Aldehydes, Ketones & Carboxylic Acids - Example- Hydrogen Cyanide Addition

Slide 2: Nucleophilic Addition Reactions of Aldehydes and Ketones

Aldehydes and ketones can undergo nucleophilic addition reactions due to the polar carbonyl group.
Nucleophiles attack the electrophilic carbon of the carbonyl group.
The product is often an alcohol, where the carbonyl group is replaced by a hydroxyl group.
Example: Addition of hydrogen cyanide (HCN) to propanal produces 2-hydroxypropanenitrile (commonly known as mandelic acid).
Mechanism: The nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate. A proton transfer leads to the formation of the alcohol product.
Other examples: Addition of water (hydration), addition of alcohols, addition of primary amines.

Slide 3: Oxidation Reactions of Aldehydes and Ketones

Aldehydes can be oxidized to carboxylic acids using strong oxidizing agents like potassium dichromate (K2Cr2O7) in acidic medium.
Ketones are resistant to oxidation and do not undergo oxidation reactions.
The mechanism involves the formation of an intermediate called the geminal diol, which is further oxidized to the carboxylic acid.
Example: Oxidation of ethanol (an aldehyde) produces acetic acid.
Other examples: Oxidation of aldehydes with Tollens’ reagent or Fehling’s solution to form silver mirror or red precipitate, respectively.
Oxidation reactions of ketones are not favored due to the absence of an easily oxidizable hydrogen atom.

Slide 4: Condensation Reactions of Aldehydes and Ketones

Condensation reactions occur between two carbonyl compounds, usually involving the loss of a small molecule like water or an alcohol.
The carbonyl compounds are often in the form of aldehydes or ketones.
The reaction is catalyzed by acids or bases.
Examples: Formation of hemiacetals and acetals, formation of imines and enamines.
A hemiacetal is formed when an aldehyde or ketone reacts with an alcohol.
An acetal is formed when a hemiacetal reacts with another molecule of alcohol.
The general mechanism involves the attack of an alcohol on the carbonyl carbon, followed by proton transfer and elimination of a water molecule.

Slide 5: Acidic Nature of Carboxylic Acids

Carboxylic acids are weak acids due to the presence of a dissociable hydrogen atom.
They can donate a proton (H+) to a base.
The dissociation of carboxylic acids in water leads to the formation of carboxylate ions.
Acidity is influenced by factors like the electron-withdrawing nature of substituents and resonance effects.
Examples: Acetic acid, Benzoic acid.
Reactions: Carboxylic acids can undergo neutralization reactions with bases, esterification reactions with alcohols, and undergo decarboxylation reactions under certain conditions.
Example equation: CH3COOH + NaOH → CH3COONa + H2O

Slide 6: Esters - Formation and Naming

Esters are derived from carboxylic acids and alcohols.
Formation: Esters can be formed through esterification reactions, where a carboxylic acid reacts with an alcohol in the presence of an acid catalyst.
Naming: Esters are named by replacing the -oic acid in the carboxylic acid name with -ate. The alkyl group attached to the oxygen atom is named as an alkyl substituent.
Example: Ethanoic acid + Methanol → Methyl ethanoate + Water
Common examples: Ethyl acetate, Methyl salicylate.
Esters have a pleasant fruity smell and are used in the manufacturing of perfumes and flavorings.
They resemble carboxylic acids in physical properties.

Slide 7: Hydrolysis of Esters

Esters can undergo hydrolysis in the presence of an acid or a base.
Acid hydrolysis: Esters react with water in the presence of an acid to form a carboxylic acid and an alcohol.
Base hydrolysis (saponification): Esters react with hydroxide ions in the presence of a base to form a carboxylate salt and an alcohol.
Mechanism: In acid hydrolysis, the ester reacts with a hydronium ion to form a tetrahedral intermediate, which then breaks down to give the carboxylic acid and alcohol.
Saponification is widely used in the preparation of soaps.
Example: Ethyl acetate + Water → Ethanoic acid + Ethanol

Slide 8: Reduction of Carboxylic Acids

Carboxylic acids can be reduced to primary alcohols using reducing agents like LiAlH4 (lithium aluminum hydride) or NaBH4 (sodium borohydride).
The carbonyl group of the carboxylic acid is reduced to a -CH2OH group.
The reaction proceeds via the intermediate formation of an aldehyde, which is subsequently reduced to an alcohol.
Example: Ethanoic acid + LiAlH4 → Ethanol
Reduction of carboxylic acids is a useful synthetic tool in organic chemistry.
The reaction is typically carried out under reflux conditions with an inert atmosphere.

