Urethane precursors

Urethanes Precursors. Polyurethanes can be produced by the reaction of oligomeric diols with diisocyanates. The properties of the polyurethanes are intimately related to the chemicals contained in the starting materials. Specifically, the molecular weight distribution of the diols and the functionality of the isocyanates affect the properties. We have found SFC useful for characterizing the building blocks of polyurethanes, namely diols and isocyanates. 

Liu, S.-Q., Pritchard, G.G., Hardman, M.J., PUone, G.J. (1994). Citrulline production and ethyl carbamate (urethane) precursor formation from arginine degradation by wine lactic acid bacteria Leuconostoc oenos and Lactobacillus buchneri. Am. J. Enol. Vitic., 45, 235-242. 

Urethane polymers are important in many fields other than home improvement and, in some of these cases, the ability to easily estimate the degree of cure can be very important. For example, in the manufacture of certain types of fuel for use in rockets, solid propellant is mixed with a urethane binder and very slowly cured in small batches. It is important for reasons of both safety and performance that the correct degree of curing is achieved. To illustrate the application of fiber optic mid-IR spectroscopy to this problem, a simulated rocket fuel mixture was obtained from an industrial partner. The material comprised a simulated propellant mixed with an uncured urethane precursor curing of this particular mixture is typically carried out batchwise at a temperature of 50°C over a period of several days. The use of a direct, in-situ probe capable of giving a clear indication of the state of cure of each batch would be of great utility. 

The polyamide copolymer of dodecanoic acid with methylenedi(cyclohexylamine) (MDCHA, PACM) was sold as continuous filament yam fiber under the tradename QIANA. As late as 1981, over 145,000 t was produced using high percentages, typically 80%, of trans, trans MDCHA isomer. The low melting raffinate coproduct left after t,t isomer separation by fractional crystallisation was phosgenated to produce a Hquid aUphatic diisocyanate marketed by Du Pont as Hylene W. Upon terrnination of their QIANA commitment, Du Pont sold the urethane intermediate product rights to Mobay, who now markets the 20% trans, trans—50% cis, trans—30% cis, cis diisocyanate isomer mixture as Desmodur W. In addition to its use in polyamides and as an isocyanate precursor, methylenedi (cyclohexyl amine) is used directiy as an epoxy curative. The Hquid diamine mixture identified historically as PACM-20 is marketed as AMICURE PACM by Anchor Chemical for performance epoxies. 

Trimethylolpropane (TMP), the reduced crossed aldol condensation product of //-butyraldehyde and formaldehyde, competes in many of the same markets as glycerol (qv) and pentaerythritol. The largest market for TMP is as a precursor in unsaturated polyester resins, short-oil alkyds, and urethanes for surface coatings (see Alkyd resins). 

With Af-acyl or Af-sulfonyl hydrazines as nucleophiles, Zincke salts serve as sources of iminopyridinium ylides and ylide precursors.Reaction of the nicotinamide-derived Zincke salt 8 with ethyl hydrazino urethane 42 provided salt 43, while the tosyl hydrazine gave ylide 44 (Scheme 8.4.14). ° Benzoyl hydrazines have also been used in reactions with Zincke salts under similar conditions.Af-amino-1,2,3,6-tetrahydropyridine derivatives such as 47 (Scheme 8.4.15), which showed antiinflammatory activity, are also accessible via this route, with borohydride reduction of the initially formed ylide 46. ... 

Among the agricultural chemicals used for the cultivation of tobacco crops we find several amines, amides and carbamates. These include dimethyldodecylamine acetate (Penar), maleic hydra-zide-diethanolamine (MH-30), and carbaryl (Sevin) as a representative of the methyl urethanes (Figure 3 , 14), It is known that small quantities of these agents are found as residues in harvested tobacco (15). To date, only diethanolamine (DELA), the water-solubilizer for maleic hydrazide in MH-30, has been studied as a possible precursor for nitrosamines in tobacco and in tobacco smoke. In 1976, more than 1,400 metric tons of maleic hydrazide had been used on U.S. tobacco (16), most of which had been applied as the MH-30 formulation with diethanolamine (14,16). 

