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ROUTESROUTESTO PHENOLTO PHENOL
A guide for A level studentsA guide for A level students
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING2008 2008
SPECIFICATIONSSPECIFICATIONS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available.
Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either clicking on the grey arrows at the foot of each page
or using the left and right arrow keys on the keyboard
PHENOLPHENOLKNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
CONTENTS
• Prior knowledge
• Synthesis from benzene
• Reactions of the OH group
• Reactions of the ring
• Benzene diazonium chloride - preparation
• Benzene diazonium chloride - reactions
PHENOLPHENOL
Before you start it would be helpful to…
• know the functional groups found in organic chemistry
• know the arrangement of bonds around atoms
• recall and explain electrophilic substitution of aromatic rings
PHENOLPHENOL
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
Preparation You cannot put an OH group directly onto a benzene ring byelectrophilic substitution, so phenol has to be synthesised ina multi-stage process
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
Preparation You cannot put an OH group directly onto a benzene ring byelectrophilic substitution, so phenol has to be synthesised ina multi-stage process
Step 1 - Nitration of benzene
reagents conc. nitric acid and conc. sulphuric acid (catalyst)
conditions reflux at 55°C
equation C6H6 + HNO3 ——> C6H5NO2 + H2O
mechanism electrophilic substitution
1
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
Preparation You cannot put an OH group directly onto a benzene ring byelectrophilic substitution, so phenol has to be synthesised ina multi-stage process
Step 2 - Reduction of nitrobenzene
reagents tin and conc. hydrochloric acid
conditions reflux
equation C6H5NO2 + 6 [H] ——> C6H5NH2 + 2H2O
mechanism reduction
2
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
Preparation You cannot put an OH group directly onto a benzene ring byelectrophilic substitution, so phenol has to be synthesised ina multi-stage process
Step 3 - Diazotisation of phenylamine
reagents nitrous acid and hydrochloric acid (use sodium nitrite)
conditions keep below 10°C
equation C6H5NH2 + HNO2 + HCl ——> C6H5N2+ Cl¯ +
2H2O
reaction type diazotisation
3
PHENOLPHENOL
Structure phenol is an aromatic alcohol with formula C6H5OH
the OH group is attached directly to the benzene ringit is an almost colourless crystalline solid
Preparation You cannot put an OH group directly onto a benzene ring byelectrophilic substitution, so phenol has to be synthesised ina multi-stage process
Step 4 - Substitution of diazo group by OH
reagents water
conditions warm above 10°C
equation C6H5N2+ Cl¯ + H2O ——> C6H5OH + N2 +
HCl
reaction type hydrolysis / substitution
4
PHENOL - PHENOL - REACTIONSREACTIONS OF THE OH GROUP
Water phenol is a weak acidit dissolves very slightly in water to form a weak acidic solutionit is a stronger acid than aliphatic alcoholsthe ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq) C6H5O¯(aq) + H+(aq)
PHENOL - PHENOL - REACTIONSREACTIONS OF THE OH GROUP
Water phenol is a weak acidit dissolves very slightly in water to form a weak acidic solutionit is a stronger acid than aliphatic alcoholsthe ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq) C6H5O¯(aq) + H+(aq)
NaOH phenol reacts with sodium hydroxide to form a salt - sodium phenoxideit is ionic and water soluble
C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l)
