Safe phosgenation

Trichloromethyl-chloroformate has been proposed as a relatively safe phosgene source for small-scale diisocyanate and polyurethane production units. Phosgene is produced upon fragmentation of this compound on a hot iron contact. 

Osterwalder U. Continuous process to fit batch operation safe phosgene production on demand. Symp. Pap.—Inst. Chem. Eng., North West. Branch. Rugby, U.K. IChemE, 1996 6.1-6.6. 

The design of an inherently safe phosgene plant has been described by workers at... 

Acylation of imidazole produces A-acylimidazoles via loss of proton from the initially-formed A-3-acyl-imidazolium salt. A-Acyl-imidazoles are even more easily hydrolysed than A-acyl-pyrroles moist air is sufficient. The ready susceptibility to nucleophilic attack at carbonyl carbon has been capitalised upon commercially available l,l -carbonyldiimidazole (CDI), prepared from imidazole and phosgene, can be used as a safe, phosgene synthon, and also in the activation of acids for formation of amides and esters via the A-acyl-imidazole. ... 

Carbamates are generally prepared from isocyanates or chloroformates (see Scheme 4.2). Since isocyanates and chloroformates are usually prepared with phosgene, the corresponding synthetic routes are subject to the relevant safety considerations regarding the phosgene source (for a safe phosgene source, see Chapter 7). Moreover, the handling of several lower alkyl isocyanates is associated with a similar hazard level (toxicity), and therefore the search for a less hazardous procedure has been intense. 

General procedure for the synthesis of AOC-amino acids. t-Amyloxycarbonyi-L-proUne [380] t-Amyl chloroformate Method B [380] Liquid phosgene (for a safe phosgene... 

Typical procedure. L-Pro-NCA 1163g [835] Gaseous phosgene (for safe phosgenation, see Chapter 7) was bubbled into a suspension of L-Pro 1162g (17.25 g, 150 mmol) in THF (400 mL) for 4 h at ca. 30 °C. The THF was then evaporated from the homogeneous solution to leave N-chlorocarbonyl-L-proline (N-COCl-L-Pro) as a yellow oil. To a solution of N-COCl-L-Pro (35.7 g, 150 mmol) in acetone (400 mL) were added Ag20 (20.4 g, 88 mmol) and Norit A (4.5 g) and the mixture was stirred for at room temperature for 1 d. The mixture was then filtered from the black Norit A and the THF could be acetone, see above the author) was evaporated to afford... 

Whenever a phosgenation reaction has to be performed, one first has to consider vhether a safe phosgene equivalent or substitute can be used, or whether phosgene itself is required. What are the criteria for making this decision ... 

If the advantages of phosgene (such as high reactivity, high yields, and pure products see the evaluation in Chapter 6) could be combined with the convenience of safe phosgene equivalents without any loss of potential reactivity, this would constitute a valuable method in preparative chemistry. This has been achieved through the method known as safety pho enation . 

Contains one cartridge for Safe Phosgene Generation, 0.02 mol, one gas-tight adapter with tubing, one dosimeter badge + paper, and instructions. 

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