Acylation
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What is acylation? (prcs. whr. acyl. grp. intrcd. anthr. mlcle.)
The process by which an acyl group is introduced into another molecule
Outline the general formula of an acyl group
R-CO-Z, where Z is a group, such as -Cl etc
What are acid derivatives?
Compounds that contain an acyl group as part of their structure and are derived from carboxylic acids
Name the two main acid derivatives
Acyl chloride and acid anhydride ((RCO)2O)
Why is the carbonyl group of an acid derivative polarised? (O >elcneg. mkng. C prt. pos. + scptbl. nuc. atck.)
The carbonyl group is polarised because oxygen is more electronegative than carbon, making the carbon δ⁺ and susceptible to nucleophilic attack.
What three factors determine how readily an acid derivative reacts with a nucleophile? • mgntd. slgtly. pos. chrg. crbnyl. crbn. • esly. lvng. grp. lst.
• The magnitude of the slightly positive charge on the carbonyl carbon • How easily the leaving group (Z) is lost
Which is more reactive - an acyl chloride or an acid anhydride?
Acyl chlorides are more reactive than acid anhydrides
Why are acyl chlorides more reactive than acid anhydrides? (Cl >elctng/ + btr. lvng. grp. inc prt. pos. chrg. crbnyl. crbn. + mkng. nuc. atck. esr.)
The chlorine group is more electronegative and a better leaving group, increasing the δ⁺ charge on the carbonyl carbon and making nucleophilic attack easier
Which nucleophiles react with acyl chlorides and acid anhydrides? (PA/Am/Alc/W)
Primary amines Ammonia Alcohols Water
What is the order of reactivity of these nucleophiles?
Primary amine > Ammonia > Alcohol > Water
At what temperature do acylation reactions typically occur?
Room temperature
What type of mechanism do acyl chlorides and acid anhydrides undergo with nucleophiles?
They undergo nucleophilic addition - elimination reactions
Product formed when the nucleophile is ammonia (NH₃) ?
An amide + HCl gas
Product formed when the nucleophile is primary amine (RNH₂) ?
An N - substituted amide + HCl gas
Products formed when the nucleophile, alcohol (ROH), is involved in nucleophilic addition - elimination reactions?
An ester + HCl gas
What is the product when the nucleophile is water (H₂O) ?
A carboxylic acid + HCl gas
Outline the mechanism for a nucleophilic addition - elimination reaction involving propanyl chloride and water
Forms: propanoic acid Compare your mechanism to the general mechanism
Outline the mechanism for a nucleophilic addition - elimination reaction involving propanyl chloride and ethanol
Forms: ethyl propanoate Check your drawing against the general mechanism and correct if relevant
Outline the mechanism for a nucleophilic addition - elimination reaction involving ethanoyl chloride and ammonia
Forms: ethanamide Check the general mechanism and correct where relevant
Outline the mechanism for a nucleophilic addition - elimination reaction involving butanoyl chloride and propylamine
N - propylbutanamide Check the general mechanism and correct where relevant
Advantages of acid anhydrides over acyl chlorides as acylating agents? (cost, chemicalness, reactions with H2O, safety)
• It is cheaper • Less corrosive • Does not react with water as readily • It is safer, produces a carboxylic acid instead of HCl as by product
Why are acid anhydrides generally safer to use than acyl chlorides? (rctns. prod. crblxyc. acd. instd. txc. crsve. HCL gs.)
Their reactions produce a carboxylic acid instead of toxic, corrosive hydrogen chloride gas
Chemical used to test for acyl chlorides? The positive result of this test? (AC tstd. w/ aqs. slvr. ntrt. - pos. rslt. whte. ppt. frms. shwng. prsnc. Cl ions)
Acyl chlorides are tested with aqueous silver nitrate (AgNO₃) Positive result: white ppt forms, showing presence of chloride ions