Relative molecular mass phosgene

Under standard conditions, phosgene is a colourless gas with a density of approximately 3.5 times that of air, in which it is non-flammable. It is easily condensed to a colourless liquid when pure, and in the cylinder it is present as the liquified gas, exerting a vapour pressure of about 157 kPa (1.55 atm) at 20 C. Its relative molecular mass is 98.9158. 

At room temperature and atmospheric pressure, carbonyl difluoride is a colourless gas which is condensable to give a colourless liquid (boiling at -84.6 C at normal atmospheric pressure [1580]) or a white solid (melting at -111.3 C [1580]). It has a pungent odour and, unlike phosgene, is rapidly hydrolysed even in ambient air. The relative molecular mass of COFj is 66.0072, and the density of the gas is estimated to be 2.744 g dm 3 [1764]. The gas is heavier than air, with a specific gravity of 2.34 at 21 C and atmospheric pressure... 

Carbonyl dibromide is a dense, colourless, mobile liquid, fuming in moist air due to hydrolysis, with an odour similar to that of phosgene [2126]. Its relative molecular mass is 187.8184. It is much less stable to dissociation than phosgene even distillation at atmospheric pressure results In a slight yellow colouration due to liberated bromine. 

Only a few of the physical properties of COBrF have been measured. Carbonyl bromide fluoride (relative molecular mass 126.91) is a colourless gas, with an odour similar to, but distinguishable from, phosgene [1195]. The melting point at atmospheric pressure of COBrF has been reported as -120 2 C [1196a], and the boiling point as -20.6 "C [1196a]. Its critical temperature occurs at +124 C, and its critical pressure is ca. 6.18 MPa [656a,1751]. 

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