1.2- Diurethans

For environmental reasons there has been interest in methods for manufacturing isocyanates without the use of phosgene. One approach has been to produee diurethanes from diamines and then to thermal eleave the diurethanes into diisocyanates and alcohols. Although this method has been used for the production of aliphatic diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate, for economic reasons it has not been adopted for the major aromatic isocyanates MDI and TDI. 

Condensation of methyl urethane, H2NC06CH3j with CH20 gives rise to the methylene diurethane (III) and this compd, under different specific conditions of refluxing, resulta in the various specific linear (IV V) and cyclic products (I II) as shown. The observations of relevance here are that the various products, both linear and cyclic, are interconvertible under acid catalysis including / into IF and conversely. The... 

A novel chemoenzymatic route to polyester polyurethanes was developed without employing highly toxic isocyanate intermediates. First, diurethane diols were prepared from cyclic carbonates and primary diamines, which were subsequently polymerized with dicarboxylic acids and glycols by using lipase CA as catalyst, yielding the polyurethanes under mild reaction conditions. 

It was found that whereas 2-fuiyl isocyanate 29 and its difunctional 2,5-homologue 30 are unstable and resinify on standing at room temperature even if kept under nitrogen, the corresponding urethanes formed with aliphatic and furanic alcohols are stable. In more general terms, both the kinetics and the mechanism of the formation of furanic urethanes and diurethanes could be rationalized on the basis of established criteria combined with the specific effects of the furan moiety (35). All the products were M y characterized and... 

Ethylenebisurethone-1-Azide Ethylene (l,2-diurethane)[Pg.107]

Ethylenediamine-N,N Dinitro-Glycolicdi-urethane Dinitrate or N N -Dinitro-H -bis-(2-nitratoethoxycarbonyl)-ethylenediamine (CA). (Called Dinitrate de diurethane glycolique de 1 ethylene-dinitramine, in French), CH3.N(N02).C00.CH2.CH2.N03... 

In order to shorten the reaction time, various heavy metal salts (zinc, lead, and manganese acetates) of weak organic acids, zinc or cobalt and tin chlorides are added to the reaction mixture [11]. For example, refluxing an uncatalyzed mixture of 3 moles of isobutyl alcohol and urea for 150 hr at 108°-126°C gives a 49% yield of the carbamate. Adding lead acetate or cobalt chloride to the same reaction lowers the reaction time to 75 hr, at which point an 88-92 % yield is obtained. In another example, ethylene glycol (1 mole) and urea (2 moles) are heated for 3 hr at 135°-155°C with Mn(OAc)2 to give a 78% yield of the diurethane [11]. The commercial production of butyl carbamate uses catalytic quantities of cupric acetate [12]. 

Bisglycidylacrylate, ethoxylated bisphenol A dimethacrylate, diurethane dimethacrylate, triethyleneglycol dimethacrylate, tricycle[5.2.1.02,6]decanedimethanol diacrylate, camphorquinone, ethyl 4-(/V,/V-dimcthylamino)benzoate, diphenyl iodonium hexafluorophosphate, 2,6-di-t-butyl-4-methylphenol, benzotriazole... 

Dicarbethoxy-l, 4,7,10-tetrazadecane see Bis (aminoethyl)-ethane-diurethane 2 B129... 

Dinitro-3,6-dicarbethoxy-3,6-diazaoctane see 1, 2-Bis (2 -nitroxyethyl-e thane-diurethane) 2B130... 

The condensation of methyl N—phenyl carbamate witli IICHO to methylene diphenyl diurethane has been studied in a batch reactor in the presence of cation exchanged resins. Unlike conventional H0SO4 catalyst, fresh resin catalysts did not form a byproduct N—benzyl compound. However, accumulation of water from repeated uses of the catalyst caused a decreased activity and the formation of the byproduct. The deactivated catalyst could be completely regenerated by drying in vacuo. Ethylacetate and toluene were found to be efficient solvents with the resin catalysts. 

Processes are under development to manufacture methylene diphenyl diisocyanate (MDI) without using toxic and corrosive phosgene. The proposed process schemes usually consist of three steps alkoxycarbonylation of nitrobenzene or aniline with CO and an alcohol to alkyl plienylcarbamate, condensation of the carbamate, and then thermal decomposition of the resulting urethane to MDI. For example, the condensation of methyl N—phcnylcarbamate (MPC), and IICHO into methylene diphenyl diurethane (MDU) is carried out in the presence of an acid catalyst. 

Ethylenebi surethane-1-Azide Ethylene-(1,2-diurethane)-l-Azide or 1-Azidoethylene-diurethane,... 

Nitration was attempted by adding drop by drop wi th stirring, 4.08g (0.02 mol) of ethylidene diurethane into a flask (cooled in ice-HCl bath), contg 2.5g (0.04 mol) of absol... 

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