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Carboxylic Acids

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A poem by Ogden NashThe ant has made himself illustrious

Through constant industry industriousSo what?

Would you be calm and placid

If you were full of formic acid?

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• The functional group of the carboxylic acid is called a carboxyl group and is represented in the following ways:

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Nomenclature and Sources of Aliphatic

Carboxylic Acids

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IUPAC Rules for Naming Carboxylic Acids1. To establish the parent name, identify the

longest carbon chain that includes the carboxyl group.

2. Drop the final –e from the corresponding hydrocarbon name.

3. Add the suffix –oic acid.

HCOOH, methanoic acid

CH3COOH ethanoic acid

CH3CH2COOH propanoic acid

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Naming Carboxylic Acids

• Other groups bonded to the parent chain are numbered and named as we have done previously.

CH3CH2CHCH2COOH

CH3

12345

3-methylpentanoic acid

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Common Names for Acids

• HCOOH Formic Formica (ant)

• CH3COOH Acetic Acetum (sour)

• CH3CH2COOH Propionic Pro (first) + Pion (fat)

• CH3(CH2)2COOH Butyric Butyrum (butter)

• CH3(CH2)3COOH Valeric Valere (strong)

• CH3(CH2)4COOH Caproic Caper (goat)

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Common Names for Acids

• CH3(CH2)6COOH Caprylic Caper (goat)

• CH3(CH2)8COOH Capric Caper (goat)

• CH3(CH2)10COOH Lauric Laurel

• CH3(CH2)12COOH Myristic Muron (perfume)

• CH3(CH2)14COOH Palmitic Palm Oil

• CH3(CH2)16COOH Stearic Stear (solid fat)

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Nomenclature of Carboxylic Acids

• Use of Greek letters:

CH3CH2CH2CH2COOH12345

CH3CH2CHCOOH

OH

-hydroxybutyric acid2-hydroxybutanoic acid

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Physical Properties of Carboxylic Acids

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Physical Properties of Carboxylic Acids

• Each aliphatic carboxylic acid molecule is polar and consists of a carboxylic acid group and a hydrocarbon group (-R).– Carbons 1-4 = water soluble– Carbons 5-8 = slightly water soluble– Carbons 8 and above = virtually insoluble in water

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Physical Properties of Carboxylic Acids

• The comparatively high boiling points for carboxylic acids are due to intermolecular attractions resulting from hydrogen bonding.

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Physical Properties of Carboxylic Acids

• Carboxylic acids are generally weak acids; that is, they are only slightly ionized in water.

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Classification of Carboxylic AcidsClassification of Carboxylic Acids

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Types of Carboxylic Acids

There are five major types of carboxylic acids in addition to the saturated monocarboxylic acids like acetic acid (CH3COOH ).

These acids are summarized and discussed in this section.

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Types of Carboxylic Acids

HOOCCH2COOH

An Unsaturated Acid (oleic acid)

An Aromatic Acid (benzoic acid )

A Hydroxy Acid ( lactic acid)

A Dicarboxylic Acid ( malonic acid)

General Formula of an Amino Acid

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Unsaturated Carboxylic Acids

• An unsaturated acid contains one or more C=C. – Acrylic acid, CH2=CHCOOH, also called propenoic

acid.

• Even one C=C bond exerts an influence on the physical and chemical properties of the acid.

Ex: stearic acid CH3(CH2)16COOH, mp = 70 ºC vs.

oleic acid CH3(CH2)7CH=CH(CH2)7COOH, mp = 16 ºC

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Aromatic Carboxylic Acids• In an aromatic carboxylic acid, the carbon

of the carboxyl group (-COOH) is bonded directly to a carbon in an aromatic ring.

COOHCOOH

CH3

benzoic acid o-toluic acid

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Dicarboxylic Acids

Dicarboxylic acids have two carboxyl (COOH) groups.

These acids undergo a decarboxylation reaction ( i.e.loss of

CO2 ) to form a monocarboxylic acid or an anhydride

as shown below.

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Citric acid is a hydroxytricarboxylic acid. It is 5-8% oflemon juice and widely distributed in plant and animal tissues. It is also an important acid in the citric acid cycle. Examples of other dicarboxylic acids are listed in Table 24.2.

