6C - Acids & Esters

Question 1

What type of intermolecular forces are present in carboxylic acids?

Answer 1

London forces

Permanent dipoles

Hydrogen bonding

Question 2

What is the solubility of carboxylic acids in water like?

Why is it like that?

Answer 2

• C=O and O-H bonds are polar ∴ COOH group can form hydrogen bodns with water, they partially dissociate
• ≤ 4Cs = soluble in water
• As no’ of Cs increase, solubility decreases as less SA to form H bonds. Hydrocarbon part of the molecules is hydrophobic

Question 3

Draw a diagram to show the formation of hydrogen bonds between carboxylic acids and water molecules

Answer 3

Question 4

Test for a carboxyl group = ?

Answer 4

Add Na₂CO_3(s)

Observation: effervescence. Bubble gas through limewater to give white precipitate - CO₂ being released

Question 5

How to carboxylic react in relation to regular acids reactions?

Answer 5

They react in the same way as a regular acid with:

Methals, metal oxides, alkalis and carbonates. They form the carboxylate ion

Question 6

Define carboxylic acid derivative

Answer 6

Carboxylic acid derivative = Compound that can be hydrolysed to produce a carboxylic acid

Question 7

Name 4 carboxylic acid derivatives and give their general structure through a drawing.

Use R to represent the variable group.

Answer 7

Esters

Acyl chlorides

Acid anhydrides

Amides

Question 8

Why are acyl chlorides very important in organic synthesis?

Answer 8

Theye’re VERY reactive

Question 9

Equation on how to form an acyl chloride from a carboxylic acid

Reagents + conditions

Answer 9

Carboxylic acid + SOCl₂ → Acyl Chloride + SO₂ + HCl

Question 10

Acyl chloride + Alcohol → ?

Answer 10

Acyl chloride + Alcohol → Ester + HCl

Question 11

Acyl chloride + Phenol → ?

Answer 11

Acyl chloride + Phenol → Ester + HCl

Question 12

Acyl chloride + Water → ?

Answer 12

Acyl chloride + Water → Carboxylic acid + HCl

Question 13

Acyl chloride + Ammonia → ?

Answer 13

Acyl chloride + Ammonia → Primary amide + NH₄Cl

Question 14

Acyl chloride + Primary amine → ?

Answer 14

Acyl chloride + Primary amine → Secondary amide + Chloride salt of primary amine

Question 15

Ethanoyl chloride + water → ?

Equation

Answer 15

CH₃COCl + H₂O → CH₃COOH + HCl

Question 16

Ethanoyl chloride + ammonia → ?

Equation

Answer 16

CH₃COCl + H₂O → CH₃CONH₂ + NH₄Cl

Question 17

Ethanoyl chloride + methylamine → ?

Equation

Answer 17

CH₃COCl + H₂O → CH₃CONHCH₃ + CH₃NH₃⁺Cl^-

Question 18

Ethanoyl chloride + phenol → ?

Equation

Answer 18

CH₃COCl + C₆H₅OH → C₆H₅OCOCH₃ + HCl

Question 19

Ethanoyl chloride + methanol → ?

Equation

Answer 19

CH₃COCl + CH₃OH → CH₃COOCH₃

Question 20

How do you name esters?

Answer 20

Alcohol first then carboxylic acid part

Question 21

Define esterification

Answer 21

Esterification = A reaction in which a carboxylic acid reacts with an alcohol to form an ester and water

Question 22

Forming esters from carboxylic acids

Reagents + conditions

Answer 22

Carboxylic acid + Alcohol ⇌ Ester + H₂O

R = Alcohol, carboxylic acid

C = Conc H₂SO_4(aq) catalyst, heat under reflux

Question 23

Forming esters from acid anhydrides

Reagents + conditions

Answer 23

Acid anhydride + Alcohol → Ester + Carboxylic acid

R = Alcohol, acid anhydride

C = Nothing in particular

Question 24

Forming esters from acyl chlorides (2 ways)

Reagents + conditions

Answer 24

Acyl chloride + Alcohol → Ester + HCl

R = Acyl chloride, alcohol

C = Nothing in particular

Acyl chloride + Phenol → Ester + HCl

R = Phenol, Acyl chloride

C = Nothing in particular

Question 25

Advantages (3) and disadvantages (2) of using acid anhydrides to prepare esters over carboxylic acids?

Answer 25

_Advantages:_ * Better yield - reaction is not reversible * No need to reflux - lower temps needed * Faster reaction _Disadcantages:_ * Potentially worse atom economy - carboxylic acid is made instead of H₂O * Acid anhydrides are more reactive but also more hazardous

Question 26

Define **hydrolysis**

Answer 26

**Hydrolysis** = A reaction with water that breaks a chemical compound into 2 compounds, the H and OH form a water molecule becomes incoorperated into 2 compounds

Question 27

What type of hydrolysis can esters undergo?

