PH1125 - Amines & Carboxylic acids

Question 1

what is an amine? (2)

Answer 1

• organic compounds containing trivalent N atoms bonded to one or more carbon atoms
• RNH2 / R2NH / R3N

Question 2

how is the classification of an amine determined?

Answer 2

• depending on the number of alkyl/aryl substituents attatched to the nirtogen

Question 3

what is an amine salt? (2)

Answer 3

• there are 4 bond coming from N

- one or more of the attachements is H

Question 4

what is a quaternary ammonium salt?

Answer 4

• if all 4 groups are alkyl/aryl (ie no H on the N)

Question 5

what are the methods and mechanisms for the preparation of an amine?

Answer 5

• nucleophilic substitution; RX + NH3 → RNH3+X- (by Sn2 reaction) then addition of -OH to form amine
• reduction; amide/nitrile → RCH2NH2 (addition of reducing agent)
• amide rearrangement; halogen and base (-OH) is added

Question 6

mechanism of alkyl halide to amine? (2)

Answer 6

• ammonia/amine + alkyle halide → amine salt + halide ion (by Sn2 reaction)
• amine salt + base (eg NaOH) → amine ( + water + Na-halide)

Question 7

how are nitriles often obtained?

Answer 7

• from an Sn2 reaction including alkyl halides and cyanide

Question 8

mechanism of reductive amination? (3)

Answer 8

• nucleophilic attack by NH3 at the carbonyl C - intermediate carbinolamine
• loss of water to form an imine
• imine reducedby H2/Raney nickel to form primary amine

Question 9

what drug is commonly prepared commercially by reductive amination?

Answer 9

• amphetamines

Question 10

what are the two reactions that amines can undergo? (2)

Answer 10

• acylation

- hofmann elimination

Question 11

what are amines acylatd by to give amides? (2)

Answer 11

• acid chlorides

- acid anhydrides

Question 12

mechanism of amine acylation to form amide? (3)

Answer 12

• C=O bond curl arrow to O and lone pair in N of amine to C of acid chloride
• O- (from double bond that just broke) to bond and C-Cl bond to Cl
• N-H bond curly arrow to N+ and Cl- (that just came off) to H on N

Question 13

what is the hofmann elimination reaction? (2)

Answer 13

• quaternary ammonium salts can be converted into amide and alkenes on heating
• reaction occurs via an elimination reaction (E2)

Question 14

what is the hofmann product and why? (2)

Answer 14

• the least substituted alkene (simplest)

- owing to steric hinderance in the transition state

Question 15

where does the acidity in carboxylic acids come from?

Answer 15

• resonance stabilisation of carboxylate ion

- the greater the stabiliation, the greater the acidity

Question 16

what is a carboxylic acid dimer?

Answer 16

• two H boned carboxylic acids

Question 17

what are the methods of preparing a carboxylic acid? (3)

Answer 17

• ester + water → carboxylic acid + alcohol
• amide + water → carboxylic acid + amine
• nitrile + water → carboxylic acid + ammonia

Question 18

what is the mechanism of base-induced ester hydrolysis? (ester + alkyl) (4)

Answer 18

• double bond curly arrow to O and nucleophile (eg -OH from sodium hydroxide) -ve charge to C (this form an alkoxide intermediate)
• intermediate then forms R-COOH group and -OR
• -OR to H in carboxylic acid functional group and OH bond curly arrow to O; this forms R-COO- and HOR
• dilute acid (H3O+) is added to form carboxylic acid

Question 19

what reagent is used the oxidation of primary alcohols and what are the products? (2)

Answer 19

• jones reagent (strong oxidising agent)

- primary alcohol → aldehyde → carboxylic acid

Question 20

what is the jones reagent?

Answer 20

• CrO3 + H2SO4 → H2CrO4

Question 21

what do aldehydes require to form carboxylic acids? (2)

Answer 21

• mild oxidising agents (eg tollens)

- Ag+(NH3)

Question 22

how would you convert carbon dioxide to a carboxylic acid (4)

Answer 22

• grignard carboxylation with R-MgBr
• C=O double bond curly arrow to O and R-MgBr bond to C
• formation of C-COO- and +MgBr
• dilute acid (H3O+) added to form carboxylic acid

Question 23

what is an alpha carbon?

Answer 23

• the carbon adjacent to a functional group

Question 24

what are anions?

Answer 24

• weak bases that can act as nucleophiles

Question 25

how can esters be formed from anions?

Answer 25

• reaction between reactive alkyl halide and carboxylate anion to produce an ester and the halide ion
• this is an Sn2 reaction

Question 26

carboxylic acid to alcohol? (2)

Answer 26

• LiAlH4 and H3O+

- reduction

Question 27

what products can be formed from the nucleophilic substitution of a carboxylic acid? (4)

Answer 27

• acid chloride
• anhydride
• ester
• amide

※ conversion of hydroxy group into a good leaving group

Question 28

carboxylic acid to acid chloride?

Answer 28

• SOCl2

Question 29

carboxylic acid to acid anhydride?

Answer 29

• carboxylic acid (nucleophile) and acid chloride

Question 30

synthesis of aspirin?

Answer 30

• salicylic acid + acetic anhydride + acid (H+)

Question 31

carboxylic acid to ester mechanism? (4)

Answer 31

• activation of C=O
• nucleophilic addition
• transfer of proton converting OH to H2O (improvement of leaving group)
• loss of H2O and regeneration of H+

Question 32

how would you convert an amide to a carboxylic acid and amine? (2)

Answer 32

• hydrolysis

- H+ and H2O

Question 33

how would you convert an amide to amine? (2)

Answer 33

• reduction

- LiAlH4