Carboxylic Acids + Derivatives Flashcards
What is a carboxylic acid and it’s functional group ?
-COOH (C=O and C-OH)
How do you name carboxylic acids ?
Carbon chain length -oic acid.
Are carboxylic acids soluble in water ?
•Yes, acid group forms hydrogen bonds with water
•Carbon chain length affects solubility
What intermolecular forces are there in carboxylic acids ?
Hydrogen bonds and van ver waals
What are esters (functional group), what are they formed from ?
•They are formed from carboxylic acids and alcohols
•RCOOR (C=O C-O-C)
Write an equation for the reaction of ethanoic acid and propan-1-ol
CH3COOH + CH3CH2CH2OH -> CH3COOCH2CH2CH3 + H2O
How do you name esters ?
•Start with the group that replaced the H, then acid suffix
•Eg, propanol + ethanoic acid = propylethanoate
What characteristic physical properties do esters have ?
Volatile, fruity smells
What are the uses of esters ?
Flavourings, perfumes (long chain)
Solvents, plasticisers (short chain)
What are some common natural esters ?
Fats and oils
How are carboxylic acids polarised ?
C d+
Both O d-
Write an equilibrium formed by ethanoic acid in solution ?
CH3COOH -> CH3COO- + H+
What happens to the negative charge in an ethanoate ion in terms of electrons ?
Electrons become delocalised and are shared across the whole group
How would you distinguish carboxylic acids from other OH containing compounds ?
Add NaHCO3, acids will produce sodium salt, water and CO2
Write an equation for the reaction of ethanoic acid and sodium hydroxide
CH3COOH + NaOH -> CH3COONa + H2O
Write an equation for the reaction of ethanoic acid and NaCO3
2CH3COOH + Na2CO3 -> 2CH3COONa + H2O + CO2
What catalyst is needed for the formation of esters from alcohols and carboxylic acids ?
Concentrated strong acid eg H2SO4
What catalyst is needed for the hydrolysis of esters ?
Dilute strong acid eg H2SO4
What is an alternative method of hydrolysis of esters ?
Base hydrolysis
What are the advantages of base hydrolysis of esters ?
Reaction goes to completion due to neutralisation by base - more product in the mixture catalysed by hydrolysis
Which alcohols forms the esters that make up animal and vegetable oils ?
Glycerol / propan-1,2,3-triol
What is the difference between oil and fat ?
Oils are liquid at room temperature fats are solids
Fats are usually saturated
What are the products of producing fats and oils ?
Propan-1,2,3-triol and sodium salts of the acids that make up the ester (hydrolysed with NaOH)
What are the uses of Propan-1,2,3-triol and sodium salts ?
Soaps and cleaning products
What does the long hydrocarbon chain of the carboxylate ion do ?
Mixes with grease (conditioner)
What does the COO- group do ?
Mixes with water
Why does a carboxylate ion with a long hydrocarbon chain make a good cleaning agent ?
Carboxylate ion mixes with the grease which can then be removed from water
What is the IUPAC name of glycerol ?
Propane-1,2,3-triol
What are some common uses of glycerol ?
•Used in pharmaceutical and cosmetic preparations, eg stops cream drying
•A solvent in many medicines eg toothpaste
•A solvent in the food industry eg food colourings
•Plasticisers
How do you make biodiesel (general equation and conditions)
•NaOH catalyst, 60C
•Lipid + 3CH3OH -> 3 methyl esters + glycerol
What is transesterification?
Converting one type of ester to another
What kind of seed is biodiesel made from ?
Rapeseed oil or soybean oil
How is the reaction mixture of biodiesel purified and separated?
•Setting tank or centrifuge
•Remove remainder with water
•Add acid to neutralise excess alkali catalyst
•Soap is formed, easy to remove.
What is an issue with producing biodiesel ?
Crops that could be used for food are used for fuel
What are carboxylic acid derivatives ?
Molecules that have an acyl group as a part of their structure, formed from carboxylic acids
Name two carboxylic acid derivatives and give their functional groups
Acyl chlorides RCOCl
Acid anhydrides RCOOCR / (RCO)2O
Draw the mechanism for the acylation of a nucleophile by an acid derivative
•C d+ O d- (C=O)
•Arrow from lone pair of Nu- to d+ of C, further arrow from C=O to O
•This gives O negative charge, arrow from lone pair of O to bond, further arrow from C-X to X.
What factors effect how readily the acylation of a nucleophile by an acid derivative occurs ?
*Magnitude of the d+ charge on the carbonyl group (electronegativity of group being substituted)
*How easily the group being substituted is lost
*How readily the nucleophile will donate electrons.