Slide 9: Decarboxylation Reactions of Carboxylic Acids

Certain carboxylic acids can undergo decarboxylation reactions when heated or under specific conditions.
In decarboxylation, the carboxyl group is lost as carbon dioxide (CO2), leaving behind a hydrocarbon.
The reaction is often catalyzed by heat or strong bases.
Example: Decarboxylation of acetic acid (CH3COOH) produces methane (CH4).
This reaction is an important step in the formation of natural gas and is also used in the synthesis of certain organic compounds.
Decarboxylation reactions are significant in biological processes like the Krebs cycle.

Slide 10: Nomenclature Rules and Summary

Nomenclature rules for aldehydes, ketones, and carboxylic acids:
1. Find the parent chain containing the highest priority group.
2. Number the parent chain starting from the end nearest to the highest priority group.
3. Assign numbers to substituents and write their names alphabetically as prefixes.
4. For aldehydes, change the -e ending of the corresponding alkane name to -al.
5. For ketones, change the -e ending of the corresponding alkane name to -one.
6. For carboxylic acids, change the -e ending of the corresponding alkane name to -oic acid.
Summary: Aldehydes, ketones, and carboxylic acids are important classes of organic compounds. They have distinct properties, reactions, and nomenclature rules. Understanding their chemistry is crucial in organic synthesis and drug discovery processes.

Slide 11: Example - Hydrogen Cyanide Addition

Aldehydes and ketones can undergo nucleophilic addition reactions with hydrogen cyanide (HCN) to form cyanohydrins.
Hydrogen cyanide adds to the carbonyl group, resulting in the formation of a cyanohydrin.
Example: Addition of hydrogen cyanide to propanal produces 2-hydroxypropanenitrile (commonly known as mandelic acid).
Equation: HC=O + HCN → HC(OH)(CN) (propanal + HCN → 2-hydroxypropanenitrile)
The process involves the nucleophilic attack of the cyanide ion on the carbonyl carbon.
The reaction is reversible, and the cyanohydrin can be hydrolyzed to regenerate the aldehyde or ketone.

Slide 12: Example - Hydration (Addition of Water)

Aldehydes and ketones can undergo hydration reactions, which involve the addition of water to the carbonyl group.
The product is typically a geminal diol, where a hydroxyl group is attached to the carbonyl carbon.
Example: Hydration of ethanal produces ethane-1,2-diol.
Equation: CH3CHO + H2O → CH3CH(OH)2 (ethanal + water → ethane-1,2-diol)
The reaction is catalyzed by either an acid or a base.
The addition of water occurs through the nucleophilic attack of a water molecule on the electrophilic carbonyl carbon.
Geminal diols can be further oxidized to form carboxylic acids.
Hydration is an important step in the breakdown of glucose during cellular respiration.

Slide 13: Example - Addition of Alcohols

Aldehydes and ketones can react with alcohols to form hemiacetals and acetals.
The reaction involves the nucleophilic attack of the alcohol on the carbonyl carbon.
Hemiacetals have a hydroxyl (-OH) group and an alkoxyl (-OR) group attached to the same carbon.
Acetals have two alkoxyl (-OR) groups attached to the same carbon.
Example: Addition of methanol to propanal produces hemiacetal and acetal compounds.
Equation: CH3CH2CHO + CH3OH → CH3CH(OH)OCH3 (propanal + methanol → 1-hydroxy-2-methoxypropane)
```
  CH3CH(OH)OCH3 + CH3OH → CH3CH(OMe)2   (hemiacetal + methanol → 1,1-dimethoxypropane)
```
The reaction is reversible, and acetals can be hydrolyzed back to aldehydes or ketones in the presence of acid or base.

Slide 14: Example - Oxidation of Aldehydes

Aldehydes can be oxidized to carboxylic acids using strong oxidizing agents like potassium dichromate (K2Cr2O7) or potassium permanganate (KMnO4) in acidic medium.
The carbonyl group of the aldehyde is oxidized to a carboxyl group.
Example: Oxidation of ethanol (an aldehyde) produces acetic acid.
Equation: CH3CHO + [O] → CH3COOH (ethanal + oxidizing agent → acetic acid)
The reaction involves the loss of two hydrogen atoms.
The oxidizing agent provides the necessary oxygen for the oxidation process.
Ketones are not easily oxidized due to the absence of a reactive hydrogen atom.
Tollens’ reagent or Fehling’s solution can be used to distinguish between aldehydes and ketones based on their oxidation behavior.

