carboxylic acids and esters

Question 1

are carboxylic acids strong or weak acids?

Answer 1

weak acids that slightly dissociate when in solution, forming a H+ ion and a carboxylate ion, RCOO-

Question 2

reaction of carboxylic acids with carbonates

Answer 2

they produce a carboylate salt, water and CO2

Question 3

are small chain carboxylic acids soluble in water

Answer 3

yes, as they can form hydrogen bonds with water molecules between the lone electron pair on an oxygen atom and a delta+ hydrogen atom

Question 4

boiling point of a carboxylic acid

Answer 4

relatively high. due to the dimerization fo the carboxylic acid group

Question 6

miscibility of carboxylic acids

Answer 6

short chains are miscible with water up to butanoic acid. this solubility quickly reduces due to other longer aliphatic (hydrophobic) chain

Question 7

pKa with acids

Answer 7

the lower the value of pka the more acidic

Question 8

why is the pka value of propanoic acid higher than ethanoic and methanoic acid

Answer 8

methanoic acid - 3.75
ethanoic acid - 4.76
propanoic acid - 4.87

An increasing size of alky groups pushes electron density, destabilising the COOH. making the acidity weaker

Question 9

why is the pka value of chloroethanoic acid higher than trichloroethanoic acid

Answer 9

chloroethanoic acid - 2.86
trichloroethanoic acid- 0.66

chlorine is an electron withdrawing carboxylate, so it is less negative and more stable

Question 10

reaction to make COOH

Answer 10

oxidation of alcohol
- primary alcohol
- reflux
- acidified K2Cr2O7

Question 11

reactions of COOH

Answer 11

reduction of COOH
- lialh4 in dry ether
- reflux
- primary alcohol

oxidation of COOH

esterification

Question 12

how are esters formed/ esterification

Answer 12

• alcohols reaction with carboxylic acid
• strong acid catalyst H2SO4
• reflux

Question 13

features of esters

Answer 13

• low boiling points
• good solution for other polar molecule
• sweet-smelling compounds

Question 14

uses of esters

Answer 14

• perfume industry
• flavourings in the food industry
• plasticisers to make plastics more flexible

Question 15

hydrolysis of esters with acid

Answer 15

• dilute acid HCL
• heat under reflux

CH3CO2CH3 + H2O <=> CH3CO2H + CH3CH2OH

Question 16

problem with the hydrolysis of esters with an acid

Answer 16

its a reversible reaction and therefore does not give a good yield

Question 17

hydrolysis of esters with an alkali

Answer 17

• sodium hydroxide
• heat under reflux

Question 18

positives of the hydrolysis of an ester with an alkali

Answer 18

the carboxylate anion is resistant to attack by weak nucleophiles (e.g. alcohol). so the reaction is not reversible and goes into completion.

Question 19

features of a micelle

Answer 19

• hydrophilic head - polar CO2- end of fatty acid
• hydrophobic tail - long non-polar hydrocarbon chain

Question 20

biodiesel

Answer 20

vegetable oils can be converted into biodiesel by reaction with methanol in the presence of a catalyst (strong alkali).

Question 21

acid derivatives that could take place in an addition elimination reaction

Answer 21

• ester
• acid
• acyl chloride
• acid anhydride

Question 22

addition elimination
acid chloride -> amide

Answer 22

• reagent NH3
• acid chloride added to concentrated ammonia

Question 23

addition elimination
acid chloride -> ester

Answer 23

• reagent - alcohol
• alcohol added to acyl chloride at room temperature

Question 24

addition elimination
acid chloride -> carboxylic acid

Answer 24

• reagent H2O
• room temperature

Question 25

addition elimination
acid anhydride -> amide

Answer 25

• reagent concentrated NH3
• room temp

Question 26

addition elimination
acid anhydride -> carboxylic acid

Answer 26

• reagent H2O
• room temp