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139 Cards in this Set
- Front
- Back
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Where do Arenes occur naturally?
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materials such as crude oil, coal, and can be produced in refineries from crude oil
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What is a benzene derivative?
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A benzene ring where one of the Hydrogen atoms has been replaced by an atom or group of atoms
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What can benzene be used for?
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synthesis of other aromatic materials such as ethylbenzene, phenol and styrene. small quantities can be used to make materials such as detergents, explosives, pharmaceuticals or dyestuffs
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What are the properties of benzene?
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Colorless liquid
Sweet odour Highly flammable |
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2 natural sources of aromatic compounds?
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volcanoes
forest fires |
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Comment on the suggested linear structure for benzene, with several double bonds
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Benzene was rather unreactive for a molecule that was considered to be highly unsaturated; it did not take part in many of the reactions of alkenes.
Therefore this suggested structure was unlikely to be correct. |
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What was Kekulé's proposed structure of benzene?
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A six-membered ring of carbon atoms joined by alternate single and double bonds.
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What are the problems with Kekulé's proposed structure of benzene?
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It failed to explain the chemical and physical properties of benzene fully, such as:
Low Reactivity carbon-carbon bond lengths Hydrogenation |
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Explain the low reactivity of Kekulé's proposed structure of benzene
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If C=C double bonds were present then benzene would react in a similar way to alkenes
Each C=C double bond would be expected to decolourise bromine water. This does not happen, nor does benzene take part in other electrophilic addition reactions expected from C=C bonds in alkenes. |
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How did Kekulé account for the lack of reactivity in his proposed structure of benzene?
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He suggested that benzene has two different forms, differing only by positions of C=C double bonds. These forms are in such a rapid equilibrium that approaching bromine molecules could not be attracted to a double bond before the structure changed.
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Explain the problem with the carbon-carbon bond lengths in Kekulé's proposed structure of benzene
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Kekulé structure of alternating single and double bonds was represented as a symmetrical molecule. However C-C bonds and C=C double bonds have different lengths.
X-Ray studies showed that all six carbon-carbon bonds were all the same length, 0.139nm. |
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Explain the problem with the hydrogenation of Kekulé's proposed structure of benzene
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When cyclohexene reacts with H, the enthalpy change of hydrogenation is -120 kJ/mol. Therefore for cyclohexa-1,3,5-triene, Kekulé's proposed structure of benzene, reacts with H, the expected enthalpy of hydrogenation is -320 kJ/mol.
However, the actual enthalpy change of hydrogenation of benzene is -208 kJ/mol. Therefore the actual structure of benzene has less energy than Kekulé's proposed structure, and is 152 kJ/mol more stable. This energy is the delocalised (resonance) energy of benzene. |
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Delocalised model of benzene
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cyclic hydrocarbon with 6 C, 6 H
C arranged in a planar hexagonal ring each C attached to 2 other Cs and one H shape around each C is trigonal planar, bond angle 120 C has 4 outer shell electrons, 3 used for bonding to other atoms (called sigma bonds). other electron is in a 2p orbital above and below plane of C atoms. overlap of this electron produces a system of pi bonds which spread over all 6 C atoms. p electrons no longer held between just 2 C atoms. p electrons spread all over the ring, said to be delocalised |
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benzene does not, under normal conditions:
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decolourise bromine water
react with strong acids such as HCl react with halogens: chlorine, bromine or iodine |
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Why does benzene not undergo addition reactions?
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in an addition reaction, electrons from the delocalised system would need to bond to the atom or group of atoms being added. this would result in a product less stable than benzene therefore not energetically favourable. addition reaction would disrupt the delocalisation of the ring structure
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Why does benzene take part in substitution reactions?
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organic product retains delocalisation, and hence stability of the benzene ring
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Exposure to benzene can cause
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cancer in humans. Continual exposure can result in anaemia or leukaemia. (carcinogen)
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Who was credited for the determination of the structure of benzene
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Kathleen Lonsdale
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Who discovered the ring structure of benzene?
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Friedrich August Kekulé von Stradonitz
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What is the equation, and conditions needed for the preparation of nitrobenzene (nitration of benzene)?
