Making And Using Alcohols
Hydration Of Ethene
H2C=CH2 + H2O ---H3PO4 / 300C / 60 atm ---> CH3CH2OH
The reaction is reversible, and so converstion of ethene is comcomplete; so they pass through over and over up to 95% conversion.
C6H12O6 --- Yeast / 37C ---> 2CH3CH2OH + 2CO2
-Ethanol produced can only reach 14% concentration as at this point the yeast doesn't work.
Also has to be undertaken in a vaccum to reduce incomplete conversion.
-Ethanol can be used in drinks, having to be distilled for higher percentages.
-It can also be as an additive to fuel to increase the octave rating.
-Methylated spirits consists of partially ethanol; used as a fuel.
-Methanol can be used as a clean burning fuel, and as a feedstock.
Properties Of Alcohols
-Hydrogen bonds form between adjacent alcohol molecules.
-The volatility and boiling point is affected by these strong bonds compared to other alkanes (etc.), so more energy is needed to break these intermolecular forces.
-Alcohols can dissolve in water as H bonds form between the polar -O-H groups in alcohol and water.
-Solubility decreases with increase in alcohol size as a larger part of the molecule is the carbon chain; and these do not form hydrogen bonds.
Classification Of Alcohols
-The -OH group is attached to a C atom with no alkyl groups, or one alkyl group.
-The -OH group is attatched to a C atom bonded to two alkyl groups.
-The -OH group is attached to a C atom bonded to three alkyl groups.
Combustion Of Alcohols
In a plentiful supply of oxygen, alcohols will burn completely:
-C2H5OH + 3O2 -> 2CO2 + 3H2O
Oxidation Of Alcohols
-C3H7OH + [O] --- K2Cr2O7 / H2SO4 / Distil ---> C2H5CHO + H2O
-This produces a aldehyde and water. (I.e. Propanal) The distillation prevents total conversion into a carboxylic acid.
-With excessive oxidising agent, the reaction will reach the carboxylic acid stage; and during lab work you will need to reflux the mixture so it is fully reacted.
-C3H7OH + 2[O] ---K2Cr2O7 / H2SO4 / Reflux ---> C2H5COOH + H2O
Oxidation Of Alcohols (Cont.)
-These become oxidised into ketones, which cannot be oxidised further.
-C4H9OH + [O] --- K2Cr2O7 / H2SO4 / Heat ---> CH3C=OCH2CH3 + H2O
-Resistant to oxidation and do NOT react.
Test for Primary/Seconday/Tertiary alcohols:
-Esterification is the reaction of an alcohol with a carboxylic acid to form an ester and water.
-Requires a concentrated acid catalyst, such as sulfur dioxide.
-This is shown in the diagram as the removal of water to form an ester.
-Esters are used as adhesives, solvents and flavourings.
To prepare an ester:
-Add 1cm3 of the carboxylic acid and the alcohol.
-Place in a water bath of 80 degrees for 5 minutes.
-Pour the product into cold water, forming a sweet smelling oil.
Dehydration Of Alcohols
-Dehydration is an elimination reaction in which water is removed from a saturated molecule to form an unsaturated molecule.
-A concentrated H2SO4 catalyst is required and a large amount of heat.
-The alcohol must be under reflux for around 40 minutes, to eliminate all water.
This works for cyclic alcohols also: