1,2,4-Trimethylbenzene

1,2,4-Trimethylbenzene (CAS 95-63-6) is the most abundant isomer in commercial trimethylbenzene mixtures derived from petroleum naphtha. It appears in detailing products as a minor aromatic constituent of Stoddard solvent and similar petroleum co-solvents, typically at sub-1% concentrations in the finished product formulation. The substance carries a rich hazard profile at the pure-substance level — including flammability, skin and eye irritation, and STOT SE 3 (H336 narcotic effects from vapor inhalation at high concentrations). In consumer detailing products where the substance is present at 0.5–<1% in a predominantly aqueous formulation, the concentration is below mixture-classification thresholds for most of these health codes. The STOT SE 3 (H336) narcotic-effects code requires prolonged exposure to vapors at concentrations materially higher than those produced by sub-1% content in a water-based spray; the contribution to product-level classification is the chronic systemic concern documented via STOT RE 2 (H373) in products where the aromatic petroleum fraction is present at sufficient combined concentration. Environmentally, the substance is not readily biodegradable and carries substance-level Aquatic Chronic 2 (H411). The aquatic toxicity flag is relevant at product level when petroleum-distillate co-solvents including this constituent enter wash runoff via the drain pathway.