Dimethyl Sulfate CAS 77-78-1: Key Physical & Chemical Data

Dimethyl Sulfate (DMS, CAS 77-78-1) is a colorless, oily liquid widely recognized as a powerful methylating agent in organic synthesis, with the chemical formula (CH₃O)₂SO₂. This compound plays a crucial role in industries like pharmaceuticals, dyes, and pesticides, where understanding its physical and chemical properties is essential for safe handling, precise reactions, and regulatory compliance. Just like knowing the boiling point of water helps a chef control cooking, grasping DMS characteristics ensures chemists can predict its behavior without surprises. In this article, we explore the key dimethyl sulfate properties, including its physical and chemical attributes, to help you navigate its use in lab and industrial settings.

Chemical Identity

Basic Chemical Information

Dimethyl Sulfate, often abbreviated as DMS, is a diester of sulfuric acid and methanol, making it a versatile tool in chemical reactions. Here's a quick overview of its identification:

The dimethyl sulfate molecular structure features a central sulfur atom bonded to two methoxy groups (-OCH₃) and two oxygen atoms in a sulfate framework, resembling a molecular "bridge" that transfers methyl groups—like a courier delivering packages in a chemical assembly line. This structure underpins its reactivity as a methylating agent, commonly used to add methyl groups to amines, phenols, and acids in organic synthesis.

Physical Properties

Physical Characteristics

Dimethyl Sulfate's physical properties make it a practical yet demanding compound to work with, influencing everything from storage to reaction setup. It's a colorless, oily liquid with a faint onion-like or aromatic odor that can linger like a subtle kitchen spice you didn't quite intend. Here's a breakdown:

These physical and chemical properties of dimethyl sulfate highlight its stability under normal conditions but sensitivity to moisture, where it hydrolyzes slowly, releasing methanol and sulfuric acid—like a slow leak in a pipe that eventually causes damage. Its low vapor pressure reduces evaporation risks, making it suitable for controlled lab environments.

Chemical Properties

Reactivity and Behavior

Dimethyl Sulfate's chemical properties stem from its strong electrophilic nature, driven by the methyl groups attached to the sulfate, which make it an excellent methylating agent. It reacts vigorously with nucleophiles, donating methyl groups in a process akin to a stamp machine imprinting labels on envelopes, enabling the synthesis of methylated compounds essential for drugs and dyes.

Key aspects include:

• Reactivity: Highly reactive with water, producing methanol (CH₃OH) and sulfuric acid (H₂SO₄) via hydrolysis: (CH₃O)₂SO₂ + 2 H₂O → 2 CH₃OH + H₂SO₄. This reaction is exothermic and can be violent if not controlled.

• Incompatible Substances: Avoid strong bases (e.g., NaOH), amines, water, and alcohols, as they trigger rapid decomposition—like mixing baking soda and vinegar for an unexpected fizz.

• Stability: Stable under dry, cool conditions (below 20°C) but decomposes at high temperatures or in moisture, releasing toxic fumes.

• Hazardous Decomposition Products: Carbon monoxide (CO), sulfur oxides (SOx), and methanol vapors, which pose inhalation risks.

These DMS characteristics ensure it's a precise tool in synthesis but demand careful management to prevent hazards.

Key Reactions and Applications

Dimethyl Sulfate's reactivity as a methylating agent shines in applications like converting phenols to anisoles or amines to dimethylamines, crucial for pharmaceutical intermediates and dye production. In the lab, it's used for O- and N-methylation, where its efficiency speeds up reactions without needing harsh conditions. Industrially, it's vital in pesticide synthesis and polymer modification, leveraging its ability to add methyl groups for enhanced stability—like upgrading a basic recipe with a key ingredient for better results. However, its toxicity requires alternatives like dimethyl carbonate in green chemistry.

Handling and Storage Considerations

For safe use, store Dimethyl Sulfate in a cool, dry, well-ventilated place in tightly sealed glass or stainless steel containers, away from moisture and incompatibles—think of it like sealing spices to keep out humidity. Reference the Safety Data Sheet (SDS) for specifics, and always use PPE including gloves, goggles, and respirators due to its carcinogenic potential and irritant effects.

Summary Table of Dimethyl Sulfate Properties

This table encapsulates the core dimethyl sulfate properties, aiding quick reference for professionals.