A2 25 Qu - Frankly Chemistry · A2 TOPIC 25 ORGANIC SYNTHESES Questionsheet 1 Questionsheet 2 ......
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ORGANIC SYNTHESES A2 TOPIC 25 Questionsheet 1 Questionsheet 2 Questionsheet 3 Questionsheet 4 Questionsheet 5 Questionsheet 6 Questionsheet 7 Questionsheet 8 Questionsheet 9 Questionsheet 10 Questionsheet 11 Questionsheet 12 Questionsheet 13 Questionsheet 14 QUESTIONSHEETS A2 Level CHEMISTRY 19 marks 15 marks 17 marks 21 marks 16 marks 14 marks 10 marks 20 marks 13 marks 19 marks 19 marks 18 marks 17 marks 17 marks SINGLE STAGE ALIPHATIC SYNTHESES NOT INVOLVING NITROGEN COMPOUNDS MULTI-STAGE ALIPHATIC SYNTHESES NOT INVOLVING NITROGEN COMPOUNDS SINGLE STAGE ALIPHATIC SYNTHESES INVOLVING NITROGEN COMPOUNDS MULTI-STAGE ALIPHATIC SYNTHESES INVOLVING NITROGEN COMPOUNDS SYNTHESES INVOLVING AN INCREASE IN CHAIN LENGTH AROMATIC SYNTHESES NOT INVOLVING DIAZONIUM SALTS AROMATIC SYNTHESES INVOLVING DIAZONIUM SALTS TEST QUESTION I TEST QUESTION II TEST QUESTION III TEST QUESTION IV PREPARATIVE TECHNIQUES I (Preparation of 1-bromobutane) PREPARATIVE TECHNIQUES II (Preparation of phenylamine) PREPARATIVE TECHNIQUES III (Nitration) Curriculum Press – Licence Agreement: Paper copies of the A-Level Chemistry Questionsheets may be copied free of charge by teaching staff or students for use within their school, provided the Photocopy Masters have been purchased by their school. No part of these Questionsheets may be reproduced or transmitted, in any other form or by any other means, without the prior permission of the publisher. All rights are reserved. This license agreement is covered by the laws of England and Wales © Curriculum Press March 2008. Curriculum Press • Bank House • 105 King Street • Wellington • Shropshire • TF1 1NU ress urriculum C P www.curriculum-press.co.uk Authors Trevor Birt John Brockington Donald E Caddy Kevin Frobisher Andrew Jones Andy Shepherd Adrian Bond Stuart Barker Editors John Brockington Stuart Barker
Transcript of A2 25 Qu - Frankly Chemistry · A2 TOPIC 25 ORGANIC SYNTHESES Questionsheet 1 Questionsheet 2 ......
ORGANIC SYNTHESESA2 TOPIC 25
Questionsheet 1
Questionsheet 2
Questionsheet 3
Questionsheet 4
Questionsheet 5
Questionsheet 6
Questionsheet 7
Questionsheet 8
Questionsheet 9
Questionsheet 10
Questionsheet 11
Questionsheet 12
Questionsheet 13
Questionsheet 14
QUESTIONSHEETS A2 LevelCHEMISTRY
19 marks
15 marks
17 marks
21 marks
16 marks
14 marks
10 marks
20 marks
13 marks
19 marks
19 marks
18 marks
17 marks
17 marks
SINGLE STAGE ALIPHATIC SYNTHESES NOT INVOLVINGNITROGEN COMPOUNDS
MULTI-STAGE ALIPHATIC SYNTHESES NOT INVOLVINGNITROGEN COMPOUNDS
SINGLE STAGE ALIPHATIC SYNTHESES INVOLVINGNITROGEN COMPOUNDS
MULTI-STAGE ALIPHATIC SYNTHESES INVOLVINGNITROGEN COMPOUNDS
SYNTHESES INVOLVING AN INCREASE IN CHAIN LENGTH
AROMATIC SYNTHESES NOT INVOLVING DIAZONIUM SALTS
AROMATIC SYNTHESES INVOLVING DIAZONIUM SALTS
TEST QUESTION I
TEST QUESTION II
TEST QUESTION III
TEST QUESTION IV
PREPARATIVE TECHNIQUES I (Preparation of 1-bromobutane)
PREPARATIVE TECHNIQUES II (Preparation of phenylamine)
PREPARATIVE TECHNIQUES III (Nitration)
Curriculum Press – Licence Agreement:Paper copies of the A-Level Chemistry Questionsheetsmay be copied free of charge by teaching staff or studentsfor use within their school, provided the PhotocopyMasters have been purchased by their school. No part ofthese Questionsheets may be reproduced or transmitted,in any other form or by any other means, without theprior permission of the publisher. All rights are reserved.This license agreement is covered by the laws of Englandand Wales © Curriculum Press March 2008.
