Urethanes , reactions formaldehyde with

The reactions of urethanes (carbaniic esterst with formaldehyde foDmv the pattern characteristic of the related amides. Under alkaline conditions ar room Temperature ethylurethane reacts with formaldehyde solution to give methyloliirethane, melting at 53 C- . 

The nature of the aromatic substituents is apparently not critical for SSRI activity, as indicated by the structure of duloxetine (23-5), where one ring is replaced by thiophene and the other by naphthalene. The synthesis starts as above by the formation of the Mannich base (23-1) from 1-acetyl thiophene with formaldehyde and dimethyl-amine. Treatment of that intermediate with the complex from lithium aluminum hydride and the 2R,3S entantiomer of dimethylamino-l,2-diphenyl-3-methyl-butane-2-ol gives the S isomer (23-2) in high enantiomeric excess. Treatment of the aUcoxide from (23-2) and sodium hydride with 1-fluoronaphthalene leads to the displacement of halogen and thus the formation of ether (23-2). The surplus methyl group is then removed by yet another variant of the von Braun reaction that avoids the use of a base for saponifying the intermediate urethane. Thus, reaction of (23-3) with trichloroethyl formate leads to the A -demethylated chlorinated urethane (23-4). Treatment of that intermediate with zinc leads to a loss of the carbamate and the formation of the free secondary amine duloxetine (23-5) [23]. 

Toluene diisocyanale is widely used in the manufacture of urethane plastics, particularly the urethane foamed plastics. Another isocyanate, diphenylmethane 4,4 -diisocyanaie, is produced by reaction of aniline and formaldehyde, followed by reaction with phosgene hcho coo.. 

A series of compounded flame retardants, based on finally divided insoluble ammonium phosphate together with char-forming nitrogenous resins, has been developed for thermoplastics.23 These compounds are particularly useful as intumescent flame-retardant additives for polyolefins, ethylene-vinyl acetate, and urethane elastomers. The char-forming resin can be, for example, an ethyle-neurea-formaldehyde condensation polymer, a hydroxyethyl isocyanurate, or a piperazine-triazine resin. Commercial leach-resistant flame-retardant treatments for wood have also been developed based on a reaction product of phosphoric acid with urea-formaldehyde and dicyandiamide resins. 

A synthetic variant is to react firstly the polyether with a small quantity of TDI. The resultant extended polyether, containing urethane groups, participates together with urea groups in polycondensation reactions with aqueous formaldehyde. Thus a true nonaqueous dispersant is formed in situ, with an aminoplast block and a polyether block, which probably assures the efficient stabilisation of the resulting aminoplast dispersion. 

Diisocyanates are an important class of chemicals of commercial interest, which are frequently used in the manufacture of indoor materials. such as adhesives, coatings, foams and rubbers (Ulrich, 1989). In some types of particle board, the diisocyanates have replaced formaldehyde. Isocyanates are characterized by the electrophilic -N=C=0 group, which can easily react with molecules containing hydroxy groups, such as water or alcohols. On hydrolysis with water, primary amines are formed, while a reaction with alcohols leads to carbamates (urethanes). Polyurethane (PUR) products are then obtained from a polyaddition of diisocyanate and diol components. Compounds commonly used in industrial surface technology are 4,4 -diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). The diisocyanate monomers are known as respiratory sensitizers and cause irritation of eyes, skin and mucous membrane. Therefore, polyisocyanates such as HDI-biuret and HDI-isocyanurate with a monomer content <0.5 % are used for industrial applications, and isocyanate monomers will not achieve high concentrations in ambient air. Nevertheless, it is desirable to measure even trace emissions from materials in private dwellings. 

Condensation polymers are classified as polyesters, polyamides, polyurethanes, and ether polymers, based on the internal functional group being ester (-COO-), amide (-CONH-), urethane (-OCONH-), or ether (-0-). Another group of condensation polymers derived by condensation reactions with formaldehyde is described under formaldehyde resins. Polymers with special properties have been classified into three groups heat-resistant polymers, silicones and other inorganic polymer, and functional polymers. Discussions in all cases are centered on important properties and main applications of polymers. 

Curtius discovered two general reactions named after him, the first the conversion of an acid R-COOH into the amine R-NH2, or the aldehyde R-CHO and ammonia, by way of the azide R-CO-Ng and urethane and the second the conversion of an azide into an isocyanate. A long research with H. Franzen showed that hexylene aldehyde, CgH -CHO, is present in green plants and is probably a reduction product of hexoses, but formaldehyde was never found. This threw doubt on Baeyer s hypothesis (see p. 779) and this has been abandoned (see p. 728). 

Mannich reaction n. The condensation of ammonia or a primary or secondary amine with formaldehyde and a compound containing at least one hydrogen atom of pronounced activity. The active hydrogen replaced by an aminomethyl or substituted aminomethyl group. This reaction has been employed in producing mannich polyols for use in making urethane foams. 

Diaminodiphenylmethane n (DDM, methyl-enediamine, MD). A silvery, crystalline material obtained by heating formaldehyde aniline with aniline hydrochloride and aniline. It is used as a curing agent for epoxy resins and as an intermediate in making diisocyanates for urethane elastomers and foams by reaction with phosgene. Possible occupational hazards in the use of DDM are toxic hepatitis and liver damage. 

The best-known representative of the class of segmented polyether esters is the combination of polybutylene terephthalate as the hard component with polyether glycol as the soft component. The presence of polyether components causes a sensitivity to thermal-oxidative degradation in this class of materials. In non-stabilized form, these polymers cannot be processed. Their main oxidation product is formic acid. Moreover, re-formed monomers (terephthalic acid) of the polymer can collect on the surface and form a white, hard-to-remove deposit that changes the gloss level and color [512], Oxidative degradation reactions can be inhibited by primary and secondary antioxidants. Acidolysis caused by the formic acid can be controlled by adding acid acceptors that will bind either the precursor of formic acid, formaldehyde, or the acid itself. Acid amides, urethane, or urea are utilized as acid acceptors [86]. 

Some of the curing adhesives require heat, whereas others react at room temperature with the help of catalysts, and in some instances with activation by light. Again, it is an advantage to make a bond without the aid of an oven. Among the adhesives which can be processed in the cold, with proper formulation, are resorcinol formaldehyde, unsaturated polyesters, methyl methacrylate, cyanoacrylate esters, epoxies, and urethanes. The polymerization reaction is usually exothermic, so that the glue line may become somewhat warmer than the ambient... 

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