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A2 Chemistry > 6C - Acids & Esters > Flashcards

6C - Acids & Esters Flashcards

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1
Q

What type of intermolecular forces are present in carboxylic acids?

A

London forces

Permanent dipoles

Hydrogen bonding

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2
Q

What is the solubility of carboxylic acids in water like?

Why is it like that?

A
  • 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
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3
Q

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

A
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4
Q

Test for a carboxyl group = ?

A

Add Na2CO3(s)

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

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5
Q

How to carboxylic react in relation to regular acids reactions?

A

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

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

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6
Q

Define carboxylic acid derivative

A

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

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7
Q

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

Use R to represent the variable group.

A

Esters

Acyl chlorides

Acid anhydrides

Amides

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8
Q

Why are acyl chlorides very important in organic synthesis?

A

Theye’re VERY reactive

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9
Q

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

Reagents + conditions

A

Carboxylic acid + SOCl2 → Acyl Chloride + SO2 + HCl

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10
Q

Acyl chloride + Alcohol → ?

A

Acyl chloride + Alcohol → Ester + HCl

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11
Q

Acyl chloride + Phenol → ?

A

Acyl chloride + Phenol → Ester + HCl

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12
Q

Acyl chloride + Water → ?

A

Acyl chloride + Water → Carboxylic acid + HCl

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13
Q

Acyl chloride + Ammonia → ?

A

Acyl chloride + Ammonia → Primary amide + NH4Cl

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14
Q

Acyl chloride + Primary amine → ?

A

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

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15
Q

Ethanoyl chloride + water → ?

Equation

A

CH3COCl + H2O → CH3COOH + HCl

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16
Q

Ethanoyl chloride + ammonia → ?

Equation

A

CH3COCl + H2O → CH3CONH2 + NH4Cl

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17
Q

Ethanoyl chloride + methylamine → ?

Equation

A

CH3COCl + H2O → CH3CONHCH3 + CH3NH3+Cl-

18
Q

Ethanoyl chloride + phenol → ?

Equation

A

CH3COCl + C6H5OH → C6H5OCOCH3 + HCl

19
Q

Ethanoyl chloride + methanol → ?

Equation

A

CH3COCl + CH3OH → CH3COOCH3

20
Q

How do you name esters?

A

Alcohol first then carboxylic acid part

21
Q

Define esterification

A

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

22
Q

Forming esters from carboxylic acids

Reagents + conditions

A

Carboxylic acid + Alcohol ⇌ Ester + H2O

R = Alcohol, carboxylic acid

C = Conc H2SO4(aq) catalyst, heat under reflux

23
Q

Forming esters from acid anhydrides

Reagents + conditions

A

Acid anhydride + Alcohol → Ester + Carboxylic acid

R = Alcohol, acid anhydride

C = Nothing in particular

24
Q

Forming esters from acyl chlorides (2 ways)

Reagents + conditions

A

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

25
Q

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

A

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
26
Q

Define hydrolysis

A

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

27
Q

What type of hydrolysis can esters undergo?

A

Acid hydrolysis

Alkaline hydrolysis (also known as saponification)

28
Q

Acid hydrolysis of esters → ?

Reagents + conditions

A

Ester + H2O ⇌ Carboxylic acid + Alcohol

R = Dilute H2SO4(aq)or HCl(aq) to provide H+, H2O

C = Heat under reflux

29
Q

Alkaline hydrolysis of esters → ?

Reagents + conditions

A

Ester + Aqueous hydroxide ions → Carboxylate salt + Alcohol

R = Ester, OH- (usually from KOH or NaOH)

C = Heat under reflux

30
Q

What are the 2 methods of producing polyesters?

A

Method 1:

Dicarboxylic acid + Diol → Polyester + H2O

Method 2:

Monomer with both a carboxyl group and alcohol group

31
Q

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

A

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

32
Q

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

A

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

33
Q

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

A

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

34
Q

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

A

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
35
Q

2 advantages of using reduced pressure filtration?

A
  • 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
36
Q

Why is a buchner funnel made of thick glass?

A

So it can withstand the pressure created by the vaccum

37
Q

Name a method used to purify an organic solid

A

Recrystallisation

38
Q

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

A

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
39
Q

What does the rate of successful crystallisation depend upon?

A

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
40
Q

Define saturated solution

A

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

41
Q

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

A
  • Transfer loss
  • Some product is still left in the solution

A2 Chemistry (17 decks)

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