Carbonyl, carboxylic acids and esters

Conditions for aldehyde oxidation:

60°

____ are easily oxidised but ____ are not

aldehydes

ketones

Aldehydes and ketones can be reduced to alcohols by ____

sodium tertahydridoborate (III) NaBH₄ and heat and H20

equation for reaction between a ketone and NaBH₄

CH₃COCH₂CH₃ + 2［H］→ CH₃CH(OH)CH₂CH₃

Aldehydes and ketones contain a ____ bond

polar C=O

Where is the partial positive and negative charge?

+ CARBON

- Oxygen

What part of ketones or aldehydes can be attached by nucleophiles?

partially positive carbon

Mechanism for nucleophilic addition on aldehyde and ketones with :H- ion:

Hydride ion, from NaBH₄:

Ketones/aldehydes reaction with hydrogen cyanide + what forms?

hydroxynitride

cn-

how is reaction carried out?

in alkaline solution containing potassium cyanide. alkaline solution is needed to generate nucleophile :CN-

How can presence of C=O can be detected?

2,4-dinitrophenylhrazine (2,4-DNP)

How to make bradys reagent and what colour is it?

4-DNP is dissolved in methanol + sulphuric acid

pale orange solution

What forms if a carbonyl group is present if Brady’s reagent is added?

orange ppt

ppt can be used further to identify original aldehyde?

filtering, purifying and drying, measuring melting temperature

What is the other name of Tollen’s reagent?

silver nitrate in aq ammonia

What happens when reacted with aldehyde?

colourless solution of silver complex is reduced to metallic silver when it oxidises an aldehyde.

Silver mirror

equations for tollens reagent

Ag⁺ (s) + e^- —> Ag (s)

R-C(H)=O +［O］—> R-C(OH)=O

Why do shorter chain carboxylic acids dissolve readily in water?

form hydrogen bonds with water

Solubility of carboxylic acids ____ as chain length ____ because ____

decreases

increases

chain is hydrophobic

Why is -OH group in carboxylic acids more acidic than -OH group in alcohols?

C=O group pulls electrons away from -OH group, making hydrogen atom more partially positive and therefore easier to remove

what forms when H is removed from carboxylic acid group?

charge and double bond character is shared evenly across both oxygen atoms

equation of carboxylic acid reaction with alkali:

CH₃COOH _(aq) + NaOH _(aq) —> CH₃COO^-Na^{+ _(aq)} + H₂O

equation of carboxylic acid and metal oxide:

2CH₃COOH_(aq) + CaO _(s) —> (CH₃COO^-)₂Ca²⁺ + H₂O

equation of carboxylic acid and metal carbonate:

2CH₃COOH_(aq) + CaCO_{3 (aq)} —> (CH₃COO^-)₂Ca²⁺ +CO₂ + H₂O

What is used to differentiate between carboxylic acids and phenols?

Metal carbonates as carboxylic are acidic enough

Hydrolysis definition:

reaction were water breaks chemical compound into compounds. H and OH in water molecules become incorporated into 2 compounds

ester display formula

acyl chloride display formula

acid anhydride display formula

amide display formula

carboxylic acids react with alcohols to make an ___ + conditions needed

ester

heat + acid catalyst

alcohol and carboxylic acid to ester

how are esters named?

1st part: ____thyl derived from alcohol

2nd part: ____oate derived from acid

Hydrolysis is the opposite of _____

esterification

How to carry out acid hydrolysis?

ester+ water+ warm + sulphuric acid catalyst

reaction doesn’t go to competition

CH₃COOCH₂CH₃ + H₂O —>< CH₃COOH + CH₃CH₂OH

What is alkaline hydrolysis?

1st reaction goes to completion, rather than reaching equilibrium

Forms a carboxylate salt

CH₃CH₂COOCH₃ + NaOH —> CH₃CH₂COO^-Na⁺ + CH₃OH

carboxylate salt can be made in carboxylic using dilute acid

CH₃CH₂COO^- + H⁺ —> CH₃CH₂COOH

Acyl chloride group

COCl

What suffix is used for things with acyl chloride group?

-oyl chloride

How are acyl chlorides formed?

carboxylic acids + thionyl chloride (SOCl₂)

equation for formation of acyl chloride

CH3CH2COOH + SOCl2 —> CH3CH2COCl +SO2 + HCl

What are the partial charges of acyl chlorides?

carbon atom of C=O group is partially pos and O and Cl are partially neg

what is leaving group of acyl chlorides and why?

Cl because C-Cl bond isn’t very strong

what are acyl chlorides susceptible to?

nucleophilic attack, in addition-elimination reaction

general equation of substitution of chlorine atom by nucleophile:

ROCl + Nu^- —> RCONu + Cl^-

How does acyl chloride react with water?

vigorous

equation for acyl chloride with water

CH3COCl —H20—> CH3COOH + HCl

acyl chlorides reaction with alcohols?

