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Year 2 - Chem > Organosulfur > Flashcards

Organosulfur Flashcards

1
Q

What is the pauling electronegativity of sulfur?

A

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

Same VE of oxygen

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2
Q

What is a thiol and how is it prepared?

A

R-SH

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

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3
Q

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

A

Thiol product can do second SN2 to form a sulfide

Can alternatively use thiourea as nucleophile to stop this

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4
Q

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

A

The oxn state of sulfur changes rather than carbon

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5
Q

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

(e.g. iodine)

A

2 R-SH → R-S-S-R

Forms a disulfide

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6
Q

What happens when disulfides are treated with midl reducing agents?

e.g. zinc & acids

A

R-S-S-R → 2 R-SH

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7
Q

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

A

S-S nearly twice as strong as O-O

O-H stronger than S-H

Thermodynamically favours disulfide

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8
Q

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

A

Oxidation of dislufide

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9
Q

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

A

Oxidation of suilfinic acid / acidification of sulfinate salt

Or thiosulfonate and base

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10
Q

How are sulfinate salts generated?

A

Reduction of sulfonyl chlorides

Or reaction of grignard with sulfur dioxide

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11
Q

How is sulfonic acid prepared?

A

Sulfonation of aromatics - uses SO3 and H2SO4

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

Stong oxidation of thiols

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12
Q

What is reverse aromatic sulfonation?

A

Heat, H2O and catalytic H2SO4

Reverses reaction

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13
Q

What is a sulfide and how is it made?

A

R-S-R’

Produced by: R-SH + R’-X → R-S-R’

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14
Q

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

A

+SR3 X-

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

Made by sulfide (R-S-R’) + R’‘-X

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15
Q

How are sulfoxides formed and what is their structure?

A

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

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16
Q

What is a sulfoxonium salt and how is it produced?

A

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

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17
Q

What is a sulfone and how are they formed?

A

Prepared by: sulfoxide + mCPBA or KMnO4

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18
Q

What is a thiosulfinate and how are they formed?

A

Oxidation of disulfide (e.g. H2O2)

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19
Q

What is a thiosulfonate and how are they prepared?

A

Oxidation of a thiosulfinate

Add OH- to make sulfenic and sulfinic acids

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20
Q

How does the nucleophilicity of sulfur compare to oxygen?

A

Oxgen - less nucleophillic but more basic

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

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21
Q

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

A

O - harder nucleophile so requires a harder electrophile

S - softer nucleophile so softer electrophile

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22
Q

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

A

Zn attacks Cl and causes S-

S- attacks R to give sulfone

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23
Q

How do thiols react with π-electrophiles?

A

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

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24
Q

How can dithiane be made?

A

1,3-dithiol + HCHO and BF3

Can use RCHO to add R to C between the S

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25
Q

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

A

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

26
Q

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

A

SO2 gas + E+R- →

27
Q

How do sulfonic acids react with alcohols?

A

R’-OH attacks S and R’-O-SOR

28
Q

What are sulfur dioxide - amine complexes?

A

amine-SO2 complexes are convenient SO2 surrogates

solid version of gaseous reagent, are called lewis adducts

29
Q

How does sulfur stabilise an adjacent -ve charge?

A

Traditional view - delocalisation into the sulfur d-orbitals

Current view - polarisability at S, and -ve hyperconjugation

30
Q

How can an aldehyde be made from a halide?

A

Dithiane + BuLi then + R-X, followed by Hg(II) and H2O

31
Q

What is the synthon formed from dithiane and BuLi?

32
Q

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

A

Sub dithiane made from 1,3-dithiol and RCHO

33
Q

How can dithiane be used in the peterson olefination?

34
Q

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

A

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

35
Q

What is the relative acidity of sulfoxides and sulfides?

A

Sulfoxides are more acific than sulfides

Sulfoxide alkylation chem useful

36
Q

How do sulfenate esters react in a stereospecific way?

A

2,3-sigmatropic rearranement to allylic sulfoxides

Allows for group to enone and regenerate the enone in the process

37
Q

What is the Julia olefination?

A

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

38
Q

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

A

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)

39
Q

What is the mechanism of the Julia olefination?

40
Q

What is the mechanism of the elimination in the Julia olefination?

(modern thought)

41
Q

What is the modified Julia-Kocienski reaction?

A

Aldehyde to E-alkene

Single-stepped variant

Reagents: sulfonyl anion (tetrazole or benzothiazole) and KHMDS, then aldehyde

42
Q

What is the mechanism of the Julia-Kocienski olefination?

43
Q

What is KHMDS?

A

Potassium hexamethyldisilazide

Strong non-nucleophilic base

44
Q

What is the Ramberg-Backlund olefination?

A

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

45
Q

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

A

Reagents: NaIO4 followed by HCl, and then adding mCPBA

46
Q

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

47
Q

What is a sulfur ylide?

A

Compound where +S-C- is present

48
Q

How are sulfur ylides formed?

A

Base (NaH) and +vely charge S species

E.g. sulfonium or sulfoxonium salt

49
Q

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

A

Sulfur ylide: S=O weaker so epoxide formed

Phosphorus ylide: P=O stronger so can make C=C alkene

50
Q

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

A

Sulfonium ylides: kinetic control, irreversible

Sulfoxonium ylides: thermodynamic control, reversible, not as reactive

51
Q

How do sulfur ylides react with ketones?

A

Forms epoxides

52
Q

How do sulfur ylides react with enones?

A

Sulfonium ylide - kinetic control, attacks carbonyl and forms epoxide

Sulfoxonium ylide - thermo control, attacks alkene and forms cyclopropanone + DMSO

53
Q

How can cyclobutanones be made from sulfur ylides?

A

Carbonyl + Cyclopropyl sulfonium

54
Q

What is the Sommelet-Hauser rearrangement?

A

Functionalisation of ortho-position in aromatics

Add aldehyde to orthoposition of benzylchloride

55
Q

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

A

Add SO2 to protect, heat will deprotect

56
Q

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

A

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

57
Q

What is the Pummerer rearrangement?

A

Alkyl sulfoxide rearranges to an α-acyloxy–thioether

Uses: NaIO4 and acetic acid

58
Q

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

A

Aldehydes/ketones → Alkanes

Reagents: TsNHNH2 (instead of hydrazine) then NaBH4 and ROH

59
Q

What is the Bamford-Stevens synthesis?

A

Tosylhydrazones with strong base gives alkenes

When unsymmetrucial can give mix of products as can eliminate either side

60
Q

What is the eschenmoser fragmentation?

A

Enone to alkynes and carbonyls via α,β-epoxyketones

Reagents: NaOH & H2O2 then ArSO2NHNH2

61
Q

How can you make an enone from a ketone?

A

LDA & PhS-SPH then NaIO4

62
Q

What is the Grieco elimination?

A

Aliphatic 1º alcohol to a terminal alkene via o-nitrophenyl selenoxide intermediate

Reagents: PBu3 and nitrophenyl selenoxide, then H2O2

Year 2 - Chem (23 decks)

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