Carboxylic Acids, Esters and Fatty Acids

Question 1

What is the structure of a carboxylic acid?

Answer 1

• contains carboxyl functional group COOH
• includes a carbonyl (C=O) group and a hydroxyl (O-H) group
• the bonds are in a planar arrangement
• are isomeric with esters: -‘RCOOR’

Question 2

What is the nomenclature of a carboxylic acid?

Answer 2

Remove -e from alkane and replace with -OIC ACID.

Question 3

Describe the solubility of carboxylic acids.

Answer 3

• acids are very soluble in organic solvents
• soluble in water due to hydrogen bonding
• small one dissolve readily in water
• as mass increases, solubility decreases
• benzoic acid is fairly insoluble in cold water but soluble in hot

Question 4

Describe the boiling point properties etc. of carboxylic acids.

Answer 4

• increases as size increases (incr. van der Waals forces)
• they have high boiling points for their relative masses, arises from inter-molecular hydrogen boding due to the polar O-H group
• additional intermolecular attractions = more energy to separate molecules

Question 5

Describe the acidic behaviour of COOH (carboxylic acids).

Answer 5

• the polar carbonyl group enables the hydroxyl group to ionise partly in water
• this ionisation is due to delocalisation of the negative charge over the carbon and two oxygen atoms spreading the negative charge and increasing the stability of the anion
• COOH are weak acids as they partially disassociate into carboxylate ions and hydrogen ions

Question 6

What are the products of carboxylic acid’s reactions with metal, metal oxide, metal hydroxide and metal carbonate?

Answer 6

CA + metal -> salt + hydrogen
CA + metal oxide -> salt + water
CA + metal hydroxide -> salt + water
CA + metal carbonate -> salt + water + carbon dioxide

Question 7

What is the nomenclature of salts made from carboxylic acids?

Answer 7

• oate

Question 8

What is the analytical use of carboxylic acids?

Answer 8

Carboxylic acids are strong enough acids to liberate CO2 from carbonates. Phenols are also acidic but are not strong enough to liberate CO2.

Question 9

Preparation of carboxylic acids:

What are the oxidation/hydrolysis equations of aldehydes, primary alcohols and esters?

Answer 9

• Ox. of aldehydes: RCHO + [O] -> RCOOH
• Ox. of primary alcohols: RCHOH + 2[O] -> RCOOH + H2O
• Hydr. of esters: RCOOR + H2O -> RCOOH + ROH

Question 10

What is the structure of an ester and its nomenclature?

Answer 10

STRUCTURE: Sub. an organic group for the H in acids.
NOMENCLATURE: First part from the alcohol, second part from the acid. Extension is -oate.

Question 11

What are esters made from?

Answer 11

Carboxylic acid + Alcohol -> Ester + Water.

Question 12

What are esters used for?

Answer 12

• to flavour food
• to make sweet smelling perfumes, toiletries etc.
• as solvents
• as plasticisers to make polymers soft and flexible

Question 13

What are the reagent, conditions and equation for esterification? Use ethanoic acid and methanol as an example.

How can products be seperated?

Answer 13

REAGENTS: alcohol and acid catalyst (e.g. conc. H2SO4)
CONDITIONS: Reflux
EQUATION: CH3COOH + CH3OH -> CH3COOCH3 + H2O
Separated via fractional distillation! ~

Question 14

Draw an ester linkage.

Answer 14

O
||
R - C - O - R’

Question 15

PREPARATION OF ESTER FROM AN ACID ANHYDRIDE:

1) What are anhydrides made of?
2) Reagents, conditions, general equation and notes?

Answer 15

REAGENTS: alcohol and acid anhydride
CONDITIONS: reflux under dry conditions
GENERAL EQ.: alcohol + acid anhydride -> ester + carb. acid
NOTES: reaction is irreversible and no catalyst is needed also, products can be separated via fractional distillation

Question 16

What is hydrolysis the opposite of?

Answer 16

Esterification: ester + water carboxylic acid + alcohol

e.g. ethyl methanoate -> HCOOH methanoic acid + C5H6OH ethanol

Question 17

What are the reagents and the conditions of the hydrolysis of an ester?

Answer 17

REAGENTS: aqueous acid or alkali
CONDITIONS: reflux

Question 18

What are the products of the hydrolysis of an ester (both alkali and acidic)?

Answer 18

acidic: carboxylic acid + alcohol
alkali: water soluable ionic salt (e.g. CH3COO-Na+) + alcohol
- the carboxylic acid can be made by treating salt with HCl
CH3COO-Na+ +HCl -> CH3COOH + NaCl

Question 19

What are the physical and chemical properties of an ester?

Answer 19

• no hydrogen bonding
• insoluble in water
• fairly unreactive
• hydrolysed to acids

Question 20

What are the features of saturated and unsaturated fatty acids?

Answer 20

• saturated: no double bonds

- unsaturated: contains double bonds

Question 21

In which type of fatty acids do cis-trans isomers occur?

Answer 21

unsaturated

Question 22

Describe cis and trans in fatty acids.

Answer 22

• cis: 2 Hs on same side of double bond
  molecule bent at the double bond
  all natural fatty acids cis
• trans: 2 Hs on opposite sode of double bond
  molecule is straight, man-made fatty acid

Question 23

What are trigycerides?

Answer 23

• triesters of the alcohol glycerol (propane-1,2,3-ol) & fatty acids
• can be saturated (animal fats like butter & lard, solid at RT)
• can be unsaturated (veg oil like sunflower, liquid at RT)

Question 24

How do you make a triglyceride?

Answer 24

glycerol + 3x fatty acids -(esti…/conden…)-> triglyceride + 3x H2O

• the triglyceride contains 3 ester functional groups

Question 25

What is cholesterol?

Answer 25

It is a soft, waxy material found in cell membranes and transported in your bloodstream. It is partly produced by your body and partly absorbed from animal products you eat e.g. eggs, meat and dairy products.

Question 26

What are the 2 types of cholesterol?

Answer 26

- 'bad': low density lipoprotein (LDL) cholesterol | - 'good': high density lipoprotein (HDL) cholesterol

Question 27

What does bad cholesterol do?

Answer 27

- can clog blood vessels - increases risk of high blood - increases risk of CHD (coronary heart disease) - increases risk of strokes

Question 28

What does good cholesterol do?

Answer 28

- removes bad cholesterol, taking it to the liver to be destroyed - high levels can give protection from heart disease

Question 29

What are trans fats and what do they do?

Answer 29

- triglycerides made of trans fatty acids, almost all man made - are in foods like biscuits, crisps, chips and cakes - incr. amount of bad cholesterol but red. good cholesterol

Question 30

How can bad cholesterol be increased?

Answer 30

- by eating food with trans fats and saturated fats

Question 31

What type of unsaturated fats are there?

Answer 31

- polyunsaturated: several double bonds (shown to reduce bad cholesterol) - monounsaturated: one double bond per chain

Question 32

Where can unsaturated fats be found?

Answer 32

plant oils such olive and sunflower

Question 33

How are plant oils made 'spreadable' margarines?

Answer 33

By treating oils with hydrogen to saturate some of the double bonds (hydrogenation) in their triglycerides molecules, straightening out their chains. It also converts cis isomers into trans isomers, thus increasing their melting points.

Question 34

What is biodiesel?

Answer 34

- a renewable fuel made from vegetable oil or animal fat that can be used in diesel engines - it is carbon neutral - it is a mixture of methyl and ethyl esters of fatty acids

Question 35

How do you make biodiesel?

Answer 35

- by reacting triglycerides (oil or fats) with methanol or ethanol - methanol or ethanol are used as they are cheap, renewable and burn more efficiently

Question 36

Where can the materials needed to make biodiesel be obtained from?

Answer 36

- veg oil: can be new, low grade oil or waste oil from fish & shops and restaurants - animal fat: chicken fat, waste fish oil and lard from meat processing

Question 37

What are the benefits of biodiesel?

Answer 37

- biodegradable and non-toxic - fuel and exhaust emissions are less pleasant - high flashpoint

Question 38

Draw a simple acid anhydride.

Answer 38

O O O | | | | e.g. // C C CH3 - C / \ / \ > O R O R' CH3 - C \\ O