Tetrakis-ureas

This tetrakis-urea was expected to self-assemble in apolar media by hydrogen bond formation between urea moieties of two different units. The analogous behavior of calix[4]arene tetrakis-ureas is well documented [75], but, in contrast to the corresponding calix[4]arene capsules, those deriving from 31 would feature hydrogen bond donor sites within the cavity (Fig. 5). 

Figure 26 Chemdraw diagrams of (a) the tris-urea and (b) the tetrakis-urea acycles, and (c) the sulfate complex with the tetrakis-urea host.

CioH4oBr2MgN2oOiOf Hexakis(urea)magnesium dibromide tetrakis(urea), 45B, 783... 

Finally, a modification has been carried out in which a polyacrylate emulsion is added to a normal tetrakis(hydroxymethyl)phosphonium sulfate [55566-30-8] (THPS), urea, and TMM fire-retardant treatment in an attempt to completely alleviate the strength loss during the finishing. Indeed, better retention of tensile properties is achieved with no loss in fire resistance (85). 

LRC-100Finish. The use of LRC-100 flame retardant for 50/50 polyester cotton blends has been reported (144). It is a condensation product of tetrakis(hydroxymethyl)-phosphonium salt (THP salt) and A/A7,A7 -trimethylphosphoramide [6326-72-3] (TMPA). The precondensate is prepared by heating the THP salt and TMPA in a 2.3-to-l.0-mole ratio for one hour at 60—65°C. It is appUed in conjunction with urea and trimethylolmelamine in a pad-dry-cure oxidation wash procedure. Phosphoms contents of 3.5—4.0% are needed to enable blends to pass the FF 3-71 Test. 

The salt ia this case is tetrakis(hydroxymethyl)phosphonium chloride [124-64-1]. The corresponding sulfate salt [55566-30-8] is also produced commercially as are urea-containing formulations of both salts. The latter formulations are actually used to flame retard the textiles (see Flame retardants FOR textiles). 

The tetrakis(hydroxymethyl)phosphonium chloride so formed is the major ingredient with urea-formaldehyde or melamine-formaldehyde resins for the permanent flame-proofing of cotton cloth. 

Uranium, pentakis(dimethyl sulfoxide)dioxy-stereochemistry, I, 74 Uranium, pentakis(urea)dioxy-stereochemistry, 1,74 Uranium, tetrakis(bipyridyl)-stereochemistry, I, 94 structure, 1, 24... 

Preparation of cyclic urea derivatives by the intramolecular condensation of l,l,3,3-tetrakis(2-chloroethyl)urea [106]. 

Other most successful durable treatment is based on tetrakis (hydroxymethyl) phosphonium derivatives. Very well-known brand marketed as Proban CC (Rhodia, previously Albright Wilson) involves padding of tetrakis (hydroxymethyl) phosphonium chloride (THPC) urea solution onto the cotton fabric, curing with ammonia in a specially designed reactor to generate a highly cross-linked three-dimensional polymer network. The fabric is then treated with hydrogen peroxide, which converts P3+ to the P5+ state. The reactions are shown in Scheme 24.2. Other similar commercial product is Thor s Aflammit P. In literature many combinations of tetrakis (hydroxymethyl) phosphonium derivatives with other salts have been reported,50 but the most successful so far has been the THPC-urea-NH3 system discussed earlier. 

The first question that arises is how does triplet oxygen interact with reduced flavin in what is a spin-forbidden reaction We originally noted the similarity, both electronic and structural, between reduced flavin and tetrakis(dimethylamino)ethylene (33). In the presence of triplet oxygen, 33 reacts rapidly to give the corresponding urea. This... 

The 1 1 cocrystal of 2-amino-5-nitrothiazole with 4-aminobenzoic acid comprises two constituent molecules associated by a hydrogen-bonded graph set dimer through the carboxylic group across the N/N site of the thiazole [0-H...N, 2.614(3)A N-H...O, 2.991(3)A] [144], 2-Bromo-5-nitrothiazole [145], tetrakis (mefa-acetato)bis[2-(2-thionyl)-amino-5-nitrothiazole]-dirhodium-II-dihydrate [146], and /V-(4-melhoxyben/yl (-/WS-nilro-1,3-thia/ol-2-yl) urea [147] have been studied by X-ray analysis. 

Although inorganic salts can provide excellent flame-retardant properties for cellulose, reasonable laundering durability must be incorporated into any finish destined for apparel use. The most successful durable flame retardants for cellulose are based on phosphorous- and nitrogen-containing chemical systems that can react with the fibre or form crosslinked structures on the fibre. The key ingredient of one of these finishes is tetrakis(hydroxymethyl)phosphonium chloride (THPC), made from phosphine, formaldehyde and hydrochloric acid (Fig. 8.11). THPC reacts with urea to form an insoluble structure on cellulose in a pad-dry-cure process (Fig. 8.12). 

Roxel process. A process for increasing the flame resistance of cotton by chemically modifying the fiber, i.e., by applying a formulation consisting of tetrakis(hydroxymethyl)phosphonium chloride (THPC), triethylolamine, and urea in aqueous solution. These substances cross-link with the hydroxyl groups of the cellulose to form an efficient and durable protective medium. This process is used in the manufacture of blankets, curtains, bed linen, and industrial safety garments. 

The formation of 3,5-bis(methoxymethyl)-5,6-dihydro-27/-l,3,5-oxadiazin-4(3//)-one (114 R = MeOCH2) by reaction of urea with methanal under carefully controlled acidic methanolic conditions has been shown to proceed via cyclization of the tris(hydroxyethyl) urea (113) as outlined in Scheme 11 <89BCJ1930>, rather than via a tetrakis(hydroxymethyl)urea or a perhydro-1,3,5-oxadiazin-4-one as suggested originally <36BCJ248>. 7V-Methylurea under the same conditions gives the 3-methoxymethyl-5-methyl derivative (114 R = Me) but in only 27% yield. 

X-ray crystal structures, 397 tetrakis(perfluoroalkanesulfonates), 418 tetraphenylporphyrin, 440 thioacetylacetonato, 439 thiocyanates, 380 thioethers, 418 thiolates, 418 thiosemicarbazones, 434 thiourea, 421 tin-containing ligands, 370 trialkyIsilyloxides, 389,391 triazenes, 378 triethylamine, 371 trihydroxyglutaric acid, 412 tris(diketonates), 399 tropolonates, 402 urea, 382 water, 384... 

The stabilizer systems for polyacetals are invariably composed of a hindered phenol with a costabilizer. The hindered phenols in use are 2,2 -methylenebis-(4-methyl-6-tert-butyl-phenol), 1,6-hexamethyle-nebis-3-(3,5-di-rert-butyl-4-hydroxyphenyl)-propionate, and pentaerythrityl-tetrakis-3-(3,5-di-fert-butyl-4-hydroxyphenyl)-propionate. A large number of nitrogen-containing organic compounds have been described as costabiKzers for polyacetals, e.g., dicyandiamide, melamine, terpolyamides, urea, and hydrazine derivatives. The effectiveness of these compounds is based on their ability to react with formaldehyde and to neutralize acids, especially formic acid, formed by oxidation. In addition to nitrogen compounds, salts of long-chain fatty acids (e.g., calcium stearate, calcium ricinoleate, or calcium citrate) are also used as acid acceptors. The practical concentrations are 0.1-0.5% for the phenolic antioxidant and 0.1-1.0% for the costabilizer. 

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