2921.51 - o-, m-, p-Phenylenediamine, diaminotoluenes, and their derivatives; salts thereof:

This HTS category, 2921.51, encompasses specific aromatic diamines and their derivatives, along with their salts. The primary substances within this classification include ortho-, meta-, and para-phenylenediamine, as well as diaminotoluenes. These compounds are characterized by the presence of two amine groups (-NH2) attached to an aromatic ring. Their applications are diverse, often serving as intermediates in the synthesis of dyes, pigments, polymers, and other specialty chemicals.

The distinction between 2921.51 and its sibling category, 2921.59 ("Other"), lies in specificity. While 2921.59 covers any remaining aromatic polyamines and their derivatives not explicitly enumerated elsewhere, 2921.51 is reserved for the precisely defined compounds mentioned above. This creates a clear demarcation, ensuring that established and widely used aromatic diamines are classified under their specific codes, facilitating more accurate trade data and customs procedures.

Within the scope of 2921.51, further subdivisions are provided to refine the classification based on specific chemical identities and their salt forms. Subcategory 2921.51.10.00 details particular compounds such as 4-Amino-2-(N,N-diethylamino) toluene hydrochloride, meta-phenylenediamine, ortho-phenylenediamine, toluene-2,4-diamine, toluene-2,5-diamine, and toluene-2,5-diamine sulfate. The existence of an "Other" subcategory at the next level indicates that while 2921.51 is specific, there may be further derivatives or salts of the enumerated compounds that do not warrant their own distinct subheading.