Carboxylic Acids Flashcards
EsterAcid hydrolysis
Reagent
What it forms
Equation
Heat with aqueous acid HCl
Forms a carboxylic acid and alcohol
Eater + water —> (H+/heat) acid + alcohol
Converting carboxylic Acids to acid chlorides
Reflux with either phosphorus pentachloride PCl5 or sulfur dichloride oxide SOCl2
NUCLEOPHILIC substitution
Anhydrous conditions- because otherwise the acid chloride will hydrolyse back to the acid
What are the products in making acid chlorides using phosphorus pentachloride?
Acid chloride
POCl3
HCL
What are the products in converting acid chlorides with sulfur dichloride oxide SOCl2
Acid chloride
SO2
HCl
Why is SOCL2 preferred when converting carboxylic acids to acid chlorides?
Because only gaseous co-products are formed. The product in PCl5 (POCl3) is a liquid which means you’d have to separate the acid chloride which is also a liquid- this would be difficult
Ester Alkaline hydrolysis
Heat with NaOH (aq)
Forms sodium salt of acid and alcohol
2- obtain a Carboxylic acid by adding strong hydrochloric acid to the sodium salt as sodium salts are fairly soluble
Hydrolysis of acid chlorides
What happens when ethanoyl chloride is opened?
They produce carboxylic acids
NUCLEOPHILIC substitution
When ethanoyl chloride is opened - misty fumes of HCl is seen- it reacts wth water vapour in the air
How soluble are aliphatic acids?
Fairly soluble in water eg ethanoic
How soluble are aromatic acids in water?
Sparingly soluble e.g benzoicacid
How to form a aromatic carboxylic acid from a. Sodium salt?
Treat sodium salt of benzoicacid with HCl and the benzoicacid will precipitate out of solution as ts sparingly soluble
How do isolate the product?
Filter product
Wash with cold solvent water
Recrystallise from hot water
Dry crystals in oven just below MP
How are aromatic carboxylic acids formed?
Acids are produced by the oxidisation of a side chain of an aromatic compound. Aromatic compound is heated with aqueous alkaline KMnO4 where the alkali is Na2CO3
This produces a sodium salt of the acid
Salt is then acidified with hydrochloric acid to produce the aromatic acid
Reagent used in the formation of aromatic carboxylic acids
And conditions
Aqueous alkaline potassium manganate (VII)
(Use HCl to acidify salt)
Condition: heat
Steps of forming aromatic carboxylic acids
Aromatic compound
(Alkaline aqueous KMnO4 + heat)
Sodium salt produced of the carboxylic acid
(HCl) acidified salt
Aromatic acid formed
Method of decarboxylation
- React carboxylic acid with aqueous sodium hydroxide which forms sodium salt
- Heat sodium salt with soda lime (NaOH)
- hydrocarbon formed with 1 less C
- Carbon dioxide gas isn’t evolved
Mass spec can be used to identify the hydrocarbon and hence the patent carboxylic acid
