

10

HO2C(CH2)8CO2H

decanedioic acid

sebacic acid

make Nylon 10-x

 

© Ronald W. Rinehart 2002-2006  Structures drawn with CS ChemDraw and MDL ISISDraw

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