Organosulfur

Question 1

What is the pauling electronegativity of sulfur?

Answer 1

Electronegativity of S is χ2.5, where C is the same

Same VE of oxygen

Question 2

What is a thiol and how is it prepared?

Answer 2

R-SH

Prepared from: R-X + NaSH → R-SH + NaX, where X is a halide

Question 3

What is a problem with doing an SN2 with NaSH and R-X?

Answer 3

Thiol product can do second SN2 to form a sulfide

Can alternatively use thiourea as nucleophile to stop this

Question 4

What happens when thiols or other sulfur compounds are oxides/reduced?

Answer 4

The oxn state of sulfur changes rather than carbon

Question 5

What happens if you use a mild oxidising agent on a thiol?

(e.g. iodine)

Answer 5

2 R-SH → R-S-S-R

Forms a disulfide

Question 6

What happens when disulfides are treated with midl reducing agents?

e.g. zinc & acids

Answer 6

R-S-S-R → 2 R-SH

Question 7

Why do disulfides form but peroxides don’t under simimlar conditions?

Answer 7

S-S nearly twice as strong as O-O

O-H stronger than S-H

Thermodynamically favours disulfide

Question 8

How can sulfenic acids (R-SOH) be made?

Answer 8

Oxidation of dislufide

Question 9

How can a sulfinic acid (R-SOOH) be made?

Answer 9

Oxidation of suilfinic acid / acidification of sulfinate salt

Or thiosulfonate and base

Question 10

How are sulfinate salts generated?

Answer 10

Reduction of sulfonyl chlorides

Or reaction of grignard with sulfur dioxide

Question 11

How is sulfonic acid prepared?

Answer 11

Sulfonation of aromatics - uses SO₃ and H₂SO₄

Sulfonation of alkanes - bisulfite + terminal alkenes, or bisulfite alkylated by alkyl halides

Stong oxidation of thiols

Question 12

What is reverse aromatic sulfonation?

Answer 12

Heat, H₂O and catalytic H₂SO₄

Reverses reaction

Question 13

What is a sulfide and how is it made?

Answer 13

R-S-R’

Produced by: R-SH + R’-X → R-S-R’

Question 14

What is the structure of a sulfonium salt and how is it made?

Answer 14

⁺SR₃ X^-

Where each R group can be different, and have trigonal planar structure

Made by sulfide (R-S-R’) + R’‘-X

Question 15

How are sulfoxides formed and what is their structure?

Answer 15

Formed from oxidation of sulfide using: NaIO₄ or H₂O₂ or mCPBA

Question 16

What is a sulfoxonium salt and how is it produced?

Answer 16

Formed via: sulfoxide + R-X, the S in sulfoxide is nucleophile

Question 17

What is a sulfone and how are they formed?

Answer 17

Prepared by: sulfoxide + mCPBA or KMnO₄

Question 18

What is a thiosulfinate and how are they formed?

Answer 18

Oxidation of disulfide (e.g. H₂O₂)

Question 19

What is a thiosulfonate and how are they prepared?

Answer 19

Oxidation of a thiosulfinate

Add OH- to make sulfenic and sulfinic acids

Question 20

How does the nucleophilicity of sulfur compare to oxygen?

Answer 20

Oxgen - less nucleophillic but more basic

Sulfur - more nucleophillic but less basic, nucleophillic even in higher oxidation states

Question 21

What is the hard/soft nature of O and S?

Answer 21

O - harder nucleophile so requires a harder electrophile

S - softer nucleophile so softer electrophile

Question 22

How does an arylsulfonyl chloride react with Zn and R-I?

Answer 22

Zn attacks Cl and causes S-

S- attacks R to give sulfone

Question 23

How do thiols react with π-electrophiles?

Answer 23

Add rapidly with them

When C=O π system a lewis acid can aid this

When C=C π system a sulfide forms as attacks twice

Question 24

How can dithiane be made?

Answer 24

1,3-dithiol + HCHO and BF₃

Can use RCHO to add R to C between the S

Question 25

How does R^- react with S-S or S-O containing compounds?

Answer 25

R- attacks S and breaks S-S or S-O bond

Question 26

How can a compound, R-SO₂E, where E is an electrophile be made?

Answer 26

SO₂ gas + E⁺R^- → ## Footnote ![]()

Question 27

How do sulfonic acids react with alcohols?

Answer 27

R'-OH attacks S and R'-O-SOR

Question 28

What are sulfur dioxide - amine complexes?

Answer 28

amine-SO₂ complexes are convenient SO₂ surrogates solid version of gaseous reagent, are called lewis adducts

Question 29

How does sulfur stabilise an adjacent -ve charge?

Answer 29

Traditional view - delocalisation into the sulfur d-orbitals Current view - polarisability at S, and -ve hyperconjugation

Question 30

How can an aldehyde be made from a halide?

Answer 30

Dithiane + BuLi then + R-X, followed by Hg(II) and H₂O ## Footnote ![]()

Question 31

What is the synthon formed from dithiane and BuLi?

Answer 31

![]()

Question 32

How can a specific ketone be made from a substituted dithiane?

Answer 32

Sub dithiane made from 1,3-dithiol and RCHO ![]()

Question 33

How can dithiane be used in the peterson olefination?

