Topic 6- alcohols

Another name for the alcohol functional group

hydroxyl

Why do alcohols have higher boiling points than their corresponding alkane

Alkanes have London forces only. Alcohols are polar cus of O-H so hand London and H bonds

Why is the boiling point of long chain alcohols only slightly longer than their corresponding alkane

The longer the chain, the contribution of London forces increases and the relative importance of H bonding is reduced

Why does alcohols solubility decrease as length increases

The non polar carbon chain can’t form H bonds. So a greater part of the molecule is unable to bond. so shorter Shaun’s are more soluble.

Equation for the combustion of ethanol

C2H5OH + 3O2 → 2CO2 + 3H2O

How does the balanced equation for the combustion of alcohols change as the carbon chain increases

O2 increases by 1.5.

CO2 increases by 1.

H2O increase by 1

Reactants, products and conditions for chlorination of 1° and 2° alcohols

React with phosphorus (V) chloride (PCl5).

Products= haloalkane + POCl3 + HCl.

Happens at room temp

Reactants, products and conditions for chlorination of 3° alcohols

Alcohol + HCl → haloalkane + H2O.

Happens at room temp and when shaken

Reactants, products, and conditions for the 1/2 reaction of bromination of alcohols (to make the HBr to react with the alcohol)

React KBr + 50% conc H2SO4 (sulphuric acid).

Products = HBr + KHSO4 (potassium hydrogen sulphate).

Needs to be heated

Reactants, products, and conditions for the 2/2 reaction of bromination of alcohols

Alcohol + HBr → haloalkane + H2O

Reactants, products, and conditions for iodination of alcohols

Red phosphorus + iodine + alcohol heated under reflux.

2P + 3I2 → 2PI3.

Alcohol + PI3 → haloalkane + H3PO3 (phosphonic acid)

What’s an elimination reaction

Smaller molecule removed form larger parent molecule

Steps in dehydration of alcohols

Under alcohol reflux heat with conc phosphoric acid or conc sulfuric acid.

Removes H2O from adjacent carbons forming C=C

Steps in oxidation of 1° alcohols

1) Alcohol + [O] → aldehyde + H2O.

2)Aldehyde + [O] (heat under reflux) → carboxylic acid

OVERAL EQUATION) alcohol + 2[O] → carboxylic acid + H2O

In oxidising a 1° alcohol, why can aldehydes be oxidised further

The C bonded to the O, after its first oxidation, still has another H atom to remove to be oxidised further.

Between carboxylic acids and aldehydes, which has the highest boiling point

Carboxylic acids cus they can from H bonds

Steps in oxidation of 2° alcohols

Alcohol + [O] (heat under reflux) → ketone + H2O

Why can’t ketones be oxidised further

The C attached to the O has no more H atoms do remove after the 1st oxidation

Properties of ketones

Can’t form H bonds (cus they don’t have H attached to an O) so are volatile (becomes a gas easily) and low boiling point

Why can’t 3° alcohols oxidise

C atom bonded to the OH isn’t bonded to any H atoms… so it’s easily oxidised

Why heat under reflux

Ensures as much of the product forms as possible

How does simple distillation work and what is its advantages

Separate liquids with boiling point difference >25°c.

Advantage= faster and easier than fractional

When’s fractional distillation used

Separate liquids with close boiling points. Or to separate several compounds.

What’s used for solvent extraction

Separating funnel.

The product or impurities must be more soluble in added solvent

How to reimpose water form an organic liquid

use a drying agent.

E.g. anhydrous metal salts e.g. Anhydrous calcium sulfate, Mg sulfate.

Anhydrous salt = powder, hydrated salt= crystalline so add til salt remains powdery.

Remove drying agent by filtration.

What will impurities to to boiling and melting point

Lower melting p, raise boiling