Chapter 26 Carbonyls And Carboxylic Acids Flashcards
What is the carbonyl functional group?
C==O
State the two organic compounds that have the carbonyl functional group
Aldehydes
Ketones
Where the carbonyl functional group positioned on an aldehyde?
Carbonyl functional group if found on the end of the carbon chain
State the structural formula of an aldehyde
CHO
Where is the carbonyl functional group positioned on a ketone?
In the middle of the carbon chain
State the structural formula of a ketone
CO
Name the carbonyl group which can be oxidised to produce a carboxylic acid
Aldehyde
Describe the process of the oxidation of aldehydes
Aldehydes can be oxidised to carboxylic acids when refluxed with the oxidising agent acidified potassium dichromate.
This results in a colour change from orange to green
Aldehydes can also be oxidised to a carboxylic acid when reacted with Tollens reagent to give a silver mirror precipitate
State the equation for the oxidation of propanal
CH3CH2CHO + [O] —> CH3CH2COOH
Describe the nature of the C==O double bond
The C==O consists of 3 σ bonds resulting from the direct overlap of orbitals and a π bond formed from the sideways overlap of adjacent p orbitals creating a π bond above and below the plane of the Carbon and Oxygen atom.
This means the C==O has a trigonal plane shape with a bond angle of 120 degrees.
The C==O is polar due to the difference in electronegativity.
Oxygen is slightly negative and Carbon is slightly positive
State the name of the attacker which reacts with aldehydes and ketones
Nucleophile
What mechanism do carbonyl compounds carry out?
Nucleophilic addition
What is a nucleophile?
Electron pair donor
What mechanism do alkenes carry out?
Electrophilic addition
State the two types of nucleophilic addition in carbonyl compounds
Reduction of the carbonyl compounds
Reaction of carbonyl compounds with Hydrogen cyanide
State the reducing agent required for the reduction of carbonyl compounds
Reagent- NaBH4 followed by the addition of water
State the nucleophile needed for the reduction of carbonyl compounds reaction
Hydride ion= H-
Sourced from NaBH4
Write the equation for the reduction of propanal
CH3CH2CHO + 2[H] —> CH3CH2CH2OH
What is the product for the reduction of an aldehyde?
Primary alcohol
What is the product for the reduction of a ketone?
Secondary alcohol
Write the equation for the reduction of propanone
CH3COCH3 + 2[H] ——> CH3CHOHCH3
State the reagent needed for the nucleophilic addition of hydrogen cyanide
Reagent- mixture of H2SO4 and NaCN to provide the hydrogen cyanide in the reaction
Why can HCN not be used directly in the nucleophilic addition mechanism?
Toxic
State the product of the nucleophilic addition reaction with HCN?
Hydroxynitrile
Why is the nucleophilic addition reaction mechanism of hydrogen cyanide useful?
It increases the length of the carbon chain
Describe the process for the nucleophilic addition reaction with NaBH4
1- Lone pair of electrons from the hydride ion is attracted to the slightly positive Carbon atom in the C==O
2- A dative covalent bond is formed between the H- ion and the Carbon atom of the C==O
3- The π bond of the C==O breaks by heterolytic fission forming a negatively charged intermediate
4- The oxygen atom of the intermediate donates a pair of electrons to the H atom of water.
A hydroxide ion is also formed
Describe the nucleophilic addition reaction with NaCN/ H+
1- The lone pair of electrons from the CN- ion is attracted to the slightly positive carbon atom in the C==O so a dative bond forms
2- The π bond in the C==O breaks by heterolytic fission forming a negatively charged intermediate
3- The intermediate donates a pair of electrons to a hydrogen ion to form the product
The product is a hydroxynitrile
What reagent is used to test for carbonyl compounds?
2,4-DNP detected the C==O in aldehydes and ketones
Describe the process used to test for carbonyl compounds
-React organic substance with 2,4-DNP
-The result of an orange ppt indicates a carbonyl compound (aldehyde or ketone)
-Filter and dry ppt
-Determine the melting point of the purified derivative
-Compare the melting point to known data values
What is the positive result when testing for 2,4-DNP?
