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CARBOXYLIC ACIDS

CARBOXYLIC ACIDS . and. ESTERS. Part 5 Compounds containing the carbonyl group Carboxylic acids and esters know that carboxylic acids are weak acids, but they will liberate CO 2 from carbonates.

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CARBOXYLIC ACIDS

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  1. CARBOXYLIC ACIDS and ESTERS

  2. Part 5 Compounds containing the carbonyl group • Carboxylic acids and esters • know that carboxylic acids are weak acids, but they will liberate CO2 from carbonates. • know that carboxylic acids and alcohols react, in the presence of a strong acid catalyst, to give esters. • know that esters can have pleasant smells. • know the common uses of esters (e.g. as solvents, plasticisers and food flavourings). • know that esters can be hydrolysed, including the production of soap, glycerol and higher fatty acids from naturally-occurring esters.

  3. CARBOXYL COMPOUNDS - STRUCTURE Structure • contain the carboxyl functional group COOH • includes a carbonyl (C=O) group • and a hydroxyl (O-H) group the bonds are in a planar arrangement H • are isomeric with esters...

  4. CARBOXYL COMPOUNDS - STRUCTURE Carboxylic acids form a homologous series HCOOHCH3COOH C2H5COOH With more carbon atoms, there can be structural isomers C3H7COOH (CH3)2CHCOOH

  5. CARBOXYL COMPOUNDS - NOMENCLATURE Nomenclature Remove e from the parent alkane and add ...OIC ACID. Side chain positions are based on the C in COOH being 1 e.g. CH3COOH is called ethanoic acid as it is derived from ethane.

  6. CARBONYL COMPOUNDS - NOMENCLATURE HCOOH methanoic acid CH3COOH ethanoic acid CH3CH(CH3)CH2COOH 3-methylbutanoic acid C6H5CH2COOHphenylethanoic acid CH3C(CH3)2COOH 3,3-methylpropanoic acid

  7. CARBONYL COMPOUNDS - NOMENCLATURE HCOOH methanoic acid CH3COOH ethanoic acid CH3CH(CH3)CH2COOH 3-methylbutanoic acid C6H5CH2COOHphenylethanoic acid CH3C(CH3)2COOH 2,2-dimethylpropanoic acid

  8. CARBOXYL COMPOUNDS – IR IDENTIFICATION 2500–3300cm-1 1600–1700cm-1 ALCOHOL CARBOXYLIC ACID ESTER O-Habsorption O-H + C=O absorption C=O absorption DifferentiationCompound O-H C=O ALCOHOLX CARBOXYLIC ACID   ESTERX 

  9. CARBOXYL COMPOUNDS - IDENTIFICATION e.g. Propanoic acid 2500–3300cm-1 1600–1700cm-1

  10. CARBOXYL COMPOUNDS - IDENTIFICATION e.g. Ethanoic acid 2500–3300cm-1 1600–1700cm-1

  11. PHYSICAL PROPERTIES BOILING POINT Increases as size increases - 101°C 118°C 141°C 164°C due to increased van der Waals forces Boiling point is higher for “straight” chain isomers. 164°C 154°C Greater branching = lower inter-molecular forces = lower boiling point

  12. PHYSICAL PROPERTIES BOILING POINT cont. Carboxylic acids have high b.p,’s for their relative mass... …due to the effect of hydrogen bonding. CompoundFormulaMrb.p./°C Comments ethanoic acidCH3COOH60118H-bonding propan-1-olC3H7OH6097H-bonding propanalC2H5CHO5849permanent dipole-dipole butaneC4H1058- 0.5basic Van derWaals

  13. HYDROGEN BONDING PHYSICAL PROPERTIES BOILING POINT cont. Carboxylic acids have high b.p,’s for their relative mass... …due to the effect of hydrogen bonding. Arises from inter-molecular hydrogen bonding due to polar O—H bonds: extra inter-molecular attraction = more energy to separate molecules

  14. HYDROGEN BONDING PHYSICAL PROPERTIES SOLUBILITY Carboxylic acids are soluble in organic solvents and … they are also soluble in water due to hydrogen bonding: Small molecular mass ones dissolve readily in cold water As mass increases, the solubilities decrease. Benzoic acid is fairly insoluble in cold but is soluble in hot water.

  15. CARBOXYL COMPOUNDS - CHEMICALPROPERTIES PREPARATION Oxidising a primary alcohol or an aldehyde (primary alcohol can be firstly oxidised to an aldehyde) RCH2OH + [O]  RCHO + H2O CH3CH2CH2OH + [O]  CH3CH2CHO propan-1-ol propanal (excess oxidising agent oxidises aldehyde to the acid) RCHO + [O]  RCOOH CH3CH2CHO + [O]  CH3CH2COOH propanal propanoic acid The [O] notation represents the oxidising agent, e.g. Warm acidified potassium dichromate solution.

  16. CARBOXYL COMPOUNDS - CHEMICALPROPERTIES PREPARATION – other methods for reference Hydrolysis of esters RCOOR + H2O  RCOOH + ROH Hydrolysis of acyl chlorides RCOCl + H2O  RCOOH + HCl Hydrolysis of nitriles RCN + 2H2O  RCOOH + NH3 Hydrolysis of amides RCONH2 + H2O  RCOOH + NH3

  17. Reactions of carboxylic acids 1. With carbonates 2. With bases 3. With alcohols

  18. REACTIONS OF CARBOXYLIC ACIDS With carbonates (or hydrogencarbonates). Carboxylic acids are weak acids (not fully dissociated in aqueous solution): RCOOH(aq) Ý RCOO- + H+ carboxylate ion hydroxonium ion

