Topic 6E - Alcohols (Organic Chemistry) Flashcards
What is a primary alcohol?
When there is an -OH functional group on a carbon attached only one other carbon
What is a secondary alcohol?
When there is an -OH functional group on a carbon which is attached to two other carbons
What is a tertiary alcohol?
When there is an -OH functional group on a carbon which is attached to three other carbons
What is the name of the primary, secondary and tertiary alcohol C4H9OH?
Primary - Butan-1-ol
Secondary - Butan-2-ol
Tertiary - Methylpropan-1-ol
Why are the boiling temperatures of alcohols higher than their corresponding alkanes?
Due to the addition of Hydrogen Bonding
Why is ethanol very water soluble?
Due to the ability of ethanol to form hydrogen bonds between the -OH and the water molecule
The solubility of alcohols decreases with…
Increasing carbon chain length
Why does solubility decrease with increasing carbon chain length?
This is because the large, insoluble hydrocarbon portion of the molecule outweighs the influence of the -OH group
Write the word equation and balanced symbol equation for the combustion of methanol
methanol (l) + oxygen (g) -> Carbon dioxide (g) + water (l)
2CH3OH + 3O2 -> 2CO2 + 4H2O
Write the word and symbol equation of the reaction of sodium with ethanol
Sodium + Ethanol -> Sodium ethoxide + Hydrogen
Na + CH3CH2OH -> CH3CH2O-Na+ + 1/2H
What is a way to safely dispose a small amount of unwanted sodium?
To react the sodium with ethanol
What is the name of reaction where the -OH functional group is swapped for a halogen?
A substitution reaction
In the Chlorination of primary and secondary alcohols what is the reagent?
PCl5 (Phosphorus Pentachloride)
In the Chlorination of primary and secondary alcohols what are the conditions?
No heating is required but the reaction should be done in a fume cupboard as HCl gas is produced which is toxic
Write a word and symbol equation for reaction of the primary alcohol ethanol and PCl5 in Chlorination
Ethanol + Phosphorus Pentachloride -> Chloroethane + Phosphorus oxychloride + Hydrogen Chloride
CH3CH2OH + PCl5 -> CH3CH2Cl + POCl3 + HCl
What is the reaction used to test for the presence of the -OH functional group in primary and secondary alcohols?
Chlorination
What is the positive result of the present of the -OH functional group, when testing for it with PCl5?
Clouds of misty fumes due to the HCl gas, these will turn damp blue litmus paper red
In the Chlorination of tertiary alcohols what is the reagent?
Shaken with Concentrated HCl
In the Chlorination of tertiary alcohols what are the conditions?
Room Temperature
Write a symbol equation for the reaction of the tertiary alcohol tert-butyl alcohol with HCl in Chlorination
(CH3)3COH + HCl -> (CH3)3CCl + H2O
In the Bromination of alcohols, what are the reagents?
- Solid KBr
- H2SO4 with a 50% concentration
In the Bromination of alcohols what are the conditions?
Heat under reflux (2nd step)
What are the 2 different equations for the first step of the Bromination of Alcohols?
KBr (s)+ H2SO4 (aq) -> KHSO4 (aq) + HBr (g)
2KBr (s) + H2SO4 (aq) -> K2SO4 (aq) + 2HBr (g)
Write the general equation (using ethanol) for the second step of the Bromination of alcohols
CH3CH2OH + HBr -> CH3CH2Br + H2O
Why is it important to use 50% concentrated sulphuric acid rather than fully concentrated acid?
As using a fully concentrated acid would cause all of the Br- ions to be oxidised to Br2 rather than Her which is what is needed
Write an equation for the first step in the Iodination of alcohols
2P + 3I2 -> 2PI3
What are the reactants and conditions in the first step of the Iodination of alcohols?
Reactants:
- Damp red phosphorus
- Iodine
Conditions
- Warmed
Write an equation for the second step of the Iodination of alcohols using ethanol
3CH3CH2OH + PI3 -> 3CH3CH2I +H3PO3 (phosphonic acid)
What are the conditions required for the second step of the Iodination reaction with alcohols?
Heat under reflux
What is the definition of a dehydration reaction?
