Topic 17.3 Carboxylic acids Flashcards
Carboxylic acid group
(-oic acid suffix)
O
II
R-C-OH
Bonding in carboxylic acids
Many reactions involve the loss of a H+ ion, this produces a carboxylate ion in which the charges are evenly distributed across C-O bonds.
Physical properties of carboxylic acids
-Hight boiling point due to presence of hydrogen bonds
-Boiling point increase with chain length (increased London forces)
-Pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a dimer
-Shorter chains are soluble as they can form H bonds as they don’t contain a bulky group in the way
-Weakly acidic
Preparation of carboxylic acid: By oxidation
This uses a primary alcohol or aldehyde along with an oxidising agent, usually acidified potassium dichromate.
CH3CH2CH2OH + 2[O] —> CH3CH2COOH + H2O
Preparation of carboxylic acid: By hydrolysis
They can be formed by hydrolysis of nitriles under reflux with either dilute or aqueous alkali.
Acidic hydrolysis: CH3CH2CN + H+ + 2H2O –> CH3CH2COOH + NH4+
Alkaline hydrolysis: CH3CH2CH2CN + OH- + H2O –> CH3CH2CH2COO- + NH3
Reactions with carboxylic acids diagram
Reactions with carboxylic acids: Reduction
Carboxylic acids can be reduced to primary alcohols, but not to aldehydes
Reducing agent: lithium tetrahydridoaluminate (lithium aluminium hydride)
Acyl Chloride
-Known as acid chlorides
-General formula: RCOCl
-The C in RCOCl is attached to 2 electronegative atoms, so it is electron deficient (this means it is susceptible to attack by nucleophiles).
Reactions of Acyl chlorides: Water
Reactions of Acyl chlorides: Alcohols
Reactions of Acyl chlorides: Conc. Ammonia solution
Reactions of Acyl chlorides: Amines
Esters
-Colourless liquids
-Relatively low melting points/ boiling points
-Insoluble in water
-Present in: perfumes, food flavourings, solvents
-Pleasant smell
Esterification
-Esters are formed from the reaction of an alcohol and a carboxylic acid
-Esters form in the presence of HCl or sulphuric acid (which acts as acids)
-The O-H bond in the alcohol and the C-O bond in the carboxylic acid will break
-A new bond between the oxygen atom from the alcohol and the carbon atom in the carboxylic acid
Naming an ester
-Alcohol ends in -ly
-Acid ends in -oate
-Alcohol first, then acid