Phosgene large scale production

For larger amounts we recommend the gas-phase pyrolysis of 4,5-dicyano-l,3-dithiol-2-one (8) [Eq. (3)], which is readily available from sodium cyanide, carbon disulfide, and phosgene [16]. Both the starting materials and most of the pyrolysis products are extremely toxic, and the price to be paid for large-scale production is hence high. 

Alternative approaches starting from ethylene carbonate (itself a phosgene equivalent), better suited to the large-scale production of oxalyl chloride, have been developed according to the scheme below [103] ... 

The first large-scale use of chlorine was for bleaching paper and cotton textiles it also is widely used as a germicide for public water supplies. Presently it is used principally in production of the chemical compounds sulfur chloride, thionyl chloride, phosgene, aluminum chloride, iron(ni) chloride, titaniura(IV) chloride, tin(IV) chloride, and potassium chlorate. 

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. 

N-Methyl-N-methoxycarbamoyl chloride made by phos-genation of methoxy methyl amine hydrochloride is a very useful intermediate for the synthesis of N-methoxy ureas herbicides. However, we found the method to be unsatisfactory for the production on a large scale, because of rather low yields and also of technical difficulties. To overcome these problems, we developed a new procedure based on the reaction of phosgene with methoxy methyl amine sulfate as depicted in scheme 124. Sulfuric acid formed is easily removed by decantation (Ref. 177). 

Among the more than 30 methods available for the preparation of isocyanates, phosgenation of primary amines or their hydrochlorides still remains the most popular. The method is employed on a large scale for the industrial production of mono and polyisocyantes. 

We end this section with a further question arising from the discussion in the previous section. Should the slow substitution of phosgene by DMC be associated only vdth the slow turnover of chemical processes No. There are various examples of faster changes of technology even in large-scale chemical productions, while in... 

Next to phenol the herbicide isoproturon is one of the few cumene derivatives with any large-scale importance. Nitration of cumene yields 2-/4-nitrocumene in the ratio 35 65. The 4-isomer is recovered by vacuum distillation and is then reduced to cumidine (4-isopropylaniline). (Cumidine can also be produced by ammonolysis of 4-isopropylphenol, which arises as a by-product during the oxidation of 1,4-diisopropylbenzene to produce hydroquinone). Cumidine is reacted with phosgene to give 4-isopropylphenyl isocyanate. Reaction of 4-isopropyl-phenyl isocyanate with dimethylamine yields isoproturon, which in Western Europe is produced in quantities of around 6,000 tpa. 

Another large-scale application of chlorine is the production of isocyanates. The standard process is the phosgenation of amines. Most plants produce the necessary phosgene on site, from chlorine and carbon monoxide ... 

Isocyano-2-methyl)-propyl-l-]-alkyl-carbonate [(2-Isocyano-2-methyl)-propyl-l-]-alkyl-carbonates (Ip) were developed by Lindhorst in collaboration with Ugi and have been referred to as the Lindhorst isocyanides [64], The synthesis of Ip and its analog are very simple (Scheme 7.44). Commercially available 4,4-dimethyl-2-oxazoline 135 can be deprotonated by "BuLi in anhydrous THF at -78° C and the resulting lithium alcoholate lo is captured with alkyl chloroformate (R = Me, Et, allyl, Bn) to provide 80% of the desired product as colorless crystals or oil (Scheme 7.44). It can be further purified by vacuum distillation. This one-step method offers several advantages (i) it does not involve phosgene or derivatives thereof, (ii) (p-isocyano-ethyl)-alkyl carbonates are stable and can be stored at room temperature, and (iii) it can be employed in a large-scale synthesis. 

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