Compounds containing Carbonyl Groups

What is the difference between Ketones and Aldehydes

•Aldehydes have their carbonyl group at the end of a carbon chain. Their names end in -al.

•Ketones have their carbonyl group within the carbon chain. Their names end in -one and often have a number indicating the carbon with the C=O group.

What can be oxidised to aldehydes

Primary alcohols can be oxidised to aldehydes

What can be oxidised to carboxylic acids

Primary alcohols can be oxidised to aldehydes and further to carboxylic acids

What oxidising agent is used

acidified potassium dichromate(VI) (K2Cr2O7) as an oxidising agent.

What reagent is used to oxidise primary alcohols to aldehydes?

K2Cr2O7 + H2SO4 (heat & distil off product)

What reagents can be used to oxidise aldehydes to carboxylic acids?

K2Cr2O7 + H2SO4 (heat or reflux), Tollen's reagent (heat), or Fehling's solution (heat)

What does [O] represent in oxidation reactions?

The oxidising agent.

What does R represent in the context of alcohol oxidation?

An alkyl group.

What is the color change of dichromate(VI) ion during oxidation?

It changes from orange (Cr2O72-) to green (Cr3+).

How can you control alcohol oxidation to get aldehydes or acids

•Gently heating the alcohol with acidified K2Cr2O7 in a distillation set-up stops at the aldehyde product.

•Refluxing the alcohol (or aldehyde) with acidified K2Cr2O7 continues the oxidation to the carboxylic acid.

What is produced when secondary alcohol is oxidised?

Ketones are produced when secondary alcohols are oxidised with acidified K2Cr2O7.

Can it be oxidised further?

Ketones cannot be oxidised further by acidified K2Cr2O7.

Why do aldehydes, but not ketones, cause a color change when reacted with acidified potassium dichromate(VI)?

•Aldehydes can be oxidised by oxidising agents such as acidified potassium dichromate(VI) to form carboxylic acids.

•The colour change observed during this oxidation is from orange to green, as the Cr(VI) in the dichromate ion is reduced to Cr(III).

•However, ketones do not undergo oxidation under the same conditions, so colour change is seen.

Explain why this difference in reactivity occurs

This difference in reactivity occurs because the hydrogen atom attached to the carbonyl carbon in an aldehyde is weakly acidic, so it is easily displaced. By contrast, ketones lack that weakly acidic hydrogen, so oxidation does not occur.

Explain the process of reducing aldehydes and ketones to alcohols

•Aldehydes and ketones can be reduced to primary and secondary alcohols respectively using reducing agents like sodium borohydride (NaBH4) dissolved in a mixture of water and methanol.

Explain why this undergo nucleophilic addition

•Carbonyl compounds undergo nucleophilic addition reactions because the carbonyl carbon is electrophilic due to the polarisation of the C=O double bond, which makes it susceptible to attack by nucleophiles.

Draw the mechanism of carbonyl reduction

1.) The reducing agent provides hydride ions (H-) which act as nucleophiles.

2.) The hydride ion attacks the partially positive carbonyl carbon, forming a new C-H bond.

3.) Protons from the solvent, such as water, are added to the oxygen, forming the hydroxyl group (-OH).

What product is formed when aldehydes or ketones react with hydrogen cyanide (HCN) in a nucleophilic addition reaction?

Aldehydes and ketones can react with hydrogen cyanide (HCN) in nucleophilic addition reactions to produce hydroxynitriles which conains both the cyano (-CN) and hydroxy (-OH) substituents. This reaction is useful because it increases the length of the carbon chain by 1 carbon atom.

How is HCN handled?

Hydrogen cyanide is toxic so it is often generated in situ by mixing sodium cyanide or potassium cyanide with dilute sulfuric acid.

Draw the mechanism of hydroxynitrile formation

1.) CN- attacks the partially positive carbonyl carbon, transferring the electrons to oxygen.

2.) Protonation of oxygen by water (or acid) to give the -OH group.

What is a racemic mixture?

a racemic mixture contains equal amounts of both enantiomers

How is a racemic mixture formed?

