Alcohols – Organic Chemistry | Chemistry | CSEC CXC lessons online – Study Guide

Alcohols - Organic Chemistry

The Alcohols have the general formula CnH2n +1 OH

 

The Properties of Ethanol

It is a good solvent.  Many substances that do not dissolve in water dissolve in ethanol.

The boiling temperature is 78 degrees Celsius

 

Uses of Ethanol

Ethanol is used to make many substances a few of these being: polish, inks, dyes, a wide range of pharmaceuticals and alcohols.

Ethanol is used in alcoholic drinks and

this ethanol is obtained by anaerobic fermentation of carbohydrates e.g. fruits

 

CARBOHYDRATES  → ETHANOL + CARBON DIOXIDE

(Enzymes supplied by yeast)

 

Reactions of Alcohols

The functional group of Alcohols is the –OH group.

The reactions of Alcohols are based on this group.

 

Some alcohols react with the very reactive metals

Metals high in the electrochemical series e.g. Na. Li, Mg, Ca react with the alcohols lower in the alcohol series (methanol, ethanol, and propanol).

2Na(S) + 2CH3CH2OH (g) → 2 CH3CH2ONa(s) + H2 (g)

Alcohols undergo oxidation with powerful oxidizing agents such as acidified potassium dichromate and acidified potassium manganate (vii).

They convert alcohols to organic acids.

In these reactions an intermediate aldehyde is formed.

 

Rxn: CH3CH2OH + KMnO4/H+ → H2O + CH3CHO (ethanal )

(intermediate)

CH3CHO + KMnO4/H+ → CH3COOH ethanoic acid

The reaction mixture changes colour from purple to colourless.

With potassium dichromate (VI) the colour change is from orange to green.

 

 

The Breathalyser Test

This test is based on the fact that high levels of ethanol vapour in the breath reduce acidified K2Cr2O7 (potassium dichromate) crystals from orange to green

 

 

Dehydration to Alkenes

CH3CH2OH                 →                    CH2 = CH2

Ethanol                                                  Ethene

 

 

 

Conditions for dehydration

Ethanol is heated with excess H2SO4 (conc.) at 170 degrees Celsius or passing ethanol vapour over activated alumina (Al2O3) heated to 450 degrees Celsius

 

Conversion of Alcohols to esters

Organic acid + Alcohol                        →                         Ester + Water

Conc. H2SO4

as catalyst

 

Combustion of Alcohol

The combustion is highly exothermic and they are combusted with O2

e.g. CH3CH2OH + 3O2             →                 2CO2 + 3H2O + heat

 

 

Citation: Lambert and Mohammed (1993), Chemistry for CXC Halley court, Jordon Hill Oxford.