Additions phosgene formation

The reaction of phosgene with hydrogen fluoride offers a potentially attractive route to the synthesis of carbonyl difluoride. However, the hydrogen chloride co-product of the reaction, represented in Equation (13.4) has a boiling temperature (-83.1 C) very close to that of COFj (-84.6 "C). In addition, azeotrope formation occurs, so that the two materials are only separated with great difficulty using normal distillation techniques. Separation of the two materials may be affected using aliphatic nitriles (such as ethanenitrile) or aromatic hydrocarbons (such as toluene) in which HCl is more readily absorbed relative to COF j [629,630]. Alternatively, the separation may be affected by adsorption of the HCl onto a metal fluoride, SO 3 or PjOj, which do not react at all readily with the COFj [2069]. 

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. 

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]. 

Phosgene addition is continued until all the phenoHc groups are converted to carbonate functionahties. Some hydrolysis of phosgene to sodium carbonate occurs incidentally. When the reaction is complete, the methylene chloride solution of polymer is washed first with acid to remove residual base and amine, then with water. To complete the process, the aqueous sodium chloride stream can be reclaimed in a chlor-alkah plant, ultimately regenerating phosgene. Many variations of this polycarbonate process have been patented, including use of many different types of catalysts, continuous or semicontinuous processes, methods which rely on formation of bischloroformate oligomers followed by polycondensation, etc. 

In the formation of tert-butyl azidoformate by the addition of phosgene to alcohols followed by the addition of Na nitride or hydrazoic acid in the presence of pyridine, reaction of phosgene with the azide can cause the formation of expl carbazide (Ref 9)... 

The mechanism of the condensation in Part D probably involves thioformylation of the metallated isocyanoacetate followed by intramolecular 1,1-addition of the tautomeric enethiol to the isonitrile. This thi2izole synthesis is analogous to the formation of oxazoles from acylation of metallated isonitriles with acid chlorides or anhydrides. " Interestingly, ethyl formate does not react with isocyanoacetate under the conditions of this procedure. Ethyl and methyl isocyanoacetate have been prepared in a similar manner by dehydration of the corresponding N-formylglycine esters with phosgene and trichloromethyl chloroformate, respectively. The phosphoryl chloride method described here was provided to the submitters by Professor U. Schollkopf and is based on the procedure of Bohme and Fuchs. The preparation of O-ethyl thioformate in Part C was developed from a report by Ohno, Koi/.uma, and Tsuchihaski. " ... 

The authors identified the epoxide CH3Cl-COC-CH3Cl that they attributed to the addition of carbonyl oxide (1) to the olefin, which has not been clearly demonstrated [31, 32]. The epoxide formation has also been observed in the case of the ozonization of tetrachloroethylene [33-35] which yielded tri-chloroacetyl chloride (CCl3-CO-Cl) and phosgene (C12C=0) (Scheme 7) and in the case of a highly hindered olefin like compound (Scheme 8). 

Syntheses of C-3 and C-10 modified 14-OH-taxoids bearing 1,14-carbonate were carried out starting from 7-TES-143-OH-DAB-1,14-carbonate (89), which was prepared by reaction of 143-OH-DAB (75) with TES-C1 in pyridine/DMF followed by carbonate formation with phosgene in 64% yield for the two steps (Scheme 18).43 The C-10 modifications were introduced by treating baccatin 89 with LiHMDS at -40 °C, followed by the addition of the appropriate electrophiles, which gave baccatins 90a-g in good to excellent yields (Scheme 18).43... 

Addition of DBU to a solution of 149 in THF induced an elimination reaction accompanied by loss of a molecule of CO2 and provided the unstable amine 150, which was converted in situ into isocyanate 151 by reaction with phosgene and triethylamine. After filtration to remove hydrochloride salts, the solution of 151 was treated with samarium (II) iodide in the presence of lithium chloride. These conditions, which had been previously determined to be optimal for spirooxindole generation on a model system, provided compound 152 as an inseparable 7 1 mixture of diastereoisomers [43]. The major component of this mixture was determined by NOE analysis to have the required configuration, which is consistent with bond formation from the less hindered, convex face of 151 (Scheme 35). 

The chloroformyl radical C1CO is less stable than FCO but nonetheless is of atmospheric significance due to its ability to participate in the oxidation of CO to C02. The first step of this process is the formation of Cl CO either by the addition (equation 81) of chlorine to carbon monoxide or by photolysis of phosgene (equation 82). 

Isatoic anhydride has been prepared by prolonged refluxing of a mixture of anthranilic acid and ethyl chlorocarbonate,2 a reaction usually accompanied by formation of considerable monoethyl or/and diethyl isatoate or by action of phosgene upon anthranilic acid in a solution the acidity of which is moderated by occasional addition of sodium carbonate.2 The method described is based upon a patented procedure 3 in which, under conditions not fully specified, phosgene is passed into a solution of anthranilic acid hydrochloride with no subsequent adjustment of the acidity. 

Unfortunately, in the design of Figure 112, the chloroform is also in contact with water. This amplifies the formation of hydrochloric acid as water reacts with phosgene to yield additional HCl ... 

Mixing of ethereal solutions of phosgene and 4-(4 -nitrobenzyl)pyridine results in the formation of a precipitate (3.1), which gives a violet product (3.2) on addition of an alkali [1202] ... 

The addition of a small quantity of thymol (10 p.p.m.) to crude CHCI3, exposed to air and mild steel for a week, prevented the production of phosgene by inhibiting the formation of the precursor peroxides [ICI53]. 

Chloroethane is decomposed on exposure to a flame to produce some phosgene [1527]. The decomposition of tetrachloroethene (commonly known as "Per") on a steel hot plate (>300 C), in the presence of air, resulted in the formation of a small quantity of phosgene, and the addition of water (0.1%) was noted to enhance the decomposition to COCl [ICI54],... 

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