Chapter 16 - Organic Synthesis Flashcards
test - alkene (unsat hydrocarbon)?
R: Br2 water, shake
O: Br decolourised - the Br2 adds across the double bond in an addition reaction
test - haloalkane?
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
test - carbonyl (C=O) - acidified potassium dichromate?
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
test - carbonyl (C=O) - Tallens?
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
test - carbonyl (C=O) -Fehling’s solution?
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)
3 tests for carbonyl are?
- acidified potassium dichromate
- tallens
- fehling’s solution
test - Carboxylic Acid - Universal Indicator?
R: Universal Indicator
O: pH of weak acid = CAs r weak acids
test - CA) -add a reactive metal?
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)
test - CA - metal carbonate?
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
test - alcohol?
R: warm w CA and a few drops of H2SO4
O: sweet smell bc ester formed
3 tests for CA are?
- UI
- reactive metal
- metal carbonate
give 3 reasons why % yield is less than 100%?
- mass lost when transferring containers
- incomplete reaction
- impure reactants/ side reactions
when an alcohol group is attached to a benzene ring, this is called a ?
phenol - a diff FG
Thiele tube ?
- 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
what is the most efficient way to cool the condenser?
to have cold water in at the bottom and out at the top
What is the distillation adapter used for?
- used to connect the flask to the condenser
when is distillation used?
- 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
filtering under reduced pressure?
- 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.
seperating funnel?
- 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
what apparatus do you need to be able to heat under reflux?
- round bottom/ pear shaped flask
- condenser
- rubber tubing
- stand and clamp
- heat source (usually a bunsen burner, tripod and gauze or a heating mantle)
what does a quickfit apparatus contain?
- round bottom or pear shaped flask
- receiver
- screw-tap adaptor
- condenser
- still head
heating mantle?
can be used when heating flammable liquids so that there is no naked flame present
when setting up apparatus, be careful that…
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
to carry out a distillation, you need?
- round bottom or pear shaped flask
- condenser
- rubber tubing
- heat source
- stand n clamp
- screw-cap adaptor
- still head
- thermometer
for distillation, water enters?
water always enters the condenser at the lowest point. for distillation this is the closest point to the receiver adaptor
explain the process of distillation?
- 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
how to separate an organic layer from an aqueous/ H2O layer?
- Ensure that the tap of the seperating funnel is closed
- pour the mixture of liquids into the seperating funnel, place a stopper in the top of the funnel, and invert to mix contents
- allow layers to settle
- add some water to see which layer increases in V - this is the aqueous layer
- 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
- place a 2nd conical flask under the seperating funel to collect the other layer
what if the impure product contains acid impurities?
- 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
what if there is water left in the organic product?
- 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
Procedure for drying an organic liquid?
- 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
what is organic synthesis?
the prep of complex molecules from simple starting materials
