770 



SCIENCE 



[N. 8. Vol. XXVII. No. 698 



whether a 1,3 diearbonyl derivative, like 

 aeetoaeetic ether, is a ketone, CH3CO.- 

 CH,COOR, or an alcohol, CHjCCOH):- 

 CH.COOR, are questions which could not 

 really find their final answer by the 

 older methods of the study of derivatives, 

 although at the time that was the best we 

 could do. According to the present views, 

 which J. Traube first presented, we have 

 in solutions of the tautomeric compounds 

 both forms in equilibrium with each other; 

 for instance, we have 



and 



CeHnCO.NHj ^ CsH^C (OH) : NH 



CHaCO.CHjCOOR^CHjCCOH) : CHCOOR. 



According to the laws of equilibrium and 

 kinetics, if a given reagent, for instance an 

 alkali, uses up the one form, say by neu- 

 tralization, the whole material can be 

 changed in the same way; the other form, 

 inert in regard to a particular reagent, re- 

 generates the active form continuously by 

 a one-sided reaction. Thus, even if the 

 unstable form existed in only minimal 

 quantity, it could be the source of the 

 actual product of the reaction, and that is 

 why the old method of proof by the study 

 of derivatives must be considered faulty. 

 The isolation of the two closely related 

 forms has not only confirmed this modern 

 view by the qualitative observation that the 

 forms are mutually convertible into each 

 other, but Wislicenus, Claisen, Kuester and 

 others have measured quantitatively the 

 velocities of transformation of tautomers 

 and have determined a number of the 

 equilibrium constants. With the proof by 

 Knorr, showing that in the solid phase 

 only one tautomer can exist in stable form, 

 the whole matter has received a definite, 

 sharp setting. That the subject is one of 

 interest not only to organic chemists, but to 

 all of us, is evident from the fact that our 

 indicators, phenolphthalein, methyl orange 

 and others, seem to owe their valuable 



property of changing their tint, in passing 

 through the neutral point, to conditions of 

 tautomerism affecting the chromophoric 

 groups in these compounds. 



And so we find physico-chemical methods 

 of investigation of the greatest advantage 

 in the treatment of the three important 

 classes of organic compounds which have 

 the same molecular weight and composition 

 but different character and identity— 

 namely, isomers, tautomers and stereo- 

 isomers. 



But the organic compounds themselves, 

 their structure and the arrangement of 

 their atoms in space, represent in a way 

 the least important side of organic chem- 

 istry — far more important are their reac- 

 tions, the changes to which we can subject 

 them, the things we can do with them. 

 For on these changes all the scientific and 

 technical applications and our very life 

 depends. It is in particular to the study 

 of some phases of this question of organic 

 reactions that I wish to call your attention 

 this morning. To take a concrete case, the 

 reversible reaction of esterification and 

 saponification 



CH3COOCH3 + HOH ?=* CH3COOH -t- CHjOH 



has been an important one ever since its 

 study helped establish our fundamental 

 law of chemical equilibrium. But the re- 

 action has been important in other direc- 

 tions as well, for early investigations 

 showed that either action is greatly ac- 

 celerated by the addition of an acid like 

 hydrochloric acid; since the acid did not 

 seem to change or to take part in the reac- 

 tion, it was said to act by its mere pres- 

 ence as a catalytic agent; and this is a 

 typical reaction from which important laws 

 regarding catalysis were laid down. There 

 are hosts of reactions in organic as in in- 

 organic chemistry in which we use one 

 ingredient or the other to accelerate the 

 action, or rather to make it go at all. It 



