Aldehydes, Ketones, and carboxylic acids

Aldehydes  The 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 KMnO 4,KCr 2 O 7, CuO. Carbonyl group

Aldehydes  Examples: Methyl alcohol Formaldehyde Ethyl alcohol Acetaldehyde Toluene Benzaldehyde

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 group  Drop the ending e and replace it by al

IUPAC NameCommon Name MethanalFormaldehyde EthanalAcetaldehyde PropanalPropionaldehyde 2-MethylpropanalIsobutyraldehyde

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. VanillinFormaldehydeCinnamic adehyde

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  Reduction:  Alcohol Examples: Ethanal Ethanol 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)

Ketones  Secondary alcohol  oxidation  ketone Isopropyl alcohol 2- Propanol Acetone Propanone AcetophenoneChloracetophenone (tear gas)

Naming of Ketones IUPAC  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. 3-Hexanone Ethylpropylketone 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. Dihydroxy acetone 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  monosaccharides Ketal / Acetal  Di- and Polysaccharides

Carboxylic acids Preparation Oxidation of aldehydes AcetaldehydeAcetic acid Benzaldehyde Benzoic acid

 Stepwise oxidation of a primary alcohol  carboxylic acid  Direct oxidation of primary alcohols  acids Methylalcohol Formaldehyde Formic acid Ethyl alcohol Acetic acid

Naming of carboxylic acids IUPAC 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 Ethanoic acid Acetic 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. Ethanedioic aic Oxalic acid Propanedioic acid Malonic acid Butanedioic acid Succinic acid Citric acid

Naming of carboxylic acids Examples:

Properties and Reactions of Carboxylic acids  Weak acids Hydrogen ion Acetate ion Acetic acid  React with bases to form salts and water CH 3 CHOOH + NaOH CH 3 CHOONa+H2OH2O

Properties and Reactions of Carboxylic acids  React with bases to form salts and water CH 3 CHOOH + NaHCO 3 CH 3 CHOONa+H2OH2O+CO 2 Sodium bicarbonate HCOOH + Na 2 CO 3 HCOONa+H2OH2O+CO 2 2 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 Ca 2+ 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 cycle  Energy production Lactic acid 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  Acetylsalicylic acid (Aspirin): analgesic, antipyretic, aginst rheumatic fever ( الحمى الروماتيزمية ), prevention of blood clots from forming (Note: contraindicated after Surgery)  helps in preventing heart attacks, bleeding of stomach (not to be taken on empty stomach) Acetylsalicylic acid