OCR A Jan 2011 Paper 4 Q4

Answers available below

4 Read the passage below and answer the questions that follow. -Amino acids can be synthesised in the laboratory by the two synthetic routes below. Synthesis 1 An -chlorocarboxylic acid is reacted with an excess of concentrated ammonia solution. The resulting solution is neutralised to produce an -amino acid. Cl CH(R)COOH concentrated ammonia solution step 1 H2NCH(R)COO step 2 neutralisation H2NCH(R)COOH Synthesis 2 An aldehyde is reacted with an aqueous solution of potassium cyanide and ammonium chloride. The resulting product is hydrolysed with aqueous acid and then neutralised to produce an -amino acid. RCHO KCN(aq)/NH4Cl (aq) H2NCH(R)CN aqueous acid followed by neutralisation H2NCH(R)COOH (a) A chemist attempted the synthesis of the -amino acid alanine (where R is CH3) using synthesis 1. (i) Write the equation for the reaction of Cl CH(CH3)COOH with excess concentrated ammonia solution, NH3(aq), in step 1 of synthesis 1. (ii) A disadvantage of synthesis 1 is that the -amino acid can react further. For example, in the synthesis of alanine, an impurity with molecular formula C6H11NO4 is also formed. Draw the structure of this impurity. [1]OCR 2011 [1]<br /> (b) A chemist attempted the synthesis of the -amino acid aspartic acid (where R is CH2COOH) using synthesis 2. (i) Draw the skeletal formula of the organic compound that could be used to synthesise aspartic acid using synthesis 2. (ii) Draw 3D diagrams of the optical isomers of aspartic acid. [1] [2] (c) Many pharmaceuticals also have a chiral centre. Discuss two possible disadvantages of producing a chiral drug as a mixture of stereoisomers. State two ways in which a single optical isomer might be synthesised.[4]OCR 2011 [Total: 9] Turn over<br />

Show answer