•Aldehydes and unsymmetrical ketones contain a planar carbonyl group (C=O) which allows attacking reagents to approach from either side with equal likelihood.
•This leads to the formation of racemic mixtures containing both enantiomers in equal amounts.

For example, when ethanal reacts with acidified potassium cyanide to produce a racemic mixtures

1.) The planar C=O double bond allows the CN- nucleophile to attack from either side of the plane.

2.) Attacking from above or below the plane produces two different enantiomers.

3.) Since both directions of attack are equally likely, the reaction yields equal amounts of both enantiomers of 2-hydroxypropanenitrile, resulting in a racemic mixture.

Does a symmetrical ketone form a racemic mixture

•In contrast, symmetrical ketones do not form racemic mixtures when attacked by nucleophiles.

•Due to their symmetry, attack from either side of the carbonyl group produces the same product rather than two different enantiomers.

•For instance, when propanone reacts with acidified potassium cyanide, the product is the non-chiral molecule 2-hydroxy-2-methylpropanenitrile.

Explain why aldehyde can be distinguished from ketones

Aldehydes can be distinguished from ketones because aldehydes are readily oxidised into carboxylic acids, while ketones cannot.

Explain how you can distinguish between aldehydes from ketones

Three commonly used reagents are:

•Tollens' reagent
•Fehling's solution
•Acidified potassium dichromate

Using Tollens' reagent

•Tollens' reagent is a colourless solution containing complexed silver ions, [Ag(NH3)2]+, formed by the addition of aqueous ammonia to silver nitrate.

•When warmed with an aldehyde, the Ag+ ions in Tollens' reagent undergo reduction to Ag, depositing silver metal as a silver mirror. No reaction occurs with ketones.
-Remember equation.

Using Fehling's solution

•Fehling's solution contains blue copper(II) complex ions dissolved in aqueous sodium hydroxide.

•When warmed with an aldehyde, the copper(II) ions are reduced to a red precipitate of copper(I) oxide, Cu2O. No reaction occurs with ketones.

-Remember equation

Using acidified potassium dichromate(VI)

•Heating an aldehyde with acidified potassium dichromate(VI) causes oxidation to a carboxylic acid.

•The orange dichromate(VI) ions (Cr2O72-) act as the oxidising agent, being reduced to green Cr3+ ions. Ketones do not react.
-Remember equation

Colour for each oxidising equation

What functional group do carboxylic acids contain?

-COOH

What ions do carboxylic acids dissociate into in aqueous solution?

In an aqueous solution, carboxylic acids partially dissociate into hydrogen (H+) ions and carboxylate (RCOO-) ions.

Why are carboxylic acids considered weak acids?

Because most molecules partially dissociate

Are carboxylic acids polar

Yes, the carboxyl group is polar

Explain why

•Carboxylic acids are polar due to the electronegative oxygen atoms drawing electrons away from the hydrogen atoms.

•This polarity allows carboxylic acids to readily form hydrogen bonds with each other and with water molecules.

•Hydrogen bonding makes small carboxylic acids very soluble in water, as they can form hydrogen bond with water molecules.

What are the 2 ways to form carboxylic acids?

Carboxylic acids can be synthesised through various methods:

•Oxidation of primary alcohols or aldehydes with oxidising agents such as acidified potassium dichromate (K2Cr
2O7).
•Hydrolysis of esters involves refluxing esters with either dilute hydrochloric acid (HCl), water, or aqueous sodium hydroxide (NaOH).
The general reaction is:
RCOOR' + H2O ⇌ RCOOH + R'OH

What is the general formula for oxidation of primary alcohols or aldehydes with K2Cr2O7/KMnO4

The general reactions are:
RCH2OH + [O] ➔ RCHO + H2O + [O]➔ RCOOH

What is the general formula for hydrolysis of esters

The general reaction is: RCOOR' + H2O ⇌ RCOOH + R'OH

Carboxylic acids react with carbonates

•Carboxylic acids react with carbonates to form a carboxylate salt, carbon dioxide and water.

•The carbon dioxide rapidly evolves as bubbles when the reaction occurs.

