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CHY1101 - Organic chemistry > Hydrogenation > Flashcards

Hydrogenation Flashcards

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1
Q

How do you control catalytic hydrogenation?

A

Using different metals catalysts

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2
Q

What do additives do?

A

Adds more selectivity

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3
Q

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

A

Temperature and pressure

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4
Q

What type of process is catalytic hydrogenation?

A

Chemoselective

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5
Q

What are the pros of using H2?

A

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

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6
Q

What are the cons of LiAlH4/NaBH4?

A

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

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7
Q

What is the process of hydrogenation of alkenes?

A

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

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8
Q

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

A

Usually syn-addition

Catalyst, conditions and substrate

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9
Q

What is syn addition?

A

Both hydrogens are on the same face of the molecule

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10
Q

Why does syn addition take place?

A

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

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11
Q

What happens to the melting point when alkenes are removed?

A

The melting point decreases

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12
Q

What type of process is the hydrogenation of alkynes?

A

two step process
Alkyne to alkene
Alkene to alkane

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13
Q

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

A

No

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14
Q

What are the three components of a lindlar catalyst?

A

Pd
CaCO3
Pb(OAc)2

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15
Q

How is a lindlar catalyst structured?

A

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

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16
Q

What is the function of CaCO3 in a lindlar catalyst?

A

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

17
Q

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

A

Poison preventing the over reduction

18
Q

What does the lindlar catalyst do?

A

Allows the reaction to stop at the intermediate Z alkene

19
Q

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

A

NH2

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

20
Q

How is an imine formed?

A

RNH2 + C=O

Condensation reaction

21
Q

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

A

Amine

22
Q

What type of reaction is hydrogenation and why?

A

Chemoselective

C=N is a weaker bond than C=O

23
Q

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

A

Amine

24
Q

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

A

Alcohol

25
Q

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

A

Restrict the process to just benzyl groups

26
Q

What is formed when you hydrogenate nitro groups?

A

Amines

27
Q

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

A

Palladium and platinum

28
Q

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

A

Add a weak acid

It prevents the product amine poisoning the catalyst

29
Q

What is Raney Nickel?

A

RaNi

Made up of Ni and H2

30
Q

What is the structure of RaNi like?

A

Has a large surface area, finely divided form of nickel

Honeycomb structure

31
Q

What is RaNi made from?

A

nickel-aluminium alloy

32
Q

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

A

It dissolves the aluminium

33
Q

In de-sulfurisation, which bonds do you hydrogenate?

A

The two C-S bonds

34
Q

Why do you hydrogenate the two C-S bonds?

A

They are weaker than the C-O bonds

35
Q

What does RaNi not reduce? Why?

A

Alkenes

Chemoselective reduction

36
Q

What is the easiest functional group to hydrogenate?

A

Acyl Chloride

37
Q

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

A

Acyl chloride
Nitro
Alkyne
Aldehyde

38
Q

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

A 
Ketone 
Benzyl 
Cyanide 
Ester 
Conjugated system
39
Q

What is the hardest functional group to hydrogenate?

A

A conjugated system

CHY1101 - Organic chemistry (22 decks)

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