Melamine

Description

Melamine, or 1,3,5-triazine-2,4,6-triamine, is formally a trimer of cyanamide, but its most common manufacturing method is heating dicyandiamide under pressure. It has many industrial uses; the chief one is its reaction with formaldehyde to produce thermosetting plastics and cleaning products. This toxic compound has been in the "news" in recent years because of its use in China as an adulterant in infant formula and pet food to increase the apparent protein content of these products.

Chemical properties

Melamine is a white solid organic compound whose molecules consist of a sixmembered heterocyclic ring of alternate carbon and nitrogen atoms with three amino groups attached to the carbons. Condensation polymerization with methanal or other aldehydes produces melamine resins, which are important thermosetting plastics.

The Uses of Melamine

Melamine can be used to make high-pressure laminating resins (e.g., decorative countertops), molded compounds (e.g., dinnerware), and surface coating resins (e.g., appliance finishes and automotive topcoats). Additional major products are textile and paper treatment resins. Miscellaneous uses include adhesive resins for gluing lumber, plywood, and flooring, and resins for leather tanning agents.

Production Methods

Melamine is prepared almost exclusively by the urea process—the action of ammonia on urea. It is produced worldwide.

Preparation

The standard route to melamine is from urea. Urea is heated in the presence of ammonia at 250-350??C and 4--20 MPa. The reaction probably involves the simultaneous dehydration and hydration of urea to form cyanamide and ammonium carbamate; trimerization of the cyanamide then leads to melamine:

Thus only 50% of the urea used gives melamine in one step and ammonium carbamate has to be separated and converted to urea for recycling. Despite this limitation, the urea route is the most economical of currently available routes.

Reactivity Profile

Melamine is incompatible with strong oxidizing agents and strong acids. Neutralizes acids in exothermic reactions to form salts plus water. May be incompatible with isocyanates, halogenated organics, peroxides, phenols (acidic), epoxides, anhydrides, and acid halides. Flammable gaseous hydrogen may be generated in combination with strong reducing agents, such as hydrides.

Contact allergens

Melamine-formaldehyde resin (MFR) results from condensation of melamine and formaldehyde. It is anactive ingredient of strong (reinforced) plasters, such as industrial or some dental plasters used for molding.It is also used as a textile finish resin. MFR acts as an allergen generally because of formaldehyde releasing.

First aid

If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.

Storage

Store in tightly closed containers in a cool, well-ventilated area away from strong oxidizers and strong acids.

Purification Methods

Crystallise Melamine from water or dilute aqueous NaOH. It sublimes at ~240℃ on prolonged heating.