CHEMICAL MICROSCOPY 



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Org. Chem., 21, 1217 (1956). 



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Chem., 31, 148 (1959). 



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Donald E. Laskowski 



NITROGEN-BONDED RADICALS: 

 IDENTIFICATION 



Most of the really excellent microcrystal 

 tests known for organic compounds are due 

 to basic nitrogen, but the crystals are so 

 affected and modified by other elements and 

 radicals, even quite separated from the ni- 

 trogen atom, and by the whole structure, 

 that they identify the molecule of a specific 

 substance as a whole. That they can do so 

 is, in fact, their great value. However, some- 

 times it may be as well, and more conven- 

 ient, to distinguish closely related com- 

 pounds by precisely the points in which they 

 differ. The difference may be in the radicals 

 on a basic nitrogen atom, which volatilize 

 while still attached to it in a deamination re- 

 action. For example, the three USP drugs 

 levarterenol, epinephrine, and isoproterenol, 

 all diphenols and of similar uses, decompose 

 spontaneously in alkaline solution to give 

 ofT respectively, ammonia, methylamine, and 

 isopropylamine, which can be distinguished 

 readily by microcrystal tests in a hanging 

 drop. 



Still more important are cases where it is 

 desired to learn the identity of radicals on 

 the nitrogen atom as a step in analysis, 

 either in identifying an unknown as some- 

 thing already known, or in formulating the 

 structure of a compound whose precise con- 

 stitution is not known. In either case there 

 are of course chemical tests, such as those 

 given by Feigl, for distinguishing primary, 

 secondary, and tertiary amines; but the 

 microcrystal tests are more definite and 

 show exactly what radicals are attached to 



the nitrogen atom, provided the deamination 

 reaction can be obtained. With many com- 

 pounds, stable to alkali alone, alkaline oxida- 

 tion with permanganate will cause deamina- 

 tion, the nitrogen carrying with it any simple 

 carbon-hydrogen (non-oxygenated) radical 

 attached to it, as it comes off. 



For example, hydroxyamphet amine and 

 methoxamine yield ammonia in this way, 

 while phenylephrine and ephedrine yield 

 methylamine (ephedrine volatilizes slowly 

 unchanged, if not oxidized). Hordenine in 

 the same way yields dimethylamine, cho- 

 line yields trimethylamine, and N-ethyl- 

 ephedrine yields methylethylamine. A test 

 of an antibiotic, the exact structure of which 

 was not known, showed that the amine com- 

 ing off, either spontaneously from alkaline 

 solution or more rapidly with alkaline oxida- 

 tion, was unmistakably dimethylamine, 

 showing that the nitrogen atom bore two 

 methyl groups in the original compound. 



Hanging-drop tests above an alkaline so- 

 lution apply also, of course, to basic com- 

 pounds that are themselves volatile. Also 

 there are cases where an ester is soon hy- 

 drolyzed by alkali, and if basic nitrogen is 

 present in the part that supplies the alcohol 

 rather than the acid of the ester, the simpler 

 basic compound resulting will very probably 

 be volatile, as occurs with procaine and other 

 synthetic anesthetics. Such decomposition 

 compounds can be detected and identified by 

 microcrystals in the hanging drop. However, 

 the tests given below are suggested specifi- 

 cally for the simplest compounds resulting 

 from deamination. The same tests are of 

 course directly applicable to any minute 

 amounts of the lower amines, whether 

 formed by decomposition of a larger mole- 

 cule or already individual compounds. The 

 tests may be useful in several fields, e.g., 

 botanical chemistry, as well as food and drug 

 work. 



Procedure. Stir a very little of the sub- 

 stance into a drop of 5% NaOH in the de- 

 pression of a cavity slide. Set a plain slide 



46 



