CHEMISTRY FORM 5 ORGANIC CHEMISTRY -CARBOXYLIC ACID AND ITS DERIVATIVES

CHEMISTRY FORM 5 ORGANIC CHEMISTRY -CARBOXYLIC ACID AND ITS DERIVATIVES

UNAWEZA JIPATIA NOTES ZETU KWA KUCHANGIA KIASI KIDOGO KABISA:PIGA SIMU:0787237719

ALSO READ;

1. O’ Level Study Notes All Subjects
2. A’ Level Study Notes All Subjects
3. Pats Papers

ORGANIC CHEMISTRY -CARBOXYLIC ACID AND ITS DERIVATIVES

These are organic compound with carboxylic group

as functional group.
They can be aliphatic or aromatic
Carboxylic group result after mixing carbonyl group and hydroxyl group.

ORGANIC CHEMISTRY -CARBOXYLIC ACID AND ITS DERIVATIVES

NOMENCLATURE OF CARBOXYLIC ACIDS

Example

i)   

Name Propanoic acid

ii)  

name 3 – Pentanoic acid Or Pent -3-enoic acid

iii) Name: 4 – aminopentanoic acid

 PREPARATION OF CARBOXYLIC ACID

i). OXIDATION

a) Oxidation of alcohol

Alcohol can be oxidised by strong oxidising agent like

andKMnO₄ to give carboxylic acid.

Where

  is a strong oxidising agent

EXAMPLE

If oxidising agent is weak or is in limited amount aldehyde is formed.

b/ Oxidation of carbonyl compound

Aldehyde can be oxidised easily to give carboxylic acids
i.e

Where

is oxidising agent

Example

Ketones resist oxidation but under drastic (vigorous) condition  it can form carboxylic acid

Example

 

NOTE
Methanoic acid cannot be prepared by this method (Oxidation method) . Since it can farther oxidised to

and

ii) HYDROLYSIS

Acyl compound can be hydrolysed to give carboxylic acid

b/ Acidic hydrolysis of Nitrile

Generally

Example

III FORM GRIGINARD REAGENT

Carbon dioxide reacts with Grignard reagent followed by acidic hydrolysis to form carboxylic acid.

Generally:-

 

Example

 

PHYSICAL PROPERTIES OF CARBOXYLIC ACIDS

Carboxylic  acid has highest boiling point among alcohol phenol carbonyl compound or easy other hydrocarbons with comparable molecular weight due to stronger hydrogen bonding existing between molecules of carboxylic acids.

Alcohol phenol carbonyl compound or any other hydrocarbons because they come capable of making strong hydrogen bonding with water and high polarity of carboxylic group.
I.e

Carboxylic acid is capable of undergoing dimerisation when it is in the hydrocarbon solvent it or any other similar solvent without hydrogen bonding

ACIDIC BEHAVIOUR OF CARBOXYLIC ACID

Carboxylic acids have higher acid strength than alcohol and phenol.

For aliphatic carboxylic acids strength depend on:-

i/ length of carbon chain

ii/ Type of substituent in carboxylic acid

The acidic strength decrease with increase in length of carbon chain due to strong positive effect exerted by longer alkyl group.

When substituent carboxylic acid is stronger electronegative element like halogens which exert –I acidic strength is increase due to following reason:-

i/ Negative inductive effect weakens

bond by reducing electron density in bond . Thus making easier to release hydrogen
proton.

ii/ Negative inductive effect stablised the carboxylate ion formed after releasing hydrogen proton by withdrawing ( partial
withdraw) – Very charged electron.

In aromatic acid the acidic strength depend on whether the substituent in benzene ring is activator or deactivator

When the substituent is activator the acidic strength with decrease and if it is deactivator the acidic strength will increase.

Example

Qn. Starting with less acidic arrange the following organic compound according to increase in acidic strength.

 

CHEMICAL REACTION OF CARBOXYLIC ACIDS

I. REACTION WHICH  INVOLVE – COOH (CARBOXYLIC GROUP)

a/ Reaction with sodium bicarbonate ( sodium hydrogen carboxylic acid reacts with sodium bicarbonate to give solid carbonate and bubble of

are formed.

Generally:-

Example

 

The reaction showed one of the differences between carboxylic acid on one side and alcohol and phenol on another. Ie alcohol and phenol do not react with

b) Reaction with alkali

Under this heading carboxylic acid reacts with alkali like

Generally

And

Example

i)

·         Phenol reacts with

and in the some way so the reaction gives of one of the similarities between alcohol and phenol.

c) Reaction with strong metals

·         Carboxylic acid react with strong metals to give carboxylic salt and hydrogen gas is evolved.

·         Generally

·        

Where M is the strong metal

Example

i/

ii/

Alcohol and phenol also react with strong alkaline metals

 

II. REACTIONS WHICH REPLACE

FROM CARBOXYLIC GROUP

a) HALOGENATION

Carboxylic acid react with halogenating agent like PX₅, PX₃ and SOX₂ to form acyl halide

Example

b) Reaction with alcohol (Ester formation)

Carboxylic acid reacts with alcohol in presence of acidic medium like sulphuric acid to form ester.

Generally:-

Example

i)

BUT

CHEMICAL TEST OF CARBOXYLIC ACIDS

a/ REACTION WITH ALCOHOL

Carboxylic acid reacts with alcohol in presence of acid

The reaction is very important in distinguishing carboxylic acid from phenol is phenol do not react with alcohol verifying that carboxylic acid is more acidic than phenol

b/ REACTION WITH SODIUM BICSRBONATE

Carboxylic acid reacts with sodium bicarbonate to give effervescence of carbon dioxide gas which turn lime water milky

The reaction gives another difference between carboxylic acid and phenol as phenol do not give effervescence acidic than phenol.

 

c/ REACTION WITH  

Ferric chloride test
carboxylic acid reacts with to give Iron (III) carboxylic (alkanoate ) which appear as buff colourled compound

The reaction is important in distinguish between alcohol, phenol and carboxylic acid

•  Alcohol give no change indicating that there is no reaction between alcohol and Iron (III) chloride
• Phenol give purple/violet coloured compound
• Carboxylic give buff coloured compound

f/ FORMATION OF ESTER
Acyl chloride reacts with phenol in presence of

to form ester

I.e.

Example

Acyl chloride also reacts with alcohol to form ester although with alcohol there is no need of NaOH_(aq)