  19. REACTIONS OF CARBOXYLIC ACIDS With carbonates (or hydrogencarbonates). Carboxylic acids are weak acids (not fully dissociated in aqueous solution): RCOOH(aq) Ý RCOO- + H+ but... they arestronger acids than carbonic acid so they will drive out carbon dioxide from carbonates or hydrogencarbonates Can be used as a test for a carboxylic acid 2RCOOH + Na2CO3 2RCOO- + CO2 + H2O 2CH3COOH + Na2CO3 2CH3COO-Na++ CO2 + H2O ethanoic acid sodium ethanoate

  20. REACTIONS OF CARBOXYLIC ACIDS With carbonates (or hydrogencarbonates). 2RCOOH + Na2CO3 2RCOO- + CO2 + H2O 2CH3COOH + Na2CO3 2CH3COO-Na++ CO2 + H2O ethanoic acid sodium ethanoate The acid can be liberated from its salt by treatment with a stronger acid. e.g. RCOO¯ Na+(aq) + HCl(aq) RCOOH + NaCl(aq) Conversion of an acid to its water soluble salt followed by acidification of the salt to restore the acid is often used to separate acids from a mixture.

  21. REACTIONS OF CARBOXYLIC ACIDS With bases / alkalis - neutralisation Carboxylic acids will neutralise bases: RCOOH + NaOH  RCOO-Na+ + H2O 2CH3CH2COOH + NaOH  2CH3CH2COO-Na++ H2O propanoic acid sodium propanoate

  22. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) Conditions Product Equation

  23. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions Product Equation

  24. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product

  25. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation

  26. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate water

  27. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Carboxylic acids will react with the organic equivalent of a base – an alcohol: Reagent(s) alcohol + strong acid catalyst (e.g. conc. H2SO4 ) Conditions reflux Product ester Equation e.g. CH3CH2OH(l) + CH3COOH(l) CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate water Note: 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

  28. REACTIONS OF CARBOXYLIC ACIDS With alcohols - esterification Naming esters Named from the original alcoholand carboxylic acid: CH3OH + CH3COOH ÝCH3COOCH3+ H2O fromethanoic acidfrom methanolMETHYLETHANOATE e.g. CH3CH2OH(l) + CH3COOH(l) Ý CH3COOC2H5(l) + H2O(l) ethanol ethanoic acid ethyl ethanoate water

  29. USES OF ESTERS Although being fairly chemically unreactive, esters are useful as ... • smells and flavourings apple 2-methylbutanoate pear 3-methylbutylethanoate banana 1-methylbutylethanoate pineapple butylbutanoate rum 2-methylpropylpropanoate orange octylethanoate raspberry ethylmethanoate grape methyl anthranilate

  30. ESTERS Although the size of the molecules varies, it seems that the presence of the COO group is vital to the kind of smell

  31. USES OF ESTERS Although being fairly chemically unreactive, esters are useful as ... • solvents nail varnish remover - ethyl ethanoate glue solvent - ethyl ethanoate

  32. USES OF ESTERS Although being fairly chemically unreactive, esters are useful as ... • plasticisers - a substance which when added to a material, usually a plastic, makes it flexible, resilient and easier to handle. Citrate plasticiser esters include triethyl citrate, acetyl triethyl citrate, tributyl citrate, acetyl tributyl citrate and tri-(2-ethylhexyl)-citrate. They are produced from citric acid and are used to plasticise vinyl resins used in applications including medical equipment and packaging films.

  33. ESTERS AND CARBOXYLIC ACIDS – COMPARISONS CARBOXYLIC ACIDESTER Classification R-COOHR-COOR Functional Group PROPANOIC ACID METHYL ETHANOATE Name Physical properties O-H bond gives rise No hydrogen bonding to hydrogen bonding; insoluble in water soluble in water Chemical properties acidic fairly unreactive react with alcohols hydrolysed to acids

  34. HYDROLYSIS OF ESTERS Hydrolysis - the opposite of esterification ESTER + WATER CARBOXYLIC ACID + ALCOHOL  HCOOH + C2H5OH METHANOIC ETHANOL ACID ETHYL METHANOATE  CH3COOH + CH3OH ETHANOIC METHANOL ACID METHYL ETHANOATE

  35. HYDROLYSIS OF ESTERS Products of hydrolysis depend on conditions… Acidic CH3COOCH3 + H2O CH3COOH + CH3OH Alkaline …the organic product is a water soluble ionic salt CH3COOCH3 + NaOH CH3COO¯ Na+ + CH3OH The carboxylic acid can be made by treating the salt with HCl: CH3COO¯ Na++ HCl  CH3COOH + NaCl

  36. One of the organic chemical reactions known to ancient man was the preparation of soaps through a reaction called saponification. Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap. NATURALLY OCCURING ESTERS - TRIGLYCERIDES Triglycerides are the most common component of edible fats and oils OH They are esters of the alcohol glycerol (propane-1,2,3-triol) A typical acid an example of a saturated fatty acid is palmitic acid, CH3-(CH2)14-CO2H

  37. One of the organic chemical reactions known to ancient man was the preparation of soaps through a reaction called saponification. Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap. NATURALLY OCCURING ESTERS - TRIGLYCERIDES Triglycerides are the most common component of edible fats and oils OH They are esters of the alcohol glycerol (propane-1,2,3-triol) A typical acid an example of a saturated fatty acid is palmitic acid, CH3-(CH2)14-CO2H For each glycerol molecule three palmitic acid molecules would react to form the triglyceride...

  38. One of the organic chemical reactions known to ancient man was the preparation of soaps through a reaction called saponification. Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap. NATURALLY OCCURING ESTERS - TRIGLYCERIDES Alkaline hydrolysis of this triglyceride regenerates the glycerol and the salt of the acid

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