Sulphur Chemistry Flashcards
True or False
The C-S bond is polarised?
False
Carbon-Sulfur bond isn’t polarised due to similar electronegativities
Decscribe the reactivity and oxidation states and coordination number of sulphur
- Sulphur is a good nucleophile
- Sulphur can access oxidation states 0, 2, 4, 6 and coordination numbers from 0-7 (large atom can hybridise with 3d orbitals
Sulfonium salts react how?
Sulphonium salts are potent electrophiles
(considered natures version of Me-I)
How do the following two reagents react
Hint: sulfonium salt
It is a way to methylate the nitrogen
What is a sulfonium ylide
A positive charged sulphur which stabilises a negative substituent - in this case methylene
How do these following reagents + NaH (strong base) react to form a sodium ylide
- Nu attack of sulfur towards Me, causing Me-I bond to break
- Deprotonation using base
What is the strength of the P=O bond vs S=O bond
And hence how does this affect its chemistry
S=O bond is weaker
Hence Sulfonium ylides behave quite differently to phosphonium ylides (as it was the strong P=O bond which drives its chemistry)
Sulfonium ylides are instead driven by the leaing group ability
What is formed when we react cyclohexanone with the following phosphorus ylide
- The usual triphenylphosphine oxide
- And an alkene
What happens when we react the same cyclohexanone with a sulfonium ylide instead
- When reacting with a sulfonium ylide will form a epoxide instead
- No removal of oxygen due to much weaker S=O bond
What is the mechanism for the following reaction
- Attack by methylene to δ⁺C, resulting in the breaking of the C=O bond
- LP on oxygen attack carbon, causing C-S bond to break as its a good leaving group
Sulfonium ylides can also form aziridine (when the nitrogen is stabilised by an anion)
What is the mechanism for the following reaction
- KOtBu deprotonates the adjacent to the sulfur forming the ylide
- LP on carbon attack the imine carbon, causing the C=N to break
- LP of N attacks the C next to the sulfur, causing the C-S bond to break
The following ylide is unstable (no EWG)
What happens when you react it with the following enone
Makes an epoxide
Made through irreversible 1,2-addition
The following ylide is stable (has EWG)
What happens when you react it with the following enone
Form Cyclopropane
Made through reversible 1,4-addition
What is the difference in the reagenets required to make a stable vs unstabilised ylide?
Strong base = unstabilised
Weak base = stabilised
What is the mechanism to produce cyclopropane from the stabilised ylide
- Thermodynamic product
- Deprotonation by Na₂CO₃
- 1,4-addition
What is the kinetic product of the following reaction from the stabilise ylide
- Reaction is reversible
- 1,2-addition
What is an additional way to stabilise a sulfonium ylide?
Having a S=O on the sulphur
How can we make a sulfonium ylide stabilised by oxygen from the following reagents?
- Nu attack by Sulfur to methyl
- Deprotonation by NaOH
How does the sulfoxonium ylide react with the compound shown
