Esters C.I. 13.5 What are they? How are they made?  Formed when an alcohol reacts with a carboxylic acid.  Very slow reaction, unless! an acid catalyst used (usually sulphuric acid)  A condensation reaction  The condensation reaction between the hydroxyl group and the carboxylic acid known as esterification .  Reverse reaction = ester hydrolysis Naming Named after alcohol & carboxylic acid from which they are derived. Names of esters end in –oate. CH 3 C CH 2 O O CH 3 ethyl ethanoate this part from the acid and is named after it this part comes from the alcohol & is named after it let’s name some esters! Structural formulae Although the previous structural formula are the clearest way of showing esters, they can draw out in a shortened form. ethyl ethanoate CH 3 C CH 2 O O CH 3 Either… Or… CH 3 C CH 2 O O CH 3 In this version the acid part has been written first  Identify the group attached to the C=O – this is from the acid  The group attached to the –O- is from the alcohol. Wait! What’s that smell? • Esters have strong, sweet smells. • Their bouquet is often floral or fruity. • This means they are used in food flavourings & perfumes. • Also, very good at dissolving organic compounds so often used as solvents. ester fragrance ethyl methanoate raspberries 3-methylbutyl ethanoate pears ethyl 2-methylbutanoate apples phenylmethyl ethanoate jasmine Esters from phenols • -OH group in phenol less reactive to esterification, requires a more vigourous reagent. • Use of ethanoic acid in esterification is also known as ethanoylation. • Ethanoic anhydride is a more vigourous ethanoylating agent OH Esters from phenols • Ethanoic anhydride used as it is reactive but not too dangerous. • Ethanoyl chloride is much more reactive, but, also toxic and hazardous to use. • Ethanoic anhydride & ethanoyl chloride are described as acylating agents  using an acylating agent is the only way to esterify a phenol  alcohols can be esterified using acylating agents or by reacting with a carboxylic acid. Ester hydrolysis  Breakdown of an ester by water.  Process sped up by catalysis  Can use an acid to catalyse (H 2 SO 4 )  Alkali catalysts (e.g. sodium hydroxide) can also be used but instead of producing carboxylic acid a carboxylate salt is formed.  Alkaline hydrolysis goes to completion & hence is usually preferred. This is why it is a condensation reaction because water is produced! R R’C H 2 O + O H H O O R’C R O O + ⇋ Definition of a condensation reaction = two molecules reacting to form a larger molecule with the elimination of a small molecule such as water CH 3 CH CH 2 O O CH 3 CH 2 C CH 3 O O CH CH 3 O O ethyl methanoate methyl propanoate methyl methanoate . hydroxyl group and the carboxylic acid known as esterification .  Reverse reaction = ester hydrolysis Naming Named after alcohol & carboxylic acid. What are they? How are they made?  Formed when an alcohol reacts with a carboxylic acid.  Very slow reaction, unless! an acid catalyst used (usually