Chapter 26: Carbonyls and Carboxylic Acids Flashcards
What is the functional group that aldehydes and ketones share?
Carbonyl
Where is the carbonyl group located on aldehydes and ketones?
Aldehydes - end of carbon chain
Ketones - middle of carbon chain
Why can ketones not undergo oxidation reactions?
Lack of reactivity
What can aldehydes be oxidised to? How do you oxidise aldehydes?
Oxidised to CARBOXYLIC ACIDS when refluxed with acidified sodium/potassium dichromate and dilute sulfuric acid.
Why are the properties of a C=O bond different to a C=C bond?
C=O is polar and therefore attract nucleophiles towards the slightly positive carbon .
What type of addition reaction do Carbonyl compounds undergo vs alkenes?
Alkenes - ELECTROPHILIC addition
Carbonyl - NUCLEOPHILIC addition
What does reacting aldehydes and ketones with sodium tetrahydridoborate do? (NaBH4)
NaBH4 acts as a reducing agent and reduces them to alcohols.
What is produced when an aldehyde and ketone are reacted with NaBH4?
Aldehyde - PRIMARY alcohol
Ketone - SECONDARY alcohol
When writing the equation for reduction with NaBH4 with aldehyde/ketone what should you remember?
+2[H] and then NaBH4/H20 over the arrow
What does reacting carbonyl compounds with HCN (hydrogen cyanide) do?
Increases the length of the carbon chain.
What is the type of reaction between HCN and a carbonyl compound?
Addition
What must you remember when carrying out a reaction with HCN?
Fume cupboard because HCN is an extremely poisonous liquid that boils slightly above room temperature.
List the step of the mechanism between NaBH4 and a carbonyl.
- Hydride ion from NaBH4 acts as a nucleophile
- Dative covalent bond between carbon and hydride ion
- Pi bond of C=O breaks through heterolytic fission
- Oxygen donates electrons to hydrogen of water molecule (dative covalent bond)
- Intermediate has been protonated to form an alcohol + OH-
What is the name of the product form HCN?
Hydroxynitrile
What reagent do you use to detect the Carbonyl group?
2,4 DNP (Brady’s Reagent)
What reagent do you use to distinguish between aldehydes and ketones?
Tollen’s Reagent
Describe how you use 2,4 DNP to detect the carbonyl group.
- Add 2,4 DNP to sample
- Forming of yellow/orange precipitate means presence of ketone/aldehyde.
Describe how Tollen’s Reagent can be used to distinguish between ketones and aldehydes.
Ketones cannot be oxidised whereas aldehydes can.
Tollen’s reagent is a solution of SILVER NITRATE in aq ammonia.
Silver IONS(ag+) act as oxidising agents and become reduced to SILVER (ag) when an aldehyde is present to form a SILVER MIRROR.
Give the half equation of silver ions being reduced to silver in the Tollen’s reagent.
Ag+(aq) + e- —-> Ag(s)
What functional groups do carboxylic acids have?
Carbonyl and Hydroxyl
What bonds can carboxylic acids do and why?
Hydrogen bonding due to the polar OH bonds with lone pairs of oxygen.
What property does the hydrogen bonding give carboxylic acids?
Solubility
but with increasing carbon chain, the solubility decreases.
Carboxylic acids are WEAK acids. What does this mean?
Hydrogen atoms partially dissociate.
HCOOH (aq) —> H+ (aq) + HCOO-(aq)
What kind of reactions do Carboxylic Acids undergo with metals?
REDOX
forming a carboxylate salt and HYDROGEN GAS
What kind of reaction do Carboxylic Acids undergo with bases (alkalis, metal oxides and carbonates)?
NEUTRALISATION
Alkalis&Metal oxides form carboxylate salt and WATER
Carbonates form carboxylate salt and WATER AND CO2
What are the 4 derivatives of carboxylic acids?
esters, acyl chlorides, acid anhydrides, amides
What are derivatives?
when compounds can be hydrolysed to form their parent compound (CA).
How are esters formed?
CA warmed with alcohol with sulfuric acid catalyst - esterification
How are esters named?
ALCOHOL -yl + CARBOXYLIC ACID -oate
How are Acyl chlorides formed?
CA reacted with THIONYL CHLORIDE (SOCl2) to form acyl chloride + so2 + HCl (FUME CUPBOARD NEEDED!)
How are acyl chlorides named?
-oyl chloride
What are the 2 methods of hydrolysing esters?
- reflux with dilute aqueous acid
2. reflux with aqueous alkali
How does refluxing with dilute aqueous acid cause hydrolysis of esters?
dilute aq - water for hydrolysis
acid acts as a catalyst
What is formed form alkaline hydrolysis of esters?
carboxylate ion and alcohol
Why are acyl chlorides useful in organic synthesis?
They are very reactive and can easily be converted to carboxylic acid derivatives.
How do you form an ester with an acyl chloride?
React with alcohol.
Hydrogen chloride also formed.
With which alcohol can only acyl chlorides be reacted with in order to form an ester and why?
PHENOL
because cannot form ester with carboxylic acids as they’re not reactive enough.
Form phenyl ester + hydrogen chloride
What does a reaction of acyl chloride and water produce?
Carboxylic acid and hydrogen chloride.
What does a reaction of acyl chloride with ammonia and amine produce?
Ammonia - primary amide
amine - secondary amide
