4.2.3 - Organic Synthesis

What is reflux used for in organic chemistry?

Heating reaction mixtures for long periods without losing volatile products

Why is a condenser used in reflux?

To condense vapours back into liquid and prevent loss

Why must a reflux condenser not be sealed?

Pressure build up could cause explosion

What is added to reaction mixtures during reflux to prevent bumping?

Anti bumping granules

What do anti bumping granules do?

They produce small bubbles for smooth boiling

What oxidising agent is used for alcohol oxidation?

Potassium dichromate VI in acid

What is the formula of the oxidising agent used?

K2Cr2O7 in dilute sulfuric acid

What is the reaction of primary alcohol under reflux?

Primary alcohol to carboxylic acid

What is the equation for oxidation of propan 1 ol under reflux?

CH3CH2CH2OH + 2[O] → CH3CH2COOH + H2O

What is observed during oxidation with dichromate?

Orange solution turns green

Why does dichromate change colour?

Cr2O7 2 minus is reduced to Cr3 plus

What is distillation used for in organic chemistry?

Separating and collecting volatile products

What is the purpose of distillation in oxidation reactions?

To collect aldehyde as it forms

What is the reaction of primary alcohol under distillation conditions?

Primary alcohol to aldehyde

What is the equation for partial oxidation of propan 1 ol?

CH3CH2CH2OH + [O] → CH3CH2CHO + H2O

Why is aldehyde distilled off immediately?

To prevent further oxidation to carboxylic acid

What is the difference between reflux and distillation in oxidation?

Reflux allows full oxidation distillation prevents further oxidation

What is used as a heating method in organic chemistry instead of flames?

Electric heater

Why are naked flames avoided in organic chemistry?

Organic compounds are often flammable

What is the apparatus used for reflux?

Round bottom flask and condenser

Where should the condenser be connected in reflux?

Directly on top of the flask with no gaps

What direction does water flow in a condenser?

In at the bottom out at the top

Why does water enter the condenser from the bottom?

To ensure full filling and efficient cooling

What is the purpose of distillation apparatus?

To separate liquids by boiling point

Where should the thermometer bulb be placed in distillation?

At the entrance to the condenser

What is collected during distillation?

Liquid with desired boiling point

What is the purpose of a separating funnel?

To separate immiscible layers

Which layer is usually organic in a separating funnel?

The less dense upper layer

What is washing the organic layer used for?

To remove impurities such as acids

What does sodium hydrogencarbonate remove in purification?

Acid impurities

What gas is produced when sodium hydrogencarbonate is used?

Carbon dioxide

Why must pressure be released during washing?

To prevent pressure build up from CO2

What does sodium chloride solution do in purification?

Helps separate organic and aqueous layers

What is a drying agent used for?

Removing water from organic liquids

What are examples of drying agents?

Anhydrous sodium sulfate and calcium chloride

What must a drying agent be like?

Insoluble and unreactive with product

How is a dried organic liquid separated from drying agent?

Decanting

What does decanting mean?

Carefully pouring off liquid leaving solid behind

What is the overall sequence after reaction in organic synthesis?

Separate wash dry distil

What is nucleophilic substitution in haloalkanes?

Replacement of halogen by nucleophile

What is electrophilic addition?

Addition reaction involving electrophiles attacking pi bond

What is free radical substitution?

Substitution involving radicals under UV light

What is required for alkane halogenation?

UV light

What conditions are used for alkene electrophilic addition with HBr?

Room temperature

What is required for alcohol to carboxylic acid oxidation?

Excess oxidising agent and reflux

What is required for alcohol to aldehyde oxidation?

Gentle heating and distillation

What is required for full oxidation of alcohol?

Excess oxidising agent under reflux

What is catalytic cracking used for?

Breaking long chain hydrocarbons into smaller molecules

What is polymerisation condition?

High pressure and catalyst

What is nucleophilic substitution condition for haloalkanes?

Aqueous solution and reflux

What reagent is used for nucleophilic substitution of haloalkanes?

Aqueous KOH

What is the general synthetic route starting from alkane?

Alkane to haloalkane to alcohol to aldehyde or acid

What is the role of sulfuric acid in oxidation?

Provides acidic conditions with dichromate

What is the main safety concern in reflux?

Pressure build up and flammability

What is the main safety concern in distillation?

Flammable vapours

What is the role of a Liebig condenser?

Cooling vapours into liquid

What is the correct water flow direction in reflux condenser?

Bottom to top

What is the purpose of synthetic routes in chemistry?

To convert starting materials into target organic compounds

What is the general trend in oxidation of primary alcohol?

Alcohol to aldehyde to carboxylic acid

What determines product in alcohol oxidation?

Conditions and amount of oxidising agent