Infra-red spectra of sodium salts of some primary nitroparaffins. Z. BUCZKOWSKI and T. URBAŃSKI

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1 Spectrochimica Acta, 902, Vol. IS, pp. 87 to 94. Pcrgamon Press Ltd. Printed in Northern Ireland Infra-red spectra of sodium salts of some primary nitroparaffins Z. BUCZKOWSKI and T. URBAŃSKI Warsaw Institute of Technology (Politechnika) Warszawa 0, Poland (Received 2 November 96) Abstract Infra-red spectra of sodium salts of a few primary nitroparaffins have been examined, and compared with spectra of the nitroparaffins. The characteristic feature of the spectra of sodium salts is lack of both symmetric and asymmetric N0 2 frequencies. Two bands corresponding to C=N vibrations (c. 660 and 600 cm - ) and a band at approximately 70 cm -, presumably N * О vibration, are present in the spectra of sodium salts. A hypothesis is proposed that sodium salts of primary nitroparaffins may exist in two isomeric cis and trans forms. IT IS known that the generally admitted structure [] of the aci-form of nitroparaffins or "nitronium acids" (I) and that of the aci-anion (II) was in doubt for some time (See Ref. [2]). R OH R O- \ / \ / C=N C=N / \ / \ R' O R' О (I) (И) Although the investigations of KORNBLUM and his co-workers [3] seemed to confirm the correctness of the formulae (I) and (II), we have tried to obtain more information on the structure of the sodium salts of a few nitroparaffins using infrared absorption. So far only a few papers dealing with infra-red spectroscopy of aci-nitrocompounds and their O-acyl derivatives [4-] have been published. In all of them a [] A. HANTZSCH, Ber. deut. Chem. Ces. 32, 575 (899); 35, 20, 226, 00 (902): 39, 39, 073 (906). [2] G. W. WHELAND, Advanced Organic Chemistry (3rd Ed.) p. 75. John Wiley, New York (960). [3] N. KORNBLUM, N. N. LICHTIN, J. T. PATTON and D. C. IFFLAND, J. Am. Chem. Soc. 69, 307 (947); N. KORNBLUM, J. T. PATTON and J. B. NORDMANN, Ibid. 70, 746 (948). [4] J. P. FREEMAN and K. S. MCCALLUN, J. Org. Chem. 2, 472 (956). [5] E. H. WHITE and W. J. CONSIDINE, J. Org. Chem. 22, 745 ( 957) ; J. Am. Chem. Soc. 80, 626 (958). [6] H. E. ZIMMERMANN and T. E. NEVINS, J. Am. Chem. Soc. 79, 6559 (957). [7] S. S. NOVIKOV, К. K. BABIEVSKII and I. S. KORSAKOVA, Doklady Akad. Nauk S.S.S.R. 25, 560 (959). [8] P. D. BARTLETT, E. R. WEBSTER, С E. DILLS and H. G. RICHEY, Jr., Ann. Chem. Liebigs 623, 27 (959). [9] M. M. SHEMIAKIN, D. N. SHIGORIN, L. A. SHCHUKINA and E. P. SIOMKIN, Izvest. Akad. Nauk S.S.S.R. Otdel. Khim. Nauk 695 (959). [0] J. H. BOYER and H. ALUL. J. Am. Chem. Soc. 8, 4237 (959). [] Z. ECKSTEIN and T. URBAŃSKI, Bull. acad. polon. se/. 8, 579 (I960), 87