Answer 33

![]()

Question 34

How can a ketone be fragmented into an aldehyde and carboxylic acid / ester?

Answer 34

Ketone + 2LDA + 2PhS-SPh then base (OH for carboxylic acid or alkoxide for ester) then Hg(II) and acid ![]()

Question 35

What is the relative acidity of sulfoxides and sulfides?

Answer 35

Sulfoxides are more acific than sulfides Sulfoxide alkylation chem useful

Question 36

How do sulfenate esters react in a stereospecific way?

Answer 36

2,3-sigmatropic rearranement to allylic sulfoxides Allows for group to enone and regenerate the enone in the process ![]()

Question 37

What is the Julia olefination?

Answer 37

Preparation of E-alkene from phenyl sulfones & aldehydes/ketones Reagents: n-BuLi then aldehyde then halide, which gives intermediate Then Na(Hg) and EtOH to give E-alkene R groups on alkene are from aldehyde and halide

Question 38

What are the purpose of the reagents in the julia olefination?

Answer 38

LDA - deprotonation of C next to sulfone Ac₂O - adds into the aldehyde, makes it -OAc so good LG Na(Hg) - active and reduces product (SET)

Question 39

What is the mechanism of the Julia olefination?

Answer 39

![]()

Question 40

What is the mechanism of the elimination in the Julia olefination? (modern thought)

Answer 40

![]()

Question 41

What is the modified Julia-Kocienski reaction?

Answer 41

Aldehyde to E-alkene Single-stepped variant Reagents: sulfonyl anion (tetrazole or benzothiazole) and KHMDS, then aldehyde

Question 42

What is the mechanism of the Julia-Kocienski olefination?

Answer 42

![]()

Question 43

What is KHMDS?

Answer 43

Potassium hexamethyldisilazide Strong non-nucleophilic base

Question 44

What is the Ramberg-Backlund olefination?

Answer 44

Multistep coupling of two haloalkanes to give an olefin (can select reagents for Z or E) Goes via sulfide and then α-halo sulfone, choice of base then gives either E or Z olefin + SO₂

Question 45

How do you convert a sulfide to an α-halo sulfone?

Answer 45

Reagents: NaIO₄ followed by HCl, and then adding mCPBA ## Footnote ![]()

Question 46

How do you convert an α-halo sulfide to an olefin?

Answer 46

![]()

Question 47

What is a sulfur ylide?

Answer 47

Compound where ⁺S-C^- is present

Question 48

How are sulfur ylides formed?

Answer 48

Base (NaH) and +vely charge S species E.g. sulfonium or sulfoxonium salt

Question 49

What is the difference between ketone and sulur/phosphorus ylide reaction?

Answer 49

Sulfur ylide: S=O weaker so epoxide formed Phosphorus ylide: P=O stronger so can make C=C alkene

Question 50

How does being a sulfonium or sulfoxonium change the reactivity of sulfur ylides?

Answer 50

Sulfonium ylides: kinetic control, irreversible Sulfoxonium ylides: thermodynamic control, reversible, not as reactive

Question 51

How do sulfur ylides react with ketones?

Answer 51

Forms epoxides

Question 52

How do sulfur ylides react with enones?

Answer 52

Sulfonium ylide - kinetic control, attacks carbonyl and forms epoxide Sulfoxonium ylide - thermo control, attacks alkene and forms cyclopropanone + DMSO

Question 53

How can cyclobutanones be made from sulfur ylides?

Answer 53

Carbonyl + Cyclopropyl sulfonium ## Footnote ![]()

Question 54

What is the Sommelet-Hauser rearrangement?

Answer 54

Functionalisation of ortho-position in aromatics Add aldehyde to orthoposition of benzylchloride ![]()

Question 55

How can SO₂ be used to mask a diene for synthesis?

Answer 55

Add SO₂ to protect, heat will deprotect ## Footnote ![]()

Question 56

What is the stability of S-analogues of oxonium ions?

Answer 56

S-analogues less favoured as orbital size not matched for efficient overlap

Question 57

What is the Pummerer rearrangement?

Answer 57

Alkyl sulfoxide rearranges to an α-acyloxy–thioether Uses: NaIO₄ and acetic acid ![]()

Question 58

What is the mild varient of the Wolff-Kishner reduction of ketones?

Answer 58

Aldehydes/ketones → Alkanes Reagents: TsNHNH₂ (instead of hydrazine) then NaBH₄ and ROH ## Footnote ![]()

Question 59

What is the Bamford-Stevens synthesis?

Answer 59

Tosylhydrazones with strong base gives alkenes When unsymmetrucial can give mix of products as can eliminate either side ![]()

Question 60

What is the eschenmoser fragmentation?

Answer 60

Enone to alkynes and carbonyls via α,β-epoxyketones Reagents: NaOH & H₂O₂ then ArSO₂NHNH₂ ![]()

Question 61

How can you make an enone from a ketone?

Answer 61

LDA & PhS-SPH then NaIO₄ ## Footnote ![]()

Question 62

What is the Grieco elimination?

Answer 62

Aliphatic 1º alcohol to a terminal alkene via o-nitrophenyl selenoxide intermediate Reagents: PBu₃ and nitrophenyl selenoxide, then H₂O₂ ![]()