Carbonyl And Carboxylic Acids Flashcards
What is the structure of bonds in carbonyl group
+ draw it
- carbonyl group consisted of C=O
This bond is polar due to different electronegativity of elements
Dipoles therefore on the Carbon (+) and Oxygen (-)
Draw the formation of double bond in carbonyl group
See notes
2 p orbitals on Carbon and oxygen which overlap to form a pi bond abounded and below plane. As oxygen is more electronegative that carbon the oxygen side of the overlap is larger
Draw the formation of double bond in carbonyl group
See notes
2 p orbitals on Carbon and oxygen which overlap to form a pi bond abounded and below plane. As oxygen is more electronegative that carbon the oxygen side of the overlap is larger
Describe production of aldehyde
Oxidation of primary alcohol
- distil off the aldehyde with acidified potassium dichromate (Cr2O7 2-/ H+)
- Cr2O7 2-/H+ turns from orange to green as it gets reduced
- distillate collected = aldehyde
Oxidation properties of carbonyl compounds
Aldehydes
- easily oxidised into acids
Ketones
- only oxidised under vigorous conditions
Ways to identify carbonyl group/ compounds
1) peak at 1400-1600 cm-1 on IR spec
2) orange precipitate formed with 2,4- dinitrophenylhydrazine
3) tollen’s test
Aldehyde = silver mirror produced Ketone = remains colourless
4) Fehling’s solution
Aldehyde = red precipitate formed. Ketone = no reaction
How is addition reactions different in carbonyl and alkenes
And why
Carbonyl
- C=O bond is polar
Attacked by nucleophiles
So nucleophilic addition
Alkene
- C=C bond is non polar
Attacked by electrophile
So electrophilic addition
Reaction for nucleophilic addition (reduction) of aldehyde and ketones
Reagent
Conditions
Mechanism
Products
Equation
Reagent - sodium borohydride NaBH4
Conditions - aqueous or alcoholic solution
Mechanism - nucleophilic addition
Products - aldehyde —> primary alcohol
Ketones —> secondary alcohol
Equation- CH3CHO + 2[H] —> CH3CH2OH
CH3COCH3 + 2[H] —> CH3CHOHCH3
Mechanism of nucleophilic addition (reduction) of aldehyde
See notes
Remember to put the dipoles on the carbon and oxygen
1) H- acts as nucleophile and attacks the C(+)
An electron pair from the C=C moves onto O asking it -ive
A lone pair on oxygen removes a proton from water
Overall, there is addition of hydrogen
Reaction of HCN and aldehyde
- reagents
-conditions
- products
- equation
-mechanism
Reagent = potassium cyanide with dilute acid
Conditions - reflux
Products - hydroxynitrile
Equation- CH3CHO + HCN —> CH3CH(OH)CN
Mechanism- nucleophilic addition
see notes
Draw the mechanism for reaction between HCN and aldehyde
Nucleophilic addition
1) draw the dipoles on carbon and oxygen
2) CN- acts as a nucleophile and attacks the slightly positive C
One of the C=O bond breaks; a pair of electrons goes onto the O
3) A pair of electrons is used to form a bond with H+
4) Overall, there is the addition of HCN
Compare the boiling points of carboxylic acids, aldehydes, ketones and alcohols
Carboxylic acid and alcohols have higher b.p that aldehydes and ketones
as aldehydes and ketones have no H group so don’t form H bonds which are strong and require more enters to break than London forces alone.
Explain the tollen’s test (silver mirror test)
+ results
Tollen’s reagent = ammoniacal silver nitrate solution
Acts as a mild oxidising agent and will oxidise aldehydes but not ketones
Silver(I) ion is reduced to silver
+ if positive (aldehyde) silver precipitate forms
Ketones remain colourless > negative result
How can you identify a carbonyl group with 2,4-dinitrophenylhydrazine? + how can you use this to identify aldehyde and ketone if tollen’s test not possible
If Brandy’s reagent added (yellow solution) & carbonyl group present
a yellow/orange precipitate will form
This orange precipitate can be recrystallised to from pure crystals
Then used to measure melting point
Then compare melting point to a database to determine aldehyde/ketone
How can you use Fehling’s solution to identify aldehyde/ketone
Method of hydrogenation (reduction) with hydrogen + aldehyde/ketone + conditions
+ equations
A nickel or platinum catalyst needed
Aldehyde
CH3CHO + H2 —> CH3CH2OH
Ketone
CH3COCH3 + H2 —> CH3CHOHCH3
Describe solubility of carboxylic acids
- very soluble in organic solvents
- soluble in water due to H bonds
- small ones dissolve readily in cold water
- as mass increases the solubility decreases
Describe boiling points of carboxylic acids
Increases as size increases - increased London forces
Carboxylic acids have high boiling points for their relative masses
Arise from inter- molecular hydrogen bonding due to polar O-H bonds
Additional inter-molecular attraction = more energy to separate molecules