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Hydroxy Acids• Hydroxy acids have the functional group

of an alcohol and a carboxylic acid.

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Hydroxy AcidsMalic acid and tartaric acid are two other common

-hydroxy acids found in apples and grapes respectively.

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Amino Acids• Each amino acid molecule has a carboxyl

group that acts as an acid and an amino group that acts as a base.

• About 20 biologically important amino acids, each with a different group represented by R, are found in nature.

NH2CHCOOH

RThe R group does not necessarily represent an alkyl group in amino acids.

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Preparation of Carboxylic Acids

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Preparation of Carboxylic Acids

• oxidation of an aldehyde or primary alcohol

• oxidation of alkyl groups attached to aromatic rings

• hydrolysis of nitriles

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Oxidation of an Aldehyde or a Primary Alcohol

H

CR

Hprimary (1o)

alcohol

OH[O]

O

CR H + H2O[O]

O

CR OH

[O] = Cr2O72-

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Oxidation of Alkyl Groups Attached to an

Aromatic RingAlkyl benzenes are oxidized in basic solution to the carboxylate salt and then protonated with acid to formbenzoic acid.

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Hydrolysis of Nitriles

• RCN + 2 H2O RCOOH + NH4+

H+

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Chemical Properties of Carboxylic Acids

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Chemical Properties of Carboxylic Acids

1. Acid-Base reactions

2. Substitution reactions• acid chlorides

• acid anhydrides

• esters

• amides

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Acid-Base Reactions• Because of their ability to form hydrogen

ions in solution, acids in general have the following properties:

1. Sour taste2. Change blue litmus to red and affect other

suitable indicators.3. Form water solutions with pH values less than

7.4. Undergo neutralization reactions with bases for

form water and a salt.

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Acidity of Carboxylic Acids

H3C

C

O

OH + H2O H3C

C

O

O- + H3O+

H3C

C

O

OH + NaOH H3C

C

O

O-Na+ + H2O

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Substitution Reactions

• acid chlorides

• acid anhydrides

• esters

• amides

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Acid Chloride Formation

Acid chlorides are prepared by reacting thionyl chloride (SOCl2) and a carboxylic acid.

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Reactivity of Acid Chlorides

Acid chlorides are very reactive and will hydrolyze back to the carboxylic acid if exposed to moisture.

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Acid Anhydride Formation•An organic anhydride is formed by the elimination of water from two molecules of carboxylic acid.

RC

OH

O

R'C

HO

O

+

RC

O

O

R'C

O

+ H2O

anhydride

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Ester Formation• An ester is formed by the reaction of an

acid with an alcohol or a phenol; water is also produced in the reaction:

RC

OH

O

R'HO

+

RC

O

O

R'+ H2OH+

carboxylicacid

alcohol ester

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Nomenclature of Esters

Nomenclature of Esters

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Nomenclature of Esters• The alcohol part is named first, followed

by the name of the acid modified to end in –ate.

RC

O

O

R'

acid alcohol

H3CC

O

O

CH3

ethanoateoracetate

methyl

methyl ethanoate ormethyl acetate

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Occurrence and Physical Properties

of Esters

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Properties of Esters• Simple esters derived from monocarboxylic

acids and monohydroxy alcohols are colorless, generally nonpolar liquids or solids.

• Low- and intermediate-molar-mass esters (both acids and alcohols up to about 10 carbons) are liquid with characteristic (usually fragrant or fruity) odors.

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Occurrence and Properties of Esters

• High-molar-mass esters (formed from acids or alcohols of 16 or more carbons) are waxes and are obtained from various plants.– They are used in furniture wax and automobile

wax preparations.– Carnauba wax contains esters of 24-and 28-

carbon fatty acids and 32- and 34-carbon alcohols.

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Chemical Properties of

Esters

Chemical Properties of

Esters

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Hydrolysis

• The most important reaction of esters is hydrolysis – the splitting of molecules through the addition of water.

• A catalyst is often required.– An acid or base– In living systems, enzymes act as catalysts.

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Acid Hydrolysis

• The hydrolysis of an ester involves the reaction with water to form a carboxylic acid and an alcohol.

