2.7 - Alcohols and Carboxylic acids Flashcards
Alcohols are a homologous series in which one of the hydrogen atoms in the alkane has been replaced by -OH
Functional group?
General formula?
-OH
C(n)H(2n+1)OH
How do you produce ethanol (most widely used alcohol)?
Ethene + steam
CH2=CH2(g) +H20(g) –>and <— CH3CH2OH
What are the conditions generally used in hydration of ethene?
300 degrees C
60-70 atm
phosphoric acid catalyst
Why the specific conditions for hydration of ethene?
Temp - forward reaction is exothermic, so yield would be greatest at low temp, this gives a slow rate of reaction so 300 C is a compromise
Pressure - 2 moles of reactants give 1 mole of products so a higher pressure will give a higher yield increasing rate of reaction
Catalyst - Increases the rate of the reaction, but doesn’t effect yield
What is fermentation?
An enzyme catalysed reaction that converts sugar into ethanol
What happens in a fermentation reaction?
Sugar dissolves in water, adding yeast and leaving the mixture in a warm place. Yeast contains enzymes that catalyse the reaction.
What is the formula of the fermentation reaction involving glucose and how is ethanol then separated from aqueous solution?
C6H1206 —> 2C2H5OH + 2CO2
Starch (from crops) –enzymes–> glucose –yeast–> Ethanol + CO2
CO2 escapes as gas but the ethanol has to be separated from the remaining liquid mixture. Boiling temp of ethanol is 80 C and therefore to sperate it from an aqueous mixture, fractional distillation is needed
See NC 1
Biofuel research needed
What is the dehydration of alcohols? Give an equation and the catalyst used
A molecule of water is eliminated from the alcohol (H atom and OH group are removed from adjacent C atoms), producing a (double bond) alkene.
CnH2n+1OH –> CnH2n +H20
Concentrated sulphuric acid - catalyst
Similar to elimination of hydrogen halides from halogenoalkanes
Give the classification of alcohols
Primary - the OH- is joined to a C that is itself, joined to only 1 other C
Secondary - the OH- is joined to a C that is joined to 2 other C’s
Tertiary - the OH - is joined to a C that is joined to 3 other C’s
See NC 2
What can be used to oxidise alcohols? Why is it acidified?
Acidified potassium dichromate (VI) can be used to oxidise many alcohols. Since dichromate (VI) will only behave satisfactorily as an oxidising in the presence of H+ the oxidation is generally carried out by heating the alcohol with a mixture of aqueous potassium dichromate (VI) and sulfuric acid
What happens in the oxidation of primary alcohols? What functional groups are formed?
1st stage: 2 H are lost - one from the alcohol OH and one from adjacent carbon. This creates an C=O. Product formed is an aldehyde with functional group -CHO
2nd stage: Oxygen atom is added to aldehyde to form carboxylic acid with the functional group -COOH
See NC 3
What happens in the oxidation of secondary alcohols? What functional groups are formed?
2 hydrogens are lost and a double bond C=O is formed. This resulting compound is called a Ketone and it has the functional group -C=O
See NC 3
What happens in the oxidation of tertiary alcohols? What functional groups are formed?
As there is no hydrogen on the carbon atom adjacent to the OH- group that can be lost , no reaction can occur
See NC 3
Therefore how can you test for primary and secondary alcohols?
Acidified potassium dichromate (K2Cr2O7) changes colour from orange to green in the presence of primary and secondary alcohols (basis of breathalyser test)