2 I ISS Z. BUCZKOWSKI and T. URBAŃSKI frequency ()S- Milo cm very characteristic of the aci-iht roparalhns lias been reported. It is assigned to the C = N stretching vibration bands which obviously do not exist in spectra of "normal" nitroparaffins. However most of the authors [4, 5, 7-0] did not report bands characterizing the OH group present in the structures (). Only ZIMMERMAN and NEVINS [6] and ECKSTEIN and URBAŃSKI [] observed in some aci-nitrocompounds the presence of a broad band cm - and 3422 cm -, respectively. This should be assigned to a hydrogen bonded OH group. The only papers of infra-red spectra of sodium salts of nitroparaffins were given by MATHIEU and MASSIGNON [2] who examined sodium salt of -nitropropane, BELIKOV et al. [3] who examined sodium and potassium salts of phenylnitromethane and BROWN [4] who examined potassium salts of grem-dinitroparaffins of general formula R С (N0 2 ) 2 K. BROWN found two frequencies: 242 and 62 cm -, which he assigned to the nitro groups. Recently JONATHAN [5] published the results of examination of sodium salts of nitromethane and similarly assigned two bands, and cm - to the asymmetric and symmetric N0 2 vibrations respectively. EXPERIMENTAL Nitroethane. -nitropropane, -nitrobutane, -nitropentane, -nitrohexane (commercial grade) were purified by distillation. Sodium salts were prepared by the standard method, by allowing sodium ethoxide to react with the ethanolic solutions of nitroparaffins. The precipitated sodium salts were separated and washed with anhydrous ether. The nitrogen content was determined to check their purity. Sodium salt of nitroethane. Found N, 4-7 ; C 2 H NNa requires N, 4-4 per cent. Sodium salt of -nitropropane. Found N, 2-9; C 3 H e 0 2 NNa requires N, 2-6 per cent. Sodium salt of -nitrobutane. Found N, -5; C 4 H NNa requires N, -2 per cent. Sodium salt of -nitropentane. Found N, 0-3 ; C 3 H 0 O 2 NNa requires N, 0- per cent. Sodium salt of -nitrohexane. Found N, 8-9; C 6 H NNa requires N, 9- per cent. Infra-red absorption spectra in the range from 800 to 750 cm - were determined by means of IKS-2 (USSR production) single-beam and Hilger H-800 double-beam spectrophotometers with sodium-chloride optics. Liquid substances (all nitroparaffins) were examined in layers of capillary thickness. The sodium salts were used in form of Nujol mull. In the case of -nitropentane two thicknesses were used, a thinner layer above ca. 350 cm 4 and thicker below this point. Standard spectra of gaseous ammonia and atmospheric moisture were used for calibration. The frequencies are recorded in Table and the spectra are given in Figs. -5. DISCUSSION The main feature of the spectra of sodium salts of aci-nitroparaffins is the [2] J. P. MATHIEU and D. MASSIGNON, Compt. rend. 2, 783 (940). [3] W. M. BELIKOV, S. G. MAIRANOVSKII, C. B. KORCHENNAYA, S. S. XOVIKOV and W. A. KLIMOVA, Izvest. Akad. Nauk S.S.S.R. Otdel. Khim. Nauk 675 (9(H)). [4] J. F. BROWN Jr., J. Am. Chem. Soc. 77, 634 (955). [5] N. JONATHAN, J. Mol. Spectrosc. 5, 0 (960).

3 Infra-red spectra of sodium salts of some primary nitroparaffins 89 E S О S s ce Ы) с Il > a О Д 'A w _ У- t I Ю : с с с > m > > I- СО 00 CS 00»SСО 00 CO i -н О О О Ol с»я 00 и с <м oj х. Ci cc IM С- С- * Î 00 -н с с 00 Ю ОС 00 - S S с Г~СО СО О 00 с «СО СМ СМ СМ 8 u > m? X l~ О l~ -* -н О О 3 3 J3 а œ с Q in i~ ~ ем СО СО 0- см 6 s R -t cc ООО О: X X св > ^СМ с О с сс ~ с: с с с - ot 3 3 с с с с с с с

4 90 Z. BUCZKOWSKI and T. URBAŃSKI i u i n II L (if V - Nitropropane 750,500,250, Wave number, cm-' W a v e п и т Ь е Г c m-. Fig.. (top) Infra-red spectrum of nit roethane. (Bottom) I.R. spectrum of Na salt of nitroethane. Fig. 2. (Top) Infra-red spectrum of -nitropropane. (Bottom) I.R. spectrum of Na salt of -nitropropane. disappearance of both frequencies of N0 2 stretching vibrations in the spectra of the salts and appearance of new bands: near 600 cm - and near 70 cm -. Asymmetric, N0 2 stretching vibrations Very strong bands were found at cm - in nitroparaffins. None of the salts of aci-nitroparaffins gave this band. symmetric N0 2 stretching vibrations Strong bands cm - were shown by all the nitroparaffins. They were absent in their salts.

