CXXIV.—A property of ethyl tartrate
Journal of the Chemical Society Transactions
a paper by Messrs. Lowry and Cutter dealing with ethyl tartrate, in which they state (i) that " almost all commercial samples of ethyl tartrate are yellow in colour," a similar colour having been also observed in one of their own samples. " This colour is undoubtedly due to an impurity, since it can be removed by freezing out and centrifuging the crystalline ester." And, (ii), " The purified esteq developed a yellow colour when heated in the distilling flask, and gave a yellow distillate, the
... w distillate, the colour of which disappeared, however, after a few hours." This colour, they regard as an indication of purity rather than of impurity in the sample (pp. 537-538) and they regarded it as perhaps the result of a reversible dehydration Since 1895 I have been aware that under certain circumstances ethyl tartrate may develop a transient green colour and from time to time I have carried out experiments on this subject, but since these have not reached the stage I should have wished, they have not previously been referred to. In view, however, of Lowry and Cutter's work I should like now t o indicate briefly the conclusions which have so far been arrived at. The green substance which Lowry and Cutter rightly regard as an impurity, and which can be fractionated out of the ester, possesses the remarkable property not mentioned by them that, when present in the ethyl tartrate in quantities not too large, it becomes perfectly colourless on standing for some time. The impurity therefore possesses the characteristic which Lowry and Cutter attribute to specially pure ethyl tartrate. Since substances the colour of which fades on standing and returns again on re-heating are uncommon and possess a peculiar interest, the matter is perhaps one of importance, and I have therefore constantly kept it in mind. The f i s t indication of the cause of this green colour was given by a slight accident during distillation, whereby it considerably too rapid stream of air was sucked for a short time through the ester a t a temperature of about ZOO". The first runnings in the distillation then came over bright green, almost grass green, in colour, but on standing for a time became colourless or practically so. Even in such a case, however, the substance producing this effect is probably present only in small quardity, since it does not much lower the rotation of the ester; but that it is not an indication of purity in the ethyl tartrate but merely an (p. 544).