h u g . , 1930
INFRARED SPECTRA OF ETHANOLAMINE-ALDEHYDE I’KOL)UC~.Y [CONTRIBUTION FROM THE N A V A L
8073
RESEARCH LABORATORY]
Infrared Spectra and Structure of Reaction Products of Ethanolamine and Aromatic Aldehydes1 BY L. W. DAASCH AND URHOE. HANNINEN In the course of studies on aldehyde-amine condensation products for use as rubber vulcanization accelerators, the structure of the products of ethanolamine and aromatic aldehydes assumed importance in the work of correlating structure with accelerator activity. The reaction between ethanolamine and benzaldehyde, for example, could lead either to a Schiff base or to an oxazolidine ring system. Meltsner and co-workers2 reported the products obtained from the reaction of aromatic aldehydes with ethanolamine to be oxazolidine ring systems of Type I.
zaldehyde and ethanolamine, the problciri is to decide between the two structures
Oxazolidine ring structure aiid (V) fi-CH=N-CH2CH20H
Schiff base structure
This can be done by means of well-established relationships which exist between molecular structure and infrared absorption, such as have been found for hydrocarbon groups and for many other molecular groups both a t this laboratory and elsewhere.6 On this basis it may be said that structure (I) will exhibit: (1) absorption characteristic of an N-H link but none characteristic of an alcoholic 0-H link, (2) no absorption characteristic of the C=N link, (3) a group of 0 CHz fourteen bands which will be identical with those which characterize an aromatic ring attached to a (111) (IV) secondary carbon atom of an alkyl group; and Recently, Goodson and Christopher, in study- that structure (V) will exhibit : (1) characteristic ing condensation reactions of ethanolamine with 0-H absorption but no N-H absorption, (2) salicylaldehyde and o-chlorobenzaldehyde, re- characteristic C=N absorption, (3) a group of ported ultraviolet absorption spectra for these about fourteen bands which will be similar but products. The reaction product of salicylalde- not identical with those for a mono-alkyl-subhyde and ethanolamine was assigned a Schiff base stituted aromatic ring. Further, both structures structure (11) from a comparison of its ultraviolet will exhibit similar absorptions due to the preslink and CH, groups, but absorption spectrum with that of a known Schiff ence of the C-0base (111). The reaction product of o-chloro- it may be expected that structure (I) will exhibit a benzaldehyde with ethanolamine was reported greater number of strong bands which cannot be to be 2-(2-chlorophenyl)-oxazolidine(IV) from a accounted for by various groups since (I) has a similar comparison with 2-phenyloxazolidine (I) five-membered ring structure (which produces whose structure was assigned by analogy with strong bands not easily correlated) while (V) has known oxazoles and by its method of prepara- not. As shown in Fig. 1, the reaction product has a tione4 Five aromatic aldehyde-ethanolamine con- strong band a t 3280 cm-I. This must be due to densation products, including those prepared by free N-H, to hydrogen-bonded N-H or to hyGoodson and Christopher, have been investi- drogen-bonded 0-H. To differentiate between gated. The structure of these compounds was these possibilities the product was examined obtained through a study of their infrared spectra. in very dilute carbon tetrachloride solutions so as to decrease the effect of hydrogen bonding. Discussion Under these conditions the intensity of the band Considering first the reaction product of ben- was greatly diminished (showing that intermolecular hydrogen bonding had. existed), and a (1) The opinions contained herein are the authors’ and are not to strong sharp band appeared a t 3625 crn.-l. be construed as official or reflecting the views of the Department of the Navy. Article not copyrighted. According to previous experience a t this labora(2) Meltsner, Waldman and Kremers, THISJ O U R N A L , 62, 3494 tory and to the correlations of Barnessa and of (1940). (3) Goodson and Christopher, { b i d . , 71, 1117 (l
