Organic chemistry topic 17 ( aldehydes, ketones , carboxylic acids , esters,Acyl chlorides Flashcards
I want an aldehyde ? How do I make it ?
2
- distill and heat primary alcohol
- partial oxidation with potassium dichromate
- orange to greeen
How do I make a carboxylic acid?
?
2
- Reflux with potassium dichromate
- Primary ALCOHOL
- heat
- orange to green
Name all tests for aldehyde and ketone ?
4
1 ) fehlings and bens
2) Tollens
3) potassium dichromate
4) Brady’s
Positive test for Brady’s test ? What does it test for ? Condition? PPt? 4
- tests for carbonyl group = ketones and aldehydes
- dissolved in methanol , concentrated h2so4
- if it’s positive and aldehyde and ketone is present then = BRIGHT ORANGE PPt
What mechanism does the cyanide + aldehyde or ketone ? 1
- nucleophilic ADDITION
What reagents can we use for the cyanide reaction ?
2
- HCN
- KCN in cold alkaline solution
Positive test in fehlings and bens solution colour ?
1
- Blue to brick red
Outline tollens test ?
3
2 reagents and ppt?
- add silver nitrate and nh4cl should form a:
SILVER MIRROR PPT
When aldehyde is present
How do you form an Ester ?
3
- CONC ACID CATALYST ( HCL or h2so4)
- DISTILL CARB ACID + ALCOHOL
To obtain pure product you should:
Add na2co3 to remove any carb acid left( because it’s a reversible reaction )
How do we get a carb acid or alcohol from an ester?
4
What’s it called?
- REFLUX
- dilute hcl or h2so4
- acid hydrolysis
- reversible
How do we carry out base hydrolysis on an Ester ?
4
- REFLUX
- with weak base NAOH
- you get the carboxylate ion and an alcohol
- IRREVERSIBLE
How do we carry out triodomethane reaction ?
What does it test for ?
3
- tests for : methyl carbonyl group next to carbon
- add NAOH and I2 ∧heat
- yellow ppt should form for positive result
Why is the triodomethane reaction useful?
1
- shortens the carbon change by one
What mechanism is the liAlH4 reducing reaction ?
- nucleophilic addition
What is the liAlH4 ?
What does it do ?
- reducing agent
- converts the aldehyde and ketone back to the ALCOHOL !
How do I make ketone ?
3
A reflux secondary alcohol
Potassium dichromate
Orange to green
How can I oxidise a tertiary alcohol ?
1
Burn it
Solubility of carboxylic acids ( as the carbon chain increases) …
1
- the solubility decreases
Hydrolysis (acid) of Nitriles forms ?
- conditions ?
2
- Carboxylic acid + NH4CL
- reflux with dilute HCL
Carboxylic acid + NAOH —>
With carbonates ?
2
- salt and water
Sodium ethanoate
With carbonates forms :salt, water and CO2
How can we reduce Carboxylic acid ? What do we use ?
( why in dry ether )
4
- liAlH4 in DRY ETHER( so no H+ is present otherwise; H- + H+ —> H2 ( BANG) )
- you can reduce the Carboxylic acid to a primary alcohol!
Functional group of Ester ?
1
-COO-
Ester are made by ? Used for ? Conditions and reaction ? 4 two ways if making an ester
- Carboxylic acid and alcohol (or acyl chloride and alcohol,non reversible reaction and produces hcl too )
- reversible reaction
- REFLUX & CONC sulfuric acid catalyst
- forms Ester and water !
- used for flavourings ( and scents )
- pear , banana , pineapple ( etc )
In the hydrolysis of an Ester why do we use DILUTE h2so4?
3
- it’s an equilibrium reaction
-Carboxylic acid+alcoholEster + water
If the catalyst is dilute the water concentration rises and the equilibrium shifts to the LHS forming the acid and water !
How is base hydrolysis of an Ester more efficient than acid hydrolysis ?
