122 The Philippine Journal of Science isu 



phthaloxime is red, and its absorption spectrum shows a shallow 

 color band at - = 2040. The alkali salts are purple, and give 



A 



very strong selective absorption with a broad, deep band heading 

 at the same wave length. The effect of alkali, therefore, is 

 identical with thiophthaloxime and phthaloxime. The presence 

 of thionyl does not reverse the spectroscopic changes due to salt 

 formation. Furthermore, two thionyl groups are readily in- 

 troduced into phthalimide, while only one could be introduced 

 into phthaloxime. Thus chemical and spectroscopic evidence 



C=0 



C=NOH 



is in complete accord with the structural formula for phthal- 

 oxime, and we consider that this may now be accepted as correct. 

 Thiophthaloxime in alcohol gives a deep red solution and an 

 absorption spectrum with a band in the color region. The addi- 

 tion of alkali greatly increases the width and persistence of this 

 band, and at the same time nearly obliterates selective absorption 

 in the ultra-violet. It is evident that an ascending scale may 

 be arranged, corresponding to increasing activity of the side 

 ring with phthaloxime, thiophthaloxime, salts of phthaloxime, 

 and salts of thiophthaloxime. The first member of the series 

 causes no selective absorption in the visible region of the spec- 

 trum, and corresponds to the structural formula given above. 

 The substitution of thionyl for carbonyl results in a consider- 

 able increase of activity, sc much so that thiophthaloxime, 

 although possessing the same molecular arrangement as phthal- 

 oxime, nevertheless is a brilliant red and causes a color band 

 in solutions of hundredth molar concentration. We consider 

 this due to conjugation between thionyl and oximido groups, 

 as represented by the formula : 



C= S •.. 



C6H4^^0 H 



The equilibrium in this direction is considerably less important 

 than in the case of salts of phthaloxime as the tendency for 

 conjugation between thionyl sulphur and hydrogen is less than 

 between carbonyl oxygen and metal. 