•This observable effervescence serves as a simple test to confirm the presence of a carboxylic acid.

For example, ethanoic acid reacts with sodium carbonate to form sodium ethanoate and water:

2CH3COOH(aq) + Na2CO3(s) ➔ 2CH3COONa(aq) + CO2(g) + H2O(l)

Carboxylic acids react with bases

•Carboxylic acids are neutralised by bases such as metal oxides and hydroxides to form carboxylate salts and water.

For example, ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water:

CH3COOH(aq) + NaOH(aq) ➔ CH3COONa(aq) + H2O(l)

How are esters made?

•Esters, characterised by the -COO- functional group, are made by heating carboxylic acids with alcohols in the presence of concentrated H2SO4 catalyst.

For example, ethanoic acid reacts with ethanol to form the ester ethyl ethanoate and water:

CH3COOH(aq) + CH3CH2OH(aq) ⇌ CH3COOCH2CH3(aq) + H2O(l)

What are esters?

Esters are organic compounds formed from the reaction between a carboxylic acid and an alcohol, where a molecule of water is removed during the process.

Formula for ester

R is an alkyl or aryl group from the carboxylic acid.

COO- is the ester functional group.

R' is an alkyl or aryl group from the alcohol.

How to name esters

1.) The first part comes from the alcohol used and is the alkyl (R) group.

2.) The second part comes from the carboxylic acid used. The acid ending is replaced by 'oate' to give the second part of the name.

Commercial uses of esters

•Flavourings and perfumes - Due to their often sweet, fruity scents, esters are popular in the food and fragrance industries.

•Solvents - They are effective in dissolving other organic substances and have relatively low boiling points, making them suitable for use in chemical processes and manufacturing.

•Plasticisers - By incorporating them into plastics, they enhance flexibility. However, over time, these plasticisers may evaporate, causing the plastic to become brittle.

Ways of synthesizing esters

There are primarily three methods for synthesising esters:

1. From alcohols and carboxylic acids
2. From alcohols and acyl chlorides
3. From alcohols and acid anhydrides

From alcohols and carboxylic acids (Esterification)

•Mix the carboxylic acid and alcohol under reflux with an acid catalyst, such as H2SO4, in a reaction known as esterification.

•Applying an excess of alcohol can drive the reaction towards the formation of the ester product.

•The resulting ester can be isolated using fractional distillation.

From alcohols and acyl chlorides

•Mixing acyl chloride with alcohol at room temperature leads to a rapid and vigorous reaction, producing an ester and hydrochloric acid gas.

From alcohols and acid anhydrides

•Combine the acid anhydride with alcohol at a warm temperature to produce an ester and a carboxylic acid.

•Fractional distillation is used for separation.

Two ways to hydrolyse an ester

Acid hydrolysis
Base hydrolysis

Acid hydrolysis

The ester is heated under reflux with a dilute acid, such as HCl or H2SO4, to produce a carboxylic acid and an alcohol.

Base hydrolysis

When the ester is heated under reflux with a dilute base like NaOH, the products are a carboxylate salt and alcohol. This method is generally irreversible due to the stability of the carboxylate salt.

What are animal fats and vegetable oils a type of?

Animal fats and vegatable oils are esters

What are they made from

They are made from the alcohol glycerol (propane-1,2,3-triol) and long chain fatty acids. (Specifically, they are triglycerides)

What is the structure of triglyceride

Esters that contain one glycerol and three fatty acids

Differences between fats and oils

•Whether a triglyceride is a solid fat or liquid oil depends on the structure of its fatty acid chains and the resulting intermolecular forces:

-Saturated fatty acids - Found in animal fats, these contain only single carbon-carbon bonds, resulting in straight hydrocarbon chains. The straight chains allow tight packing of fat molecules, enabling stronger intermolecular forces between them. These stronger forces raise their melting point, causing them to be solid at room temperature.

-Unsaturated fatty acids - Found in vegetable oils, these contain carbon-carbon double bonds which cause kinks or bends in the hydrocarbon chains. The bent shapes prevent close packing of oil molecules, resulting in weaker intermolecular forces. These weaker forces lower their melting point, allowing them to remain liquid at room temperature.

