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Further Organic Chemistry (Carboxylic acids (Reactions: (With metals (acid…
Further Organic Chemistry
Alcohols
homologous series:
C
n
H
2n+2
an alkane with an OH group replacing an H atom
Naming:
root-#-ol
If >2 carbons, the # shows the position of the OH
eg. propan-1-ol
Production of ethanol
Fermentation
conversion of glucose to ethanol and carbon dioxide
yeast added to sugar solution – yeast produces zymase to catalyse the reaction
C6H12O6 ––zymase––> 2C2H5OH + 2CO2
Requires anaerobic conditions – ethanol would be oxidised to ethanoic acid
=> valve used which allows CO2 to escape without allowing air (oxygen) to enter
Optimum temp: 30°c
Produces alcohol of no more than 15% conc – would poison yeast
=> distilled – requires additional energy input
Is a
batch process
– takes time, reaction vessel has to be emptied and refilled => limits rate of production
Steam + Ethene
Carried out at high temp and pressure – 300°c, 60-70atm
Reactants passed over a phosphoric acid catalyst
Favoured in countries which do not produce sugar cane, particularly with supplies of oil
–> ethene produced by cracking
Is a
continuous process
– ethene and steam continually fed into reaction vessel and ethanol continually removed
=> rapid production of larger quantities of purer alcohol
Pure ethanol used as a solvent, and can be blended with petrol for use in car engines
Oxidation of ethanol
Burning in air
Combustion reaction
CH3CH2OH + 3O2 –––> 2CO2 + 3H2O
Incomplete combustion: ethanol + 2O2 –––> 2CO + 3H2O
Microbial oxidation
ethanol –––> ethanoic acid
Laboratory oxidation of alcohols
Uses an potassium dichromate (oxidising agent) acidified with dilute H2SO4
Requires heat, colour change from orange to green
Oxidising agent provides oxygen => written as [O]
ethanol + 2[O] ––H2SO4, heat––> ethanoic acid + H2O
Dehydration of ethanol
Elimination reaction
Ethanol –––> ethene + water
Ethanol vapour passed over catalyst of hot aluminium oxide
–> ethene collected over water
Carboxylic acids
Homologous series:
C
n
H
2n+1
COOH
Alkanes with hydrogen replaced by COOH group
Referred to as
organic acids
Reactions:
With metals
acid + metal –––> salt + hydrogen
Salt KA
carboxylate
salt
With metal carbonates
acid + metal carbonate –––> salt, carbon dioxide, water
Carbon dioxide can be tested for
Esters
Similar to carboxylic acid functional group (-COOH)
–> Hydrogen replaced by an alkyl group
Very volatile, very distinctive sweet smells
–> often used in foods/perfumes
Formation:
KA
esterification
, or
condensation
Alcohol + carboxylic acid ––acid catalyst, heat ––> ester + water
eg. ethanol + ethanoic acid –––> ethyl ethanoate + water
Condensation polymerisation
join monomers into a polymer
For each join between monomers a small molecule is released (eg. H2O, HCl)
Polyesters
formed using same reaction as esters
–> a dicarboxylic acid reacted with a diol
Dicarboxylic acid – has two carboxylic acid groups
Diol – has two alcohol groups
Polyamides
eg. Nylon
Used to manufacture carpets, ropes, clothing etc.
Dicarboxylic acid + diamine
Forms an amide link (-CONH-) to make the polymer