Alcohols

Why does solubility of alcohols decrease as the carbon chain length increases

The chains are non-polar so exhibit london dispersion forces only and disrupt the hydrogen bonding network which forms between nthe alcohol functional group and water molecules.

What are the conditions needed for the dehydration of alcohols

Heated in the presence of concentrated sulphuric acid or phosphoric acid (H3PO4)

What kind of mechanism does dehydration take place by

Via elimination reaction

Outline the mechanism by which the dehydration of alcohols occurs

What is needed for the halogenation of alcohols

A halogenating agent

What is the halogenating agent for the chlorination of alcohols

Phosphorous pentachloride (PCl5)

What is formed in the chlorination of alcohols

• chloroalkanes

• Misty HCl fumes

• Phosphoryl chloride (POCl3)

What is the halogenating agent for the chlorination of a tertiary alcohol

Concentrated HCl

What are the conditions necessary for the bromination of alcohols

• Heated under reflux

• With sodium bromide or potassium bromide

• 50% concentrated sulphuric acid

What are the steps involved in the bromination of alcohols and what is formed

• an acid base reaction occurs between the sulphuric acid and the K/NaBr

• HBr is formed

• HBr reacts with alcohol in a substitution reaction

• Water and bromoalkane is formed

What are the steps required in the iodination of alcohols and what is formed

• red phosphorous is reacted with iodine

• Forms phosphorous (III) iodide (PI3)

• Phosphorous (III) iodide reacts with alcohol to form iodoalkane and phosphoric (III) acid

Give the equation for the reaction between red phosphorous and iodine

2P + 3I2 → 2PI3

Give the equation for the reaction between phosphorous (III) iodide and an alcohol

PI3 + 3CH3(OH) → 3CH3I + H3PO4

What is observed when acidified potassium dichromate (VI) solution is used to oxidise a chemical

Colour change from orange to green

Give the ionic half equation for potassium dichromate (VI) when it is used as an oxidising agent

Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

What are the conditions necessary for the oxidation of alcohols

Heating with a mixture of dilute sulphuric acid with sodium/potassium dichromate (VI) solution

What is formed when primary alcohols are heated with acidified potassium dichromate (VI) in distillation

An aldehyde

What is the general structural formula for aldehydes

What is the iupac suffix for aldehydes

-al

What is formed when primary alcohols are heated under reflux with acidified potassium dichromate (VI)

Carboxylic acid

Why are anti-bumping granules used

They provide a large surface area which provides nucleation sites for smaller bubbles to form on and prevent larger and potentially hazardous bubbles from forming

Why is the ethanal obtained in the distillate in the partial oxidation of ethanol pure and not contain any unreacted ethanol

Ethanol exhibits hydrogen bonding, ethanal does not

Why is it necessary for alcohols to be heated under reflux for it to be fully oxidised

Allows reaction to be heated in order to significantly increase the rate of reaction while avoiding organic products or reactants with low boiling points from boiling and escaping from reaction vessels

What do secondary oxidise to form

Ketones

What is the general structural formula of ketones

What is the IUPAC suffix for ketones

-one

Why can’t tertiary alcohols be oxidised to form

There are no hydrogen atoms bonded to the central carbon atom to which the alcohol functional group is bonded

Give the half equation for the oxidation of methanol to methanal

CH3OH → HCHO + 2e- + 2H+

Give the full redox equation for the reaction between methanol and acidified dichromate (IV) ions

Cr2O72- + 8H+ + 3CH3OH → 2Cr3+ 7H2O + 3HCHO

Write a half-equation for the oxidation of ethanol to ethanoic acid

H2O + CH3CH2OH → CH3COOH + 4H+ + 4e-

Write the full redox equation for the reaction between ethanol and acidified dichromate (VI) ions

2Cr2O72- + 16H+ + 3CH3CH2OH → 4Cr3+ + 11H2O + 3CH3COOH

What is used to test for the alcohol functional group

Phosphorous (V) chloride

What is formed/observed for the positive test for an alcohol functional group

Steamy fumes of HCl gas, as well as a chloroalkane and POCl3

What are the two substances used to test for aldehydes

• Tollen’s Reagent (ammonium silver nitrate, [Ag(NH3)2]+)

• Fehling’s solution (containing Cu2+ ions)

Describe and explain the positive result for the test for Aldehydes using Tollens’ Reagent

• The aldehyde is oxidised to a carboxylic acid, and the silver ions are reduced to silver (REDOX reaction)

• Colourless solution goes to form a silver mirror

Describe and explain the positive result for the test for aldehydes using Fehling’s solution

• Aldehydes reduce Cu2+ to Cu+ giving a red precipitate of copper (I) oxide

• Blue solution forming red precipitate (Cu2O)

What are the conditions used for the hydration of ethene

• 300˚C

• Phosphoric acid (H3PO4) catalyst

• 60-70 atm

What are the advantages of hydration

• no other products are formed leaving already pure ethanol

• Continuous process so fast

What are the disadvantages of hydration

• requires expensive equipment

• Conditions required need a lot of energy which is costly

• Uses non-renewable ethene

Outline the mechanism for the electrophilic addition of H+/H2O to ethene

What are the conditions used in the fermentation of glucose

• 38-40˚C

• Zymase from the yeast acts as a catalyst

• Anoxic/anaerobic conditions

Give the equation for the fermentation of glucose

C6H12O6 → 2CO2 + 2C2H5OH

What are the advantages of fermentation

• Cheaper equipment

• Less energy, cheaper

• Glucose/sugar used is a renewable resource

What are the disadvantages of fermentation

• Non-continuous/batch process

• Long process

• Product formed (ethanol) is not pure so needs to be purified

• Crops used for growing the sugar can take up a lot of space

Why is the use of ethanol as a fuel considered “carbon-neutral”

The amount of carbon dioxide produced in combustion and fermentation is equal to that taken in during photosynthesis (everything cancels out)

Why is the use of ethanol as a fuel not considered “carbon-neutral”

Transportation and purification of fermentation produced ethanol produced additional emissions of carbon dioxide