Commercial production phosgene

In the multistep production of IPDI, isophorone is first converted to 3-cyano-3,5,5-trknethylcyclohexanone (231—235), then hydrogenated and ammoniated to 3-aminomethyl-3,5,5-trknethyl-l-aminocyclohexane (1) (236,237), also known as isophorone diamine (IPDA). In the final step IPDA is phosgenated to yield IPDI (2) (238). Commercial production of IPDI began in the United States in 1992 with the startup of Olin s 7000 t/yr plant at Lake Charles, Louisiana (239), and the startup of Hbls integrated isophorone derivatives plant in Theodore, Alabama (240). Hbls has a worldwide capacity for IPDA of 40,000 t/yr. 

Commercially, the PMDA mixtures are normally treated with phosgene to produce the corresponding isocyanates. These isocyanate mixtures, commonly called polymeric MDI (PMDI), are sold direcdy and have varied chemical compositions. The 4,4 -MDI can be separated from the PMDI products by distillation or crystallisation (31,32). The amount of 4,4 -MDI that is removed depends on marketing conditions. The residues are also viable commercial products. 

Carbon tetrachloride [56-23-5] (tetrachloromethane), CCl, at ordinary temperature and pressure is a heavy, colorless Hquid with a characteristic nonirritant odor it is nonflammable. Carbon tetrachloride contains 92 wt % chlorine. When in contact with a flame or very hot surface, the vapor decomposes to give toxic products, such as phosgene. It is the most toxic of the chloromethanes and the most unstable upon thermal oxidation. The commercial product frequendy contains added stabilizers. Carbon tetrachloride is miscible with many common organic Hquids and is a powerhil solvent for asphalt, benzyl resin (polymerized benzyl chloride), bitumens, chlorinated mbber, ethylceUulose, fats, gums, rosin, and waxes. 

The above processes are only selected examples of a vast number of process options. In the case of carbonylation, the formation of by-products, primarily isocyanate oligomers, allophanates, and carbodiimides, is difficult to control and is found to greatly reduce the yield of the desired isocyanate. Thus a number of nonphosgene processes have been extensively evaluated in pilot-plant operations, but none have been scaled up to commercial production of diisocyanates primarily due to process economics with respect to the existing amine—phosgene route. Key factors preventing large-scale commercialization include the overall reaction rates and the problems associated with catalyst recovery and recycle. 

Quantitative analytical procedures for the determination of phosgene are necessary for hygienic and environmental purposes, in addition to those methods required for its commercial production and use. The required analytical range of concentrations may thus vary from the p.p.t. level to virtually 100%. In particular, the 1995 UK low exposure limit value for... 

Specifications for the analysis of phosgene will depend upon the end-use application, but a typical analysis of the liquid commercial product may be as given in Table 4.4 [ICI69,ICI78]. Military specifications for use in munitions (COClj, >98% free Cl, <1% acid (HCl), <0.5% residue, <0.5%) also exist [1394a], and the analysis of phosgene for isocyanate manufacture (for polyurethane production) has been described in detail [4S8a]. 

In a surprising reaction, A/,A/ -diphenylmethylene diamine (a possible intermediate formed in the commercial production of TDI, see Section 4.7.1.1) reacts with phosgene by cleavage of a carbon-nitrogen bond to give a mixture of products [2086] ... 

BENZENE HEXACHLORIDE, y (gamma) isomer or y-BENZENE HEXACHLORIDE (58-89-9) C H Cls Noncombustible however, the commercial product may be dissolved in a flammable solvent. The flash point will depend on the solvent used. If this material comes in contact with oxidizers, fire and explosions may result. Contact with alkalis, strong bases, amines, amides, and inorganic hydroxides may cause the formation of hydrogen chloride gas. Incompatible with alkali metals ozone, powdered metals such as aluminum, iron, potassium, sodium, zinc. Conosive to metals. Combustion caused the formation of toxic fumes of chlorine, hydrogen chloride, and phosgene. On small fires, use dry chemical power (such as Purple-K-Powder), water spray, foam or CO2 extinguishers. 

Despite the apparent simplicity of the chemistry, the commercial production of phosgene is carried out by a relatively small number of large chemical companies that have developed the know-how to handle the toxic and corrosive phosgene product. Because of its extreme toxicity, most production is captive for immediate use in downstream processes. There is no on-site storage of phosgene, and the phosgene inventory in downstream processes is minimized. 

Triphenylphosphine oxide from the commercial production of vitamin A by a Wittig reaction is recycled by reaction with phosgene to give the phosphine dichloride and reduction of the dichloride to triphenylphosphine with elemental phosphorus (461. Polymeric phosphine oxides have been converted to phosphine dichlorides with oxalyl chloride and then reduced to phosphine with diisobutylaluminum hydride (471. 

