Acyl Chlorides and Purifying Organic compounds

Question 1

What is the functional group of acyl chlorides?

Answer 1

-COCl

Question 2

Draw the displayed formula for 4-hydroxy-2,3-dimethylpentanoyl chloride

Answer 2

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Question 3

How do acyl chloride names end?

Answer 3

-oyl chloride

Question 4

How are acyl chlorides named?

Answer 4

The carbon atoms are numbered from the end with the acyl functional group. (This is the same as with carboxylic acids)

Question 5

Give the list of substances acyl chlorides loose their chlorine to

Answer 5

• Water
• Alcohols
• Ammonia
• Primary amines

Question 6

Describe how each substance reacts with ethanoyl chloride, an equation for each substance and products

Answer 6

• Water: A vigorous reaction with cold water, producing a carboxylic acid.
• Alcohols: A vigorous reaction at room temperature, producing an ester. (methanol)
• Ammonia: A violent reaction at room temperature, producing an amide.
• Primary amines: A violent reaction at room temperature, producing an N-substituted amide. (ethylamine)

Check physical flashcards for equations.

Question 7

Which process is acyl chlorides reacting with alcohols faster than?

Answer 7

Esterification

Question 8

What is given off when Cl is substituted by an oxygen or nitrogen?

Answer 8

• Misty fumes of hydrogen chloride are given off

Question 9

What type of substances react in the same way as Acyl Chlorides

Answer 9

• Acid Anhydrides react in the same way as Acyl Chlorides

Question 10

What are acid anhydrides and how do you name them?

Answer 10

• acid anhydrides is made from two identical carboxylic acid molecules
• If you know the name of the carboxylic acid, they’re easy to name- just take away ‘acid’ and add ‘anhydride’

Question 11

What is the difference between acid anhydride reacting with water, alcohol, ammonia and amines and Acyl Chlorides reacting with them?

Answer 11

• With acid anhydrides the reactions are less vigorous
• You get carboxylic acids instead of HCl

Question 12

Give the equation for the reaction of ethanoic anhydride with methanol to produce methyl ethanoate and ethanoic acid

Answer 12

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Question 13

draw in diagrams of two molecules of ethanoic acid to form ethanoic anhydride and water

Answer 13

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Question 14

What type of reactions do Acyl Chlorides undergo?

Answer 14

Nucleophilic Addition-Elimination reactions

Question 15

Why do acyl chlorides undergo nucleophilic addition-elimination reactions?

Answer 15

• In acyl chlorides, both the chlorine and the oxygen atoms draw electrons towards themselves
• Carbon has a slight positive charge
  It is easily attacked by nucleophiles

Question 16

Describe the reaction between methanoyl chloride and methanol and draw its mechanism

Answer 16

• Methanol is the nucleophile here.
• It attacks the partially positive carbon on the acyl chloride, and a pair of electrons from the C=O bond are transferred to the oxygen.
• Now the pair of electrons on the oxygen reform the double bond and the chlorine’s kicked off.
• The chlorine now bonds with the hydrogen in the hydroxyl group.
• And hydrogen chloride’s eliminated

Mechanisms: Check physical flashcards for answers

Question 17

Give one purpose of ethanoic anhydride and how this product is made

Answer 17

• Ethanoic anhydride is used for the manufacture of Aspirin
• React salicylic acid with ethanoic anhydride or ethanoyl Chloride
  Aspirin is an ester

Question 18

Draw out the reaction of salicylic acid and ethanoic anhydride to produce aspirin and ethanoic acid

Answer 18

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Question 19

Why is Ethanoic anhydride used instead of ethanoyl chloride

Answer 19

• Ethanoic anhydride is cheaper
• Less corrosive and safer
• Reacts more slowly with water
• And doesn’t produce dangerous hydrogen chloride fumes

Question 20

Give the diagram mechanism of ethanoyl chloride and ethylamine reacting together at room temperature

Answer 20

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Question 21

What are most products of organic reactions riddled with?

