Carboxyllic acids and Derivatives

Question 1

What two functional groups do carboxyllic acids have?

Answer 1

• the carbonyl group (-C=O)
• the hydroxyl group (-OH)

Question 2

How does having two groups influence the properties of the two groups?

(In terms of the OH group and acidicty)

Answer 2

-Oh group in carboxylic acids is much more acidic than the -OH group in alchols.

Question 3

Why is the -OH in carboxyllic acids much more acidic than in alcohols?

Answer 3

• X-ray diffraction studies of the carboxylate ion show that the two carbon-oxygen bonds are of equal length.
• This suggests the negative charge is distributed evenly over the carboxylate group and is delocalised.
• This delocalisation means the carboxylate is less likely to join up with the H+ ion again (the carboxylate ion is
  made more stable).
• When alcohols OH bond breaks to release H atom, there is no way of delocalising the -ve charge, which reains firmly on the oxygen atom, that intense negative charge will be highly attractive towards H+ ions so the alchol will instantle reform.

This is why carboxylic acids are more acidic than alcohols.

Question 4

What is an ester? [general formula]

Answer 4

a derivative of carboyllic acids
RCOOR’

Question 5

How do you name an ester?
+ what is the structure

Answer 5

alkyl group + -oate
eg: methanol + ethanoic acid = methyl ethanoate
CH3OH+CH3COOH = CH3COOCH3 + H2O

Question 6

Uses of short chain esters

Answer 6

• flavourings and perfumes (have pleasant fruity smell)
• solvents
• plastercisers

Question 7

What are esters with longer carbon chains?

Answer 7

fats and oils

Question 8

Why are carboxyllic acids weak acids?

Answer 8

because they only partially dissociate in solution
RCOOH ⇌ RCOO- + H+
equilibirum lies well over to the left

Question 9

How do you test for carboxyllic acids?

Answer 9

add sodium hydrogencarbonate to release CO2, causes effervesence
CH3COOH (aq) +NaHCO3(aq) –> CH3COONa (aq) + H2O (l) + CO2 (g)

Question 10

What is a salt produced by a carboxyllic acid called?

Answer 10

carboxylate

Question 11

General acid base reactions with carboxylic acids

theres 4

Answer 11

• metal + carboxylic acid –> salt + hydrogen
• metal oxide/hyrdoxide + carboxylic acid —> salt + water
• metal carbonate + carboxylic acid –> salt + water + carbon dioxide
• ammonia + carboxylic acid –> ammonium salt

Question 12

How to name carboxylates (salts) vs how to write them

Answer 12

name : metal + carboxylic acid stem +oate
(magnesium ethanoate)
write : the convention is to put the metal at the end of the salt’s formula
(CH3COO-)2 Mg2+

Question 13

How do you make an ester?
Do you need a catalyst? what is it?
What kind of reaction is it?
also what’s the byproduct?

Answer 13

• carboxylic acid + alcohol
• strong acid catalyst
• reversible reaction (forms an equilibrium mixture of reactants and products)
• byproduct is water

Question 14

Explain the hydrolysis of esters

Answer 14

The carbonyl carbon atom (C=O) of an ester has a δ+ charge and is therefore attachked by water acting as a (weak) nucleophile

Question 15

What makes a nucleophile weak?

Answer 15

A highly electronegative atom is a poor nucleophile because it is unwilling to share its electrons. As electronegativity increases, nucleophilicity decreases.
oxygen is very electronegative

Question 16

Give a general equation for the hydrolysis of esters

Answer 16

(H+ catalyst)
RCOOR’ + H2O ⇌ RCOOH + R’OH

Question 17

What’s the difference between fats and oils?
why?

Answer 17

Oils are liquid at RT
Oils (liquids at room temperature) contain more carbon to carbon double bonds than fats (solid at room temperature).

Question 18

Desribe the structure of oils and fats?

Answer 18

Contain three molecules of long chain carboxylic acids (fatty acids) attatched to a glycerol molecule.
They are esters of propane-1,2,3-triol (glycerol)

Question 19

What happens when you hydrolyse fats and oils in alkaline conditions

Answer 19

produces glycerol and soap

Question 20

Uses of glycerol

Answer 20

• used in pharmatceuticals and cosmetics, because it attracts water it can be used to prevent ointments and creams from drying out.
• solvent in many medicines, present in toothpaste
• solvent in food industry, ie solvent in food colourings
• used to plasticise various materials like sheets and gaskets, cellophane.

Question 21

How do plasticisers work?

Answer 21

Plastisicers are introduced between molecules of a poloymer which makes up the material and by allowing them the molecules to slip over each other the material becomes flexible and smooth . PVS may contain up to 50% plasticiser such as hexandioic acid. Over time the plasticiser leaks away leaving the plastic brittle and inflexible.

Question 22

What is biodiesel

Answer 22

renewable fuel as it is made from oils derived from crops such as rape seed. (rape seed oil is a triglyceride ester)

Question 23

How is biodiesel made?

Answer 23

oil reacted with methanol (with a strong alkali as a catalyst) to form a mixture of methyl ester which can be used as fuel in diesel vehicles

Question 24

Can oils and fats be hydrolysed?

Answer 24

Yes (oil/fat + 3H2o–> glycerol + 3 fatty acid chains 3R-COOH)