26-Carbonyls And Carboxylic Acids Flashcards
Can you oxidise aldehydes
Yes
Product of oxidation of aldehydes
Carboxylic acid
Reaction conditions for oxidation of alcohols
o Reflux
o Acidified potassium dichromate (H2SO4 (dilute) / K2Cr2O7 )
o Dichromate (VI) ions turn from orange to green
Equation of oxidation of propan-1-ol in excess oxidising agent
Can you oxidise Ketones
No
Why can’t you oxide ketones
• Oxidation = addition of oxygen or loss of hydrogen
o ketones do not have the essential H-group need to be removed (cannot produce the water side product)
How to distinguish between ketones and aldehydes - basic
• lack of reactivity is one way to distinguish between aldehydes and ketones
How does the C=O influence reactivity
Difference between C=O and C=C
• C=C in alkenes is non-polar = reacts via electrophilic addition
• In carbonyls, the e- density lies closer to more electronegative O atom, resulting in a dipole: Cδ+=Oδ- = polar
• Nucleophiles are attracted to (and attack) the slight positive charge on the C atom in carbonyls.
• Aldehydes + ketones can therefore react with some nucleophiles via nucleophilic addition
Reactions of aldehydes
- oxidise to carboxylic acids
- reduction to primary alcohol
- formation of hydroxynitrile
Type of reaction between NaBH4 and aldehyde
Reduction
NaBH4
• Used as a reducing agent to reduce aldehydes and ketones to alcohols
What is NaBH4
Sodium tetrahydridoborate (III)
Side products of NaBH4 and aldehyde
BH3 and Na salt
Reaction conditions for reduction of aldehyde
warmed with aqueous NaBH4 - remember AQUEOUS
Draw reaction of reduction of aldehyde + side products
Draw reaction of reduction of aldehyde + side products
Nucleophilic Addition Mechanism for aldehydes and ketones:
Reaction of ketones
- reduction to form secondary alcohols
- formation of hydroxynitriles - HCN
Why is the reaction between HCN and aldehyde/ketone important
increases length of a carbon chain
Reaction conditions between HCN and ketone / aldehyde
H2SO4 and NaCN
What type of reactions is aldehyde / ketone with HCN
Nucleophilic addition
Why don’t we use HCN by itself
colourless + extremely poisonous liquid that boils slightly above room temp. Cannot be safely used in the lab
NaCN and sulfuric acid are used instead to generate the HCN in the reaction
Draw overall reaction for propanal and HCN
Nucleophilic Addition Mechanism for propanal and HCN
Nucleophilic Addition Mechanism for propanal and HCN - what is the nucleophile
:-CN
Lone pair + negative charge on the carbon!!
How to detect carbonyl compounds in BOTH aldehydes and ketones
Use Brady’s reagent
What is Brady’s reagent
2,4 – dinitrophenylhydrazine (2,4-DNP/2,4-DNPH) dissolved in methanol and sulfuric acid
Colour change of Brady’s reagent
• Brady’s reagent = pale orange solution
• In the presence of carbonyl group: yellow/orange precipitate
What is the precipitate formed in positive Brady’s reagent
2,4-dinitrophenylhydrazone
How to identify 2,4-dinitrophenylhydrazone
o Purify the precipitate – filtration (separates solid from solution)
o Solid is recrystallised to form a pure sample
o Melting point is measured and recorded, and compared to a data base.
How to distinguish between aldehyde and ketone
Tollens reagent
What is tollens reagent
o solution of silver nitrate in aq. ammonia
o colourless
How to use Rollins reagent
o warm gently in water bath
Colour change in tollens reagent
• In the presence of an aldehyde, a silver mirror (precipitate) is formed.
• Ketones will not react with Tollens’ reagent – remains colourless.
Oxidising agent in tollens
Ag+
Reduction + oxidation reaction in tollens
Why is -COOH soluble
• C=O and O-H bonds both polar
• Can form H-bonds with water
• Carboxylic acids with up to 4 C-ato
Trend in -COOH solubility
• Carboxylic acids with up to 4 C-atoms are soluble
• As the number of C-atoms increases, solubility decreases as the non-polar carbon chain has a greater effect on the solubility.
