A study of physical and chemical effects of conjugation of carbon-carbon and carbon-nitrogen double bonds

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1936

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ln view of the fact that a study of the addition reactions of the simple ethylene bond and the carbonyl bond has been for over seventy-five years a subject of extensive investigation, and that years of experimental work by thousands of organic chemists has contributed to this voluminous field, it is at once seen that the subject of this investigation is a very broad one indeed. For no one can question the fact that the C=N bond is capable of undergoing a considerably greater number of reactions than either the C=C or the C=O complex. Furthermore complexity is added to the problem by introducing the C=C group into conjugation with the C=N linkage. The nature and properties of the conjugated complex, C=C-C=N has not been studied systematically, as have the systems -C=C-C=C- and C=C-C=O. The close relationship between the C=N, C=C, and C=O groups, has led to the belief however that the unsaturated complex -C=C-C=N- would exhibit abnormal properties as a result of conjugation. Although compounds such as the diolefines and ∝,β-unsaturated ketones have been studied quite extensively because of the physical and chemical properties which they exhibit as a result of conjugation, ∝,β-unsaturated Schiff bases and hydrazones have not been heretofore considered from this standpoint. For this reason, it has been the aim of this investigation to make a study of the known reactions of the C=N complex, to compare these with those known for the system C=C-C=N, and where this information is lacking to supply it by means of the required experimental research. Since beginning this work it has been found that whereas much is known about the carbon-nitrogen double bond as an isolated unit in various compounds only slight attention has been given to the carbon-carbon and carbon-nitrogen conjugated double bonds. For example over three pages in Beilstein are required to list the various reactions of benzal aniline while only a fraction of a page is devoted to cinnamal aniline. For only one class of reagents, namely the halogens, can it be said that Schiff's bases and other compounds possessing the C=C-C=N complex, have been studied in sufficient detail to characterize their behavior. Data on all other reagents are either lacking entirely or else are very incomplete. The problem being of such broad scope it was not noped that the missing experimental data necessary to clarify the subject would be obtained by one person in the comparatively short time which was available. The work thus necessary will doubtless require the time and effort of several investigators during a prolonged period. However it has been hoped that this preliminary study will bring clarity to certain phases of the problem, and so sort and correlate the facts previously obtained by others as to be a valuable aid to those who may wish to attempt a more complete solution. As is true of much original research, this study has shown that certain points (for example, the reduction of benzal aniline with zinc and acetic acid) the nature of which was considered as definitely known, have actually not until now been satisfactorily elucidated. Further work will doubtless reveal other such cases. Furthermore it has been found hard to stay on the problem originally outlined, for certain classes of compounds have been discovered in the course of this work which are in themselves interesting, and a study of the properties of these, while perhaps contributing nothing to the original aim of this investigation, is nevertheless justifiable from a scientific standpoint

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