Compounds formed by substituting H atoms of ammonia, NH3, with alkyl or aryl groups.
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What are primary amines?
Compounds in which one H atom in NH3 has been substituted.
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Give an example of a primary amine.
Ethylamine (or aminoethane)
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What are secondary amines?
Compounds in which 2 H atoms in NH3 have been substituted.
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Give an example of a secondary amine.
Dimethylamine (acts as a base because it has a lone pair of electrons).
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What are tertiary amines?
Compounds in which the 3 H atoms in NH3 have been substituted.
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Give an example of a tertiary amine.
Trimethylamine
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How is phenylamine formed?
When nitrobenzene is reduced by refluxing in the presence of tin and concentrated hydrochloric acid.
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A salt will also form with the preparation of phenylamine - why?
Because of the presence of HCl.
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What is the name of the salt formed in the preparation of phenylamine?
Phenylammonium chloride
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What is the NH3 acting as when bromoehtan is heated with a concentrated solution of excess ammoinia in ethanol?
NH3 acts as a nucleophile by donating a lone pair of electrons on the N to the C of the C-Br bond
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Why is ammonia considered as a weak base?
In water it accepts a proton, H+, through coordinate bonding and forms the ammonium ion NH4+ and the hydroxide ion, OH-
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Give the order of decreasing base strength of 3 bases.
Ethylamine --> Ammonia --> Phenylamine
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Why are all amines basic?
The nitrogen atom carriesa non-bonding pair of electrons that can accept a proton
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Why is phenylamine the weakest base?
The benzene ring has drawn the lone pair of electrons away from the amine group - the benzene ring withdraws the e- from nitrogen
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What forms when an amine reacts with an acid?
Salts - because amnes are bases
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What are ethanoylation reactions?
Reactions that introduce the CH3CO group into a molecule
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What happens in ethnoylation reactions with ethanoyl chloride?
H is lost from the amine (as H+) and Cl is lost from CH3COCl (as Cl-)
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How is nitrous acid, HNO3, generated 'in situ' with amines?
By the slow addition of sodium nitrite, NaNO2, to the amine disssolved in a mineral acid, like HCl
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How do aliphatic amines react with nitrous acid?
When it is at room temperature to produce bubbles of nitrogen gas, water and other organic products
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How does phenylamine react with nitrous acid?
It reacts at room temperature to generaate bubbles of nitrogen gas and phenol
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What happens if the reaction between nitrous acid and phenylamine occurs below 10 degrees celcius?
This is known as diazotisation and the product is a diazonium salt - phenyldiazonium chloride
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What is the diazonium ion?
-N2+
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Why is an excess of nitrous acid used?
It ensures that all the phenylamine is converted into phenyldiazoniumchloride
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What happens if diazonium salts are isolated themselves?
They are explosively unstable
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What is the azo group?
R-N=N-R'
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What is are the names of the dyes formed from aromatic amines?
Diazonium dyes / Azo dyes
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What happens when the phenyldiazonium ion undergoes a coupling reaction with a phenol in alkaline solution?
Electrophilic substitution taes place on carbon 4 of the phenol, H+ is released and a bright yellow compound of 4-hydroxyphenylazobenzene forms
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What is a chromophore?
The group of atoms in the molecule responsible for the colour
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What do the alternate single and double bonds mean in the 4-hydroxyphenylazobenzene?
It is a conjugated system - the overlapping of the p-electrons across an intervening single bond can increase the overall stability of the compound through extensicve delocalisation (Conjugation)
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What do conjugated systems absorb?
Electromagnetic radiation
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What provides the great energetic stability of chromophores?
The extensive delocalisation of the pi electrons on the two benzene rings cia the -N=N- group
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Give an example of a chromophore.
The indicator methyl orange
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Describe why methyl orange is orange in colour.
The compound absorbs all other colour wavelengths in the visible region apart from the orange. The orange wavelength is refected instead of absorbed and the colour is seen
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What is an important coupling reaction to remember?
The reaction between phenyldiazonium chloride and napthalene-2-ol
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What is napthalene?
The simplest polyaromatic compound - it consists of 2 fused benzene rings with the molecular formula C10H8
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Other cards in this set
Card 2
Front
What are primary amines?
Back
Compounds in which one H atom in NH3 has been substituted.
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