3- Phospholene 1-oxide

A less efficient method for the preparation of phospholes involves the bromination of phospholene oxides (5), the deoxygenation of the dibromophospholane oxides (6) so obtained with trichlorosilane, and finally dehydrobromination of dibro-mophospholanes 7 (Scheme 3) [30, 31]. 

The step 1 product was diluted with 1500 ml toluene to a final concentration of 0.013 mol/L. The mixture was then treated with 1,3-dimethyl-3-phospholene oxide and heated to 90°C while the cyclization reaction was monitored by Fouier transform infrared (FTIR). When the characteristic—NCO peak was eliminated in the macrocyclic carbodiimide (2134 cm-1), the reaction was stopped, concentrated, dried, and the crude product isolated. The crude product was purified by liquid column chromatography on silica gel using either ethyl acetate or ethyl acetate/ -hexane, 9 1, respectively, and the product isolated. 

TABLE 2. Physical Properties of Step 2 Macrocyclic Carbodiimides Prepared by Ring Closure of Step 1 Product Using l,3-Dimethyl-3-phospholene Oxide... 

Symmetrical carbodiimides, i.e., molecules with the same substituent on both nitrogen atoms, are best prepared from alkyl or aryl isocyanates in the presence of a phospholene oxide catalyst, the byproduct being carbon dioxide gas. No solvent is required for this reaction. Unsymmetrical carbodiimides or alkylarylcarbodiimides are also obtained from isocyanates, either by reaction with amines and subsequent dehydration of the intermediate... 

Polymeric catalysts are also developed. For example, phospholene oxide modified divinylbenzene/styrene copolymers, as well as a polystyrene anchored triph-enylarsine oxide catalyst were prepared. The solid phase catalysts can be removed by filtration after partial conversion of an isocyanate to the carbodiimide. Such a catalyst is useful for the preparation of carbodiimide modified liquid MDl (4,4 -diisocyanatodiphenylmethane) products, which are of considerable commercial interest. 

Also, selective reaction of the para isocyanate group in 2,4-TDI 59 is observed using a phospholene oxide catalyst to form the diisocyanate 60, mp 113-115... 

The reaction of sterically hindered aromatic diisocyanates with bases or phospholene oxide catalysts afford oligomeric carbodiimides having terminal isocyanate groups. If the catalytic conversion of 4,4 -diphenylmethane diisocyanate (MDI) is conducted in the... 

The reaction of hexamethylene diisocyanate with a phospholene oxide catalyst affords low molecular weight trifunctional oUgomers, in which the isocyanate and the carbodiimide groups are cotrimerized with the generated carbon dioxide to give six-membered ring cycloadducts. A diisocyanate byproduct is used as a masked isocyanate. ... 

Polyhexamethylenecarbodiimide, an insoluble condensation reagent for the synthesis of peptides, is obtained in the reaction of hexamethylene diisocyanate with a phospholene oxide catalyst in NMP. The isocyanate end groups are reacted with ethanol. Linear polycarbodiimides, upon reaction with adipic acid, form polyureides. For example, reaction of the 2,4-TDI derived carbodiimide with adipic acid in DMF produces the polymer, mp295°C.222... 

Melt processable linear polycarbodiimides cannot be obtained in the polymerization of aromatic diisocyanates with a phospholene oxide catalyst.However, some of the high molecular weight polymers can be molded into clear tough films, but the tensile properties of these films decrease with increasing temperature. ... 

Modification of poly(carbodiimide) foams with polyols afford hybride foams containing urethane sections. However, the thermal stabilities of the poly (urethane carbodiimide) foams are lower. Using isocyanate trimerization catalysts, such as l,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazine, in combination with the phospholene oxide catalyst gives poly(isocyanurate carbodiimide) foams with improved high temperature properties. The cellular poly(carbodiimide) foams derived from PMDI incorporate six-membered ring structures in their network polymer structure. ... 

However, heating of phenylcarbonyl isocyanate in the presence of a phospholene oxide catalyst gives 2,6-diphenyl-4-benzoylimino-l,3,5-oxadiazine20. ... 

Macromolecules with carbodiimide linkages in their repeat units are obtained from aliphatic and aromatic diisocyanates using a phospholene oxide catalyst. However, instead of linear polymers, only crossUnked thermosets are obtained in this manner. In contrast, linear polymers with pendant carbodiimide units are obtained from poly(vinyl azide) by subsequent reaction with triphenylphosphine to formpoly(phosphine imines) followed by reaction with monoisocyanates to generate the Unear poly(carbodiimides). 

