Aldehydes, Ketones, and carboxylic acids

RO

H

AldehydesThe term Aldehyde come for the

words alcohol dehydrogenation.

Preparation: Oxidation of primary alcohols according to the following equation:

Note: Oxidation can be considered as removal of hydrogens. [O] can be obtained from oxidazing agents such as

KMnO4,KCr2O7,CuO.

Carbonyl group

ROH + [O] R

O

AldehydesExamples:

Methyl alcohol Formaldehyde

Ethyl alcohol Acetaldehyde

Toluene Benzaldehyde

CH3

[O]+

O H

HH

OHH

O

H+ [O]

CH3H

OHCH3

O

H+ [O]

Aldehydes

Note: The formation of acetaldehyde in the liver is

partailly responsible for liver cirrhosis.

The formation of formaldehyde and ist oxidation product formic acid are responsible for the systematic toxicity of methyl alcohol (methanol).

The side chain in toluene is more susceptible to oxidation than the benzne ring.

IUPAC Nomenclature of Aldehydes

The aldehyde group is always at the end of the chain (carbon 1)

Aldehydes end in al Take the name of the longest chain cotaining the

aldehyde groupDrop the ending e and replace it by al

CH3

CH3

Br

CH3

O

6-bromo-5,7-dimethyloctanal

CH3

CH3

BrCl

O

3-bromo-5-chloro-4-methylhexanal

IUPAC Name Common Name

Methanal Formaldehyde

Ethanal Acetaldehyde

Propanal Propionaldehyde

2-Methylpropanal Isobutyraldehyde

Uses of aldehydes

40% Formaldehyde in water (Formalin): used for disinfection of excerta, rooms, clothing (Mechanism: hardening of proteins), in embalming (التحنيط) water, and as preservative for biological specimens.

Benzaldehyde: preparation of flavoring agents, parfums, drugs, and dyes.

Vanilllin (Vanilla beans) and cinnamic aldehyde (cinnamon bark): flavoring agents.

O H

OHOCH3

Vanillin

HO

HFormaldehyde Cinnamic adehyde

O

Tests of aldehydes

Adehydes are good reducing agents. Glucose contains an aldehyde group. Therefore, it can

react as an aldehyde, and can be detected in urin using special solutions such as Benedicts, Fehlings, or Tollens reagent.

Reactions of aldehydes

Oxidation: Acid

RH

OR

O

OH+ [O]

Reduction: Alcohol

RH

OR

H

OH+ [H]

Examples:

CH3 O [H]+CH3

OHEthanal EthanolO

[H]+

OH

Benzaldehyde Benzylalcohol

Reactions of aldehydes

Biological oxidation-reduction reactions in the are crried out in the body by substances called coenzymes. One coenzyme is NAD+

(Nicotinamide Adenine Dinucleotide)

CH3 OH + NAD+CH3 O + NADH

KetonesSecondary alcohol oxidation ketone

CH3 CH3

OH

+ [O]CH3 CH3

O

Isopropyl alcohol2- Propanol

AcetonePropanone

CH3O OCl

Cl

Acetophenone Chloracetophenone (tear gas)

Naming of KetonesIUPAC Aldehydes end in -one Take the name of the longest chain Drop the ending e and replace it by -one Common Each alkyl group attached to the carbonyl group is

named and the word ketone is added afterward.

CH3 CH3

O

3-HexanoneEthylpropylketone

CH3 CH3

ClClO

4,4-dichloro-2-pentanone

Uses of Ketones Acetone is a good solvent for fats and oils

(previuosly used in finger nail polish). Present in small amounts in blood and urine (in

normal individuals). Present in large amounts in blood and urine and

expired air in case of untreated diabetes mellitus. Dihydroxy acetone is an intermediate in

carbohydrate metabolism.

