Module 6: Carbonyls, Carbocylic Acid, Acyl And Esters Flashcards
Carbonyls
What are carbonyl compounds
Aldehydes and ketones
Carbonyls
What is the carbonyl functional group
C=O
Carbonyls
Where is the carbonyl group in aldehydes
At end of chain
Carbonyls
What is aldehydes suffix
-al
Carbonyls
Where is the carbonyl group in ketones
In middle of group
Carbonyls
What is the suffix for ketones
-one
Carbonyls
How are carbonyls made
Oxidising alcohols
Carbonyls
What is used to oxidise alcohol s
Oxidising agent acidified potassium dichromate H+/K2Cr2O7
Carbonyls
How do you form an aldehyde
Partially Oxidise a primary alcohol in distillation
Carbonyls
How do you form a ketone
Fully oxidise a secondary alcohol in reflux
Testing for carbonyl compounds
What is used to test
2,4-DNP
Testing for carbonyl compounds
What does 2,4-DNP detect
Prescience of carbonyl functional group in aldehydes and ketones
Testing for carbonyl compounds
What is observed when 2,4-DNP in presence of carbonyl
Yellow-orange precipitate is formed
Testing for carbonyl compounds
How is 2.4-DNP used in practical
Dissolved in methanol and sulfuric acid as asa a solid is very hazardous and explosive
Testing for carbonyl compounds
What is 2,4-DNP
2,4-dinitrophenylhydrazine
Testing for carbonyl compounds
Practical method for testing carbonyls
- Add 5cm 2,4-DNP solution to clean test tube this is in excess
- Use pippete add 3 drops of unknown compound and leave to stand
- Is no yellow crystals form add few drops of sulfuric acid
- A yellow orange precipitate indicates presence of group
Testing for carbonyl compounds can 2,4-DNP test for carboxylic acid
No
Testing for carbonyl compounds
How can you identify compounds using 2,4-DNP
Orange precipitate is a derivative of carbonyl compounds each different produces a crystalline precipitate with a different melting point so can measure melting point and compare to known
Testing for carbonyl compounds
How can you distinguish between aldehyde and ketone
Using tollens reagent
Testing for carbonyl compounds
What does the tollens reagent use to distinguish
Fact that an aldehyde can be easily oxidised to a carboxylic acid and a ketone cannot
Testing for carbonyl compounds
What is tollens reagent
Clear solution of silver nitrate in aqueous ammonia
Testing for carbonyl compounds
What happens to tollens reagent in prescience of aldehyde
Silver mirror is formed
Testing for carbonyl compounds
Practicals for tollens reagent
- In clean test tube add 3cm^3 aqueous silver nitrate
- Add aqueous silver hydroxide to test tube until a brown precipitate of silver oxide is formed, Ag2O
- Add dilute ammonia solution until brown precipitate just dissolves to form a clear colourless solution this is tollens
- Pour 2 cm depth of unknown solutions to clean test tube
- Add equal volume of tollen
- Leave test tube to stand in beaker of warm water about 50’C for 10-15 mins then observe if silver mirror formed
Testing for carbonyl compounds
Ionic equation for use of tollens
Ag(NH3)2+ (aq) + e- —> Ag(s) + 2NH3 (aq)
Reactions of carbonyls
How can you change carbonyls ack to alcohols
Reduction
Reactions of carbonyls
What is used to reduce carbonyls (general)
Reducing agent
Reactions of carbonyls
What symbol represents reducing agent
[H]
Reactions of carbonyls
What are aldehydes reduced to
Primary alcohol
Reactions of carbonyls
Equation for reducing aldehyde
RCHO + 2[H] —> RCH2OH
Reactions of carbonyls
What are ketones reduced to
Secondary alcohol
Reactions of carbonyls
Equation for reducing ketone
RCOR’ + 2[H] —> RCHOHR’
Reactions of carbonyls
What reducing agent is often used
NaBH4 dissolved in water with methanol
(Sodium borohydride
Reactions of carbonyls
What kind of reaction is reduction
Nucleophilic additons
Reactions of carbonyls
Why is reduction nucleophilic addition
Nucleophile attacks molecule and extra group is added
Reactions of carbonyls
Description of mechanisms for recution
Reducing agent supplied hydride ions H- which has a lone pair of electrons so its a nucleophile and can attack the delta positive carbon on carbonyl group
Electron pair from C=O moves onto o making it -ve
Lone pair of oxygen removes proton from water and over there is addition of hydrogen
Reactions of carbonyls
What ions the other common reaction
Hydrogen cyanide
Reactions of carbonyls
What does hydrogen cyanide and carbonyls produce
Hydroxynitrile molecules (with -OH and -CN group )
Reactions of carbonyls
What type fo reaction is carbonyl and hydrogen cyanide
Nucleophilic addition
Reactions of carbonyls
What is hydrogen cyanide so what’s does it do in water
Weak acid so partially dissolves to form H+ and CN- ion s
Reactions of carbonyls
Partial dissociation of HCN
HCN <=> H+ + CN-
Reactions of carbonyls
Mechnaism for reaction with HCN
CN- ion attacks slightly positive carbon atom and donates a pair of electrons to it both electrons from double bond transfer to oxygen
H+ bond to oxygen to form hydroxyl group
Reactions of carbonyls
What is true for HCN
Highly toxic gas
Reactions of carbonyls
How is HCN used in laboratories
Solution of acidified hydrogen cyanide in fume cupboard
Reactions of carbonyls
For reduction what is the condition
Aqueous or alcoholic
Reactions of carbonyls
What is the condions of HCN
Reflux
Reactions of carbonyls
Equation for HCN with ethanal
CH3CHO + HCN —> CH3CH(OH)CN
Reactions of carbonyls
What is the reaction with HCN useful for
Adding an extra C atom to a chain as CN can then be converted to carboxylic acid or amines
Reactions of carbonyls
What is the reaction with HCN useful for
Adding an extra C atom to a chain as CN can then be converted to carboxylic acid or amines
Carboxylic acid
What is the functional group
-COOH
Carboxylic acid
What are carboxylic acids
Weak acids
Carboxylic acid
What happens to carboxylic acid in water
Partially dissociate into carboxylate ions and H+ ions
Carboxylic acid
Where does the equilibrium lie in the dissociation
Towards left as most of molecules don’t dissociate
Carboxylic acid
What are they often used as
In organic synthesis as starting materials or intermediates to make more useful compunds
Carboxylic acid
What is the name of the functional group
Carboxyl group
Carboxylic acid
What type of imf can they form
Hydrogen bonds
Carboxylic acid
Whycan they form hydrogen bonds
C=O and O-H bond polar and Lone electron pair on oxygen to hydrogen also to water molecules
Carboxylic acid
Are they soluble
Yes
Carboxylic acid
Why are they soluble
Form hydrogen bonds to water molecules
Carboxylic acid
What happens to solubility at number of carbon atoms increase and why
Solubility decreases as non polar carbon chain has a greater effect on the overalll polarity fo the molecule
Carboxylic acid
Why are carboxylic acids more soluble then alcohol
Can form two hydrogen bonds for every one molecule with a carboxyl group
Carboxylic acid
Are they strong acuds
No weak
Carboxylic acid
What happens when dissolved in water
Partially dissociate
Carboxylic acid
Partial dissociation of methanoic acid
HCOOH(aq) <==> H+(aq) + HCOO-(aq)
Carboxylic acid reactions
What type of reactions do they undergo with what
Redox reactions with metals
Neutralisation reactions with bases