December 21, 1906.] 



SCIENCE. 



821 



when selectively excited tends to give off per- 

 ceptible intensities of radiation corresponding 

 to every possible mode of molecular motion. 

 Another aspect of increased rapidity of 

 spreading of energy among the various modes 

 of motion of a gas with increased temperature 

 is that the spectrum of a very hot gas when 

 excited by the electric current tends to show 

 many lines that are invisible when the gas is 

 relatively cool. Thus the spectrum of the 

 mercury arc has no red lines when the vapor 

 is relatively cool, but when the vapor is very 

 hot red lines appear. 



W. S. Franklin. 



NOTES ON ORGANIC CHEMISTRY. 

 THE NITRATION OF ANILINE. 



It is generally stated in text-books of or- 

 ganic chemistry that aniline and nitric acid, 

 of tolerably high concentration, yield resinous, 

 tarry, or carbonaceous material from which no 

 definite compounds can be isolated, whereas, 

 in the presence of a large excess of concen- 

 trated sulphuric acid, nitration of the aniline 

 takes place without difficulty. This behavior 

 is explained by assuming that in the first case 

 the nitric acid attacks the amino group of 

 aniline more readily than it affects the benzene 

 nucleus, but that the former is ' protected ' by 

 the concentrated sulphuric acid. 



Several objections can be made to this ex- 

 planation, among which the following may 

 be mentioned: (1) Aromatic amines form 

 stable compounds (nitrates) with nitric acid, 

 but with nitrous acid the products (nitrites, 

 diazonium derivatives, etc.) are, in general, 

 highly unstable. (2) The primary products 

 of the action of aniline on nitric acid or sul- 

 phuric acid are, presumably, aniline nitrate, 

 CjH^NHjNOj, and aniline hydrogen sulphate, 

 CgH.NHjSO.H, respectively, and it is not ap- 

 parent why the amino group is less well ' pro- 

 tected ' in the former compound than in the 

 latter. 



Guided by these and other considerations, 

 we began, some months ago, a study of the 

 action of nitric acid on aniline and on aniline 

 nitrate, and of the behavior of certain deriva- 

 tives of aniline towards nitric acid alone and 



when mixed with acetic acid, oxalic acid, tri- 

 chloracetic acid and sulphuric acid, respect- 

 ively. The aniline derivatives employed in- 

 cluded only those in which one or both of the 

 hydrogen atoms of the amino group have been 

 replaced, such as acetanilide, CbH^NHCOCHj, 

 or oxanilide, 



COv 



CO/ 



A preliminary account of our work has re- 

 cently appeared,^ and we hope to publish fur- 

 ther communications on the subject in the 

 course of a few months. The object of this 

 note is to call attention to certain of our re- 

 sults which we think may be of some general 

 interest. Nitric acid of any concentration 

 up to 75.33 per cent, when mixed with aniline 

 in equimolecular proportion forms the nitrate, 

 provided a suitable temperature is maintained, 

 but the slightest excess of acid, if of compara- 

 tively high concentration, changes this color- 

 less nitrate to a reddish pink compound. This 

 may be kept for a day or two if it remains 

 sufficiently cool, but, more or less quickly, 

 depending on the temperature and on the ex- 

 cess of acid, it darkens, blackens and may 

 become incandescent. The color is instantly 

 discharged by a drop of water and is regener- 

 ated by more acid. 



In the formation of mononitro deriva- 

 tives of the substituted anilines referred 

 to above, the position taken by the nitro 

 group (ortho, meta, para) appears to de- 

 pend on two factors: (a) the nature of this 

 substituting group, i. e., whether it be nega- 

 tive (acidic), positive (basic), or neutral; (b) 

 the strength, not concentration, of the acid 

 which has been mixed with the nitric acid. 

 Should this conclusion be justified by our 

 subsequent experiments, it will be seen that, 

 as we can vary each of the above factors be- 

 tween very wide limits, the possibility is af- 

 forded of varying a in the same direction as 

 h or in an opposite one, in order to prepare 

 some desired isomer. Moreover, similar con- 

 ditions might reasonably be expected to apply 

 to the nitration of compounds in general, and 

 if to nitration, then also, so far as experi- 



^Amer. Chem. Jour., 36, 605 (1906). 



