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A2 Chemistry > amines > Flashcards

amines Flashcards

1
Q

what are amines?

A

compounds based on ammonia

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2
Q

what is a primary amine?

A

when one of the hydrogens on the ammonia has been replaced by an alkyl group

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3
Q

what is a secondary amine?

A

when two of the hydrogens on the ammonia molecule have been replaced by alkyl groups

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4
Q

what is a tertiary amine?

A

when all three of the hydrogens on the ammonia have been replaced by alkyl groups

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5
Q

what is a quarternary ammonium compound?

A

formed from a tertiary amine where the lone pair on the hydrogen forms a coordinate bond to another alkyl group

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6
Q

why are small amines soluble?

A

they can form hydrogen bonds with water

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7
Q

how do small tertiary amines form h bonds with water?

A

the lone pair on the nitrogen forms h bond to the delta positive on the hydrogen on the oxygen

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8
Q

explain the relationship between solubility and length of hydrocarbon chain?

A

less soluble as hydrocarbon chain increases bc hydrocarbon chain has to force its way between water molecules

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9
Q

how can you make a primary amine?

A

halogenoalkane and ammonia

reduction with a nitrile

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10
Q

explain how primary amines can be made from halogenoalkanes

A

heat halogenoalkane and excess conc ammonia in ethanol in a sealed test tube

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11
Q

name the mechanism of the production of a primary amine from a halogenoalkane?

A

nucleophilic substitution

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12
Q

why can ammonia act as a nucleophile?

A

has a lone pair on the nitrogen

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13
Q

why does further substitution happen when a primary amine is made?

A

because the primary amine has a lone pair on the nitrogen so it can act as a nucleophile and react with the halogenoalkane

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14
Q

what is the major product when excess ammonia is used

A

primary amine

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15
Q

what is the major product when excess halogenoalkane is used?

A

quarternary amine

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16
Q

give some of the uses of quarternary ammonium salts

A

cationic surfactants which are found in detergents, fabric softeners and conditioners

17
Q

give the reagents and conditions for the reduction of a nitrile to form an amine

A

ethanolic KCN
with hydrogen
nickel catalyst
OR a reducing agent eg. lithium tetrahydridoaluminate IN ETHER

18
Q

give the equation of a nitrile being reduced

A

R-CN + 2H2 (or 4[H])—-> RCH2NH2

19
Q

by what process is phenylamine made

A

reduction of nitrobenzene

20
Q

give the equation of the reaction of nitrobenzene

A

RNO2 + 6[H] —-> RNH2 + 2H2O

21
Q

give the conditions for the reduction of nitrobenzene

A

heat under reflux
in the presence of a tin catalyst
conc HCl
conc NaOH

22
Q

why do you use a sealed test tube when making a primary amine?

A

so that the ammonia gas doesn’t escape

23
Q

give the two stages of the reaction of ammonia with halogenoalkane

A

NH3 + R-X —> RNH3+X-

RNH3+X- + NH3 —-> RNH2 + NH4X

24
Q

in the reduction of nitrobenzene, why is conc NaOH added?

A

because adding the acid gives the protonated form of the benzene. The NaOH removes the H+ to form water/

25
Q

what are the uses of aromatic amines?

A

manufacture of dyes

26
Q

what is a base?

A

a proton acceptor

27
Q

why can ammonia and amines act as bases?

A

they have a lone pair on the nitrogen which can form a coordinate bond to protons

28
Q

ammonia + acid —>

A

ammonium salt

29
Q

amine + acid —->

A

alkyl ammonium salt

30
Q

give an equation and explain how it shows that amines are weakly basic

A

RNH2 + H2O —-> RNH3+ + OH-

equilibrium lies to the left bc the amines only partially dissociate so the solution is only partially basic

31
Q

what does the strength of a base depend on?

A

the availability of the lone pair

32
Q

why are tertiary amines the strongest base?

A

because they have the most alkyl groups which have positive inductive effect so the lone pair is most available

33
Q

why are aromatic amines the weakest base?

A

because the lone pair overlaps with the delocalised pi system so the lp is delocalised into it. the lp isnt readily available for

34
Q

what is a disadvantage of using the nitrile method to make amines?

A

toxic KCN gas produced

35
Q

what is a disadvantage of using the halogenoalkane method to make amines?

A

further substitution happens so more than one product so lower yield

36
Q

how could you distinguish between samples of aqueous ammonia and amines?

A

use a pH meter

ammonia has a lower pH than amine

A2 Chemistry (17 decks)

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