amines
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| 🇬🇧 | 🇬🇧 |
| What is the commercial use of amines | Used as intermediates in the synthesis of medicines and fibres |
| Where do amines occur in nature | They occur among protiens, vitamins, alkaloids and hormones. |
| What synthetic examples are there of amines | Polymers, dyestuffs and drugs |
| Two biologically active compounds of amine | Adrenaline and ephedrine ( both contain secondary amino group, used to increase blood pressure) |
| Structure of amines | Nitrogen orbitals in amines is sp3 hybridised and the geometry is pyramidal. and the angle C-N-E ( H or C) is less than 109.5 degree |
| Angle in case of trimethylamine | 108 degrees |
| What are aliphatic amines | An amine in the molecule of which there are no aromatic rings directly on nitrogen atom |
| How do you give common names for amines | Alkylamine but we add di or tri before it when 2 or more groups are same |
| IUPAC names for amines | Alkanamines |
| How are arylamines named in IUPAC | We replace the e of arene by amine |
| How are nitro compounds made into amines | Reducing them by passing H2 gas through them in presence of Ni, Pd or Platinum |
| Why is reduction with iron scrap and HCl preferred | Because FeCl2 formed gets hydrolysed to release HCl during the reaction, thus only a small amount of HCl is required to initiate the reaction. |
| Explain ammonolysis | The process of cleavage of the C-X bond by ammonia molecule |
| How is ammonolysis carried out | It is carried out in a sealed tube at 373 K, the primary amine thus obtained behaves as a nucleophile and can further react with alkyl halide to form secondary and tertiary amines and finally quaternary ammonium salt. |
| How is the free amine obtained from ammonium salt | By treatment with a strong base |
| What is the disadvantage of ammonolysis | The yeild is a mixture of primary, secondary and tertiary amines and also a quaternary ammonium salt. |
| When do nitriles reduce to give primary amines | On reduction with lithium aluminium hydride or catalytic hydrogenation |
| What are the catalysts used in reduction of nitriles | H2/Ni Na(Hg)/C2H5OH |
| What are amides | R-CO-NH2 |
| Reduction of amides gives amine | LiAlH4 and H2O |
| Gabriel phthalimide synthesis | It is used to prepare primary amine |
| Phthalimide on treatment with ethanolic potassium hydroxide forms | Potassium salt of phthalimide |
| How do you get N-alkylphthalimide from potassium salt of pthaminide | By heating with alkyl halide |
| Why can't aromatic primary amines be prepared from it | Because aryl halides do not undergo nucleophilic substitution with anion formed by phthalmide |
| What is the hoffmann bromamide degradation reaction | Preparation of primary amines by treaing an amide with bromine in an aqueous or ethanolic solution of NaOH |
| What is the odour of lower aliphatic amines | Fishy odour |
| What is the order of solubility of amines | It decreases with increase in molar mass due to increase in size of the hydrophobic alkyl part |
| Amines are soluble in | Organic solvents like alcohols |
| What is the order of boiling point for amines | Primary >secondary>tertiary |
| Why is the boiling point of primary amines high | Because of steric hinderance |
| What makes amines reactive | Diff. in E.N. b/w N and H atoms and the presence of unshared pair of electrons on N |
| How do amines behave and why | As nucleophiles due to the presence of unshared electon pair on nitrogen |
| Basic character of amines | React with acid to form salts |
| Amines reaction with base like NaOH | They regenarate to parent amines |
| Amines salts solubility | They are soluble in water and insoluble in organic solvents live ethers |
| Explain the basic nature of amines by pKb or Kb values | PKb value of ammonia is 4.75 aliphatic amines pKb values lie in the range of 3 to 4.22 |
| Why are aliphatic amines stronger bases than ammonia | Due to +I effect of alkyl groups leading to high electron density on the nitrogen atom |
| Why then are aromatic amines weaker than ammonia | Due to electron withdrawing nature of aryl group |
| What does basic character of amines depend on | It depends on the ease of formation of the cation by accepting a proton from the acid. the more stable the cation is relative to the amine more basic is the amine |
| Relation of alkyl group with amines and basicity | The alkyl group causes an +I effect and hence nitrogen readily loses electrons. also due to dispersal of +ve charge due to +I effect |
| Order of basicity of amines in the gaseous state | Tertiary amines >secondary amines>primary amines>NH3 |
