Analía Bellizzi – Chemistry Classes

Ronald Reagan High School


Carboxylic acids

From your syllabus


I Carboxylic acids (exemplified by ethanoic acid and benzoic acid)

(i) Formation from primary alcohols and nitriles
(ii) Salt, ester and acyl chloride formation

II Acyl chlorides (exemplified by ethanoyl chloride)

(i) Ease of hydrolysis compared with alkyl and aryl chlorides
(ii) Reaction with alcohols, phenols and primary amines

III Esters (exemplified by ethyl ethanoate and phenyl benzoate)

(i) Formation from carboxylic acids and from acyl chlorides
(ii) Hydrolysis (under acidic and under basic conditions)
(iii) Uses of esters

Learning outcomes

Candidates should be able to:

(a) describe the formation of carboxylic acids from alcohols, aldehydes and nitriles

(b) describe the reactions of carboxylic acids in the formation of

(i) salts, by the use of reactive metals, alkalis or carbonates
(ii) esters
(iii) acyl chlorides

(c) explain the acidity of carboxylic acids and of chlorinesubstituted ethanoic acids in terms of their structures

(d) describe the hydrolysis of acyl chlorides

(e) describe the reactions of acyl chlorides with alcohols, phenols and primary amines

(f) explain the relative ease of hydrolysis of acyl chlorides, alkyl chlorides and aryl chlorides

(g) describe the formation of esters from carboxylic acids or acyl chlorides, using ethyl ethanoate and phenyl benzoate as examples

(h) *describe the acid and base hydrolysis of esters

(i) describe the formation of polyesters (see also Section 10.8)

(j) state the major commercial uses of esters, e.g. solvents, perfumes, flavourings

Carboxylic acids

 Carboxylic acids – Nomenclature

Take the prefix that corresponds to the total number of carbon atoms in the molecule (see naming alkanes in the alkanes page) and addanoic acid to form the name, e.g. CH3COOH is ethanoic acid.

Carboxylic acids – Reactions

(1) With metals and bases :

Carboxylic acids will react with metals (such as sodium),

2RCOOH(aq) + 2Na(s) → 2RCOO-Na+(aq) + H2(g)

and with both weak and strong bases such as sodium carbonate (weak) and sodium hydroxide (strong),

RCOOH(aq) + NaOH(s) → RCOO-Na+(aq) + H2O(l)

2RCOOH(aq) + Na2CO3(s) → 2RCOO-Na+(aq) + H2O(l) + CO2(g)

With all these reactions a metal carboxylate salt is formed (e.g. sodium ethanoate).

(2) With alcohols :

When carboxylic acids are mixed and heated with alcohols, with a little concentrated sulphuric acid as a catalyst to remove the water product, esters are produced.

(3) Formation of acyl chlorides :

Carboxylic acids can be turned into a much more reactive molecule, called an acyl (or acid) chloride by reacting them with a chlorinating agent such as phosphorus pentachloride (PCl5) or thionyl chloride (SOCl2) :

2RCOOH + PCl5 → 2RCOCl + POCl3 + H2O

2RCOOH + SOCl2 → 2RCOCl + SO2 + H2O

The reaction needs to be conducted in distillation appartus so that the product can be separated from the carboxylic acid starting material.

To name an acyl chloride take the prefix that corresponds to the total number of carbon atoms in the molecule (see naming alkanes in the alkanes page) and add anoyl chloide to form the name, e.g. CH3CH2COCl is propanoyl chloride.

Acyl chlorides perform the same reactions as their parent carboxylic acids, except that they react at room temperature and generate hydrogen chloride as a byproduct. They give very exothermic reactions. They must be kept in a dry atmosphere as they will react with the slightest amount of moisture to regenerate the carboxylic acid.

RCOCl + NH3 → RCONH2 + HCl