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What is toluene diisocyanate (TDI)?

Views: 289     Author: Vickey     Publish Time: 2023-07-03      Origin: Site

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What is toluene diisocyanate (TDI)?

The chemical formula of toluene diisocyanate (TDI), an organic substance, is CH3C6H3(NCO)2. Commercially significant isomers include 2,4-TDI (CAS: 584-84-9) and 2,6-TDI (CAS: 91-08-7), two of the six potential isomers. Although 2,4-TDI is synthesized in its pure form, it is frequently sold as blends of the 2,4 and 2,6 isomers, respectively, in the 80/20 and 65/35 ratios. With 34.1% of the worldwide isocyanate market in 2000, it is the second-largest producer after MDI.In 2000, almost 1.4 billion kilos were generated.All TDI isomers are colorless, while commercial examples can have a yellow tint.

Synthesis

Dinitrotoluene, 2,4-diaminotoluene (TDA), and toluene are used in the three processes necessary to make 2,4-TDI. In order to create TDI, the TDA is then phosgenated, or treated with phosgene.The last stage yields HCl as a byproduct and is a significant industrial hydrochloric acid source.

The raw TDI mixture is distillated to create TDI (80/20), an 80:20 combination of 2,4-TDI and 2,6-TDI. Pure 2,4-TDI and TDI (65/35)—a 65:35 combination of 2,4-TDI and 2,6-TDI—can be created by differentiation or separation of TDI (80/20).

Applications

To create carbamate (urethane) linkages, the isocyanate functional groups in TDI combine with hydroxyl groups. In TDI, the two isocyanate groups react at various rates: The 4-position reacts about four times as quickly as the 2-position. Due to its symmetry, 2,6-TDI possesses two isocyanate groups with comparable reactivity, much like the 2-position on 2,4-TDI.

However, because both isocyanate groups are linked to the same aromatic ring, a change in one isocyanate group's reactivity will affect the second isocyanate group's reactivity. It is occasionally used as a rocket propellant. It is employed in the creation of stiff, highly temperature-stable polyurethane foams.

Hazards

For oral contact, the LD50 for TDI is 5800 mg/kg, while for vapor, the LC50 is 610 mg/m3. TDI is categorized by the European Community as "very toxic," notwithstanding the low toxicity that is shown.

Due to the classification of toluene diisocyanate as a potential occupational carcinogen, the Occupational Safety and Health Administration in the United States has set a permissible exposure limit with a ceiling of 0.02 ppm (0.14 mg/m3), whereas the National Institute for Occupational Safety and Health has not established a recommended exposure limit. On August 13, 2015, two enormous explosions were brought on by various chemicals at a chemical warehouse located in Tianjin, China.

Handling, personal protective equipment, exposure monitoring, transit, storage, sampling and analysis of TDI, handling incidents, and health and environmental topics are all covered in the information supplied.All major producers of TDI are members of the International Isocyanate Institute,whose aim is the promotion of the safe handling of TDI in the workplace, community, and environment.High-level exposure can result in reactive airways dysfunction syndrome.

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