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C6H6 + HNO3 --> C6H5NO2 + H2O
HNO3 + H2SO4 --> NO2+ + HSO4- + H2O NO2+ (nitryl cation/ nitronium ion) is used as the electrophile) H2SO4 is used as a catalyst. 50 degrees Celsius. |
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Outline the process of the nitration of benzene
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Nitrating mixture is prepared in a round-bottomed or pear-shaped flask.
Concentrated nitric acid and concentrated sulfuric acid are mixed together carefully while cooling the mixture in a beaker of cold water. Benzene is then added carefully to the nitrating mixture, keeping below 50 degrees Celsius. After all Benzene has been added, a reflux condenser is fitted to the flask and the mixture is heated at 50 degrees Celsius in a water bath (any higher will result in multiple nitro group subsitutions). |
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What are the properties and uses of nitrobenzene?
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Pale yellow liquid
Starting material in the preparation of dyes, pesticides and pharmaceuticals (like paracetamol). |
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Nitration of methylbenzene
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Nitrates with a mixture of concentrated nitric and sulfuric acids.
Reaction faster than nitration of benzene. Produces 2,4,6-trinitromethylbenzene (aka trinitrotoluene, TNT) - explosive. |
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Halogenation of benzene
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Benzene can only react with halogens in the presence of a halogen carrier, such as: FeCl3, FeBr3, AlCl3, AlBr3.
This is an electrophilic substitution reaction; hydrogen atom replaced by a halogen. |
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What are the conditions for the chlorination of benzene? What is one use for chlorobenzene?
Use an equation in your answer to show the chlorination of benzene. |
Reacts at RTP in the presence of AlCl3, FeCl3 or Fe (as the halogen carrier) to produce chlorobenzene
Used as a solvent and in the production of pesticides C6H6 + Cl2 --> C6H5Cl + HCl |
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What are the conditions for the bromination of benzene? What is one use for bromobenzene?
Use an equation in your answer to show the bromination of benzene. |
Reacts at RTP in the presence of AlBr3, FeBr3 or Fe (as the halogen carrier) to produce bromobenzene
Used in the preparation of pharmaceuticals C6H6 + Br2 --> C6H5Br + HBr |
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Outline how benzene undergoes electrophilic subsititution
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Electron dense ring attracts an electrophile which accepts a pair of the pi-electrons from the delocalised ring to form a new covalent bond.
An intermediate forms that contains both the electrophile and hydrogen atom that is being substituted. The delocalised pi-electron cloud is disrupted and the intermediate is less stable than benzene. The unstable intermediate rapidly loses the hydrogen as an H+ ion. The delocalised ring of electrons reforms and stability is restored. |
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Why is a halogen carrier needed in the halogenation of benzene (use bromine as an example)?
Use equations in your answer. |
(Using Bromine): Br+ is a more powerful electrophile than Br2.
Br2 + FeBr3 --> Br+ + FeBr4- Termination: H+ + FeBr4- --> FeBr3 + HBr |
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What do you observe if bromine is added to cyclohexene?
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Solution changes from orange to colourless.
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How does Bromine react with cyclohexene?
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pi-bonds in cyclohexene contains localised electrons sited above and below the two carbon atoms in the double bonds. This produces a region of high electron density.
When bromine approaches cyclohexene, electrons in pi-bond repel electrons in Br-Br bond, inducing a dipole in the Br2 molecule, it is now polar. pi-electron pair from the double bond is now attracted to the slightly positive bromine atom, causing the double bond to break, forming a new bond between one carbon atom and one bromine atom, forming a positively charged carbocation. the bond between the two Br atoms breaks by heterolytic fission, forming a bromide ion. the Br- ion is attracted towards the intermediate carbocation, forming a covalent bond. This produces 1,2-dibromocyclohexane. |
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What do you observe if bromine is added to benzene?
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No reaction takes place, bromine mixture remains orange.
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What do you observe if bromine is added to benzene in the presence of a halogen carrier catalyst (iron filings, iron(III) bromide)?
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Bromine is decolourised (orange to colourless), and white fumes of hydrogen bromide gas are observed.
