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amines

for the mechansim of forming a tertiary amine, why is a primary amine used?
i thought that once a secondary amine is made, it reacts with the haloalkane and then the tertairy amine reacts and so on replacing the H on the previous amine

Reply 1

charco

Study Forum Helper

Original post by esmeralda123

sorry, you lost me ...

RNH₂ + 2R'Cl --> R₃N + 2HCl

Reply 2

username3718068

Original post by esmeralda123

reacting a primary amine with excess haloalkane with produce the secondary amine through nucleophilic substitution.
Then the secondary amine will react with more excess haloalkane to produce tertiary amine and then quartenary ammoinum salt.

Even if you used ammonia, you can get a mixture of primary amine secondary amine, tertiary amine, quarternary ammonium salt via nucleophillc substituion reactions.

The process is:
haloalkane + ammonia -> primary amine + ammonium halide
primary amine + ammonia -> secondary amine + ammonium halide
secondary amine + ammonia - > tertiary amine + ammonium halide
tertary amine + ammonia -> quaternary ammonium salt

This should help to show the pattern of the reaction.
So even if you used primary amine, the reaction will produce tertiary amine.
If you used secondary amine, you will produce tertiary amine.
If you used ammonia, you will produce tertiary amine.

(edited 6 years ago)

Reply 3

debbie394

Original post by dip0

i don't understand the mechanism for the formation of the tertiary amine from the reaction of methylamine and chloroethane.

Reply 4

HateOCR

Primary amines keep reacting with excess halogenoalkanes until a tertiary amine is formed

Reply 5

username3718068

Original post by esmeralda123

i don't understand the mechanism for the formation of the tertiary amine from the reaction of methylamine and chloroethane.

Mechanism

I was meant to mention "amine formed has +1 formal charge in the N atom" but mentioned "ammonium chloride" by mistake in the picture

I also have named the products wrongly in the picture by mistake.
the ionic salt product formed at each stage should be called methyl ammonium chloride

(edited 6 years ago)

mechanism.png79.0KB

Reply 6

username3718068

Original post by charco

sorry, you lost me ...

RNH₂ + 2R'Cl --> R₃N + 2HCl

This reaction equation is incorrect because you don't form HCl, you form R-NH3+Cl-.
The equation MUST be written like this:

2RNH2 + R'Cl-> RN(R')H + R-NH3+Cl-

Reply 7

charco

Study Forum Helper

Original post by dip0

This reaction equation is incorrect because you don't form HCl, you form R-NH3+Cl-.
The equation MUST be written like this:

2RNH2 + R'Cl-> RN(R' :wink:

H + R-NH3+Cl-

The products depend on the ratio of the reactants. If excess haloalkane is used you will get a quaternary salt.

Reply 8

username3718068

Original post by charco

The products depend on the ratio of the reactants. If excess haloalkane is used you will get a quaternary salt.

Thats correct, but you also have to note that the R-NH2 is acting as a base and a nucleophile.
So for your single reaction (not the overall reaction), both the RNH2 molecules will be reacting with the R'Cl to produce R-NH3+Cl- and the secondary amine.