Unit 5 Organic Reactions

including benzene, phenol, amines, phenylamine, benzediazonium compounds, amides. organic reactions for the edexcel unit 5 syllabus

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Unit 5 Organic Chemistry Reactions
Benzene
Combustion
In excess air, benzene burns to form carbon dioxide and water.
C 6H 6 + 71
2O2 6CO2 + 3H 2O
In limited air, it burns with a smoky flame forming carbon and water.
C 6H 6 + 11
2O2 6C + 3H 2O
Free-Radical Addition
Chlorine ­ bubble chlorine into boiling benzene in the presence of ultraviolet light, and
addition takes place. The chlorine radicals add on, one at a time to the benzene ring until all
the -bonds have been broken. (Bromine acts similarly)
Hydrogen ­ when heated with a Nickel catalyst, hydrogen adds on and cyclohexane is
formed.
Electrophilic Substitution
Mechanism ­ given that and electrophile E+ adds on to a carbon atom on the benzene ring:

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Nitration - when concentrated nitric acid, and a catalyst of concentrated sulphuric acid are
warmed together at 60 degrees under reflux, nitrobenzene and water are formed. The
electrophile is the ­NO2 group, which is formed by a protonated nitric acid molecule. (below
55 degrees, the reaction is too slow, above 65 degrees, a second nitrogen dioxide group Is
substituted onto the ring.)
Halogens ­ with a catalyst of anhydrous iron halide, chlorine and bromine react rapidly with
benzene, if the reagents are dry.…read more

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Sulfonation ­ benzene reacts with fuming sulphuric acid at 40 degrees under reflux. The
electrophile is the SO3. The products are benzesulphonic acid and water:
Alkenes ­ benzene adds onto alkenes to form a branched chain alkane substituted into the
benzene ring (except with ethene, as it has too few carbons)
Detergents ­ add a long chain alkene and benzene, then sulphonate the product, then
neutralise with sodium hydroxide to form a detergent.…read more

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Reacts with concentrated nitric acid, more nitro groups substitute to give
2,4,6-trinitrophenol
Phenol as an acid
Water ­ forms the phenate ion:
C 6H 5OH + H 2O H 3O+ + C 6H 5O-
Sodium hydroxide ­ reacts in a neutralisation reaction to form the salt sodium phenate and
water
Sodium- reacts with metallic sodium to form hydrogen and the salt sodium phenate
Sodium hydrogencarbonate/ sodium carbonate ­ phenol is a weaker acid than carbonic acid,
so it does not liberate carbon dioxide from either…read more

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Acid chlorides, aromatic ­ reacts in aqueous solution to create C6H5O- ions, which are a
stronger nucleophile than phenol molecules.
Benzoic Acid
When warmed with concentrated nitric and sulphuric acids, 3-nitrobenzoic acid and water are
formed.
2-methlynitrobenzene
Preparation
Add the nitrating mixture, consisting of concentrated nitric and sulphuric acids, and mix with
benzene, then heat in a water bath at 50 degrees.
After refluxing, the mixture is cooled and water added to dilute the acids.…read more

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Reduction of a nitrile/amide ­ reduced by LiAlH4 in dry ether, then hydrolysis of the adduct
with dilute acid
As a Base
Water ­ they react reversibly, forming OH- ions
Acids ­ when reacted with an acid, a salt is formed.…read more

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The tin (Sn) acts as a catalyst. It is oxidised to provides the electrons used to reduce the
nitrobenzene in the presence of the acid.…read more

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Acid chloride - Reacts with, like an aliphatic primary amine, an acid chloride to form a
secondary amine. The phenylamine acts as a nucleophile
Nitrous acid ­ nitrous acid is unstable, and has to be made is situ by mixing a solution of
sodium nitrate, NaNO2 with excess dilute hydrochloric acid.
This reacts with the phenylamine to form benzenediazonium chloride in an exothermic
reaction. The temperature must be maintained between 0 and 10 degrees.…read more

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Phenylamine ­ with vigorous shaking, a yellow precipitate is formed:
Amides
Preparation
Ammonia and an acid chloride
Hydrolysis
When boiled under reflux with either aqueous acid or alkali, amides are hydrolysed. E.g.
ethanamide hydrolysed with dilute acid:
Polyamides
Condensation polymerisation ­ formed from two different monomers, each with two
identical functional groups, or in some cases, a single monomer that has two different
functional groups:
e.g. Kevlar:
e.g. Nylon:
Addition Polymerisation ­ a polymer formed from monomers containing a C=C group.…read more

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E.g poly(ethanol) ­ the monomer does not exist. The polymer is
manufactured by reacting the polymer polyvinylacetate with methanol in a transesterification
reaction.…read more

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