Curriculum Press • Bank House • 105 King Street • Wellington • Shropshire • TF1 1NU
ressurriculumCPwww.curriculum-press.co.uk
AuthorsTrevor Birt John BrockingtonDonald E Caddy Kevin FrobisherAndrew Jones Andy ShepherdAdrian Bond Stuart Barker
EditorsJohn BrockingtonStuart Barker
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SINGLE STAGE ALIPHATIC SYNTHESES NOT INVOLVING NITROGEN COMPOUNDS
19
a) How could CH3CH
2Br be prepared, in a one stage synthesis, from each of the following compounds?
Give the reagent (or reagents) and essential conditions in every case.
(i) CH3CH
3
Reagent(s) ............................................................................................................................................. [1]
Conditions ............................................................................................................................................. [1]
(ii) CH2=CH
2
Reagent(s) ............................................................................................................................................. [1]
Conditions ............................................................................................................................................. [1]
(iii) CH3CH
2OH
Reagent(s) ............................................................................................................................................. [2]
Conditions ............................................................................................................................................. [1]
b) What reagents and conditions are needed for each of the following conversions?
(i) CH3CH(OH)CH
2CH
3 → CH
3CH=CHCH
3
Reagent(s) ............................................................................................................................................. [2]
Conditions ............................................................................................................................................. [1]
(ii) CH3CHO → CH
3CHOH
Reagent(s) ............................................................................................................................................. [2]
Conditions ............................................................................................................................................. [1]
(iii) CH3CH
2CH
2CH
2OH → CH
3CH
2CH
2CHO
Reagent(s) ............................................................................................................................................. [2]
Conditions ............................................................................................................................................ [2]
c) Write equations for the conversions of propanoic acid into each of the following.(i) Propyl propanoate
....................................................................................................................................................................... [1]
(ii) Sodium propanoate
....................................................................................................................................................................... [1]
TOPIC 25 Questionsheet 1
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15
MULTI-STAGE ALIPHATIC SYNTHESES NOT INVOLVING NITROGEN COMPOUNDSThe following reaction scheme depicts a synthesis of propane
a) Give the reagents and conditions for each of the following steps:
I ......................................................................................................................................................................
.................................................................................................................................................................. [3]
III ......................................................................................................................................................................
.................................................................................................................................................................. [3]
IV ......................................................................................................................................................................
.................................................................................................................................................................. [3]
b) Compound A may be used to produce propane-1,2-diol . Suggest a route by which this might be done,starting with bromine.
[3]c) How might Compound B be converted back to A?
Reagent(s) ..................................................................................................................................................... [2]
Conditions .................................................................................................................................................... [1]
CH3CH
2CH
2OH
CH3CHCH
3 CH3CHCH
3
CH3CH=CH
2
II
I
III
(A)
(B)
TOPIC 25 Questionsheet 2
BrOH
IV
CH3COCH
3
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SINGLE STAGE ALIPHATIC SYNTHESES INVOLVING NITROGEN COMPOUNDS
a) Give the reagents and conditions you would use to convert 2-bromopropane, CH3CHBrCH3, into each of the
following:
(i) 2-aminopropane, CH3CH(NH
2)CH
3
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
(ii) 2-methylpropanenitrile, CH3CH(CH
3)CN
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
b) How would you convert 2-methylpropanenitrile into each of the following?
(i) 1-amino-2-methylpropane, CH3CH(CH
3)CH
2NH
2
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
(ii) 2-methylpropanoic acid, CH3CH(CH
3)COOH
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
c) 2-methylpropanoic acid, CH3CH(CH
3)COOH, can be converted into 2-methylpropanamide in 2 stages, the
first involving reaction with ammonia to form X, which is then heated to form the product.
(i) State the type of compound and structure for X and give the structure of the product
Type of compound ............................................................................................................................... [1]
Structure of X ....................................................................................................................................... [1]
Structure of product ............................................................................................................................. [1]
(ii) What are the two successive types of reaction involved in this conversion?
.............................................................. ................................................................. [2]
d) Suggest a method by which the crude 2-methylpropanamide might be purified, explaining your reasons.
