Chlorinating efficiency phosgene

Chlorination of methyl 2,3(l >4//)-quinoxalinedion-5-ylcarboxylate was efficiently achieved by reaction with phosgene in DMF at room temperature in 90% yield <1999JHC1271>. Other procedures using phosphoryl chloride alone or with phosphoms pentachloride or A, A -dimethylaniline decrease remarkably the yields of dichloroquinoxaline. 

A thorough work on the photocatalytic oxidation of TCE was performed by Nimlos et al. (1993), who identified, apart from CO2 and HCl, also CI2, dichloroacetyl chloride (DCAC (CHCI2COCI)), CO, and phosgene (COCI2), known to be much more toxic than TCE. The high quantum efficiency observed in this case (50-80%) was attributed to a chain reaction initiated by the formation of chlorine atoms, similar to the scheme proposed for the... 

Both reagents have proved to be useful substitutes for phosgene in all its main applications. Indeed, they are sold commercially as the efficient equivalents of 2 and 3 phosgene molecules respectively in processes yielding chloro-formates, carbonates, carbamates, ureas and isocyanates, as well as in chlorinations, carboxylations and dehydrations (For a recent review of Triphosgene use in organic synthesis, see Ref. 33). 

Chloroform is also prepared by chlorination of methane but also by treatment of ethanol with bleaching powder. Because of its tendency to decompose, chloroform contains phosgene, hydrogen chloride, and chlorine as well as other chlorination products of methane it is usually stabilized by addition of 0.5-1.0% of ethanol. The impurities formed by decomposition are removed by washing with water or dilute potassium hydroxide solution. Further purification, which is usually superfluous, can be effected as for methylene dichloride. The same drying agents as in that case may be used of these, calcium chloride and phosphoric oxide are most efficient in removing also the ethanol. 

Phosgene was extensively used as a war-gas, either in shells, or in drums, which were hurled by projectors and exploded when they struck the earth. A mixture of phosgene and liquid chlorine was allowed to escape from cylinders when a cloud attack was made. Phosgene and mustard gas (393) were the most efficient gases used during the recent war. A concentration of 0.3 milligram of phosgene in 1 liter of air is toxic to animals. 

Rapid boiling causes cooling, which tends to decrease the rate of boiling to the point where bumping can be very bad. The external application of sufficient heat by means of an infrared lamp is very effective in overcoming the trouble and in maintaining steady ebulhtion. About one-half of the volume of the liquid in the reaction tube is slowly pumped away in order to remove dissolved phosgene and chlorine. All of the liquid is not pumped away, as otherwise solid chlorocarbons will deposit. The tube is removed to an efficient dry-box, opened, and the product filtered and washed with carbon tetrachloride. None of the chlorides reported appear to be appreciably soluble in carbon tetrachloride. ... 

The following section highlights some selected recent applications of the use of phosgene equivalents in the preparation of Vilsmeier-type chlorinated derivatives of amides and ureas. Thionyl chloride, carbonyl bromides, phosphorus oxychloride, phosgene, triphosgene, oxalyl chloride, and p-toluenesulfonyl chloride are all efficient oxophilic promoters capable of generating Vilsmeier-type chloro imi-nium ion intermediate 1770 by reaction with formamides, particularly dimethyl-formaraide, and ureas. 

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