AQA Chemistry A-level 3.3.9: Carboxylic Acids and Esters Detailed Notes PDF

AQA Chemistry A-level 3.3.9: Carboxylic Acids and Esters Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

AQA Chemistry A-level 3.3.9: Carboxylic Acids and Esters Detailed Notes This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.3.9.1 - Carboxylic Acids and Esters Carboxylic Acids These organic compounds are recognised by the ​functional group -COOH​ containing a carbonyl group (C=O) and an -OH acid group. They are produced from the oxidation of 1​o alcohols under ​reflux​. Carboxylic acids are ​weak acids that slightly dissociate ​when in solution, forming a ​H+​​ ion and a ​carboxylate ion​, RCOO-. Example: They react ​as acids with carbonates ​to produce a carboxylate salt, water and CO​2​. Example: Small chain carboxylic acids are able to form ​hydrogen bonds​ ​with water molecules​ between the lone electron pair on an oxygen atom and a ∂+ hydrogen atom. This makes them ​soluble in water​. Example: https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Esters Carboxylic acids can ​react with alcohols​ in the presence of a ​strong acid catalyst​ to form esters​. This reaction is ​esterification​ and is carried out under reflux. Example: A method for remembering the reaction is: ‘remove the -OH from the acid and the hydrogen from the alcohol to make water. Then stick the acid and alcohol together’. Esters are ​sweet smelling compounds ​used in food flavourings and perfumes. They have ​low boiling points​ and also make ​good solvents​ for other polar molecules. Triglyceride Esters Vegetable oils and fats​ are esters of naturally occuring ​glycerol​ (propane-1,2,3-triol). This alcohol undergoes esterification to form ​triglyceride esters​. Example: Biodiesel​ is an ester produced from ​vegetable oils and methanol​ in the presence of a strong acid catalyst. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Hydrolysis Ester hydrolysis is the ​reverse reaction ​to esterification, converting esters back into alcohols and carboxylic acids. This is done by ​adding water​ but can be carried out under ​different conditions​ to produce different products. Acidic Conditions This produces a ​simple reverse reaction​ back to an alcohol and a carboxylic acid. Alkaline Conditions The carboxylic acid produced reacts further with the base to ​form a salt​. The production of this salt is called ​saponification​. Salts such as this are commonly used as soaps​ because they have ​hydrophilic and hydrophobic​ properties. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc 3.3.9.2 - Acylation Carboxylic acids have ​derivative molecules​ where the -OH group is replaced by another group. There are three main derivatives: Acid Anhydrides​ ​- Formed when water is removed from two carboxylic acids. Acyl Chlorides​ ​- React violently due to the very polar -COCl group. Amides​ ​- Reacts to form N-substituted amides. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Reactions of Derivatives These compounds react via ​nucleophilic addition-elimination reactions​. In these reactions, the addition of a nucleophile leads to the elimination of a product under ​aqueous conditions​. Mechanism Acyl chlorides can react with other compounds too: + Water = Carboxylic Acid + Alcohol = Ester + Ammonia = Amide + Amines = N-substituted Amide Aspirin This is an ester produced from ​salicylic acid and ethanoic anhydride​. Example: Ethanoyl chloride​ can also be used to produce aspirin however it is not used in industry as it is expensive ​and produces ​harmful HCl fumes ​as part of the reaction.​ Ethanoic anhydride​ is much safer for industrial use. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc