alcohols

General formula of alcohols

CnH2n+1OH

Suffix used to name alcohols

-ol, with the position number of the OH group if needed

Prefix used when OH is present alongside a functional group that takes a suffix, e.g. a carboxylic acid

hydroxy-

Name of CH3CH(OH)COOH

2-hydroxypropanoic acid

How to name alcohols with 2 or more OH groups

use di, tri and keep the e on the stem, e.g. ethane-1,2-diol and propane-1,2,3-triol

Name of CH3CH(OH)CH2CH3

butan-2-ol

Primary alcohol

an alcohol where the carbon bonded to the OH group is attached to 1 other carbon

Secondary alcohol

an alcohol where the carbon bonded to the OH group is attached to 2 other carbons

Tertiary alcohol

an alcohol where the carbon bonded to the OH group is attached to 3 other carbons

Example of a primary alcohol

propan-1-ol

Example of a secondary alcohol

propan-2-ol

Example of a tertiary alcohol

methylpropan-2-ol

Bond angle of H-C-H and C-C-O in alcohols

109.5 degrees (tetrahedral, 4 bonding pairs)

Bond angle of H-O-C in alcohols

104.5 degrees (bent, 2 bonding pairs and 2 lone pairs)

Why the H-O-C angle is smaller than 109.5 degrees

lone pairs repel more than bonding pairs

Why alcohols have relatively high boiling points and low volatility

they form hydrogen bonds between alcohol molecules

Why smaller alcohols dissolve in water

they can form hydrogen bonds with water molecules

Oxidising agent used to oxidise alcohols

potassium dichromate(VI), K2Cr2O7, with dilute sulfuric acid

Colour change when dichromate oxidises an alcohol

orange Cr2O7 2- reduces to green Cr3+

Symbol used to represent oxygen from the oxidising agent in simplified equations

[O]

Product of partial oxidation of a primary alcohol

aldehyde

Reagents for partial oxidation of a primary alcohol

potassium dichromate(VI) solution and dilute sulfuric acid

Conditions for partial oxidation of a primary alcohol

limited dichromate, warm gently and distil off the aldehyde as it forms

Ending of an aldehyde name

-al

Why aldehydes do not need a number in the name

the C=O is always on the first carbon of the chain

Equation for partial oxidation of propan-1-ol

CH3CH2CH2OH + [O] → CH3CH2CHO + H2O

How to write an aldehyde in a condensed formula

CHO not COH, e.g. CH3CH2CHO

Purpose of distillation

to separate an organic product from its reaction mixture

How to maximise yield of aldehyde when distilling

only collect the distillate at the approximate boiling point of the aldehyde

Where the thermometer bulb should be in distillation

at the T junction leading to the condenser

Why water goes in at the bottom of the condenser

it flows against gravity, which cools more efficiently and prevents back flow

Why electric heaters are used for organic chemicals

organic chemicals are highly flammable and could ignite with a naked flame

How to improve the yield of distillate

cool the collection flask in ice

Product of full oxidation of a primary alcohol

carboxylic acid

Conditions for full oxidation of a primary alcohol

excess potassium dichromate(VI) and dilute sulfuric acid, heat under reflux

Equation for full oxidation of propan-1-ol

CH3CH2CH2OH + 2[O] → CH3CH2COOH + H2O

Purpose of reflux

to heat a reaction mixture for a long time without losing volatile vapours, as the condenser returns them to liquid

Why the top of the condenser must never be sealed

gas pressure could build up and cause the apparatus to explode

Purpose of anti-bumping granules

to prevent vigorous uneven boiling by making small bubbles form instead of large ones

