2922.21 - Aminohydroxynaphthalenesulfonic acids and their salts:

HTS Code 2922.21 specifically encompasses aminohydroxynaphthalenesulfonic acids and their salts. These are organic compounds featuring a naphthalene ring system that has been substituted with an amino group (-NH2), a hydroxyl group (-OH), and a sulfonic acid group (-SO3H) or its salt form. These molecules are characterized by their complex chemical structures, often utilized as intermediates in the synthesis of dyes and pigments due to the chromophoric properties imparted by the naphthalene and amino/hydroxyl groups, and the solubility provided by the sulfonic acid moiety.

This category is distinct from its sibling, HTS 2922.29 ("Other"), which serves as a residual category for aminohydroxynaphthalenesulfonic acids and their salts not otherwise specified. HTS 2922.21, therefore, is reserved for those compounds explicitly defined or commonly recognized within this specific chemical family. The parent category, "Amino-naphthols and other amino-phenols, other than those containing more than one kind of oxygen function, their ethers and esters; salts thereof," sets the broader scope for compounds with amino and hydroxyl functionalities, with 2922.21 focusing on those also containing a sulfonic acid group on a naphthalene core.

Within HTS 2922.21, further subdivisions are provided to classify specific, commonly traded aminohydroxynaphthalenesulfonic acids and their salts. These subcategories, such as those for Chicago acid, H acid, and others, are established to provide a more granular classification based on the precise structural isomer and salt form of the compound. This detailed breakdown is crucial for accurate duty assessment and trade statistics, as different isomers or salts can have varying applications and market values. The "Other" subcategory under 2922.21.25.00 serves as a catch-all for any aminohydroxynaphthalenesulfonic acids and their salts not explicitly listed in the preceding specific subheadings.