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Why does benzene only react with bromine in the presence of a halogen carrier catalyst?
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benzene has delocalised pi-electrons spread over all 6 carbon atoms in the ring, whereas alkenes have pi-electrons localised above and below the 2 carbon atoms in the double bond. therefore benzene has a lower electron density than alkenes.
when non polar molecules, like bromine, approaches benzene there is insufficient pi-electron density above and below any two carbon atoms to cause the necessary polarisation of the bromine molecule. a halogen carrier produces a more powerful electrophile, such as Br+. the greater charge on the halide ion is able to attract the pi-electrons from benzene so that the reaction can take place |
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What are the properties of PCBs (polychlorinated biphenyls)?
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fire resistant
relatively unreactive poor conductors of electricity |
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What are the uses of PCBs (polychlorinated biphenyls)?
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coolants
insulating fluids transformers capacitors plasticisers in paint and cement carbonless copy paper |
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What is an aromatic alcohol?
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A benzene ring with an -OH group attached to a side chain.
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What are the properties of Phenol?
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Solid at RTP
Slightly soluble in water |
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Comment on the solubility of Phenol in water
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Slightly soluble in water as the -OH group forms H bonds with water molecules.
The presence of a benzene ring makes phenol less soluble in water than alcohols. |
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Reaction of Phenol with Sodium Hydroxide
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Phenol is dissolved in water, forming a weak acidic solution by losing an H+ ion from the -OH group:
C6H5OH + aq <--> C6H5O- Phenol is neutralised by aqueous sodium hydroxide to form the salt sodium phenoxide, C6H5O-Na+ and water. C6H5OH + NaOH --> C6H5O-Na+ + H2O |
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Reaction of Phenol with a metal (use Sodium as an example)
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When a reactive metal such as sodium is added to phenol, the metal effervesces producing Hydrogen gas. The organic product sodium phenoxide, C6H5O-Na+ is a salt.
2C6H5OH + 2Na --> 2C6H5O-Na+ + H2 |
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What is Joseph Lister famous for?
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The first person to treat wounds with dressing coated in carbolic acid (phenol). He insisted that surgeons washed their hands and sterilised their instruments with a solution of 5% phenol before carrying out operations.
It was also used on the the whole operating theatre, killing bacteria before wounds could be infected. This increased the success rate of amputations, however phenol was found to be caustic and made some surgeons very ill. Lister then found that boric acid was a better and safer antiseptic. |
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Comment on the reaction of phenol with bromine
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Phenol undergoes electrophilic substitution with bromine. Unlike benzene, the reaction takes place at RTP without the need of a halogen carrier catalyst.
When bromine water is added to an aqueous solution of phenol, the orange bromine colour disappears and a white precipitate of 2,4,6-tribromophenol is formed. |
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What is a test for phenol?
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The reaction between phenol and bromine.
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Comment on the relative ease of bromination of phenol compared with the bromination of benzene
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The increased reactivity occurs because a lone pair of p-orbital electrons on the oxygen atom in the phenol group is drawn into the benzene ring.
This creates a higher electron density in the ring structure and the ring is activated. The increased electron density polarises bromine molecules, which are then attracted more strongly towards the ring structure than in benzene. |
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What are some uses of Phenol?
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alkyl phenols - Found in surfactants and detergents
chlorophenols - Found in antiseptics and disinfectants such as TCP and Dettol salicyclic acid - Preparation of aspirin and other pharmaceuticals bisphenol - Production of epoxy resins for paints |
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What is the carbonyl functional group?
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C=O
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Why doesn't the carbonyl bond react in the same way as the double bond in an alkene?
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The oxygen atom is more electronegative than the carbon atom. This creates a dipole in the C=O bond because the bonded electrons are attracted towards the oxygen.
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What are aromatic aldehydes and ketones?
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Compounds containing both a benzene ring and a carbonyl group.
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Comment on the properties and uses of benzaldehyde
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At room temperature it is a colourless liquid with a pleasant almond-like odour.
It is used to make almond essence, an ingredient in Bakewell tarts. It also gives the flavour to the marzipan found under the icing on traditional Christmas cakes. |
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What is phenylethanone used for?