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
TOPIC 25 Questionsheet 3
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MULTI-STAGE ALIPHATIC SYNTHESES INVOLVING NITROGEN COMPOUNDS
This question is about the following series of reactions:
a) Give the reagents and reaction conditions which you would use to carry out:
Step I ............................................................................................................................................................
....................................................................................................................................................................... [3]
Step II .............................................................................................................................................................
....................................................................................................................................................................... [3]
Step III .............................................................................................................................................................
....................................................................................................................................................................... [3]
Step IV ......................................................................................................................................................... [2]
b) State the type of reaction occurring in:
Steps I & III ................................................................................................................................................... [2]
Step IV .......................................................................................................................................................... [1]
Step V ............................................................................................................................................................ [1]
c) Give the structure of the final product of this synthesis, J.
....................................................................................................................................................................... [1]
d) The crude product is formed as a solid after the final stage. Outline the procedure you would use to obtain apure sample of this product.
...........................................................................................................................................................................
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [4] Quality of language [1]
CH3CH
2Br CH
3CH
2CN
CH3CH
2NH
2 CH3CH
2COOH
III IV
V
CH3CH
2OH
I
II
TOPIC 25 Questionsheet 4
J
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SYNTHESES INVOLVING AN INCREASE IN CHAIN LENGTH(including nitriles from halogenoalkanes with cyanide)
A route for the synthesis of butanedioic acid 1,4-diaminobutane from ethane is given below:
H2C=CH
2
Br2
N≡CCH2CH
2C≡N
HOOCCH2CH
2COOH
a) What conditions should be used for step I?
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
b) Name the product, Z, of this reaction.
....................................................................................................................................................................... [1]
c) Give the reagents and reaction conditions required for step II.
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
d) How can step III be achieved?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
e) How can step IV be achieved?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]e) Suggest how you would produce 2,3-dimethylbutanedioic acid, using buta-1,3-diene as your starting material.
[5]
Z
I
II
III
TOPIC 25 Questionsheet 5
IVH
2NCH
2CH
2CH
2NH
2
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14
AROMATIC SYNTHESES NOT INVOLVING DIAZONIUM SALTS
Methylbenzene, C6H
5CH
3, may be used as a starting point for the production of a number of other aromatic
compounds. An example of such a use is given below:
a) Suggest the reagents and reaction conditions to be used for step I. Name the product of this step.
Reagents and conditions ....................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [4]
Name of product ............................................................................................................................................ [1]
b) What type of reaction takes place in step II? How might this reaction be achieved?
Type of reaction ............................................................................................................................................. [1]
Achievement .................................................................................................................................................. [2]
c) Give the name and structure of the compound R.
...........................................................................................................................................................................
....................................................................................................................................................................... [2]d) What type of compound is the final product S?
....................................................................................................................................................................... [1]
e) Why is it better to convert P into S via R than to produce S directly from P and Q?
...........................................................................................................................................................................
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
PCl5II
I
S
RQ
P
N
CH2-O-CO
CH2OH
COOHCH3
TOPIC 25 Questionsheet 6
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AROMATIC SYNTHESES INVOLVING DIAZONIUM SALTS
4-Aminobenzenesulfonic acid is used as the starting point for the following series of reactions:
a) What conditions would be used for step I?
....................................................................................................................................................................... [1]
b) Name the type of reaction occurring in:
Step I ............................................................................................................................................................. [1]
Step II ............................................................................................................................................................ [1]
Step III ........................................................................................................................................................... [1]
c) Give the structures of C, D, and E.
C =
[1]
D =
[1]
E =
[2]
d) Suggest a common use for D and E
....................................................................................................................................................................... [1]
NaNO2 & HCl(aq)I
IIC D
III Add phenolin NaOH(aq)
H2N SO
3H
Add C6H
5N(CH
3)
2in weakly acidic solution
E
TOPIC 25 Questionsheet 7
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TEST QUESTION I
A compound H, molecular formula C6H
12, decolourises bromine water when shaken with it. On treatment with
hot acidic potassium manganate(VII) solution, two organic products, J and K, are obtained; J reacts with sodiumhydrogencarbonate solution to release CO
2, and on reduction produces L, which is miscible with water and has
a relative molecular mass of 46. K produces an orange-yellow crystalline precipitate M when treated with2,4-dinitrophenylhydrazine, but does not react with ammoniacal silver nitrate solution. On reduction, K producesN. K, N and L all yield a yellow precipitate P when treated with iodine and aqueous sodium hydroxide.
a) What is the yellow precipitate P? What does its formation tell you about the structures of K, N and L?
