Optically Active Phosphorus-Compounds

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ONE of the most fascinating problems of organic chemistry consists in the attempt to prepare compounds the molecules of which are devoid of planes of symmetry, and are therefore capable (like a screw or a glove) of existing in two forms, usually distinguished as left-handed and right-handed; these have the property of rotating the plane of polarisation of a beam of light to equal extents in opposite directions. Such compounds usually contain an “asymmetric” atom linked to four or five radicles all differing from one another; but compounds have recently been prepared in which the asymmetry cannot be attributed to any single atom, but is a property of the whole molecule (see NATURE, vol. Ixxxii., p. 266, December, 1909; this vol., p. 93, March 16). In addition to carbon (linked to four different radicles), asymmetry has been traced by Pope and his colleagues to atoms of pentavalent nitrogen and of tetravalent tin, sulphur, and selenium, whilst Kipping has added tetravalent silicon to the list. The latest addition, that of pentavalent phosphorus, forms the subject of a recent paper by Prof. Meisenheimer in the Berlin Berichte. Two or three years ago this author described a new type of isomerism in the case of nitrogen, the chief characteristic of which was the presence of only four different radicles attached to the pentavalent atom instead of the five that had usually been thought necessary to give rise to optical activity. The conclusions then arrived at have been confirmed by the recent preparation of methylethylaniline oxide, in pure crystals, which displayed a large optical activity when dissolved in dry benzene, both the dextro and the laevo forms of the oxide having been separated and examined. The new phosphorus compound is of precisely similar composition, having the formula CH3x