In the traditional process, the following reaction occurs:
(Methylamine + Phosgene ® MIC + Hydrochloric Acid)
In the DuPont catalytic process, the following reactions occur:
Environmentally Benign Reagent for Carbonylation or Methylation
Dimethylcarbonate (DMC) is an alternative to toxic and dangerous phosgene, dimethyl sulphate, or methyl chloride. DMC is easy to handle, offers economic advantages, and is a versatile derivatives performer. It uses readily available, low-cost raw material, a clean technology, and a clean product. The result is a route based on the oxidation of carbon monoxide with oxygen in methanol as follows:
This process operates at medium pressure using a copper chloride catalyst (see Figure 3.6.5).
The conventional industrial reaction involves activating the C— H bond by chloride oxidation. A variety of commercial processes use the resulting chlorobenzenes to produce substituted aromatic amines. Since neither chlorine atom ultimately resides in the final product, the ratio of the byproduct produced per pound of product generated in these processes is unfavorable.
In addition, these processes typically generate waste streams that contain high levels of inorganic salts which are expensive and difficult to treat.
Michael K. Stern, of Monsanto, uses nucleophilic substitution for hydrogen to generate intermediates for manufacturing 4-amino-diphenylamine, eliminating the need for halogen oxidation (see Figure 3.6.6). Stern and coworkers synthesize p-nitroaniline (PNA) and p-phenylenedi-amine (PPD) using nucleophilic aromatic substitution for hydrogen instead of a pathway using chlorine oxidation. Benzamide and nitrobenzene react in the presence of a base under aerobic conditions to give 4-nitrobenzanilide in high yield. Further treatment with methanolic ammonia gives PNA and regenerates benzamide.
This example includes processes for producing ethylben-zene, methyl tert-butyl ether (MTBE), and ethyl tert-butyl ether (ETBE), and many other processes.
Historically, the AlCl3 catalyst system has been the technology for ethylbenzene synthesis. However, the disposal of the waste stream presented an environmental problem. The Mobil ZSM-5 catalyst permits a solid-catalyst, vapor-phase system which gives yields comparable to the AlCl3, catalyzed system but without the environmental problems associated with AlCl3.
A new, strongly acidic, ion-exchange catalyst is replacing more acid catalyst applications for producing MTBE, ETBE, olefin hydration, and esterification. The high-temperature catalyst, Amberlyst 36, can tolerate temperatures up to 150°C. Compared to sulfuric acid, the selectivity of the acidic resins is higher, product purity is better, and unlike acid, separating the product from the catalyst is not a problem.
Petrochemicals from Renewable Resources
This example describes making alpha-olefins from car-boxylic acids.
A catalytic technique (the Henkel process) offers a green alternative for making alpha-olefins because it can produce them from fatty acids instead of from petroleum. In the reaction, an equimolar mixture of a carboxylic acid and acetic anhydride is heated to 250°C in the presence of a palladium or rhodium catalyst as follows:
This reaction causes the carboxylic acid to undergo de-carbonylation and dehydration to a 1-alkene having one
Gas Vent Methanol Recycle
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