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Questions

Q1.

Benzenecarboxylic acid (benzoic acid) and phenylmethanol (benzyl alcohol) are compounds whichoccur naturally and have a wide range of uses. For example, benzenecarboxylic acid is used as a foodpreservative and phenylmethanol is used as a solvent.

A laboratory seuence for the preparation of these two compounds is shown below.

(a) !n the first step of the synthesis, benzene reacts with hydrogen chloride and carbon monoxide inthe presence of aluminium chloride in an electrophilic substitution called the "attermann#$och reaction.%he hydrogen chloride and carbon monoxide together behave as if they form the unstable speciesmethanoyl chloride (&''l).

(i) xplain why benzene undergoes substitution rather than addition reactions. A detailed descriptionof the bonding in benzene is notreuired.

(2)

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(ii) "ive the mechanism for step *, including the formation of the electrophile.(4)

(iii) !dentify the reagents and essential conditions used in the remaining steps of the seuence. +oumay assume that the correct reaction temperatures are being used.

(4)

tep -

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tep .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................

/(b) 0henol reacts faster than phenylmethanol in electrophilic substitution reactions. uggest why thisis so.

(4)

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(Total for question = 14 marks)

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Q2.

!buprofen is a nonsteroidal anti#inflammatory drug (1A!2) widely used as an analgesic (pain reliever). !twas discovered in the *345s by the Boots "roup which developed a six step synthesis from -#methylpropylbenzene. %he synthesis shown below was introduced in the *335s by the B&' 'ompanyand received a 0residential "reen 'hemistry 'hallenge award in *336. %he citation noted that thesynthesis has 7ust three steps, all of which are catalytic, and an effective atom economy of 338. Both

syntheses are carried out in solution.

(a) (i) uggest why a three step synthesis is li9ely to be :greener: than a six step process.

(1)

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(ii) ;hy does the use of catalysts ma9e processes :greener: (as well as faster)sing your 2ata Boo9let, explain how infrared spectroscopy can be used to distinguish betweenthe two structures shown below.

(2)

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(d) !buprofen is a chiral molecule and only one of its enantiomers is biologically active. &owever,although the synthesis produces a racemic mixture, an isomerase enzyme in the body converts theinactive enantiomer into the active enantiomer.

(i) xplain the term :chiral molecule:.(1)

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(ii) ?ar9 with an asteris9 (/) the chiral centre on the structure of ibuprofen below.(1)

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(iii) xplain the term :racemic mixture:.(1)

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(iv) uggest twobenefits that arise from the isomerization of the inactive enantiomer of ibuprofen.(2)

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(Total for question = 18 marks)

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ark !cheme

@*.

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Q2.

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