Hydrogenation

Question 1

How do you control catalytic hydrogenation?

Answer 1

Using different metals catalysts

Question 2

What do additives do?

Answer 2

Adds more selectivity

Question 3

What reaction conditions do you need to look at in catalytic hydrogenation?

Answer 3

Temperature and pressure

Question 4

What type of process is catalytic hydrogenation?

Answer 4

Chemoselective

Question 5

What are the pros of using H2?

Answer 5

There is no waste as you use both H+
Atom efficient
Catalytic at 0.00000001 mol%

Question 6

What are the cons of LiAlH4/NaBH4?

Answer 6

B/Al waste
H+/OH pollution released
Only use 1/6 atoms

Question 7

What is the process of hydrogenation of alkenes?

Answer 7

H2 absorbed onto a metal surface
Alkene coordinates metal
There is a stepwise addition of H2 to the alkene

Question 8

What type of addition is hydrogenation of alkenes? What does it depend on?

Answer 8

Usually syn-addition

Catalyst, conditions and substrate

Question 9

What is syn addition?

Answer 9

Both hydrogens are on the same face of the molecule

Question 10

Why does syn addition take place?

Answer 10

Takes place on a surface so it cant rotate for second addition

Question 11

What happens to the melting point when alkenes are removed?

Answer 11

The melting point decreases

Question 12

What type of process is the hydrogenation of alkynes?

Answer 12

two step process
Alkyne to alkene
Alkene to alkane

Question 13

In the hydrogenation of alkynes, can you stop at the intermediate Z-alkene?

Answer 13

No

Question 14

What are the three components of a lindlar catalyst?

Answer 14

Pd
CaCO3
Pb(OAc)2

Question 15

How is a lindlar catalyst structured?

Answer 15

Palladium on calcium carbonate which is then poisoned with Pb(OAc)2

Question 16

What is the function of CaCO3 in a lindlar catalyst?

Answer 16

Replaces carbon as the support to release the product alkene more easily

Question 17

What is the purpose of Pb(OAc)2 in the lindlar catalyst?

Answer 17

Poison preventing the over reduction

Question 18

What does the lindlar catalyst do?

Answer 18

Allows the reaction to stop at the intermediate Z alkene

Question 19

If an amine has a hydroxyl group attached too, which group reacts to form the imine? Why?

Answer 19

NH2

The lone pair is more available as it is less electronegative, it has a higher pKa

Question 20

How is an imine formed?

Answer 20

RNH2 + C=O

Condensation reaction

Question 21

What is formed when an imine goes through a hydrogenation reaction?

Answer 21

Amine

Question 22

What type of reaction is hydrogenation and why?

Answer 22

Chemoselective

C=N is a weaker bond than C=O

Question 23

When you remove phenyl groups, what does a benzylamine become?

Answer 23

Amine

Question 24

When you remove phenyl groups, what does a benzylether become?

Answer 24

Alcohol

Question 25

When you remove benzyl groups, what does the co-ordination of arena to Pd surface do?

Answer 25

Restrict the process to just benzyl groups

Question 26

What is formed when you hydrogenate nitro groups?

Answer 26

Amines

Question 27

What are the most common metals used for the hydrogenation of nitro groups?

Answer 27

Palladium and platinum

Question 28

What might you need to add when you hydrogenate the nitro groups? Why?

Answer 28

Add a weak acid | It prevents the product amine poisoning the catalyst

Question 29

What is Raney Nickel?

Answer 29

RaNi | Made up of Ni and H2

Question 30

What is the structure of RaNi like?

Answer 30

Has a large surface area, finely divided form of nickel | Honeycomb structure

Question 31

What is RaNi made from?

Answer 31

nickel-aluminium alloy

Question 32

What is the function of the concentrated NaOH in the formation of RaNi?

Answer 32

It dissolves the aluminium

Question 33

In de-sulfurisation, which bonds do you hydrogenate?

Answer 33

The two C-S bonds

Question 34

Why do you hydrogenate the two C-S bonds?

Answer 34

They are weaker than the C-O bonds

Question 35

What does RaNi not reduce? Why?

Answer 35

Alkenes | Chemoselective reduction

Question 36

What is the easiest functional group to hydrogenate?

Answer 36

Acyl Chloride

Question 37

Which functional groups are considered easy to hydrogenate and above an alkene?

Answer 37

Acyl chloride Nitro Alkyne Aldehyde

Question 38

Which functional groups are considered hard to hydrogenate and are below an alkene?

Answer 38

``` Ketone Benzyl Cyanide Ester Conjugated system ```

Question 39

What is the hardest functional group to hydrogenate?

Answer 39

A conjugated system