amines’ acyl’chlorides’ hydroxynitriles’ aldehyde · pdf fileammonia...
Post on 15-Mar-2018
245 Views
Preview:
TRANSCRIPT
ammonia methylamine phenylamine
Amines are nitrogen-‐containing organic compounds derived from ammonia, where one or more of the hydrogen atoms has
been replaced by an alkyl or aryl group.
Primary amines
Seconday amines
TerMary amines
Quaternary ammonium ion
caMonic surfactant e.g. hair condiMoner What is happening to the hydrogen number around the
Nitrogen atom as you move across the page
methylamine ethylamine propylamine
diethylamine
If two idenMcal R groups are aPached, the prefix di– is used, and if three idenMcal groups are present, then tri– is used.
triethylamine
Amines are named using the suffix –amine.
3-‐aminopropanoic acid
1,2-‐diaminopentane
2-‐aminoethanoic acid
If other funcMonal groups are present in the molecule, the presence of amine groups is denoted using the amino– prefix.
AliphaMc and aromaMc amines
Aroma8c amines contain a benzene ring directly aPached to the NH2 group.
l they act as nucleophiles and take part in reacMons involving donaMon of the lone pair
The delocalized system of the benzene group is able to incorporate the lone pair of electrons from the nitrogen atom, meaning that aromaMc amines have different properMes to aliphaMc amines.
l they act as Brønsted–Lowry bases (H+ acceptors).
ReacMons of amines as bases Amines accept protons (H+) from acids to form salts:
ethylamine ethylammonium chloride
CH3CH2NH2(aq) + HCl(aq)→ CH3CH2NH3 Cl-‐(aq) + H2O(l)
Quaternary ammonium ion
+
RelaMve base strength
NH3 4.75
3.36
3.27
Compound pKb
9.38
CH3NH2
(CH3)2NH
C6H5NH2
The strengths of weak bases are measured on the pKb scale. The smaller the number on this scale, the stronger the base is.
What is the trend? Can you explain the trend in terms of the availability of lone pair of electrons on the nitrogen for donaMon to the hydrogen ion?
Strength of base (strongest to weakest order) R-‐-‐à-‐-‐-‐NH2 more than NH3 more than C6H5-‐-‐ß-‐-‐NH2
R group has a posiMve inducMve effect and increases the electron density on the N atom. Thus N lone pair is more available to be donated to a proton, hence amine molecule can funcMon as a strong base. Benzene group withdraws electron density from the nitrogen atom and incorporates this into the delocalised electron system within the benzene ring. Thus, N lone pair is less available to be donated to a proton and therefore funcMons as a weak base.
Basic Buffer= aliphaMc amine + strong acid (e.g. HCl) or amine salt or NH4Cl
Nucleophilic subs8tu8on with excess NH3 and haloalkane promotes primary amine forma8on
δ+
δ−
Reac,on does not stop at first amine product. The primary amine itself undergoes nucleophilic subs,tu,on with haloalkane
excess NH3
Secondary/TerMary amines
Secondary amine
δ+ δ-‐
Primary amine
subsMtuted amines are more nucleophilic than NH3 (due to alkyl inducMve effect)
Excess NH3 favours 1° amine producMon Excess Haloalkane favours 3° and 4° amine producMon
Amine + Haloalkane (R-‐X)
Via nucleophilic subsMtuMon mechanism: NH3 + 1° R-‐X à 1° Amine 1° Amine + 1° R-‐X à 2° Amine 2° Amine + 1° R-‐X à 3° Amine 3° Amine + 1° R-‐X à
promoted if excess NH3
promoted if excess R-‐X
Making aliphaMc amines
of nitrile
Nucleophilic subsMtuMon involving the haloalkane and NH3 generates a mixture of 1°, 2°, 3°, 4° amines due to further subsMtuMon reacMons involving the product(s) and haloalkane
