ALCOHOLS

How do you name alcohols?

• have the -ol ending

• if there are other functional groups they could have the hydroxy- prefix

What is the shape of alcohols?

• tetrahedral between the H-C-H bonds and the C-C-O bonds

• bond angles are 109.5

• bent between the H-O-C

• bond anglea are 104.5

What’re the boiling points of alcohols?

they have a low volatility and high boiling points due to their ability to form hydrogen bonds between alcohol molecules

Why can smaller alcohols dissolve in water?

they can form hydrogen bonds to water molecules

What is a primary alcohol?

where only 1 carbon is attached to the carbon adjoining the oxygen

What is a secondary alcohol?

where 2 carbons are attached to the carbon adjoining the oxygen

What is a tertiary alcohol?

where 3 carbons are attached to the carbon adjoining the oxygen

What oxidising agent causes alcohols to oxidise?

potassium dichromate

What occurs in the partial oxidation of primary alcohols?

• forms an aldehyde

• reagent- potassium dichromate solution and dilute sulfuric acid

• conditions - use a limited amount of dichromate, warm gently, distill out the aldehyde as it forms

What is distillation used for?

• separation technique

• separates an organic product from its reacting mixture

• only collect the distillate at the approximate boiliing point

Where should the bulb of the thermometer be during distillation?

at the T junction connecting to the condenser to measure the correct boiling point

Why does water go into the bottom of the condenser during distillation?

allows more efficient cooling and prevents back flow of water

Why are electric heaters often used rather than bunsen burners during distillation of organic chemicals?

organic chemicals are often highly flammable and could set on fire with a naked flame

Draw a diagram of distillation?

What occurs during the full oxidation of primary alcohols?

• forms a carboxylic acid

• reagent - potassium dichromate solution and dilute sulfuric acid

• conditions - use an excess of dichromate, heat under reflux

When is reflux used?

when heating organic reaction mixtures for long periods as the condenser prevents organic vapours from escaping by condensing them back to liquids

Why should you never seal the end of the condenser during reflux?

the build up of gas pressure could cause the apparatus to explode

Why are anti-bumping granules added to the flask in distillation and reflux?

prevents vigorous, uneven boiling by making small bubbles

Draw a diagram of a refluxer

What happens in the oxidation of secondary alcohols?

• forms a ketone

• reagent - potassium dichromate and dilute sulfuric acid

• conditions - heat under reflux

Why can tertiary alcohols not be oxidised?

there is no hydrogen atom bonded to the carbon with the -OH group

What is tollens reagent?

formed by mixing aqueous ammonia and silver nitrate

What happens when you use tollens reagent to distinguish between aldehydes and ketones?

• heat gently

• aldehydes are oxidised by tollens reagent so a silver mirror forms coating on the inside of the test tube

What happens when you use fehlings solution to distinguish between aldehydes and ketones?

• heat gently

• aldehydes are oxidised by fehlings solution into carboxylic acids and the blue ions turn to a red precipitate

How can you test for the presence of a carboxylic acid?

add sodium carbonate which will fizz and produce carbon dioxide

What occurs when an alcohol is dehydrated?

• an alkene forms

• reagents - concentrated sulfuric acid or phosphoric acid

• conditions - warm, under reflux

• acid catalysed elimintation

What is the mechanism for an acid catalysed elimation?

Where does the H+ come from in the acid catalysed elimination mechanism?

from the conc H2SO4 or conc H3PO4

What’re the 2 ways to form ethanol?

• fermentation

• from ethene

What occurs in fermentation?

• glucose → ethanol + carbon dioxide

• conditions: yeast, no air, warm (30-40)

What occurs when using ethene to get ethanol?

• ethene from cracking of fractions from distilled crude oil

• hydration/ addition

• conditions: high temp (300), high pressure (70atm) strong acid catalyst

What is the optimum temperature for fermentation?

• 38 degrees

• lower temperatures means the reaction is too slow

• higher temperatures means the yeast dies and enzymes denature

What’re advantages to using fermentation?

• sugar is a renewable resource

• production uses low level technology

• cheap equipment

What’re advantages to using ethene to make ethanol?

• faster reaction

• purer product

• continuous process

What’re disadvantages to fermentation?

• batch process which is slow and gives high production costs

• ethanol needs to be purified by fractional distillation

• depletes land used for growing food crops

What’re disadvantages to using ethene to make ethanol?

• high technology equipment needed

• ethene is non-renewable

• high energy costs for pumping to produce high pressures

What is the mechanism for the acid catalysed addition mechanism for the hydration of ethene?

What is biofuel?

a fuel produced from plants

What does carbon neutral mean?

an activity which has no net annual carbon emissions to the atmosphere