A-level Chemistry/OCR/Chains, Energy and Resources/Alcohols, Halogenoalkanes and Analysis/Alcohols
There are six reactions of alcohols that you must be aware of for this module. For each you must be able to remember the reactants, products and conditions. For some of them you must be able to draw the mechanisms from memory.
Remembering all of these reactions can be made easier with the SHOCED (or SHOCKED with K missing) Mnemonic:
Halogen alkane formation
Reactants: An alcohol (e.g. propanol C3H7OH),
Sodium Metal (Na)
Products: A “sodium salt” (e.g. sodium methoxide) [alkoxide]
C3H7OH + Na → C3H7O-Na+ + 0.5 H2
Halogen Alkane Production (Electrophilic substitution)
Reactants: An alcohol (e.g. ethanol), a hydrogen halide (e.g. HBr)
Products: a Halogen alkane (e.g. bromoethane), water
Conditions: no special
C2H5OH + HBr → C2H5Br + H2O
Conditions: Acidified Potassium Dichromate (VI) or Sodium Dichromate is used as an oxidising agent. Reaction occurs in reflux.
The products that form from oxidation depend on the structure of the alcohol.
The oxidation of the primary alcohol, ethanol with K2Cr2O72- / H+ is as follows: CH3CH2OH + [O] → CH3CHO (the aldehyde; ethanal)
Remember: Oxidation is defined as the gain of Oxygen AND/OR the loss of hydrogen.
Primary alcohols: oxidise to aldehydes and then to carboxylic acids
Secondary alcohols: Oxidise to ketones
Tertiary alcohols: Cannot be oxidised
(Complete) Combustion of any alcohol produces carbon-dioxide and water.
Burning completely in an excess of oxygen
C2H5OH + 3O2 → 2CO2 + 3H2O
However, incomplete combustion can occur when oxygen is not in excess (lack of oxygen) which can cause carbon monoxide (CO) or even carbon residue (C) to form as the products.
Remember the basic principle:
ACID + ALCOHOL → ESTER + WATER (as quoted from Dr. Carmel Stanley of Barnsley College)
An alcohol (e.g. ethanol) + a carboxylic acid (e.g. ethanoic acid) → an ester (e.g. ethyl ethanoate) and water
Conditions: H2SO4 (sulphuric acid) Catalyst
Reactants: An alcohol
Products: Alkene + water
Conditions: hot and concentrated sulphuric acid
An alcohol can be formed by the hydration of the alkene; ethene, shown below:
CH2=CH2(g) + H2O(g) → CH3CH2OH(g)
Conditions: 300 degrees Celsius
60 atm of pressure
H3PO4 (phosphoric acid) catalyst.