Part 4.
The chemistry of ALCOHOLS
Doc Brown's
Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK
KS5 A/AS GCE IB advanced level organic chemistry students US K12 grade 11 grade 12 organic chemistry
Part 4.6
Miscellaneous reactions of alcohols with:
(1) metallic sodium,
(2) acid chlorides, (iii) carboxylic acids
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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
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
4.6.3 Reaction of alcohols with
acid chlorides
This is a
nucleophilic addition of an alcohol to acid/acyl chlorides,
subsequent elimination on esterification to give the ester and
hydrogen chloride.
(i) ethanoyl chloride
+ ethanol ==> ethyl ethanoate + hydrogen chloride
+ CH3-CH2-OH ===>
+ HCl
(ii) ethanoyl chloride +
phenol ==> phenyl ethanoate + hydrogen chloride
+
===>
+ HCl
(iii) pentanoyl chloride +
ethanol ===> ethyl pentanoate + hydrogen chloride
+
===>
+ HCl
For
mechanism see
Esterification of acid
chlorides with alcohols
to give an ester mechanism
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INDEX of notes on ALCOHOLS
chemistry
All Advanced Organic
Chemistry Notes
Index of GCSE/IGCSE Oil - Useful Products
Chemistry Revision Notes
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