Chloroform in the presence of ari and sunlight oxidises slowly to form a highly poisounous compound called phosgene or carbonyl chloride.
`underset("Chloroform")(2HCl_(3)) + underset(Air)(O_(2)) overset(hv)(rarr) underset("Phosgene")(2COCl_(2)) + 2HCl`
To avoid the oxidation or chlorofom it is kept in dark or yellow coloured bottles and filled up to the brim.
