A comparative study of piperazino-acetic acid and analogous compounds, especially their behaviour on oxidation

Abstract

The view has been expressed that the copper salt of piperazino-acetic acid could exist in two isomeric forms, a blue and a green; the aim of the present investigation was to determine the nature of the isomerism. A successful method for preparing the pure blue copper salt has been worked out and the physical and chemical properties of this and of the green solid have been studied; determinations of molecular weight and attempts to ascertain relative copper ion concentrations revealed no essential difference between the two substances in these respects. Copper salts of related acids have been prepared in an attempt to determine the part of the molecule essential to the change. The effect of modification of conditions of preparation of the green solid from the blue salt has been investigated. Attempts to prepare a green salt of constant composition failed, and attempts to determine its nature by treatment with p-toluene-sulphonyl chloride, phenyl isothiocyanate, picric acid etc., gave few positive results. The general indication of the above work was that oxidation was taking place during the colour change; accordingly the action of various oxidising agents on piperazino-acetic acid was studied. Cold aqueous hydrogen peroxide was found to give a definite product which was isolated and investigated. The action of oxidising agents on amino-acids and amines is discussed; it is shown that by the action of hydrogen peroxide on piperazino-acetic acid an amine-oxide is produced which can be converted into a secondary hydroxylamine, a change involving transference of oxygen within the molecule. An explanation is given of this change and of the part played by alcohol in effecting it. Finally, it has been shown that the colour change in the copper salt is due to aerial oxidation and that the green solid contains the same secondary hydroxylamine.