Salts are ionic compounds formed by replacing the carboxylic hydrogen with a metal or ammonium cation, while esters are formed by reaction with an alcohol, yielding a covalent –COOR group. The traded chemical name or CAS number will indicate which form is present; when in doubt, request a binding ruling from CBP.

Several tariff lines within 2916 — especially acrylic and methacrylic acid derivatives of Chinese origin — are subject to Section 301 measures. The measure applies at the specific 10-digit HTS line level, so importers should verify applicability line by line rather than assuming coverage across the entire heading.

Phenylacetic acid and its salts occupy their own subheading (291634) within the aromatic monocarboxylic acid group. It is a DEA-listed chemical precursor, so importers and exporters must comply with DEA registration and reporting requirements in addition to standard customs entry.