Carbamates and Ureas

The carbamate anti rotamer is usually favored by 1.0-1.5 kcal mol-1 for steric and electrostatic reasons [33]. Energy difference may be even close to zero in the case of certain carbamates which may be roughly found as a 50 50 mixture of syn and 

Dipole moments of ground state (CS) and two possible syn and anti transition states calculated at the 6-31 G //6-31 C level for R2 = R3 = Me [34], 

Due to competitive conjugation, ureas have barriers to rotation lower than the corresponding amides. Urea isomerization proceeds either via a classical CTI (AHi = 18.5 1.6 kcal mol ) or a whole-body flip (AHi = 15.5 1.2 kcal mol-1), i.e. from trans-trans to cis-cis. 

The direct synthesis of toluene diisocyanate (TDI) starting from dinitrotol- 

The reaction has been extended to other phenyl isocyanates. Performed in alcoholic solvents it yields the corresponding carbamates, with better yields using milder conditions, whereas ureas are obtained in presence of amines (Table VIII). 

In all these reactions the expensive palladium based catalysts can be replaced by elementary selenium [65] (even sulfur [66] in some cases). The yields are good but industrialization of this new type of catalyst might be difficult because of the toxicity and the volatility of selenium. 

Some heterocycles have been prepared from orthosubstituted nitro compounds [72,73]  

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Because an excess of ammonia is fed to the reactor, and because the reactions ate reversible, ammonia and carbon dioxide exit the reactor along with the carbamate and urea. Several process variations have been developed to deal with the efficiency of the conversion and with serious corrosion problems. The three main types of ammonia handling ate once through, partial recycle, and total recycle. Urea plants having capacity up to 1800 t/d ate available. Most advances have dealt with reduction of energy requirements in the total recycle process. The economics of urea production ate most strongly influenced by the cost of the taw material ammonia. When the ammonia cost is representative of production cost in a new plant it can amount to more than 50% of urea cost. 

Liquid paraffin carbamate and urea herbicides stabilization and enhancement spray solution, 20% in toluene, water investigation [241]... 

The Ford hydroglycolysis process is an example of a combined approach for die depolymerization of PURs. In a reactor, polyurethane foam is reacted with a mixture of water, diethylene glycol, and alkali metal hydroxides at high temperature to form polyols. When sodium hydroxide is added as a catalyst, a cleaner polyol is formed because all of the carbamates and ureas in the product are converted into amines and alcohols by hydrolysis.33... 

Tnethanolanune carbamate and urea stabilization herbicides as dansyl denvatives... 

Anthranilic acid derivatives of genus D that possess carbamate and urea linkers (W contains an oxygen or nitrogen atom directly linked to the carbonyl carbon, e.g., compounds 18 and 19 respectively) were claimed as GPR109A agonists in a patent application [65]. 

The use of a nitrogen nucleophile in the side chain (as an amide) also leads to an intramolecular 1,4-addition under the standard conditions for the palladium-catalyzed 1,4-oxidation reactions52. Nitrogen nucleophiles employed for this reaction comprise tosy-lamides, carboxamides, carbamates and ureas. The reactions are run in acetone-acetic acid with p-benzoquinone (BQ) as the oxidant. In most cases highly stereo- and regioselective reactions were obtained and some examples are given in Table 3. 

Spengler and Jumar [90] used a spectrophotometric method and thin layer chromatography to determine carbamate and urea herbicide residues in sediments. The sample is extracted with acetone, the extract is evaporated in vacuo at 40°C and the residue is hydrolysed with sulphuric acid. The solution is made alkaline with 15% aqueous sodium hydroxide and the liberated aniline (or substituted aniline) is steam distilled and collected in hydrochloric acid. The amine is diazotized and coupled with thymol, the solution is cleaned up on a column of MN 2100 cellulose power and the azo-dye is determined spectrophotometrically at 440nm (465nm for the dye derived from 3-chloro- or 3.4-dichloroaniline) with correction for the extinction of a reagent blank. 

Estimated half-lives for chlorinated hydrocarbon pesticides vary widely [16, 22] Aldrin, 1-9 Dieldrin, 3-7 Chlordane, 1-8 Heptachlor, 1-4 and DDT, 3-10 years. Half-lives for PCBs range from one year to 16 years [23]. Other types of pesticides, e.g. organophosphates, triazines, carbamates and ureas, are generally less persistent [16, 24],... 

FIGURE 1.12 CSPs on the basis carbamate and urea-linked cinchonan-calixarene hybrid selectors as examples for CSPs with complementary enantioselectivity profiles. (Reproduced from K.H. Krawinkler et al., J. Chromatogr. A, 1053 119 (2004). With permission.)... 

A series of imidazo[l,5-a]quinoxaline amides, carbamates, and ureas which have high affinity for the y-aminobutyric acid A/benzodiazepine receptor complex was developed. Compounds within this class have varying activities ranging from antagonists to full agonists. However, most analogs were found to be partial agonists as indicated by [ S]TBPS and Cl current ratios. Many of these... 

BuLi-TMEDA , are similarly powerful directors (Scheme 54). By contrast, the related amides, carbamates and ureas (125, R = COAr, CONR2, CO2R) usually undergo ben-zylic a-lithiation (see Section II.B). The bias can be shifted towards ortholithiation by additional electron-withdrawing substituents on the ring . 

Carboxy substituted diazepines 226 and 229 react with phenyl isocyanate to afford pyrimido diones 227 and 230, correspondingly (Scheme 48, Section 3.1.1.3 (1993JHC897)). N-Hydroxymethylation on an indole ring annulated to benzaze-pinone, as well as formation of the corresponding carbamate and urea, has been described (2004MI1076). 

Addition of Carbamic Acids Synthesis of Vinylic Carbamates and Ureas... 

Various halogenated and nitrated aniline derivatives are used in the manufacture of dyestuffs and carbamate and urea based pesticides. Many of these compounds are suspected to be carcinogenic. 

Additional methods considered for 304(h) rule making and the parameters measured are the following (the numbers in parentheses indicate the number of compounds included in the method) 622, organophosphorus pesticides (19) 623, 4,4 -methylene bis(2-chloroaniline) 626, acrolein and acrylonitrile (2) 627, dinitroaniline pesticides (5) 628, carbofuran 629, cyanazine 630, dithiocarbamates (15) 631, carbendazim and benomyl 632, carbamate and urea pesticides (7) and 633, organonitrogen pesticides (7). Most of these are... 

Amides, carbamates, and ureas can be generated by nucleophilic cleavage of resin-bound esters, carbonates, and carbamates, respectively, with amines (Figure 3.20). These reactions only proceed well if sufficiently reactive resin-bound derivatives are used. 

Figure 3.20. Formation of amides, carbamates, and ureas by nucleophilic cleavage with amines.

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