Micronotes by Dr. Savita Desai.

Online notes on www.devchandcollege.org

Organo sulphur compounds: [4 lectures, 5 marks]

R-SH thioalcohols, R-S-R thioethers, RCHS Thioaldehydes, RCSR’ thioketones etc are organo sulphur compounds.

Chemistry of thioalcohols/thiols:

Thioalcohols: these are Sulphur derivatives of corresponding alcohols/ alkylderivatives of Hydrogen sullphide.

Nomenclature:

compound Common names IUPAC names R-SH Alkyl thioalcohol/ alkyl mercaptan Alkane thiol CH3-SH Methyl thioalcohol/ methyl mercaptan Methane thiol C2H5-SH Ethyl thioalcohol /mercaptan Ethane thiol

CHCH3

CH3

SH

Isopropyl thioalcohol /mercaptan Propane-2-thiol

Methods of formation:

1. From alkyl halides:

C2H5-Cl NaSH C2H5-SH NaClheat+ +

2. From Alcohol: vapours of alcohol and H2S are passed over heated thoria catalyst.

C2H5-OH SH2C2H5-SH

ThO2

Heat

H2 O

alcohol thiol

+ +

3. From Grignard reagent:

C2H5-Mg-X S C2H5-SH

thiol

C2H5-S-Mg-X

intermediateethyl Mg halide

OH

XMg+ +

Chemical Properties: S is less electronegative than O, also S has less tendency to form double bond with O hence, shows different chemical properties.

A] Properties similar to alcohols:

1. Reaction with alkali metal:

C2H5-SH

thiol

Na C2H5-SNa+2 2 + H2

Na-ethyl sulphide

Micronotes by Dr. Savita Desai.

Online notes on www.devchandcollege.org

2. Reaction with carboxylic acid and acid chlorides:

C2H5-SH

thiol

CH3COOH H2 O+acetone

CH3COSC2H5 +ethyl thio acetate

C2H5-SH

thiol

CH3COCl H Cl+acetyl chloride

CH3COSC2H5 +ethyl thio acetate

3. Reaction with aldehyde and ketones:

C2H5-SH

thiol

CH3CHO H

CH3

SC2H5

SC2H5

C H2 O+2

acetaldehyde

thioacetaldiethyl methyl mercaptol

+

C2H5-SH

thiol

CH3COCH3 CH3

CH3

SC2H5

SC2H5

C H2 O+2

acetone

thioketaldiethyl dimethyl mercaptol

+

B] Properties different from alcohols:

1. Mild oxidation

C2H5-SH

thiol

H2O2 C2H5-S-S-C2H5H2 O

mild+ + 2

diethyl disulphide

2. Strong oxidation.

C2H5-SH

thiol

[O]strong

SO3HC2H5+ 3

ethane sulphonic acid

Chemistry of Thioethers:

These are Sulphur derivatives of corresponding ethers/ dialkyl derivatives of Hydrogen sullphide

Nomenclature:

compound Common names IUPAC names R-S-R diAlkyl thioether Dialkyl sulphide CH3-S-CH3 dimethyl thioether Dimethyl

sulphide C2H5-S-C2H5 diethyl thioether Diethyl sulphide

Micronotes by Dr. Savita Desai.

Online notes on www.devchandcollege.org

Methods of formation:

1. From alkyl halides

C2H5-I K2S C2H5-S-C2H5 KI+2 + 2

ethyl iodide K-sulphide thioether

2. From thiosalt and alkyl halide:

C2H5-I C2H5-S-Na C2H5-S-C2H5NaI+ +

ethyl iodide Na-ethyl mercaptide thioether

3. From thiols and alkenes:

C2H5-SH C2H5-S-C2H5CH2 CH2 +thioetherethane thiolethene

Chemical Properties:

1. Reaction with alkyl halide,

2. Mild oxidation

3. Strong oxidation

4. Addition of halogens

5. Hydrolysis

C2H5-S-C2H5

C2H5I

C2H5C2H5

C2H5

S

H2O2

C2H5C2H5

O

SHNO3

C2H5C2H5

O

S

O

Br2

C2H5C2H5

Br

S

Br

H2 OC2H5OH

-H2Sthioether

+I-

triethyl sulphonium iodide

mild oxidation

diethyl sulphoxide

strong oxidation

diethyl sulphone

diethyl sulphide dibromide

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