Carbonyl group compounds and reactions

Intro to compounds containing the carbonyl (>C=O) group, also alcohols, reactions of alcohols, aldehydes, carboxylic acids, ketones and esters

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Introduction

What do carboxylic acids, aldehydes, ketones and esters have in common?

What is the functional groups of:

Carboxylic acids?

Alcohols?

Aldehydes?

Ketones?

Esters?

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Carboxylic acids, Aldehydes, and Ketones all contain the carbonyl group (>C=O)

The functional group of:

Carboxylic acids is -COOH

Alcohols is -OH

Aldehydes is -CHO

Ketones is >C=O

Esters is -COOR

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Oxidation of alcohols

Reagent: acidified potassium dichromate (IV) , K2Cr2O7

Orange-green colour change as dichromate ion is reduced to green Cr3+ cation

oxidant represented by [O] in eqn.

Primary Alc. is oxidised to an Aldehyde and then (if refluxed) a carboxylic acid

Secondary Alc. is oxidised to a ketone

Tertiary Alc. is not easily oxidised (but a stronger reagent eg acidified KMnO4 can break C=C bond, producing a mixture of compounds w. shorter carbon chains)

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Tests to distinguish b/n aldehydes and ketones

These are redox reactions

both give ve tests for aldehydes

Fehling's soln.

soln. turns from blue to brick red ppt.(precipitate)

as blue Cu 2+ ions are reduced to CuO which is brick red

Tollens' reagent

silver mirror effect around test tube

as Ag+ ions are reduced to Ag

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Reactions of Aldehydes and Ketones

Nucleophilic addition eg with Hydrogen Cyanide

The nucleophile ( CN:- remember the lone pair) attacks the slightly +ve charge on the C atom of the C=O grp

Reaction intermediate has an O: atom w. a -ve charge

an e pair from this atom forms a covalent bond w. a H ion, forming a hydroxynitrile


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Reduction of acids/aldehydes and ketones to Alcoho

Oxidation reactions of alcohols to make acids/aldehydes/ketones can be reversed by reduction.

a strong reducing agent is needed eg NaBH4 in water, or LiAlH4 in non-aqueous solvent eg methanol

reducing agent represented as 2[H] in equation

acid/aldehyde reduced to primary alc.

ketone reduced to secondary alc.

These are also nucleophilic addition reactions

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Esters

Esters are formed when an alcohol and a carboxylic acid react together in the presence of a strong, conc. acid catalyst eg H2SO4, with Na2CO3 soln to neutralize excess acid

Known as esterification

This is also a condensation reaction as a water molecule is released from where the acid and alcohol join.

names are eg methyl ethanoate (methanol + ethanoic acid)

Esterification reactions are reversible, low yield (therefore there is an equilibrium)

reverse reactions are hydrolysis (splitting with water) forming an Alc. and a carboxylic acid

Esters have a fruity smell/flavour

test for an alcohol by making an ester (+ve test = 'fruity smell')

USES: confectionery, solvents and as plasticisers (molecules that reduce rigidity eg in PVC)

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Soaps

Soaps are salts of long-chain carboxylic acids (fatty acids) produced by ester hydrolysis

Fatty acids are derived from lipids which are naturally occurring tri-esters

Fats and oils are hydrolysed to produce soaps by boiling w. NaOH (aq) (called saponification)

glycerol is a by-product of this and has uses in pharmaceutical/cosmetic industries

soaps are anionic detergents. They emulsify oils because the -vely charges carboxyl grp is hydrophilic (attracted to water) and the +vely charged hydrocarbon chains are attracted to oil, not water (hydrophobic). When soap is added to an oil-water mixture and this is then shaken, the oil is broken up into small droplets.

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