Unit 14: Investigate organic chemistry reactions in order to gain skills in preparative organic chemistry Learning Aim D

Bromobutane from butan-1-ol Practical 1: Bromobutane from butan-1-ol

U14 A4 Q1 Reactants were butan-1-ol and HBr. Products were 1-bromobutane and water An alcohol functional group was converted into a haloalkane by nucleophilic substitution. Balanced equation (draw yourself):

U14 A4 Q2 Mechanism for nucleophilic substitution:

U14 A4 Q3 Reagents used were KBr and H2SO4 as acidic conditions are required for this reaction. Looking at the mechanism, the OH on the alcohol needs to be protonated to allow substitution by a Br- ion. This also generates the HBr required. KBr was used in the reaction to make bromobutane – if KCl was used then chlorobutane would have been made. Sodium hydrogen carbonate was used after the reaction to neutralise any excess acid. It is a weak base. A stronger base such as NaOH would have led to a vigorous reaction during neutralisation. NaOH would also have led to the OH substituting the Br in bromobutane to re-make the butanol. Calcium chloride was used to remove any remaining traces of water from the sample.

U14 A4 Q4 Initially the H2SO4 was added slowly at room temperature for safety reasons as any higher a temperature would have led to a violent reaction and too much HBr gas being produced, which is corrosive. The reaction was then heated to reflux to ensure complete substitution had taken place.

U14 A4 Q5 Follow the method below, using your numbers. C4H10O + HBr → C4H9Br + H2O Moles of butanol used = grams/molar mass = 8.0/74 = 0.108 moles As there is a 1:1 molar ratio between C4H10O and C4H9Br, moles of C4H9Br expected is also 0.108 moles Actual moles of C4H9Br is grams/molar mass = 9.0/136.9 = 0.0657 moles % yield = (actual/expected) x 100 = (0.0657/0.108) x 100 = 60.8% Use your mass of butan-1-ol used Use your mass of 1-bromobutane obtained

U14 A4 Q6 How does your boiling point compare with the actual boiling point of bromobutane? Was the temperature flickering? Comment on the purity. Comment on the % yield – why did you not get 100% yield? What other methods could you have used to check on the purity? Strengths and weaknesses of reaction conditions used? Think about your % yield and purity obtained and how these can be improved.

Oxidation of ethanol to ethanal Practical 2: Oxidation of ethanol to ethanal

U14 A4 Note: On page 8, the observation for test 1 is a orange precipitate was seen which confirms the presence of a carbonyl group (you took pictures of this – you could add this to your assignment). On page 8, the observation for test 2 is a silver mirror was seen, which confirms that an aldehyde was made in the reaction.

U14 A4 Q1 Reactant was ethanol and an oxidant (sodium dichromate) Products were ethanal and water An alcohol functional group was converted into an aldehyde by a oxidation reaction Balanced equation (draw/write yourself):

U14 A4 Q2 N/A

U14 A4 Q3 Reagents used were sodium dichromate and concentrate sulphuric acid. Alcohols are oxidised to aldehydes using concentrated sulphuric acid and an oxidant. The oxidant could also have been potassium dichromate.

U14 A4 Q4 The flask was only heated briefly and then the Bunsen flame turned off as the ethanol and oxidant were added from the dropping funnel at room temperature. This is because the boiling point of ethanal is only 200C, so a higher temperature was not required to distill it off.

U14 A4 Q5 Follow the method below, using your numbers. First find the mass of ethanol used – you all used 4cm3. Mass = density x volume = 0.784 x 4 = 3.136 g

U14 A4 Q5 Follow the method below, using your numbers. Moles of ethanol used = grams/molar mass = 3.136/46 = 0.0682 moles As there is a 1:1 molar ratio between ethanol and ethanal, moles of ethanal expected is also 0.0682 moles Actual moles of ethanal is grams/molar mass = 2.5/44 = 0.0568 moles % yield = (actual/expected) x 100 = (0.0568/0.0682) x 100 = 83.3% Use your mass of ethanol obtained

U14 A4 Q6 Comment on the results of test 1 and test 2 – do they confirm you made ethanal? Comment on your infra-red spectra. What does it tell you about purity of ethanal? Any other techniques you could use to check the purity of the organic liquid made (ethanal)? Comment on the % yield – why did you not get 100% yield? Strengths and weaknesses of reaction conditions used? Think about your % yield and purity and how these can be improved.

Nitration of methylbenzoate Practical 3: Nitration of methylbenzoate

U14 A4 Q1 Reactant was methyl benzoate Product was methyl 3-nitrobenzoate A aromatic ring was nitrated to give a nitro benzene Balanced equation (draw/write yourself): C8H8O2 + NO2+ → C8H7O4N + H+

U14 A4 Q2 Mechanism for electrophilic substitution:

U14 A4 Q3 Reagents used were concentrated nitric and sulphuric acids. These are the typical reagents used for nitration reactions. This mixture produces the nitronium ion, NO2+, which is the electrophile in the reaction with the benzene ring.

U14 A4 Q4 The reaction mixture was not allowed to exceed 100C. At a higher temperature, there is a danger of more than one nitro group being substituted onto the benzene ring.

U14 A4 Q5 Follow the method below, using your numbers. C8H8O2 + NO2+ → C8H7O4N + H+ Moles of methyl benzoate used = grams/molar mass = 4.0/136 = 0.0294 moles As there is a 1:1 molar ratio between C8H8O2 and C8H7O4N, moles of C8H7O4N expected is also 0.0294moles Actual moles of C8H7O4N is grams/molar mass = 1.0/181 = 0.00553 moles % yield = (actual/expected) x 100 = (0.00553/0.0294) x 100 = 18.8% Use your mass of butan-1-ol used Use your mass of product obtained

U14 A4 Q6 How does your melting point compare with the actual melting point of methyl 3-nitrobenzoate? Comment on the purity. Comment on the % yield – why did you not get 100% yield? What other methods could you have used to check on the purity? Strengths and weaknesses of reaction conditions used? Think about your % yield and purity obtained and how these can be improved.