1978: UCC carbaryl production changed to isocyanate process (phosgene + methylamine → methyl isocyanate; methyl isocyanate + naphthol → carbaryl) in Institute East Carbamoylation Center; isocyanate process claimed to involve higher overall yields, fewer losses from hydrochloride adduct by-products, less waste and environmental impact, and fewer and less severe corrosion problems.
1978: Sophisticated drum-filling operation enables MIC to be shipped to customers in France, India, Brazil, and United States.
Literature describes four general routes to carbaryl (http://www.exchemistry.com/sevin.html):
1. 1-naphthol + phosgene then + methylamine (chloroformate process),
2. 1-naphthol + methyl isocyanate (isocyanate process),
3. 1-naphthol + methyl carbamoyl chloride, and
4. 1-naphthol + dimethyl urea.
In principle, these four approaches may also apply to any of the carbamates; as far as is known, however, only the chloroformate process was used as an alternative to the isocyanate process, and that was for carbaryl, and that was abandoned.
1979: UCC shuts down MIC Unit 1 because of lower projected demand.
1984: UCC methomyl and Larvin production started using isocyanate process in Institute West Carbamoylation Center on old olefins site.
1984: Toluene diisocyanate site converted to Miscellaneous Carbamates Unit for aldicarb, Standak, Broot, and Zectran.
3 December 1984: Bhopal accident.
1985: MIC destruction capacity and other safety enhancements added at Institute.
23 April 1985: Boros (UCC) report on possible research alternatives:
1. Aqueous medium for aldicarb oxime + MIC reaction (similar to DuPont 1970 patent).
2. Onepot process for aldoxycarb (aldicarb oxime + methyl isocyanate (water) → aldicarb; aldicarb + H2O2/HCOOH → aldoxycarb [Standik]).
3. General process for carbamates: ROH + CO + CH3NH2 (Pd/O2) → carbamate + H2O (caustic, chlorine, phosgene, MIC eliminated; need high Pd productivity and recovery) (based on Asahi Chemical article in Journal of Organic Chemistry, 1984).