The reaction of diisocyanates with a phospholene oxide catalyst in a hydrocarbon solvent at room temperature produces thermoset polymers. For example, reaction of MDI1 with a... 

Using highly hindered aromatic diisocyanates, such as 6, with a phospholene oxide catalyst produces oligomeric carbodiimides 7 ... 

When the less hindered 2,4-tolylene diisocyanate is reacted with a phospholene oxide catalyst linear oligomeric carbodiimides are obtained which have been reacted with a variety of nucleophiles to give poly(ureas), poly(acyl ureas), poly(formamidines) and poly-(guanidines) by addition across the N=C=N group. Also, reaction of the oligomeric carbodiimides with acrylic or methacrylic acid affords linear polymers, which can be further polymerized by free-radical type processes. Also, reaction of the carbodiimide oligomers obtained from 2,4-TDI with adipic acid in DMF produces a polyureid. ... 

Using the aliphatic hexamethylene diisocyanate 10 with a phospholene oxide catalyst at 20-50 °C, the generated carbon dioxide is incorporated into the isocyanate... 

When the reaction of hexamethylenediisocyanate is conducted with a phospholene oxide catalyst in NMP, followed by reacting terminal isocyanate groups with ethanol, a polymer... 

A negative working photoresist system is obtained using a oligocarbodiimide derived from 2,4-TDI and a phospholene oxide catalyst. m-Tolylisocyanate is used as the chain stopper. To this soluble linear polycarbodiimide a photoamine is added, which generates... 

Cellular poly(carbodiimides) derived from polymeric isocyanate (PMDI) can be continuously produced using a phospholene oxide catalyst. As the component temperature is increased from 25 °C to 80 °C at a constant catalyst level, foam densities decrease with increasing component temperatures, with an expected corresponding decrease in compressive strength. The foam friability also decreases with increasing component temperature. 

I became involved in carbodiimide chemistry in my research work on isocyanates at the former Donald S. Gilmore Research Laboratories of the Upjohn Company in North Haven, CT. Carbodiimides are readily synthesized from isocyanates using a phospholene oxide catalyst. This reaction can be conducted without a solvent, and the byproduct is carbon dioxide. We used this reaction in the manufacture of a liquid version of MDI (4,4 -diisocyanatodiphenylmethane), which today is sold in huge quantities worldwide. By reacting MDI with dicarboxylic acids in a vented extruder we manufactured a family of thermoplastic polyamide elastomers, which are sold today by the Dow Chemical Company. Also, N-sulfonylcarbodiimides were synthesized for the first time in our laboratories. They are the precursors of the antidiabetic sulfonamides, such as Upjohn s Tolbutamide (Orinase). Because of the close relationship of isocyanates with carbodiimides we studied many linear and cyclic carbodiimide reactions, especially their cycloaddition reactions. 

A convenient preparation of a new class of 1-L-a-amino acid derivatives of 2-phospholene oxides (405) involves amination of ( ) l-chloro-2-phospho-lene oxides (406) with enantiomerically pure L-a-amino acid esters (407) (Figure 71). ... 

Historically, phospholanium salts have been prepared by quaternization in high yield of a selected phospholane with an alkyl halide. Although numerous methods exist for the preparation of the desired phospholanes (recently reviewed ), most of these have major drawbacks, including (1) very critical conditions, such as reaction time, dilution effects, and temperature (2) expensive and/or difficult to manipulate reagents and (3) the necessity of a multistep synthetic sequence giving overall low yields of phospholane. A general example of the latter would be the reaction of a substituted dihalophosphine with a 1,3-diene and hydrolysis to the phospholene oxide, which then can be catalytically reduced to the phospholane oxide and subsequently converted to the phospholane. ... 

Two-Step Process. A mixture composed of 100 g of 4,4 -diphenylmethane diisocyanate and 1.1 g of l-phenyl-3-methyl-l-phospholene oxide is stirred for 3 minutes at room temperature. After carbon dioxide is evolved 4.0 g of 2,4,6-tris(dimethylaminomethyl) phenol is added into the reaction mixture. The mixture generates a reaction exotherm and expands to form a foamed product. After curing at 125°C for one hour, the resultant foam is colorless and posesses low friability. 

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