- 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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- 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.
- 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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- 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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