carboxylic acids since the carboxyl group is polar, carboxylic acids contain dipole-dipole forces,...

CARBOXYLIC ACIDS

• Since the carboxyl group is polar, carboxylic acids contain dipole-dipole forces, London forces and are able to hydrogen bond.

• Therefore carboxylic acids will have high melting and boiling points and will be soluble in water.

• Contain the carboxyl functional group

C

O

OH

NAMING CARBOXYLIC ACIDS

1. Identify the longest chain containing the carboxyl group, remove the “e” and add “oic acid”.

Examples

C

O

HO

methanoic acid

C

H3C

O

OH

ethanoic acid

H

Naming Carboxylic Acids

• Any substituents are numbered using the lowest sum.

• The carboxyl carbon is always C-1 on a chain, so no locator number is needed. Carboxylic acids rank over aldehydes, ketones, alcohols, alkenes and alkynes

Examples:O

OH

O

OH

COOH O

OH

propanoic acid

benzoic acid

2-ethylhexanoic acid pent-3-enoic acid

O OH

O

O OH

O

OH

5-oxo-2-propylhexanoic acid

2-(3-hydroxypropyl)hexanedioic acid

Multiple Carboxyl Groups

• When naming multiple carboxyl groups, the suffix –dioic acid is used for acids with a carboxyl group at each end of the parent chain.

• Note that the full alkyl name is used (the ‘e’ is not dropped)

Examples:

O O

HO OH

O OHO

OH

propanedioic acid

2-ethyl-5-methylhexanedioic acid

Ring StructuresKeep the “e” and add suffix “carboxylic acid”.

O

OH

O

OH

OOH

cyclohexanecarboxylic acid

cyclohexanedicarboxylic acid

Expanded Molecular FormulasCarboxyl group is represented by COOH

O

OH

HOOCCH2CH2CH2CH3

COMMON ORGANIC ACIDS

C

O

HO

formic acidmethanoic acid

(ant sting)

H

C

H3C

O

OH

acetic acidethanoic acid

(vinegar 3-4 % solution)

O

OH

butyric acidbutanoic acid(rancid butter)

HO

O

OH

lactic acid2-hydroxypropanoic acid

(causes muscle cramps due to O2 debt)

Making Carboxylic Acids: An Oxidation Reaction

aldehyde + water carboxylic acidKMnO4

H2Cr2O7

C C

O

ethanal

HH

H

H

+ H2OKMnO4

H2Cr2O7C C

O

HHO

H

H

ethanoic acid(acetic acid)

+ 2H+

What is an ester?

R

C

O

R'

O

• Made from an alcohol and a carboxylic acid.

Making an Ester

carboxylic acid + alcohol ester + waterH2SO4

C

O

OH

ethanoic acid(acetic acid)

+ + H2OCH

H

O

HC

H

H

H

C

O

C

H

H

H

C

H

H

H

O

methanol methylethanoate(methylacetate)

H2SO4/

H

NAMING• An ester has two parts – the part that comes from the alcohol

and the part that comes from the carboxylic acid

• Convert the suffix “(a)nol” ending of the alcohol to ‘yl’

• Convert the ‘oic acid’ ending of the carboxylic acid to “oate”

i.e. “alkyl oate”

• Note the space between the alkyl and oate names

CH2CH3

C

O

H3C

O

methyl propanoate

alcohol Carboxylic acid

Side Chains on the Alcohol Side• The carbon atoms that are attached to an oxygen atom

are assigned as C-1 (this means that you are numbering atoms from the middle of the molecule)

HH

C

H3

C 3

CO

C

O

H3

C

12

1-methylethyl ethanoate

(isopropyl ethanoate)

• If there is a side chain attached to the alcohol part, then the side chain names are attached to the ‘akyl’ part of the ester name

12

Side Chains on the Acid Side

• It there are side chains attached to the carboxylic acid part, then the side chain names are attached to the ‘oate’ part of the ester name

HH

C CC

OC

O

H3

HC

HC3

3 ethyl 2-methylpropanoate12

32

Side Chains Everywhere!

HH

C CC

OC

O

H3

HC

HC3

3

HC3

HC3

12

3

41

2

1-methylethyl 2-methylbutanoate

More Reactions of Esters

Hydrolysis (breaking down an ester)

ester + excess water alcohol + carboxylic acid

CO

HOethanoic acid(acetic acid)

++ H2O

H2SO4/

C H

H

O

H CH

HH

CO

CH

HH

CH

HH

O

methanolmethylethanoate(methylacetate)

H2SO4/

H

Waxes• Waxes are mixtures of esters having carbon

chains in the range of 16 to 34 carbons on each side of the ester linkage.

H3C(H2C)7

CO

(CH2)29CH3

O

Example

Beeswax

• Since the hydrocarbon chains are so long, waxes are very water repellant.

• Biological Importance: fruit, leaves, insects

Fats and Oils• Fats and oils are triesters of glycerol that contain at least one fatty acid.• Fatty acids are carboxylic acids that contain 14-18 carbons and having varying degrees of

unsaturation

H C C

H

C

OH

glycerol1,2,3-propanetriol

OH

HH

H

OH

stearic acid

CH3(CH2)15 C

O

OH

glycerol + 1 fatty acid --> monoglyceride + water

glycerol + 2 fatty acids --> diglyceride + water

glycerol + 3 fatty acids --> triglyceride + water

Salicylates

• Contain salicylic acid.• Most common is acetyl salicyclic acid “ASA”

(AKA aspirin) which is used for pain relief and as an antiseptic.

HO

O

HO

salicylic acid

O

OHO

acetyl salicylic acidASA

O

OH

Odours of Selected Esters• Esters occur naturally in many plants and

are responsible for the odours of fruits and flowers. Synthetic esters are often added as flavourings to processed foods, and as scents to cosmetics and perfumes.