![]() ![]() Despite the indicated low toxicity, TDI is classified as “very toxic” by the European Community. The LD50 for TDI is 5800 mg/kg for oral contact and LC50 of 610 mg/m 3 for the vapour. It is used in the production of rigid polyurethane foams with a high temperature stability. ![]() It is also sometimes used in rocket propellants. However, since both isocyanate groups are attached to the same aromatic ring, reaction of one isocyanate group will cause a change in the reactivity of the second isocyanate group. 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. ![]() The two isocyanate groups in TDI react at different rates: The 4-position is approximately four times more reactive than the 2-position. The isocyanate functional groups in TDI react with hydroxyl groups to form carbamate (urethane) links. 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). ĭistillation of the raw TDI mixture produces an 80:20 mixture of 2,4-TDI and 2,6-TDI, known as TDI (80/20). This final step produces HCl as a byproduct and is a major source of industrial hydrochloric acid. Finally, the TDA is subjected to phosgenation, i.e., treatment with phosgene to form TDI. 2,4-TDI is prepared in three steps from toluene via dinitrotoluene and 2,4-diaminotoluene (TDA).
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