Acetanilide as protecting group: Direct nitration of aniline with HNO3/H2SO4 fails because: (a) in acidic conditions, -NH2 is protonated to -NH3+ (meta director), and (b) free -NH2 causes oxidation. Acetylation converts -NH2 to -NHCOCH3, which is a milder o/p-director resistant to oxidation, enabling selective para-nitration to give p-nitroacetanilide. Hydrolysis then gives p-nitroaniline — the industrial synthesis of a key dye intermediate.

p-Nitroacetanilide para selectivity: The -NHCOCH3 group directs to ortho and para positions. Para is the major product because the ortho positions are sterically hindered by the acetamido group. This is an example of steric control overriding purely electronic directing effects.

Iodoform as a diagnostic test in unknown compound identification: When an unknown compound gives a yellow precipitate with I2/NaOH, it confirms the presence of a CH3CO- group (or a group that can be oxidized to it). This was historically used to identify and characterize methyl ketones before modern spectroscopy.

Lassaigne's test in pharmaceutical quality control: New synthesized drug candidates are subjected to Lassaigne's test to confirm the presence of heteroatoms (N, S, halogens) expected from the structure. Discrepancies indicate synthesis errors or contamination.

KMnO4 as a volumetric standard and oxidant: KMnO4 is used widely in industrial water treatment (oxidizes organic impurities, Fe2+, Mn2+), as a bleaching agent in textile industry, and in analytical laboratories to standardize solutions. Its self-indicating property makes it economical (no indicator needed).

Fehling's test in food analysis (reducing sugars): Fehling's test is used to detect reducing sugars (glucose, fructose, maltose) in food science and clinical labs. Sucrose (non-reducing) gives negative Fehling's.

Salt analysis in forensic and industrial chemistry: Systematic qualitative salt analysis (cation and anion group analysis) is used in forensic labs to identify unknown salts in criminal evidence, in water quality testing, and in soil analysis for agricultural applications.

Bromine water as a rapid unsaturation test: While bromine water decolorization detects C=C and C≡C, it also precipitates 2,4,6-tribromophenol from phenol (different mechanism — electrophilic aromatic substitution, not addition). The formation of a white precipitate with Br2/H2O is specific to activated aromatic rings with -OH or -NH2 groups.