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:

Sodium Substitution
Halogen alkane formation
Oxidation
Combustion
Esterification
Dehydration

Sodium Substitution

Reactants: An alcohol (e.g. propanol C₃H₇OH),
Sodium Metal (Na)
Products: A “sodium salt” (e.g. sodium methoxide) [alkoxide]
Conditions: n/a
C₃H₇OH + Na → C₃H₇O^-Na⁺ + 0.5 H₂ nd the alphenic acid change in phenol by this reaction

C6H5SO3Na + NaOH - C6H5ONa+ Na2SO3+H2O        NOW C6H6ONa REACT WITH  HCL AND MADE PHENOL BY THIS REACTION

 C6H5ONA + HCL - C6H5OH +NaCl

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

Oxidation

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 K₂Cr₂O₇^2- / 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

Combustion

(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.

Esterification

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

Dehydration

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=CH_2(g) + H₂O_(g) → CH₃CH₂OH_(g)
Conditions: 300 degrees Celsius
60 atm of pressure
H₃PO₄ (phosphoric acid) catalyst.