Molecule Profile

Ethane-1,2-dithiol · EDT · CAS 540-63-6

C₂H₆S₂ · MW 94.19 g/mol

Identifiers

Table 1. Identifiers and registry data for 1,2-ethanedithiol.

Identifier	Value
IUPAC Name	Ethane-1,2-dithiol
Synonyms	1,2-Ethanedithiol; Ethylene dithiol; 1,2-Dimercaptoethane; Dithioglycol; EDT; Ethylene mercaptan; 2-Mercaptoethanethiol
CAS Number	540-63-6
EC Number	208-752-3
Beilstein (BRN)	505946
SMILES	SCCS
InChI	InChI=1S/C2H6S2/c3-1-2-4/h3-4H,1-2H2
Molecular Formula	C₂H₆S₂
Molecular Weight	94.19 g/mol
FEMA Number	3484

Source: PubChem; NIST Chemistry WebBook (2024).

Molecular Structure

Skeletal structural formula of 1,2-ethanedithiol showing the two terminal thiol groups — Figure 1. Molecular structure of 1,2-ethanedithiol (skeletal formula).Adapted from NIST Chemistry WebBook.

EDT consists of a two-carbon backbone terminated by thiol groups at each end. Rotation about the central C–C bond gives two principal conformations: the anti form, in which the sulfur atoms are opposed, and the gauche form, in which they are approximately syn-periplanar. The anti conformer is the more stable by roughly 3.8 kJ/mol in the gas phase.

The gauche conformer is significant in coordination chemistry because the two sulfur donors are pre-organised for chelation. Key bond lengths and angles are summarised below.

Table 2. Selected bond lengths and angles of 1,2-ethanedithiol.

Parameter	Value	Unit	Source
C–S bond length	1.81	Å	NIST WebBook
S–H bond length	1.34	Å	NIST WebBook
C–C bond length	1.53	Å	NIST WebBook
C–S–H angle	96	°	NIST WebBook
S–C–C angle	110	°	NIST WebBook
Anti / gauche ΔE	≈ 3.8	kJ/mol	lit.

Source: NIST Chemistry WebBook (2024); literature values.

Physical Properties

The compound is a colourless to pale yellow mobile liquid with a persistent odour. It is practically insoluble in water but mixes freely with most organic solvents.

Table 3. Physical properties of 1,2-ethanedithiol.

Property	Value	Unit	Source
Appearance	Colorless to pale yellow liquid	—	lit.
Odor	Strong, repulsive (rotten cabbage)	—	lit.
Melting Point	−41	°C	lit.
Boiling Point	144–146	°C	lit.
Density (25 °C)	1.123	g/mL	lit.
Refractive Index	n²⁰/D 1.558	—	lit.
Vapor Pressure	4.8	mmHg	at 20 °C
Vapor Density	3.2	—	air = 1
Flash Point	44–50	°C	closed cup, reported range
Water Solubility	Insoluble	—	lit.
Solubility	Miscible with common organic solvents	—	lit.

Source: NIST Chemistry WebBook (2024); literature values (lit.).

Chemical Properties

Acidity (pKa)

The two thiol groups deprotonate at pKa values of approximately 8.96 and 10.54, giving the mono- and dithiolate anions. In alkaline media both sulfur centres can be deprotonated, which underpins the molecule's use as a dianionic bridging ligand.

Oxidation behaviour

Exposure to air or mild oxidants readily forms disulfide-linked oligomers and cyclic polysulfides through S–H coupling. This reactivity requires storage under inert atmosphere and is exploited deliberately in thiol-ene and thiol-Michael transformations.

Coordination ability

Each sulfur atom carries a soft donor character, allowing EDT to act as a bidentate chelating ligand that forms five-membered chelate rings with transition metals. The ligand stabilises square-planar Ni(II), Pd(II) and Pt(II) complexes (Housecroft & Sharpe, 2018).

Soft–soft interactions

As a soft donor, EDT binds preferentially to soft metal centres such as Hg(II), Ag(I), Tl(I) and Au(I) under the principle of hard–soft acid–base matching. This selectivity is the chemical basis for its use in heavy-metal capture (Pearson, 1963).

Spectroscopic Data

Table 4. Characteristic infrared absorptions (cm⁻¹).

