3.5 Alcohols Flashcards
What are some properties of alcohols?
They are a homologous series Functional group OH General formula: Cn H2n+1 OH The prefix hydroxy is used if another functional group is present V-shaped on the end High boiling points
Why do alcohols have high boiling points?
The have hydrogen bonding
What are the types of alcohol?
The carbon with the OH functional group has
Primary - only 1 other carbon attached
Secondary - 2 other carbons attached
Tertiary - 3 other carbons attached
What are some uses of alcohols?
Perfumes/ aftershave
Mouthwash
Used in manufacture of drugs, detergents and inks
Does ethanol dissolve in water? Why?
Yes
They both have hydrogen bonding
How can we produce alcohols?
Fermentation
Hydration of alkenes
What is involved in fermentation of alcohols?
Yeast, sugar and water is heated between 30-40 degrees (37 optimum)
After several days the flask will contain around 15% ethanol = mixture of alcohol and water
As yeast is living this is a natural process - anaerobic respiration takes place
What is the equation for fermentation?
Glucose ——> ethanol + CO2
Over the arrow: enzymes in yeast
Under the arrow: 30-40 degrees
What is produced in fermentation?
A mixture of ethanol and water
The only product - alcoholic drinks
Why is the temperature conditions as they are for fermentation?
Too low = prevents respiration of the yeast
Too high = denatures the enzymes
What is used to acquire the pure alcohol from fermentation - in the lab?
Fractional distillation
Alcohol boils at 80 degrees
Water boils at 100 degrees
What are some advantages and disadvantages for fermentation?
Renewable sugars used
Aqueous solution of ethanol - could be good if small quantities are needed
Batch process - labour intensive requiring people to change batches
Requires a lot of energy for fractional distillation
How does hydration of alkenes take place?
Ethene is reacted with water(steam)
Using phosphoric acid as a catalyst - H3PO4
Requires high temperature and pressure
Done on a large industrial scale that the majority of alcohols are made from
What is the mechanism for hydration of alkenes?
First arrow from the double bond of the alkene to the H+ ion
A carbocation is formed - second arrow from the lone pair of the oxygen in water to the positive carbon
The water is now attached to the chain with a + charge on the oxygen - the arrow goes from the middle of the O-H on to the oxygen
The alcohol and H+ ion are the final products
What are some advantages and disadvantages for hydration?
Non renewable as the alkenes are from crude oil
Fast continuous process
Pure product - better for larger quantities
Where did the H+ ion come from in hydration and dehydration? Significance?
The phosphoric acid
It takes part in the reaction but is still considered a catalyst as it is regenerated at the end
What is carbon neutral?
No overall carbon dioxide emissions
What is an example of carbon neutral?
Plants absorbing CO2 via photosynthesis
Fermented into ethanol (5-10%) used in biofuels in cars - as it burns nicely with less CO2 produced
Combustion - when the biofuel is used in the cars producing little CO2
The CO2 taken in balances that which is given out
What is dehydration of alcohols?
Turns the alcohol back into an alkene by removing water from it
How does dehydration take place?
Ceramic wool is soaked in an alcohol and heated with aluminium oxide granules
OR
Using phosphoric acid as a catalyst (not the aluminium oxide)
What is the mechanism for dehydration?
First arrow from the lone pair on the oxygen in the alcohol to the H+ ion
On intermediate where the H is attached to the alcohol (like water attached) - first arrow from the middle of the C-O to the oxygen
Then from a the middle of a C-H bond to the middle of the C-C bond
Forming an alkene, water and a H+ ion
What is the simplest oxidation of alcohols?
Combustion producing CO2 + H2O
What is the usual oxidising agent? Written in equations as?
Acidified Potassium dichromate (VI)
- often acidified with dilute sulphuric acid
[O] - you use this as oxygen when balancing
What is the colour change in oxidation of alcohols?
Orange to green
Dichromate (VI) ions are orange
Chromate (III) ions are green
