2831 - Dithionites and sulfoxylates:

Heading 2831 encompasses dithionites and sulfoxylates, which are inorganic chemical compounds. These substances are characterized by the presence of the dithionite (S₂O₄²⁻) or sulfoxylate (SO₂²⁻) anion. Dithionites, commonly known as hydrosulfites, are powerful reducing agents widely used in various industrial applications, such as textile dyeing as a reducing agent for vat dyes, and in paper manufacturing for pulp bleaching. Sulfoxylates, while less common, also serve as reducing agents and in specific chemical syntheses.

As a category within Section VI, Chapter 28, heading 2831 focuses specifically on these sulfur oxyanions, distinguishing them from other inorganic chemicals. Unlike categories such as inorganic acids or bases, or simple salts of sulfuric acid (covered elsewhere in Chapter 28), this heading is reserved for compounds containing the unique dithionite or sulfoxylate functional groups. Its position within the chapter reflects its classification as a distinct chemical compound type.

The subcategories within heading 2831 further refine classification based on the cation. Subheading 2831.10 specifically covers dithionites and sulfoxylates that are salts of sodium, which are the most commercially significant forms. The residual category, 2831.90.00.00, is designated for all other dithionites and sulfoxylates not based on sodium, ensuring comprehensive coverage for these specialized reducing agents across various chemical formulations.