Orange ppt
How can aldehydes and ketones be distinguished from one another?
Using Tollens reagent- ammoniacal silver nitrate which indicates the presence of aldehydes
Describe the process of testing for an aldehyde
-Add Tollens reagent to the organic substance
- Put the substance into a water bath to 50 degrees
- A silver mirror confirms the presence of an aldehyde
What substance is being reduced when testing for aldehydes?
Silver
Write the reduction equation of silver when testing for aldehydes
Ag^+ (aq) + e- —-> Ag (s)
What substance is oxidised when testing for aldehydes?
Aldehyde IS OXIDISED TO A CARBOXYLIC ACID
Write the equation for the oxidation of the aldehyde when testing for aldehydes
-CHO + [O] —> -COOH
Describe the process of making Tollens reagent
-Aqueous NaOH is added to aqueous silver nitrate until a brown precipitate of silver oxide is observed
-Dilute aqueous ammonia is then added until the precipitate just dissolves
State the functional group for a carboxylic acid
-COOH
Describe how the boiling point increases as chain length or branching increases
As chain length increases, the boiling point increases because there are more London forces which require more energy to be overcome.
As branching increases in carboxylic acids, the boiling point decreases because there is less surface contact between the molecules meaning the London forces are weaker and require less energy to be overcome.
Describe the solubility of carboxylic acids
Carboxylic acids are soluble in water and organic solvents because they are able to form hydrogen bonds
However, as the chain length increases the carboxylic acids become less soluble because the long non polar carbon chains have a greater effect on the overall polarity of the molecule.
How can carboxylic acids react?
-With metals during redox reactions
-With metal oxides, metal hydroxides and carbonates during neutralisation reactions
- With SOCl2 to form an acyl chloride
-With alcohol and concentrated H2SO4 to produce an ester
How do carboxylic acids react with metals?
Carboxylic acid + metal —-> carboxylate salt + hydrogen
State the equation for the redox reaction of propanoic acid and Ca
2CH3CH2COOH + Ca —-> (CH3CH2COO-)2Ca2+ + H2
H is reduced from +1 in propanoic acid to 0 in H2
Ca is oxidised from 0 in Ca to +2 in Calcium propanoate
How do carboxylic acids react with metal oxides?
Carboxylic acids + metal oxide —-> carboxylate salt + water
State the equation for the neutralisation reaction between ethanoic acid and potassium oxide
2CH3COOH + K2O ——> 2CH3COO-K+ + H2O
State what would be observed in the neutralisation reaction between a carboxylic acid and metal oxide
Observe the metal oxide dissolving
How do carboxylic acids react with metal hydroxides ?
Carboxylic acid + metal hydroxide —-> carboxylate salt + water
State the equation for the reaction of methanoic acid and Magnesium hydroxide
2HCOOH + Mg(OH)2 —-> (HCOO-)Mg2+ + 2H2O
State what would be observed in the neutralisation reaction between a carboxylic acid and metal hydroxide?
The metal hydroxide solid would dissolve
State what would be observed in the redox reaction between a carboxylic acid and metal
Metal dissolving
Bubbles of hydrogen gas forming
How do carboxylic acids react with carbonates?
Carboxylic acid + carbonate ——> carboxylate salt + carbon dioxide + water
State the equation for the neutralisation reaction between butanoic acid and sodium carbonate
2CH3CH2CH2COOH + Na2CO3 —> 2CH3CH2CH2COO-Na+ + CO2 + H2O
State what would be observed in the neutralisation reaction between a carboxylic acid and metal carbonate
The solid metal carbonate would dissolve
Bubbles of CO2 would be produced
What is the test for the carboxyl group?
Reacting with a carbonate is used to test for the carboxyl group
If a carbonate added to a carboxylic acid, effervescence of CO2 produced
What are esters?
Derivatives of carboxylic acids where the hydroxyl hydrogen is replaced with an alkyl group
How are esters named?
