Ch. 24 Flashcards
Amines
Organic derivative of ammonia
Are arylamines and heterocyclic amines or alkylamines more basic? Why?
Alkylamines are more basic b/c the nitrogen lone-pair electrons are delocalized by interation with the aromatic pi system and resonance stabilization is lost when protonated
Heterocyclic Amines
Compounds with one more nitrogen atoms as part of a ring
How are alkylamines prepared?
- SN2 reaction of ammonia/amine with an alkyl halide
2. Gabriel Amine Synthesis
Reductive Amination Reaction
Ketone/aldehyde is treated with amine in the presences of a reducing agent. (ex. NaBH4)
What are amines a result of?
Hofmann and Curtius rearrangements of carboxylic acid derivatives
migration of the -R group bonded to the carbonyl carbon to yield a product that has one less carbon atom than the starting material
Hofmann Elimination
E2 elimination of amines to yield alkenes
- Quaternized treatment with iodomethane (CH3I)
- Heated with silver oxide (Ag2O)
Diazotization
Conversion of arylamines with nitrous acid into arenediazonium salts (ArN2+X-)
Sandmeyer Reaction
Replacement of diazonio group with other subsitutents to give variety of substitued aromatic compounds.
Diazonium Salts undergo? What is the result?
Coupling with phenols and arylamines; brightly colored azo compounds
What common function group is the most abundant and have the richest chemistry?
Amines
Are amines basic or nucleophilic? Why?
Both; due to the domination of the lone-pair electrons on nitrogen
larger the Kb; smaller the pKb= stronger the base; weak acid ~vice versa
larger the Ka; smaller the pKa= weaker the base; strong acid~ vice versa
How does electron-withdrawing substituents affect substitued aniline? What about electron donating substituents?
EWS = weaken the basicity EDS = increase basicity
Are alkylamines basic or acidic?
Basic; pH=7.3; exist almost entirely in their protonated form
Saturated Heterocyclic Amines vs Unsaturated Heterocyclic Amines
Saturated have the same chemistry as their open-chain analogs
Unsaturated are aromatic; (ex. imidazole, pyridine, and pyrimidine)
Amides (ex. pyrrole) are nonbasic b/c all electrons are used in bonding
How are arylamines prepared?
- Nitration of an aromatic ring
2. Reduction
What are reductive methods of amines?
LiAlH4 reduction of amides, nitriles and azides
Amines Reactions
- SN2 reaction with alkyl halides
- Nucleophilic acyl substitution with acid chlorides
- Hofmann Elimination; E2 Elimination
What can be prepared from arenediazonium salts?
Aryl chlorides, bromides, iodides, and nitriles
Reduction of nitriles reagents
- NaCN or
2. 1.LiAlH4,ether 2. H2O
Reduction of amides reagents
- LiAlH4, ether
2. H2O
Reduction of nitrobenzenes reagents
- H2, Pt or
- Fe, H3O+ or
- SnCl2, H3O+
SN2 Alkylation of alkyl halides reagent
NaOH
SN2 Alkylation of alkyl halides reactants/products
Ammonia –> Primary
Primary –> Secondary
Secondary –> Tertiary
Tertiary –> Quarternary ammonium
Gabriel Amine Synthesis reagents
- KOH 2. R-X
2. NaOH, H2O
Reduction of Azides reagents
- Na+ -N3, ethanol
2. 1. LiAlH4, ether 2. H2O
Reductive Amination reagents
NH3, NaBH4/NaBH(OAc)3
Hoffman Rearrangement reagents
NaOH, Br2, H2O
Curtius Rearrangement reagents
- Na+ -N3, ethanol
2. H2O, heat
Hoffman Elimination Reagents
- CH3I
2. Ag2O, heat
Diazotization reactants
HNO2, H2SO4
Structure of Amines
three amine bonds with lone pair occupy the corners of a tetrahedron
Properties of Amines
- amine with three different substituents is chiral
- two amine enantiomers interconvert by pyramidal inversion
- rapid at room temperature
- amines with fewer than 5 carbons are water-soluble and form hydrogen bonds
- smell nasty
Do amines or alkanes have higher boiling points?
Amines
What type of amines do not undergo reductive amination?
Tertiary amines
Sandmeyer Reaction reactants/prodcuts
CuCl, CuBr, or NaI –> aryl halides
CuCN –> aryl nitriles
Cu2O and Cu(NO3)2 –> Phenols
Diazonium Coupling Reaction
electrophilic aromatic substitution usually occuring at the p-position of the activated ring
Heterocylic amines undergo what reaction?
Electrophilic substitution; reaction occurs at the 2-position b/c the positions are more stable
Is pyridine a stronger or weaker base than pyrrole? How about alkylamines? Pyrimidine?
Pyridine is a stronger base than pyrrole but a weaker base for alkylamines. Pyridine is a more basic than pyrimidine.
Pyridine
nitrogen-containing analog of benzene
Pyrimidine
Two nitrogens in the 1 and 3 positions of a six-membered ring
What does the reactivity of polycyclic heterocylic compound depend on?
Type of heteroatom and size of the ring
Purines
4 nitrogens (3 pyridine-like and 1 pyrrole-like) in a fused ring
Primary and secondary amines IR absorption range?
Primary: 3350-3450 cm-1
Secondary: 3350 cm-1
sharper and less intense than alcohol absorptions
Nitrogen Rule
compound with an odd number of nitrogens has an odd numbered molecular weight/ion.