RC

HO

O

R'OH

+

RC

O

O

R' + H2OH+

carboxylicacid

alcoholester

or enzyme

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Alkaline Hydrolysis (Saponification)• Saponification is the hydrolysis of an ester by a

strong base (NaOH or KOH) to produce an alcohol and a salt (or soap if the salt formed is from a high-molar-mass acid).

• Notice that in saponification, the base is a reactant and not a catalyst.

O-Na+C

R

O

R'OH

+

RC

O

O

R'+ NaOH H2O

saltalcoholester

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Glycerol EstersGlycerol Esters

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Fats and Oils• Fats and oils are esters of glycerol and

predominantly long-chain fatty acids.

• Fats and oils are also called triacylglycerols or triglycerides, since each molecule is derived from one molecule of glycerol and three molecules of fatty acid:

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H C O

C OH

C OH

H

H

C R

O

C R'

O

C R"

O

General formula for a triacylglycerol

glycerolportion

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TriacylglycerolThe structural formulas of triacylglycerol molecules differ because:

1. The length of the fatty acid chain varies from 4 to 20 carbons, but the number of carbon atoms in the chain is nearly always even.

2. Each fatty acid may be saturated or unsaturated and may contain one, two, or three C=C.

3. A triacylglycerol may, and frequently does, contain three different fatty acids.

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• The most abundant unsaturated acids in fats and oils contain 18 carbon atoms.

• In all of these naturally occurring unsaturated acids, the configuration about C=C is cis.

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Physical Differences Between Fats & Oils

• Fats are solid; oils are liquid at room temperature

• Fats contain a larger portion of saturated fatty acids whereas oils contain greater amounts of unsaturated fatty acids.– Polyunsaturated means that each molecule of

fat contains several C=C.

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Comparison of Fats & Oils

• Fats come from animal sources:

–Lard from hogs, tallow from cattle and sheep

• Oils come from vegetable sources:

–Olives, corn, peanut, soybean, canola

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Hydrogenation of Glycerides

• Hydrogen adds to the C=C of oil to saturate it and form fats:

• H2 + -CH=CH- -CH2-CH2-

• In practice, only some of the C=C are allowed to become saturated.– Partial hydrogenation

Ni

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Hydrogenolysis

• Triacylglycerols can be split and reduced in a reaction called hydrogenolysis (splitting by hydrogen).

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Hydrolysis

• Triacylglycerols can be hydrolyzed, yielding fatty acids and glycerol.

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Saponification

• The saponification of a fat or oil involves the alkaline hydrolysis of a triester.

• The products formed are glycerol and the alkali metal salts of fatty acids, which are called soaps.

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Soaps and Synthetic Detergents

Soaps and Synthetic Detergents

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Soaps and Synthetic Detergents

• In the broadest sense possible, a detergent is simply a cleansing agent.

• A soap is distinguished from a synthetic detergent (syndet) on the basis of chemical composition and not on the basis of function or usage.

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Soaps• Salts of long-chained fatty acids are

called soaps.

• Fat or oil + NaOH Soap + Glycerol

66Cleansing action of soap.

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Synthetic Detergents - AnionicThe one great advantage these synthetic detergents have over soap is that their Ca+2, Mg+2, and Fe+3 salts, as well as their Na+1 salts, are soluble in water. Therefore, they are nearly as effective in hard water as in soft water.

OSO3-Na+

sodium lauryl sulfate

nonpolar hydrophobic end,grease soluble

polar hydrophilic end,water soluble

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Synthetic Detergents – Nonionic• The molecule of a nonionic detergent contains a

grease-soluble component and a water soluble component.

• Some of these substances are especially useful in automatic washing machines because they have good detergent, but low sudsing, properties.

CH3(CH2)10CH2-O-(CH2CH2O)7-CH2CH2OH

grease soluble,hydrophobic water soluble, hydrophilic

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Biodegradability

Biodegradable organic substances are those that can be

readily decomposed by microorganisms in the environment.

For example detergents with straight-chain alkyl benzenes are biodegradable.

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Biodegradability

However detergents with branched-chain alkyl benzenesare not biodegradable.

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