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STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement STRUCTURE OF CARBOXYLIC ACIDS • contain the carboxyl functional group COOH • the bonds are in a planar arrangement • include a carbonyl (C=O) group a hydroxyl (O-H) group and HOMOLOGOUS SERIES Carboxylic acids form a homologous series HCOOH CH3COOH C2H5COOH HOMOLOGOUS SERIES Carboxylic acids form a homologous series HCOOH CH3COOH C2H5COOH With more carbon atoms, there can be structural isomers C3H7COOH (CH3)2CHCOOH NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting with the C in COOH being 1 • as in alkanes, prefix with alkyl substituents • side chain positions are numbered relative to Carbon atom number 1 e.g. CH3 - CH(CH3) - CH2 - CH2 - COOH is called 4-methylpentanoic acid NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules • select the longest chain of C atoms containing the COOH group; • remove the e and add oic acid after the basic name • number the chain starting with the C in COOH being 1 • as in alkanes, prefix with alkyl substituents • side chain positions are numbered relative to Carbon atom number 1 BUTANOIC ACID 2-METHYLPROPANOIC ACID NAMING CARBOXYLIC ACIDS Acids are named according to standard IUPAC rules Many carboxylic acids are still known under their trivial names, some having been called after characteristic properties or their origin. Formula HCOOH CH3COOH C6H5COOH Systematic name methanoic acid ethanoic acid benzenecarboxylic acid (trivial name) formic acid acetic acid benzoic acid origin of name latin for ant latin for vinegar from benzene CHEMICAL PROPERTIES Carboxylic acids are weak acids. They can donate protons, but they only partially dissociate into their ions. weak acids CH3COOH (aq) CH3COO¯(aq) + H+(aq) CHEMICAL PROPERTIES Carboxylic acids display typical reactions of an acid and form salts, called carboxylates: 1. acid + base salt + water, eg. CH3COOH + NaOH (aq) ——> CH3COO¯Na+ (aq) + H2O (l) ethanoic acid sodium ethanoate 2. acid + carbonate salt + water + CO2, eg. CH3COOH + NaCO3 (aq) ——> CH3COO¯Na+ (aq) + H2O (l) + CO2 (g) ethanoic acid sodium ethanoate QUALITATIVE ANALYSIS Carboxylic acids are strong enough acids to release CO2 from carbonates. Phenols are also acidic but not are not strong enough to release CO2 ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation Notes e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester ESTERIFICATION Reagent(s) alcohol + strong acid catalyst (e.g conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) ethanol ethanoic acid CH3COOC2H5(l) + H2O(l) ethyl ethanoate Notes Conc. H2SO4 is a dehydrating agent - it removes water causing the equilibrium to move to the right and thus increases the yield of the ester Naming esters Named from the original alcohol and carboxylic acid CH3OH + CH3COOH methanol ethanoic acid CH3COOCH3 + H2O METHYL ETHANOATE ESTERS Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE Preparation From carboxylic acids or acyl chlorides Reactivity Unreactive compared with acids and acyl chlorides ESTERS Structure Substitute an organic group for the H in carboxylic acids Nomenclature first part from alcohol, second part from acid e.g. methyl ethanoate CH3COOCH3 METHYL ETHANOATE ETHYL METHANOATE Preparation From carboxylic acids or acyl chlorides Reactivity Unreactive compared with acids and acyl chlorides Isomerism Esters are structural isomers of carboxylic acids STRUCTURAL ISOMERISM – FUNCTIONAL GROUP Classification Functional Group Name CARBOXYLIC ACID ESTER R-COOH R-COOR PROPANOIC ACID METHYL ETHANOATE Physical properties O-H bond gives rise to hydrogen bonding; get higher boiling point and solubility in water No hydrogen bonding insoluble in water Chemical properties acidic reacts with alcohols fairly unreactive hydrolysed to acids USES OF ESTERS Despite being fairly chemically unreactive, esters are useful as ... • flavourings apple pear banana pineapple rum • solvents nail varnish remover - ethyl ethanoate • plasticisers 2-methylbutanoate 3-methylbutylethanoate 1-methylbutylethanoate butylbutanoate 2-methylpropylpropanoate HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH METHANOIC ACID ETHYL METHANOATE + C2H5OH ETHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH METHANOIC ACID ETHYL METHANOATE METHYL ETHANOATE + C2H5OH ETHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL HCOOH + METHANOIC ACID C2H5OH ETHANOL ETHYL METHANOATE CH3COOH ETHANOIC ACID METHYL ETHANOATE + CH3OH METHANOL HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> CH3COO¯ Na+ + CH3OH HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt HYDROLYSIS OF ESTERS Hydrolysis is the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL The products of hydrolysis depend on the conditions used... acidic CH3COOCH3 + H2 O alkaline CH3COOCH3 + NaOH CH3COOH + CH3OH ——> CH3COO¯ Na+ + CH3OH If the hydrolysis takes place under alkaline conditions, the organic product is a water soluble ionic salt The carboxylic acid can be made by treating the salt with HCl CH3COO¯ Na+ + HCl ——> CH3COOH + NaCl NATURALLY OCCURING ESTERS - TRIGLYCERIDES • triglycerides are the most common component of edible fats and oils • they are esters of the alcohol glycerol (propane-1,2,3-triol) CH2OH CHOH CH2OH Saponification • • • • alkaline hydrolysis of triglycerol esters produces soaps a simple soap is the salt of a fatty acid as most oils contain a mixture of triglycerols, soaps are not pure the quality of a soap depends on the oils from which it is made ACYL CHLORIDES Nomenclature Chemical Properties Named from the corresponding carboxylic acid remove -ic add -yl chloride CH3COCl ethanoyl chloride C6H5COCl benzene carbonyl (benzoyl) chloride • • • • colourless liquids which fume in moist air attacked at the positive carbon centre by nucleophiles these include water, alcohols, ammonia and amines undergo addition-elimination reactions ACYL CHLORIDES Reagent Water Product(s) carboxylic acid + HCl (fume in moist air / strong acidic solution formed) Conditions room temperature Equation CH3COCl(l) Mechanism addition-elimination + H2O(l) ——> CH3COOH(aq) + HCl(aq) ACYL CHLORIDES Reagent Alcohols Product(s) ester + hydrogen chloride Conditions reflux in dry (anhydrous) conditions Equation CH3COCl(l) Mechanism addition-elimination Note + CH3OH(l) ——> CH3COOCH3(l) + HCl(g) esters can also be made from acids and alcohols via carboxylic acids slower, reversible, low yield via acyl chlorides faster, better yield, must be dry ACYL CHLORIDES Reagent Ammonia Product(s) amide + hydrogen chloride Conditions Low temperature and excess ammonia; vigorous reaction. Equation CH3COCl(l) + NH3(aq) ——> CH3COCl(l) + 2NH3(aq) ——> or Mechanism addition-elimination CH3CONH2(s) + HCl(g) CH3CONH2(s) + NH4Cl(s) ACYL CHLORIDES Reagent Amines Product(s) N-substituted amide + hydrogen chloride Conditions anhydrous Equation Mechanism CH3COCl + C2H5NH2 ——> CH3CONHC2H5 + HCl or CH3COCl + 2C2H5NH2 ——> CH3CONHC2H5 + C2H5NH3Cl addition-elimination - similar to that with ammonia. REVISION CHECK What should you be able to do? Recall and explain the physical properties of carboxylic acids Recall the structures of carboxylic acids, esters and acyl chlorides Recall the acidic properties of carboxylic acids Recall and explain the esterification of carboxylic acids Write balanced equations representing any reactions in the section Recall and explain the structure and naming of esters Recall the methods for making esters Recall the conditions for, and products of, the hydrolysis of esters. CAN YOU DO ALL OF THESE? YES NO You need to go over the relevant topic(s) again Click on the button to return to the menu WELL DONE! Try some past paper questions AN INTRODUCTION TO CARBOXYLIC ACIDS AND THEIR DERIVATIVES THE END © JONATHAN HOPTON & KNOCKHARDY PUBLISHING