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It is used to create fragrances that resemble cherry, honeysuckle, jasmine and strawberry.
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What has cinnamon commonly been used for?
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It has been used in medicines to treat coughing, hoarseness and sore throats.
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Comment on the oxidation of primary, secondary and tertiary alcohols.
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Primary: Alcohol -> Aldehyde -> Carboxylic Acid
Secondary: Alcohol -> Ketone Tertiary: Does not oxidise |
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What oxidising mixture is used in the oxidation of alcohols?
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potassium dichromate and sulfuric acid
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What happens to the potassium dichromate when oxidising alcohols and aldehydes?
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It is reduced and changes colour from orange to green
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Write an equation for the oxidation of ethanol (primary) to ethanal
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CH3CH2OH + [O] --> CH3CHO + H2O
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What do you need to do when preparing aldehydes in the lab by oxidising alcohols, and why?
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Distil the aldehyde from the reaction mixture as it is formed.
This prevents the aldehyde from oxidising further to a carboxylic acid. |
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What is the process of oxidising an aldehyde to a carboxylic acid?
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Heat under reflux and then distil the product off.
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Write an equation for the oxidation of ethanal to ethanoic acid
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CH3CHO + [O] --> CH3COOH + H2O
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Write an equation for the oxidation of propan-2-ol to propanone
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CH3CHOHCH3 + [O] --> CH3COCH3 + H2O
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What reducing agent is used to reduce carbonyl compounds?
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Sodium Tetraborohydride, NaBH4
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How are carbonyl compounds reduced?
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NaBH4 is used as the reducing agent, and water is often used as the solvent.
The reaction is usually carried out by warming the carbonyl compound with the reducing agent. |
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Write an equation for the reduction of propanal
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CH3CH2COH + 2[H] --> CH3CH2CH2OH
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Write an equation for the reduction of pentan-2-one
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CH3COCH2CH2CH3 + 2[H] --> CH3CH(OH)CH2CH2CH3
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What is citronellal?
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An aldehyde which gives citronella oil a distinctive lemon scent. It also has insect-repellent properties and is effective at repelling mosquitoes.
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Outline the process of nucleophilic addition when reducing aldehydes and ketones
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Reacts with NaBH4.
The BH4- ion acts as a source of hydride ions which acts as the nucleophile. The electron-deficient carbon atom in the polar C=O double bond is attacked by the hydride ion. The lone pair of electrons from the :H- ion forms a bond with the carbon atom. The pi-bond in the C=O bond breaks to produce a negatively charged intermediate. The intermediate donates an electron pair to a hydrogen atom on a water molecule, forming a dative covalent bond and a hydroxide ion. The organic addition product is an alcohol. |
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Where have aldehydes been used in industry?
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Perfumes, such as Chanel No 5.
There are many synthetically produced aldehydes used in perfumes, such as hexyl cinnemaldehyde and decanal. |
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Why is hexyl cinnamaldehyde used in perfumes?
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It has a floral, jasmine fragrance
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Why is decanal used in perfumes?
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It provides a fragrance of violets, roses and oranges
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What is 2,4-DNPH?
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2,4-dinitrophenylhydrazine
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What is Brady's reagent?
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A solution of 2,4-DNPH in a mixture of methanol and sulfuric acid
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What do you observe when Brady's reagent is added to a ketone or an aldehyde?
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A yellow or orange precipitate is formed, known as a 2,4-dinitrophenylhrazine derivative, confirming the presence of a carbonyl functional group
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What is Tollen's reagent?
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A weak oxidising agent used to distinguish between aldehydes and ketones
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How is Tollen's reagent made?
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aqueous sodium hydroxide is added to aqueous silver nitrate until a brown precipitate of silver oxide is formed
Dilute aqueous ammonia is then added until the precipitate just dissolves |
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What colour is Tollen's reagent?
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Colourless
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What is Tollen's reagent also known as?
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Ammoniacal silver nitrate
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What do you observe when adding Tollen's reagent to an aldehyde?
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Silver grey solid (silver mirror) is formed
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What do you observe when adding Tollen's reagent to a ketone?
