Organic chemistry review
Francine Taylor-Campbell, Contributor

POINTS TO NOTE

Alcohols can be prepared by the hydration of alkenes. Alcohols have the general formula Cn H2n+1OH. Carboxylic acids are generally weak acids and have the formula Cn H2n+1COOH. Alcohols and carboxylic acids combine to produce esters which have the general formula RCOOR' where R is an alkyl group such as CH33 and C2H5.

REACTIONS OF ALCOHOLS (USING ETHANOL)

1. Alcohols burn in air or oxygen to produce carbon dioxide, heat and energy:

2C₂H₅OH (l) + 7O₂ (g) ===== 4CO₂ (g) + 6H₂O (g)

2. Alcohols react with metals, such as Na, Li, Mg and Ca, to yield hydrogen gas and to form salts called alkoxides. The reaction is similar to the reaction of metals with water because of the presence of -OH (H2O can be written as H - OH):

2Na (s) + 2C₂H₅OH (l) === 2C₂H₅OHa (aq) + H₂ (g) sodium ethoxide

3. Alcohols can be oxidised to organic acids using powerful oxidising agents, such as acidified potassium dichromate (VI) or acidified potassium permanganate (VII) solution.

C₂H₅OH (l) + 2[O] ====== CH₃COOH(aq) + H₂O (l) Ethanoic acid

The oxygen is from the oxidising agent. If potassium permanganate is used, the reaction mixture changes from purple to colourless; and if potassium dichromate is used, the mixture changes from orange to green, as the dichromate VI ion is reduced to green chromium III ion. This forms the basis for the breathalyser test for drunken drivers.

4. Alcohols can undergo dehydration reactions to the corresponding alkene using concentrated sulphuric acid (170 0C)or passing the vapour activated alumina (Al2O3):

C₂H₅OH (l) ====== C₂H₄ (g) + H₂O This reaction effectively removes water from the alcohol to form the alkene.

5. Alcohols react with acids to form esters:

C₂H₅OH + CH₃COOH === CH₃COOC₂H₅ + H2O Ethylethanoate

REACTIONS OF ORGANIC ACIDS

1. Organic acids are weak acids (incompletely dissociated in solution) and can react with metals to form salts and liberate hydrogen:

2Na (s) + 2CH₃COOH (aq) ===== 2CH₃COONa (aq) + H₂(g) sodium ethanoate

Only the hydrogen of the -COOH is replaceable in these acid type reactions.

2. Acids react with oxides and hydroxides of metals:

MgO (s) + 2CH₃COOH (aq) ==== (CH₃COO)₂Mg (aq) + H₂O
Magnesium ethanoate

3. Organic acids react with carbonates and hydrogencarbonates to form salts and carbon dioxide:

CH₃COOH (aq) + NaHCO₃ (aq) =====CH₃COONa (aq) + CO₂ (g) + H₂O

4. They react with alcohols to produce esters in a reaction called an esterification reaction. Ester formation is a type of condensation reaction in which a large molecule is formed from the joining of two reactive groups with the elimination of a small molecule such as H₂O.

Esters can be hydrolysed (broken down) using acid or alkali to yield the acid (or salt of the acid) and alcohol that formed the ester.

Visual arts student-teacher, Tamu Wright, shows a few of her art pieces to a student of Cumberland High on February 12.	These students mount a display inside the school's Library at Cumberland High School on February 12. The display was used to mark Environment Week, February 11-15. -Anthony Minott/Freelance Photographer

Francine Taylor-Campbell is an independent contributor.