The Preparation of 1- Bromobutane
Aim : To prepare 1-Bromobutane.
Background : The most common way of preparing alkyl halides, which are very useful intermediates in syntheses, is the replacement of the OH group of an alcohol by a halogen.
This replacement is a nucleophilic substitution reaction, and alcohols do not undergo nucleophilic substitution reactions because hydroxide ison is strongly basic and a poor leaving group. However, alcohols readily undergo nucleophilic substitutions if the hydroxyl group is first activated to produce a better leaving group, so reaction is carried out in the presence of a strong acid. The acid protonates the alcohol to create a suitable leaving group, water, for the SN2 reaction.
In this experiment 1-butanol will be converted to 1-bromobutane by an SN2 reaction.
CH3CH2CH2CH2OH (aq) + HBr (aq) -----> CH3CH2CH2CH2Br (aq) + H2O (l)
CH3CH2CH2CH2-OH + HBr [IMAGE] CH3CH2CH2CH2-OH2 (+) Br(-) [IMAGE] CH3CH2CH2CH2-Br + H2O SN2
Reaction is nucleophilic substitution, and the products are impure, and so various stages of purification are required before a sample of reasonable purity can be obtained.
I'm planning to produce 20 g of 1-Bromobutane as a result of this experiment.
Amount of Butan-1-ol needed:
C4H9OH (aq) + HBr (aq) -----> C4H9Br (aq) + H2O (l)
74 : 70 : 137 : 18 ÃŸ Relative Molecular Mass.
Proportion is 74 to 137 at 100% yield, so 137 g of Bromobutane will be formed from 74 g of Butan-1-ol.
I will produce 20 g of 1-Bromobutane, my planned yield is 70%.
At 70% yield : (137/100) x 70 = 95.9 g (1 mole)
I want 20 g of C4H9Br so;
( 20 x 74 ) / 95.9 = 15.5 g , so :
Production of 1-Bromobutane will require 15.5 g of Butan-1-ol to obtain the full amount at 70% yield.
* Butan-1-ol, 7.72 g. (C4H9OH)
* Sodium Bromide (powdered). (NaBr)
* Concentrated Sulphuric Acid. (H2SO4)
* Concentrated Hydrochloric Acid. (HCl)
* Dilute Sodium Carbonate. (Na2CO3)
* Calcium Chloride. (CaCl2)
* Ethanol. (C2H5OH)
* Dilute Nitric Acid. (HNO3)
* Dilute Sodium Hydroxide. (NaOH)
* 0.1 M Silver Nitrate Solution. (Approx. 2.5 g in 250 cm3)
* Round flask, 250 cm3
* Tap funnel to fit still head
* Ice-water bath
* Reflux condenser
* Thermometer, 0-110Â°C
* Still head
* Conical flask, cm3
* Test tubes
* Beaker, 250 cm3
* Teat pipette
Mechanism for this synthesis is a nucleophilic substitution. Here are steps:
1. Since alcohols do not undergo a nucleophilic substitution without the presence of a strong acid, these are usually called as acid catalised reactions, because acid acts like a catalyst.
2. Sulphuric Acid attacks to the lone pairs of electrons on the oxygen.
3. Since Sulphuric Acid acted as a proton donor, Hydrogen joins onto the Oxygen. Water is released (condensation). As a result Carbon will have a positive charge, now turned into a Carbocation.
4. Sodium Bromide will dissolve in water, which will act as a solvent. As a result, aqueous solution of NaBr will be present, in which, NaBr will exist as Na+ and Br -. The Bromide ion, having a negative charge, will be attracted to Carbocation, bond will form between, and 1-Bromobutane is formed.
Many chemicals used in the experiment pose a hazard so I will need to be very careful during the experiment. Therefore, I will be carrying out a risk assessment using the hazcards to find out which chemicals I should be very careful with and make sure that all of the safety precautions are followed all the time.
1. Sulphuric Acid ( H2SO4 )
When contacted with skin or eyes it can cause serious burns and harm. Concentrated Sulphuric Acid that I will be using poses a real threat since solutions with a molarity...
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