1.1.3.3- Tetramethylurea

Arita and coworkers introduced a mixed matrix composed of triethanolamine, 1,1,3,3-tetramethylurea (8) and triethylenetetramine for analyzing glycosphingolipids in the negative-ion mode this gives results similar to those obtained with 1-thioglycerol. ... 

Glycosidation (13,302). Glycosidation of 2-acetamido-3,4,6-triacetyl-2-deoxy-a-D-glucopyranosyl chloride (1) mediated by Sn(OTf)2 provides exclusively P-glycosides. The most satisfactory base is 1,1,3,3-tetramethylurea, and CH2CI2 is the preferred solvent.2... 

The synthesis of N-(2-mercaptoethyl)-3,5-dimethylpyrazole and the workup procedure are performed in air, but the resultant thiol can best be stored under a nitrogen atmosphere. In air, the thiol is resistant to oxidation for several weeks, but the disulfide slowly crystallizes from the oil. According to the NMR spectra, the product is quite pure, but may still contain a small amount of 1,1,3,3-tetramethylurea (up to 5%). The reaction with 1,3-dichloro-2-propanol was carried out in a water/tetrahydrofuran mixture with sodium hydroxide, and appeared to proceed smoothly and in almost quantitative yields.2 This new reaction path to pyrazole-thioether ligands opens the road to the development of new chelating ligands. 

NMR has been used to study ligand exchange in non-coordinating solvents for a series of Be(C104)2-4L (L = trimethyl phosphate, DMSO, DMA, DMF, NMA, 1,1,3,3-tetramethylurea, dimethyl methylphosphonate and dimethyl phenylphosphonate) complexes. 3H NMR studies show that the mode of activation for exchange on beryllium varies from dissociative to associative depending upon L and the nature of the non-coordinating solvent.127 128... 

Glycosidation.4 p-D-Glucosides are obtained stereospecifically by reaction of acetobromoglucose with a protected sugar in CH2C12 in the presence of Sn(OTf)2 (1 equiv.) and a base (1 equiv. of collidine, diisopropylethylamine, or 1,1,3,3-tetramethylurea). Addition of 4 A molecular sieves ensures anhydrous conditions. Yields are 30-60%. 

The fact that phenyl selenoglycosides are rendered unreactive if an organic base such as collidine or 1,1,3,3-tetramethylurea is employed instead... 

In contrast, dipolar aprotic solvents possess large relative permittivities (sr > 15), sizeable dipole moments p > 8.3 10 ° Cm = 2.5 D), and average C.f values of 0.3 to 0.5. These solvents do not act as hydrogen-bond donors since their C—H bonds are not sufficiently polarized. However, they are usually good EPD solvents and hence cation sol-vators due to the presence of lone electron pairs. Among the most important dipolar aprotic solvents are acetone, acetonitrile [75], benzonitrile, A,A-dimethylacetamide [76, 77], A,A-dimethylformamide [76-78], dimethylsulfone [79], dimethyl sulfoxide [80-84], hex-amethylphosphoric triamide [85], 1-methylpyrrolidin-2-one [86], nitrobenzene, nitro-methane [87], cyclic carbonates such as propylene carbonate (4-methyl-l,3-dioxol-2-one) [88], sulfolane (tetrahydrothiophene-1,1-dioxide) [89, 90, 90a], 1,1,3,3-tetramethylurea [91, 91a] and tetrasubstituted cyclic ureas such as 3,4,5,6-tetrahydro-l,3-dimethyl-pyr-imidin-2-(l//)-one (dimethyl propylene urea, DMPU) [133]. The latter is a suitable substitute for the carcinogenic hexamethylphosphoric triamide cf. Table A-14) [134]. 

This equation accounts for experimental association constant values higher than theoretical ones because KA > Ki. Moreover, we may deduce that when cations are equal, KA is smaller for smaller anions, which means that they have a greater charge density and thus are more basic, since K2 is lower for them. On the contrary, KA values decreasing with an increase in the size of the anion have been observed in aprotic solvents like TMS (II), acetone (41), nitrobenzene (42), nitromethane (43), acetonitrile (44), and 1,1,3,3-tetramethylurea (45). This order can be understood if one considers that in this class of solvents the anions are scarcely solvated so that association is affected mainly by the strength of cation-anion interaction, which, with the cations being equal, increases with an increase in the anion charge density. 

TETRAMETHYLUREA see TDX250 TETRAMETHYLUREE (FRENCH) see TDX250 N,N,N,N -TETRAMETIL-FOSFORODIAMMIDO-FLUORURO (ITALIAN) see BJE750 TETRAMINE see HOIOOO... 

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