Organic Synthesis

Question 1

What is organic synthesis?

Answer 1

The science of making organic moleces which cannot be sourced in sufficient quantitied naturally, normally via multistep sequences of reactions.

Question 2

Apart from making molecules what else can synthesis be used for?

Answer 2

It can also be used to confirm the structure of a molecule deduced using chemical testing and spectroscopy. Once it has been synthesised if the spectroscopic data match then the structure has been confirmed

Question 3

How is the overall yield of a multistep synthesis given?

Answer 3

In a multistep synthesis each step will have a molar yield. To get the overall yeild of the syntheimsis you multiply each individual percentage together and then multiply by 100. Multiply the percentages as fractions of 100 though.

Question 4

What are the reactanrs and reaction conditions for free radical substitution?

Answer 4

Halogen with UV light to initiate

Question 5

What are the reactanrs and reaction conditions for electrophillic addition- hydration

Answer 5

Catalytic H2SO4 in water

Question 6

What are the reactanrs and reaction conditions for reduction?

Answer 6

H2 and Ni

LiAlH4 in ethoxyethane solvent

Question 7

What are the reactanrs and reaction conditions for electrophillic addition

Answer 7

Aqeous Br2

Aqueous HBr (gives bromoalkane)

Question 8

What are the reactanrs and reaction conditions for nucleophillic substitution

Answer 8

Excess concentrated NH3 in ethanol solvent, heat

Halogenoalkane in ethanol solvent, heat

Excess halogenoalkane in ethanol solvent, heat

Large excess of halogenoalkane in ethanol, heath

KCN in ethanol, heat

PCl5 or SOCl2

P2O5

Question 9

Elinination - dehydration

Answer 9

Concentrated H2SO4, heat

Question 10

What are the reactanrs and reaction conditions for partial oxidation?

Answer 10

K2Cr2O7 and dilute H2SO4, distil

Question 11

What are the reactants and reaction conditions for full oxidation?

Answer 11

Excess K2Cr2O7 and dilute H2SO4

Question 12

What are the reactants and reaction conditions for hydrolysis?

Answer 12

Heat with dilute H2SO4

Question 13

What are the reactants and reaction conditions for nucleophillic addition?

Answer 13

Concentrated solution of HCN and acidification

Question 14

What are the reactants and reaction conditions for nucleophillic substitution- hydrolysis?

Answer 14

H2O

Aqueous NaOH, heat and then dilute acid

5 mol dm-3 HCl, heat for 24 hours

Question 15

What are the reactants and reaction conditions for nucleophillic substitution - condensation?

Answer 15

Alcohol with concentrated H2SO4

Alcohol and a base

Ammonia or amine

Question 16

What are the reactants and reaction conditions for nucleophillic substitution- dehydration?

Answer 16

Amine and heat

Question 17

What is often an important consideration when selecting reactions to achieve a particular synthesis?

Answer 17

The fact that functional groups bonded directly to a benzene ring are likely to behave differently from those bonded to saturated structures

Question 18

What is the target molecule in organic synthesis?

Answer 18

The molecule that we wish to prepare

Question 19

What are the chemicals used at the start of a synthesis known as?

Answer 19

Starting materials

Question 20

When devising synthesis of a target molecule what is the easiest way to do this?

Answer 20

Work backwards from the target molecule to areive at the starting material, using your knowledge of what carbon groups need to be joined and what functional groups need to be created

Question 21

When desiging a synthesis what factors will influence your final choice of pathway?

Answer 21

• the availability and cost of a suitable starting material from which the target molecule can be synthesized
• the number of stages needed to convert the starting material to the target molecule
• whether more than one product is formed during any stage resulting in the need to purify a mixture
• the number and cost of any seperation and purification processes required
• the percentage yield that can be expected from the overall process
• the atom economy of the overall process
• the mass of the desired product divided by the mass of the reactants used often expressed as a percentage
• the amount of waste generated from the overall process
• whether toxic or hazardous chemicals and solvents are required
• additional problems involved in scaling the synthesis to manufacturing proportions, particularly special designs for chemical plant and safety considerations

Question 22

What will the main considerations for a commercial synthesis be? What does this mean?

Answer 22

The main considerations will be cost and safety.

This means processes that use very high temperatures or pressures are normally avoided as the use of these conditions is both expensive and dangerous. It also means the use of toxic chemicals and solvents must be minimised. If solvents must be used then non-flammable, easily recyclable and non-toxic ones should be considered