3
How do you obtain a carboxylic acid ?
- it’s not reversible
- used dilute NAOH
- you get Carboxylate ion and alcohol
- you have to react it with dilute HCL to obtain a carboxylic acid
How are polyesters formed ?
1
- condensation reaction
What are the requirements to form a polyester ?
What is removed from each ?
4
- Dicarboxylic acid
-Diols
( so 2 groups on each )
Note:
-from carboxylic acid —> OH IS ALL REMOVED
-from Diol —> ONLY H IS REMOVED
What’s the functional group for acyl chlorides ?
Formula ?
What makes them reactive ?
3
-COCL-
Formula : C(n) H(2n-1)OCl
-they easily lose their Cl
Acyl chloride + water —>?
1
- carboxylic acid and HCL
Acyl chlorides + alcohols =>
1
ESTER + HCl
Acyl chlorides + NH3=>?
1
AMIDE + HCL
Acyl chlorides + AMINES =>?
1
N substituted AMIDE + HCl
What happens in Sn1?
What kind of isomer does it form ?
What kind of products take sn1?
3
1- group breaks off leaving planar intermediate
2-nucleophile attacks ( it can attack from either side of the intermediate )
3-this gives rise to 2 optical isomers
SN1 is usually taken by tertiary halogenoalkanes
What happens in SN2?
What molecule takes SN2?
Isomers ?
4
1- one step reaction
2-nucleophille always attack opposite side to the leaving group of the TRANSITION STATE
3-only one OPTICALLY ACTIVE SINGLE ENANTIOMER
This rotates the plane polarised light differently to the reactant
What’s an ENANTIOMER?
2
-optical isomers produced by chiral carbon
What’s a Racemic mixture ?
2
A mixture which contains equal quantities of each ENANTIOMER of a chiral compound
Aldehydes and ketone have low boiling points becauseeeee ….
1
No hydrogen bonding within themselves
Why are short aldehydes and ketones soluble in water ?
1
They form Hydrogen bonds with water
Why are long chain aldehydes and ketones not soluble In water ?
3
- long carbon chain = hydrophobic is it disturbs hydrogen bonds within the water molecule
- if the hydrocarbon chain is long enough then the VDW’s forces will be great and so will the hydrogen bonding
whats the strongest intermolecular bond in an aldehyde or ketone-why ? 2
-C=O is a polar bond .
-This means it can form Permanent DIPOLE -DIPOLE
forces
why are long chain aldehydes less soluble in water ?
4
- in aldehyde solubility is due to the hydrogen bonding between the C=O and the balance between the hydrophobic carbon chain
- in longer aldehydes , the Hydrophobic region is bigger meaning that they aren’t soluble in water.
Reducing with LiAlH4 in aldehydes or ketones is the same as … 1
- adding H2 to the double bond .
What does Tollen’s reagent do to an aldehyde? 1
oxidise it to a Carboxylic acid
whats a positive test in the iodoform test - triiodomethane reaction ?
yellow ppt of CHI3 always produced .
checks for —ch3—c=o group
Why does sodium ethanoate have a higher melting point than Ethanoic acid ? 2
- sodium ethanoate has ionic bonding and this is harder to over come than the hydrogen bonds between Ethanoic acid molecules .
hydrolysis of a nitrile with aq hcl = ?
2
1)R—-COOH + NH4Cl
so ammonium chloride + carb acid
hydrolysis + heat a nitrile with dilute NaOH
2
R—CO2- Na+ + NH3
carboxylate ion + ammonia
why do we need dilute acid to hydrolyse an ester yet a concentrated acid to make an ester ?
3
we need dilute HCl hydrolyse ester as it is reversible reaction.
ester+ water acid+alcohol
so if water is in excess than equilibrium shift to the RHS so hydrolysis happens quicker !
hence why dilute ( higher concentration of water molecules ) acid catalyst is used .