Answer 27

Acid hydrolysis Alkaline hydrolysis (also known as saponification)

Question 28

Acid hydrolysis of esters → ? Reagents + conditions

Answer 28

**Ester + H₂O ⇌ Carboxylic acid + Alcohol** **R** = Dilute H₂SO_4(aq)or HCl_(aq) to provide H⁺, H₂O **C** = Heat under reflux

Question 29

Alkaline hydrolysis of esters → ? Reagents + conditions

Answer 29

**Ester + Aqueous hydroxide ions → Carboxylate salt + Alcohol** **R** = Ester, OH^- (usually from KOH or NaOH) **C** = Heat under reflux

Question 30

What are the 2 methods of producing polyesters?

Answer 30

_Method 1:_ **Dicarboxylic acid + Diol → Polyester + H₂O** _Method 2:_ **Monomer with both a carboxyl group and alcohol group**

Question 31

Why must **dilute** acids be used in acid hydrolysis of esters and not conc?

Answer 31

H₂O is needed as a reagent. It's used to push equil to favour RHS ∴ dilute acid must be used

Question 32

Why can't 100% yield ever be achieved through acid hydrolysis of esters?

Answer 32

The reaction is reversible ∴ a byproduct will always be produced hence not 100% yield

Question 33

Name the practical method used to seperate a solid product from a solvent or liquid mixture

Answer 33

Filtration under reduced pressure - buchner funnel experiment - think aspirin!

Question 34

Explain how to carry out filtration under pressure (8 steps)

Answer 34

Technique used to seperate a solid product from a aqueous or liquid reaction mixture. _Apparatus:_ * Buchner flask, buchner funnel, pressure tubing and filter paper _Method:_ 1. Connect one end of the pressure tubing to the vaccum outlet or to the filter pump whilst attaching the other end of the rubber tubing to the buchner flask 2. Fir buchner funnel to the buchner flask ensureing there's a snug fit - usually obtained by using a buchner ring or buchner bung 3. Switch on vaccum pump. check for good suction by placing hand across the top of the funnel 4. Place a piece of filter paper inside the buchner funnel + wet it with a little of the same solvent used in preparing the solid. Filter paper needs to be stuck to the buchner funnel 5. Pour reaction mixture slowly from a beaker onto centre of the filter paper 6. Rinse out the beaker with the solvent so that all solid crystals collect in the buchner funnel 7. Rinse the crystals in the buchner funnel with more solvent + leave the under suction for a few min so crystals start to dry 8. Transfer filter paper w/ crystals onto a glass dish + let it air dry

Question 35

2 advantages of using reduced pressure filtration?

Answer 35

* Much quicker way of seperating out the crystals than ordinary filtration as air pressure pushes the solution through the filter * Can be left running after filtration is complete to draw air over the filtered solid and partially dry it

Question 36

Why is a buchner funnel made of thick glass?

Answer 36

So it can withstand the pressure created by the vaccum

Question 37

Name a method used to purify an organic solid

Answer 37

Recrystallisation

Question 38

Explain the process of recrystallisation + it's uses (4 steps)

Answer 38

Technique used to purify an organic solid. Solid product obtained after filtration contains impurities. Recrystallisation is used to obtain a purer sample of a compound by exploiting the difference in solubility of substances in different solvents at different temperatures. _Method:_ 1. Pour a quantity of the chosen solvent into a conical flask * If the solvent is flammable, warm it over a water bath. If the solvent is H₂O, place the conical flask on a tripod + gauze over a bunsen and warm the water 2. Tip impure sample into a second conical flask or beaker 3. Slowly add the solvent to the impure sample until it dissolves in the solvent. Add the minimum volume of solvent needed to dissolve the solid 4. Once solid dissolved, allow solution to cool. Crystals of desired product should form. When no more crystals form, folter the crystals under reduced presure (buchner funnel) to obtain the dry crystalline solid

Question 39

What does the rate of successful crystallisation depend upon?

Answer 39

Need to use the right solvent. Usually achieved through an educated guess and trial & error. * The aim is to have the desired compound (C) dissolve in the hot solvent but be insoluble (or have low solubility) when cold

Question 40

Define **saturated solution**

Answer 40

**Saturated solution** = A solution when you add more solute it won't dissolve anymore

Question 41

Why does purification by recrystallisation always lead to a loss of product?

Answer 41

* Transfer loss * Some product is still left in the solution