Chapter 26 Carbonyls Flashcards
What is a carbonyl compound, aldehyde and ketone?
Carbonyl- any compound contain a C=O
Aldehyde- C=O at the end of a compound (aka 1 hydrogen still attached to the carbon of the C=O)
Ketone- C=O anywhere other than the end of a compound
How do you name aldehydes and ketones?
Aldehydes- end with al, if prefix, formyl
Ketones- end with one, if prefix, oxo
How can aldehydes be oxidised, give an equation?
React with Na2Cr2O7 and H+, heat under reflux, carboxylic acid
Aldehyde + [O] —/ Carboxylic Acid
Why can ketones not be oxidised?
The contain no hydrogens that can be lost, directly attached to the C of the C=O
(Oxidation=loss of hydrogen as well)
Why can carbonyl compounds undergo nucleophilic addition?
C=O polar, slight positive of the carbon
Nucleophiles attack carbon, lone pair upon oxygen, can be easily protonated
What are the conditions, reagents, and equation for the reduction of a carbonyl?
Carbonyl + 2[H] –/ Alcohol
React with aqueous NaBH4 (Effectively hydride ions, need water)
What are the conditions and reagents for producing a hydroxynitrile from a carbonyl?
React with H2SO4/NaCN to produce HCN
In situ as HCN poisonous
Protonated by acid
What compound detects carbonyl compounds and what occurs? Give the specific components on the reactant.
2,4 DNP in methanol and Sulphuric acid / Brady’s reagent
Pale orange to a yellow/orange precipitate
Condensation reaction between hydrazine and carbonyl, with C=O replaced with C=N
How can using 2,4 DNP help determine the identity of the carbonyl compound?
The precipitate is a 2,4 dinitrohydrozone derivative
Purify by filtering under reduced pressure, recrystallising, filter again
Check the melting point of the compound and compare to the data base
How can you detect an aldehyde instead of a ketone?
Add Tollen’s reagent, AgNO3 in NH3
AND HEAT IN A WATER BATH
Aldehydes can be oxidised into carboxylic acids, Ag+ is reduced to Ag, acting as oxidising agents
So a silver mirror is produced
Ketones cannot be oxidised further so the solution remains colourless
What are carboxylic acids? How do you name carboxylic acids?
R- COOH
Always the highest priority, only carboxy on a side chain
-Oic Acid, no need to number at starting from 1
e.g 3-hydroxybutanoic acid
Why are carboxylic acids soluble in water?How does solubility change as the carbon chain gets longer?
Hydroxyl and Carbonyl can form hydrogen bonds with water
Increasing the chain length increases the contribution of the non-polar carbon chain, contribution of polar carboxyl decreases
So less soluble
What happens when carboxylic acids are in water?
They partially disassociate, weak acids
Resonance stabilised carbanion
What are the acid reactions of carboxylic acids?
React with a metal to form a salt and hydrogen, fizzing, disapears
React with metal oxides/hydroxides to form salt and water, disappears
React with metal carbonates to form salt, CO2 and water- fizzing, disappears- organic test for COOH
What are esters? How do you name them?
R-COO-R’
Chain of C=O is -oate, other side is alkyl chain
If functional groups on chain, start numbering from carbon joined to the O, treat as two separate chains, two different numbers
e.g methyl propanoate
3-chloro-2-methybutyl 2-bromopropanoate
How do you form esters from alcohols and carboxylic acids?
React with acid (sulphuric) catalyst
Forms ester and water, condensation reaction
Reflux, warm
What is acid hydrolysis of esters?
React the ester with aqueous sulphuric acid and heat under reflux
Reforms alcohol and carboxylic acid
Reversible reaction, same products as previous reactants and catalyst
What is the alkaline hydrolysis of esters?
Heat under reflux with NaOH
Forms a carboxylate salt (if named hydroxide used) or carboxylate ion, resonance stabilised
And alcohol
Irreversible
Also called saponification
What are acid anhydrides? How do you name acid anhydrides?
R-C-OOOC-R’
If the same on either side, just once, ethanoic anhydride
If different list in alphabetical
e.g Methanoic Propanoic Anhydride
How can you produce an ester using an acid anhydride?
Ethanoic Anhydride + Butan-1-ol —/ Butyl Ethanoate + Ethanoic Acid
Produces ester and carboxylic acid, no catalyst needed
How can you produce an ester using an acyl chloride?
Ethanoyl Chloride + Butan-1-ol –/ Butyl Ethanoate + HCl
No catalyst, ester + HCl
How can you make an ester, 3 ways?
Alcohol + Carboxylic Acid
Alcohol + Acid Anhydride
Alcohol + Acyl Chloride
What can form an ester with phenol?
Acid Anhydrides and Acyl Chlorides- reactive enough
NOT Carboxylic Acids
What is the order of reactivity of carbonyls?
Carboxylic Acid < Acid Anhydride < Acyl Choride
How can you make acyl chlorides from carboxylic acids? Give an equation
Reaction with thionyl chloride SOCL2
Carboxylic acid + SOCl2 —/ Acyl Chloride + SO2 + HC
Needs to be done in a fume hood, toxic gases
What is an acyl chloride? How do you name them?
C=O bonded to a more electronegative element
Acyl Chloride- C=O bonded to Cl
Very reactive
Ethanoyl Chloride
What are the main 3 reactions of acyl chlorides and acid anhydrides?
With water to form carboxylic acids
With amines/NH3 to form amides
With alcohols to form esters
What is the reaction between an acyl chloride and ammonia?
Acyl Chloride + 2NH3 —/ Primary Amide + NH4Cl
What is the reaction between an acyl chloride and an amine?
Acyl Chloride + 2CH3NH2 —/ CH3NHCOR + CH3NH3+Cl-
Acyl Chloride + Amine —/ Secondary Amide + carbammonium salt
What is the reaction between an acyl chloride and water?
Acyl Chloride + H2O —/ Carboxylic Acid + HCl
vigorous, steamy toxic fumes
How are carboxylic acids reduced, and what is formed?
LiAlH4
Form primary alcohols
Do carboxylic acid derivatives react with 2,4 DNP?
No, only aldehydes and ketones
No other carbonyls as resonance stabilised by the lone pair
Can carboxylic acids react with ammonia?
Yes- normally acid-base reaction
Rate too slow normally to form amides but think about condensation polymers, polyamides
Depends on conditions
What are the steps for using 2,4 DNP?
Brady’s reagent, 2,4DNP in methanol and sulphuric acid
Add an excess to a test tube
Then adda few drops of the organic compound and see if crystals form
Then add H2SO4 if crystals still do not form
An orange precipitate suggests a carbonyl
Why does methanoic acid dissolve in water? How does this relate to the methanoate ion?
Polar O-H bond and C=O, forms hydrogen bonds with water
Methanoate ion not rly a large factor when it comes to dissolving as so few disassociate