How is soap made?

Soap is produced by hydrolysing fats and oils through boiling with a strong alkali solution, such as sodium hydroxide. This reaction breaks down the ester bonds in triglycerides, forming glycerol and sodium salts of the fatty acids. These sodium salts make up the soap.

General formula for making of soap

Fat + Sodium Hydroxide → Glycerol + Sodium Salt

What is biodisel

Biodiesel is a mixture of methyl esters of long-chain carboxylic acids.

How is biodisel made?

Biodiesel is produced by reacting vegetable oils with methanol in the presence of a potassium hydroxide catalyst. This reaction leads to the formation of glycerol and methyl esters of fatty acids, which serve as effective substitutes for diesel fuel.

General formula for making of biodiesel

Oil + Methanol → Glycerol + Methyl Ester

is biodiesel renewable?

Yes

Why

•Biodiesel is considered a renewable fuel because it is derived from plant-based oils that can be replenished relatively quickly through agricultural processes, unlike fossil fuels that take millions of years to form.

•As a result, biodiesel offers a more environmentally friendly alternative to traditional fossil fuels.

What are amides

Carboxylic acid derivatives where -OH is replaced with amino group

What are the structures of amides

R ( C = O ) N R 1 R 2 , where R, R 1 , R 2 represents a hydrocarbon or a hydrogen substituent.

How to name amides

use carboxylic acid name

drop -ic and add -amide

use N to denote alkyl groups attached to nitrogen atom

What are acid anhydrides?

Derivatives of carboxylic acids formed by substitution of the -OH group by an alkanoate

What is the structure of acid anhydrides

Acid anhydrides are made from two carboxylic acid groups joined together

Naming of acid anhydrides

take the name of the parent acid, and replace the word "acid" by "anhydride

What are acyl chlorides?

•A derivative of carboxylic acids, where the -OH group is replaced by a -Cl group so instead of COOH its COCl
(Similar to acyl chlorides, acid anhydrides and amides are also derivatives of carboxylic acids.)

How do you name an acyl chloride?

Replace the suffix '-oic acid' of the parent carboxylic acid with '-oyl chloride'.

How do you number the carbon chain in an acyl chloride?

Number the carbon chain starting from the end closest to the -COCl group.

What mechanism is involved when acyl chlorides/acid anhydrides are reacted with either water, alcohols, ammonia and primary amines.

nucleophilic addition-elimination reaction

How reactive are acyl chlorides and why is that so?

Acyl chlorides are highly reactive due to their polar C=O bond and the chlorine atom, which is READILY displaced.

Reactions of acyl chlorides with water

This reaction is vigorous, even at low temperatures, and reforms the carboxylic acid. The reaction also produces steamy fumes of hydrogen chloride gas.

Reactions of acyl chlorides with alcohols

At room temperature, this reaction is vigorous, producing an ester and HCl.

Reactions of acyl chlorides with concentrated ammonia

This reaction occurs violently at room temperature, resulting in a primary amide and HCl.

Reactions of acyl chlorides with primary amines

This reaction occurs violently at room temperature, resulting in a secondary amide and HCl.

Acyl chloride mechanism

1.) Addition - A nucleophile attacks the carbonyl carbon, which carries a partial positive charge, leading to the formation of a tetrahedral intermediate.

2.) Elimination - The chloride ion leaves, and the carbonyl group is reformed, with HCl being released.

Manufacturing aspirin

Aspirin is produced industrially by reacting salicylic acid with an excess of ethanoic anhydride, a derivative of acyl chloride.

Why is ethanoic anhydride used instead of ethanoyl chloride

1.) Ethanoic anhydride is cheaper than ethanoyl chloride.

2.) It is less corrosive, reducing the need for specialised equipment.

3.) It reacts more slowly with water, allowing for better control during the manufacturing process.

4.) It produces ethanoic acid as a by-product, which is less hazardous than the corrosive hydrogen chloride gas generated by ethanoyl chloride.