WM - organic reactions *01 *03

Question 1

phenols - structure

Answer 1

have benzene rings with -OH group attached

various other groups can also be attached

Question 2

Phenols - test for

Answer 2

Iron(III) chloride solution

- if you add phenol to a neutral iron(III) chloride solution and shake, you get a purple solution

Question 3

phenols - acidic nature

Answer 3

phenols are weak acids
- they dissolve a little bit in water to form a phenoxide ion (O-) and an H+ ion, so the solution formed is weakly acidic

Question 4

phenols - reaction with alkalis

Answer 4

phenols react with alkalis to produce a salt and water

eg. phenol + sodium hydroxide –> sodium phenoxide + water

Question 5

phenols - reaction with carbonates

Answer 5

don’t react

eg. sodium carbonate is not a stong enough base to remove the hydrogen ion from phenol

Question 6

phenols - how to tell them apart from carboxylic acids

Answer 6

carboxylic acids react with carbonates (and alkalis) and give off CO2 gas

phenol doesn’t react with carbonates
phenol doesn’t give off CO2 when react with alkali

Question 7

phenols - reaction with acid anhydrides

Answer 7

phenols react with acid anhydrides to form an ester and a carboxylic acid

Question 8

phenols - how to tell them apart from alcohols

Answer 8

alcohols react with carboxylic acids to make an ester and water

phenols do not react with carboxylic acids to form an ester

(both form an ester and carboxylic acid when reacting with acid anhydride)

Question 9

alcohols - reaction with carboxylic acids

Answer 9

esterification reaction (also condenstation)

• heat carboxylic acid and alcohol with an acid catalyst (conc. sulfuric/hydrochloric acid)
• form an ester and water

Question 10

alcohols - reactions with acid anhydrides

Answer 10

alcohol + acid anhydride –> ester + carboxylic acid

Question 11

alcohols - oxidation reactions

Answer 11

products possible

• carbonyl compounds (ketone and aldehyde)
• carboxylic acid

need to use the oxidising agent acidified potassium dichromate(VI)

Question 12

alcohols - oxidation of primary alcohols

Answer 12

primary alcohol –> aldehyde –> carboxylic acid

Question 13

alcohols - oxidation of secondary alcohols

Answer 13

secondary alcohol –> ketone

Question 14

alcohols - oxidation of tertiary alcohols

Answer 14

arent oxidised

Question 15

alcohols - primary alcohol method

Answer 15

can control how far the reaction goes
1. gently heat with potassium dichromate(VI) and sulfuric acid in a flask produces an ALDEHYDE
- to get just the ALDEHYDE need to get it out of the oxidising agent - DISTILLATION APPARATUS
(the aldehyde boils at a lower temp. than the alcohol so evaporates and is distilled off immediately)

2. to produce CARBOXYLIC ACID needs to be vigorously oxidised
   - alcohol mixed with excess oxidising agent and heated UNDER REFLUX

Question 16

alcohols - secondary alcohol method

Answer 16

under reflux using acidified potassium dichromate(VI)

Question 17

dehydrating alcohols - methods

Answer 17

1. Ethanol vapour is passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3 - the catalyst provides a large surface area for the reaction.
2. reflux ethanol with excess concentrated sulfuric acid at 170degreesC.

Question 18

dehydrating alcohols - using hot catalyst method

Answer 18

ceramic wool is soaked in ethanol, pumice stone or Al2O3 is heated, the alkene gas collects in an inverted cylinder in a water bath

Question 19

dehydrating alcohols - reflux method

Answer 19

• heat solution in a flask fitted with a vertical Liebig condenser - this causes the solution to continuously boil/evaporate and then condense back into the flask, giving it time to react
• heat solution electronically; hot plates, heating mantles.

Question 20

dehydrating alcohols - reflux method mechanism

Answer 20

DRAW THIS
The conc. sulfuric acid acts as a dehydration agent in the elimination reaction

1. the hydroxyl group will bond to the H+ ions from the strong acid.
   - the alcohol is protonated, giving the atom a +ve charge
2. the +vely charged oxygen will pull electrons away from the neighbouring carbon, and water will ‘fall off’
   - creates an unstable carbon intermediate
3. the carbocation loses H+ and the alkene is formed

Question 21

alcohols - substitution reactions

Answer 21

alcohols will react with halide ions (eg. HCl) to produce a haloalkane

the -OH group is replaced by the halide (other product is made of the OH lost and what’s left of the halogen)

Question 22

practical techniques - refluxing

Answer 22

makes sure you don’t lose any volatile organic substances

1. organic reactions can be slow and the substances are usually flammable and volatile (low boiling points). if you heat them with a bunsen burner they’ll evaporate or catch fire before they have time to react
   - reflux gets around it
2. to reflux, heat the solution in a flask with a vertical Liebig condenser, this causes the solution to continuously boil/evaporate and then condense back into the flask, giving it time to react
3. heat the solution electronically (hot plates and heating mantles) this avoids naked flames that might ignite the compounds

Question 23

practical techniques - distillation

Answer 23

separates substances with different boiling points

1. to distil a mixture, gently heat it in distillation apparatus. the substances will evaporate out of the mixture of increasing boiling point
2. when an evaporated substance enters the condenser, it is cooled and condenses back to a liquid, which can be collected by placing a flask at the open end of the condenser
3. a thermometer shows the boiling point of the substances that is evaporating at any given time. if you know the boiling point of your pure product, you can use the thermometer to find out when its evaporating and therefore when to collect it
4. sometimes a product is formed that will go on to react further if its left in the reaction mixture
   - if the product has a lower boiling point than the starting material, the reaction can be carried out in distillation apparatus, the product is distilled from the reaction mixture as soon as it forms, and is collected in a separate container.
   - primary alcohols

Question 24

practical techniques - redistillation

Answer 24

volatile liquids can be purified by redistillation
1. after distillation the product will probs still contain impurities

2. if a product and its impurities have different boiling points, then redistillation can be used to separate them.
   - just use same distillation technique
3. when the liquid you want boils collect the pure product
4. when the thermometer shows the temperature is changing, put another flask at the end of the condenser because a different liquid is about to be delivered