Chapter 16 - Organic Synthesis

Question 1

test - alkene (unsat hydrocarbon)?

Answer 1

R: Br2 water, shake
O: Br decolourised - the Br2 adds across the double bond in an addition reaction

Question 2

test - haloalkane?

Answer 2

Reagents: AgNO3(aq), Ethanol, H2O
Observation: AgCl: white precipitate, AgBr: cream, AgI: yellow
why? the halogen atom is displaced as a halide ion, the halide ion reacts with Ag+ ions to form a precipitate

Question 3

test - carbonyl (C=O) - acidified potassium dichromate?

Answer 3

R: acidified potassium dichromate
O: Aldehyde: CC from orange -> green, ketone: no colour change
why? the orange solution containing dichromate ions is reduced to a green solution con. chromium (III) ions

Question 4

test - carbonyl (C=O) - Tallens?

Answer 4

R: Tallens - a sol. of AgNO3 & Ammonia - Ag(NH3)2OH
O: Aldehydes: Silver Mirror formed, Ketones: No Silver Mirror
y? the silver ions are reduced upon heating w an aldehyde, silver metal forms

Question 5

test - carbonyl (C=O) -Fehling’s solution?

Answer 5

R: Fehling’s solution
O: aldehyde = dark red precipitate forms from orig blu solution, Ketone = No precipitate forms
y? The blue Cu(III) ions are reduced to give a precipitate of Cu(I) Oxide (red)

Question 6

3 tests for carbonyl are?

Answer 6

• acidified potassium dichromate
• tallens
• fehling’s solution

Question 7

test - Carboxylic Acid - Universal Indicator?

Answer 7

R: Universal Indicator
O: pH of weak acid = CAs r weak acids

Question 8

test - CA) -add a reactive metal?

Answer 8

R: add a reactive metal
O: Effervescence of a gas: This gas can be tested - the gas would burn w a squeaky pop if CA (H2)
y? The CA is reacting as an acid: Metal + Acid -> salt + H2(g)

Question 9

test - CA - metal carbonate?

Answer 9

R: add a metal carbonate
O: Effervescence of gas - this gas can be tested - when bubbled through limewater, limewater will turn cloudy
y? CA reacting as an acid: Metal Carbonate + Acid -> Salt + CO2 + H2O

Question 10

test - alcohol?

Answer 10

R: warm w CA and a few drops of H2SO4
O: sweet smell bc ester formed

Question 11

3 tests for CA are?

Answer 11

• UI
• reactive metal
• metal carbonate

Question 12

give 3 reasons why % yield is less than 100%?

Answer 12

• mass lost when transferring containers
• incomplete reaction
• impure reactants/ side reactions

Question 13

when an alcohol group is attached to a benzene ring, this is called a ?

Answer 13

phenol - a diff FG

Question 14

Thiele tube ?

Answer 14

• when an organic solid melts, it melts over a v small temp range
• the melting temp can b determined using this
• fill a capillary tube w about 1/2cm depth solid
• attach the tube to a thermometer w a smaller rubber band
• insert the sample into a Thiele tube so that the sample is nearly in the middle of the oil.
• Heat the arm of the Thiele tube w a burner, gently and continuously, noting the temps when the samples starts and finishes melting

Question 15

what is the most efficient way to cool the condenser?

Answer 15

to have cold water in at the bottom and out at the top

Question 16

What is the distillation adapter used for?

Answer 16

• used to connect the flask to the condenser

Question 17

when is distillation used?

Answer 17

• when trying to make an aldehyde by oxidising a primary alcohol
• more usually it is used to separate p from r and other impurities after a reflux

Question 18

filtering under reduced pressure?

Answer 18

• using a Buchner funnel and Buchner flask n pump
• is like filtering using a funnel, filter paper, conical flask, gravity allows the filtrate to collect om the conical flask and so the solid residue stays in the funnel
• the flask is connected to a pump & the filtrate is sucked thru allowing the separation to take place much faster & giving a drier solid residue.

Question 19

seperating funnel?

Answer 19

• many organic reactions produce water as a by product
• the vast majority of organic compounds are not water soluble so pouring the mixture into a separating funnel and waiting will result in 2 layers
• the denser liquid will always sink to the bottom - this is almost always H2O
• open the tap to collect the 2 diff layers in sep flasks .
• if % yield is less important than purity, then u may want to use a 3rd container to collect the small part where the 2 layers meet

Question 20

what apparatus do you need to be able to heat under reflux?

Answer 20

• round bottom/ pear shaped flask
• condenser
• rubber tubing
• stand and clamp
• heat source (usually a bunsen burner, tripod and gauze or a heating mantle)

Question 21

what does a quickfit apparatus contain?

Answer 21

• round bottom or pear shaped flask
• receiver
• screw-tap adaptor
• condenser
• still head

Question 22

heating mantle?

Answer 22

can be used when heating flammable liquids so that there is no naked flame present

Question 23

when setting up apparatus, be careful that…

Answer 23

condensers should be clamped only loosely as the outer glass jacket is very fragile & easily broken. Never put a stopper in the top of the condenser as then you would have a closed system and pressure would build up inside as the heated air expanded - this could result in the apparatus exploding

Question 24

to carry out a distillation, you need?

Answer 24

• round bottom or pear shaped flask
• condenser
• rubber tubing
• heat source
• stand n clamp
• screw-cap adaptor
• still head
• thermometer

Question 25

for distillation, water enters?

Answer 25

water always enters the condenser at the lowest point. for distillation this is the closest point to the receiver adaptor

Question 26

explain the process of distillation?

Answer 26

• flask is heated and mixture starts to boil. The diff liquids in the mixture will have diff BPs.
• the liquid w the lowest BP is the most volatile and will boil first
• the vapour moves out of the flask up into other parts of the apparatus, leaving behind the less volatile components.
• when the vapours reach the cold condenser, they condense and become a liquid
• this liquid then drips into the collecting flask

Question 27

how to separate an organic layer from an aqueous/ H2O layer?

Answer 27

1. Ensure that the tap of the seperating funnel is closed
2. pour the mixture of liquids into the seperating funnel, place a stopper in the top of the funnel, and invert to mix contents
3. allow layers to settle
4. add some water to see which layer increases in V - this is the aqueous layer
5. place a conical flask under the seperating funnel, remove the stopper and open the tap until the whole of the lower layer has left the funnel
6. place a 2nd conical flask under the seperating funel to collect the other layer

Question 28

what if the impure product contains acid impurities?

Answer 28

• these can be removed by adding (aq)Na2CO3 and shaking the mixture in the seperating funnel
• any acid present will react w the sodium carbonate releasing CO2
• The aq Na2CO3 layer is removed and the organic layer washed w water before running both layers off into 2 seperate flasks

Question 29

what if there is water left in the organic product?

Answer 29

• removed by adding a drying agent - an anhydrous inorganic salt that readily takes up water to become hydrated
• the most common drying agents are: anhydrous CaCl2, anhydrous CaSO4, anhydrous MgSO4

Question 30

Procedure for drying an organic liquid?

Answer 30

• add it to a conical flask
• using spatula, add some of the drying agent and gently swirl contents to mix together
• place a stopper on the flask to prevent your product from evap away. Leave for abt 10 mins
• if solid has stuck together in a lump, there is still some water present. Add some more drying agent until some solid is dispersed in the sol as a fine powder
• decant the liquid from the solid into another flask. If the liquid is dry it should be clear

Question 31

what is organic synthesis?

Answer 31

the prep of complex molecules from simple starting materials