Synthesis 7-9 Flashcards
How can carboxylic acids be prepared?
1) Oxidising primary alcohols or aldehydes - The primary alcohol/aldehyde is heated under reflux with acidified potassium dichromate solution.
2) Hydrolysing nitriles - Nitriles can be heated under reflux with an aqueous acid and undergo hydrolysis. The hydrogen ions of the acid act as a catalyst.
3) Hydrolysing esters - Esters can be heated under refulx with an aqueous acid or alkali as a catalyst and undergo hydrolysis. The catalyst helps move the equilibrum to the products side.
4) Hydrolysing amides - Amides can be heated under reflux with an aqueous acid or alkali as a catalyst and undergo hydrolysis. The catalyst helps move the equilibrum to the products side.
What reactions can carboxylic acids undergo?
1) Carboxylic acids can react with some metals, carbonates and alkalis to form salts.
2) They can react with alcohols to form esters in a condensation reaction.
3) They can react with amines to form alkylammonium salts which can then be heated to form amides.
4) They can react with lithium aluminium hydride in ether (ethoxyethane) in a reduction reaction to form primary alcohols. The LiAlH4 acts as a strong reducing agent which reduces the carboxylic acid to the primary alcohol.
What are amines?
Amines are organic derivatives of ammonia, where one or more hydrogen atoms in ammonia have been replaced by alkyl groups. They can either be primary, secondary or tertiary depending on the number of alkyl groups attached to the nitrogen atom.
How do you name amines?
The name should always end in ‘amine’, and it is prefixed by the names of the alkyl groups (in alphabetical order) attached to the nitrogen atom.
What are some physical and chemical properties of amines?
- Primary and secondary amines can hydrogen bond between eachother due to the N-H bond (tertiary amines cannot do this because they don’t have an N-H bond). This means that primary and secondary amine have higher boiling points than theyre isomeric tertiary amines.
- Smaller amines with a low molecular mass are soluble in water due to hydrogen bonding.
- Amines are weak bases and dissociate slightly in aqueous solution. In the reaction, the lone pair of electrons on the nitrogen atom accept a proton from the water molecule, creating alkylammonium ions and hydroxide ions. The hydroxide ions make the solution alkaline.
What reactions can amines undergo?
- Amines can react with mineral acids, such as hydrochloric acid, to form salts.
- Amines can react with carboxylic acids to form salts.m In this reaction, water is lost and an amide can be formed.
What is benzene?
Benzene is the simplest armoatic hydrocarbon and is a colourless liquid. It’s molecular formula is C6H6 which shows it is deficiant in hydrogen atoms, suggesting it is unsaturated.
Why does benzene resist addition reactions?
Addition reactions would disrupt the electron delocalisation which would reduce the stability of the ring.
How can bonding in benzene be explained?
- The six carbon to carbon bonds in benzene are equal in length and strength which means they are intermediate between a single bond and double bond. - Bonding in benzene can be explained in terms of sp^2 hybridisation, sigma bonds and a pi molecular orbital containing delocalised electrons.
- Each carbon atom is sp^2 hybridised and each sp^2 hybrid orbital forms a sigma bond with two other carbon atoms and one hydrogen atom. The remaining p orbitals from each carbon atom overlap side on with eachother to form one pi molecular orbital containing 6 delocalised electrons (1 from each p orbital).
- Benzene therefore has 12 sigma bonds and one pi molecular orbital containing delocalised electrons. The pi orbital is responsible for benzene’s unusual stability.
What reactions can benezene undergo?
Benzene’s delocalised electrons means it acts as a nucleophile and is susceptible to attack by electrophiles. Therefore, benzene can undergo elecrophilic substitution reactions.
Describe the chlorination/bromination reaction of benzene, including the reagents and catalysts.
- The electrophiles, Cl+/Br+ are generated by reacting the reagent, Br2/Cl2 with AlCl or FeCl3 as a catalyst.
- The catalyst removes a negative Br/Cl ion from the molecule and so becomes AlCl4- or FeCl4-.
- The electrophilic Br+/Cl+ then attacks the benzene molecule and becomes chlorobenzene/bromobenzene.
Describe the nitration reaction of benzene, including the reagents.
- The electrophilic nitronium ion (NO2+) is produced from the reaction between the two reagents - concentrated nitric acid and sulfuric acids.
- The nitric acid loses a water molecule to become a nitronium acid and the sulfuric acids lose a proton.
- The electrophilic nitronium ion then attacks the benzene molecule and becomes nitrobenzene.
Describe the sulfonation reaction of benzene, including the reagents.
- The electrophilic HOSO2+ is produced from the reagent, concentrated sulfuric acid (H2SO4) reacting with itself.
- The electrophilic HOSO2+ then attacks benzene to create benzenesulfonic acid.
Describe the alkylation reaction of benzene, including the reagents and catalysts.
- When benzene is alkylated it reacts with a haloalkane as the reagent in the presence of AlCl3 as a catalyst.
- For example, the reagent could be CH3Cl which reacts with the catalyst AlCl3 and the CH3+ electrophile is formed which attacks benzene and becomes methylbenzene.
- Methylbenzene can be regarded as a substitued alkane where one of the hydrogen atoms in methane has been replaced by a C6H5 group known as a phenyl group. Therefore methylbenzene can also be called phenylmethane.
Why can graphite conduct electricity, but benzene cannot?
- Graphite has a layer structure similar to a network of fused benzene rings which means the delocalised electrons can extend over the whole layer which allows graphite to conduct electricity.
- However, the delocalised electrons in benzene are resticted to one molecule even when many benzene molecules are put together. They are unable to jum from one molecule to the the other.
- Therefore, graphite can conduct electricity because its layers allowes the delocalised electrons to move between molecules, but the delocalised electrons in benzene are confined to one small molecule.