Wavenumber (cm⁻¹)	Assignment
2555 (w)	S–H stretch
2925 (m)	C–H stretch (CH₂)
1415 (m)	CH₂ scissoring
1250 (m)	CH₂ twisting / C–C stretch
720 (w)	C–S stretch

Source: literature values (lit.).

Table 5. ¹H NMR data (CDCl₃).

δ (ppm)	Multiplicity	Integration	Assignment
2.68	multiplet	4H	CH₂ (S–CH₂–CH₂–S)
1.35	triplet	2H	SH (thiol proton)

Source: literature values (lit.).

Table 6. ¹³C NMR data (CDCl₃).

δ (ppm)	Assignment
≈ 28.5	CH₂ (C–S)

Source: literature values (lit.).

Table 7. Principal mass spectral fragments (EI, 70 eV).

m/z	Ion	Relative abundance
94	M⁺ (C₂H₆S₂)	base peak region
61	[M – SH]⁺	major
46	[CH₂S]⁺	major
27	[C₂H₃]⁺	minor

Source: NIST Chemistry WebBook (2024).

Thermodynamic Data

Table 8. Thermodynamic properties of 1,2-ethanedithiol.

Property	Value	Unit	Source
ΔcH°(liquid)	−2794.90 ± 0.92	kJ/mol	NIST WebBook
ΔfH°(gas)	−9.30 ± 1.10	kJ/mol	NIST WebBook
ΔfH°(liquid)	−54.00 ± 1.10	kJ/mol	NIST WebBook
ΔvapH°	44.70 ± 0.10	kJ/mol	NIST WebBook
Cp,gas (298 K)	106.37	J/(mol·K)	Joback method
IE	9.30	eV	NIST WebBook
logP(oct/water)	0.846	—	Crippen method

Source: NIST Chemistry WebBook (2024); Joback and Crippen estimation methods.

Reactivity

7.1Carbonyl Protection — 1,3-Dithiolane Formation

Under acid catalysis EDT condenses with aldehydes and ketones to give 1,3-dithiolanes, a widely used strategy for protecting carbonyl groups against nucleophilic and basic conditions. The cyclic dithioacetal is subsequently removed with mercury(II) salts or oxidative reagents (Wuts, 2014).

R₂C=O + HSCH₂CH₂SH → R₂C(SCH₂CH₂S) + H₂O

Reaction 1. Acid-catalysed formation of a 1,3-dithiolane from EDT.Conditions: p-TsOH or BF₃·OEt₂, refluxing benzene or toluene, Dean–Stark removal of water.

7.2Thiol-Ene and Thiol-Michael Addition

The terminal S–H bonds undergo rapid radical thiol-ene addition to alkenes and base-catalysed thiol-Michael addition to activated alkenes. Because EDT carries two equivalent thiols, it functions as a cross-linker in the preparation of polymer networks and surface grafts (Hoyle & Bowman, 2010).

HSCH₂CH₂SH + 2 CH₂=CH–R → R–CH₂CH₂–S–CH₂CH₂–S–CH₂CH₂–R

Reaction 2. Double thiol-ene addition across EDT.Conditions: Photoinitiator (DMPA) with UV light, or amine catalyst at ambient temperature.

7.3Metal Complexation

EDT reacts with transition-metal halides to give chelate complexes in which the two sulfur donors occupy adjacent coordination sites. The resulting five-membered ring imparts thermodynamic stability that is reflected in the strong binding of soft metal ions (Housecroft & Sharpe, 2018).

MCl₂ + HSCH₂CH₂SH → [M(SCH₂CH₂S)] + 2 HCl

Reaction 3. General chelation of a divalent metal by EDT.Conditions: Anhydrous conditions, inert atmosphere; base to neutralise liberated acid.

References

Housecroft, C. E., & Sharpe, A. G. (2018). Inorganic chemistry (5th ed.). Pearson.
Hoyle, C. E., & Bowman, C. N. (2010). Thiol-ene click chemistry. Angewandte Chemie International Edition, 49(9), 1540–1573.
NIST. (2024). 1,2-Ethanedithiol. NIST Chemistry WebBook, SRD 69. https://webbook.nist.gov
Pearson, R. G. (1963). Hard and soft acids and bases. Journal of the American Chemical Society, 85(22), 3533–3539.
PubChem. (2024). 1,2-Ethanedithiol. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov
Wuts, P. G. M. (2014). Greene's protective groups in organic synthesis (5th ed.). Wiley.