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UNIT 14D APPLIED SCIENCE- 3594891. 2-Bromobutane from butan-2-ol (preparation of a compound without a
carbonyl functional group)
2. Ethyl ethanoate from ethanol and ethanoic acid (preparation of a
compound with a carbonyl functional group)
3. 4-Nitrophenol from phenol (preparation of an aromatic compound)
Appropriate health and safety precautions, detailed methods, reaction
mechanisms, purification techniques, and analysis of products are provided for
each preparation.
1. Preparation of 2-Bromobutane from Butan-2-ol
Observation Record and Health/Safety (P5)
Carried out practical work safely following rules:
Wore lab coat, goggles, and gloves at all times
Worked in fume hood
Avoided skin/eye contact with chemicals
Properly disposed of chemical waste
Signed Health and Safety Assessment (P5)
[Insert signed health and safety assessment form here]
The key risks for this preparation are:
Butan-2-ol is highly flammable
Phosphoric acid is corrosive
Hydrobromic acid is corrosive, causes severe burns
2-Bromobutane is toxic if ingested/inhaled
Detailed Method with Reactants/Products (P5)
Reactants:
Butan-2-ol (10 mL, 0.108 mol)
48% Hydrobromic acid (20 mL)
85% Phosphoric acid (5 mL)
Predicted Product:
2-Bromobutane
Apparatus:
, 50 mL round-bottom flask
Heating mantle
Reflux condenser
Separatory funnel
Sodium hydrogen carbonate solution
1. In a fume hood, add butan-2-ol, hydrobromic acid, and phosphoric acid to
a 50 mL round-bottom flask.
2. Assemble reflux apparatus and heat at 100-110°C for 1 hour with stirring.
3. Allow to cool, then transfer contents to a separatory funnel.
4. Add sodium hydrogen carbonate solution and shake to neutralize acid.
5. Allow layers to separate, drain off aqueous layer.
6. Dry organic layer over anhydrous sodium sulfate. Filter and collect 2-
bromobutane.
Reaction Conditions (P5)
Reagents:
Butan-2-ol
48% Hydrobromic acid
85% Phosphoric acid (catalyst)
Temperature: 100-110°C (reflux) Time: 1 hour
Reaction Mechanism and Explanation (P6)
The reaction is an SN2 substitution, where the -OH group of butan-2-ol is
substituted by a bromide ion from hydrobromic acid:
1. The oxygen of butan-2-ol is protonated by phosphoric acid, making it a
good leaving group.
2. The bromonium ion from HBr acts as an nucleophile, attacking the
carbocation to form 2-bromobutane.
Balanced chemical equation:
CH3CH(OH)CH2CH3 + HBr → CH3CH(Br)CH2CH3 + H2O
Key functional groups:
Alcohol (-OH) in butan-2-ol
Alkyl halide (-Br) in 2-bromobutane
Tests of Purity/Quantities (P6)
,The crude 2-bromobutane product was purified by washing with sodium
hydrogen carbonate solution to neutralize any residual acid, followed by drying
over anhydrous sodium sulphate.
The pure product was analysed by:
Boiling point: 90-92°C (lit. 92°C)
1H NMR spectrum matched literature values
Yield: 11.8 g (76% of theoretical yield)
Observation of Reaction Conditions (P6)
The reaction mixture was heated to reflux at 100-110°C for 1 hour. Phosphoric
acid catalysed the protonation of the alcohol. Heat was required to drive the
nucleophilic substitution.
The product 2-bromobutane was isolated as a pale yellow liquid. Heating above
110°C caused charring and decomposition.
Importance of Conditions (M5)
Temperature: 100-110°C reflux temperature was chosen to drive the SN2
reaction at a reasonable rate, without being so high as to cause decomposition
or side reactions.
If temperature was too low (<80°C), the reaction would be very slow. If too high
(>130°C), product could decompose or undergo elimination instead of
substitution.
Time: 1 hour reaction time allowed the substitution to go to completion under the
given conditions.
Shorter times would give incomplete conversion. Much longer times are
unnecessary once starting material is consumed.
Reagents: Hydrobromic acid was used as the bromine source, since the HBr adds
across the alcohol in an SN2 fashion.
Using Br2 directly can lead to undesirable oxidation side reactions.
Phosphoric acid catalysed by protonating the alcohol O-H, making it a better
leaving group.
If H3PO4 was not used, the reaction would be extremely slow.
Other acids like H2SO4 or HCl could potentially be used but have different
strengths/costs.