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
b) Identify the main functional group in K, giving your reasons.
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
c) What reagent might be used to reduce both J and K?
....................................................................................................................................................................... [1]
d) What is the main functional group present in J?
....................................................................................................................................................................... [1]
e) Write down the formulae of compounds J – N, and give their systematic names (except for M).
J ................................................................................................................................................................... [2]
K ................................................................................................................................................................... [2]
L ................................................................................................................................................................... [2]
M
[2]
N ................................................................................................................................................................... [2]
f) Hence give the name and structure of H.
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
TOPIC 25 Questionsheet 8
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13
TEST QUESTION II
A compound R has the molecular formula C7H
7NO
2, and on treatment with tin and concentrated hydrochloric
acid produces S. On treatment with an ice-cold mixture of sodium nitrite and dilute HCl, followed by the additionof phenol, S forms an orange-yellow solution. When S is reacted with ethanoyl chloride, CH
3COCl, a solid T is
produced. T is oxidised to U, which has the molecular formula C9H
9NO
3; on hydrolysis with warm aqueous
sodium hydroxide solution, the final product V is obtained, which has the same molecular formula as R.
a) Identify the hydrocarbon groups and functional groups present in S, giving your reasons.
...........................................................................................................................................................................
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [4]
b) Hence suggest a structure for R.
[1]
c) Give a possible structure for the orange-yellow compound formed from S and phenol.
[2]
d) Suggest structures for the compounds T, U and V, and name compound V.
Structure of T
[1]Structure of U
[1]Structure of V
[1]
Name of V .................................................................................................................................................... [1]
e) Why is it necessary to react S with ethanoyl chloride before oxidation to U?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
TOPIC 25 Questionsheet 9
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TEST QUESTION III
There are a number of isomers of chlorobutane, all of which react with hot ethanolic potassium hydroxidesolution to produce gaseous butenes by the elimination of hydrogen chloride: C
4H
9Cl → C
4H
8 + HCl
0.37 g of a liquid chlorobutane was heated under reflux with ethanolic KOH, and the gas produced was collectedin a gas syringe attached to the apparatus. When measured at room temperature and pressure, this gas occupieda volume of 8.0 cm3 when 1-chlorobutane was used, and 48.0 cm3 with 2-chloro-2-methylpropane.
a) Give one chemical test which would show that the gas collected was an alkene.
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
b) Why does the gas collected not contain hydrogen chloride ?
....................................................................................................................................................................... [1]
c) Draw the structures of 1-chlorobutane, 2-chloro-2-methylpropane, and the corresponding alkenes that wouldbe obtained from them.
[4]
d) Give the names and structural formulae of two additional isomers of chlorobutane that might be investigatedin a similar manner.
[4]
e) (i) Calculate the number of moles of alkene obtained from 1-chlorobutane, and hence determine thepercentage of this haloalkane that underwent an elimination reaction. (1 mole of gas occupies 24 dm3 atroom temperature and pressure.)
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [4]
(ii) Hence determine the percentage of elimination for 2-chloro-2-methylpropane.
....................................................................................................................................................................... [1]
(iii) What reaction might be occurring as well as the elimination reaction?
....................................................................................................................................................................... [1]
(iv) Comment on the differences in the amount of elimination for the two isomers.
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
TOPIC 25 Questionsheet 10
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19
TEST QUESTION IVThis question concerns the following reaction scheme:
A is a hydrocarbon, and reacts with HBr in the molar ratio of 1:1. When 1 dm3 of A is bubbled through a solutionof HBr in methylbenzene, the product B is obtained in 70% yield; the mass of product is 4.0 g.
a) Determine the molecular formulae of A and B. (1 mol of gas at room temperature & pressure occupies 24 dm3.)
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [4]
b) When B is treated with KCN under suitable conditions, D is formed; on subsequent reaction this yields E.Treatment of B with a different reagent produces C, which reacts with E in the presence of concentratedsulfuric acid to form F. State the conditions for the conversions of B to D, and D to E.
B to D ........................................................................................................................................................... [2]
D to E ........................................................................................................................................................... [2]
c) C resists oxidation with hot acidified sodium dichromate(VI).(i) Identify C, giving your reasons.
...........................................................................................................................................................................
