Carboxylic Acids And Derivatives

• The numbering always starts from the carboxylic acid end

• - dioic acid • eg ethanedioic acid

• Carboxylic acids are only weak acids in water and only slightly dissociate, but they are strong enough to displace carbon dioxide from carbonates.

• The smaller carboxylic acids (up to C4) dissolve in water in all proportions but after this the solubility rapidly reduces. • They dissolve because they can hydrogen bond to water molecules

• The effervescence caused by production of CO2 with carboxylic acids • with solid Na2CO3 or aqueous NaHCO3 can be used as a functional group test for carboxylic acids

• Carboxylic acids cannot be oxidised by using oxidised agents, but methanoic acid is an exception as its structure has effectively an aldehyde group

• It forms carbonic acid (H2CO3) which can decompose to give CO2

• Carboxylic acids react with alcohols, in the presence of a strong acid catalyst, to form esters and water • Strong acid catalyst = concentrated H2SO4 catalyst

• The reaction is reversible. The reaction is quite slow and needs heating under reflux (often for several hours or days). Low yields (50% ish) are achieved. An acid catalyst (H2SO4 is needed)

• Esters are sweet smelling compounds that can be used in perfumes and flavourings • Esters can be used as solvents for polar organic substances. Ethyl ethanoate is used as a solvent in glues and printing inks • Esters can be used as plasticisers for polymers

• Esters can have pleasant smells

• For use in perfumes they need to be non toxic, soluble in solvent such as ethanol, volatile (turns into gas easily) and not react with water

• Although polar, esters do not form hydrogen bonds because there is no hydrogen bonded to a highly electronegative atom • They have a lower boiling point than the hydrogen-bonded carboxylic acids they came from. They are almost insoluble in water

• Often pure polymers have limited flexibility because the polymer chains cannot move over each other • Incorporating some plasticiser into the polymer allows the chains to move more easily and the polymer can become more flexible

• Esters can be hydrolysed by either: • Heating with acid • or with sodium hydroxide

• Reagents: dilute acid (HCl) • Conditions: heat under reflux • This reaction is the reverse reaction of ester formation • When an ester is hydrolysed a carboxylic acid and an alcohol are formed • This reaction is reversible and does not give a good yield of the products

• Reagents: dilute sodium hydroxide • Conditions: heat under reflux • This reaction goes to completion. Using excess sodium hydroxide will ensure the ester is completely hydrolysed • The carboxylic acid salt product is the anion of the carboxylic acid • The anion is resistant to attack by weak nucleophiles such as alcohols, so the reaction is not reversible

• Addition of a strong acid such as HCl to the carboxylic acid salt will convert the salt to the carboxylic acid form

• Fats and oils are esters of glycerol and long chain carboxylic acids (fatty acids)

• Vegetable oils and animal fats can be hydrolysed to give soap, glycerol and long chain carboxylic (fatty) acids

• Glycerol (propane-1,2,3-triol) forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues.

• Soaps are the sodium or potassium salts of long chain carboxylic acids, produced by the alkaline hydrolysis of fats or oils • The carboxylate ion (COO-) end is hydrophilic and mixes with water. The long non-polar hydrocarbon chain is hydrophobic and mixes with grease • So this allows the grease and water to mix and be washed away