17C: Carboxylic Acids

Question 1

Carboxylic acid structure and chemistry

Answer 1

1) H+ dissosciates in equilibrium - weak acid
R-COOH -> RCOO- + H+ ( eq lies to left)
2)negative charge delocalised across the 2 O atoms, giving stability to the carboxylate ion
3)IMF: high mp/bp due to H boding between molecules (dimers)
4)solubility; soluble in water due to H bonds: increased chain length delocalised e-
5)test: add Na2CO3, NaHCO3 ( s or g) - effervescence due to neutralisation and release of CO2

Question 2

different ways of producing carboxylic acids

Answer 2

1) primary alcohol: reflux, H+/cr2o7-
2)aldehydes: reflux, H+/cr2o7-
3)esters reflux, dil. HCL, acid hydrolysis
4)nitriles: reflux, dil. HCL, acid hydrolysis
R-CN + 2H2O + HCL –> R-COOH + NH4CL
5)acyl chlorides: room temp, H2O, nucleophilic addition/elimination, hydrolysis

Question 3

reduction of carboxylic acids

Answer 3

reagent: LiAlH4 in dry ether
RCOOH + 4(H) –> RCH2OH + H2O
reaction cannot be stopped at aldehyde

Question 4

carboxylic acid –> acyl chloride

Answer 4

reagent: PCl5 (phosphorus pentachloride)
RCOOH + PCl5 –> RCOCL + POCl3 + HCL
conditions: anhydrous conditions; as acyl chloride readily reacts (hydrolyses) with H2O
distillation: to separate R-COCl from POCl3 (liquids)

Question 5

neutralisation of carboxylic acid

Answer 5

reagent: alkali/base
ethanoic acid + sodium –> sodium ethanoate + water
test for R-COOH

Question 6

esterification of carboxylic acids

Answer 6

reagent: alcohol/conc h2sO4

RCOOH + R-OH –> RCOOR + H2O

Question 7

producing esters

Answer 7

1)reacting a carboxylic acid with alcohol in acidic conditions: esterification
2)carboxylic acid+ alcohol –> ester + water
3) conc h2so4 and distillation
4) ester has lwoer bp than carboxylic acid and alcohol therefore distillation

Question 8

why conc h2so4 used in producing esters

Answer 8

1) speeds up the reaction (H+ ions act as catalyst)

2) dehydrating agent: removes H2O and shifts eq to the right

Question 9

naming esters

Answer 9

_____yl(alcohol chain)_____oate(carboxylic acid chain)

Question 10

hydrolysis of esters

Answer 10

1) opposite of esterification
2) splitting an ester with water
3) acid hydrolysis
4) alkaline hydrolysis

Question 11

Acid hydrolysis

Answer 11

1) ester + water –> alcohol + carboxylic acid (dil hcl)

2) carboxylic acid produced is protonated (in acidic conditions)

Question 12

alkaline hydrolysis

Answer 12

1) ester + alkali –>alcohol + caroboxylic acid salt

2) add H+ to produce full acid

Question 13

acyl chloride + water

Answer 13

room temp
RCOOH + HCL (steamy fumes)
violent reaction

Question 14

acyl chloride + alchol

Answer 14

room temp
RCOOR + HCl (steamy fumes)
will also esterify with phenol, RCOOH will not

Question 15

acyl chloride + ammonia

Answer 15

room temp

RCOCl + 2NH3 conc –>RCONH2 (primary amide) + NH4+CL- (white smoke)

Question 16

acyl chloride + primary amine

Answer 16

room temp

RCOCL + 2RNH2 (primary amine) –> RCONHR (secondary amide - n subsituted amide) + R-NH3Cl- (amine salt)

Question 17

polyester

Answer 17

example of condensation polymerisation

where a small molecule is released as a by product of the bond forming