Carboxylic acids, Esters, Acyl chlorides

Question 1

What is the functional group of a carboxylic acid?

Answer 1

COOH

Question 2

What do carboxylic acids act as and what does this mean they do in aqueous solution?

Answer 2

Act as weak acids so partially dissociate into their hydrogen and carboxylate ions in aqueous solution

Question 3

Describe the nature of carboxylic acid boiling points and explain why they are of this value?

Answer 3

High boiling points due to their ability to hydrogen bond with each other

Question 4

How soluble are carboxylic acids?

Answer 4

Smaller carboxylic acids are very soluble because they can hydrogen bond with water however as carbon chain increases solubility decreases as the carbon chain interferes with the hydrogen bonds

Question 5

What is the first way you can prepare a carboxylic acid?

Answer 5

Oxidising a primary alcohol or aldehyde by heating under reflux with acidified potassium dichromate

Question 6

What is the second way you can prepare a carboxylic acid?

Answer 6

Hydrolysis of nitriles either by refluxing them with HCL and water (acid hydrolysis) or reflux with an alkali then adding dilute acid (alkaline hydrolysis)
Acid hydrolysis RCN+2H20+HCL = RCOOH + NH4CL
Alkaline hydrolysis RCN + OH- + 2H20 = RCOO- + NH3
RCOO- + H+ = RCOOH

Question 7

What is the reaction of a carboxylic acid with LiAlH4?

Answer 7

RCOOH + 4[H] = ROH + H2O forms alcohol

Question 8

What is the reaction of carboxylic acids with bases?

Answer 8

RCOOH + Na2CO3 = RCOO-Na+ +H2O forms salt

Question 9

What is the reaction of carboxylic acids with PCl5?

Answer 9

RCOOH + PCl5 = RCOCl + POCl3 + HCl forms acyl chloride

Question 10

What is the reaction of carboxylic acids with alcohols in the presence of an acid catalyst and heating under reflux?

Answer 10

RCOOH + HOR reversible= RCOOR’ + H2O forms ester

Question 11

What is the ester functional group?

Answer 11

RCOOR’

Question 12

What is the acyl chloride functional group?

Answer 12

RCOCl

Question 13

What is the reaction of acyl chlorides with water?

Answer 13

RCOCl + H2O = RCOOH + HCl (g) forms a carboxylic acid

Question 14

What is the reaction of acyl chlorides with alcohols?

Answer 14

RCOCl + HOR = RCOOR’ + HCl (g) forms an ester

Question 15

What is the reaction of acyl chlorides with concentrated ammonia?

Answer 15

RCOCl + NH3 = RCONH2 + HCl (g) forms amide

Question 16

What is the reaction of acyl chlorides with amines?

Answer 16

RCOCl + NH2CH3 = RCONH2 + HCl (g) forms N - amides

Question 17

What is the first way to hydrolyse esters and what is the issue with it?

Answer 17

Acid hydrolysis - reflux with dilute acid
RCOOR’ +H2O reversible = RCOOH + ROH
Lower yield as the reaction is reversible

Question 18

What is the second way to hydrolyse esters ?

Answer 18

Alkaline hydrolysis - Reflux ester with dilute alkali
RCOOR’ + OH- = RCOO- + ROH
RCOO- + H+ = RCOOH
Higher yield as reaction is not reversible

Question 19

What is the first way to make esters and what are the issues with it?

Answer 19

RCOOH + ROH reversible= RCOOR’ + HCl (g)
Requires an acid catalyst and heating under reflux
Reversible lower yield
Harder to purify as both products are liquids

Question 20

What is the second way to make esters?

Answer 20

RCOCl + ROH = RCOOR’ + HCl (g)
Doesn’t require a catalyst
Not reversible so higher yield
HCl lost as gas so no purification required

Question 21

How are polyesters formed?

Answer 21

Formed through condensation polymerisation of dicarboxylic acids and diols
Used to make synthetic fibres, fabrics and carpets as they are strong and shrink resistant