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amines


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sakhi rathore


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what is the commercial use of amines
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used as intermediates in the synthesis of medicines and fibres

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amines - Detalles

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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
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
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.
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
Gabriel phthalimide synthesis
It is used to prepare primary amine
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 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 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
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
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
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
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