3.9 carboxylic acids

• draw the functional group of a carboxylic acid :

  functional group

  
• how is a carboxylic acid an acid?

  the Hydrogen in the OH group gets lost as H+
• is carboxylic acid weak or strong and why?

  weak acid because it partially dissociates but strong enough to displace carbondioxide in carbonates
• what are three properties of carboxylic acids?

  1. weak acids
  2. high boiling/melting point
  3. soluble in water (until butanoic acid)
• what happens when 2 carboxylic acids form?

  dimers due to hydrogen bonding
• why are carboxylic acids soluble in water?

  they can form hydrogen bonds with the water molecules
• how are carboxylic acids salts stabilised?

  by delocalisation
• how are carboxylic acid salts stabilised by delocalisation

  • when the H+ ion is lost, the Pi cloud from the c=o is evenly distributes
  • now there is 2 equal length c-o bonds which is more stable and is more likely to form
• describe the strength of a carboxylic acid depending on its chain length/alkyl group:

  • the longer the chain ,
  • the more the electron density is pushed to the COO- ion
  • making it more negative
  • therefore less strong
• describe the strength of a carboxylic acid due to an electronegative atom like chlorine:

  • chlorine is electronegative so withdraws electron density from the COO- ion
  • making it less negative (more positive)
  • so more stable and a stronger acid
• ESTERIFICATION:

  • write the reaction
  • what are the conditions required ?

  1. alcohol + carboxylic acid ⇌ ester + water
  2. heating under reflux and a strong acid catalyst
• what are two 'features' of an esterification reaction

  1. very slow
  2. low yeild
• what are three functions/uses of esters?

  1. sweet smelling compounds used in perfumes and flavouring
  2. plasticisers
  3. solvents for polar organic molecules
• how are esters used in perfumes/flavourings? (4)

  • they have to be non-toxic
  • they cant react with water
  • they have to be volative
  • they should be able to dissolve in solvents like ethanol
• how are esters used in plasticisers?

  they make the pure polymer chains flexible by allowing the chains to move more easily
• how are esters used as solvents?

  • although they are polar, they cant form hydrogen bonds as there's no hydrogen bonded to a highly electronegative atom
  • they are almost insoluble in water
  • they have lower boiling points that the carboxylic acids they come from
• what are two reagents that hydrolyse esters?

  dilute sodiumhydroxide and dilute hydrochloric acid
• hydrolysis of esters using dilute HCl:

  • write the word equation
  • write the conditions
  • whats the yield like

  1. ester + water ⇌ alcohol + carboxylic acid
  2. condition : heat under reflux and an acid catalyst
  3. low yield due to it being reversible
• hydrolysis of esters using dilute NaOH

  • write the word equation
  • conditions
  • products

  • ester + sodiumhydroxide → carboxylic acid salt + alcohol
  • conditions: heat under reflux and adding excess NaOH to ensure the reaction goes into completion
• what is the product of hydrolysis of esters using NaOH (carbolylic acid salt )?

  how do you get rid of it?

  • an anion of carboxylic acids
  • they are resistant to attacks from weak nucleophiles like alcohol so the reaction is not reversible
  • reacting the carboxylic acid salt with a strong acid -> carboxylic acid
• what are fats and oils made of?

  glycerol and long chain hydrocarbons
• what is the IUPAC name of glycerol?

  propan-1,2,3-triol
• what are the products of the hydrolysis of animal fats and vegetable oils?

  glycerol, long chain carboxylic acids and soaps
• what does the bonding in glycerol allow it to do and what are the uses?

  • hydrogen bonding so it is readily soluble in water
  • used in cosmetics, food and glue
• what does the property of soaps allow it to do?

  • at the end of the long carboxylic chain , the CO2- is polar and hydrophyllic so it mixes with water
  • the rest of the hydrocarbon is non-polar and hydrophobic so can mix with the grease , this allows water and grease to wash away
• what is biodiesel ?

  mixture of methyl esters of long chain carboxylic acid
• how do make biodiesel?

  reacting vegatable oil with with methanol and a strong ALKALI catalyst
• is biodiesel carbon-neutral?

  • yes because it can be argued that the carbon produced when the biofuel is burnt it releases the same amount of carbondioxide thats been extracted from the air during photosynthesis of the plant
  • however this doesnt consider irrigation , extracting oil and the heating for the process
  • if the energy comes from fossil fuels its not carbon neutral
• why are acyl chlorides and acid anhydrides more reactive than carboxylic acids and esters?

  because they have good leaving groups due to less effective delocalisation
• what are the main differences between acid anhydrides and acyl chlorides?

  their by-products, acylchlorides produce hydrochloric acids whereas acid anhydrides produce RCOOH
• acyl chlorides reaction with water:

  • what are the reagents
  • what are the conditions
  • what are the products
  • what can you observe
  • what is the mechanism called

  1. water
  2. room temperature
  3. carboxylic acid and hydrochloric acid
  4. white steamy fumes of hydrochloric acid
  5. nucleophilic addition elimination mechanism
• acyl chlorides reaction with alcohol

  • what Is the reagent
  • what do they produce
  • what are the conditions
  • what can be observed
  • what's the mechanism called

  1. alcohol
  2. ester and HCl
  3. room temperature
  4. white steamy fumes of HCl
  5. nucleophilic addition elimination
• acid anhydrides reaction with alcohol

  • what's the reagent
  • whats the products
  • what are the conditions

  1. alcohol
  2. ester and carboxylic acids
  3. room temperature
• why is using acylchlorides and acid anhydrides better than using carboxylic acids to produce esters?

  because the reaction isn't reversible and its quicker
• acyl chloride reaction with ammonia (NH3)

  • what are the reagent ( write the equation )
  • what are the products
  • what is an observation
  • what are the conditions

  1. RCOCl + 2NH3 -> RCONH2 + NH4Cl
  2. primary amide + NH4Cl
  3. room temperature
  4. white smoke of NH4Cl
• acid anhydride and ammonia (NH3)

  • reagent (write the equation)
  • product
  • condition

  1. ammonia
  2. primary amide + RCO2-NH4+
  3. room temperature
• acyl chloride and primary amine ( 2Ch3NH2)

  • reagent
  • products
  • conditions


  1. primary amine
  2. secondary amide ( RCONHCH3) and CH£NH3+Cl-
  3. room temperature
• acid anhydride and primary amine (2CH3NH2)

  • reagent
  • product
  • conditions

  1. primary amine (2CH3NH2)
  2. secondary amine ( RCONHCH3 ) and
  3. room temperature
• draw a delocalized carboxylic acid

  delocalisation

  
• draw the oxidation of methanoic acid

  oxidation