Carboxylic Acids, Esters & Fats

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Carboxylic Acids

  • Functional groups is -COOH.
  • Suffix is -oic acid.
  • Found in rancid butter, citrus fruits and ant stings.
  • Carboxylic acids with between 1-4 C's are very soluble due to the highly polar C=O and O-H allow the acid to form H-bonds with H2O molecules. This doesn't apply so much to acids with higher amounts of C's, as the C chain is relatively insoluble.
  • Carboxylic acids are weak compared to nitric, hydrochloric etc.
  • They take part in typical acid reactions and the salts formed are called carboxylates:

  • Reacting with metals:
    -There will be effervescence and H gas produced, as well as a salt.
    -CH3COOH + Na -> CH3COO- + 1/2H2
  • Reactions with bases:
    -Salt and water formed.
    -CH3CH2COOH + KOH -> CH3CH2COO-K+ + H2O
  • Reactions with carbonates:
    -Salt, water and carbon dioxide formed.
    -2HCOOH + Na2CO3 -> 2HCOO-Na+ + CO2 + H2O 
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Esters

  • Can be formed with a carboxylic acid and an alcohol, with a concentrated acid catalyst.
    -This is esterification, and conc. H2SO4 is usually used.
    -CH3CH2COOH + CH3CH2OH -> CH3CH2COOCH2CH3 + H2O (water is formed!!!)
  • They can also be formed from an acid anhydride and an alcohol.
    -This gives a much better yield, and is done under heat.
    -(CH3CO)2O + CH3OH -> CH3COOCH3 + CH3COOH
  • Esters are hydrolysed to be broken down using water.
  • Acid hydrolysis:
    -Heated under reflux with H2SO4(aq)/HCl(aq).
    -CH3COOCH2CH2CH3 + H2O <---HCl(aq)---> CH3COOH + CH3CH2CH2OH
    -This forms both original products, with NO SALTS; but is reversible.
  • Alkaline hydrolysis:
    -NaOh(aq)/KOH(aq) is refluxed with the ester, this reaction is non-reversible.
    -The basis of soap making, saponification; forms a SALT.
    -CH3CH2COOCH2CH3 + NaOH -> CH3CH2COO-Na+ + CH3CH2OH 
  • Esters are used for flavourings and perfumes, such as oil of wintergreen etc.
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Fats & Oils

  • Animal and vegetable fats/oils are esters of long-chained carboxylic acids, called fatty acids.
  • Fats and oils are very similar and are only seperated by melting points.
  • Triglycerides occur naturally and are triesters of glyerol and 3 fatty acids.
  • It is possible to get triglycerides that are unsaturated/saturated depending on C=C bonds.
  • If there is one C=C it is monounsaturated and any more then it is polyunsaturated.
  • Shorthand for fatty acids consists of:
    -The first number representing the number of C's
    -The second representing the number of C=C's.
    -The bracket represents the position.
    -18:2 (9,12).
  • Forming triglycerides:
    -Can also be saturated/unsaturated depending on C=C's in the fatty acids.
    -Glycerol + 3CH3(CH2)14COOH -> Triglyceride ester
     
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(Example)

  • Just to display what actually occurs:
     
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Diet & Health

  • There are E/Z isomers of fatty acids:
    -Cis form can't pack together so exist as oils
    -Trans form can pack together so have higher melting points than cis
  • Trans fats:
    -HDL's carry cholesterol out of the blood and then out the body, and are 'good'
    -LDL's carry cholesterol into the blood and deposit on artery walls, and are 'bad'
  • Triglyerides are used as biodiesel:
    -Made by transesterification, reacted with ethanol in the presence of Na/K catalyst. 
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