The alcohol is named first, then the carboxylic acid
Suffix: -oate
State the ways in which esters can be made using esterification
-Carboxylic acid and alcohol
-Acid anhydride and alcohol
-Acyl chloride and alcohol
State the conditions needed to make an ester using a carboxylic acid and alcohol
Concentrated H2SO4 and heated under reflux
State the equation for the esterification of methanoic acid and propan-1-ol and name the ester formed
Carboxylic acid + alcohol ⇌ ester + water
HCOOH + CH3CH2CH2OH ⇌ HCOOCH2CH2CH3 + H2O
Forms propyl methanoate
State the conditions needed to make an ester using an acid anhydride and alcohol
Reflux under dry conditions
The acid anhydride is warmed with the alcohol
No concentrated Sulfuric acid is used
The reaction is not reversible
State the equation for the esterification of ethanoic anhydride and ethanol and name the ester formed
Acid anhydride + alcohol —-> ester + carboxylic acid
(CH3CO)2O + CH3CH2OH —-> CH3COOCH2CH3 + CH3COOH
Forms ethyl ethanoate
State the conditions needed to make an ester using acyl chloride and alcohol
Reflux under dry conditions
State the equation for the esterification of ethanoyl chloride and methanol and name the ester formed
Acyl chloride + alcohol —> ester + hydrogen chloride
CH3COCl + CH3OH —-> CH3COOCH3 + HCl
Methyl ethanoate formed
State two ways that esters can be hydrolysed
-Hot aqueous acid
-Hot aqueous alkali
What is the acidic hydrolysis of esters?
Ester + water ⇌ carboxylic acid + alcohol
Esters are hydrolysed with hot aqueous acid
State the equation for the acidic hydrolysis of propyl methanoate
HCOOCH2CH2CH3 + H2O ⇌ HCOOH + CH3CH2CH2OH
What is the alkali hydrolysis of esters?
Ester + metal hydroxide —-> carboxylate salt + alcohol
Esters is hydrolysed with hot aqueous alkali
State the equation for the alkaline hydrolysis of propyl methanoate with NaOH
HCOOCH2CH2CH3 + NaOH —-> HCOO- Na+ + CH3CH2CH2OH
What is an acid anhydride?
Two carboxylic acids joined minus a water molecule
Draw the general formula of an acid anhydride
R
\
C ==O
/
O
\
C==O
/
R
How can the R groups of the acid anhydride structure differ?
The R groups can be the same or different
If they are different then the structure is known as a mixed anhydride
How is an acid anhydride named?
Using the first name of the carboxylic acid(s) present then anhydride
What is acyl chloride?
A derivative of a carboxylic acid where the OH is replaced by Cl
How are acyl chlorides named?
First name is the carboxylic acid
Suffix -oyl chloride
How are acyl chlorides made?
Reacting carboxylic acids with thionyl chloride, SOCl2
Carboxylic acid + thionyl chloride —> acyl chloride + Sulfur dioxide + hydrogen chloride
State the conditions needed to make acyl chlorides
Dry
State the equation needed to make propanoyl chloride from propanoic acid and thionyl chloride
CH3CH2COOH + SOCl2 —-> CH3CH2COCl + SO2 + HCl
Explain why conditions must be dry when making acyl chlorides
Conditions must be dry otherwise the acyl chloride produced may react with water to form a carboxylic acid
State the different reactions of acyl chlorides
-Be used to make esters including phenyl esters which are not possible with carboxylic acids
-Be used to make carboxylic acids
-Be used to make primary and secondary amides
How are acyl chlorides used to make esters?
Acyl chloride + alcohol —> ester + hydrogen chloride
How are acyl chlorides used to make carboxylic acids?
Acyl chloride + water —> carboxylic acid + hydrogen chloride
How are acyl chlorides are used to make primary amides?
Acyl chloride + ammonia —-> primary amide + hydrogen chloride
What are primary amides?
Where the N is bonded to one carbon
How are acyl chlorides used to make secondary amides?
Acyl chloride + amine —> secondary amide + hydrogen chloride
What are secondary amides?
The Nitrogen is bonded to 2 carbon atoms
Why should the preparation of esters from acyl chlorides be conducted under dry conditions?
Conditions must be dry otherwise the acyl chloride produced may react with water to form a carboxylic acid
