Organic 4 Alcohols Flashcards
Solubility decreases with increased chain length….
Because as the non polar section/ carbon chain length increases, the hydroxyl group becomes less significant
Aldehyde
C=O at end of molecule
Ketone
C=O in middle of molecule
Oxidation
Removal of hydrogen
Addition of oxygen
Acidified potassium manganate (Vl) [O]
Heated with alcohol, alcohol oxidises the solution
Purple to colourless
Acidified potassium dichromate [O] + H2SO4
Orange to green
H+/K2Cr2O7
Weaker oxidising agent so is used for oxidising primary alcohols to aldehydes then stopping there
Fehlings solution
Blue to red
Presence of aldehyde
(Copper (ll) ions dissolved jn NaOH)
Benedict’s solution
Blue to brick red precipitate
Copper ll ions dissolved in Na2CO3
Reduced to copper l oxide
Primary alcohol to aldehyde
Heat alcohol in excess with [O]
Aldehyde evaporates into condensing chamber and distilled off immediately
Primary alcohol to carboxylic acid
Excess [O]
Heat under reflux
Secondary alcohol to ketone
Reflux with acidified potassium dichromate
Alcohol ➡️alkene
Reagent
Type of reaction
Concentrated phosphoric acid
Elimination, dehydration
Heat
Hydrogen ions act as catalyst (released by the acids)
Alcohol ➡️alkene mechanism description (not required to learn)
Hydrogen ion accord lone pair on oxygen, bonds to it
Molecule now electron deficient so C-O bond breaks by Heterolytic fission releasing H2O
Carbocation makes molecule unstable
C-H bond breaks by Heterolytic fission and the electrons migrate forming a C=C
Releases a H+ so a H+ has been regenerated hence it’s a catalyst
Test for carboxylic acids
Add sodium carbonate
Effervescence due to release of CO2 (neutralisation)
Alcohol ➡️chloroalkane
Reagent
Type and mechanism
PCl5
Nucleophilic substitution
Produces choroalkane, phosphorus chlorate (POCl3) and HCl (whispy fumes)
Alcohol ➡️bromoalkane
Reagent
HBr produced in situ
Alcohol mixed with potassium bromide and 50% concentrated sulfuric acid to produce HBr and K2SO4
Reflux then distil to separate
OH replaced by bromide
Alcohol ➡️iodoalkane
Phosphorous tri iodide (PI3) produced in situ
Red phosphorus and iodine reacted together
Reflux then distil
Produces H3PO3 too
Why does melting and boiling temperature increase with increased chain length
Stronger London (induced dipole) forces
Drawbacks of biofuels (bio ethanol)
Not carbon neutral due to manufacture (fertilisers), transport and powering agricultural machinery
Fermentation is a slow, batch process so may not meet fuel/electricity demands
Land used for these crops will take land away from food production
Less energy released compared to traditional alkane fuels- cars will be less efficient