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No reaction
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Comment on the reaction between Tollen's reagent and aldehydes and ketones
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Aldehydes are easily oxidised to carboxylic acids
Ketones are not oxidised |
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Outline the process of identifying a carbonyl compound after it has been identified as an aldehyde or ketone
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The yellow/orange solid 2,4-DNPH derivative is slightly impure and is filtered and recrystallised to produce a purified sample of yellow or orange crystals of the 2,4-DNPH derivative. This is then filtered and allowed to dry.
Melting point of the purified derivative is measured and recorded, then compared to a database or table to identify the original aldehyde or ketone |
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Give some examples of carboxylic acids and where they are found
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methanoic (formic acid) - sting of ants
ethanoic (acetic) acid - vinegar butanoic acid - rancid butter citric acid - citric fruits oxalic acid - rhubarb malic acid - apples hexanoic acid - smell of goats and farmyard animals |
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Comment on the solubility of carboxylic acids
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The highly polar C=O bonds and O-H bonds allow carboxylic acid molecules to form hydrogen bonds with water molecules.
As the number of carbon atoms in the carboxylic acid increases, solubility decreases. This is a result of the longer non-polar hydrocarbon chain in the molecule, which does not interact with the water molecules |
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Are carboxylic acids basic or acidic?
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they are weak acids
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What is the carboxylate ion?
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COO-
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Comment on the reaction between a carboxylic acid and a metal.
Give an example, including an equation |
Forms a salt and hydrogen gas - during the reaction there is effervescence.
ethanoic acid + sodium --> sodium ethanoate + hydrogen gas CH3COOH + Na --> CH3COO-Na+ + 1/2H2 |
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Comment on the reaction between a carboxylic acid and a base.
Give an example, including an equation |
Reacts with aqueous bases, such as metal hydroxides. Forms a salt and water.
propanoic acid + potassium hydroxide --> potassium propanoate + water CH3CH2COOH + KOH --> CH3CH2COO-K+ + H2O |
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Comment on the reaction between a carboxylic acid and a carbonate.
Give an example, including an equation |
Aqueous carboxylic acid reacts with carbonates, forming a salt, carbon dioxide and water.
Methanoic acid + sodium carbonate --> sodium methanoate + carbon dioxide + water 2HCOOH + Na2CO3 --> 2HCOO-Na+ + CO2 + H2O |
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How do you make an ester?
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React a carboxylic acid with an alcohol in the presence of an acid catalyst, usually concentrated sulfuric acid
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What is the equation for the esterification of ethyl propanoate from propanoic acid and ethanol?
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propanoic acid + ethanol ---> ethyl propanoate + water
CH3CH2COOH + CH3CH2OH --> CH3CH2COOCH2CH3 + H2O |
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Comment on the nomenclature of an ester, using propanol and ethanoic acid as an exmaple
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the alcohol provides the alkyl part of the name, and the carboxylic acid provides to alkanoate part of the name:
PROPanol + ETHANoic acid --> PROPylETHANoate + water |
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How do you prepare an ester when using an acid anhydride?
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Gently heat the acid anhydride with the alcohol
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State a reason for the esterification of acid anhydrides instead of carboxylic acids
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the esterification of an acid anhydride gives a much better yield than preparations from carboxylic acids
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What is the equation for the esterification of methyl ethanoate from ethanoic anhydride and methanol?
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ethanoic anhydride + methanol --> methyl ethanoate + ethanoic acid
(CH3CO)2O + CH3OH --> CH3COOCH3 + CH3COOH |
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What is the reverse of esterification called?
