Organic carbonates and carbamates

Owing to the rising demand of organic carbonates and carbamates, extensive investigations have been carried out to set up new eco-friendly procedures for synthesis of these intermediates. 

The classical syntheses of organic carbonates and carbamates involve the direct or indirect utilization of phosgene or its substimtes (Scheme 16.15). 

Apart from aryl esters and amides of carboxylic acids, aryl carbonates, and carbamates, other types of organic compound have been reported to undergo PFR. They include oxalates, formiates, sulfonates, sulfonamides, thioesters, selenoesters, and telluroesters. 

Biochemically Nonspecific Group. Organic phosphates and carbamates inhibit pseudocholinesterase and other esterases. Toxicity and enzymatic inhibitory power are augmented by phenothiazine derivatives but reduced by chemicals which are SER- and esterase-stimulating but not by carbon tetrachloride. 

Use Organic synthesis, especially of isocyanates, polyurethane and polycarbonate resins, carbamates, organic carbonates, and chloroformates pesticides herbicides dye manufacture. 

The ph3 ological rdle of the amidases, and how these enzymes intervene in the elaboration of materials by whose aid urea and uric acid, the two principal nitrogenous constituents of the urine, can be formed, has already been discussed. Ammonium salts represent, in fact, one of the principal sources of urea for, converted to anunonium carbonate and carbamate, they are rapidly dehydrated by the cells of the kidneys to form urea. It would even appear that uric acid, at least with animals such as birds and reptiles that produce large quantities of this substance, also has its origin in the liver, the hepatic organ of birds being capable of transforming ammonia salts, accompanied or not accompanied by ternary substances, into uric add and not... 

Phosgene has been used extensively as an organic synthetic reagent to prepare isocyanates, carbamates, organic carbonates, and chloroformates used in the manufacture of polyurethane and polycarbonate resins, pesticides, herbicides, and dyes. Although not flammable, because phosgene is... 

Srivastava, R. Srinivas, D. Ratnasamy, P. Zeolite-based Organic-Inoiganic Hybrid Catalysts for Phosgene-fiee and Solvent-free Synthesis of Cyclic Carbonates and Carbamates at Mild Conditions Utilizing CO. Appl. Catal. A Gen. 2005, 289, 128-134. 

A simpler nonphosgene process for the manufacture of isocyanates consists of the reaction of amines with carbon dioxide in the presence of an aprotic organic solvent and a nitrogeneous base. The corresponding ammonium carbamate is treated with a dehydrating agent. This concept has been apphed to the synthesis of aromatic and aUphatic isocyanates. The process rehes on the facile formation of amine—carbon dioxide salts using acid haUdes such as phosphoryl chloride [10025-87-3] and thionyl chloride [7719-09-7] (30). 

The use of NBD-Cl for the fluorescence analysis of alkylamine-generating pesticides has been investigated [173]. A two-phase reaction system is employed for the hydrolysis and labeling of N-methyl- and N,N-dimethyl-carbamate pesticides. The residue is hydrolyzed in 0.1 M sodium carbonate and the liberated amine is treated with NBD-Cl in an organic phase (IBMK, isobutyl methyl ketone) above the aqueous layer. An aliquot portion of the organic layer is used for chromatography. The reactions involved are shown in Fig. 4.65. 

Recently, organic carbamates have been synthesized by the reaction of amines and alkyl halides with scC02 in the presence of potassium carbonate and an onium salt (Bu4N)Br [52]. In order to ascertain the carbonyl-active species (carbonate or C02 ), the reaction was carried out also with potassium phosphate instead of the carbonate salt the similar results obtained confirmed that scC02 acted in the process not only as a solvent but also as a carboxylating agent. 

Dialkyltin compounds catalyze the preparation of carbamates from aromatic amines and organic carbonates. 

Leaving groups in the Tsuji-Trost reaction include acetates, halides, ethers, carbonates, sulfones, carbamates, epoxides, and phosphates. Reviews (a) Tsuji, J. In Handbook of Organopalladium Chemistry for Organic Synthesis, Negishi, E. deMeijere, A., Eds. Wiley-lnterscience New York, 2002 Vol II, Palladium-Catalyzed Nucleophile Substitution Involving Allyl Palladium, Propargyl-palladium and Related Derivatives, pp. 1669-1687. (b) Frost C. G. Howarth, J. Williams, J. M. J. Tetrahedron Asymmetry 1992, 3, 1089-1122. 

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