Phosgene-free process

An analogue of the transesterification process has also been demonstrated, in which the diacetate of BPA is transesterified with dimethyl carbonate, producing polycarbonate and methyl acetate (33). Removal of the methyl acetate from the equihbrium drives the reaction to completion. Methanol carbonylation, transesterification using phenol to diphenyl carbonate, and polymerization using BPA is commercially viable. The GE plant is the first to produce polycarbonate via a solventiess and phosgene-free process. 

This method of transesterification is of high technical interest. Particularly the reaction of bisphenol A with diphenyl carbonate is a preferred phosgene-free process because biphenyl carbonate can be obtained directly from phenol and dimethyl carbonate.The latter is an industrial product made from CO and methanol. 

Scheme 5.3 BASF Phosgene-free process for I DPI manufacture.

Daicel Chemical Industries in Japan patented a promising phosgene-free process involving the reaction of an aliphatic diamine with dimethyl carbonate (DMC) to produce carbamate esters, which are then thermally converted to the corresponding aliphatic diisocyanates [38] (Scheme 5.4). It is noteworthy that this process could be a total phosgene-free process since the reactant, DMC, can be made directly from methanol and carbon dioxide (or urea) and eliminates the use of phosgene [39]. 

Union Carbide also patented a phosgene-free process for making hexamethylene diisocyanates [40] (Scheme5.5). In this later process, 1,6-hexanediamine was reacted with dry-ice, trimethylchlorosilane, and trichlorophenylsilane to form a halosilyl carbamate intermediate and then converted to the corresponding diisocyanate. However, it should be noted that trichlorophenylsilane used in this process is on the EPA s Extremely Hazardous Chemicals List (40 CFR Part 355, Appendix A). 

In 1980, Akzo also developed a new phosgene-free process to make trons-1,4-diisocyanatocyclohexane directly from 1,4-cyclohexanedicarboxylic acid (or its ester)... 

Hunter, D. and Rotman, D. (1994) Hills plans diisocyanate unit based on new phosgene-free process. Chem. Week,... 

Zengel, H.G. (1980) A new phosgene free process for trans-cyclohexane-1,... 

Quite recently, novel cyclization reactions involving CO to give carbocydic and heterocyclic compounds, which are characteristic for mthenium catalysts, have been developed. Ruthenium complexes provide new avenues for cydization reactions. In addition, CO is often used as a reducing agent, and reductive carbonylations of nitro compounds catalyzed by mthenium complexes are very attractive reactions that provide phosgene-free processes [3]. 

Daicel Phosgene-Free Process to Produce Diisocyanates Via... 

Alternative Phosgene-Free Process to Methyl Isocyanate... 

Carbonylation of alcohol group, methanol to dimethyl carbonate (DMC) and dimethyl oxalate (DMO), phenol to diphenyl carbonate (DPC), is very important chemical process in the current chemical industry. Dialkoxyl carbonate is key material for phosgene free process. The electrocarbonylation has great advantages to compare with a conventional catalytic carbonylation with O2. A particular advantage of electrocarbonylation is to be able to suppress CO2 formation by oxidation of CO because oxidizing power can be controlled as finely as one millivolt and there is no oxygen. 

Many examples of phosgene-free processes, mainly concerning the carbonylation of aryl nitro derivatives, have been claimed. Some of the most representative, cited in part in the Kirk-Othmer Encyclopedia of Chemical Technology (4th ed., vol. 19), are illustrated belotv. 2,4-Dinitrotoluene undergoes reductive carbonylation with CO to form 2,4-toluene diisocyanate (TDI) in the presence of palladium catalysts [209-213]. A variation on this process involves capturing the isocyanate formed with methanol, followed by thermolysis of the bis(carbamate) 326 [212]. 

A phosgene-free process for preparing urethane and carbonate monomers and polymers has been reported [257]. The process involves reaction of CO2 with amines (e.g. 4,4 -methylenebis(cydohexylamine)), alcohols, or amino alcohols in the presence of an amidine- or guanidine-type base (e.g. N-cydohexyl-N, N, N",N"-tetra-ethylguanidine), followed by treatment of the resulting ammonium carbamate or carbonate salt with a primary or secondary hydrocarbyl halide of a specified structure in a polar, aprotic solvent (e.g. N-methylpyrroUdinone). When hydrocarbyl dihalides or -polyhalides are used in the second step, polyurethanes and polycarbonates are formed. 

Aliphatic isocyanates are produced by either phosgene-based processed or phosgene-free processes (note that the molecule named phosgene contains... 

The high toxicity of phosgene has resulted in intensive work on the development of phosgene-free processes for diisocyanate manufacture. The development has been successful for only a few aliphatic diisocyanates, but ca. 95 % of all isocyanates produced in an industrial scale are aromatic. 

---