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A possible synthesis of 1,4-diaminobenzene from phenylamine is shown in the following figure. 1. (a) A suitable reagent for step 1 is CH3COCl.
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1,4-diaminobenzene is an important intermediate in the production of polymers such as Kevlar and also of polyurethanes, used in making foam seating. A possible synthesis of 1,4-diaminobenzene from phenylamine is shown in the following figure.
(a) A suitable reagent for step 1 is CH 3 COCl Name and draw a mechanism for the reaction in step 1. Name of mechanism ...................................................................................... Mechanism (5)
(b) The product of step 1 was purified by recrystallisation as follows. The crude product was dissolved in the minimum quantity of hot water and the hot solution was filtered through a hot filter funnel into a conical flask. This filtration removed any insoluble impurities. The flask was left to cool to room temperature. The crystals formed were filtered off using a Buchner funnel and a clean cork was used to compress the crystals in the funnel. A little cold water was then poured through the crystals. After a few minutes, the crystals were removed from the funnel and weighed. A small sample was then used to find the melting point. Give reasons for each of the following practical steps. The minimum quantity of hot water was used ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ The flask was cooled to room temperature before the crystals were filtered off ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ The crystals were compressed in the funnel ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ A little cold water was poured through the crystals ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (4)
(d) In an experiment starting with 5.05 g of phenylamine, 4.82 g of purified product were obtained in step 1. Calculate the percentage yield in this reaction. Give your answer to the appropriate number of significant figures. Percentage yield = ...............................% (3) (e) A reagent for step 2 is a mixture of concentrated nitric acid and concentrated sulfuric acid, which react together to form a reactive intermediate. Write an equation for the reaction of this intermediate in step 2. ........................................................................................................................ (1) (f) Name a mechanism for the reaction in step 2. ........................................................................................................................ (1) (g) Suggest the type of reaction occurring in step 3. ........................................................................................................................ (1) (h) Identify the reagents used in step 4. ........................................................................................................................ (1) (Total 18 marks)
Consider the following reaction sequence starting from methylbenzene. (a) Name the type of mechanism for reaction 1. ........................................................................................................................ (1)
(b) Compound J is formed by reduction in reaction 2. (i) Give a reducing agent for this reaction. ............................................................................................................... (1) (ii) Write an equation for this reaction. Use [H] to represent the reducing agent. ............................................................................................................... (1) (iii) Give a use for J. ............................................................................................................... (1)
Equations for the hydrogenation of cyclohexene and of benzene, together with the enthalpies of hydrogenation, are shown. (a) (i) Use these data to show that benzene is 152 kJ mol−1^ more stable than the hypothetical compound cyclohexa−1,3,5−triene. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (1)
(ii) State, in terms of its bonding, why benzene is more stable than cyclohexa−1,3,5−triene. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (1) (b) Three carbon−carbon bonds are labelled on the structures shown. These bonds are of different lengths. Write the letters w , x and y in order of increasing bond length. ........................................................................................................................ (1)
(c) The structures of two cyclic dienes are shown. (i) Use the enthalpy of hydrogenation data given opposite to calculate a value for the enthalpy of hydrogenation of cyclohexa−1,4−diene. ............................................................................................................... ............................................................................................................... (1) (ii) Predict a value for the enthalpy of hydrogenation of cyclohexa−1,3−diene. ............................................................................................................... (1) (iii) Explain your answers to part (i) and part (ii) in terms of the bonding in these two dienes. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (3) (Total 8 marks) Kevlar is a polymer used in protective clothing. The repeating unit within the polymer chains of Kevlar is shown. (a) Name the strongest type of interaction between polymer chains of Kevlar. ........................................................................................................................ (1)
(iv) Name and outline a mechanism for the formation of X from chlorobenzene and the reactive intermediate in part (iii). Name of mechanism ...................................................................................... Mechanism (4) (Total 11 marks) This question is about acylium ions, [RCO] + (a) The acylium ion Write an equation for this fragmentation. Include in your answer a displayed formula for the radical formed. ........................................................................................................................ (2)