What effect do the Cl and O atoms in acyl chlorides/acid anhydrides have on the partial charge of the carbonyl atom ?
They increase the d+ charge by attracting electrons, this means that they react more readily with nucleophiles
Which are more reactive: Acyl chlorides or acid anhydrides ?
Acyl chlorides
What is the name of the mechanism by which acyl chlorides and acid anhydrides acylate nucleophiles?
Nucleophilic addition-elimination
If the nucleophile is ammonia for the acylation of acyl chlorides or acid anhydrides, what are the products of the reaction ?
An amide
Write an equation for the reaction of ethanoyl chloride and ammonia
CH3COCl + 2NH3 -> CH3CONH2 + NH4Cl
Draw / describe the mechanism for the reaction of ethanoyl chloride and ammonia
*d+ on C, d- on O and Cl of ethanoyl
*Arrow from lone pair of N (NH3) to d+ C
*This produces intermediate whereby the C=O becomes C-O and NH3 joins C, there is now N+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from N+-H to N+.
If the nucleophile is a primary amide, what are the products of the acylation of acyl chlorides or acid anhydrides ?
N-Substituted amide
Write an equation for the reaction of ethanoyl chloride and methylamine
CH3COCl + CH3NH2 -> CH3CONHCH3 + CH3NH3Cl
Draw / describe the reaction of ethanoyl chloride and methylamine
*d+ on C, d- on O and Cl of ethanoyl
*Arrow from lone pair of N (CH3NH2) to d+ C
*This produces intermediate whereby the C=O becomes C-O and CH3NH2 joins C, there is now N+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from N+-H to N+.
If the nucleophile is an alcohol, what are the products of the acylation of acyl chlorides or acid anhydrides ?
An ester
Write an equation for the reaction of ethanoyl chloride and ethanol
CH3COCl + CH3CH2OH -> CH3COOCH2 + HCl
Draw / describe the mechanism for the reaction of ethanoyl chloride and ethanol
*d+ on C, d- on O and Cl of ethanoyl chloride
*Arrow from lone pair of O (ethanol) to d+ C
*This produces intermediate whereby the C=O becomes C-O and ethanol joins C via the OH group, there is now O+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from O+-H to O+.
If the nucleophile is water, what are the products of the acylation of acyl chlorides or acid anhydrides ?
Carboxylic acids (hydrolyses ester linkage)
What is the name of the reaction of the acylation of acyl chlorides/acid anhydrides with water as a nucleophile?
It is a hydrolysis reaction
Write an equation for the reaction of ethanoyl chloride and water
CH3COCl + H2O -> CH3COOH + HCl
Draw / describe the mechanism for the reaction of ethanoyl chloride and water
*d+ on C, d- on O and Cl of ethanoyl chloride
*Arrow from lone pair of O (H2O) to d+ C
*This produces intermediate whereby the C=O becomes C-O and water joins C via the O , there is now O+ and O-
*Arrow from lone pair of O- to C-O, arrow from C-Cl to Cl and arrow from O+-H to O+.
What is a commercially important acylation reaction ?
The manufacture of aspirin
What are the advantages if using ethanoic anhydride as a acylating agent over ethanoyl chloride ?
*It is cheaper, less corrosive and does not react readily with water
*It is safer as ethanoic acid is produced rather than HCl which is corrosive.
What would you observe in a melting point determination if the sample was not pure ?
*The sample would melt over a large temperature range (more than 3 C)
*Samples melting point may be below the theory value due to impurities disrupting structure.
Why might the melting point of a substance appear different from its true value ?
The temperature of the material in the apparatus may be different to the temperature reading displayed - apparatus error
When removing flue gasses, what are the issues ?
Disposal of large amounts of CaSO3, and CO is produced
What conditions are needed to form methyl esters from an acid anhydride or acyl chloride
React with methanol and heat gently under reflux
When purifying via recrystallisation, why is the minimum volume of hot solvent required used ?
So that a saturated solution is created, this means that as many crystals will fall out of the solution as possible when it is cooled
Why is the solution filtered hot when purifying by recrystallisation ?
To remove insoluble impurities and ensure that crystals do not form in the filter paper
Why is the solution cooled in an ice bath when purifying by recrystallisation ?
To ensure that as many crystals as possible fall out of solution - yield is higher
Why are the crystals washed with cold water when purifying by recrystallisation ?
To remove soluble impurities
How would you separate the crystals from the reaction mixture when purifying by recrystallisation ?
Filter under reduced pressure using a Buchner funnel
Why may the %yield of purifying by recrystallisation be below 100% ?
*Product is lost during filtration, drying and weighing - not all product is transferred from one piece of equipment to another
*Product is left dissolved in the solution - some does not crystalise
*Some is left on filter paper.