Functionalization of the double bond of 2-azabicyclo[2.2.2]oct-5-ene derivatives has been shown to be remarkably regjoselective. Thus, oxymercuration [112] and selenohalogenation [113] lead to adducts which are convenient precursors of iso-quinuclidin-5-one and -6-one, respectively. This means an excellent control of the polarity at the double bond termini by the nitrogen atom (Note that simple allylic urethanes also undergo regioselective oxymercuration). 

Phthalimidoglutaric acid (18), readily prepared from glutamic acid and phthalic anhydride, has served as a precursor for the preparation of several interesting condensation polymers (76MI1110l). For example, it is readily transformed (Scheme 7) into diisocyanate (19), which was utilized for the preparation of a number of optically active polyureas (by reaction with diamines), polyurethanes (by reaction with diols) and polyurea-urethanes (by reaction with amino alcohols). 

Pd(0)/phosphine complexes, or their precursors, in the presence of a suitable co-base, have also been shown to promote, in good yields (66-100%), the formation of allylic carbamates from various primary and secondary aliphatic amines, pressurized C02 and allylic chlorides, in THF, at ambient temperature [87a]. The choice of the added co-base (Base), used for generating the carbamate salt RR NC02 (BaseH)+, was found to be critical for high yields of O-allylic urethanes. The use of a guanidine (CyTMG) or amidine (DBU) base was optimal for this system (see also Section 6.3.1). ft is assumed that this chemistry passes catalytically through a mechanism similar to that illustrated in Scheme 6.19. This involves nucleophilic attack by carbamate anion on a (tt-allyl) palladium species, formed by the oxidative addition of the allylic chloride to a palladium(O) intermediate. 

In order to control the pore texture in carbon materials, blending of two kinds of carbon precursors, the one giving a relatively high carbonization yield and the other having a very low yield, was proposed and called polymer blend method [112], This idea gave certain success to prepare macroporous carbons from poly(urethane-imide) films prepared by blending poly(amide acid) and phenol-terminated polyurethane prepolymers [113]. By coupling this polymer blend method with... 

Organic isocyanates are the major building blocks of urethane structural adhesives. They can be synthesized by a variety of routes, but most of the commercially available isocyanate compounds used in adhesives are made by the reaction of a precursor primary amine or amine salt with phosgene, followed by dehy-drohalogenation. The reaction with phosgene usually is carried out at a relatively low temperature, less than 60°C, and then the temperature is raised to 100-200°C to remove the HC1. 

Methods for the capillary gas chromatographic separation of optical isomers of chiral compounds after formation of diastereoisomeric derivatives were developed. Analytical aspects of the GC-separation of diastereoisomeric esters and urethanes derived from chiral secondary alcohols, 2-, 3-, 4- and 5-hydroxy-acid esters, and the corresponding jf- and -lactones were investigated. The methods were used to follow the formation of optically active compounds during microbiological processes, such as reduction of keto-precursors and asymmetric hydrolysis of racemic acetates on a micro-scale. The enantiomeric composition of chiral aroma constituents in tropical fruits, such as passion fruit, mango and pineapple, was determined and possible pathways for their biosynthesis were formulated. 

The best known and most widely used diazoalkane is diazomethane (95 equation 39). Preparative methods for diazomethane involve, in general, the nitrosation of a methylamine derivative (93), followed by cleavage under alkaline conditions. Methylamine derivatives used have included the urethanes, ureas,carboxamides, sulfonamides, guanidines and even the methylamine adducts of unsaturated ketones and sulfones. N-nitroso-N-methyl p-toluenesulfonamide (Diazald, Aldrich) is currently the most commonly used diazomethane precursor. Diazomethane is both toxic and explosive. Although in the past it has been purified by codistillation with ether, it is now usually generated, stored and used as an ether solution without distillation. 

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