5 Infra-red spectra of sodium salts of some primary nitroparaffins 9 Л ] A / >* M 7^ Â i _ ' * If I- Nitrobutane l-nitropentane I Û n A p i / Г V Na salt of I - nitrobutane Fig. 3. butane, Wave number, (Top) Infra-red spectrum of -nitro- (Bottom) I.R. spectrum of Na salt of -nitrobutane. Wave 250 К number, Fig. 4. (Top) Infra-red spectrum of l-nitropentane. (Bottom) I.R. spectrum of Na salt of -nitropentane. Bands at cm- and cm" Two bands, one of medium or low intensity near 660 cm - and another one of very high intensity near 600 cm -, are present in the spectra of all the salts. They are absent in nitroparaffins. Our assignment of these bands to C=N stretching vibrations is in agreement with the data of other authors [4 ] as mentioned above. It remains difficult however to explain why two bands are present in the spectra of all salts so far examined. It might suggest that the double maximum of the band is due to asymmetry of the crystal lattices. In order to examine this, we examined the absorption of the sodium salt of -nitropropane in alcoholic solution in this region.

6 92 Z. BUCZKOWSKI and T. UIIBAŃSKI л л li 4f~ T - Nitrohexane Wave number, cm - Fig. 5. (Top) Infra-red spectrum of -nitrohexane. (Bottom) I.R. spectrum of Na salt of -nitrohoxano. There was no change of the absorption spectrum, two maxima being still present. Thus the influence of the crystal lattice upon the absorption maxima of this band seems to be ruled out. Another possible cause of the two maxima in question could be the existence of two isomeric sodium salts. All investigated samples of the salts would in this case be composed of mixtures of two isomers. So far it is difficult to find the answer to the structure of the isomers. We suggest a tentative explanation that two geometrical isomers (la) and (lb) deriving from primary nitroparaffins were possible.

7 Infra-red spectra of sodium salts of some primary nitroparaffins 93 H O H 0-Na+ \ / \ / C=N C=N / \ / \ R 0-Na+ R 0 (la) (lb) Indeed it is known that C=C stretching vibrations in cis-trans isomers of the compounds of a general formula CHR =CHR 2 differ appreciably [6]. SHEPPARD and SIMPSON [7] gave the values 657 and 673 cm - for cis and trans isomers of simple olefin derivatives respectively. A special study will be carried out on the possibility of isomerism of the salts and O-derivatives of aci-nitroparaffins. Band at cm - This strong band exists in all the sodium salts. We suggest that it should be assigned to N * 0 vibrations. This could be regarded as similar to N >- 0 vibrations in N-oxides. E.g. pyridine N-oxide has a group of atoms C=N similar to i О this in aci-nitroparaffins of the formula (I) and the frequency of it is 270 cm -. It is subjected to large shifts under the influence of various substituents [6]. Band at cm" We assign tentatively this band to the bond С N vibration in nitroparaffins. It is similar to that suggested by HASZELDINE [8]: cm -. The intensity of the bands decreases with an increase of size of the alkyl group. The bands are absent in the salts with an exception of the salt of -nitrobutane which shows a very weak absorpt ion al S70 cm (possibly an overtone or combinai ion frequency), whereas he corresponding nitroparaffin gives a strong band at 86 cm -. Some other bands The strong band enr is present only in nitroparaffins and absent in their salts. It resembles the deformation frequency of CH 2 group in paraffin chains and the absence in sodium salt of nitroethane seems to suggest this assignment. However it is absent in salts of -nitropropane and higher nitroparaffins, where CH 2 group (or groups) are present. In the light of these facts the assignment of the band cannot yet be made. As a conclusion of the discussion it can be pointed out that most experimental facts recorded above agree with the formula (I) of the aci-nitroparaffins. Thus: () Both NO,-frequencies are absent in the spectra of nitroparaffins. (2) Two frequencies C=N appear in the spectra of sodium salts and it is possible that two geometric isomers are responsible for existence of the bands. 6] L... BELLAMY, The Infra-red Spectra of Complex Molecules. Methuen, London (968). I 7] N. SHEPFARD and D. M. SIMPSON, Quart. Revs. (London) 6, (952). I 8] K. N. HASZELDINE, J. Chem. Soc (953).

8 94 Z. BUCZKOWSKI and T. URBAŃSKI (3) The frequency N >- O is probably present in the spectra of sodium salts. (4) The frequency С N is absent in the spectra of sodium salts. Note When this paper was ready for publication, a new paper by JONATHAN [9] came to our notice. His results do not affect our main conclusions although some assignments are different. Acknowledgement We are much indebted to Mr. P. GLUZIŃSKI for measurement of spectra in a Hilger H-800 spectrophotometer. [9] N. JONATHAN, J. Mol. Spectrosc. 7, 05 (90).