Product of oxidising a secondary alcohol

ketone

Conditions for oxidising a secondary alcohol

potassium dichromate(VI) and dilute sulfuric acid, heat under reflux

Ending of a ketone name

-one

When a ketone name needs a position number

when it has 5 or more carbons, e.g. pentan-2-one

Equation for oxidation of propan-2-ol

CH3CH(OH)CH3 + [O] → CH3COCH3 + H2O

Can ketones be oxidised further by dichromate

no

Can tertiary alcohols be oxidised by dichromate

no, because there is no hydrogen on the carbon bonded to the OH group

Why aldehydes and ketones can be distinguished by oxidation

aldehydes can be oxidised to carboxylic acids but ketones cannot

Tollens' reagent

aqueous ammonia mixed with silver nitrate, the active substance is [Ag(NH3)2]+

Conditions for Tollens' test

heat gently

Positive result of Tollens' test

a silver mirror forms on the inside of the test tube (aldehyde)

Result of Tollens' test with a ketone

no visible change

What happens to the silver ions in Tollens' test

silver(I) ions are reduced to silver atoms

Equation for Tollens' test with ethanal

CH3CHO + 2Ag+ + H2O → CH3COOH + 2Ag + 2H+

Fehling's solution

a solution containing blue Cu2+ ions

Conditions for Fehling's test

heat gently

Positive result of Fehling's test

blue solution changes to a red precipitate of Cu2O (aldehyde)

Result of Fehling's test with a ketone

no reaction

Equation for Fehling's test with ethanal

CH3CHO + 2Cu2+ + 2H2O → CH3COOH + Cu2O + 4H+

Test for a carboxylic acid

add sodium carbonate, it fizzes and produces carbon dioxide

Dehydration reaction

removal of a water molecule from a molecule

Reaction of alcohol dehydration

alcohol → alkene

Reagents for dehydration of an alcohol

concentrated sulfuric acid or concentrated phosphoric acid

Conditions for dehydration of an alcohol

warm under reflux

Role of the acid in alcohol dehydration

dehydrating agent and catalyst

Type of reaction in alcohol dehydration

acid catalysed elimination

Equation for dehydration of propan-1-ol

CH3CH2CH2OH → CH2=CHCH3 + H2O

Alkenes formed from dehydrating butan-2-ol

but-1-ene and but-2-ene, with more but-2-ene formed

Isomers that but-2-ene can exist as

E and Z isomers

Benefit of making alkenes from alcohols

a possible route to polymers without using monomers derived from oil

Equation for fermentation of glucose

C6H12O6 → 2CH3CH2OH + 2CO2

Conditions for fermentation

yeast, no air, 30 to 40 degrees C

Optimum temperature for fermentation

around 38 degrees C

Why fermentation is too slow at low temperatures

the reaction rate is too slow

Why fermentation fails at high temperatures

the yeast dies and the enzymes denature

Why fermentation is done without air

air oxidises the ethanol to ethanoic acid (vinegar)

Advantages of fermentation

sugar is renewable and it uses low level technology and cheap equipment

Disadvantages of fermentation

slow batch process with high production costs, impure ethanol that needs fractional distillation, and it uses land that could grow food crops

Equation for industrial production of ethanol from ethene

CH2=CH2(g) + H2O(g) → CH3CH2OH(l)

Conditions for industrial hydration of ethene

300 degrees C, 70 atm, concentrated H3PO4 catalyst

Source of ethene for industrial ethanol production

cracking of fractions from distilled crude oil

Type of reaction in industrial ethanol production

hydration (addition)

Hydration

the addition of water to a molecule

Advantages of making ethanol from ethene

faster reaction, purer product, continuous process (cheaper manpower)

Disadvantages of making ethanol from ethene

high technology equipment (expensive), ethene is non-renewable, high energy costs for pumping to high pressure

Biofuel

a fuel produced from plants

Why ethanol from fermentation can be called carbon neutral

the CO2 released on burning was absorbed from the air by photosynthesis as the plant grew

Why biofuel ethanol may not be carbon neutral

energy for irrigation, fractional distillation and processing may come from fossil fuels

Definition of carbon neutral

an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere

Equation for photosynthesis

6CO2 + 6H2O → C6H12O6 + 6O2

Equation for combustion of ethanol

2CH3CH2OH + 6O2 → 4CO2 + 6H2O

Net CO2 balance for ethanol biofuel

for every 6 CO2 absorbed, 6 CO2 are emitted, so there is no net contribution