Download what are acyl chlorides?

Acyl Chlorides
Dean Martin
City and Islington College
Topic
Chemistry - Acyl Chlorides
Aims
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To help introduce students to naming and the reactions to Amides
Aimed at 16-19 year olds
Level
Level 3
Method
PowerPoint slides, ALL can be hand-outs, some slides have questions and answers (could
be done as a group discussion)
Equipment
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Projector
Laptop
Pens
Hand-Outs
Duration
>30 Mins
LEARNING OUTCOME
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7th functional group – acyl chlorides (or acid chlorides)
Drawing acyl chlorides
Naming acyl chlorides
Physical properties of acyl chlorides
Chemical properties of acyl chlorides
WHAT ARE ACYL
CHLORIDES?
The acyl group is a hydrocarbon group attached to a
carbon-oxygen double bond:
Acyl chlorides (also known as acid chlorides)
are one example of an acid derivative. In
this case, the -OH group has been replaced
by a chlorine atom.
NAMING ACYL
CHLORIDES
The easiest way of thinking about the names is to see the relationship
with the corresponding carboxylic acid:
NAMING ACYL
CHLORIDES
What is the name of that acid chloride?
Step 1: Name the longest chain
Step 2: Change the -e to -oyl chloride
Step 3: Name and number the side chain
LEARNING CHECK
Name the following acid chlorides
methanoyl chloride
pentanoyl chloride
5 methyl heptanoyl chloride
LEARNING CHECK
Draw the following acid chlorides
1. butanoyl chloride
2. 2 methyl hexanoyl chloride
3. 3,5,6 trimethyl octanoyl chloride
PHYSICAL PROPERTIES
OF ACYL CHLORIDES
Appearance
An acyl chloride like ethanoyl chloride is a colourless
fuming liquid. The strong smell of ethanoyl chloride is
a mixture of the smell of vinegar (ethanoic acid) and
the acrid smell of hydrogen chloride gas.
The smell and the fumes are because ethanoyl
chloride reacts with water vapour in the air.
PHYSICAL PROPERTIES
OF ACYL CHLORIDES
Solubility in water
Acyl chlorides can't be said to dissolve in water
because they react (often violently) with it. The
strong reaction means that it is impossible to
get a simple aqueous solution of an acyl
chloride.
PHYSICAL PROPERTIES
OF ACYL CHLORIDES
Boiling points
It is a polar molecule, and so has dipole-dipole
attractions between its molecules as well as van der
Waals dispersion forces. However, it doesn't form
hydrogen bonds. Its boiling point is therefore higher
than, say, an alkane of similar size (which has no
permanent dipoles), but not as high as a similarly
sized alcohol (which forms hydrogen bonds in
addition to everything else.)
REACTIVITY OF
ACYL CHLORIDES
Substitution of the chlorine atom by other groups
Acyl chlorides are extremely reactive, and in their reactions the
chlorine atom is replaced by other things.
Taking ethanoyl chloride as typical, the initial reaction is of this kind:
The reactions involve things like water, alcohols and phenols, or
ammonia and amines. All of these particular cases contain a very
electronegative element with an active lone pair of electrons either oxygen or nitrogen.
THE REACTION OF ACYL
CHLORIDES WITH WATER,
ALCOHOLS AND PHENOL
Each substance contains an -OH group.
In water, this is attached to a hydrogen atom.
In an alcohol, it is attached to an alkyl group - shown in the
diagrams below as "R".
In phenol, it is attached to a benzene ring. Phenol is
C6H5OH.
THE REACTION
WITH WATER
Adding an acyl chloride to water produces the
corresponding carboxylic acid together with steamy
acidic fumes of hydrogen chloride.
The reaction is usually extremely vigorous at room
temperature.
THE MECHANISM
REACTION
Between Ethanoyl, Chloride and Water
The first stage (the addition stage of the
reaction) involves a nucleophilic attack on the
fairly positive carbon atom by one of the lone
pairs on the oxygen of a water molecule.
The second stage (the elimination stage)
happens in two steps. In the first, the carbonoxygen double bond reforms and a chloride ion
is pushed off.
That is followed by removal of a hydrogen
ion by the chloride ion to give ethanoic acid
and hydrogen chloride.
THE REACTION
WITH ALCOHOLS
an ester
This is an easy way of producing an ester from an alcohol
because it happens at room temperature, and is irreversible.
Making an ester from an alcohol and a carboxylic acid (the usual
alternative method) needs heat, a catalyst and is reversible - so
that it is difficult to get a 100% conversion.
THE MECHANISM
REACTION
Between Ethanoyl Chloride and Ethanol
The first stage (the addition stage of the
reaction) involves a nucleophilic attack on the
fairly positive carbon atom by one of the lone
pairs on the oxygen of an ethanol molecule.
The second stage (the elimination stage)
happens in two steps. In the first, the carbonoxygen double bond reforms and a chloride ion
is pushed off.
That is followed by removal of a hydrogen
ion by the chloride ion to give ethyl
ethanoate and hydrogen chloride.
THE REACTION
WITH PHENOLS
The reaction between phenol and ethanoyl chloride
isn't quite as vigorous as that between alcohols and
ethanoyl chloride. The reactivity of the -OH group is
modified by the benzene ring.
THE REACTION OF:
Acyl Chlorides with Ammonia and Primary Amines
Each substance contains an -NH2 group. In ammonia, this is
attached to a hydrogen atom. In a primary amine, it is attached to an
alkyl group (shown by "R" in the diagram below) or a benzene ring.
THE REACTION
WITH AMMONIA
You normally add the ethanoyl chloride to a concentrated
solution of ammonia in water. There is a very violent reaction
producing lots of white smoke - a mixture of solid ammonium
chloride and ethanamide. Some of the mixture remains
dissolved in water as a colourless solution.
THE MECHANISM
REACTION
Between Ethanoyl Chloride and Ammonia
The first stage (the addition stage of the
reaction) involves a nucleophilic attack on the
fairly positive carbon atom by the lone pair on
the nitrogen atom in the ammonia.
The second stage (the elimination stage)
happens in two steps. In the first, the carbonoxygen double bond reforms and a chloride ion
is pushed off.
That is followed by removal of a hydrogen ion
from the nitrogen.
THE REACTION WITH
PRIMARY AMINES
The reaction with methylamine
The reaction looks exactly the same as the one with ammonia.
The methylamine is again used as a concentrated solution in
water. There is a violent reaction producing a white solid mixture
of N-methylethanamide and methylammonium chloride.
THE MECHANISM
REACTION
Between Ethanoyl Chloride and Ethylamine
The first stage (the addition stage of the reaction)
involves a nucleophilic attack on the fairly positive
carbon atom by the lone pair on the nitrogen atom in
the ethylamine.
The second stage (the elimination stage)
happens in two steps. In the first, the carbonoxygen double bond reforms and a chloride ion
is pushed off.
That is followed by removal of a hydrogen ion
from the nitrogen.
THE REACTION WITH
PRIMARY AMINES
The reaction with phenylamine (aniline)
There is no essential difference between this reaction and the
reaction with methylamine, except that the phenylamine is a brownish
liquid, and the solid products tend to be stained brownish.
the product molecule might be drawn
looking like this:
CONCEPT MAP
Acid chlorides
The reaction of acyl
chlorides with water,
alcohols and phenol
The reaction of acyl
chlorides with ammonia and
primary amines
For further information please contact The STEM Alliance
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