WM - organic reactions *01 *03 Flashcards
phenols - structure
have benzene rings with -OH group attached
various other groups can also be attached
Phenols - test for
Iron(III) chloride solution
- if you add phenol to a neutral iron(III) chloride solution and shake, you get a purple solution
phenols - acidic nature
phenols are weak acids
- they dissolve a little bit in water to form a phenoxide ion (O-) and an H+ ion, so the solution formed is weakly acidic
phenols - reaction with alkalis
phenols react with alkalis to produce a salt and water
eg. phenol + sodium hydroxide –> sodium phenoxide + water
phenols - reaction with carbonates
don’t react
eg. sodium carbonate is not a stong enough base to remove the hydrogen ion from phenol
phenols - how to tell them apart from carboxylic acids
carboxylic acids react with carbonates (and alkalis) and give off CO2 gas
phenol doesn’t react with carbonates
phenol doesn’t give off CO2 when react with alkali
phenols - reaction with acid anhydrides
phenols react with acid anhydrides to form an ester and a carboxylic acid
phenols - how to tell them apart from alcohols
alcohols react with carboxylic acids to make an ester and water
phenols do not react with carboxylic acids to form an ester
(both form an ester and carboxylic acid when reacting with acid anhydride)
alcohols - reaction with carboxylic acids
esterification reaction (also condenstation)
- heat carboxylic acid and alcohol with an acid catalyst (conc. sulfuric/hydrochloric acid)
- form an ester and water
alcohols - reactions with acid anhydrides
alcohol + acid anhydride –> ester + carboxylic acid
alcohols - oxidation reactions
products possible
- carbonyl compounds (ketone and aldehyde)
- carboxylic acid
need to use the oxidising agent acidified potassium dichromate(VI)
alcohols - oxidation of primary alcohols
primary alcohol –> aldehyde –> carboxylic acid
alcohols - oxidation of secondary alcohols
secondary alcohol –> ketone
alcohols - oxidation of tertiary alcohols
arent oxidised
alcohols - primary alcohol method
can control how far the reaction goes
1. gently heat with potassium dichromate(VI) and sulfuric acid in a flask produces an ALDEHYDE
- to get just the ALDEHYDE need to get it out of the oxidising agent - DISTILLATION APPARATUS
(the aldehyde boils at a lower temp. than the alcohol so evaporates and is distilled off immediately)
- to produce CARBOXYLIC ACID needs to be vigorously oxidised
- alcohol mixed with excess oxidising agent and heated UNDER REFLUX
alcohols - secondary alcohol method
under reflux using acidified potassium dichromate(VI)
dehydrating alcohols - methods
- Ethanol vapour is passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3 - the catalyst provides a large surface area for the reaction.
- reflux ethanol with excess concentrated sulfuric acid at 170degreesC.
dehydrating alcohols - using hot catalyst method
ceramic wool is soaked in ethanol, pumice stone or Al2O3 is heated, the alkene gas collects in an inverted cylinder in a water bath
dehydrating alcohols - reflux method
- heat solution in a flask fitted with a vertical Liebig condenser - this causes the solution to continuously boil/evaporate and then condense back into the flask, giving it time to react
- heat solution electronically; hot plates, heating mantles.
dehydrating alcohols - reflux method mechanism
DRAW THIS
The conc. sulfuric acid acts as a dehydration agent in the elimination reaction
- the hydroxyl group will bond to the H+ ions from the strong acid.
- the alcohol is protonated, giving the atom a +ve charge - the +vely charged oxygen will pull electrons away from the neighbouring carbon, and water will ‘fall off’
- creates an unstable carbon intermediate - the carbocation loses H+ and the alkene is formed
alcohols - substitution reactions
alcohols will react with halide ions (eg. HCl) to produce a haloalkane
the -OH group is replaced by the halide (other product is made of the OH lost and what’s left of the halogen)
practical techniques - refluxing
makes sure you don’t lose any volatile organic substances
- organic reactions can be slow and the substances are usually flammable and volatile (low boiling points). if you heat them with a bunsen burner they’ll evaporate or catch fire before they have time to react
- reflux gets around it - to reflux, heat the solution in a flask with a vertical Liebig condenser, this causes the solution to continuously boil/evaporate and then condense back into the flask, giving it time to react
- heat the solution electronically (hot plates and heating mantles) this avoids naked flames that might ignite the compounds
practical techniques - distillation
separates substances with different boiling points
- to distil a mixture, gently heat it in distillation apparatus. the substances will evaporate out of the mixture of increasing boiling point
- when an evaporated substance enters the condenser, it is cooled and condenses back to a liquid, which can be collected by placing a flask at the open end of the condenser
- a thermometer shows the boiling point of the substances that is evaporating at any given time. if you know the boiling point of your pure product, you can use the thermometer to find out when its evaporating and therefore when to collect it
- sometimes a product is formed that will go on to react further if its left in the reaction mixture
- if the product has a lower boiling point than the starting material, the reaction can be carried out in distillation apparatus, the product is distilled from the reaction mixture as soon as it forms, and is collected in a separate container.
- primary alcohols
practical techniques - redistillation
volatile liquids can be purified by redistillation
1. after distillation the product will probs still contain impurities
- if a product and its impurities have different boiling points, then redistillation can be used to separate them.
- just use same distillation technique - when the liquid you want boils collect the pure product
- when the thermometer shows the temperature is changing, put another flask at the end of the condenser because a different liquid is about to be delivered
