Nitrogen compounds (Chapter 37)

Nitrogen containing compound T.N.T. Proteins Enzymes Drugs CH3 NO2

Amines R-NH2 R-N-R” R’ R-N-H R’ R + R-N-R” Br- R’ Aliphatic Aromatic 1o amine 2o amine 3o amine 4o ammonium cpds Aromatic R-NH2 R-N-R” R’ R-N-H R’ R + R-N-R” Br- R’ NH2

IUPAC names CH3NH2 Methanamine (CH3)2NH N-methylmethanamine (CH3)3N N,N-dimethylmethanamine C6H5NH2 Phenylamine (aniline)

Formation of amines Alkylation of NH3 RX + NH3  R-NH2 + R2-NH + R3N + R4N+X- (NH3 in large excess, 1o amine as main product) 1o Amine from Amides and Nitriles R-CN  RCH2NH2 (H2/Ni or LiAlH4) RCONH2  RCH2NH2(LiAlH4 /ether than H+)

Formation of Amines C6H5-NO2  C6H5-NH2 Reducing agent: H2/Ni or HCl,Fe (or Zn, Sn, SnCl2) then OH-

Basicity of Amines NH3 pKb = 4.74 CH3NH2 3.36 CH3CH2NH2 3.25 CH3CH2CH2NH2 3.33 (CH3)2NH 3.28 (CH3)3N 4.30 C6H5NH2 9.4

Basicity of Amines R H N: H O R H N + OH- Order of basicity: 2o > 1o > 3o > NH3 > C6H5NH2 Why?

Explanation Solvation of protonated amine in water by hydrogen bonding (more H, better solvation) NH3>1o>2o>3o R H N + H2O H2O H2O

Explanation Effect of the inductive electron push of the R groups Increase the basicity Stabilize the alkylammonium ion 3o>2o>1o>NH3 R N: R N H +

Explanation Lone pair e- partly incorporated into benzene ring Less ready for protonation NH2 .. NH2 ..- +

Reactions Salt Formation NH2 + HCl NH3+ Cl- NH2 + H2O + NaCl NaOH ?

Reactions Amide Formation O O R-NH2 + CH3CCl  CH3CNHR + HCl O O High m.p. Used in identification

Reaction with Nitrous acid HNO2 prepared by NaNO2 + HCl 1o aliphatic amines RNH2 + NaNO2 + HCl  [RN+N]Cl- Aliphatic Diazonium salt (unstable) H2O ROH R+ + N2 (evolution of N2 serves as a test for 1o amine) -H+ C=C X- R-X

Reaction with Nitrous acid 1o aromatic amine NH2 + NaNO2 + HCl  N+N Cl- (stable at temp.<5oC, greater stability by dispersing charge into the benzene ring)

Mechanism -H2O HO N O .. H+ N+ O .. H2O+ N O N O Ar NH2 .. Ar NH2 + N

Stability of Ar-N+N N N: +

Benzenediazonium salt C6H5-N2+ Cl- C-N bond heavily polarized away from benzene ring C atom accept Nu: (against the norm of aromatic chemistry) Has considerable synthetic value

Benzenediazonium salt Can be replaced by a variety of function groups High yield No multiple substitution Ar-N2+ CuCl ArCl CuBr ArBr CuCN ArCN I- ArI H2O ArOH + N2

Coupling reaction .. OH N=N+: O- + NaOH Ice cold 1 (Napthalen-2-ol) N+= N- HO Ice cold 1 Orange II, Azo dye (1876) Also serve as a test for 1o aromatic amine