in a bubbler 68 by a current of chlorine entering through 85 and ucl 3 thus passes to the state of ucl 4 the aqueous phase charged with ucl 4 leaves the bubbler through the pipe 93 and enters an extractor 66 in this extractor 66 ucl 4 passes from the 8 n hydrochloric medium into the organic phase entering 66 through the pipe 86 the organic phase charged with ucl 4 leaves the extractor 66 through 84 and supplies the exchange battery 11 the 8 n hydrochloric aqueous phase exhausted of ucl 4 leaves the extractor 66 through 76 a portion of this hydrochloric solution is directed to a distillation apparatus 70 and the remainder to which there is added through 71 water coming from the still 70 in order to bring its normality to about 3 n enters through 102 re extractor 71 wherein the 3 n hydrochloric phase encounters in counter current the organic phase loaded with ucl 4 coming through the pipe 79 from the exchange battery 11 the acidity conditions are such that almost the whole of the ucl 4 passes into the 3 n hydrochloric aqueous phase the organic phase freed of ucl 4 leaves the re extractor 71 through the pipe 94 and is introduced into a separator 95 where the degradation products of the tbp are removed through 96 this separator may be a chamber for washing by na 2 co 3 the degradation products of the tbp comprise vigorous complexants and can entrain a portion of the enriched ucl 4 the fraction of these products which retain ucl 4 corresponding to the production is removed.