Organic Synthesis

Question 1

What is a Grignard Reagent made of and what is its purpose

Answer 1

Used to lengthen carbon chaain

Made of Halogenoalkane + Magnesium in Dry ether + Heat under reflux

Question 2

Show how a Grignard reagent is made with reactants and products

Answer 2

CH3CH2Br + Mg = CH3CH2MgBr

the mg fits in before the br

Question 3

Why do Grignard reagents work

Answer 3

Mg has a lower electronegativity to Carbon = Carbon is slightly negative/delta negative

Grignard reagents are Nucleophiles due to the negative carbon that can attack delta positive carbons in C=O Bonds

Question 4

What does a Grignard reagent form when reacting with water

Answer 4

Alkane + Mg(OH)Br

This is why reactions must be done in dry conditions

Question 5

What does a Grignard reagent form with carbon dioxide

Answer 5

Carboxylic acid + Mg(OH)Br

1- CH3CH2MgBr + CO2 = CH3CH2COO-MgBr

2- CH3CH2COO-MgBr + HCl(aq) = CH3CH2COOH + Mg(OH)Br

Question 6

What needs to be done in the second step to the intermediate formed to get final product in grignard reactions

Answer 6

Hydrolyse product with dilute HCl(aq)

= always produces Mg(OH)Br

Question 7

What forms when Grignard reagent reacts with any aldehyde apart from methanal

Answer 7

2 alcohol / Secondary Alcohol + Mg(OH)Br

Question 8

What forms when Grignard reagent reacts with ketones

Answer 8

3 Alcohols / tertiary alcohol + Mg(OH)Br

Question 9

overview of what forms when grignard reagents react with
water
carbon dioxide
methanal
aldehydes but methanal
ketones

Answer 9

alkane

carboxylic acid

1 alcohol

2 alcohol

3 alcohol

Question 10

Hazard

Risk

Answer 10

substance that could cause harm

likelihood that a hazard causes harm

Question 11

Recrystallisation method

Answer 11

1- Dissolve solid in min vol of warm solvent
2- dissolve while still hot
3- Cool solution collected in Ice bath
4- Filter under suction in Buchner funnel with Filter paper wth few drops cold solvent to make seal

Question 12

purpose of hot and cold filtration in recrystallisation

Answer 12

warm = Desired product is soluble in warm solvent and passes through filter = removes insoluble impurities

Cold = desired product is insoluble in cold solvent = removes soluble impurities

= must choose solvent that desired product is completely soluble in hot but completely insoluble in cold

Question 13

Melting point determination method

Answer 13

1- add powdered solid sample to melting point capillary tube
2- place tube in melting pint apparatus
3- raise temp slowly to obtain accurate melting temp

Question 14

what is melting point determination used for

Answer 14

Used to estimate purity of a sample by comparing value to data book

if pure =
melting point will be sharp rather than over several degrees
melting point will match data book value

Question 15

Purpose of distillation and how does it do this

Answer 15

Separate substances by Boiling Point = gently heat mixture

1- If desired product has a Lower BP = it will evaporate and rise up the column to condense and collect

2-if desired product has a higher BP = it will not be able to rise the column and condense out , remains in flask

Question 16

Purpose of steam distillation

Answer 16

Used to separate a insoluble liquid from an aqueous solution = separate substances with very high BPs

Question 17

Method of steam distillation

Answer 17

1- Steam is bubbled through reaction mixture = lowers the boiling point and allows product to be distilled out
2- If desired product has a lower BP to impurities = evaporates out flask with steam and collects
3- Produces mix of desired product and water = can be separated due to difference in densities in separating funnel

= used as lowers the BP so do not have to heat so high

Question 18

What do you use to remove an acid impurity

Answer 18

Sodium Hydrogen Carbonate
= neutralises acid and produces = CO2 + Salt

Question 19

What can be use as a drying agent

Answer 19

Anhydrous Calcium Chloride
= remove aqueous substances = filter solution to remove drying agent

Question 20

What does Fractional distillation seperate

Answer 20

Multiple liquids with different BPs

uses a fractionating column that gets cooler near the top