CL 16- organic synthesis

Question 1

heating under reflux

diagram

Answer 1

set up procedure as in diagram (round-bottomed flask, condenser, water in at bottom and out at top, heat at bottom)

Question 2

why add anti-bumping granules to heating under reflux?

Answer 2

before the flask is heated they’re added so the contents boil smoothly (without them, large bubbles form at the bottom of the liquid and make the glassware vibrate or jump violently)

Question 3

distillation

diagram

Answer 3

round-bottomed flask, heat at bottom, thermometer and bung, condenser on arm, water in at bottom and out at top, feeding into conical flask

Question 4

describe how to separate an organic layer from an aqueous layer using a separating funnel

procedure

Answer 4

1. pour the mixture of liquids into a separating funnel making sure the tap is closed, invert.
2. allow layers to separate, top layer has lowest density and usually organic
3. run off the aqueous layer at the bottom by collecting in a conical flask

Question 5

examples of drying agents

definition and examples

Answer 5

an anhydrous inorganic salt that readily takes up water to become hydrated
e.g. anhydrous calcium chloride, anhydrous magnesium sulfate

Question 6

describe the process used to dry an organic liquid

method

Answer 6

1. add drying agent to organic liquid with spatula and swirl
2. place stopper on conical flask to prevent evaporation of product
3. continue adding until free flowing, fine powder solid (if the solid has stuck together there is still water present)
4. decant the liquid from the solid into another flask (if liquid is dry, it should be clear)

Question 7

after drying agent…

redistillation purpose

Answer 7

(after drying agent used) there are still traces of water left in liquid, so distillation is used to purify the liquid

Question 8

recrystallisation

method (on wall anyway) with reasoning

Answer 8

1. warm the impure sample with solvent (to dissolve the pure product and soluble impurities)
2. filter the hot mixture (to remove insoluble impurities)
3. allow solution to cool slowly (to allow crystals of the pure product to form)
4. filter the cold mixture (to separate the pure product from soluble impurities)
5. wash the solid with a small amount of cold solvent (to separate the pure product from contaminated solvent)
6. dry the solid (to spearate the pure product from pure solvent)

Question 9

reactants, conditions and mechanism

alkane→haloalkane

Answer 9

halogen, UV light, free radical substitution

Question 10

alkene→alkane

Answer 10

H₂, Ni catalyst, electrophilic addition

Question 11

alkene→haloalkane

Answer 11

hydrogen halide, electrophilic addition

Question 12

alkene→alcohol

Answer 12

H₂O (steam), H₃PO₄ catalyst, electrophilic addition

Question 13

alcohol→alkene

Answer 13

H₂SO₄, heat

Question 14

alcohol→haloalkane

Answer 14

NaBr, H₂SO₄

Question 15

haloalkane→alcohol

Answer 15

NaOH, nucleophilic substitution

Question 16

primary alcohol oxidisation

Answer 16

H⁺/Cr₂O₇²⁻
* aldehyde formed w/ distillation
* carboxylic acid formed w/ reflux

Question 17

secondary alcohol oxidisation

Answer 17

H⁺/Cr₂O₇²⁻
ketone formed (under reflux)