Tetramethyl urea

The reaction of phosphines and alkyl halides presents an alternative way to generate phosphonium electrophiles (Scheme 3.8). In particular, the combination of a phosphine and carbon tetrabromide (the Appel reaction) allows for in situ formation of a phosphonium dibromide salt (48, X = Br). Treatment of a hemiacetal donor 1 with the phosphonium halide 48 initially provides the oxophosphonium intermediate 38 (X = Br). However, the oxophosphonium intermediate 38 can react with bromide ion to form the anomeric bromide intermediate 49 (X = Br) with concomitant generation of phosphine oxide. With the aid of bromide ion catalysis (i.e. reversible, catalytic formation of the more reactive P-anomeric bromide 50) [98], the nucleophile displaces the anomeric bromide to form the desired glycoside product 3. The hydrobromic add by-product is typically buffered by the presence of tetramethyl urea (TMU). 

Starting materials which are only sparingly soluble in water may require solvents that are either partially or entirely organic. Diazotization can either be carried out as usual with an aqueous sodium nitrite solution, or alternatively with nitrosylsul-furic acid or an organic nitrite. Appropriate solvents must be stable to the reactants. Examples include aromatic hydrocarbons, chlorohydrocarbons, glycol ethers, nitriles, esters, and dipolar aprotic solvents, such as dimethyl formamide, dimethyl sulfone, tetramethylene sulfone, tetramethyl urea, and N-methylpyrroli-done. 

To a solution of silver triiluoromethanesulfonate (7.71 g, 30 mmol) in dry dichloromethane (100 mL) at —40°C in the dark is added dropwise a solution of 9-fluorenylmethoxycarbonyl serine benzyl ester 11 (8.45 g, 20 mmol), 2,3,4-tri-O-benzoyl-a-D-xylopyranosyl bromide 12 (11.14 g, 21.2 mmol) and tetramethyl urea (3.65 g, 31.4 mmol) in dichloromethane (100 mL). After 18 h of stirring at room temperature, the precipitate is filtered off and washed with dichloromethane (200 mL). The organic solution is washed with water (200 mL), 1% KHCOj solution (twice 200 mL) and water, dried with Na SO, and concentrated in vacuo. The crude product is recrystallized from ethyl acetate-n-hexane. (If the reaction was not complete, chromatography on silica gel 60 in toluene/ethanol 9 1 is recommended). Yield 15 g (87%) mp 136°C, [ot]D -27.8° (c 1.3, CHC13), Rf 0.64 (toluene/ethanol 26 1). 

Recently, the reduction of an N-terminal pyrrolidone carboxylic acid residue of proteins with diborane in tetrahydrofuran or tetramethyl urea was attempted with some success the N-terminal pyrrolidone carboxylic acid residue may thus be identified by its conversion to proline... 

Fig. 3. Solvent effect on the yield of 2-phenylpyrrole [89KGS29I] I, DMSO 2, HMPA 3, l-methyl-2-pyrrolidone 4, sulfolane 5, PEG 6. tetramethyl urea. Catalyst KOH (0.5 mol/L), for other reaction conditions see Fig. 1.

The melting point of DADMAC was found to be 151-152.5 °C [32]. The crystalline product is very hygroscopic and soluble in water, alcohols, acetone, 1-me-thyl-2-pyrrolidone, tetramethyl urea, or dimethylformamide. XH-NMR analysis of the pure DADMAC shows the following signals s 6.93 (N-CH3) d 6.05 (N-CH2-) m 3.53-4.50 (-CH=CH2) ppm [32]. 

The counter anion has a decisive effect on the type of complex formed with N,N,N, N -tetramethyl urea (TMU). 

In these complexes anion coordination must be present with the exception of perchlorate. Lanthanide contraction may also be an influencing factor. The molecular structure [ 189] of Eu(TMU)3(N03)3 shows the presence of bidentate nitrates with a coordination number of nine. The coordination polyhedron is neither the tricapped trigonal prism nor the monocapped square antiprism which may be due to the small bite of nitrate ligand. The dimethyl acetamide (DMA) complexes behave similarly as those of tetramethyl urea (TMU) with less steric requirements as evidenced by the synthesis of [180-182] La(DMA)8(C104)3, La = La-Nd La(DMA)7(C104)3, La=Sm-Er La(DMA)6(C104)3, La = Tm-Lu. 

The selenium-sihcon linker 1.46 (104), obtained from hydroxy PS resin and methyl glyoxylate through a simple five-step scheme, was coupled with a steroid scaffold to give an acetal then transformed on SP and finally cleaved with TB AF/tetramethyl urea, 1 h, 100 °C to give decorated alcohols via unstable hemiacetals with good yields and purities. 

Studies on structure and dynamics of liquids have recently been extended to solvate structure of ions in non-aqueous solutions, and to the structure of complexes with relatively complicated ligands. We can also handle special problems like hydrophobic solvation is. Diffraction studies have been performed on new solvents as e.g. trifluoroethanol [23] and tetramethyl urea [26], and on solvent mixtures [27-30]. More recently the preferential solvation of ions has been subjected by an XD investigation in MgCh-water-methMol ternary systems [31], and the solvation structure around the cations proved to undergo the change of solvent molecules proportionally to the relative concentration of the two solvents. 

One structure of a homoleptic uranyl urea compound has been reported, [U02(N,A, A -tetramethyl-urea)4][Bi2Hi2]," in which four urea groups lie in the equatorial plane of an octahedral uranium. 

Tetramethyl urea [632-22-4] Dried over BaO and distd under nitrogen. 

Tetramethyl urea, when heated at 150 C for 2 h with COF and CsF, gave the gem-difluoro derivative in low (10%) yield according to [632] ... 

The reaction is highly influenced by the solvent therefore among others NMP, DMF, dioxane, methyl formamide, dimethyl acetamide and tetramethyl urea were tested. The best results were achieved in DMF and tetramethyl urea. Using these solvents and PdCl2/CuCl or RhCl3/FeCl3 [27] as catalysts, oxidations of 10-undecenoic acid methylester, 9-decenoic acid methylester and 13-tetradecenoic acid methylester were carried out on a preparative scale (Table 2). 

A non-aqueous titration method for the drug and other hypoglycemic and diuretic agents was reported by Agarwal and Walash (17). The drug In tablet or pure form was dissolved 1n tetramethyl urea and titrated with 0.1 N lithium methoxide In benzene-methanol medium. The end point was determined using 0.2X azo violet In toluene as indicator. Recovery ranged from 98.8X to 101.6X. 

TEEE thermoplastic elastomer etherether TMU tetramethyl urea... 

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