chapter 6 - organic synthesis

what is included in the standard set of quickfit apparatus?

1) round bottom or pear-shaped flask

2) receiver

3) screw-tap adaptor

4) condenser

5) still head

apparatus needed for reflux?

• round bottom or pear-shaped flask

• condenser

• rubber tubing

• stand and clamp

• heat source

what would you use when heating flammable liquids?

• a heating mantle, so that there is no naked flame present

what are anti-bumping granules used for?

• so that the contents will boil smoothly

what would happen if granules were not used?

• large bubbles form at the bottom of the liquid and make the glassware vibrate or jump violently

why should you never put a stopper at the top of a condenser?

• because otherwise you will have a closed system

• pressure will build up inside as the heated air expands

• which could result in apparatus exploding

how does water enter and leave condenser?

• water enters - bottom

• water leaves - top

  • this ensures that the outer jacket is full

what does heating under reflux enable?

• it enables a liquid to be continually boiled whilst the reaction takes place

• this prevents volatile components from escaping and the flask from boiling dry

what is distillation used for?

• it separates a pure liquid from its impurities

apparatus needed for distillation?

• round bottom or pear-shaped flask

• condenser

• rubber tubing

• heat source

• clamp and stand

• screw-cap adaptor

• receiver adaptor

• still head

• thermometer

how to know which layer is the aqueous layer and which is the organic layer?

• add water to your mixture

• the layer that gets bigger is the aqueous layer

how to separate the 2 layers?

• by using a separating funnel

• ensure that the tap of separating funnel is closed at first

• pour mixture of liquids into a separating funnel, place a stopper in the top of the funnel and invert to mix the contents

• allow the layers to settle

• add some water to see which layer will increase in volume- this is aqueous layer

• place a conical flask under the separating funnel, remove the stopper and open tap until whole of the lower layer has left the funnel

• place a second conical flask under the separating funnel to collect the other layer

• label flasks so that you don’t muddle them

how to remove traces of water from organic product?

• by using a drying agent

what is a drying agent?

• an anhydrous inorganic salt that readily takes up water to become hydrated

common anhydrous salts?

• anhydrous calcium chloride (drying hydrocarbons)

• anhydrous calcium sulfate (general drying)

• anhydrous magnesium sulfate (general drying)

process for drying an organic liquid?

• add the organic liquid to a conical flask

• using a spatula, add some of the drying agent to the liquid and gently swirl the contents to mix together

• place a stopper on the flask to prevent product from evaporating away. leave for about 10 mins

• if the solid has all stuck together in a lump, there is still some water present. add more drying agent until some solid is dispersed in the solution as a fine powder

• decant the liquid from the solid into another flask. if the liquid is dry, it should be clear

redistillation?

• sometimes organic liquids have boiling points that are relatively close together, so your prepared sample may still contain some organic impurities

• the distillation apparatus is cleaned and dried and set up again so that a second distillation can be carried out

  • this time only collect the product with the boiling point of the compound you are trying to make

  • the narrower the boiling range, the purer the product

conditions needed for fermentation?

• yeast enzyme

• anaerobic conditions

• temp range: 25 - 40C

how do you know when fermentation of glucose is complete?

• no more bubbles/gas/CO2

equation for fermentation of glucose to produce ethanol?

• C6H12O6 (aq) → 2C2H5OH(l) or (aq) + 2CO2(g)

use of mass spectroscopy outside the lab?

• breathalysers

• monitoring of air pollution

• MOT emission testing

compare sustainability of the 2 methods of manufacturing ethanol in terms of:

• availability of starting materials and energy requirements

• atom economy

availability

• sugar is renewable because it can be grown

• ethane is finite because it is obtained by processing of crude oil

energy:

• fermentation: energy is required for distillation

• hydration: energy is required to generate steam

atom economy and waste products:

• atom economy for hydration is greater than the atom economy for fermentation

• in fermentation, CO2 is produced in addition to ethanol

• whereas in hydration, only ethanol is produced

• atom economy of fermentation could be increased by finding a use CO2