• Dicarboxylic acids are very soluble
Reactions of -COOH
- Redox reactions occur with metals
- Neutralisation reactions occur with bases
(metal oxides, alkalis and carbonates)
Both neutralisation reactions and redox reactions of -COOH form…
carboxylate salts
How to name carboxylate salts
ions are named by changing the –ic acid ending to -ate
Redox reaction of -COOH - describe overall
• Aqueous carboxylic acids react with metals to form hydrogen gas and a carboxylate salt
Observations of Redox reaction of -COOH
o Metal dissolves
o Effervescence
Write reaction between propanoic acid and magnesium - include state symbols
Neutralisation reaction of -COOH with metal oxides - describe overall
• Aqueous carboxylic acids reacts with metal oxides or alkalis to form a carboxylate salt and water
Neutralisation reaction of -COOH with carbonates - describe overall
• Aqueous carboxylic acids reacts with carbonates to form a carboxylate salt, water and carbon dioxide
Observations of neutralisation reaction of -COOH
o Metal oxide will dissolve
o Effervescence
o If -COOH is in excess = solid carbonates will dissolve
Write reaction for…
Propanoic acid + calcium oxide
Propanoic acid + sodium hydroxide
Propanoic acid + sodium carbonate
Test for carboxyl group
• Aqueous carboxylic acids reacts with carbonates to form a carboxylate salt, water and carbon dioxide
• Carboxylic acids are the only common organic group sufficiently acidic to react with carbonates
What’s common between carboxylic acid derivatives
Draw general structure of ester
Formation of ester - 2 ways
• alcohol + carboxylic acid -> ester + water
• also be formed from acid anhydrides
Reaction conditions of alcohol + carboxylic acid
warmed with H2SO4 catalyst
Draw reaction + name of products of propan-1-ol and Ethanoic acid
How to name esters
• Named after the parent carboxylic acid
-oic acid is replaced with –oate
• The alkyl chain attached to the O (from the alcohol) is added as the first word
(-ol becomes –yl)
Name these
Reaction of esters
• Hydrolysis of esters
o Acid + alkaline
Process of acid hydrolysis of esters + reaction conditions
• Ester is heated under reflux with dilute aqueous acid.
Products of acid hydrolysis of ester
carboxylic acid and an alcohol
Is acid hydrolysis reversible
Yes
Draw acid hydrolysis of ethyl propanoate
Process of alkaline hydrolysis of esters + products
• Ester is heated under reflux with aqueous hydroxide ions.
Products of alkaline hydrolysis of esters
carboxylate ion and an alcohol
What’s different if NaOH is used in alkaline hydrolysis
forms the sodium salt not the ion
Is alkaline hydrolysis reversible
No - irreversible
What happens to the sodium carboxylate salt …
needs to get protonated by an acid (such as HCl) to form the carboxylic acid (-COOH)
Draw alkaline hydrolysis of ethyl propanoate
Acid hydrolysis vs alkaline hydrolysis of esters
General structure of acyl chlorides
How to form acyl chloride
• Parent carboxylic acid reacted with thionyl chloride (SOCl2)
• Products = acyl chloride, SO2 and HCl
Reaction conditions for formation of acyl chlorides
• Reaction must be carried out in a fume hood
Draw reaction scheme for formation of acyl chloride
How to name acyl chlorides
• Named after parent –COOH
• -oic acid and replaced with –oyl chloride
Reactions of acyl chlorides + what is the type
• addition-elimination reactions:
o Reaction with alcohols and phenols to form esters
o Hydrolysis to form carboxylic acids
o Reaction with ammonia and amines to form amides
Reaction between acyl chloride and alcohol
Forms an ester
Why are acyl chlorides easily converted into -COOH derivatives
• Acyl chlorides are extremely reactive; and so are easily converted into –COOH derivatives
General equation for acyl chloride + alcohol
General reaction between acyl chloride + phenol
Draw reaction between propanoyl chloride + ethanol
Draw reaction for propanoic chloride + phenol - bit idk if this is right because it includes the conditions of NaOH and heat which is not what Saunders said
So conditions of acyl chloride and phenol
Possibly NaOH and heat
Draw mechanism for reaction of methanoyl chloride and ethanol
Draw mechanism for reaction of methanoyl chloride and phenol - again reaction conditions?
Can a carboxylic acid and phenol make an ester
• COOH are not reactive enough to form esters with phenols
• Acyl chlorides are much more reactive
Formation of carboxylic acid from acyl chlorides - type of reaction
Hydrolysis
General equation for Hydrolysis of acyl chlorides
Observations of hydrolysis of acyl chloride
• Very vigorous reaction
• Dense, steamy HCl fumes
Nucleophile of hydrolysis of acyl chloride
Water
Draw reaction of hydrolysis of propanoyl chloride
Draw NUCLEOPHILLIC ADDITION-ELIMINATION mechanism for the reaction between methanoyl chloride and water
What type of reaction is the Formation of primary amides from acyl chlorides
Condensation reaction
What happens if you react acyl chloride and ammonia - description
• The nitrogen atom in ammonia and amines has a lone pair of electrons which can be used to attack the carbonyl carbon atom in the acyl chlorides
Produce of ammonia + acyl chlorides
• The product is a primary amide (when reacted with ammonia) or secondary amide (when reacted with primary amines) AND ammonium chloride
Draw reaction between ethanoyl chloride and ammonia
General equation of acyl chloride + ammonia
Type of reaction for acyl chloride and ammonia
Nucleophilic addition - elimination
Draw reaction between propanoyl chloride and ammonia
Draw reaction between propanoyl chloride and methyl amine
Draw the mechanism for methanoyl chloride and ammonia
How to make a secondary amide
Acyl chloride + primary amine
Write general reaction for formation of secondary amide
Draw reaction between ethanoyl chloride and a primary amine
What is an acid anhydride
two carboxylic acid groups joined together.
Reactions of acid anhydrides
• React similarly to acyl chlorides with alcohols, phenols, water, ammonia and amines
How reactive are acid anhydrides
• Less reactive than acyl chlorides = useful
Reaction names of acid anhydrides
- esterification - with alcohols
Acid anhydride esterification reaction conditions
No acid catalyst needed
Write AND draw the reaction for acid anhydride and phenol AND name products
Draw reaction scheme for Ethanoic anhydride and Ethanol
