ORGANIC CHEMISTRY - carboxylic acids and derivatives

Question 1

what is a carboxylic acid? functional group?

Answer 1

• COOH ( C=O , C-OH)

Question 2

how do you name carboxylic acids?

Answer 2

-oic acid

Question 3

are carboxylic acids soluble in water? why? what influences their solubility?

Answer 3

• yes
• acid group can form hydrogen bonds with water molecule
• hydrocarbon chain length influences their solubility

Question 4

what are the intermolecular forces in carboxylic acids?

Answer 4

hydrogen bonds
vdw

Question 5

what are esters? functional group, general formula?

Answer 5

• formed from carboxylic acids + alcohols
  RCOOR

Question 6

how do you name esters?

Answer 6

alcohol (yl) carboxylic acid (oate)

Question 7

what characteristic physical properties do esters have?

Answer 7

volatile, pleasant, fruity smells

Question 8

what are some uses of esters?

Answer 8

perfumes
flavourings
plasticisers

Question 9

what are some common natural esters?

Answer 9

fats and oils

Question 10

write the equation for the equilibrium formed by an ethanoic acid in a solution?

Answer 10

CH3COOH ( aq) ⇌ CH3COO- (aq) + H+(aq)

Question 11

what happens to the negative charge on the ethanoate ion in terms of electrons?

Answer 11

electrons delocalise so the negative charge is shared across the whole of the carboxylate group

Question 12

how can you distinguish carboxylic acids from other -OH containing compounds?

Answer 12

add NaHCO3
sodium salt, water and co2 produced

Question 13

write an equation of the reaction of ethanoic acid and NaOH?

Answer 13

CH3COOH + NaOH —> H2O + CH3COO-Na+

Question 14

write an equation for the reaction of ethanoic acid with Na2CO3?

Answer 14

2CH3COOH + Na2CO3 —> H2O + CO2 + 2CH3COO-Na+

Question 15

what catalyst is needed for the formation of esters from alcohols and carboxylic acids?

Answer 15

concentrated H2SO4

Question 16

what catalyst is needed for the hydrolysis of esters?

Answer 16

dilute strong acid H2SO4

Question 17

what is an alternative method for hydrolysis?

Answer 17

base hydrolysis

Question 18

what are the + of base hydrolysis?

Answer 18

reaction goes to completion due to neutralisation by base

Question 19

what alcohol makes up esters founds in animals and vegetable oils?

Answer 19

propane- 1,2,3 triol

Question 20

what is the difference between oil and fat?

Answer 20

oil - (l) at room temp unsaturated
fats - (s) saturated

Question 21

products of hydrolysing fats and oils?

Answer 21

prpoane-1,2,3-triol
sodium salts of the acids that make up the acid

Question 22

uses of products from fat + oil hydrolysis?

Answer 22

soaps and cleaning products

Question 23

what does the long hydrocarbon chain of the carboxylate ion do?

Answer 23

mix with grease

Question 24

what does the COO- group do?

Answer 24

mix with water

Question 25

how does the carboxylate ion with a long hydrocarbon chain make a good cleaning agent?

Answer 25

means that grease can be removed with water

Question 26

systematic name of glycerol?

Answer 26

propane-1,2,3-triol

Question 27

common uses of glycerol?

Answer 27

- prevents creams from drying out - solvent in medicine

Question 28

how do you make biodiesel?

Answer 28

NaOH catalyst 60 degrees lipid + 3CH3OH ---> 3methyl ester + glycerol

Question 29

what are the problems with producing biodiesel?

Answer 29

crops used to make food are being used to make fuel

Question 30

what are carboxylic acid derivatives?

Answer 30

molecules that have the acyl group as part of their structure, formed from carboxylic acids

Question 31

draw the mechanism for the acylation of a nucleophile by an acid derivative

Answer 31

drawing on pmt

Question 32

which factors determine how readily the acylation of a nucleophile by an acid derivative occurs?

Answer 32

- magnitude of the delta + charge on the carbonyl group which depends on the electronegativity of the group being substituted - how readily the nucleophile will electrons - how easily the group being substituted is lost

Question 33

What effect does the chlorine and oxygen atoms in the acyl chloride have on the partial charge on the carbonyl carbon?

Answer 33

Increases the partial positive charge by attracting electrons = they react more readily with nucleophiles

Question 34

are acyl chlorides or acid anhydrides more reactive?

Answer 34

acyl chlorides

Question 35

what is the name of the mechanism by which acyl chlorides and acid anhydrides acylate nucleophiles?

Answer 35

nucleophilic addition - elimination

Question 36

if the nucleophile is ammonia for the acylating of acyl chlorides or acid anhydrides, what are the products of the reaction?

Answer 36

an amide

Question 37

if the nucleophile is a primary amine, what are the products of the acylation of acyl chlorides and acid anhydrides?

Answer 37

N-substituted amide

Question 38

if the nucleophile is an alcohol ,what are the products of the acylation of acyl chlorides and acid anhydrides?

Answer 38

an ester

Question 39

if the nucleophile is water, what are the products of the acylation of acyl chlorides and acid anhydrides?

Answer 39

carboxylic acid ( hydrolyses the ester linkage)

Question 40

write an equation for the reaction of ethanoyl chloride and water?

Answer 40

CH3COCl +H2O ---> CH3COOH + HCl

Question 41

what is a commercially important acylation reaction?

Answer 41

the manufacture of aspirin

Question 42

what are the + of using ethanoic anhydride as an acylating agent over ethanoyl chloride.

Answer 42

cheaper less corrosive does not react readily with water safer as ethanoic acid is produced than HCl which is corrosive.

Question 43

what would you observe for the melting point of an impure sample?

Answer 43

sample melts over a large range sample mp below accepted value due to impurities disrupting structures

Question 44

why is mp diff to true value?

Answer 44

apparatus error

Question 45

when removing flue gases, what are the issues?

Answer 45

disposal of large amounts of CaSO3 and CO3 is produced

Question 46

when purifying by recrystallisation, why is the minimum volume of hot solvent used?

Answer 46

so a saturated solution is created, so many crystals will be formed as soon as possible

Question 47

why is the solution filtered hot when purifying by recrystallisation?

Answer 47

to remove insoluble impurities and to ensure that crystals do not form in filter paper

Question 48

why is the solution cooled by an ice bath when purifying by recrystallisation?

Answer 48

to ensure that as many crystals as possible fall out of the solution - higher yield

Question 49

why are crystals washed with cold water when purifying by recrystallisation?

Answer 49

to remove soluble impurities

Question 50

how will you remove crystals from the reaction mixture when purifying by recrystallisation?

Answer 50

filter under reduced pressure using a Buchner funnel

Question 51

why might percentage yield be below 100%?

Answer 51

product lost by filteration, drying and weighing product is left dissolved in the solution - some does not crystallise sample is still wet