Acyl Chlorides Dean Martin City and Islington College

Topic Chemistry - Acyl Chlorides Aims  To help introduce students to naming and the reactions to Amides  Aimed at 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  Projector  Laptop  Pens  Hand-Outs Duration >30 Mins

L EARNING O UTCOME 7 th functional group – acyl chlorides (or acid chlorides) Drawing acyl chlorides Naming acyl chlorides Physical properties of acyl chlorides Chemical properties of acyl chlorides

W HAT 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 In this case, the -OH group has been replaced by a chlorine atom.

N AMING ACYL CHLORIDES The easiest way of thinking about the names is to see the relationship with the corresponding carboxylic acid:

N AMING 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

L EARNING C HECK Name the following acid chlorides methanoyl chloride pentanoyl chloride 5 methyl heptanoyl chloride

L EARNING C HECK Draw the following acid chlorides 1.butanoyl chloride 2.2 methyl hexanoyl chloride 3.3,5,6 trimethyl octanoyl chloride

P HYSICAL P ROPERTIES OF A CYL C HLORIDES 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.

P HYSICAL P ROPERTIES O F A CYL C HLORIDES 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.

P HYSICAL P ROPERTIES O F A CYL C HLORIDES 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.)

R EACTIVITY O F A CYL C HLORIDES 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: wateralcoholsphenols ammoniaamines 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.

T HE 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 C 6 H 5 OH.

T HE 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.

T HE MECHANISM REACTION 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 carbon- oxygen 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. Between Ethanoyl, Chloride and Water

T HE 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.

T HE MECHANISM REACTION 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 carbon- oxygen 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. Between Ethanoyl Chloride and Ethanol

T HE 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.

T HE REACTION OF : Each substance contains an -NH 2 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. Acyl Chlorides with Ammonia and Primary Amines

T HE 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.

T HE MECHANISM REACTION 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 carbon- oxygen double bond reforms and a chloride ion is pushed off. That is followed by removal of a hydrogen ion from the nitrogen. Between Ethanoyl Chloride and Ammonia

T HE REACTION WITH PRIMARY AMINES 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 reaction with methylamine

T HE MECHANISM REACTION 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 carbon- oxygen double bond reforms and a chloride ion is pushed off. That is followed by removal of a hydrogen ion from the nitrogen. Between Ethanoyl Chloride and Ethylamine

T HE 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:

C ONCEPT MAP Acid chlorides The reaction of acyl chlorides with water, alcohols and phenol The reaction of acyl chlorides with ammonia and primary amines

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