....................................................................................................................................................................... [3]
(ii) Hence give the identities of B, D and E.
B = ............................................................................ D = .............................................................................
E = ................................................................................................................................................................. [3]
d) Give the structural formula of F.
....................................................................................................................................................................... [1]
e) State the conditions for the conversion of B into C.
....................................................................................................................................................................... [2]
f) How could A be obtained from B?
....................................................................................................................................................................... [2]
A
HBr
KCN
(C5H
9N)
(C5H
10O
2)
Conc H2SO
4
(C9H
18O
2)
B
C D
E
F
TOPIC 25 Questionsheet 11
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PREPARATIVE TECHNIQUES I (Preparation of 1-bromobutane)
In an experiment to prepare 1-bromobutane, 10 g of sodium bromide, 10 cm3 of water and 6.0 g of butan-1-ol wereplaced in a round-bottomed flask fitted with a reflux condenser. 18 g of concentrated sulfuric acid were then slowlyadded over a period of 10 minutes, with the flask standing in a cold water bath, after which the mixture was gentlyboiled under the reflux condenser for 45 minutes. The apparatus was cooled and rearranged for distillation with thecondenser in a sloping position. Distillation was carried out until no more oily droplets were collected.
The distillate comprised two liquid layers which were separated in a separating funnel. The upper aqueous layerwas discarded and the lower organic one was returned to the separating funnel, where it was shaken with 10 cm3
of concentrated hydrochloric acid. After separation, the lower layer was again returned to the funnel, where it wasshaken with aqueous sodium hydrogencarbonate.
The organic layer was then run into a small conical flask and allowed to stand over anhydrous sodium sulfate untilit became clear. Finally, the 1-bromobutane was decanted from the sodium sulfate into a small distillation flask andpurified by distillation. Liquid boiling between 101 and 103 oC was collected in a measuring cylinder.
a) (i) Why was the concentrated sulfuric acid added slowly?
....................................................................................................................................................................... [1]
(ii) What was the point of boiling the mixture for 45 minutes?
....................................................................................................................................................................... [1]
(iii) What was the purpose of boiling under a reflux condenser?
....................................................................................................................................................................... [1]
(iv) What compounds would you expect to obtain on distillation with a sloping condenser?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
(v) What was the purpose of shaking the distillate with concentrated hydrochloric acid?
....................................................................................................................................................................... [1]
(vi) Suggest why concentrated hydrochloric acid is effective for the purpose you have stated in (v).
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
(vii) Why was the crude 1-bromobutane shaken with NaHCO3(aq), and what safety precaution must be taken
at this stage?
Reason ................................................................................................................................................... [1]
Safety precaution ................................................................................................................................... [1]
(viii) What was the purpose of standing the 1-bromobutane over anhydrous sodium sulfate?
....................................................................................................................................................................... [1]
(ix) Why was the 1-bromobutane decanted from the sodium sulfate before the final distillation?
....................................................................................................................................................................... [1]
(Continued....)
TOPIC 25 Questionsheet 12
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A2 Level TOPIC 25 Questionsheet 12 Continued
18
b) (i) Write an equation (or equations) for the preparation of 1-bromobutane.
...........................................................................................................................................................................
....................................................................................................................................................................... [1]
(ii) Calculate which reactant is the most deficient. (Assume that concentrated sulfuric acid is pure H2SO
4.)
...........................................................................................................................................................................
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
(iii) Hence calculate the theoretical yield of 1-bromobutane.
....................................................................................................................................................................... [1]
(iv) In one experiment by the above method, 5.8 cm3 of 1-bromobutane were obtained. Calculate thepercentage yield. (Density of 1-bromobutane = 1.3 g cm–3)
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
PREPARATIVE TECHNIQUES I (Preparation of 1-bromobutane)
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A2 Level TOPIC 25 Questionsheet 13
PREPARATIVE TECHNIQUES II (Preparation of phenylamine)
The stages in the preparation of phenylamine are as follows.
1. Nitrobenzene and tin are placed in a distillation flask under a water-cooled reflux condenser and concentratedhydrochloric acid is added in small portions.
2. The mixture is boiled gently for about 15 minutes.3. An excess of sodium hydroxide solution is added.4. The mixture is steam distilled.5. The distillate is transferred to a separating funnel and sodium chloride is added.6. This mixture is shaken with two successive equal volumes of ethoxyethane (ether), and the aqueous layers are
discarded.7. The ethoxyethane extract is poured into a conical flask and a few pellets of potassium hydroxide are added to
dry it.8. The ethereal solution of phenylamine is filtered into a small distillation flask and distilled to remove the
ethoxyethane.9. Cold water is drained from the condenser and final distillation is then carried out. Care is taken to collect only
that liquid which distils between 180 and 183 oC.
a) What is the purpose of the tin in stage 1?
