Alcohols, Esters and Carboxylic acid
Alcohols, Esters and Carboxylic acid
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Alcohols
Alcohols
Alcohols are compounds with the functional group OH and they can be classified as primary, secondary or tertiary depending on the number of alkyl groups attached to the carbon atom holding the OH group
Alcohols are compounds with the functional group OH and they can be classified as primary, secondary or tertiary depending on the number of alkyl groups attached to the carbon atom holding the OH group
Physical properties of alcohols
Physical properties of alcohols
Alcohols are soluble in water because they can form hydrogen bonds with water molecules.
However, the solubility decreases as the number of carbon atoms increase. This is because the presence of long hydrocarbon tail disrupts the effectiveness of hydrogen bonding
Alcohols have higher boiling points than alkanes with similar Mr due to the presence of hydrogen bonding
The boiling point increases as the number of carbon atoms increases because there are more electrons, hence more energy is required to overcome these forces
Reactions of alcohols
Reactions of alcohols
Combustion
Combustion
Reagent: Oxygen supply
Condition: Heat
Product: Carbon dioxide and water
Alcohols undergo complete combustion under excess oxygen to give carbon dioxide and water
C2H5OH + 3O2 = 2CO2 +3H2O
When oxygen is limited, carbon monoxide and carbon soot might be formed
Dehydration
Dehydration
Reagent: Excess concentrated sulfuric acid, H2SO4 or hot aluminium oxide, Al2O3
Condition: Heat at about 170*c
Product: Alkenes
When ethanol is heated with concentrated sulfuric acid, the alcohol is dehydrated, a water molecule is removed from the alcohol and ethene is produced
CH3CH2OH = CH2=CH2 + H2O
During dehydration, the OH group gets removed together with a hydrogen atom from the next door carbon atom
Alternatively, dehydration can be carried out by passing ethene through hot aluminium oxide. The ethene gas is then produced and collected over water
More than one product can be formed and also the possibility of geometric isomers in the alkanes. This is due to different hydrogen being removed form the alcohol
POOR GETS POORER
Reaction with sodium metal, Na
Reaction with sodium metal, Na
Reagent: Sodium metal, Na
Condition: Room temp
Product: Alkoxides and hydrogen gas (nitrile to amine)
Acids react with metals to produce hydrogen gas and a salt. Alcohols are very weak acids, so they undergo this reaction as well
When sodium metal is added to ethanol, the sodium metal sinks and bubbles of hydrogen gas are observed and the salt formed is sodium ethoxide, a white solid
2CH3CH2OH + 2Na = 2CH3CH2O-Na+ + H2
This reaction can be used as a test for hydroxy, OH group because if bubbles are observed, then a hydroxy group are present
Substitution to give halogenoalkanes
Substitution to give halogenoalkanes
The OH group of the alcohol can be substituted by a halogen to produce a halogenoalkane. The halogen can be obtained from these sources:
-Hydrogen halide, HX
-Phosphorus halide, PCl5 or PBr3 or PI3
-Thionyl chloride, SOCl2
With hydrogen halide, HX:
-The alcohol is refluxed with sodium halide, NaX and concentrated sulfuric acid, H2SO4 to produce hydrogen halide, HX
NaX + H2SO4 = HX + NaHSO4, X= Cl/Br/I
Phosphoric(V) acid is used for iodine instead of concentrated sulfuric acid
-The hydrogen halide then react with alcohol
CH3CH2OH + HX = CH3CH2X + H20
With phosphorus halide, PCL3, PCL5, PBr3, PI3 ( hot concentrated NaOH in aq is used)
-Alcohol react with phosphorus(V) chloride to produce a halogenoalkane, white fumes of hydrogen chloride is observed
CH3CH2OH + PCL5 = CH3CH2Cl + POCl3 + HCl
This can be used as a test for the hydroxy, OH group
-For phosphorus(III) halides, a halogenoalkane is also obtained. The phosphorus halides are prepared in situ by mixing red phosphorus and the halogen, requires heat
3CH3CH2OH + PX3 = 3CH3CH2X + H3PO3
With thionyl chloride, SOCl2
-Alcohols react with thionyl chloride to produce a halogenoalkane, sulfur and hydrogen chloride gas, very efficient, under refluxed
CH3CH2OH + SOCl2 = CH3CH2X + SO2 + HCl
Oxidation
Oxidation
Reagent: acidified potassium dichromate(VI), K2Cr2O7 or acidified potassium manganate(VI), KMnO4
Condition: Heat under reflux
Product: Primary alcohol- Aldehydes and carboxylic acids
secondary alcohol- Ketones
Tertiary alcohol- cannot be oxidised
For primary alcohols, if the alcohol is used in excess and the product formed is distilled off as soon as possible, aldehydes are formed
CH3CH2OH + [O] = CH3CHO + H2O
If the alcohol is limited and heated under refluxed, the primary alcohol will be oxidised to carboxylic acids.
CH3CH2OH + [O] = CH3COOH
For secondary alcohols, the secondary alcohol will be oxidised to ketone
CH3CH(OH)CH3 + [O] = CH3COCH3 + H2O
For tertiary alcohols, they will not be oxidised because there is no hydrogen atom from the carbon atom holding the OH group can be removed
For observation:
-K2Cr2O7 changes form orange to green
-KMnO4 changes from purple to colourless
Esterification
Esterification
Reagent: Carboxylic acid
Condition: Heat under refluxed with concentrated sulfuric acid, H2SO4 as catalyst
Product: Esters
Esters are derivatives of carboxylic acids. In an ester, the hydrogen from the COOH group of carboxylic acid is replaced by an alkyl group. The alkyl group came from the alcohol. Note that ester is "alcohol + carboxylic acid"
For example, to make methyl butanoate, methanol and butanoic acid are used. Both of them are heated under refluxed with the presence of a catalyst. Esters can be detected from a sweet-smelling odour.
CH3OH + CH3CH2CH2COOH = CH3CH2CH2COOCH3 + H2O
The ester bond can also be broken by hydrolysis with the use of a DILUTE acid ,H2SO4
Chapter revison
Chapter revison
Test for aldehydes and ketones
Test for aldehydes and ketones
Infra red spectroscopy
Infra red spectroscopy
Preparation and reduction of aldehydes and ketones
Preparation and reduction of aldehydes and ketones
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