alcohols Flashcards
what are alcohols
a homologous series containing the hydroxyl (oh) group
what are some commercially important alcohols
methanol , ethanol , ethane-1,2 diol
how do we classify alcohols
alcohols are classified according to the enviroment of the OH group
what are the 3 types of alcohols
primary, secondary or tertiary
how do we classify primary , secondary and tertiary
classification depends on the number of R groups (alkyl) attached to the carbon carying the OH group
why do alcohols have a lower than expected volatility
because they have higher than expected boiling points
why do alcohols have higher than expected boiling points
because they have hydrogen bonding which forms between alcohol molecules
what is the definition for volatility
volatility is the ease with which a liquid turns into a gas . volatility increases as boiling point decreases
what happens to boiliing point of the alcohols
boiling point increases with molecular size due to increased london forces . alcohols have higher boiling points than similar molecular mass alkanes due to the added prescence of inter- molecular hydrogen bonding. and more energy is needed to seperatee the molecules
what happens to the solubility of alcohols
short chain alcohols are very soluble in water because of the hydrogen bonds that form between alcohol and WATER molecules .
this happens as the OH is polar however solubility decreases as the chain length increases . this is because the carbon chain increases which is non polar and will not form hydrogen bonds with water molecules , therefore reduces the interaction water can make with the alcohol
what reactions do alcohols undergo
-combustion
-oxidation
-dehydration
-substitution
why is combustion of alcohols good
alcohols make useful fuels
-this is because they have high enphalpies of combustion(lots of energy is released)
-do not contain sulfur so there is less polution
-can be obtained from renewable resources
how can alcohols be obtained from renewable resources
-ethanol can be produced from the fermentation of glucose by yeast
what flame do alcohols burn in
a light blue flame
whats the test for water
-cobalt chloride paper from blue to pink
or
-anhydrous copper sulphate from white to blue
what alcohols can be oxidised and how
primary and secondary alcohols can be oxidised by an oxidising agent
what is the oxidising agent used
a solution containing acidified dichromate ions
how can the oxidising mixture be made
from potassium dichromate K2Cr2O7 and dilute sulfuric acid H2SO4
how will we know that oxidation takes place
oxidising agent is orange and turns to green when it reacts to form Cr3+
what are the two products that can be formed from oxidation of primary alcohols
aldehyde and carboxylic acid
how is an aldehyde made
distill off the aldehyde before it gets oxidised further in distillation , use a excess of the alcohol so that there is insufficient oxidising agent to carry through to a carboxylic acid
how is it possible to distill off the aldehyde
the aldehyde has a lower boiling point than the alcohol so it can be distilled off. this is because of the prescence of hydrogen bonds in the alcohol and not in the aldehyde
how do we make a carboxylic acid
either use an aldehyde of alcohol in reflux
how do we ensure good yeild for making a carboxylic acid
use an excess of the oxidising agent and make sure that the aldehyde formed as the half way product stays in the mixture
what will happen in reflux that we just ignore
the oxidising agent will still go green but that does not mean you have otained a carboxylic acid it means you have obtained a aldehyde and need to reflux for longer
what happens when the reflux reaction is finished
the carboxylic acid is distilled off
what do you need to remeber in reflux and distillation
a molecule of water is produced when an aldehyde or carboxylic acid
what are secondary alcohols oxidised into
secondary alcohols are oxidised to ketones and no further
what do tertiary alchols get oxidised into
tertiary alcohols do not undergo oxidiation reactions so the acidified dichromate solution remains orange
what is dehydration of alcohols
an elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule
what do you need for a dehydration reaction
- conc H2SO4 or conc H3PO4
-reflux at 180
what do you produce from dehydration of an alcohol
an alkene and water
where do you remove the atoms and add the double bond
you add the double bond between the OH and a H on adjacent molecule forming 2 isomers
what is a substitution reaction with an alcohol
substitution reactions occur when a strong acid and a substance that releases halide ions when aqueous is added to an alcohol. This occurs under reflux
what are the products in a substituon reaction of an alcohol
haloalkane and water
do amines or alcohols have higher boiling points and why
alcohols as both amines and alcohols have hydrogen bonding however oxygen has 2 lone pairs whereas nitrogen only has 1 so has fewer hydrogen bonds