Answer 21

Impurities

Question 22

What process removes water soluble impurities from a product

Answer 22

Separation

Question 23

Describe the separation technique of water soluble impurities

Answer 23

• If a product is insoluble in water then you can use separation to remove any impurities that do dissolve in water
• Pour the mixture into a separating funnel and add water
• Shake the funnel and then allow it to settle.
• The organic layer and the aqueous layer (which contains any water soluble impurities) are immiscible (they don’t mix) so separate out into two distinct layers
• Open the tap and run each layer off into a separate container

Question 24

Describe the separation technique on water insoluble impurities

Answer 24

• If the product and the impurities are both soluble in water, solvent extraction can be used
• Organic solvent in which the product is more soluble than it is in water
• Add it to the impure product solution and shake well
• The product will dissolve into the organic solvent leaving the impurities dissolved in the water.
• Run off using a separating funnel

Question 25

How can water be removed from a purified product and describe the process

Answer 25

- Drying - Separation to purify a product, the organic layer will end up containing trace amounts of water so it has to be dried - Add an anhydrous salt such as magnesium sulfate (MgSO4), or calcium Chloride. The salt is used as a drying agent, it binds to any water present to become hydrated. - When you first add the salt to the organic layer it will clump together - Keep adding drying agent until it disperses evenly when you swirl the flask - Filter the mixture to remove the solid drying agent - Pop a piece of filter paper into a funnel that feeds into a flask and pour the mixture into the filter paper

Question 26

Note

Answer 26

The filter paper can be fluted (concertina folded) to increase its surface area

Question 27

How can other impurities be removed? and explain the method

Answer 27

- Washing - The product of a reaction can be contaminated with leftover reagents or unwanted side products - Remove some of these by washing the product (which in this case means adding another liquid and shaking) - E.g. aqueous sodium hydrogencarbonate can be added to an impure product in solution to remove acid from it to give CO2 gas - The organic product can be removed using a separating funnel

Question 28

How can volatile liquids be purified?

Answer 28

By Distillation

Question 29

How does a distillation process work?

Answer 29

- Separates out liquids with different boiling points - Gently heating the mixture in a distillation apparatus - Substances will evaporate out of the mixture in order of increasing boiling point

Question 30

Describe the distillation technique including apparatus

Answer 30

- Connect a condenser to a round-bottomed flask containing your impure product in solution - Place a thermometer in the neck of the flask so that the bulb sits next to the entrance to the condenser. The temperature on the thermometer will show the boiling point of the substance that is evaporating at any given time - Heat the impure product (many organic chemicals are flammable so use an electric heater) - When the product that you want to collect boils, place a flask at the open end of the condenser to collect your pure product

Question 31

How can organic solids be purified?

Answer 31

By Re-crystallization

Question 32

Describe Re-crystallization

Answer 32

- Dissolve your solid in a hot solvent to make a saturated solution that's a solution in which the maximum possible amount of solid is dissolved in the solvent - Let it cool, as the solution cools, the solubility of the product falls. It forms crystals

Question 33

Describe the process of crystallization and include apparatus

Answer 33

- Add very hot solvent to the impure solid until it just dissolves. It's really important not to add too much solvent- this should give a saturated solution of the impure product - Filter the hot solution through a heated funnel to remove any insoluble impurities - Leave the solution to cool down slowly. Crystals of the product will form as it cools - Remove the liquid containing the soluble impurities from the crystals by filtering the mixture under reduced pressure. (To do this, you pour the mixture into a filter paper lined Buchner funnel- a flat bottomed funnel with holes in the base- that's sitting in a side-arm flask attached to a vacuum line) - Finally, wash the crystals with ice-cold solvent to remove any soluble impurities from their surface. Leave you purified crystals to dry.

Question 34

What are good indicators of purity?

Answer 34

Melting and Boiling points

Question 35

How do pure substances influence melting and boiling points

Answer 35

- If substances are impure, the melting point's are lowered and the boiling point is raised - If they are very impure, melting and boiling points will occur across a wide range of temperatures

Question 36

Describe how melting and boiling points can be detected

Answer 36

- You can use melting point apparatus to accurately determine the melting point of an organic solid. - Pack a small sample of the solid into a glass capillary tube and place it inside the heating element - Increase the temperature until the sample turns from solid to liquid - You usually measure a melting range, which is the range of temperatures from where the solid begins to melt to where it has melted completely - You can look up the melting point of a substance in data books and compare it to your measurements - Impurities in the sample will lower the melting point and broaden the melting range

Question 37

Draw the structure of ethanamide

Answer 37

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Question 38

The student purified the crude solid product, N−phenylethanamide, by recrystallisation. (i) Outline the method that the student should use for this recrystallisation

Answer 38

- Dissolve the product in the minimum volume of water / solvent (in a boiling tube / beaker) - Hot water / solvent Steps must be in a logical order to score all 4 marks - Allow the solution to cool and allow crystals to form. - Filter off the pure product under reduced pressure / using a Buchner funnel and side arm flask