O

OHOH

Dihydroxy acetone

CH3 CH3

O

Acetone

Reactions of ketones

Ketones are usually unreactive.Ketones are not easily oxidized.They can however be reduced to the

corresponding secondary alcohols.Ketones give negative tests with oxidazing

agents such as Benedict‘s reagent. However aldehyde give positive results with these reagents.

Reactions of ketones

Hemiacetals and Hemiketals

How can an acetal or a ketal be formed?Importance: Hemiketal / acetal monosaccharidesKetal / Acetal Di- and Polysaccharides

Carboxylic acids PreparationOxidation of aldehydes

CH3O + [O] CH3

O

OH

Acetaldehyde Acetic acid

O

+ [O]

OOH

Benzaldehyde Benzoic acid

Stepwise oxidation of a primary alcohol carboxylic acid

Direct oxidation of primary alcohols acids

+ [O]CH3 OH CH2 O + [O]

OOH

Methylalcohol Formaldehyde

Formic acid

CH3OH

+ [O] CH3O

OH

Ethyl alcohol Acetic acid

Naming of carboxylic acidsIUPAC Names Carboxylic acids end in –oic acid Take the name of the longest chain cotaining the

acid group. Drop the ending e and replace it by -oic Common Names Derived from the names of the aldehyde forms from

which they may be prepared

CH3O

OH

Ethanoic acidAcetic acid

Carboxyl group which yields hydrogen ions

Naming of carboxylic acids Dicarboxylic, and tricarboxylic acids are carboxylic acids

which contain two and three carboxylic acids, respectively.

OH

OO

OH

OH

O

OH

O

OH

O O

OH

Ethanedioic aicOxalic acid

Propanedioic acidMalonic acid

Butanedioic acidSuccinic acid

OH

OOHO

OHOH

O

Citric acid

Naming of carboxylic acidsExamples:

CH3

CH3

CH3

ClOH

O

2-chloro-3,4-dimethylheptanoic acid

OOH

Cl

Br4-bromo-2-chlorobenzoic acid

Properties and Reactions of Carboxylic acidsWeak acids

CH3O

OHCH3

O

O-+H+

Hydrogen ion

Acetate ionAcetic acid

React with bases to form salts and water

+CH3O

OHNaOH CH3

O

O-Na++ OH2

CH3CHOOH + NaOH CH3CHOONa + H2O

Properties and Reactions of Carboxylic acidsReact with bases to form salts and water

CH3CHOOH + NaHCO3 CH3CHOONa + H2O+ CO2

Sodium bicarbonate

HCOOH + Na2CO3 HCOONa + H2O+ CO22

Sodium carbonate

Formic acid

2

Sodium formate

Their solubility in water decreases as the length of their carbon chains increases

React with alcohols to form esters

Medically important acids Magnesium citrate cathartic (evacuation of bowel) Sodium Citrate anticoagulant (removel of Ca2+ needed for

coagulation Lactic acid results from fermentation of milk sugar (lactose)

[lactic acidboth acid and alcohol) Lactic acid is formed by anarobic energy production in the

body from Pyruvate (muscle exercise) Pyruvic acid is formed during anarobic phase of glucose

oxidation Pyruvic acid acetyl CoA Krebs cycleEnergy production

CH3O

OH

OH

Lactic acid

CH3O

OH

O

Pyruvic acid

Medically important acids Oxalic acid removal of strains, from clothing, prevention of

blood clotting (Note: Oxalic acid is a poison if taken internally) Stearic acid (C18) is a fatty acid, insoluble in water, ist salt is

used as in Soap Bezoic acid antifungal; sodium salt preservative Salicylic acid (both alcohol and acid) removal of warts and

corns

Salicylic acid

OH

O OHAcetylsalicylic acid (Aspirin): analgesic, antipyretic, aginst rheumatic fever ( ىالحم prevention of ,(الروماتيزميةblood clots from forming (Note: contraindicated after Surgery) helps in preventing heart attacks, bleeding of stomach (not to be taken on empty stomach)

O

OOH

CH3O

Acetylsalicylic acid