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Ch.36 notes – P.1 Ch.36 – Nitrogen compounds A. Introduction Nitrogen compounds in organic chemistry can be divided into two basic groups: _______________ and _______________. 1o amines: R .. N e.g. H CH3 CH3NH2 CH3CH2CHCHCH3 H NH2 2o amines: R .. N e.g. H CH3CH2-N-CH3 CH3CHCH3 H N CH3 H R 3o amines: R e.g. .. N CH2CH2CH2CH3 R CH3 R N CH2CH2CH3 Quaternary ammonium ions: R + + e.g. CH3 CH3 R N R N CH3 CH3 R Aromatic amines: NH2 H N H CH3 N Ch.36 notes – P.2 Lower members of amines are _____________ with a smell of ___________; while the higher ones are liquids with a distinctive ____________ smell. Amines have ___________ boiling points than less polar compounds due to its ______________ bonding; but they have __________ boiling points than alcohols and carboxylic acids because their hydrogen bonding are weaker. Lower members of amines are _____________ with water due to the hydrogen bonding formation with water. Ex.: Match the boiling points, 65℃, -6℃ and -88℃ with the corresponding compounds CH3CH3, CH3NH2 and CH3OH. B. Preparations of amines 1. Reduction of nitriles e.g. CH3CH2CN 2. From amides Reduction O CH3C NH2 Hofmann degradation O CH3C NH2 Ch.36 notes – P.3 3. Alkalyation of aliphatic haloalkanes R-X + NH3 R-X + RNH2 R-X + R2NH R-X + R3N A mixture of amines may be separated by ______________________________. 4. Phenylamine from reduction of nitrobenzene By treating nitrobenzene with _______ and _____________ followed by excess ____________. NO2 C. Base properties of amines Amines are similar to ammonia. e.g. .. H N H + H2O H .. R N R + H2O R NH2 + H2O Hence, amines can react with acids to form salts. Ch.36 notes – P.4 Comparison of the basic strength: pKb at 25℃ 1o amine CH3CH2NH2 3.27 CH3NH2 3.36 Ammonia NH3 4.75 Phenyl amine C6H5-NH2 9.38 Generally speaking, for basic strength: R-NH2 NH3 C6H5-NH2 Because the basic strength depends on the availability of the lone-pair electrons on the N atom, the present of alkyl group has a ________________________ and increases the basic strength. For phenyl amine, _______________ effect occurs ( or __________________ of electrons occurs) and the lone pair electrons are less available for donation: Ex.: Arrange the following compounds in the descending order of basicity: NH3 CH3CONH2 A B (CH3CH2)2NH C CH3CH2NH2 D Since amines are basic, they react with acids to from stable crystalline salts. RNH2 + HCl The amines can be regenerated by treating the salt with _________________. Ch.36 notes – P.5 D. Reactions of amines 1. Reaction with acyl chlorides O CH3 C CH3 Cl N CH3 + H NH2 O CH3 C Cl + Only ________ and ________ have the above reactions. The amides produced are ________________________________ with ______________ melting points. They are therefore useful for __________________ unknown amines. 2. Reaction with benzyol chloride The reactions are similar to acyl chloride except carried out in ________________. e.g. COCl H + COCl CH3CH2-N-H NH2 + Ch.36 notes – P.6 3. Diazonium salt formation Primary amines react with ____________________________. RH2 NH2 The aliphatic diazonium salts are unstable and are decomposed once they are formed into ___________________ and ___________________. The carbonium ion is reactive and able to react with different nucleophiles. H2O Cl- R+ NO2- The aromatic diazonium ion ( _________________________ ) is stable in cold ( ). Hence it can be isolated as crystalline salt. a) The benzenediazonium ion is decomposed at higher temperature to give phenol. + N N + H2O b) Produce halobenzene + N N Ch.36 notes – P.7 c) Produce cyanobenzene + N N d) Coupling reaction Diazonium salts can couple with phenols or phenylamines to yield ________ compounds + N G N + e.g. + N OH N + + N N(CH3)2 N + SO3H N N OH + Ch.36 notes – P.8 E. Uses of amines and their derivatives 1. Azo-compounds as highly coloured, they are used as _______ in dyeing industries. 2. Amines derivatives as ____________. Ch.36 notes – P.9 F. Amino acids Amino acids are compounds containing both the ________ and the ___________ groups, they are called __________________ compounds. Amino acids: H R C H e.g. COOH H C H COOH CH3 NH2 NH2 C COOH NH2 Except when R = H, there are chiral centres in the molecules, i.e. they are ____________________________. α-amino acids show many properties inconsistent with the general structure, e.g.: amino acids 1. are ________________________________ solids. 2. are ______________ in polar solvents but not in non-polar solvents. 3. the acidic strengths and basic strengths are _________ than expected. Amino acids exist as __________________, which are ________________. H H2N C R COOH Ch.36 notes – P.10 Two amino acids can condense together to form a ___________, i.e. a _________________. H H O C N H H H O C OH R C N H C OH R If more than three amino acid molecules join together, the polymer formed is called a ___________________. H H O N H C R H H O N C OH _______________ are polypeptides. H C R C OH Ch.36 notes – P.11 Proteins can be _____________ to reform amino acids by boiling with aqueous acid. Amino acids in a mixture can be separated by __________ __________________. The positions of the colourless amino acids are revealed by spraying the paper with ________________, which gives a ______________ colour with amino acids. Ex.: Ch.36 notes – P.12