Phospholene-1 -oxides, with isocyanates

The 2-triliuoromethyl and 2-trichloromethyl derivatives (230) were obtained in quantitative yields by treatment of a phospholene oxide with trifluoroacetyl or trichloroacetyl isocyanate, respectively, followed by addition of pyridine (Scheme 18) <77IZV927>. 

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... 

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... 

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. ... 

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... 

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. 

Aromatic isocyanates, particularly those containing electron-attracting substituents, react noticeably more easily than aliphatic isocyanates. In the former case it often suffices to leave the components for some hours at room temperature in a water-pump vacuum, whereas for aliphatic compounds boiling under reflux is usually necessary and sometimes use of a higher-boiling solvent such as decalin. The best catalysts are cyclic phosphine oxides of type (1) (phospholene oxides)862 and cyclic phosphonic diamides of type (2) (1,3,2-diazaphospholidine oxides).863 The best results were obtained with compound (1, R = C2H5) (for its preparation see Campbell et a/.862) the phenyl compound, although more readily prepared,864 is somewhat less reactive. The amounts of catalyst needed are 0.1% for (1) or 0.5% for (2). 

Polystyrenes with attached phospholene oxide rings are recoverable catalysts for converting isocyanates to carbodiimides (39). 

To address this concern uretonimine-modified isocyanates with improved low-temperature properties were prepared using 4,4 -diphenylmethane diisocyanate catalyzed with 3-methyl-l-phenyl-3-phospholene-l-oxide. The formation of uretonimine was consistently higher than uretdione formation using this catalyst. The uretonimine-modified isocyanate can be stored at temperatures substantially lower than ambient temperature while still remaining liquid. In addition it is soluble in melted 4,4 -diphenylmethane diisocyanate. 

A reactor was charged with 93.80% 4,4 -diphenylmethane diisocyanate, 6.20% 2,4 -diphenylmethane diisocyanate, and 3-methyl-1 -phenyl-3-phospholene-1 -oxide (6 ppm) as catalyst and then heated for 6 hours at 110°C. Trifluoromethanesulfonic acid (50 ppm) was then added to quench the reaction. The mixture was then cooled to 50°C and the product isolated having a 29.5% isocyanate content. 

The treatment of isocyanates with 3-methyl-l-ethyl-3-phospholene-l-oxide (71) is a useful method for the synthesis of carbodiimides748 in good yields.749 The mechanism does not simply involve the addition of one molecule of isocyanate to another, since the kinetics are first order in isocyanate and first order in catalyst. The following mechanism has been... 

The treatment of isocyanates with 3-methyl-l-ethyl-3-phospholene-l-oxide... 

An efficient method for preparation of aromatic and aliphatic carbodiimides involves the reaction of an Isocyanate with 3-methyl-1-phenyl-S-phospholene-1-oxide, the most readily prepared catalyst of Us type. ... 

The reaction is usually carried out at high temperatures (of about 200°C) in a polar solvent, such as tetramethylene sulfone, and the polyamide formation can be accelerated by the addition of l-phenyl-3-methyl-2-phospholene 1-oxide as catalyst. However, in the case of a two-step process, the reaction time of the first step must be carefully controlled, since the catalyst can also play a role in the formation of carbodiimides from two terminal isocyanate groups [36], These carbodiimides can then further react and lead to crosslinking [36], In most cases [34-39], the polymers are prepared with 4,4 -methylene bis(phenyl-isocyanate) (MDI), using adipic acid, isophtahc acid, azelaic acid, or a mixture of two of them (in order to accelerate the solubilization of the polyamide phase in the solvent) and a polyether based on tetramethylene oxide, ethylene oxide, or a mixture of propylene oxide and ethylene oxide. 

Isocyanates have been shown to undergo a high jdeld reaction with carboxylic acids to afford amides. Polymerization of aromatic diisocyanates with aromatic dicarboxylic acids was carried out in the presence of 3-methyl-l-phenyl-2-phospholene 2-oxide to afford aramids (7). The polymerization was carried out in sulfolane at 200 C. Polymers with inherent viscosities of up to 1.8 dL/g were obtained. 

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