A dehydration reaction is a specific type of elimination reaction where water is removed form a saturated molecule to form an unsaturated molecule
What is the definition of an elimination reaction?
An elimination reaction is when two atoms or a group of atom are removed from a compound to form two products
What is the general equation for the dehydration of an alcohol?
Alcohol -> Alkene + water
What are the conditions required for the dehydration of an alcohol?
- Heat under reflux
- Phosphoric acid catalyst (H3PO4)
- Collect the product via distillation
What is the oxidised dichromate (VI) ion?
Cr2O7 (2-)
What is the reduced dichromate ion?
Cr (3+)
What is the colour change you observe as the dichromate ion is reduced?
Orange to Green
What are the conditions for the oxidation of primary alcohols?
- Heat under reflux
What is the oxidising agent/reagants required from the oxidation of primary alcohols?
- Potassium Dichromate
- Sulphuric acid
Write an equation for the partial oxidation of the primary alcohol propan-1-ol to an aldehyde
propan-1-ol -> propanal + water
CH3CH2CH2OH + [O] -> CH£CH2CHO + H2O
How would you collect the partially oxidised aldehyde product?
Distill off immediately
Write the equation of the oxidation of the aldehyde propanal to a carboxylic acid
propanal -> propanoic acid
CH3CH2CHO + [O] -> CH3CH2COOH
Write the full equation for when button-1-ol is completely oxidised to butanoic acid
CH3CH2CH2CH2OH +2[O] -> CH3CH2CH2COOH + H2O
What is the oxidising agent/reagants required from the oxidation of secondary alcohols?
- Potassium Dichromate
- Sulphuric acid
What are the conditions for the oxidation of secondary alcohols?
- Heat under reflux
Write the equation for the complete oxidation of propan-2-ol?
CH3CHOHCH3 + [O] -> CH3COCH3 + H2O
How can you show that the oxidation product from secondary alcohols has been oxidised but not to a carboxylic acid?
The colour change from orange to green due to the reduction of the dichromate ion shows that the alcohol is being oxidised.
Test for the presence of a Carboxylic Acid functional group - Add Na2CO3 to your product. Bubble the effervescence through limewater and if CO2 is present the limewater should turn cloudy. Therefore a carboxylic acid would be present, or not.
NB - Carboxylic Acid + Metal Carbonate -> Salt + Carbon Dioxide + Water
How could you test to se if an organic product is an aldehyde rather than a ketone or carboxylic acid?
Aldehydes are only partially oxidised, therefore if you were to heat it under reflux in the presence of H2SO4 and Potassium dichromate there would be a colour change of orange to green.
What is a test that you can use to distinguish between an aldehyde and a ketone?
Fehlings/Benedicts test
Describe how to test for the presence of an aldehyde using the Fehlings/Benedicts test?
Add a few drops of the aldehyde to the reagent and then warm gently in a hot water bath for a few minutes
What is the positive colour change for a Fehlings/Benedicts test?
The blue solution produces a dark red precipitate of copper (I) oxide (aldehydes)
What are the three reasons why it is unlikely that your product of any reaction in organic chemistry to be pure?
- You often add excess of one reagent and so there will be unreacted starting material
- There are often extra reactions during the one that you are doing, particularly inorganic ones
- Water has been formed during the reaction or your solvent from the reaction
Why do you need anti - bumping granules when heating an alcohol?
To prevent the formation of large gas bubbles that cause violent boiling by providing a large surface area for bubbles to form on
What must you not do when distilling a solution?
Let the flask boil dry as otherwise there could be an explosion
What are the observations when sodium reacts with alcohols?
The reaction is similar to when sodium is reacted with water. However, this reaction is:
- Much less violent
- Not as exothermic
The hydrogen gas is still produced but the sodium does not melt.
What is produced when sodium reacts with alcohols?
Sodium alkoxide salts and hydrogen are produced. The salts are ionic and this is shown by including the charges of - on the oxygen o the alkoxide ion and the + of the sodium ion.
What two organic products can be formed when butan-2-ol is dehydrated?
but-1-ene or but-2-ene
What is the condition required for the dichromate ion to function as an oxidising agent?
The presence of H+ ions, therefore sulphuric acid is used to provide these