| What happens to the basicity of amines in aqueous state | The +ve charge not only gets stabalised by +I effect but also due to solvation of water molecules. hence the greater the size of the ion the less will be the solvation. |
| Order of basicity in aq. medium | Primary>secondary>tertiary |
| How is the basic strength of aniline increased | It is increased by stubstituting electron releasing groups like -OCH3,-CH3 |
| Acylation | Aliphatic and aromatic primary and secondary amines react with acid chlorides, anhydrides and ethers by nucleophilicsubstitution reaction |
| How does the reaction acylation shift the equilibrium to the right hand side | This reaction is carried out in the presence of a base stronger thanamine like pyridine which removes the HCl so formed |
| Reaction of amines with benzoyl chloride | Benzoylation |
| Carbylamine reactions | Primary amines on heating with chloroform(CHCl3) and ethanolic potassium hydroxide form isocyanides or carbylamines which are foul smelling. |
| What is special about carbylamine reaction | Used to test for primary amines does not show reaction with secondary or tertiary amines |
| Reaction with nitrous acid | Three classes of amines react differently with nitrous acid which is prepared in situ from a mineral acid and sodium nitrite |
| Primary aliphatic amines react with nitrous acid to form | Aliphatic diazonium salts which being unstable liberate N2 gas |
| Aromatic amines react with nitrous acid at low temp. to form | Diazonium salts in presence of NaNO2+HCl |
| Reaction with arylsulphonyl chloride | Hisenberg's reagent reacts with primary and secondary amines to form sulphonamides |
| What is hinsberg's reagent | C6H5SO2Cl |
| Where do we find the maximum electron density in aniiline resonance hybrid | The NH2 group is ortho and para directing and a powerful activating group |
| Bromination | Aniline reacts with bromine water at room temp. to give a white precipitate of 2,4,6-tribromoaniline |
| If we have to prepare monosubstituded aniline derivative how can the activating effect of -NH2 group be controlled | By protecting the -NH2 group by acetylation with acetic anhydride |
| Nitration of aniline | It yields tarry oxidation products in addition to nitro derivatives in t eh presence of H2SO4 |
| What happens to aniline in strongly acidic medium | It is protonated to form the anilinium ion which is meta directing |
| How can nitration reaction be controlled and p-nitro derivative can be obtained as the major products | By protecting the NH2 group by acetylation reaction with acetic anhydride |
| Sulphonation | Aniline reacts with concentrated sulphuric acid to form anilium hydrogen sulphate which on heating with sulphuric acid produces p-aminobenzene sulphonic acid |
| Common name of p-aminobenzene sulphonic acid | Sulphanilic acid |
| Aniline does not undergo friedel-craft reaction | Due to the formation with aluminium chloride, the lewis acid, which is a catalyst. due to this, nitorgen of aniline acquires positive charge and hence acts as a strong deactivating group for further reaction |
| How is benzenediazonium chloride prepared | By reaction of aniline with nitrous acid and HCl |
| Diazotisation | The conversion of primary aromatic amines into diazonium salts. due to its instability the diazonium salt is not generally stored and is used immediately after it's preparation |
| Physical properties of benzenediazonium chloride | Colourless crystalline solid. readily soluble in water and is stable in cold but reacts with water when warmed. -decomposes easily in the dry state -benzene diazonium fluoroborate is water-insoluble and stable at room temp. |
| Reaction involving displacement of nitrogen | Diazonium group being a very good leaving group is substituted by Cl,Br, I, CN, and O. |
| Replacement by halide or cyanide ion/ sandmeyer's reaction | These nucleophiles can easily be introduced in the benzene ring in the presence of Cu ion |
| Gatterman reaction | Chlorine or bromine can also be introduced in the benzene ring by treating the diazonium salt solution with corresponding halogen acid in the presence of cu powder |
| Reactions involving retention of diazo group coupling reaction | Benzene diazonium chloride reacts with phenol in which the phenol molecule at it's para position is coupled with the diazonium salt to form p-hydroxyazobenzene. |
| Importance of diazonium salts in synthesis of aromatic compounds | Aryl florides and iodides cannot be formed by direct halogenation. the cyano group cannot be introduced by nucleophilic substitution of chlorine in chlorobenzene but cyanobenzene can easily be obtained from diazonium salts |