Carbamate anions

NH3 can also be added to C02 if the addition product, i.e., the unstable carbamic acid (top right of the figure), is transformed into the stable carbamic acid anion ( carbamate ion at the bottom of the figure) ... 

Thorium compounds of anionic nitrogen-donating species such as [Th(NR2)4], where R = alkyl or sdyl, are weU-known. The nuclearity is highly dependent on the steric requirements of R. Amides are extremely reactive, readily undergoing protonation to form amines or insertion reactions with CO2, COS, CS2, and CSe2 to form carbamates. Tetravalent thorium thiocyanates have been isolated as hydrated species, eg, Th(NCS)4(H20)4 [17837-16-0] or as complex salts, eg, M4 Th(NCS)g] vvH20, where M = NH, Rb, or Cs. 

Oxygen-Gontaining Organics. Neutral and anionic oxygen-containing organic molecules form complexes with thorium. Recent work has focused on alkoxides (72), aryloxides, and carboxylates however, complexes with alcohols, ethers, esters, ketones, aldehydes, ketoenolates, and carbamates are also well known. 

Pinacryptol yellow surface-active agents [147 — 151] carbamate-based insecticides and herbicides [152] organic anions [153] sweeteners [129, 154]... 

The salts of alkyl xanthates, A/,A/ -di-substituted dithio-carbamates and dialkyidithiophosphates [26] are effective peroxide decomposers. Since no active hydrogen is present in these compounds, an electron-transfer mechanism was suggested. The peroxide radical is capable of abstracting an electron from the electron-rich sulfur atom and is converted into a peroxy anion as illustrated below for zinc dialkyl dithiocarbamate [27] ... 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

Chitosan has been recently found to be soluble in alkaline media, viz. NH4HCO3 solutions, where it assumes the ammonium carbamate form Chit-NHC02 NH4, i.e., a transient anionic form that keeps it soluble at pH 9.6, while reversibly masking the polycationic nature of chitosan. Because ammonium carbamates and NH4HCO3 decompose thermally and liberate CO2, NH3 and water, this alkaline system is suitable for producing chitosan microspheres by spray-drying (Table 1) [206]. 

These TMS-carbamate-mediated NCA polymerizations resemble to some extent the group-transfer polymerization (GTP) of acrylic monomers initiated by organo-silicon compounds [40]. Unlike GTPs that typically require Lewis acid activators or nucelophilic catalysts to facilitate the polymerization [41], TMS-carbamate-mediated NCA polymerizations do not appear to require any additional catalysts or activators. However, it is still unclear whether the TMS transfer proceeds through an anionic process as in GTP [41] or through a concerted process as illustrated in Scheme 14. 

Lithiation of alkyl groups is also possible and again a combination of donor chelation and polar stabilization of anionic character is required. Amides and carbamates can be lithiated a to the nitrogen. 

The chiral center would be installed from either Unear carbamate 15 or branched carbamate 16 via the asymmetric addition of malonate anion to the 7i-allyl Mo complex reported by Trost et al. [11] to afford the branched chiral malonate derivative 17. Decarboxylation of 17 should provide the mono-carboxylic acid 18. Masa-mune homologation with 18 affords our common precursor 14. Linear carbamate 15 was obtained from the corresponding cinnamic acid, and branched 16 was prepared in one pot from the corresponding aldehyde. 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

Tellurium coprecipitated with Mg(OH)2 Tin complexed with sodium diethyldithio carbamate Tin adsorbed onto Dowex 1-X8 anion exchange column, desorbed with 2 M nitric acid... 

The secondary aryl amine 24 is far less basic than primary or secondary alkyl amines, and does not form the carbamic acid to any detectable extent in the presence of scC02 [31]. Therefore, 24 is extracted readily from the catalyst-containing IL phase, which can be recycled without noticeable loss of activity and selectivity [13]. In fact, it transpires that the active species is more stable towards oxygen in the IL than in organic solvents. Furthermore, the choice of anion of the IL largely controls the performance of the active cationic species, allowing even the use of an otherwise inactive iridium chloride precursor [ Ir(cod)Cl 2] to form in-situ catalysts... 

In the case of carbonylation (Z)-(2-en-4-ynyl)amines, a peculiar promoting effect by CO2 has been found. In fact, CO2 buffers the basicity of the substrate, with formation of a carbamate anion, thus freeing the HI neces-... 

Fig. 43 Carbamate prodrugs [129a,b] are targets for abzyme cleavage to release a mustard [130] of enhanced cytotoxicity. ElcB hydrolysis of aryl carbonates involves the anion [131]. TSAs [132] and [133] were used to generate antibodies to catalyse a BAc2 mechanism for hydrolysis whose kinetic behaviour was evaluated with ester [134].

The correlation parameters are not well established for the carbamate ion. The determination of entropy of the aqueous salt is uncertain because of its tendency to decompose to ammonia and bicarbonate ions. Entropy of the anion has been estimated by Wagman and Goldberg of NBS at 22 cal/mol K (S° of H = 0.0). (43) This yields a salting-out coefficient for ammonia by ammonium carbamate of 0.036 kg H20/mol. 

Example Even a moderate voltage drop between nozzle and skimmer can cause the elimination of weakly bonded substituents such as CO2 in case of carbon dioxide-protected deprotonated A-heterocycles. In particular SnMes-substituted anions such as 2-(trismethylstannyl)pyrrole-A-carbamate exhibit variations in the [A-C02]7A ratio of up to a factor of 30 (Eig. 11.10). [76]... 

New brush-type phases (donor-acceptor interactions) are appearing all the time. " Examples are stationary phases comprising quinine derivatives and trichloro-dicyanophenyl-L-a-amino acids as chiral selectors. Quinine carbamates, which are suitable for the separation of acidic molecules through an ionic interaction with the basic quinine group, are also commonly used but in general they are classified with the anion-exchange type of chiral selectors (see further) because of their interaction mechanism, even though r-donor, r-acceptor properties occur. (Some separations on Pirkle-type CSPs are shown in Table 2.)... 

Part of the great efficiency of the intramolecular reactions of [26] and [27] is undoubtedly due to the correct alignment of the rigidly held nucleophile and carbonyl group. Molecular models show that in one of the conformations of [27] in which steric interactions are minimized, the phenoxide ion is immediately adjacent to the carbonyl group and in an excellent position for perpendicular attack (Bender, 1960) but other factors must also be important. Correct orientation would not explain why anionic nucleophiles are superior to neutral nucleophiles. Extensive studies have not been carried out with nitrogen nucleophiles in carbamate ester hydrolysis, but Hegarty and Frost (1972) found that carbamate [29] underwent elimination to an isocyanate. This can be contrasted with the... 

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