alcohols Flashcards
What dangers are there with some alcohols?
Methanol, ethanol, and propanol are very flammable.
Why do alcohols have a low volatility and high b.p.?
As they can form hydrogen bonds which require more energy to overcome.
Why are shorter chain alcohols more soluble in water?
The -OH functional group, which forms hydrogen bonds with water molecules making it soluble, forms a greater proportion of the molecule.
What are the reagents for the oxidation of primary and secondary alcohols and where are they from?
● An excess of…
○ Cr2O72-.
○ H+.
● From solution of potassium dichromate (VI) and dilute sulfuric acid.
Something such as hydrochloric acid cannot be used as the dichromate ions would rather oxidise this.
What is the equation for the partial oxidation of primary alcohols?
A primary alcohol reacts with [O] (the oxidising agent) to form an aldehyde and water.
E.g., propan-1-ol to propanal.
What are the reaction conditions for the partial oxidation of primary alcohols and why?
heat gently, distilling the aldehyde as it forms otherwise it will continue onto form a carboxylic acid.
What is observed (colour- wise) under the oxidation of alcohols?
Orange to green colour change.
Describe the setup for distillation with an explanation for the key points
● Bulb of thermometer at T-junction - to display the correct b.p.
● Water entering via bottom of condenser - entire condenser
will fill up before water exits.
● Electric heater - prevents highly flammable organic
compounds setting alight under a live flame.
If water enters via the top of the condenser, it would trickle down and leave without filling the whole condenser.
What is the equation for the full oxidation of a primary alcohol? Explain it
Primary alcohol + 2[O] → carboxylic acid + water
1. Two lots of oxidising agent is required; one for each stage
2. The water was produced at the first stage (when forming
aldehyde)
You can distill afterwards to remove any unreacted alcohol molecules.
What are the reaction condiJons for the full oxidation of primary alcohols and oxidation of secondary alcohols? Why?
Heating under reflux to prevent evaporation.
Describe reflux setup
● Open end - prevents build up of gas that can cause explosion
● Anti-bumping granules - prevents vigorous and uneven boiling by forming smaller bubbles
When is the reflux setup most often used?
When heating organic reaction mixtures for long periods.
What is the equation for oxidation of secondary alcohols?
Secondary alcohol + [O] → ketone + water
Why won’t tertiary alcohols oxidise?
As you need to remove a H atom from the carbon the -OH is bonded to (alongside the H from the -OH substituent group). Yet, no H is bonded to said carbon.
What are the products and conditions for the dehydration of alcohols and why?
● Forms an alkene and water.
● HEAT under reflux.
● Concentrated sulphuric or phosphoric acid catalyst.
● As we don’t want any water to form alcohols again.
In short, the same catalyst, however, without water.
