Хімія та хімічні технології/ 6. Органічна хімія

A. I. Panasenko, V. P. Buryak, T. А. Samura, A. S. Gotsulya, S. N. Kulish, V. O. Salionov

Zaporozhye State Medical University

UV ABSORPTION SPECTRA OF «LARUSANUM»

The spectral characteristic of «Larusanum». «Larusanum» is used in therapeutic practice for the treatment of tuberculosis. «Larusanum» is isonicotinoyl hydrazone furfurilidenacetone.

Therefore pyridine, 4-pyridinecarboxylic acid, furfurilidenacetone may be examined as the models.

Nonbonding electrons in the molecule of pyridine are on one of sp² hybrid orbitals of nitrogen atom. 2p_z atomic orbital is symmetric to z axis, and 2s-atomic orbital is spherically symmetric. [1]

Therefore n-π * transition in pyridine is allowed. However the value of one-electron integrals is not big due to the small overlap between 2s- and 2p atomic orbitals. This explains comparely low intensity of the n →π*-transition in pyridine. Complete absorption of n → π*-transition disappears in acid solutions [5]. It is caused with the formation of a bond between the proton and nitrogen atoms due to its lone pair of electrons:

The distinctive feature of the band of n → π*-transition of pyridine is vibrational structure , which is well replaced in the vapor spectrum at ~ 180 nm [4]. Furfurilidenacetone is characterized with two bands with maxima at 233 and 314 nm as a model compound in ethanol solutions (table. 1). The first maximum refers to the "furan" band, and the second one we consider as the result of p-π-conjugation in chloroform:

λ_maks = 314nm

Besides, we have established the intense maximum at 263 nm for isoniazid residuum, which includs in the molecule of «Larusan» (table. 1). According to the literature [3], the maximum of pyridine in ethanol, is in the same area (~ 270 nm) but it is low intensity with lg ɛ = 2,65. Thus, the maximum of model compound (isoniazid) corresponds to p-π-conjugation between the pyridine ring and carbonyl group:

λ_maks = 263nm

«Larusanum» is characterized with four absorption maxima, but for most solvents maxima appear only in two bands (table. 1). The first band with maxima or bend in the range 221 - 230 nm, is visible for solutions in concentrated sulphate acid. The second band with a maximum or bend 262 - 275 nm is observed for solutions in all solvents and corresponds to p-π-conjugation in the 4-piperidilkarbonyl chloroform.

Table 1

Spectral characteristic of furfurilidenacetone (I), isoniazid (II) and larusanum (III)

№	Compound	Solvent	λ, nm	ɛ	lg ɛ	Electron transfer
1	2	3	4	5	6	7
1.	I	95% ethanol	233 314	2190 22910	3,34 4,36	Furan band p-π- conjugation
2.	II	95% ethanol	263	4200	3,69	p-π- conjugation

Continuation of Тab. 1

1	2	3	4	5	6	7
3.	III	Water	273 334	10230 25120	4,01 4,40	p-π- conjugation p-π- conjugation
4.	III	0,1М NaOH	275 324	Inflection 20890	4,32	p-π- conjugation p-π- conjugation
5.	III	0,1М HCl	270 321	7080 19500	3,85 4,29	p-π- conjugation p-π- conjugation
6.	III	Acetate buffer solution (pH = 3.85)	272 325	8510 20420	3,93 4,31	p-π- conjugation furan band
7.	III	Conc. H2SO4	221 268 384	14130 12020 26290	4,15 4,08 4,43	p-π- conjugation p-π- conjugation p-π- conjugation
8.		95% ethanol	270 334	Inflection 29510	4.47	p-π- conjugation p-π- conjugation
9.		Cyclohexane	230 275 331	Inflection Inflection 28840	4,46	p-π- conjugation p-π- conjugation p-π- conjugation
10.		6М NaOH	275 331	Inflection 19050	4,28	p-π- conjugation p-π- conjugation p-π- conjugation
11.		Dioxane	270 319 420	Inflection 24550 8510	4.39 3.93	p-π- conjugation p-π- conjugation p-π- conjugation
12.		Chloroform	262 320 420	8510 20420 8510	3.93 4.31 3.93	p-π- conjugation p-π- conjugation p-π- conjugation

The third absorption bands with maxima at 329 - 334 nm is absent only for solutions in concentrated sulfate acid. The emergence of this band undoubtedly is connected with the p-π-conjugation, in the result of introduction in the molecule of furfurilidenacetone residuum. For the third absorption band of «Larusanum», which should be considered the main, bathochromic shift of the maximum can be observed in the transition from low-polar to a polar solvent. Thus, maximum is 319 nm in 1,4-dioxane, in chloroform-320 nm in ethanol and water - at 334 nm (table. 1).

The fourth band with maximum in the region of 384 - 420 nm is typical only for solutions of «Larusanum» in concentrated sulfate acid, 1,4-dioxane and chloroform, the occurrence of which is probably due to the formation of associates of the "Larusanum - solvent".

Conclusions

1. UV absorption spectra of «Larusanum» have been measured in 10 solvents of different polarity (purified water, 0.1 M HCl, 0.1 M NaOH), acetate buffer solution (pH = 3.85); 95% ethanol, cyclohexane, 6M NaOH, 1,4-dioxane, chloroform.

2. Learning of UV spectra of model compounds (furfurylidenacetone and isoniazid) makes in ethanol solutions.

3. Four bands of maximum in the region 221 - 230 262 - 275 319 - 334 384 - 420 nm on the spectral curve of «Larusanum» are observed; the second band of them is the most typical corresponding to р-π-conjugation in the residue of furfurilidenacetone.

Literature

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2. Машковский М. Д. Лекарственные средтва. – Харьков: Торсинг, 1988. – Т. 1 – 560 с., т. 2. – 592 с.

3. Свердлова О. В. Электронные спектры в органической химии - .: Химия, 1985. – 248 с.

4. Сильверстейн Р., Басслер Т., Морцил Т. Спектрометрическая идентификация органических соединений. М.: « Мир», 1977. – 590 с.

5. Mason S. F. The electronic spectra of N-heteroaromatic system. Pt II: Substituted monocyclic azines // J. Chem. Sоc. – 1999. – №5. – Р. 1247 – 1253.