Preparation of Urethanes

Aryl isocyanates such as those used in the preparation of these derivatives are toxic. Take normal precautions in handling them. If cyanates contact the skin, wash the affected area with soap and warm water. 

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Place 1 g of the anhydrous alcohol or phenol in a round-bottom flask, and add 0.5 mb of phenyl isocyanate or a-naphthyl isocyanate be sure to recap the bottle of isocyanate tightly to minimize exposure of the reagent to atmospheric moisture. If you are preparing the derivative of a phenol, also add 2 or 3 drops of dry pyridine as a catalyst. Affix a drying tube to the flask and warm the reaction mixture 

Flush any filtrates that contain the starting isocyanate down the drain. Pour the filtrates from the recrystallization of the product into the container for nonhalo-genated organic liquids. Put the dessicant used in the drying tube in the container for nonhazardous solids. 

The reaction between 3,5-dinitrobenzoyl chloride and an alcohol gives the corresponding ester (Eq. 25.43). This method is useful for primary, secondary, and tertiary alcohols, especially those that are water-soluble and thus are likely to contain traces of water. 

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Use of PEG-phenylcarbonate derivatives for preparation of urethane-linked PEG-proteins was reported (75). The main drawback of this approach lies in the toxicity of hydrophobic phenol residues (p-nitrophenol or 2,4,5-trichlorophenol) and their affinity to proteins. 

In 1849, Wurtz discovered the formation of aliphatic isocyanates when he reacted organic sulfates with cyanates. This represents the first recorded experimental work leading ultimately to the preparation of urethanes ... 

The first application of pyrazino[2,3-6]pyrazines as vulcanization accelerators for rubber copolymerization has been reported in CHEC-I. Some new pyrazino[2,3-A]pyrazine derivatives are in use as electrophotographic developers <90JAP(K)2135365) and light-resistant fluorescent polymers <89JAP(K)0l 153750). Some alkylsubstituted decahydropyrazino[2,3-6]pyrazines are suitable as delayed-action catalysts for the preparation of urethanes <83USP452839l>. Other pyrazinopyrazine derivatives are reported to have inhibitory effects on tomato spotted wilt virus <83MI 719-01). 

Preparation. Polyurethane foams (often referred to as urethane foams) are prepared by the reaction of a polyisocyanate with a polyol in the presence of a blowing agent, a surfactant, and a catalyst without external heating of the foaming system. The principle of preparation of urethane foams is based on the simultaneous occurrence of two reactions, i.e., polyurethane formation and gas generation in the presence of catalyst and surfactant, as shown below ... 

The preparation of urethanes from primary aliphatic and aromatic amines by oxidative carbonylation has been described in which - instead of Pd salts or complexes - lanthanide compounds, particularly of cerium, and promoters comprising alkali metal salts or quaternary ammonium salts, are used [133]. 

Hipchen [32a] also outlined the preparation of urethane-modified isocyanurate foams and gave the following recipe for one giving 19.6% isocyanurate groups ... 

Frisch KC, Reegen SL, Floutz WV, Olivier JP (1967) Complex formation between catalysts, alcohols, and isocyanates in the preparation of urethanes. Journal of Applied Polymer Science Part A Polymer Chemistry 5 35 2. 

The preparation of urethanes is discussed in Section 25.11D. Although either a phenyl- or naphthyl-substituted urethane could be prepared, the majority of the derivatives reported are the a-naphthylurethanes, and they are generally the urethanes of choice. 

While the isocyanates 17 formed by such reactions can be isolated in a pure state, their inherent reactivity means that it is often more convenient to trap them with an appropriate reaction in situ. The addition of either an alcohol or an amine to the reaction mixture facilitates the preparation of urethanes 18 or ureas 19, respectively (eq 16). ... 

In special cases only one method is available, namely in those cases in which the higher selectivity of the Outside-in method is required. For instance, in the case of a triol the Inside-out method will result in a gel, whereas such a three-functional urethane acrylate can be made by the Outside-in method. An extreme example is that the Outside-in technology makes it possible to use hydroxy-functional acrylics (polymers with at least ten OH groups per chain) as the polymers in the preparation of urethane acrylates. 

Preparation of Urethans. Urethans are prepared by refluxii azides in absolute alcohols. When the azide is originally prepared in ethereal solution, the solution is dried, a large excess of absolute alcohol is added, and most of the ether is removed, by distillation. The urethans are isolated by evaporation or distillation of the excess solvent. Urethans from higher alcohols, such as benzyl alcohol and cholesterol, are usually prejared from a small excess of the alcohol in toluene or xylene. 

Full details on the preparation of urethane derivatives of 3,4-di-O-benzyl-l,2,5,6-tetradeoxy-l,2 5,6-diimino-L-iditol from D-mannitol as well as the 3,4-dideoxy-L- Areo compounds 24 (R = C02 Bu or COiBn), from a hex-3-enitol, have been reported. (See Vol. 28, p. 230, ref. 66 for an earlier report). In both cases l,6-diamino-l,6-dideoxy-2,5-anhydroalditols were minor by-products. V-Boc-L-/V/o-l,2 5,6-bis-aziridino derivatives have proved to be versatile intermediates for the preparation of imino-alditols. For example, treatment of the 3,4-di-O-benzyl compound with diethylaluminium cyanide affords a 1 2 mixture of pyrrolidine 25 piperidine 26, and with dilithium tetrabromonickelate (Li2NiBr4) gives bromo-derivative 27 from which displacement of bromide allows further functionalization. ... 

The use of azides of carboxylic acids for the preparation of urethanes has practically the same advantages and disadvantages as the use of isocyanates. m-Nitrobenzazide is used mostly, liberating nitrogen on heating at 100 (toluene, xylene, and ligroin are used as solvents), forming m-nitrophenylisocyanate as an intermediary product, which reacts immediately with alcohols, with the formation of urethanes ... 

Esters of Carbamic Acids — Urethanes General Procedure for the Preparation of Urethanes... 

V. Preparation of Urethane Elastomer by Amine Extension of Prepolymer... 

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