Toluene diisocyanate (TDI) has two isomers: 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. The two isocyanate groups in TDI react at different rates: The 4-position is approximately four times more reactive than the 2-position. 2,6-TDI is a symmetrical molecule and thus has two isocyanate groups of similar reactivity, similar to the 2-position on 2,4-TDI. TDI (toluene diisocyanate) is one of the commonly used polyisocyanates, and polyisocyanates are polyurethane (PU) materials and important basic raw materials. TDI commonly used in polyurethane industry is a mixture of 2,4-TDI and 2,6-TDI isomers, including three commonly used brands: TDI-80/20, TDI-100 and TDI-65/35. The preceding figures indicate the content of 2,4-TDI in the composition - 80 in TDI-80/20 indicates that its composition is 80% 2,4-TDI and 20% 2,6-TDI. It is mainly used for producing flexible polyurethane foam and polyurethane elastomers, coatings, adhesives and so on.
2,4-TDI is prepared in three steps from toluene via dinitrotoluene and 2,4-diaminotoluene (TDA). Finally, the TDA is subjected to phosgenation, i.e., treatment with phosgene to form TDI. This final step produces HCl as a byproduct and is a major source of industrial hydrochloric acid.
Distillation of the raw TDI mixture produces an 80:20 mixture of 2,4-TDI and 2,6-TDI, known as TDI (80/20). Differentiation or separation of the TDI (80/20) can be used to produce pure 2,4-TDI and a 65:35 mixture of 2,4-TDI and 2,6-TDI, known as TDI (65/35).
Manufacturing: It is mainly used for producing flexible polyurethane foam and polyurethane elastomers, coatings, adhesives and so on.