Hydrolysis isocyanate sensitivity

The sensitivity of isocyanates toward hydrolysis to give primary amines and C02 achieved sad fame with the largest chemical accident in history. In 1984 in Bhopal, India, water penetrated into or was conducted into a large tank full of methyl isocyanate. The result was a massive hydrolysis of the following type ... 

The toxicity of methyl isocyanate comes as a surprise if its high sensitivity to hydrolysis is considered. But actually, it may reach its site of action in the human body largely undecomposed. This is due to the reversible addition of another nucleophile to this heterocumulene. The tripeptide gluthathione, which is supposed to protect the body against oxidizing agents, adds to the C=N double bond of the isocyanate by means of its thiol group whereby the thio-carbamate is formed. When the latter decomposes in a reversal to its formation reaction, it releases the intact toxic methyl isocyanate. 

All these substances are very sensitive to hydrolysis (89). Functionalization at the nitrogen also takes place in the reaction of the silver salt with CISO2NCO. The sulfonyl isocyanate obtained does not show typical isocyanate reactions. It solvolyzes with H20 or CH3OH without forming intermediates to (CF3SC)4NH. However, with moist air partial hydrolysis leads to the corresponding sulfonamide according to Eq. (8). A number of acyl derivatives were synthesized via Eq. (9). The oxalyl... 

The isocyanates (9) were transformed into amino derivatives by standard reactions. Acid-sensitive aminocyclopropanes were obtained preferentially from benzyr ) -naphthyl or trifluorethyl-urethanes which were cleaved by hydrogen, EtSNa/DMF or alkaline hydrolysis. The hydrazinolysis of phthalimido compounds obtained from the urethane and phthalic anhydride also was useful Trimethylsilylethanol proved to be advantageous for the isocyanate-amine conversion the resulting urethanes gave amines upon addition of Bu4N p- 161 (e.g. synthesis of amine (21) from truns-crysanthemic acid via isocyanate (20) S equation 3). Contrarily to... 

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. 

Dimethoxy carbene has been shown to behave as a carbonyl 1,1-dipole equivalent in [ 1 -E 4] cycloadditions with vinyl isocyanates also yielding functionalized adducts. However, the oxadiazole precursor requires higher thermolysis temperatures and hydrolysis of the acetals in the resultant adducts can be difficult for acid-sensitive systems. 

Coupling Processes. The coupling can be carried out as in Equation 1 by preparing a sulfonylisocyanate by treating the sulfonamide with phosgene in the presence of butyl isocyanate (BuNCO) in xylene at reflux. Frequently 1,4-diazabicyclooctane (DABCO) aids in catalyzing this reaction. The sulfonyl isocyanate which is usually an oil can be added to a solution or sus nsion of the aminoheterocycle in a solvent such as methylene chloride or acetonitrile. The desired sulfonylurea usually precipitates as a white crystalline solid. Dry conditions are essential to avoid hydrolysis of the extremely water sensitive isocyanate. 

The organotin isocyanates are very sensitive to hydrolysis, and many partially hydrolysed isocyanates such as (C6Hs)4Sn2(NCO)2(OH)2 and (C4H9)sSn4(NCO)4C)2 have been isolated. 

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