Nitrogen cmpds Flashcards
Amines
Preparation
- Reduction of nitriles to RCH2NH2
LiAlH4 in dry ether/ Ni/H2 and heat - Reduction of amide to RCH2NH2
LiAlH4 in dry ether/ H/Ni heat - Acid base
Nitrobenzene to phenylamine
Sn catalyst, HCl (aq) and heat, followed by NaOH(aq)
NaOH is added to deprotonate NH3+ attached to benzene to form phenylamine - Nu:sub of halogenoalkane
Excess NH3 in ethanol in sealed tube heat
Chemical properties of amine
Basic
NH2 is an H+ acceptor due to availability of lone pair on N
Factors affecting degree of basicity
- Delocalisation/ electron withdrawing groups
- The delocalisation of electrons from N into benzene ring/ electron rich region makes lone pair less available to accept H+ hence basicity is lower - Presence of electron donating groups
- The presence of electron donating groups makes the lone pair more available to donate l.p to H+ hence basicity increases - S character
- As S character increase (depending on hybridsation state of N) basicity decreases as lone pair is more strongly attracted to the nucleus in the hybrid orbital
Reaction of amines
- Condensation to form amide
- RCOCl
- Amine - Acid base to form CA salt
- HCl (aq)
- NH3+Cl as product - Nu:sub
- Limited RX NH3 in ethanol heat in sealed tube
- Can form primary, secondary, tertiary and quaternary - Electrophilic sub
- Trisub product 2,4,6 bromo- phenylamine
- white ppt, orange Br2 decolourises
Amides
Preparation
Condensation
RCOCl
Amine (primary, sec, tertiary)
Chemical property
Neutral because NH2 is in close proximity to electron withdrawing C=O. The highly electronegative O atom in C=O withdraws electrons from C=O bond. Lone pair on N significantly delocalises into adjacent C=O resulting in lone pair on N not being available to accept H+.
Reaction:
amides
- Acidic hydrolysis
HCl(aq), heat - Alkaline hydrolysis
NaOH(aq), heat - Reduction to form R-CH2NH2
LiAlH4 in dry ether/ H/Ni heat
Amino acid
Chemical properties
- Exists as a zwitterion which is electrically neutral
- Oppositely charged COO- , NH3+ depending on pH - Amphoteric
Acts as a buffer by regulating pH by reacting with small amounts of H+ or OH- by either protonating or deprotonating
Physical properties
Has a giant crystal ionic lattice struc with strong ionic bonds between opp. Charged groups hence high MP/BP
Reaction:
amino acids
- Peptide formation (condensation) to form protein
- Hydrolysis of protein
HCl (aq) , heat
NH2 and COOH attached to alpha C are less acidic than side chain NH2 or COOH why?
NH2
When in close proximity to a-C, NH2 is in close proximity to electron withdrawing COOH group hence lone pair on N is less available to accept H+ making it less basic. Side chain NH2 protonates in preference to alpha NH2 as it is more basic in an acidic env.
COOH
R group- COOH is attached to electron donating R group which intensifies negative charge on COOH.Therefore destabilising the side chain COOH group. Hence it is less acidic than a-COOH group which is in close proximity to an electron withdrawing NH3+ group which disperses the negative charge on COOH stabilising the a-COOH. Hence a-COOH is more acidic and dissociates in preference to R group-COOH. (deprotonates in preference since its more acidic in basic env)
- pH > pKa deprotonation