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hydrolysis
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Comment on the acid hydrolysis of esters, including reaction conditions, reagents and an equation using propyl ethanoate as an example
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Ester is heated under reflux with dilute sulfuric acid OR dilute hydrochloric acid. Ester is broken down by water, with the acid acting as a catalyst.
propyl ethanoate + water --> ethanoic acid + propan-1-ol CH3COOCH2CH2CH3 + H2O --> CH3COOH + CH3CH2CH2OH |
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Comment on the alkaline hydrolysis of esters, including reaction conditions, reagents and an equation using ethyl propanoate and sodium hydroxide as an example
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Aqueous alkaline conditions. Aqueous sodium hydroxide OR potassium hydroxide is refluxed with the ester. Reaction is non-reversible and leads to the formation of the sodium (or potassium) salt of the carboxylic acid.
ethyl propanoate + sodium hydroxide --> sodium propanoate + ethanol CH3CH2COOCH2CH3 + NaOH --> CH3CH2COO-Na+ + CH3CH2OH |
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Give two uses of esters in industry and catering
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used as perfumes and as flavourings
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Where are esters found?
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in essential oils, obtained by steam distillation of organic plant matter
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What is oil of wintergreen? What is it used for?
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the essential oil obtained from the wintergreen plant.
it can be massaged into painful muscles and joints to offer relief as deep heat. it is also used before exercising to help warm muscles up, or afterwards to relieve the aches of over-exercising |
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What did scientists discover after analysing oil of wintergreen?
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The ester methyl salicylate
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Where is benzyl ethanoate naturally found?
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in many flowers and is the main constituent of the essential oils from the jasmine flowers
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What is benzyl ethanoate used for?
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perfumery and cosmetics due to its aroma
give apple and pear flavours in drinks and foods |
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Where is benzyl ethanoate found industrially?
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perfumes
shampoos fabric softener soap hairspray deodarants |
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What is another name for the alkaline hydrolysis of an ester, and how was it derived?
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saponification, the basis of soap-making
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What important functions do fats have in the body?
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protects your organs
provides insulation acts as a long term energy store |
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What are fatty acids?
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animal and vegetable fats and oils, which are esters of long-chain carboxylic acids
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What is the difference between fats and oils?
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Their melting point.
melting point above room temperature = fat melting point below room temperature = oil |
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Where do triglycerides occur naturally?
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animal and vegetable fats
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What are triglycerides?
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triesters with three fatty acids joined to each of the alcohol groups on glyercol (propan-1,2,3-triol) through an ester linkage
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What makes a fatty acid saturated?
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Having no double bonds in the HYDROCARBON chain. The carbonyl group is not in the hydrocarbon chain
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What are a mono-unsaturated fats?
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Unsaturated fats with one double bond in the hydrocarbon chain
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What are a poly-unsaturated fats?
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Unsaturated fats with more than one double bond in the hydrocarbon chain
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Explain the shorthand notation for fatty acids, using octadeca-9,12-dienoic acid as an example
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18:2 (9,12)
First number is the number of carbons Second number indicates the number of double bonds the numbers in the brackets indicates the position(s) of the double bond(s) |
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What is a consequence of foods high in saturated fats?
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Increases the risk of heart disease by raising cholesterol levels
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Comment on unsaturated fats and their effect on our health
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they are better for us than foods high in saturated fats
however, they appear in two isomeric forms, cis and trans. cis-fats present very little danger to our health, but trans-fats increase the risk of coronary heart disease unsaturated cis-fats cannot pack closely together and so are liquid at room temperature unsaturated trans-fats are quite linear in its structure and can pack closely together. consequently, they have higher melting points than its cis isomer |
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How does the food industry handle unsaturated fats?
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Double bonds in unsaturated fats are often removed by partial hydrogenation. However the remaining double bonds may be structurally changed, with many being converted from the cis-form to the less healthy trans-form
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What is the effect of trans-fats on LDLs and HDLs?
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They raise LDL levels and increase the risk of heart disease. They also tend to lower the HDL levels
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How can biodiesel be produced?
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using waste cooking oil, or crops such as rapeseed
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What is transesterification? Comment further.
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The process to make biodiesel. Triglycerides in fats and oils are reacted with methanol or ethanol in the presence of a sodium hydroxide or potassium hydroxide catalyst. glycerol is also formed
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What is the general equation of transesterification for the production of biodiesel?
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triglyceride + 3 methanol/ethanol --> 3 biodiesel + glycerol
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What is the glycerol produced in transesterification used for?
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Sold to pharmaceutical or cosmetic industries, improving the atom economy of the process
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Why is biodiesel thought to be carbon neutral?