How can carboxylic acid be prepared (5 ways)
Oxidation of aldehydes
Hydrolysis of esters
Hydrolysis of acyl chlorides
Hydrolysis of nitriles
Hydrolysis of amides
Reaction of carboxylic acid and carbonates
Produce salt and carbon dioxide
2 RCOOH + Na2CO3 —> 2ROO-Na+ +CO2 +H2O
Reaction of carboxylic acids and metals
Produced a salt and hydrogen
2RCOOH + Mg —> (RCOO-)2Mg2+ + H2
Reaction of carboxylic acids and metal oxides
Produces a salt and water
2RCOOH + MgO —> (RCOO-)2Mg2+ + H2O
Name some derivatives for carboxylic acids
identify the acyl group for each
Ester
Acyl chloride
Acid anhydride
Amide
Acyl group = R-C=O group
Esterification reaction
1) reagents needed
2) conditions
3) equation
Reagents
- alcohol (e.g methanol) & carboxylic acid (e.g ethanoic acid)
Conditions
- reflux
Equation
CH3OH + CH3COOH —> CH3COOCH3 + H20
How to identify ester
- using name
+ identifying alkyl group
Ester will end in -oate
E.g methyl ethanoate
Alkyl group R-COO-R
Name ester made from propanol and ethanoic acid
Propanol + ethanoic acid —> propyl ethanoate
The alcohol name is the start then the carboxylic acid get the **-oic acid88 suffix replaced with -oate
Compare the synthesis of ester
From carboxylic acid and acyl chlorides
Carboxylic acids - slow, equilibrium process
Acyl chlorides - faster, but more care must be taken
How do you name an acyl chloride from carboxylic acid
To name acyl chloride
1. Remove the -Oic acid suffix from carboxylic acid
2. Replace with -oyl chloride
E.g propanoic acid —> propanoyl chloride
Chlorination reaction with carboxylic acid
1) reagents
2) conditions
3) product
4) Equation
reagents
- thionyl chloride (SOCl2)
conditions
- dry conditions
product
- acyl chloride
equation
- CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl
Physical properties of esters
Colourless liquid
Insoluble in water
Unreactive
How to name acyl chloride
Name from the corresponding acid
- remove ic and add yl chloride
E.g ethanoic acid —> ethanoyl chloride
Methods to prepare acyl chloride from carboxylic acids
Method 1
Reagent - thionyl chloride SOCl2
Conditions - dry conditions
Equation - CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl
Method 2
Regent- phosphorus(V) chloride PCl5
Conditions- dry conditions
Equation - CH3COOH + PCl5 —> CH3COCl + POCl3 + HCl
Chemical properties of acyl chlorides
- colourless liquid which fumes in moist air
- gets attacked at the + carbon centre by neucleophiles
- nucleophiles include water, alcohols, ammonia and amines
- undergo addition-elimination reactions
- much MORE REACTIVE than Carboxylic acid and acid anhydrides
Reaction of water and acyl chlorides
1) products
2) condtions
3) equation
4) mechanism
products
- carboxylic acids and HCl
conditions
- cold water
equations
- CH3COCl(l) + H2O(l) —> CH3COOH(aq) +HCl(aq)
mechanism
- addition elimination
lone pair of electrons on H2O attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and H2O is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on H20 group is also releasaed to from COOH group
(See notes)
Reactions of Alcohols and acyl chlorides
1) products
2) conditions
3) equation
4)mechanism
products
- ester + HCl
conditions
- reflux in dry conditions
equation
- CH3COCl(l) + CH3OH(l) —> CH3COOCH3(l) + HCl(g)
mechanism
- addition elimination
lone pair of electrons on oxygen of H-O-CH3 attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and OH(CH3) is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on OH(CH3) group is also releasaed to from COOH group
Reaction of amines and acyl chlorides
1) products
2) conditions
3) equation
4) mechanism
products
- N-Substituted amine + HCl
conditions
- anhydrous
equation
- CH3COCl(l) + C2H5NH2(aq) —> CH3CONHC2H5(s) + HCl(g)
CH3COCl(l) + 2C2H5NH2(aq) —> CH3CONHC2H5(l) + C2H5NH3Cl(s)
mechanism
- addition elimination
lone pair of electrons on N of NH2R attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and NH2R is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on NH2R group is also releasaed to from C-NHR group
Reaction of ammonia and acyl chlorides
1) products
2) conditions
3) equation
4) mechanism
products
- amide + HCl
conditions
- low temperature and excess ammonia
equation
- CH3COCl(l) + NH3(aq) —> CH3CONH2(s) + HCl(g)
CH3COCl(l) + 2NH3(aq) —> CH3CONH2(s) + NH4Cl(s)
**mechanism*
- addition elimination
lone pair of electrons on N of NH3 attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and NH3 is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on NH3 group is also releasaed to from C(O)-NH2 group
Identification of amines
Function group - NH2
Naming - amine ending
can be primary, secondary, tertiary and ammonium salts = quaternary
