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SolutionsIsocyanates

1. Products

  1. CH3N=C=O + H2O
  2. CH3N=C=O + CH3NH2
  3. C6H5N=C=O + CH3CH2OH
  4. OCN–R–NCO + HO–R′–OH
  1. N-Methylcarbamic acid, which loses CO2 to give methylamine.
  2. N,N′-Dimethylurea, CH3NHCONHCH3.
  3. Ethyl N-phenylcarbamate (a urethane), C6H5NHCOOCH2CH3.
  4. A polyurethane, –[CONH–R–NHCO–O–R′–O]n–.

2. Where do nucleophiles attack?

Why do nucleophiles attack the central carbon of an isocyanate?

Because it is doubly bonded to two more electronegative atoms (N and O): the resonance forms R–N−–C+=O and R–N=C+–O− show that it is very electron-deficient. Like the carbon of acyl chlorides or CO2, it is a very electrophilic carbon.

3. The Bhopal disaster

Methyl isocyanate was stored in Bhopal (India) to make an insecticide. Why did water getting into the tank in 1984 cause the disaster?

Hydrolysis of the isocyanate is very exothermic and gives off CO2. The heat released made the methyl isocyanate (bp 39 °C) boil, and the pressure broke the valves, releasing a cloud of the highly toxic gas over the city.

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