react rapidly

produce ester and misty fumes of hydrogen chloride

e.g. of reaction of acyl chlorides and alcohol

CH3COCl —CH3OH—> CH3CH(O)OCH3 + HCl

ethanoyl chloride —> methyl ethanoate + hydrogen chloride

acyl chlorides reaction with phenol

reactive enough to react with acyl chlorides

CH3COCl + HO(C6H5) —> CH3COO(C6H5) + HCl

ethanoyl chloride + phenol —> phenyl ethanoate + hydrogen chloride

acyl chlorides reaction with ammonia

nitrogen atom in ammonia has lone pair, used for nucleophilic attack on C=O group. Produces amide and hydrogen chloride

equation of acyl chloride and ammonia

CH3COCl —NH3—> CH3CONH2 + HCl

what further reaction occurs when hydrogen chloride reacts with excess ammonia

HCl + NH3 —> NH4Cl

overall reaction:

CH3COCl —2NH3—> CH3CONH2 + NH4Cl

ethanoyl chloride —> ethylamide + ammonium chloride

amide vs amine

reaction of amines and acyl chloride

react same way as with ammonia

product is substituted amide (N-substituted amide)

equation of amines and acyl chloride

CH3CH2COCl + :NH2(CH3) —> CH3CH2C(O):NHCH3 + HCl

propanoyl chloride + methylamine —> N-methylpropanamide + hydrogen chloride

if secondary amine is used then product contains two substituted alkyl groups equation:

CH3CH2COCl + :NH(CH3)CH3 —> CH3CH2C(O):N(CH3)CH3 + HCl

N,N-dimethylprioanamide

What happens if tertiary amine?

reaction does not happen

General Mechanism of aldehyde with nucleophile:

General Mechanism of a ketone: 

Addition of HCN to carbonyl compounds + name:

• The products of the reaction are hydroxynitriles

  • The nitrile group is the priority functional group so it is attached to carbon 1 and results in the suffix -nitrile

  • The hydroxyl group is not the priority functional group so the hydroxyl group is named using the hydroxy- prefix, rather than the -ol suffix

Reduction of Carbonyls:

There are a large number of reducing agents which will reduce both an aldehyde and a ketone to an alcohol

Aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols

Possibly the most common reducing agent for this is sodium tetrahydridoborate, NaBH4

You may also see this named as sodium borohydride in some sources

In an aqueous solution, NaBH4 generates the hydride ion nucleophile, :H-

The hydride ion will reduce a carbonyl group in an aldehyde or a ketone, but is not strong enough to reduce a C=C double bond

This is because it is attracted to the C in the C=O bond, but is repelled by the high electron density of the C=C bond

When this reaction takes place, it is an example of a nucleophilic addition reaction

Carboxylic acid to a primary alcohol:

Aldehyde to a primary alcohol:

Ketone to a secondary alcohol:

__________ is a reagent which detects the presence of carbonyl compounds 

2,4-dinitrophenylhydrazine (also known as 2,4-DNP)

The carbonyl group of aldehydes and ketones undergoes a ________ reaction with 2,4-dinitrophenylhydrazine

condensation

The product formed when 2,4-DNPH is added to a solution that contains an aldehyde or ketone is a ______ which can be purified by recrystallisation

deep-orange precipitate

The _______ of the formed precipitate can then be measured and compared to literature values to find out which specific aldehyde or ketone had reacted with 2,4-DNPH

melting point

Tollens' reagent contains the silver(I) complex ion ____

[Ag(NH₃)₂]⁺

Tollens' reagent forming

aqueous ammonia is added to a solution of silver nitrate

If gently warmed with Tollens' reagent, an ______ will become oxidised

aldehyde

how are esters made?

condensation reaction between a carboxylic acid and alcohol with concentrated H₂SO₄ as catalyst

what is another way of esterification?

• Esterification can also take place by reacting acid anhydrides with alcohols at room temperature

• The acid anhydrides are more reactive than carboxylic acids

• The reaction is not reversible and a higher yield is achieved.

Esters can be _____ to reform the carboxylic acid and alcohol by either dilute acid or dilute alkali and heat

hydrolysed

When an ester is heated under reflux with dilute acid (eg. sulfuric acid) what occurs + why?

an equilibrium mixture is established as the reaction is reversible

heating the ester under reflux with dilute alkali (eg. sodium hydroxide) is an _____ reaction as the ester is fully hydrolysed and what forms?

irreversible

sodium carboxylate salt which needs further acidification to turn into a carboxylic acid

hydrolysis of acyl chlorides

formation of a carboxylic acid and HCl 

addition-elimination reaction:

• A water molecule adds across the C=O bond

• A hydrochloric acid (HCl) molecule is eliminated

Formation of esters from Acyl chlorides

react with alcohols and phenols to form esters

reaction with phenols requires heat and a base

Esters can also be formed from the reaction of carboxylic acids with phenol and alcohols however, this is a slower reaction as carboxylic acids are less reactive and the reaction does not go to completion (so less product is formed)

The esterification of acyl chlorides is also an addition-elimination reaction

• The alcohol or phenol adds across the C=O bond

• A HCl molecule is eliminate

Formation of amides

• Acyl chlorides can form amides from their condensation reaction with amines and ammonia

• 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

• The product is a primary  amide (when reacted with ammonia) or secondary amide (when reacted with primary amines)

• This is also an example of an addition-elimination reaction as

  • The amine or ammonia molecule adds across the C=O bond

  • A HCl molecule is eliminated

how to make ester into carboxylic acid hydrolysis?

heat + reflux + dilute acid

CN —> COOH

aqueous acid e.g. HCl(aq)/H2SO4(aq)