Carbamate synthesis

As compared to the carbamate synthesis above, an abnormal reaction course was observed in the reaction of m-tolyloxythiocarbonylimidazole with benzylmethylamine here the phenolate is exchanged instead of the imidazole, obviously because the substituent with the lower pK is eliminated 2163... 

The results of TOF and carbamate yields are summarized in Table 1. Although PdCl2(PPh3)2 exhibited the highest activity, supported Pd exhibits good activity for the carbamate synthesis for the reductive carbonylation. 

In natural processes, metal ions are often in high oxidation states (2 or 3), whereas in chemical systems the metals are in low oxidation states (0 or 1). This fact inverts the role of the metal center, such that it acts as a one-electron sink in a natural system, but as a nucleophile in an artificial ones (see other chapters of this book and the review by Aresta et al. [109]). Nevertheless, important biochemical processes such as the reversible enzymatic hydration of C02, or the formation of metal carbamates, may serve as natural models for many synthetic purposes. Starting from the properties of carbonic anhydrase (a zinc metalloenzyme that performs the activation of C02), Schenk et al. proposed a review [110] of perspectives to build biomimetic chemical catalysts by means of high-level DFT or ah initio calculations for both the gas phase and in the condensed state. The fixation of C02 by Zn(II) complexes to undergo the hydration of C02 (Figure 4.17) the use of Cr, Co, or Zn complexes as catalysts for the coordination-insertion reaction of C02 with epoxides and the theoretical aspects of carbamate synthesis, especially for the formation of Mg2+ and Li+ carbamates, are discussed in the review of Schenk... 

The synthesis of BOA-6-O-glucoside is catalyzed by constitutive enzymes that may be upregulated. A glucosyltransferase that accepted BOA-6-OH as a substrate was measurable in protein extracts of corn roots harvested from control plants. Detoxification via glucoside carbamate synthesis is inducible and seems to be more complicated than simple A/-glucosylation (data unpublished). The biosynthesis of the compounds is part of our ongoing research. 

We tested a number of dicot species for their ability to detoxify BOA. Most of them were incubated as seedlings but some as adult plants when germination failed under laboratory conditions. Applied BOA concentration was 100 and 500 pM, incubation time was 24 h. The plants were separated into roots and shoots after incubation and the material extracted with 30% methanol. HPLC analyses of the extracts revealed remarkable differences in the detoxification capacities. Major detoxification appeared within the roots, whereas shoots were only involved when roots seemed to be overtaxed. All species tested were able to perform BOA-6-O-glucoside synthesis, but with regard to glucoside carbamate synthesis, differences became obvious (Table 4.2). 

BOA detoxification capacity of several weeds with regard to glucoside carbamate synthesis within 24 h. 

A comprehensive discussion of the most important model parameters covers phase equilibrium, chemical equilibrium, physical properties (e.g., diffusion coefficients and viscosities), hydrodynamic and mass transport properties, and reaction kinetics. The relevant calculation methods for these parameters are explained, and a determination technique for the reaction kinetics parameters is represented. The reaction kinetics of the monoethanolamine carbamate synthesis is obtained via measurements in a stirred-cell reactor. Furthermore, the importance of the reaction kinetics with regard to axial column profiles is demonstrated using a blend of aqueous MEA and MDEA as absorbent. 

Addition of Carbamates Synthesis of Vinylic Carbamates and Ureas. 127... 

Scheme 144 Example of 3

Scheme 208 COMODD as an useful tool for carbamates synthesis.

The nonphosgene production of isocyanates takes place through the thermolysis of the corresponding carbamate. The carbamate synthesis may involve a number of possible alternative ways, such as the reaction of a nitrocompound with CO, or the reaction of an amine with CO and O2, with urea and alcohol, or with a carbonic ester. Among these routes, the reaction of DMC or DPC with aliphatic amines is a very efficient way to produce carbamates. 

The non-phosgene production of isocyanates takes place through thermolysis of the corresponding carbamate. The carbamate synthesis may involve several... 

Various catalysts have been studied for these reaction processes. The major disadvantages of these reaction processes are (i) the need for an energy intensive separation step for catalyst recovery and (ii) limiting solubility of CO and O2 in the liquid reactant medium. One of the objectives of our study is to develop a heterogeneous gas-solid catalytic reaction process for the synthesis of methyl-N-phenylcarbamate involving step 3 and dimethyl carbonate involving step 4 over Cu-based catalyst. This gas-solid process would eliminate the solubility limitation and catalyst separation step, thus enhancing the overall economics of the carbamate synthesis (6-8). 

S.P. Rannard and N.J. Davis, "The Selective Reaction of Primary Amines with Carbonyl Imidazole Containing Compounds Selective Amide and Carbamate Synthesis", Org. Lett., Vol. 2, pp. 2117-2120, 2000. 

Carbamate synthesis Methyl carbamates 91% Control over exothermic conditions 2004/[54]... 

Ono, K., Fugami, K., Tanaka, S. and Tamaru, Y. (1994) Palladium catalyzed arylation of IV-alkyl O-allylic carbamates synthesis of cinnamyl alcohols via Heck arylation. Tetrahedron Lett., 35, 4133-6. 

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