2920.90 - Other:

This HTS category, 2920.90, encompasses esters of other inorganic acids of nonmetals, their salts, and their halogenated, sulfonated, nitrated, or nitrosated derivatives, that are not specifically classified elsewhere within heading 2920. This broad residual category serves as a catch-all for compounds that fit the general description of inorganic esters but do not fall under more specific subheadings like thiophosphoric or phosphite esters, nor are they the explicitly listed compound endosulfan.

To distinguish this category from its siblings, it's crucial to note what is *excluded*. Sibling entries specifically identify thiophosphoric esters (phosphorodithioates) and phosphite esters. Therefore, 2920.90 is for all other esters of inorganic acids (excluding those derived from hydrogen halides) and their salts, as well as their modified forms through halogenation, sulfonation, nitration, or nitrosation, provided these are not otherwise specified. The reference to "IX. NITROGEN-FUNCTION COMPOUNDS" in the sibling list likely points to a different chapter or a more general classification within Chapter 29 that does not specifically deal with inorganic esters.

The subcategories within 2920.90 further refine the classification. The "Aromatic:" designation indicates a subdivision based on whether the ester or its derivative possesses an aromatic structure. This distinction is significant for chemical classification as aromatic compounds often exhibit unique chemical properties and reactivity. The residual "Other" subcategory (2920.90.51.00) serves to capture any remaining items within 2920.90 that do not meet the criteria for the "Aromatic:" subdivision.