1.Synthesis
2,4-TDI is prepared in three steps from toluene, which is doubly nitrated with nitric acid to give dinitrotoluene. This step determines the isomer ratio of the ultimate TDI. Hydrogenation of the dinitrotoluene produces the corresponding isomers of 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.
2.application
The isocyanate functional groups in TDI react with a hydroxyl groups to form urethane linkages. 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. 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.
3.Hazard
The LD50 for TDI is 5800 mg/kg for oral contact and LC50 of 610 mg/m3 for the vapour. Despite the indicated low toxicity, TDI is classified as “very toxic” by the European Community.
Information is available on handling, personal protective equipment, exposure monitoring, transport, storage, sampling and analysis of TDI, dealing with accidents, and health and environmental themes. 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.
没有评论:
发表评论