....................................................................................................................................................................... [1]
b) Why is concentrated hydrochloric acid added in small portions in stage 1?
....................................................................................................................................................................... [1]
c) What is the purpose of boiling for 15 minutes in stage 2?
....................................................................................................................................................................... [1]
d) Why is sodium hydroxide added in stage 3?
....................................................................................................................................................................... [1]
e) Describe briefly what is meant by steam distillation (stage 4).
....................................................................................................................................................................... [1]
f) What is the purpose of steam distillation?
....................................................................................................................................................................... [1]
g) Why is sodium chloride added in stage 5?
....................................................................................................................................................................... [1]
h) Why does most of the phenylamine transfer itself from water to ethoxyethane (stage 6)?
....................................................................................................................................................................... [1]
i) Why are two volumes of ethoxyethane added in stage 6, rather than one larger volume?
....................................................................................................................................................................... [1]
(Continued....)
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A2 Level TOPIC 25 Questionsheet 13 Continued
17
PREPARATIVE TECHNIQUES II (Preparation of phenylamine)
j) Before discarding the aqueous layer (stage 6), how could you be certain that it was the aqueous layer –bearing in mind that both layers have a similar appearance and odour?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
k) Why is potassium hydroxide used to dry the ethereal solution (stage7), rather than phosphoric(V) oxide?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
l) State two precautions which should be taken when distilling off ethoxyethane (stage 8).
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
m) Why is cold water drained from the condenser prior to the final distillation (stage 9)?
....................................................................................................................................................................... [1]
n) Why, in the final distillation, is care taken only to collect liquid that distils between 180 and 183 oC?
...........................................................................................................................................................................
....................................................................................................................................................................... [1]
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A2 Level TOPIC 25 Questionsheet 14
PREPARATIVE TECHNIQUES III (Nitration)
17
Methyl 3-nitrobenzoate is a white solid melting at 76 0C. It can be prepared as follows:
Stage I 20cm3 concentrated sulfuric acid is poured into a small conical flask and cooled in ice to 50 C or less. 20cm3 of methyl benzoate is slowly added with swirling with the temperature kept to a maximum of 5 0C.
Stage II In a boiling tube, 4 cm3 each of each of concentrated sulfuric acid and concentrated nitric acid aremixed and the mixture cooled to 5 0C or lower. This mixture is added in small portions with swirling tothe cooled ester, the temperature being kept between 15 and 25 0C. After complete addition, thereaction mixture is allowed to stand at room temperature for 20 minutes.
Stage III The mixture is poured onto crushed ice. The cooled mixture is then filtered using a Buchner funnel andthe residue washed with water then cooled methanol.
Stage IV The crude ester is then recrystallised from methanol. After allowing to dry in air, the melting point isdetermined.
a) Why is the temperature in stage II carefully controlled?
....................................................................................................................................................................... [1]b) Give an equation to explain why the ratio of concentrated sulfuric acid and concentrated nitric acid is over 2:1
and underline the electrophile in the reaction. (Stage II)
...........................................................................................................................................................................
....................................................................................................................................................................... [3]c) (i) What is the purpose of the crushed ice? (Stage III)
....................................................................................................................................................................... [1] (ii) Give 2 reasons for using a Buchner funnel for filtration. (Stage III)
1 ............................................................................................................................................................. [1]
2 ............................................................................................................................................................. [1](iii) Why is the residue from filtration washed with (Stage III)
water? ................................................................................................................................................... [1]
methanol? ............................................................................................................................................. [1](iv) Why is the methanol that is used for washing cooled?
....................................................................................................................................................................... [1]d) Give three reasons why methanol is an ideal recrystallising solvent. (Stage III)
1 ..................................................................................................................................................................... [1]
2 ..................................................................................................................................................................... [1]
3 ..................................................................................................................................................................... [1]e) A typical yield for this preparation is 70%. Suggest two explanations for the reduced yield.
1 ..................................................................................................................................................................... [1]
2 ..................................................................................................................................................................... [1]f) How can the melting point indicate the purity of the product?
...........................................................................................................................................................................
....................................................................................................................................................................... [2]
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