21:Alcohols Flashcards
What is the functional group of alcohols
-OH
What are the physical properties of alcohols
Soluble in water (less soluble as the carbon chain gets longer)
Relatively low volatility (high boiling point)
How does the length of an alcohol’s carbon chain affect its solubility
Short chains are very soluble in water
Long chains are less soluble
Why are long chain alcohols less soluble in water
Because the alkyl group is non-polar and cannot form hydrogen bonds. e.g. octan-1-ol is only slightly soluble in water
Why are short chain alcohols very soluble in water
They can from hydrogen bonds to water
Why do alcohols have relatively high boiling points
The -OH group allows hydrogen bonding to occur and hydrogen bonds take more energy to break than induced dipole-dipole bonds.
What are the 2 methods of preparing alcohols
Hydration of alkenes
Hydrolysis of haloalkanes
What conditions are needed for the hydration of alkenes
A phosphoric acid catalyst
What type of reaction is the hydration of alkenes
electrophilic addition
What type of reaction is the hydrolysis of haloalkanes
nucleophillic substitution
What does the haloalkane react with in hydrolysis of a haloalkane
Its heated with water or with a aqueous alkali (like sodium hydroxide)
Equation for combustion of ethanol
C₂H₅OH +3O₂ → 2CO₂ +3H₂O
What is elimination
A reaction in which atoms are lost from the starting molecule without being replaced by new ones
What conditions are needed for the elimination of water from an alcohol to form an alkene
Heated with a concentrated acid usually conc. sulfuric acid or phosphoric acid
What does elimination of water from an alcohol form
an alkene
How is a haloalkane formed from alcohol
Substitution-
The -OH group is replaced by a halogen
What conditions are needed for substitution of an alcohol to make a haloalkane
Presence of an acid
What is a primary alcohol
The C atom joined to the OH group is also bonded to 1 other C atom
What is the general formula of a primary alcohol
RCH₂OH (R is any organic group)
What is a secondary alcohol
The C atom joined to the OH group is also bonded to 2 other C atoms
What is the general formula of a secondary alcohol
R₂CHOH (R is any organic group and can be the same or different)
What is a tertiary alcohol
The C atom joined to the OH group is also bonded to 3 other C atoms
What is the general formula for a tertiary alcohol
R₃COH (R is any organic group and can be the same or different)
What oxidation agent is used to convert alcohols to other organic compounds
Hot aqueous acidic potassium dichromate (K₂Cr₂O₇)
What colour change happens when an alcohol is oxidised by hot aqueous acidic potassium dichromate
Orange to green
What happens when a primary alcohol is briefly heated with aqueous acidic potassium dichromate.
It loses 2 hydrogens to form an aldehyde
What happens when a primary alcohol is heated with aqueous acidic potassium dichromate for a prolonged time
Forms a carboxylic acid
What happens when a secondary alcohol is heated with aqueous acidic potassium dichromate
Forms a ketone
Can ketones be further oxidised by hot aqueous acidic potassium dichromate
No
Can tertiary alcohols be oxidised by hot aqueous acidic potassium dichromate
No
What method is used to make aldehydes
Distillation
What method is used to make carboxylic acids
Refluxing
What method is used to make ketones
Refluxing
What is refluxing
A continuous cycle of boiling, condensing and returning to the reaction flask
What does refluxing ensure
The reaction can continue for a long time with the oxidation agent so the alcohol fully oxidises
