aldehydes, ketones, and carboxylic acids. aldehydes the term aldehyde come for the words alcohol...
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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
H
Formaldehyde 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
CH3OO
Cl
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]
CH3O
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]
O
OH
Methylalcohol Formaldehyde
Formic acid
CH3OH
+ [O]CH3
O
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
Cl
OH
O
2-chloro-3,4-dimethylheptanoic acid
OOH
Cl
Br
4-bromo-2-chlorobenzoic acid
Properties and Reactions of Carboxylic acidsWeak acids
CH3
O
OHCH3
O
O-
+H+
Hydrogen ion
Acetate ionAcetic acid
React with bases to form salts and water
+CH3
O
OH
NaOH 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 ( الحمى 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
CH3
O
Acetylsalicylic acid