is formed in a mass spectrometer by fragmentation of the molecular ion of methyl ethanoate. (b) The acylium ion (i) Write an equation to show the formation of this acylium ion by the reaction of ethanoyl chloride with one other substance. ............................................................................................................... (2) can also be formed from ethanoyl chloride. The ion reacts with benzene to form C 6 H 5 COCH 3 (ii) Name and outline a mechanism for the reaction of benzene with this acylium ion. Name of mechanism ............................................................................... Mechanism (4)
(iii) Ethanoic anhydride also reacts with benzene to form C 6 H 5 COCH 3 Write an equation for this reaction. ........................................................................................................................ (1) (Total 9 marks) Each of the following conversions involves reduction of the starting material. (a) Consider the following conversion. Identify a reducing agent for this conversion. Write a balanced equation for the reaction using molecular formulae for the nitrogen- containing compounds and [H] for the reducing agent. Draw the repeating unit of the polymer formed by the product of this reaction with benzene- 1,4-dicarboxylic acid. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (Extra space) ................................................................................................. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (5)
(ii) By considering the mechanism of this reaction, explain why the product formed is optically inactive. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (3) (Total 17 marks) Benzene reacts with ethanoyl chloride in a substitution reaction to form C 6 H 5 COCH 3. This reaction is catalysed by aluminium chloride. (a) Write equations to show the role of aluminium chloride as a catalyst in this reaction. Outline a mechanism for the reaction of benzene. Name the product, C 6 H 5 COCH 3. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (6)
(b) The product of the substitution reaction (C 6 H 5 COCH 3 ) was analysed by mass spectrometry. The most abundant fragment ion gave a peak in the mass spectrum with m/z = 105. Draw the structure of this fragment ion. (1)
(c) When methylbenzene reacts with ethanoyl chloride and aluminium chloride, a similar substitution reaction occurs but the reaction is faster than the reaction of benzene. Suggest why the reaction of methylbenzene is faster. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (2) (Total 9 marks) Many aromatic nitro compounds are used as explosives. One of the most famous is 2-methyl- 1,3,5-trinitrobenzene, originally called trinitrotoluene or TNT. This compound, shown below, can be prepared from methylbenzene by a sequence of nitration reactions. (a) The mechanism of the nitration of methylbenzene is an electrophilic substitution. (i) Give the reagents used to produce the electrophile for this reaction. Write an equation or equations to show the formation of this electrophile. Reagents .............................................................................................. ............................................................................................................... Equation ................................................................................................ ............................................................................................................... (3)
The hydrocarbons benzene and cyclohexene are both unsaturated compounds. Benzene normally undergoes substitution reactions, but cyclohexene normally undergoes addition reactions. (a) The molecule cyclohexatriene does not exist and is described as hypothetical. Use the following data to state and explain the stability of benzene compared with the hypothetical cyclohexatriene. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (Extra space) ............................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (4)
(b) Benzene can be converted into amine U by the two-step synthesis shown below. The mechanism of Reaction 1 involves attack by an electrophile. Give the reagents used to produce the electrophile needed in Reaction 1. Write an equation showing the formation of this electrophile. Outline a mechanism for the reaction of this electrophile with benzene. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (Extra space) ................................................................................................ ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (6)
(d) Explain why amine U is a weaker base than amine W. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (Extra space) ................................................................................................ ...................................................................................................................... ...................................................................................................................... (3) (Total 19 marks) Many synthetic routes need chemists to increase the number of carbon atoms in a molecule by forming new carbon–carbon bonds. This can be achieved in several ways including
(ii) Name and outline a mechanism for the reaction of benzene with this reactive intermediate. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (4) (b) Consider the reaction of propanal with HCN (i) Write an equation for the reaction of propanal with HCN and name the product. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2) (ii) Name and outline a mechanism for the reaction of propanal with HCN ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (5)
