13616.08RRR 14 The table shows the names and boiling points of four carboxylic acids with molecular formula C5H10O2. They are structural isomers. Name Boiling point /°C 2,2-dimethylpropanoic acid 164 2-methylbutanoic acid 176 3-methylbutanoic acid 177 pentanoic acid 186 (a) (i) Define the term structural isomers. [1] (ii) Explain the difference in the boiling point of 2,2-dimethylpropanoic acid and pentanoic acid. [2] (b) Pentanoic acid may be formed by the acid catalysed hydrolysis of methyl pentanoate. (i) Write the equation for this reversible reaction. [1] 13616.08RRR [Turn over (ii) A different product is formed if the hydrolysis of methyl pentanoate is carried out using dilute sodium hydroxide solution. Name the different product formed and state an advantage of the base catalysed hydrolysis of an ester rather than acid catalysed hydrolysis. [2] 13616.08RRR (c) 2-methylbutanoic acid can be prepared in a two-step synthesis. Br Step 1 Step 2 OH O OH 1-bromo-2-methylbutane 2-methylbutan-1-ol 2-methylbutanoic acid (i) State the name of the reagent and the reaction conditions required to carry out Step 1 of the synthesis. [2] (ii) State the type of reaction occurring in Step 2. [1] (iii) 2-methylbutanoic acid is reduced using excess lithium tetrahydridoaluminate(III). Write the equation for this reaction. [2] 13616.08RRR [Turn over (d) 2,2-dimethylpropanoic acid reacts with phosphorus(V) chloride to form the acyl chloride, pivaloyl chloride. This acyl chloride is used in the manufacture of insecticides and pesticides. (i) Write the equation for this reaction. [1] (ii) State two observations for the reaction between phosphorus(V) chloride and 2,2-dimethylpropanoic acid. [2]