Melamine

Description

Melamine is a chemical compound with versatile industrial uses. In the United States, it is approved for various applications, including the manufacturing of cooking utensils, plates, plastic products, paper, paperboard, and industrial coatings. MFR, found in dental plaster used for moldings and as a textile finish resin, has been identified as an allergen, causing sensitization in certain individuals. Moreover, melamine releases formaldehyde, which may contribute to its sensitizing properties. Melamine itself appears as colorless to white monoclinic crystals or prisms, or in the form of a white powder, with the characteristic property of subliming when gently heated.

Chemical Properties

White Solid

Uses

One of Melamine's significant applications is in the production of melamine-formaldehyde resin (MFR), which is an essential component in strong (reinforced) plasters. Sensitization to melamine has been reported in individuals working with MFR, such as plaster-room technicians and dental technicians.

Production Methods

The compound now is synthesized from urea.

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.

Definition

ChEBI: A trimer of cyanamide, with a 1,3,5-triazine skeleton.

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.

Flammability and Explosibility

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

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.

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.