PHENOL - PHENOL - REACTIONSREACTIONS OF THE OH GROUP
Water phenol is a weak acidit dissolves very slightly in water to form a weak acidic solutionit is a stronger acid than aliphatic alcoholsthe ring helps weaken the O-H bond and stabilises the resulting anion
C6H5OH(aq) C6H5O¯(aq) + H+(aq)
NaOH phenol reacts with sodium hydroxide to form a salt - sodium phenoxideit is ionic and water soluble
C6H5OH(aq) + NaOH(aq) ——> C6H5O¯ Na+(aq) + H2O(l)
Sodium phenol reacts with sodium to form an ionic salt - sodium phenoxidehydrogen is also producedthis reaction is similar to that with aliphatic alcohols such as ethanol
2C6H5OH(s) + 2Na(s) ——> 2C6H5O¯ Na+(s) + H2(g)
ELECTROPHILIC SUBSTITUTION
Ease the OH group is electron releasing
it increases the electron density of the delocalised system
it makes substitution much easier compared to benzene
a p orbital on the oxygen overlaps with the p orbitals in benzene
PHENOL - PHENOL - REACTIONSREACTIONS OF THE AROMATIC RING
p orbitals in the systemthe p orbital on the O overlaps with the p orbitals in the ring
ELECTROPHILIC SUBSTITUTION
Bromine the OH group is electron releasing
it increases the electron density of the delocalised system
it makes substitution much easier compared to benzene
the electron density is greatest at the 2,4 and 6 positions
substitution takes place at the 2,4 and 6 positions
phenol reacts readily with bromine water WITHOUT A CATALYST
it is so easy that multiple substitution takes place
other electrophiles such as NO2+ react in a similar way
PHENOL - PHENOL - REACTIONSREACTIONS OF THE AROMATIC RING
BENZENE DIAZONIUM CHLORIDEBENZENE DIAZONIUM CHLORIDE
Structure has the formula C6H5N2+ Cl¯
a diazonium group is attached to the ringthe aromatic ring helps stabilise the ion
BENZENE DIAZONIUM CHLORIDEBENZENE DIAZONIUM CHLORIDE
Structure has the formula C6H5N2+ Cl¯
a diazonium group is attached to the ringthe aromatic ring helps stabilise the ion
PREPARATIONreagents phenylamine, nitrous acid and hydrochloric acid
conditions keep BELOW 10°C
equation C6H5NH2 + HNO2 + HCl ——> C6H5N2+ Cl¯ + 2H2O
notes nitrous acid is unstable and is made in situ from sodium nitrite
C6H5NH2 + NaNO2 + 2HCl ——> C6H5N2+ Cl¯ + NaCl +
2H2O
the solution is kept cold to slow down decompositionof the diazonium salt
C6H5N2+ Cl¯ + H2O ——> C6H5OH + HCl + N2
DIAZONIUM SALTS - DIAZONIUM SALTS - REACTIONSREACTIONS
Benzene diazonium chloride undergoes two main types of reaction
SUBSTITUTION OFTHE DIAZONIUM GROUP nitrogen (N2) expelled
COUPLING REACTIONS nitrogen atoms are retained
DIAZONIUM SALTS - DIAZONIUM SALTS - SUBSTITUTIONSUBSTITUTION
OHreagents water (HYDROLYSIS)
conditions warm above 10°C
equation C6H5N2+ Cl¯ + H2O ——> C6H5OH + HCl + N2
use the only reasonably simple way to substitute OH phenol is an antiseptic and is used to make polymers
DIAZONIUM SALTS - DIAZONIUM SALTS - SUBSTITUTIONSUBSTITUTION
OHreagents water (HYDROLYSIS)
conditions warm above 10°C
equation C6H5N2+ Cl¯ + H2O ——> C6H5OH + HCl + N2
use the only reasonably simple way to substitute OH phenol is an antiseptic and is used to make polymers
Ireagents potassium iodide solutionconditions warm equation C6H5N2
+ Cl¯ + KI ——> C6H5I + KCl + N2
DIAZONIUM SALTS - DIAZONIUM SALTS - COUPLINGCOUPLING
reagents phenol and sodium hydroxide
conditions alkaline solution below 10°C
equation C6H5N2+Cl¯ + C6H5OH + NaOH ——> C6H5-N=N-C6H4OH + NaCl +
H2O
(4-hydroxyphenol)azobenzene YELLOW
use making azo dyes
THE AZO GROUP
SOME AZO DYESSOME AZO DYES
(4-hydroxyphenol)azobenzene YELLOW
4-phenylazophenylamine YELLOW
The first azo dye to be made
methyl orange
YELLOW IN ALKALIRED IN ACID