Note 1. Commercial chloroform is stabilized with ethanol to suppress light-induced decomposition to toxic phosgene. Such stabilizer is detrimental to imprinting because of its good hydrogen bonding properties. Ethanol-free chloroform can be obtained by fractional distillation from the commercial product. For the same reason, before use the chloroform must be dried on 4.5 A molecular traps to eliminate any trace of water. 

Following the Armistice came disruption in transportation, shortages of resources (especially coal), the cancellation of contracts, and sharp reductions in chemical production. However, industrial capacity remained intact. Clearly, it was in Germany s interest to convert wartime facilities to peacetime production as quickly as possible. The chemical industry continued to enjoy its new-found independence from overseas nitrates. Moreover, many of its wartime products found peacetime uses - for example, phosgene, picric acid, and arsenic compounds were in demand as intermediates in the production of dyes, pharmaceuticals, and other commercial products. Almost immediately, this raised a question whether the Allies could deal with the contingencies of an industry whose technology was manifestly both military and civilian. 

With a few exceptions, interfacial polycondensation has remained a laboratory method for the synthesis of polymers, since diacyl chlorides are too expensive for commercial production. The exceptions include the polycondensation of bisphenols with phosgene (see Section 26.5.1) and the synthesis of aromatic polyamides, from m-phenylene diamine, isophthaloyl chloride, and terephthaloyl chloride (Section 28.2.4). The method is also used to give wool a fluff-free finish by producing a polycondensate from sebacoyl chloride and hexamethylene diamine on the wool fiber. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

Brominated C rbon te Oligomers. There are two commercial brominated carbonate oligomer (BrCO) products. Both are prepared from tetrabromobisphenol A and phosgene. One has phenoxy end caps [28906-13-0] and the other trihromophenoxy [71342-77-3] end caps. These are used primarily in PBT and polycarbonate/acrylonittile—butadiene—styrene (PC/ABS) blends. 

Attempts have been made to develop methods for the production of aromatic isocyanates without the use of phosgene. None of these processes is currently in commercial use. Processes based on the reaction of carbon monoxide with aromatic nitro compounds have been examined extensively (23,27,76). The reductive carbonylation of 2,4-dinitrotoluene [121 -14-2] to toluene 2,4-diaLkylcarbamates is reported to occur in high yield at reaction temperatures of 140—180°C under 6900 kPa (1000 psi) of carbon monoxide. The resultant carbamate product distribution is noted to be a strong function of the alcohol used. Mitsui-Toatsu and Arco have disclosed a two-step reductive carbonylation process based on a cost effective selenium catalyst (22,23). 

Specialty Isocyanates. Acyl isocyanates, extensively used in synthetic appHcations, caimot be direcdy synthesized from amides and phosgene. Reactions of acid haUdes with cyanates have been suggested. However, the dominant commercial process utilizes the reaction of carboxamides with oxalyl chloride [79-37-8]. CycHc intermediates have been observed in these reactions which generally give a high yield of the desired products (86). 

Commercially important arenesulfonyl isocyanates are not directly accessible from the corresponding sulfonamides via phosgenation due to lack of reactivity or by-product formation at elevated temperatures. A convenient method for their preparation consists of the reaction of alkyl isocyanates with sulfonamides to produce mixed ureas which, upon phosgenation, yield a mixture of alkyl and arenesulfonyl isocyanates. The desired product can be obtained by simple distillation (16). Optionally, the oxalyl chloride route has been employed for the synthesis of arenesulfonyl isocyanate (87). 

Polycarbonates are prepared commercially by two processes Schotten-Baumaim reaction of phosgene (qv) and an aromatic diol in an amine-cataly2ed interfacial condensation reaction or via base-cataly2ed transesterification of a bisphenol with a monomeric carbonate. Important products are also based on polycarbonate in blends with other materials, copolymers, branched resins, flame-retardant compositions, foams (qv), and other materials (see Flame retardants). Polycarbonate is produced globally by several companies. Total manufacture is over 1 million tons aimuaHy. Polycarbonate is also the object of academic research studies, owing to its widespread utiUty and unusual properties. Interest in polycarbonates has steadily increased since 1984. Over 4500 pubflcations and over 9000 patents have appeared on polycarbonate. Japan has issued 5654 polycarbonate patents since 1984 Europe, 1348 United States, 777 Germany, 623 France, 30 and other countries, 231. 

The historical direct reaction route, which utilised phosgenation of a solution of BPA in pyridine, proved inefficient commercially because of the need for massive pyridine recycle. Calcium hydroxide was used as an HCl scavenger for a period of time. In the historical transesterification process, BPA and diphenyl carbonate are heated in the melt in the presence of a catalyst, driving off by-product phenol, which is recycled to diphenyl carbonate. Using a series of reactors providing higher heat and vacuum, the product polymer was eventually produced as a neat melt. 

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