A-Level organic chemistry exam revision notes on alcohols

Part 4A. The chemistry of ALCOHOLS - reactions of alcohols with sodium (Na), acid chlorides (RCOCl) and carboxylic acids (RCOOH) - chemical reagents, reaction conditions and balanced equations

Sub-index for this alcohol chemistry page Part 4.6A

Miscellaneous important reactions of alcohols

Sub-index for this page

4.6.1 Reaction with metallic sodium

4.6.2 Reaction with carboxylic acids to form esters

4.6.3 Reaction with acid chlorides to form esters

 Index of GCSE level Oil - Useful Products Chemistry Revision Notes

4.6.1 Reaction of alcohols with metallic sodium

Alcohols react with metallic sodium to form hydrogen and a solution of an alkoxide ionic salt

(i) alcohol  +  sodium  ===> an alkoxide  +  hydrogen gas

Normal 'hydrogen' gas fizzing is observed at a moderate rate, and the salt product is soluble in the alcohol itself e.g.

ethanol  +  sodium  ===>  sodium ethoxide  +  hydrogen

 2CH₃CH₂OH + 2Na ===> 2CH₃CH₂O^–Na⁺ +  H₂ 

There is some similarity with the reaction of sodium with water (Alkali Metals chemistry) and with a non-aqueous liquid acid like ethanoic acid.

(ii) sodium + water ==> sodium hydroxide + hydrogen

2Na + 2H₂O ===> 2Na⁺OH^– + H₂

(iii) sodium  + ethanoic acid  ===>  sodium ethanoate  +  hydrogen

 2CH₃COOH + 2Na ===> 2CH₃COO^–Na⁺ +  H₂ 

All three reactions give hydrogen gas, though the sodium reacts very fast with water and pretty fast with pure ethanoic acid.

The ethoxide, hydroxide and ethanoate are similar because on evaporation of the unreacted ethanol, water or acid, a solid white ionic compound is formed.

It can further be noted that relatively 'unreactive' alkanes do not react with sodium.

similarly with other alcohols ...

 (i)  methanol + sodium ===> sodium methoxide + hydrogen

2CH₃OH + 2Na ===> 2CH₃O^–Na⁺ + H₂

(iii)  propan-1-ol + sodium ==> sodium propoxide + hydrogen

2CH₃CH₂CH₂OH + 2Na ===> 2CH₃CH₂CH₂O^–Na⁺ + H₂

(iv)  butan-1-ol + sodium ==> sodium butoxide + hydrogen

2CH₃CH₂CH₂CH₂OH + 2Na ===> 2CH₃CH₂CH₂CH₂O^–Na⁺ + H₂

 

When alkoxides are mixed with water, the alkoxide salt is hydrolysed, the alkoxide ion is a strong base and removes  a proton from water.

e.g.   sodium ethoxide  +  water  ===>  ethanol  +  sodium hydroxide

CH₃CH₂O^–Na⁺ +  H₂O  ===>  CH₃CH₂OH  +  Na⁺  +  OH^-

So the final mixture will be very alkaline.

4.6.2 Reaction of alcohols with carboxylic acids to form esters

Esters are another homologous series of organic compounds (dealt with in detail on another page)

e.g.  using a little conc. sulfuric acid catalyst, and refluxing the mixture

(i) Ethyl ethanoate, an ester,  is formed by the reversible reaction of carboxylic acid and an alcohol e.g.

ethanoic acid + ethanol ethyl ethanoate + water

+ + H₂O

sometimes more simply written as

CH₃COOH + CH₃CH₂OH CH₃COOCH₂CH₃ + H₂O

General word equation: carboxylic acid  +  alcohol    ester  +  water

This is a reversible reaction, so does not go to completion. When the equilibrium point is reached, you have also reached the point of maximum yield, and, you get about ²/₃ conversion of the acid and alcohol reactants to the ester product.

(ii) butanoic acid  +  butan-1-ol    butyl butanoate  +  water

  +        +  H₂O

 

(iii) pentanoic acid  +  propan-1-ol    propyl pentanoate  +  water

  +        +  H₂O

 

Esters are used in perfumes and food flavourings. Lots of details in section 10b. for the ..

Procedure for preparing an ester, uses of esters, details of esters & carboxylic acids

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