Urea/carboxylic acids

C02 as a feedstock for organic substances will continue to be in the production of urea, carboxylic acids, and organic carbonates. On the other hand, many laboratory syntheses of organic substances derived from C02 have been published, ranging from hydrocarbons to cyclic lactones. These have recently been surveyed by Denise and Sneeden (S). 

Various physicochemical characterisation techniques were used to study tris(5-acetyl-3-thienyl)methane (TATM) inclusion compounds with l, -di-chloroalkane guests (n = 1-10). Thermogravimetric analysis allowed to determine host-guest stoichiometric ratios. From the multiplicity of the host signals in the C CP MAS NMR spectrum, the number of host molecules in the asymmetric unit of each inclusion compound was determined. It was found that only 1,9-dichlorononane and 1,10-dichlorodecane form isostructural TATM inclusion compounds. The obtained results were compared with those for urea-carboxylic acid complexes. 

In addition to third-generation ILs, a new class of ionic solvent systems, called DES, has been developed. DES are typically formed by mixing a quaternary ammonium salt, such as choline chloride, and an uncharged hydrogen-bond donor, such as urea, carboxylic acids (e.g., oxalic or amino acids), or polyols (e.g., glycerol) [11,131]. Although DES are not entirely composed of ionic species, their physicochemical properties are very close to those of common ILs [132]. 

Thus, and as previously described for viscosity, the surface tension of the DESs decreases as the ratio of the HBA increases, supporting again tire fact that addition of the salt (i.e., ChCl or ZnCl2) disrupts the extensive hydrogen bond network of the HBD (i.e., polyols, urea, carboxylic acids). Also, and as aforementioned for viscosity, the surface tension showed a linear correlation with temperature. Shahbaz et a/." used the Othmer equation to predict the surface tension of different DESs with a mean percentage error of only 2.57%. The Othmer equation is as follows ... 

Supplement (combined with Volume IV) III, 2nd 1929 195-449 Hydroxy-carboxylic acids Carbonic acid, 3. GlycoUic acid, 228. Lactic acid, 261. Tartaric acid, 481. Citric acid, 556. Urea, 42. Cyanamide, 74. Thiocyemic acid, 140. 

Diethyl malonate has uses other than m the synthesis of carboxylic acids One particu larly valuable application lies m the preparation of barbituric acid by nucleophilic acyl substitution with urea... 

Rearrangement of 0-acyi hydroxarrac acxl derivatives with base or heat to amines or urea derivatives (via isocyanates) or rearrangement of carboxylic acids via their hydroxamic acxis to amines... 

A, A -Bistrimethylsilylurea, CH2Cl2. The reagent readily silylates carboxylic acids and alcohols. The byproduct urea is easily removed by filtration. 

A/,0-Bis(trimethylsilyl)trifluoroacetamide. This reagent is suitable for the silylation of carboxylic acids, alcohols, phenols, amides, and ureas. It has the advantage over bis(trimethylsilyl)acetamide in that the byproducts are more volatile. 

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Isocyanates react with carboxylic acids to form amides, ureas, anhydrides, and carbon dioxide, depending on reaction conditions and the structure of the starting materials (Scheme 4.13). Aliphatic isocyanates more readily give amides. Aromatic isocyanates tend to react with carboxylic acids to first generate anhydrides and ureas, which at elevated temperatures (ca. 160°C) may further react to give amides. In practice, the isocyanate reaction with carboxylic acid is rarely utilized deliberately but can be an unwanted side reaction resulting from residual C02H functionality in polyester polyols. 

FIGURE 15.1 Scheme showing PLC group fractionation of soluble organic matter into fractions of aliphatic hydrocarbons, aromatic compounds with application of urea clathra-tion, and methylation of carboxylic acids in polar fractions based on experimental data given in Reference 36 to Reference 52, Reference 77 to Reference 81, and Reference 88 to Reference 89. 

The phthalide 25, obtainable by condensation of 4,4 -bisdimethyl-aminobenzophenone-2-carboxylic acid with 3-dimethylaminoacetanilide and subsequent hydrolysis, was diazotized in sulfuric acid and the resultant diazonium salt treated with copper powder to yield 26. However, better yields are reportedly obtained by carrying out ring closure of the diazonium salt in phosphoric acid.103 A further synthetic route has also been described in which phthalides undergo intramolecular cyclization in the presence of aluminum chloride and urea.104,105 Thus, Crystal Violet lactone (2) has been directly converted into phthalide 26.106... 

Many of these problems may be overcome by using ionic liquids based on sugars [35] or deep eutectic mixtures. Deep eutectic mixtures such as that derived from choline chloride and urea (m. pt. 12°C [36]) or carboxylic acids [37] can be liquids and have very low vapour pressure. They have been successfully used as electrochemical solvents, but their use in catalysis remains little explored. Urea is a fertiliser and choline chloride (Vitamin B4) is a component of chicken feed so the mixture is environmentally acceptable. 

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