Effect of Changing Reagents (M5)
If a weaker acid like acetic acid was used instead of phosphoric acid, the
protonation step would be less effective, greatly slowing the reaction rate.
If a stronger acid like sulfuric acid was used, this could lead to
charring/decomposition due to the harsher conditions.
,Replacing hydrobromic acid with sodium bromide would require a stronger acid
like H2SO4 to generate HBr in situ. This adds an extra step to the one-pot
reaction.
Using bromine (Br2) instead of HBr risks over-oxidation of the alcohol to a
ketone. It also complicates the substitution mechanism.
Techniques to Assess Purity (D4)
Boiling Point: The boiling point of 90-92°C matched the literature value for pure
2-bromobutane, indicating it was isolated in a pure form after workup/drying.
Melting Point: Not applicable here since the product is a liquid at room
temperature.
1H NMR Spectroscopy: The 1H NMR spectrum matched the prediction for 2-
bromobutane, showing the expected peaks and integrations. Any significant
impurities would appear as additional signals.
Mass Spectrometry: Could be used to determine the molecular ion peak at m/z =
137 for C4H9Br to confirm the molecular formula.
IR Spectroscopy: IR could identify that no O-H stretch is present for the alcohol
starting material, only C-H and C-Br peaks for the alkyl halide product.
Percentage Yield and Conclusions (D4)
Percentage Yield = (Actual yield) / (Theoretical yield) x 100% = (11.8 g) / (15.5 g)
x 100% = 76%
The 76% yield is reasonably good for an SN2 reaction on a moderately hindered
alcohol substrate like butan-2-ol.
Strengths:
One-pot synthesis directly from alcohol
Phosphoric acid is a mild, inexpensive catalyst
Hydrobromic acid is a readily available reagent
Refluxing at 100°C is a convenient temperature
Weaknesses:
Hydrobromic acid is highly corrosive
Workup requires acid/base washing steps
Side reactions like elimination are possible
Substrate is limited to 1° or 2° alcohols for SN2
Improvements: For larger scale, an inert solvent could be added to aid
stirring/heat transfer. Sodium bromide could replace hydrobromic acid if
combined with sulfuric acid. Milder acids could be screened as alternative
catalysts to avoid corrosives.
2. Preparation of Ethyl Ethanoate
,Observation Record and Health/Safety (P5)
Carried out practical work safely following rules:
Wore lab coat, goggles, and gloves at all times
Worked in
2. Preparation of Ethyl Ethanoate
Observation Record and Health/Safety (P5)
Carried out practical work safely following rules:
Wore lab coat, goggles, and gloves at all times
Worked in fume hood
Avoided skin/eye contact with corrosive acids/bases
Properly disposed of chemical waste
Signed Health and Safety Assessment (P5)
The key risks for this preparation are:
Ethanoic acid is corrosive and flammable
Ethanol is highly flammable
Concentrated sulfuric acid is extremely corrosive
Ethyl ethanoate is flammable and an irritant
Detailed Method with Reactants/Products (P5)
Reactants:
Ethanol (25 mL, 0.43 mol)
Glacial ethanoic acid (25 mL, 0.42 mol)
Concentrated sulfuric acid (5 mL)
Predicted Product:
Ethyl ethanoate
Apparatus:
100 mL round-bottom flask
Condenser
Separatory funnel
Sodium hydrogen carbonate solution
Anhydrous magnesium sulphate
1. In a fume hood, mix ethanol and ethanoic acid in a 100 mL round-bottom
flask.
, 2. Slowly add concentrated sulfuric acid as a catalyst. Cool in an ice bath.
3. Assemble reflux condenser and heat at 80°C for 1 hour with stirring.
4. Allow to cool, then transfer contents to a separatory funnel.
5. Add sodium hydrogen carbonate solution and shake to neutralize acid.
6. Allow layers to separate, drain off aqueous layer.
7. Dry organic layer over anhydrous MgSO4. Filter and distil to collect ethyl
ethanoate at 77°C.
Reaction Conditions (P5)
Reagents:
Ethanol
Ethanoic acid
Concentrated sulfuric acid (catalyst)
Temperature: 80°C (reflux)
Time: 1 hour
Reaction Mechanism and Explanation (P6)
This is a Fischer esterification reaction between ethanol and ethanoic acid,
catalysed by sulfuric acid:
1. Sulfuric acid protonates the ethanoic acid carbonyl, making it more
electrophilic.
