Phosgene manufacturing methods

Carbonates ate manufactured by essentially the same method as chloroformates except that more alcohol is required in addition to longer reaction times and higher temperatures. The products are neutralized, washed, and distilled. Corrosion-resistant equipment similar to that described for the manufacture of chloroformates is requited. Diaryl carbonates are prepared from phosgene and two equivalents of the sodium phenolates or with phenols and various... 

For environmental reasons there has been interest in methods for manufacturing isocyanates without the use of phosgene. One approach has been to produee diurethanes from diamines and then to thermal eleave the diurethanes into diisocyanates and alcohols. Although this method has been used for the production of aliphatic diisocyanates such as hexamethylene diisocyanate and isophorone diisocyanate, for economic reasons it has not been adopted for the major aromatic isocyanates MDI and TDI. 

A number of methods for the manufacture of polycarbonates are available but the melt process and the phosgenation process are the most important. 

The synthetic method is nowadays the most widely used for the industrial manufacture of phosgene. 

The plant for the manufacture of phosgene by the synthetic method is shown diagrammatically in Fig. 3. The carbon... 

Phosgenation of ethylene diamine type compounds is a well established method for the preparation of 2-imidazo-lidones (cyclic five membered ureas). The utility of this method is illustrated by the synthesis of a valuable intermediate (I) for D-biotine manufacture. We have developed an improved interfacial process which affords (I) in good yield and high purity as shown in scheme 213. 

The earliest methods for the manufacture of phosgene were based upon John Davy s original procedure of exposing a mixture of carbon monoxide and dichlorine to sunlight [577]. Later methods (used to a limited extent in Italy and France during World War I) involved the oxidation of tetrachloromethane or hexachloroethane with suIfur(VI) oxide or fuming sulfuric acid (see Chapter 5) [577,1778]. Alternative methods proposed for the manufacture of phosgene, but which have not been commercialized, are described in Chapter 5. 

The reaction of phosgene with cadmium sulfide is said to be a good method for the preparation of COS (see Section 9.5.7) [885], used in the manufacture of organic thio compounds, whilst reaction of COCl, with iron(III) phosphate at 300-350 C has been proposed as a synthetic method for POCI3 (see Section 9.4.5) [885]. 

A possible exception to the foregoing statement is the so-called "disproportionation" of phosgene (see Chapter 8). This process. Equation (4.15), has been proposed as an efficient method for the manufacture of tetrachloromethane, although in the present feedstock situation this process would not be economical. Indeed, at the current prices commanded for phosgene, and with the perceived availability of carbon tetrachloride, it would be more beneficial to be able to derive phosgene from CC1 , for example by oxidation or hydrolysis. 

The manufacture of any large-scale, industrially important compound is susceptible to changes in the availability of raw materials, the economic climate, legislative constraints, and the particular manufacturer s local considerations. There is little doubt, at the present time, that (under the vast majority of conditions) the synthesis of phosgene from carbon monoxide and dichlorine, catalysed by activated charcoal, constitutes the most favourable method in economic terms. 

Various processes are technically available for PC manufacture, but the one used almost exclusively at present is phase boundary interfacial polymerization [94], With this method, PC can be made very economically from phosgene and bisphenol A, and its properties profile can be varied widely. Thus, molecular weight, structural uniformity and the PC structure itself can be modified and tailored to the needs of the application and the processing method. 

A problem with liquid-liquid extraction that is often overlooked is the addition of compounds by manufacturers to prevent oxidation or decomposition of their product. For example, to prevent phosgene formation in chloroform, the solvent is often stabilized with 2% ethanol. In itself, this is no problem but when a method is to be established from the literature it may not be immediately obvious to the reader if the solvent contains ethanol (this assumes that the originating author knew the composition of the extracting solvent). The presence of ethanol can change the polarity of the solvent and affect the specificity and recovery of a method. 

WaSt6 Disposal. Because of its low boiling point and high toxicity, measures must be taken to prevent the entrance of phosgene into drains or sewers. If recycle of phosgene is not feasible, phosgene waste can be handled by one of the decomposition methods mentioned in the Manufacture section, ie, caustic scrubbing, moist activated carbon towers, or combustion. 

A characteristic example of the phosgene-based process for manufacture of polycarbonates is the synthetic method used by Dow Chemical Co. A typical variation of the process uses bisphenol A, diphenyl carbonate, phosgene, cuprous chloride, and an oxygen-containing gas. Thus, when a phenol is reacted with phosgene, a diaryl carbonate is formed, which is then reacted with a bisphenol monomer to obtain a bisphenol polycarbonate and phenol, the latter of which after separation from the polycarbonate is reacted with more phosgene, and the diaryl carbonate thus produced is cycled back into the process for reaction with the bisphenol monomer. 

Phosgene can be prepared from carbon monoxide, from halogenated hydrocarbons, from carbonaceous materials, from carbon dioxide, carbonyl sulfide or carbon disulfide, and from other oxygenated compounds [39]. The method based on the chlorination of carbon monoxide is by far the most important and has been scaled-up for the commercial manufacture of phosgene. 

Methods for the manufacture of carbonyldiimidazoles from imidazoles and phosgene in the presence of tertiary amines have recently been reported [109,110]. 

Isocyanates and polyisocyanates are manufactured on a commercial scale by the reaction of gaseous phosgene with amines or amine salt precursors [141-143]. As restrictions upon the use of very toxic materials such as phosgene and other chlorine-containing compounds within the chemical industry have become more rigorously enforced, there has been increasing interest in developing alternative methods for isocyanate production [144]. Alternative methods, such as the thermolysis of carbamates (urethanes), very often require rather drastic reaction conditions [139, 140]. 

The method of choice selected for the coupling process will depend on one of several factors. The original coupling route via the addition of the sulfonylisocyanate to the heterocyclic amine has been used for both laboratory and manufacturing scale preparations. This route provides excellent yields of high purity sulfonylurea with a minimum of by-products. It is the most direct route from basic raw materials. However, it can not be used when a substituent on the sulfonamide is sensitive to HCl or when another product, such as a cyclic dimer of the sulfonylisocyanate, is the major phosgenation product. 

There are two main methods for the manufacture of poly(2,2-bis(4 -phenyl-ene)propane carbonate), namely direct phosgenation and ester interchange. 

However, the traditional method for manufacturing DMC is from phosgene and methanol. 

Jones, Chemical Warfare Research during World War I, 176-79. The Story of the Development Division, Chemical Warfare Service, 180-82, gives a brief overview of the Development Division, which used General Electric facilities. (The report notes incorrectly that Lewisite was dubbed G-34, which was actually the code name for mustard gas. To fool the potential spies. Lewisite and related chlorarsines were new G-34, PI, and P2. Chlorpicrin was SI phosgene L3.) The CWS also began construction on another plant for Lewisite (diphenylchloroarsine) in Croyland, Peimsylvania. Crowell, America s Munitions, 399 McPherson, Report of the Director of Outside Plants, pp. 3-A, NARA, RG 175, entry 8, box 14. Harry M. St. John, Standard Methods for the Manufacture of New G-34, Development Division, Chemical Warfare Service, United States Army, Nela Park, Cleveland, Ohio, approved by F. M. Dorsey, March 29, 1919, a copy of which is held at the U S. Army Military History Institute,... 

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