4.2.3 Organic Synthesis Flashcards
(36 cards)
1
Q
what can alkanes form
A
only haloalkanes
2
Q
what is the reaction for alkane to haloalkane
A
- add halogen
- UV light
- free radical substitution!
3
Q
what can alkenes form
A
alkanes (hydrogenation)
alcohols (hydration)
haloalkanes (electrophilic addition)
4
Q
what is the reaction for alkenes to alkanes
A
- add H2
- Ni catalyst, 473K/330C, high pressure
- hydrogenation
5
Q
what is the reaction for alkenes to haloalkanes
A
- add hydrogen halide
- room temperature
- electrophilic addition!
6
Q
what is the reaction of alkenes to alcohols
A
- steam/ H2O(g)
- H3PO4 catalyst
- hydration
7
Q
what can haloalkanes form
A
alcohols
8
Q
what is the reaction of haloalkanes to alcohols
A
- add sodium hydroxide NaOH(aq)
- heat under reflux
- nucleophilic substitution/ hydrolysis!
9
Q
what things can alcohols form
A
- haloalkanes
- alkenes
- oxidation products: carboxylic acids, ketones and aldehydes
10
Q
reaction for alcohol to alkene
A
- acid catalysT (H2SO4/H3PO4)
- heat under reflux
- elimination/dehydration
11
Q
reaction for alcohols to haloalkanes
A
- add hydrogen halide in situ (made from adding sodium halide and dilute H2SO4)
- heat under reflux
- substitution
12
Q
how do you get from alcohol to carboxylic acid
A
- primary alcohol
- K2Cr2O7/H2SO4
- heat under reflux
- oxidation
13
Q
how do you get from an alcohol to aldehyde
A
- primary alcohol
-K2Cr2O7/H2SO4 - heat to distil
- oxidation
14
Q
how do you get from alcohol to ketone
A
- secondary alcohol
- K2Cr2O7/H2SO4
- heat under reflux
- oxidation
15
Q
all ways you can make haloalkanes
A
- alkane + UV + halogen
- alkene + halogen halide + room temp
- alcohol + hydrogen halide in situ + under reflux
16
Q
all the ways you can make alkenes
A
- just dehydration of alcohols (elimination)
- under reflux and acid catalyst
17
Q
all the ways you can make alkane
A
- just hydrogenation of alkenes
- add H2 over Ni catalyst at 330C
18
Q
all the ways you can make an alcohol
A
- hydration of alkenes, adding steam and a H3PO4 catalyst
- hydrolysis of haloalkanes, with NaOH, under reflux
19
Q
what are the components of Quickfit apparatus
A
- round-bottom/pear-shaped flask
- receiver
- screw-top adapter
- condenser
- still-head
20
Q
what is the 5 step process of preparing an organic liquid
A
- heat under reflux (to get liquid)
- distillation (to separate impurities)
- purify organic products (get rid of water or acid)
- dry organic product (get rid of water)
- redistillation (pure product)
21
Q
why would you heat under reflux
A
HEAT AS:
- many reactions are slow at room temperature
- so heat them to increase ROR and overcome the activation energy
UNDER REFLUX AS:
- liquid is able to be continually boiled whilst the reaction takes place
- means no volatile components escape
- or the flask doesn’t run dry
- as the vapor rises to the top, but then condenses due to the cold water in the jacket, and then drips back down
22
Q
what is the equipment for heating under reflux
A
- Liebig condenser: also has a layer of grease applied to the ground-glass joint so it can come apart easily at the end
- water goes in from the bottom and out of the top, so the outer jacket always stays full of water
- all attached to a stand and clamp to keep upright
- the top is left open, as if it was closed, the pressure would build inside as the air is heated and expands, causing it to explode
- heat is applied to the bottom of the round-bottom flask via a bunsen burner, tripod and gauze, but also could be a heating mantle if dealing with flammable liquids or a water bath if temperature doesn’t need to reach 100 degrees
- also contains anti-bumping granules inside, so the contents inside can boil smoothly
23
Q
why is distillation carried out
A
- to separate out impurities
- as once refluxed, the liquid in the flask may still contain:
1) by-products (not just the desired product)
2) remaining reactants (as the reaction may not have gone into completion)
= distil to remove
24
Q
what is the equipment needed for distillation
A
- round-bottom flask
- which has heat applied to it
- containing anti-bumping granules
- attached to a still head (greased joints so comes apart easily)
- with a bung at the top but thermometer coming through
- attached to the condenser (which is connected to water via rubber tubing)
- condenser is connected to a receiver, which leads into a beaker containing the pure liquid
25
how does distillation work
- mixture is heated
- the different liquids in the mixture have different boiling points
- the lowest boiling point one will boil first
- and move up the flask, leaving behind the less volatile components
- it reached the condenser, where it becomes a liquid again, and drips into the collecting flask
26
why may you get 2 layers when preparing an organic liquid
- one layer is the liquid you want
- the other is water
27
how do you tell which of the 2 layers of liquid is the organic component
- add water into the mixture
- the layer that gets bigger is the aqueous water layer
28
what do you use to separate out the 2 layers of liquid
a separating funnel
29
explain how a separating funnel works
- put liquids into the funnel (make sure the tap is closed)
- place a topper at the top of the funnel and invert to mix the contents
- allow the layers to settle, and ensure you know which layer is water
- place a conical flask under the funnel, remove the stopper and open the tap until one layer has fully left
- place the second flask underneath and collect the next liquid, labelling the flasks so you don't muddle them up
30
what may be present when you are preparing an organic liquid using acids
the impure product may contain acid impurities
31
how do you remove acid impurities from your impure product
- add sodium carbonate (aq)
- and shake mixture in a separating funnel
- the acid present reacts with the sodium carbonate
- and releases CO2
- open the tap of your separating funnel slowly when it is upside down (with stopper)
- this releases the gas pressure
- then remove the aqueous sodium carbonate layer and wash the organic layer with water (separating as before)
32
why may you need to dry an organic product
to remove any traces of water left
33
what do you use to dry an organic product
- a drying agent
- an anhydrous inorganic salt that readily takes up water to become hydrated
- e.g. CaCl2 (specific to hydrocarbons)
- e.g. CaSO4 and MgSO4 in general
- all in anhydrous forms
34
how do you dry an organic product
- add organic liquid to conical flask
- add in drying agent gently using a spatula and swirl gently
- place a stopper in to prevent any product from evaporating
- leave for 10 minutes (or until effervescence stops as all gas has been released and reaction over)
- if solid is stuck in clumps, water is still present, and add more drying agent until dispersed fine powder
- decant the solid from the liquid, and should be clear if all water removed
35
why may you need to carry out redistillation
for a mixture of organic liquids with similar boiling points, as prepared sample may still be impure
36
how do you carry out redistillation
- set up clean distillation apparatus again
- but boil to a narrower boiling point, so only one product evaporates
