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

It is 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. Melamine, melamine cyanurate, other melamine salts, and guanidine compounds are currently the most used group of nitrogencontaining flame retardants. Melamine is used as a flame retardant additive for polypropylene and polyethylene. Melamine cyanurate is employed commercially as a flame retardant for polyamides and terephthalates.

The Uses of Melamine

Forms synthetic resins with formaldehyde.

Definition

ChEBI: Melamine is a trimer of cyanamide, with a 1,3,5-triazine skeleton. It has a role as a xenobiotic metabolite. It is functionally related to a cyanamide. It is a conjugate base of a melamine(1+).

Definition

melamine: A white crystalline compound,C₃N₆H₆. Melamine is a cycliccompound having a six-memberedring of alternating C and N atoms,with three NH₂ groups. It can becopolymerized with methanal to givethermosetting melamine resins,which are used particularly for laminatedcoatings.

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.

General Description

Colorless to white monoclinic crystals or prisms or white powder. Sublimes when gently heated.

Air & Water Reactions

Insoluble in water.

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.

Hazard

Toxic by ingestion, skin, and eye irritant. Questionable carcinogen.

Fire Hazard

Literature sources indicate that Melamine is nonflammable.

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 (see Chap. 40)

Safety Profile

Moderately toxic by ingestion and intraperitoneal routes. An eye, skin, and mucous membrane irritant. Causes dermatitis in humans. Questionable carcinogen with experimental carcinogenic and tumorigenic data. Experimental reproductive effects. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx and CN-.

Potential Exposure

Manufactured from urea, melamine is used in the manufacture of plastics, melamineformaldehyde resins; rubber, synthetic textiles; laminates, adhesives, and molding compound

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.

Carcinogenicity

A bioassay of melamine was conducted in rats and mice by NTP. Male F344 rats and B6C3F1 mice were administered melamine in their diets at concentrations of 2250 or 4500 ppm daily for 103 weeks.Female rats were fed 4500 or 9000 ppm melamine. At the end of 111 weeks, surviving animals were killed and examined.

storage

Color Code—Blue: Health Hazard/Poison: Store in a secure poison location. Prior to working with this chemical you should be trained on its proper handling and storage. Store in tightly closed containers in a cool, well-ventilated area away from strong oxidizers and strong acids. Where possible, automatically pump liquid from drums or other storage containers to process containers. A regulated, marked area should be established where this chemical is handled, used, or stored in compliance with OSHA Standard 1910.1045.

Purification Methods

Crystallise Melamine from water or dilute aqueous NaOH. It sublimes at ~240o on prolonged heating. [Beilstein 26 I 74, 26 II 132, 26 III/IV 1253.]

Incompatibilities

Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Melamine 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, nitrides, alkali metals, and sulfides.