Slide 15: Example - Reduction of Ketones

Ketones can be reduced to secondary alcohols using reducing agents like sodium borohydride (NaBH4) or lithium aluminum hydride (LiAlH4).
The carbonyl group of the ketone is reduced to a hydroxyl group.
Example: Reduction of propanone (a ketone) produces 2-propanol (a secondary alcohol).
Equation: CH3COCH3 + 2[H] → CH3CH(OH)CH3 (propanone + reducing agent → 2-propanol)
The reaction proceeds via the formation of an intermediate known as an alkoxide ion.
Sodium borohydride and lithium aluminum hydride are strong reducing agents that provide the necessary hydride ions for the reduction process.
Reduction of ketones is an important step in the synthesis of pharmaceuticals and other organic compounds.

Slide 16: Example - Acid Hydrolysis of Esters

Esters can undergo acid hydrolysis in the presence of an acid catalyst to form carboxylic acids and alcohols.
The ester linkage is cleaved, and the products are derived from the alcohol and carboxylic acid used in the hydrolysis reaction.
Example: Hydrolysis of ethyl acetate produces acetic acid and ethanol.
Equation: CH3COOC2H5 + H2O → CH3COOH + C2H5OH (ethyl acetate + water → acetic acid + ethanol)
The reaction is catalyzed by an acid, typically sulfuric acid or hydrochloric acid.
The process involves the nucleophilic attack of a water molecule on the carbonyl carbon.
Acid hydrolysis of esters is a reversible reaction.
Esters can also undergo base hydrolysis (saponification) to form carboxylate salts and alcohols.

Slide 17: Example - Base Hydrolysis (Saponification) of Esters

Esters can undergo base hydrolysis, also known as saponification, in the presence of a strong base to form carboxylate salts and alcohols.
The ester linkage is cleaved, leading to the formation of the corresponding carboxylate ion and alcohol.
Example: Saponification of ethyl acetate produces sodium acetate and ethanol.
Equation: CH3COOC2H5 + NaOH → CH3COONa + C2H5OH (ethyl acetate + sodium hydroxide → sodium acetate + ethanol)
The process involves the nucleophilic attack of a hydroxide ion on the carbonyl carbon.
Base hydrolysis of esters is irreversible.
Saponification is commonly used in the preparation of soaps, where esters are hydrolyzed by strong bases like sodium hydroxide or potassium hydroxide.

Slide 18: Example - Esterification Reaction

Esterification is the reaction between a carboxylic acid and an alcohol to form an ester.
The carboxylic acid donates a proton (H+) to the alcohol, resulting in the formation of water and an ester.
The reaction is catalyzed by an acid, typically concentrated sulfuric acid or concentrated phosphoric acid.
Example: Esterification of ethanoic acid and methanol produces methyl ethanoate.
Equation: CH3COOH + CH3OH → CH3COOCH3 + H2O (ethanoic acid + methanol → methyl ethanoate + water)
The reaction involves the nucleophilic attack of the alcohol on the carbonyl carbon of the carboxylic acid.
Esterification reactions are equilibrium reactions, and the yield can be improved by using excess alcohol or removing water from the reaction mixture.

Slide 19: Example - Formation of Carboxylic Acid Derivatives

Carboxylic acids can undergo reactions to form derivatives such as acid chlorides, acid anhydrides, esters, and amides.
Acid chlorides are formed by reacting a carboxylic acid with thionyl chloride (SOCl2) or phosphorus trichloride (PCl3).
Acid anhydrides are formed by reacting two carboxylic acid molecules with the loss of a water molecule.
Esters can be formed through esterification reactions, as discussed earlier.
Amides are obtained by reacting a carboxylic acid with ammonia (NH3) or an amine.
These derivatives retain the carboxyl group and have distinct chemical properties.
Derivatives of carboxylic acids find applications in organic synthesis, pharmaceuticals, and polymer production.

Slide 20: Example - Decarboxylation of Carboxylic Acids

Certain carboxylic acids can undergo decarboxylation reactions under specific conditions.
Decarboxylation involves the loss of a carboxyl group (-COOH) from the parent acid, resulting in the release of carbon dioxide (CO2) and the formation of a hydrocarbon.
The reaction is often catalyzed by heat or strong bases.
Example: Decarboxylation of acetic acid (CH3COOH) produces methane (CH4).
Equation: CH3COOH → CH4 + CO2 (acetic acid → methane + carbon dioxide)
Decarboxylation is an important step in the formation of natural gas and is also used in the synthesis of certain organic compounds.
This reaction is significant in biological processes like the Krebs cycle, where carboxylic acids are decarboxylated to produce carbon dioxide and energy.

Slide 21: Example - Nucleophilic Addition of Amines

Aldehydes and ketones can undergo nucleophilic addition reactions with primary amines to form imines.
Primary amines have the general structure R-NH2, where R is an alkyl or aryl group.
The reaction involves the nucleophilic attack of the amine on the carbonyl carbon

Slide 1: Aldehydes, Ketones & Carboxylic Acids