Chemistry- organic synthesis Flashcards
what is reflux
technique used to heat volatile liquids
how does reflux work
strongly heated without losing volatile reactants and products. Volatile compounds evaporate and condense -falls back into the flask
what does volatile mean
how easily a substance will vaporize
how does a liebig condenser work
cold water running through wall, hot evaporating substances turn back into a liquid and return back to round bottomed flask.
how do we need to be careful when using flammable liquids
use water bath or electric heater: mantle
what is distillation
used to separate substances with different boiling points
how does distillation work
gently heating mixture will result in the compounds separating out in order of boiling point. knowing the boiling point of the chemical will allow you to decide how to separate the compound
what will happen if the compound has lower boiling point than starting mixture
heat to the temp of boiling point of the compound
collect product in a separate vessel
what will happen if the compound has higher boiling point than starting mixture
heat to temp of boiling temp of compound
product will remain on the round bottomed flask
what is distillation useful for
useful when you want to extract a chemical before it reacts any further.
example of distillation
oxidising primary alcohols can produce aldehydes however if aldehyde isn’t removed as soon as its formed it will oxidise to form a carboxylic acid
what is filteration
used to separate solids and liquids
what does the vacuum do
used to help separate liquid and solid components thoroughly.
vacuum creates reduced pressure in flask and pulls liquid through
Solid is left in the buchner funnel
how do we purify this further?
after distillation
recrystallisation
what is recrystallisation
method to purify solids
-solvent chosen is very important
steps for recrystallisation
- add enough solvent, impure solid dissolves
- cool the solution down slowly, crystals will start to form
- impurities will remain dissolved in solution takes longer for them to crystallise
- filter collects purified crystals, wash in cold solvent to dry of
why do we choose the solvent carefully
want impure solid to dissolve fully in hot solvent but be insoluble when its cold. if substance doesn’t dissolve in hot solvent, cant be purified further
what does measuring boiling point detect
detects impurities
how to carry out distillation to determine boiling point
1- gently heat sample, can then measure temperature at which it distils using thermometer
2.then compare this boiling point with data book value
how do we know if sample contains impurities
- if boiling point is higher than what is in data book
- sample boils over a range of temperatues
what is needed to be done if compounds have same boiling points
need to use analytical techniques such as mass spectrometry to spot impurities
how can purity of a compound be measured
can be determined by measuring the melting point
how to carry out purification
- add sample of solid into capillary tube and place into heating element
- slowly increase temperature until substance starts to melt
- temperature ranges from when it begins to melt to when it fully melts
- compare melting points (using data book values)
- if substance contains impurities the melting point will be lower and temp range substance melts at will be higher
alkanes
properties: unreactive, non-polar bond
Reactions: radical substitution
alkene
properties: non-polar bond
reactions: electrophilic addition
aromatic compounds
properties: delocalised ring
reaction: electrophilic substitution
alcohols
properties: lone pair on oxygen turns into nucleophile, polar C-OH bond
reactions:
- esterification + nucleophilic substitution
haloalkane
properties: polar c-x bond
reactions: nucleophilic substitution + elimination
what are the 7 different reaction types
- addition reaction
- substitution reaction
- elimination/dehydration
- condensation reaction
- hydrolysis
- oxidation
- reduction
addition reaction
double bond is broken, 2 molecules join together to form single product
functional groups involved: alkene, ketone, aldehydes
substitution reactions
functional group is exchanged for another one
functional groups: halogens, benzene, alcohol
elimination-dehydration
double bond is formed when a functional group is removed and released as part of a smaller molecule
condensation reaction
when two molecules join and small molecule is eliminated
carboxylic acid, amide, alcohol, acid chlorines
hydrolysis
2 smaller molecules formed by splitting lager one with water (breaking polyamides and polyesters)
oxidation
loss of electrons
1) primary alcohol to aldehydes to carboxylic acid
2) secondary alcohol to ketone
reduction
gain of electrons
primary alcohol to aldehydes to carboxylic acid
