3,4-Dichloro-1,2,5-thiadiazole
[CAS# 5728-20-1]

Identification

• Classification: Chemical reagent >> Organic reagent >> Acid halide
• Name: 3,4-Dichloro-1,2,5-thiadiazole
• Synonyms: 4,5-Dichloro-2,1,3-thiadiazole
• Molecular Formula: C₂Cl₂N₂S
• Molecular Weight: 155.01
• CAS Registry Number: 5728-20-1
• EC Number: 227-232-7
• SMILES: C1(=NSN=C1Cl)Cl

Properties

• Density: 1.7±0.1 g/cm³ Calc.^*, 1.644 g/mL (Expl.)
• Boiling point: 158.0 °C 760 mmHg (Calc.)^*, 158 °C (Expl.)
• Flash point: 49.7±21.8 °C (Calc.)^*
• Index of refraction: 1.602 (Calc.)^*, 1.561 (Expl.)

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS06;GHS07 Danger
• Risk Statements: H301-H315-H319-H335-H412
• Safety Statements: P261-P264-P264+P265-P270-P271-P273-P280-P301+P316-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	3	H301
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2A	H319
Acute toxicity	Acute Tox.	4	H312

Discovery and Applications

3,4-Dichloro-1,2,5-thiadiazole is a chlorinated heterocyclic compound with the molecular formula C₂Cl₂N₂S. It features a five-membered aromatic 1,2,5-thiadiazole ring composed of two adjacent nitrogen atoms and one sulfur atom, with chlorine substituents at the 3- and 4-positions. The thiadiazole ring system is planar and electron-deficient, making this compound an electrophilic and reactive building block in synthetic chemistry.

This compound does not occur naturally and is synthesized via halogenation of thiadiazole precursors or by cyclization of suitably substituted thiosemicarbazides under chlorinating conditions. The introduction of chlorine atoms increases the electron-withdrawing character of the molecule and enhances its reactivity toward nucleophilic aromatic substitution, a feature that is exploited in further chemical transformations.

3,4-Dichloro-1,2,5-thiadiazole has found use as an intermediate in the development of biologically active molecules, especially in the fields of agrochemistry and pharmaceuticals. The 1,2,5-thiadiazole ring system is a recognized scaffold in medicinal chemistry due to its metabolic stability and ability to engage in specific interactions with biological targets. Chlorinated derivatives such as this compound are employed to construct libraries of analogs for screening in antibacterial, antifungal, herbicidal, or antitumor studies. Substitution of the chlorine atoms with nucleophiles (amines, alkoxides, thiols) allows access to a variety of thiadiazole derivatives with tailored properties.

In materials science, 3,4-dichloro-1,2,5-thiadiazole and related compounds have been explored as components of electroactive materials, such as electron-deficient acceptors in organic electronics. The presence of two chlorine atoms on the thiadiazole ring enhances its electron-withdrawing properties and allows for fine-tuning of electronic and optical behavior when incorporated into conjugated systems. These features are valuable in applications such as organic photovoltaics, light-emitting diodes, and field-effect transistors.

Due to its chlorinated and heteroaromatic nature, 3,4-dichloro-1,2,5-thiadiazole should be handled with care in laboratory settings. It is typically a crystalline solid or low-melting-point material, and it may release harmful fumes if heated or hydrolyzed. The compound is reactive toward nucleophiles and should be stored under dry, inert conditions to prevent degradation or unwanted side reactions.

In summary, 3,4-dichloro-1,2,5-thiadiazole is a synthetically valuable heterocycle used as an intermediate in the production of bioactive molecules and functional materials. Its combination of a thiadiazole ring and two chlorine substituents enables a range of transformations important in pharmaceutical and materials chemistry.

References

2019. Recent Developments in the Synthesis of 1,2,5-Thiadiazoles and 2,1,3-Benzothiadiazoles. Synthesis, 51(18).
DOI: 10.1055/s-0039-1690679

2015. Structure, spectroscopy, and thermal decomposition of 5-chloro-1,2,3,4-thiatriazole: a He I photoelectron, infrared, and quantum chemical study. Structural Chemistry, 26(5-6).
DOI: 10.1007/s11224-015-0655-z

2003. Electroreduction of Phthalazines and 1,2,5-Thiadiazoles: Structural Factors Determining the Opening of Heterocycle. Russian Journal of Electrochemistry, 39(11).
DOI: 10.1023/b:ruel.0000003443.14644.6e