Tartrazine (Yellow No. 5) (C₁₆H₉N₄NaO₉S₂) — Properties, Uses & Safety

Overview

Tartrazine, also known as FD&C Yellow No. 5 or E102, is a synthetic azo dye with the molecular formula C16H9N4NaO9S2 and a molar mass of 534.36 g/mol. It appears as an orange-yellow powder that dissolves in water to produce a bright lemon-yellow solution. Tartrazine's color arises from its extended conjugated system, which includes an azo group (–N=N–) linking two aromatic rings — this chromophore absorbs light in the blue-violet region of the visible spectrum (around 425 nm), and the transmitted/reflected light appears yellow. This makes tartrazine an excellent teaching example for the relationship between molecular structure, conjugation, light absorption, and perceived color. Tartrazine is one of the most widely used food colorings in the world, found in candies, soft drinks, chips, cereals, mustard, ice cream, and countless processed foods. It is also used in cosmetics, pharmaceuticals (pill coatings), and even in some soaps and shampoos. The dye is approved for use by the FDA, the European Food Safety Authority, and regulatory agencies worldwide, though it has been the subject of controversy regarding potential links to hyperactivity in children and allergic reactions in sensitive individuals, particularly those with aspirin sensitivity. Some countries require warning labels when tartrazine is used. Tartrazine has no significant GHS hazard classifications at food-grade concentrations. For chemistry students, tartrazine connects organic chemistry (azo compounds, aromatic chemistry, sulfonation), spectroscopy and color theory (why molecules absorb specific wavelengths), food science and regulation, and the chemistry of dyes and pigments. It also raises important discussions about food safety testing, risk assessment, and how chemistry intersects with public health policy and consumer awareness.

IUPAC Name

5-hydroxy-1-(4-sulfophenyl)-4-[(E)-(4-sulfophenyl)diazenyl]-1H-pyrazole-3-carboxylic acid

CAS Number

1934-21-0

PubChem CID

164825

Molecular Formula

C₁₆H₉N₄NaO₉S₂

Molar Mass

534.363 g/mol

State at STP

solid

Appearance

Orange-yellow powder