C14- Alcohols Flashcards
Alcohol functional group
-OH
Polar
Physical properties of alcohols compared to alkanes
less volatile
higher mp
greater water solubility
differences caused by polarity of bond
Volatility of alcohols
in the liquid state H bonds hold the molecules together
Lower volatility than alkanes due to the additional energy needed to overcome the H bonds
Solubility of alcohols
Soluble in water due to polar OH group
Forms H bonds between OH group and water molecules
Solubility of alcohols
increasing chain length
As chain length increases the solubility of the alcohol decreases
The OH group has less of an influence
classification of alcohols
Based on number of hydrogen atoms and alkyl groups attached to the carbon atom with the OH functional group
Primary alcohols
+exception
OH group is attached to the carbon atom with 2 hydrogen atoms and one alkyl group
exception of methanol- is primary
secondary alcohols
OH group is attached to Carbon atom that is attached to one Hydrogen atom and two alkyl groups
Tertiary alcohols
OH group attached to carbon atom with 3 alkyl groups, and no hydrogen atoms
Potassium dichromate(VI) formula
K2Cr2O7
Potassium dichromate colour change
causes oxidation
Dichromate ions (VI) are orange then oxidised into green chromium (III) ions
oxidation of primary alcohols
product depends on the reaction conditions such as reagent in excess, conditions or technique used influence the product formed
Aldehydes
Further oxidised into carboxylic acids
Preparation of aldehydes
gentle heating of primary alcohols with acidified potassium dichromate
Aldehyde distilled out to prevent further oxidation or reaction into carboxylic acids
Preparation of carboxylic acids
If a primary alcohol is heated strongly under reflux
heating under reflux ensures all aldehyde undergoes oxidation to a carboxylic acid
Reflux conditions arrow
K2Cr2O7/ H2SO4
————————->
reflux
H2SO4 can be any concentrated acid
Oxidation of secondary alcohols
Oxidised into ketones
not possible to oxidise further using dichromate (VI) ions
To ensure completion, secondary alcohol is heated under reflux with oxidising mixture
Oxidising mixture symbol
[O]
Oxidation of tertiary alcohols
NO oxidation reaction
acidified dichromate(VI) remains orange
Dehydration of alcohols
Water molecule removed from starting molecule by an elimination reaction
forms Alkene
Concentrated strng acd- e.g. H2SO4
Dehydration of alcohol
Product
conditions
Heat under reflux with a concentrated acid such as H2SO4 or H3PO4
Produces an alkene
Substitution reaction of an alcohol
halides
Heat under reflux with sulfuric acid and a sodium halide, HBr formed in situ (in place)
Condition for oxidation of an alcohol
Heat the alcohol under reflux with acidified potassium (or sodium) dichromate (VI) solution
define reflux
The continuing boiling and condensing of a mixture
Why heat under reflux
to ensure completion
e.g. all aldehyde is oxidised to carboxylic acid
2 methods of production of ethanol
Hydration (react with water over a catalyst of phosphoric acid and silicon)
Fermentation ( fermentation of sugars to produce ethanol and CO2)
3 key steps to purify an organic liquid- alcohol
Use a separating funnel to separate organic and aqueous layers- remove lower layer
Dry with an anhydrous salt e.g. CaCl2
Re-distillation
conditions of reaction to produce alcohol form alkene
Steam and acid catalyst (phosphoric acid)