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When the fuel crop grows, it absorbs the same amount of carbon dioxide as is released when it is burned.
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Why is the use of biodiesels under scrutiny?
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Some poor countries are using land to produce biodiesel crops to sell to richer countries, instead of for local food crops
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What is an amine?
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A derivative of ammonia
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Give three examples of amines and their uses
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Amphetamine - treats daytime drowsiness and chronic fatigue syndrome
Phenylephrine - decongestant Adrenaline - helps the body deal with sudden stress |
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Describe the odour of amines
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'fishy'
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What is a primary amine?
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One with only one carbon chain attached to the nitrogen
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Comment on the basicity of amines
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Amines are weak bases
- has a lone pair of electrons on the nitrogen atom -can accept a proton, H+ When a base accepts a proton, a dative covalent bond forms between the lone pair of electrons on the nitrogen atom and the proton |
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How does ammonia react with protons? Use an equation to back-up your answer
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NH3 + H+ --> NH4+
NH4+ is the ammonium ion. |
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What is the general reaction of an amine with a base? Give an example using ethylamine reacting with hydrochloric acid
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base + acid --> salt
ethylamine + hydrochloric acid --> ethylammonium chloride CH3CH2NH2(aq) + HCl(aq) --> CH3CH2NH3+Cl-(aq) |
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How are aliphatic amines prepared?
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By gently warming halogenoakanes with an excess of ammonia, using ethanol as a solvent
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Write an equation for the formation of propylamine by the reaction of 1-chloropropane and ammonia, include multiple equations
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CH3CH2CH2Cl + NH3 --> CH3CH2CH2NH2 + HCl
HCl + NH3 --> NH4+Cl- |
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When preparing aliphatic amines, why is an excess of ammonia used?
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Ammonia has a lone pair of electrons and attacks the delta+ carbon atom in the polar carbon-halogen bond. The product, for example, propylamine, also has a lone pair of electrons. This can attack another molecule of the halogenoalkane, causing further substitution. An excess of ammonia is used to minimise this further substitution.
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Write an equation for the further substitution of propylamine with 1-chloropropane
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CH3CH2CH2Cl + CH3CH2CH2NH2 --> (CH3CH2CH2)2NH + HCl
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How are aromatic amines prepared? Write an equation using nitrobenzene as an example
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Nitrobenzene, and other nitroarenes can be reduced using a mixture of tin and concentrated hydochloric acid, heated under reflux, followed by neutralisation of the excess hydrochloric acid.
Nitrobenzene + 6[H] --> phenylamine + 2H2O |
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What are the two steps in the industrial preparation of dyestuffs?
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diazotisation
coupling reactions |
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Comment on the diazotisation reaction, using phenylamine as an example. Write an equation in your answer
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First stage of the prepation of dyestuffs, forming a diazonium ion.
When a mixture of nitrous acid (HNO2) and phenylamine is kept below 10 degrees C, a diazonium salt is formed HNO2 is generated in the reaction mixture by reacting together sodium nitrite, NaNO2, and excess hydrochloric acid: NaNO2 + HCl --> HNO2 + NaCl The cold nitrous acid then reacts with an aromatic amine to form a diazonium salt. Phenylamine + Nitrous acid + 2 Hydrochloric Acid --> Benzenediazonium chloride + 2 Water C6H5NH2 + HNO2 + 2HCl --> C6H5N2+Cl- |
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Comment on the coupling reaction, using the diazonium salt benzenediazonium chloride and phenol
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A coupling reaction occurs when the diazonium salt is reacted with phenol (or another aromatic compound, such as an amine) UNDER ALKALINE CONDITIONS. The two benzene rings are linked together through an azo functional group, -N=N-.
benzenediazonium chloride + phenol + sodium hydroxide (catalyst) --> C6H5N2C6H4OH + sodium chloride + water |
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What is formed after both diazotisation and coupling?
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A product which is brightly coloured compound; used as an azo dye.
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How are different dyes produced from azo-dyes?
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A reaction between phenylamine and potassium dichromate results in a purple solution in an alcohol. Using different benzene-containing compounds results in many other artificial colours
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