alcohols Flashcards
what is the functional group of alcohols
-OH
how are the alcohols classified
Primary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to one other carbon atom (or alkyl group)
Secondary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to two other carbon atoms (or alkyl groups)
Tertiary alcohols are alcohols in which the carbon atom bonded to the -OH group is attached to three other carbon atoms (or alkyl groups)
which alcohols can be oxidised
Only primary and secondary alcohols can get oxidised when mildly oxidised with acidified K2Cr2O7
Primary alcohols get mildly oxidised to aldehydes
Secondary alcohols get mildly oxidised to ketones
which alcohols cannot be oxidised
Tertiary alcohols do not undergo oxidation with acidified K2Cr2O7
what are the oxidising agents of alchols
The oxidising agents of alcohols include acidified K2Cr2O7 or acidified KMnO4
Acidified potassium dichromate(VI), K2Cr2O7, is an orange oxidising agent
Acidified means that the potassium dichromate(VI) is in a solution of dilute acid (such as dilute sulfuric acid)
For potassium dichromate(VI) to act as an oxidising agent, it itself needs to be reduced
When alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
Acidified potassium manganate(VII), KMnO4, is a purple oxidising agent
When alcohols are oxidised, the purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions
by which method are primary alcohols oxidised
distillation to produce an aldehyde
refluxing then distillation to produce carboxylic acids
what functional groups do aldehyde and ketones have
C=O
functional group of an aldehyde
CHO C=O
l
H
how can u test for the presence of the aldehyde
The presence of an aldehyde group (-CHO) in an unknown compound can be determined by the oxidising agents Fehling’s and Tollens’ reagents
fehlings solution test
Fehling’s solution is an alkaline solution containing copper(II) ions which act as the oxidising agent
When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Cu2+ ions are reduced to Cu+ ions
In the alkaline conditions, the carboxylic acid formed will be neutralised to a carboxylate ion (the -COOH will lose a proton to become -COO- )
The carboxylate ion (-COO-) will form a salt with a positively charged metal ion such as sodium (-COO-Na+)
The clear blue colour of the solution turns opaque red due to the formation of a copper(I) oxide precipitate
Ketones cannot be oxidised and therefore give a negative test when warmed with Fehling’s solution
tollens reagents test
Tollens’ reagent is an aqueous alkaline solution of silver nitrate in excess ammonia solution
Tollen’s reagent is also called ammoniacal silver nitrate solution
When warmed with an aldehyde, the aldehyde is oxidised to a carboxylic acid and the Ag+ ions are reduced to Ag atoms
In the alkaline conditions, the carboxylic acid will become a carboxylate ion and form a salt
The Ag atoms form a silver ‘mirror’ on the inside of the tube
Ketones cannot be oxidised and therefore give a negative test when warmed with Tollens’ reagent
what are the ways that alcohols can be produced
fermentation
reaction of ethene and steam
fermentation of carbs
temp= 40 degrees
pressure=atmospheric
catalyst=zymases in yeast
other requirements = yeast and anaerobic resp
raw materials= carbs
type of material= renewable
type of process=batch
reaction rate = slow
purity of ethanol= impure - capped at 15%
reaction of ethene with steam
temp= 300
pressure = 70 atm
catalyst = phosphoric acid
raw material= ethene from crude oil
raw material type = non-renewable
type of process=continuous
rate =fast
purity=pure
is the production of ethanol carbon neutral
the amount of moles produced is equal to the amount of moles released
however it is not the only process involved - carbon cycle etc
apparatus in distillations - aldehyde
-pear shaped flask
-antibumping granules
-conical flask
-condenser
-thermometer- going into condenser
-screw-cap adaptor
water flows in bottem and out top
apparatus in refluxing-carboxylic acids
vertical condenser
pear-shaped flask
no bung to prevent build up of pressure
what can be the things that a student can do wrong in aldehyde + carboxylic acid prac
reflux- bung in - causes pressure build up
water out of bottom of condenser - needs to go out top and flow upwards
apparatus not clamped
thermometer is not needed
process for oxidation equation reaction
write start molecule
draw end product
add [o] to reactant
balance h by adding h20
balance [0] in box by adding large no
elimination/dehydration of alcohols
conc sulphuric acid at 180degrees
arrow from OH- to H+
then draw bonds of +O-H
|
H
arrow middle of C-O
then arrow from adjacent H to middle to represent e- moving to form double bond
carbon that had OH on needs to have +ve charge
functional group test
C=C - add bromine water, shake
result = orange to colourless
O-H - add sodium
result = effervescence and H gas given off
C=O-H - Tollens (warm ammoniacal silver nitrate
result silver mirror
-Fehlings and warm
result = red ppt colour change from blue to red - think benedicts
C=O-O-H add sodium hydrogen carbonate
result = effervescence, CO2 produced
test limewater goes cloudy
Aldehyde and carboxyl - potassium dichromate
Organelle to Green
How to also test for alcohol
Sweet smell after fermentation
What does carbon neutral mean
An activity which has no net / overall (annual) carbon emissions to the atmosphere / air
Temp required for fermentation
25°C≤T≤42°C OR 298K≤T≤315K
