ahehe

What is a Carboxylic Acid?

An organic compound with the functional group -COOH, containing a carbonyl group and an -OH acid group. They are produced from the oxidation of primary alcohols under reflux. They are weak acids that slightly dissociate when in solution, forming a H⁺ ion and a carboxylate ion RCOO- .

They react with carbonates to form a carboxylate salt, water and CO₂ (See Image).

How can Carboxylic Acids dissolve in water?

Small chain carboxylic acids are able to form hydrogen bonds with water molecules between the lone electron pair on an oxygen atom and a δ+ hydrogen atom. This makes them soluble in water.

What is an Ester?

Esters are organic compounds with the functional group RCOO- and are formed when carboxylic acids react with alcohols in the presence of a strong acid catalyst. This reaction is called esterification and is carried out under reflux. Esters are sweet smelling compounds used in food flavourings and perfumes. They have low boiling points and also make good solvents for other polar molecules.

What are Triglyceride Esters?

These are esters formed through the esterification of glycerol (propane-1,2,3-triol) and are naturally occurring. In esterification, 1 mole of glycerol reacts with 3 moles of fatty acids in the presence of an acid catalyst.. Some examples of these are vegetable oils and fats. Biodiesel is a ester formed from vegetable oils and methanol in the presence of a strong acid catalyst.

What is Hydrolysis of an Ester?

Ester Hydrolysis is the reverse reaction to esterification, converting esters back into alcohols and carboxylic acids. This is done by adding water but can be carried out under different conditions to produce different products.

Acid Conditions - When heated under reflux with a dilute acid, an equilibrium mixture is formed (reversible reaction) which means the reaction does not go to completion.

Alkaline Conditions - When heated under reflux with a dilute alkali, the reaction is irreversible and goes to completion. It produces a carboxylate salt instead of a carboxylic acid which must be acidified to form the acid.

The production of a salt in alkaline conditions is called saponification and these salts are commonly used as soaps as they typically have hydrophilic and hydrophobic properties.

What is Acylation and what are the 3 derivative molecules?

It is a chemical reaction in which an acyl group (R-C=O) is introduced into a carboxylic acid to form a derivative molecule. The 3 different molecules that could be formed are:

Acid Anhydrides - Formed when the -OH group is replaced by an alkanoate group (RCOO^-). They have the suffix -oic anhydride

Acyl Chlorides - Formed when the -OH group is replaced by a chlorine atom. They have the suffix -oyl chloride.

Amides - Formed when the -OH group is replaced by an amino group (NH₂). They have the suffix -amide.

What is Nucleophilic addition-elimination?

They mechanism used in Acylation used to form carboxylic acid derivatives. The nucleophile attacks a carbonyl carbon and eliminates a leaving group. It is split into the two stages of addition and elimination.

Addition - The nucleophile attacks the carbon in the C=O bond and attaches to the carbon, while the oxygen gains a lone pair and negative charge from the double bond.

Elimination - The lone pair on the oxygen reforms the double bond with the carbon, the R group attached to the same group gets eliminated and the nucleophile stays attached.

Example Image shows mechanism for propanoyl chloride and ethanol.

Describe the manufacture of Aspirin and what are the industrial advantages of Ethanoic Anhydride over Ethanoyl Chloride?

Aspirin is an ester produced from acylation where salicylic acid + ethanoic anhydride → aspirin + ethanoic acid.

Advantages:

• Ethanoyl Chloride reacts readily with water, making it less safe to use.

• Ethanoic Anhydride is generally cheaper to use.

• Ethanoic Anhydride is less corrosive.

• Ethanoic Anhydride is safer as it has fewer harmful by-products.

Required Practical 10: Preparation of Organic Solids and Liquids?

Preparation of Aspirin (2-acetoxybenzoic acid) by reacting salicylic acid with ethanoic anhydride:

1. Measure out 2g of salicylic acid using a weighing boat and place it into a boiling tube.

2. Measure out 4cm³ of ethanoic anhydride and pour it into the boiling tube.

3. Carefully, add a few drops oh phosphoric acid the boiling tube.

4. Warm the mixture in a water bath for around 10-15 minutes, swirling occasionally, and then allow the mixture to cool.

5. Add some cold distilled water to remove any excess ethanoic anhydride.

6. Place the boiling tube in an ice bath to form crystals and then filter them out in a vacuum funnel.

7. Wash the crystals with a small amount of cold water and recrystalise them with a minimum volume of hot solvent

8. Cool them in an ice bath again and filter the purified crystals.

You can test the purity by seeing what the melting point of your crystals are and compare it to the true value.

What are Aldehydes, how can you test for them and how do they form?

Aldehydes are organic compounds with the functional group -CHO containing the C=O bond. The are produced from the initial oxidation of primary alcohols and oxidise further to form carboxylic acids, in the presence of potassium dichromate (Shown in Image).

Aldehydes can be tested using either Tollen’s reagent or Fehling’s solution as they produce a positive test for both.

What are Ketones, how can you test for them and how do they form?

Ketones are organic compounds with the functional group -C=O and contains a C=O bond with two R groups attached to the carbon instead of a hydrogen atom. These are produced from the oxidation of secondary alcohols with acidified potassium dichromate (Shown in Image), with no further oxidation.

Ketones show a negative test result for both Tollen’s reagent and Fehling’s solution.

How can Aldehydes and Ketones be Reduced with NaBH₄?

Oxidation used to produce Aldehydes and Ketones can be reversed with a reduction reaction, where a reducing agent of NaBH₄ is used in nucleophilic addition. The reducing agent provides the :H^- nucleophile, but a H⁺ ion is also required so the reaction takes places under aqueous conditions.

How can Aldehydes and Ketones be Reduced with KCN?

Oxidation used to produce Aldehydes and Ketones can be reversed with a reduction reaction, where a reducing agent of KCN is used in nucleophilic addition. The reducing agent provides the :CN^- nucleophile and is a form of synthesis and it extends the carbo chain by one carbon atom, producing a hydroxy nitrile.

This reaction produces a racemic mixture of two optical isomers when carried out with an aldehyde or an unsymmetrical ketone as the :CN^- ion may attack above or below the flat C=O group.

What is Optical Isomerism and a Chiral Centre?

It is a type of stereoisomerism where molecules have the same molecular formula but a different spatial arrangement of atoms in space. It occurs when there is an asymmetrical carbon within an organic molecule known as a chiral centre.

Chiral Centres are carbon atoms with four different groups bonded around it so there is no line of symmetry to the molecule.

What are Enantiomers?

Compounds with a chiral centre can exist as two optical isomers, which are know as enantiomers. These are non-superimposable mirror images of each other which are unique due to their effect on plane polarised light. Each enantiomer causes the rotation of plane polarised light by 90^o in opposite directions.

What are Racemate / Racemic Mixtures?

These are mixtures where there are equal amounts of enantiomers present in the solution. These are optically inactive as the enantiomers will cancel out each others effect on polarised light and the plane of polarised light will not change.

How do different pairs of Enantiomers form?

These form in nucleophilic addition reactions where nucleophiles are able to attack a carbonyl group from above or below the C=O bond so the two possible products are mirror images of each other and therefore are optical isomers.