3-Bromopropane-1-thiol
[CAS 75694-39-2]

Identification

• Classification: Chemical reagent >> Organic reagent >> Thiol salt
• Name: 3-Bromopropane-1-thiol
• Synonyms: omega-Bromopropanethiol
• Molecular Formula: C₃H₇BrS
• Molecular Weight: 155.06
• CAS Registry Number: 75694-39-2
• EC Number: 860-343-4
• SMILES: C(CS)CBr

Properties

• Solubility: Slightly soluble (2.8 g/L) (25 °C), Calc.^*
• Density: 1.472±0.06 g/cm³ (20 °C 760 Torr), Calc.^*
• Boiling point: 55-56 °C (12 Torr)^**
• Flash point: 56.0±22.6 °C (Calc.)^*
• Index of refraction: 1.512 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (©1994-2014 ACD/Labs)

^** Karjala, S. A.

Safety Data

• Hazard Symbols: GHS02;GHS07 WarningGHS02
• Risk Statements: H226-H302-H312-H315-H319-H332-H335
• Safety Statements: P210-P233-P240-P241-P242-P243-P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P303+P361+P353-P304+P340-P305+P351+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Flammable liquids	Flam. Liq.	3	H226
Eye irritation	Eye Irrit.	2A	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332

Discovery and Applications

3-Bromopropane-1-thiol is a small bifunctional organosulfur compound containing both a bromine substituent and a thiol (–SH) group on a three-carbon alkyl chain. Structurally, it can be viewed as a substituted propyl mercaptan in which one terminal carbon bears a bromine atom and the opposite end bears a thiol group. This combination of a good leaving group (bromide) and a nucleophilic thiol makes the molecule highly reactive in substitution chemistry.

The thiol functional group is characterized by a sulfur atom bonded to hydrogen (–SH). Thiols are significantly more nucleophilic than alcohols due to the larger size and greater polarizability of sulfur compared with oxygen. As a result, the sulfur atom readily participates in nucleophilic substitution reactions, especially in the formation of thioethers (sulfides) via attack on electrophilic carbon centers.

The bromine substituent in 3-bromopropane-1-thiol is attached to a primary carbon, making the C–Br bond relatively susceptible to nucleophilic substitution via SN2 mechanisms. This is particularly important because the molecule contains an internal nucleophile (thiol), enabling it to undergo intramolecular cyclization under suitable conditions.

One of the key chemical features of 3-bromopropane-1-thiol is its potential to form cyclic sulfur-containing compounds such as thiiranes (episulfides) or thiacyclopropane derivatives through intramolecular nucleophilic substitution. In such reactions, the thiolate form (deprotonated thiol) attacks the carbon bearing bromine, displacing bromide and forming a three-membered sulfur-containing ring.

The compound exists in equilibrium between its protonated thiol form and its thiolate anion, depending on pH. Under basic conditions, deprotonation increases nucleophilicity dramatically, making intramolecular or intermolecular substitution reactions more favorable. The thiolate form is a strong nucleophile commonly used in organic synthesis for carbon–sulfur bond formation.

From a structural perspective, the three-carbon chain is flexible and can adopt multiple conformations in solution. This flexibility influences the probability of intramolecular attack by the thiol on the brominated carbon. When the molecule adopts a favorable conformation, cyclization can proceed efficiently.

In synthetic organic chemistry, compounds like 3-bromopropane-1-thiol are useful building blocks for constructing sulfur-containing molecules, including thioethers, disulfides, and heterocycles. They are also employed as linkers in bioconjugation chemistry, where thiol–halide chemistry is used to attach molecules to surfaces or biomolecules.

The presence of both a thiol and a bromide makes the compound chemically versatile but also relatively reactive and potentially unstable under certain conditions. Thiols are prone to oxidation, forming disulfides (R–S–S–R) upon exposure to oxygen or mild oxidizing agents, which can alter the compound’s properties and reactivity.

In terms of physicochemical properties, 3-bromopropane-1-thiol is expected to be moderately polar, with limited water solubility and a strong characteristic odor typical of low-molecular-weight thiols. The bromine atom increases molecular weight and polarizability, while the thiol group contributes to hydrogen bonding (weakly) and reactivity.

Overall, 3-bromopropane-1-thiol is a highly reactive bifunctional organosulfur compound featuring both a nucleophilic thiol group and an electrophilic bromopropyl moiety. Its significance lies in its utility as a synthetic intermediate for sulfur-containing molecules and its propensity to undergo intramolecular substitution and oxidation reactions.