A: KCN, aqueous/ethanolic; intermediate CH3CH2CN propanenitrile; then, H2 /Ni catalyst B: NH3, excess NH3
Route A disadvantage: toxic KCN or expensive LiAlH4 or H2 explosive Route B: impure product, further subsMtuMon likely
Making ethylamine from methane
CH4 CH3Cl CH3CN CH3CH2NH2
1. Cl2, uv light, free radical subsMtuMon 2. Ethanolic and aqueous KCN, reflux, nucleophilic subsMtuMon 3. Either H2/Nickel catalyMc hydrogenaMon or LiAlH4
diethylamine
Op8on 1 Op8on 2 Op8on 3
Step 1 HBr electrophilic addiMon CH3CH2Br
H2, Ni addiMon (catalyMc, H2) C2H6
H2O, H3PO4 electrophilic addiMon C2H5OH
Step 2 excess NH3, nucleophilic subsMtuMon CH3CH2NH2
Br2 free radical subsMtuMon CH3CH2Br
KBr, conc H2SO4 nucleophilic subsMtuMon CH3CH2Br
Step 3 CH3CH2Br nucleophilic subsMtuMon (CH3CH2)2NH
NH3 OR CH3CH2NH2 nucleophilic subsMtuMon (CH3CH2)2NH
NH3 OR CH3CH2NH2 nucleophilic subsMtuMon (CH3CH2)2NH
CH3CN CH3CH2NH2
Step 1: Ethanolic/(aq) KCN Step 2: H2/Ni OR LiAlH4 Step 3: CH3Br
Secondary amine
Nucelophilic subsMtuMon
Sn HCl
excess NH3
Cl2 uv light
conc H2SO4 and conc HNO3, 20-‐60°C HNO3 + H2SO4 à NO2
+ + HSO4-‐ + H2O
Electrophilic subsMtuMon
Nucleophilic subs8tu8on of (chloromethyl)benzene to produce phenylmethylamine
phenylmethlyamine (chloromethyl)benzene
δ+ δ- excess NH3
Nucleophilic subs8tu8on of (chloromethyl)benzene to produce phenylmethylamine
phenylmethlyamine (chloromethyl)benzene
δ+ δ- excess NH3
BrCH2CH2Br
NCCH2CH2CN
ethanolic/aq KCN reflux Bromine(aq) H2/Ni
H2N(CH2)4NH2
Making butane-‐1,4-‐diamine
catalyMc hydrogenaMon
LiAlH4
nucleophilic subsMtuMon
SN1
SN2
electrophilic addiMon
1,2-‐dibromoethane
Acyl chloride addiMon-‐eliminaMon reacMons
Nitriles
(HA, RCHO/RCOR, catalyMc hydrogenaMon)
NaBH4 with RCHO/RCOR
Acyl chloride and primary amine
Nucleophilic addiMon-‐eliminaMon
N-‐subs8tuted amide
δ+
δ−
+ HCl
N-‐methylpropanamide
ReducMon of ketone by NaBH4 (H−) to secondary alcohol (sodium tetrahydridoborate (III)) Nucleophilic addiMon
Nucelophile is aPacking a planar C=O bond of asymmetrical ketone (or aldehyde) APack is equally likely from above or below the planar C=O group Product is a racemix mixture containing equal amounts of enanMomers ∴ op8cally inac8ve
opMcally acMve 2° alcohol
δ+
δ−
H+ from solvent
FormaMon of hydroxynitrile by acidified KCN Nucleophilic addiMon
Nucelophile is aPacking a planar C=O bond of asymmetrical ketone (or aldehyde) APack is equally likely from above or below the planar C=O group Product is a racemix mixture containing equal amounts of enanMomers ∴ op8cally inac8ve
opMcally acMve hydroxynitrile
δ+
δ−
H+ from solvent CN − ���
CN CN
ALDEHYDE
H H H
FormaMon of hydroxynitrile by acidified KCN Nucleophilic addiMon
Nucelophile is aPacking a planar C=O bond of asymmetrical ketone (or aldehyde) APack is equally likely from above or below the planar C=O group Product is a racemix mixture containing equal amounts of enanMomers ∴ op8cally inac8ve
opMcally acMve hydroxynitrile
δ+
δ−
H+ from solvent CN − ���
CN CN
ALDEHYDE
H H H
FormaMon of hydroxynitrile by acidified KCN Nucleophilic addiMon
Nucelophile is aPacking a planar C=O bond of asymmetrical ketone (or aldehyde) APack is equally likely from above or below the planar C=O group Product is a racemix mixture containing equal amounts of enanMomers ∴ op8cally inac8ve
opMcally acMve hydroxynitrile
δ+
δ−
H+ from solvent CN − ���
CN CN
KETONE
top related