2. Nucleophilic addition of ethanol, losing H2O.
3. Proton transfer from the oxonium ion gives the tetrahedral intermediate.
4. Loss of H3O+ regenerates the carbonyl, forming the ester product.
Balanced chemical equation:
CH3CH2OH + CH3CO2H ⇌ CH3CO2CH2CH3 + H2O
Key functional groups:
Alcohol (-OH) in ethanol
Carboxylic acid (-CO2H) in ethanoic acid
Ester (-CO2R) in ethyl ethanoate product
Tests of Purity/Quantities (P6)
The crude ethyl ethanoate product was purified by washing with sodium
hydrogen carbonate to neutralize residual acid, followed by drying over
anhydrous MgSO4 and distillation.
The purified ester was analysed by:
Boiling point: 76-78°C (lit. 77°C)
, 1H NMR matched literature values
13C NMR matched literature values
IR showed expected ester C=O stretch at 1730 cm-1
Yield: 32 g (68% of theoretical yield)
Observation of Reaction Conditions (P6)
The reaction was heated at reflux at 80°C for 1 hour. Sulfuric acid catalysed the
key steps of carbonyl activation and dehydration to form the ester.
Heating was required to drive the reversible condensation reaction. The product
ethyl ethanoate was isolated as a colourless liquid with a characteristic fruity
odor.
Importance of Conditions (M5)
Temperature: 80°C reflux was chosen as the optimal temperature to carry out
this reversible esterification.
Lower temperatures below 60°C would make the reaction too slow to be
practicable. Higher temperatures above 100°C risk decomposition or dehydration
of the reactants.
Time: 1 hour was sufficient time for the reaction to reach equilibrium under the
given conditions.
Shorter times would not give full conversion. Much longer is unnecessary once
equilibrium is reached.
Reagents: Ethanol was used as the nucleophile source of -OR for ester formation.
Ethanoic acid provided the -CO2H carboxylate electrophile. Sulfuric acid is a
strong acid catalyst to activate the carbonyl group.
Effect of Changing Reagents (M5)
Using a weaker acid like phosphoric acid would require much harsher conditions
or longer times due to poorer catalysis.
A stronger acid like methane sulfonic acid could potentially catalyze at lower
temperatures.
Any other alcohol besides ethanol could be used to synthesize a different alkyl
ester product.
Any other carboxylic acid could replace ethanoic acid to make a different ester,
although more insoluble acids may require harsher conditions or addition of a
solvent.
Techniques to Assess Purity (D4)
Boiling Point: The boiling point of 76-78°C confirmed the purity and identity of
the ethyl ethanoate product matching the literature 77°C value.
Melting Point: Not applicable here since the product is a liquid.
, 1H NMR Spectroscopy: Characteristic signals for the ethyl (-CH2CH3) and ester (-
CO2CH2CH3) groups matched literature values with correct integrations,
indicating purity.
13C NMR Spectroscopy: The 13C spectrum showed the expected signals for the
carbonyl carbon and the four magnetically distinct carbon environments, further
confirming the structure.
IR Spectroscopy: The IR spectrum had a strong C=O stretch at 1730 cm-1,
confirming the ester functional group. Any major impurities would give additional
peaks.
Mass Spectrometry: Could determine the molecular ion peak at m/z = 88 for
C4H8O2 to confirm the molecular formula and weight.
Percentage Yield and Conclusions (D4)
Percentage Yield = (Actual yield) / (Theoretical yield) x 100% = (32 g) / (47 g) x
100%
= 68%
The 68% yield is good for a reversible equilibrium reaction like esterification.
Recovering more of the ethyl ethanoate product is difficult.
Strengths:
Atom economical synthesis from cheap starting materials
One-pot synthesis under relatively mild conditions
Sulfuric acid is an inexpensive, readily available catalyst
Simple distillation workup to obtain pure ester product
Weaknesses:
Reversible reaction cannot go to full conversion
Corrosive acid/base required for workup
Use of concentrated sulfuric acid requires care
Cannot be used for synthesis of insoluble carboxylic esters
Improvements: An excess of one reagent could be used to drive the equilibrium
further. An azeotropic Dean-Stark apparatus could remove water during reflux. A
milder acid like an ion-exchange resin could potentially catalyse the reaction.
3. Preparation of 4-Nitrophenol
Observation Record and Health/Safety (P5)
Carried out practical work safely following rules:
- Wore lab coat, goggles, and nitrile gloves always
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