The electronic absorption spectra and quantitative determination of pirroksan

Хімія та хімічні технології/ 6. Органічна хімія

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

Zaporozhye State Medical University

THE ELECTRONIC ABSORPTION SPECTRA AND QUANTITATIVE DETERMINATION OF PIRROXAN

The spectral characteristic of pirroksan

Pirroxan 6-[β-(3'-phenylpyrrolidine-1')propionyl]-benzodioxane-1,4-hydrochloride refers to derivative benzodioxane. It is well and successfully applied in medical practice for the treatment of hypertensive crisis and other manifestations of diencephalic pathology [4].

In the molecule of the compound there are phenolic, and pyrrolidine benzodioxane cycles. All of these cycles are not connected with each other, but the molecule of pirroxan contains a carbonyl group, which is linked in the position of 6c benzodioxane ring. According to T .P. Ionaytis and his co-author [3], unsubstituted 1,4-benzodioxan is characterized with two bands λ_max and about 220 and 278.5 nm. V. A. Urba and his co-author [6] established the second vibrational structure of the absorption maximum, that would indicate ¹L_b band with a π → π *-transitions.

We have established the presence of three absorption maxima with λ_ma_x 230, 275 and 305 nm for ethanol solution of pirroxan (table 1). In the first absorption band of pirroxan in various solvents maxima  are observed in the region of 230 – 232 nm for ethanol, water and dioxane solutions. In concentrated sulphate acid λ_max bathochromic mixed to 246 nm, and in an acetate buffer solution, in 25% solution of sodium hydroxide and in chloroform the band is not observed (table 1). T .P. Ionaytis and the co-author [3] called this band conditionally β- band.

The second absorption band of pirroxan with λ_max 274 – 278 nm is high intensive and undoubtedly represents ¹L_b-band arising due to the presence in the molecule of pirroxan two benzene rings. Bathochromic shift indicates this with the transition from a low-polarity to more polar solvents:

ü      cyclohexane 270 nm;

ü      dioxane 274 nm;

ü      ethanol 275nm;

ü      purified water 276 nm;

ü      M HCl 277 nm.

λ_ma_x of pirroxan in chloroform solution  does not fit in this series because of the formation of unstable complexes. Maxima are not observed only for the solution of pirroxan in concentrated sulphate acid in the second absorption band (table 1).

The third absorption band of pirroxan with λ_max. in the range 300 - 310 nm benzodioxane cycle. The band was conditionally named as R-band by T. P. Ionaytis and his co-author [2]. It is absent in solutions of pirroxan in concentrated sulphate acid acid, but is retained in alkaline solutions (table 1).

The bends are observed of 360 and 400 nm for solution of pirroxan in the concentrated sulphate acid acid and 25% solution of sodium hydroxide (table 1).

                                                                                                 Table 1

         The spectral characteristic of pirroxan (C = 1mg%)

№

Solvent

λ, nm

ɛ

lg ɛ

Electron transfer

1.

Water

231
276
306

4,16
4,05
3,85

β-band

¹L_b-band

  р-π- conjugation

2.

0,1М NaОH

230
276
301

14130
10000

4,15
4,00
3,82

β-band

¹L_b-band

  р-π- conjugation

Continuation of Тab. 1

3.	01М HCl	231 277 305	14450 11220 7080	4,16 4,05 3,85	β-band ¹L_b-band р-π- conjugation
4.	Acetate buffer solution рН = 3,85	276 304	10230 6460	4,01 3,81	¹L_b-band р-π- conjugation
5.	Сonc. H₂SО₄	246 400	5750 3,76 The average value of the bend		β-band р-π- conjugation
6.	Ethanol	230 275 305	15490 10470 6310	4,19 4,02 3,80	β-band ¹L_b-band р-π- conjugation
7.	Saturated solution in cyclohexane				β-band ¹L_b-band р-π- conjugation
8.	25% NaOH	278 310 360	10470 8510 The average value of the bend		β-band ¹L_b-band р-π- conjugation
9.	Dioxane	232 274 306	18620 12590 7080	4,27 4,10 3,85	β-band ¹L_b-band р-π- conjugation
10.	Chloroform	278 308	13800 8510	4,14 3,93	¹L_b-band р-π- conjugation

There are no evidentiary items about the presence of these additional bands V. A. Urba and his co-author [5] and T. P. Ionaytis and his co-authors [1-3], who have carefully studied the UV absorption spectra of 1,4-dioxane and it`s derivatives.

Quantitative determination of pirroxan

It is experimentaly founded that light absorption of aqueous solutions of pirroxan obeys to the Bouguer-Lambert-Beer law in the range of concentration from 0.8 mg to 2.6% at 321 nm; from 0.8 mg to 3.2% at 276 nm; from 0.8 mg to 5.0% at 306 nm in ethanol solution - from 0.8 to 2.6 mg% at 230 nm; from 0.8 mg to 3.4% at 275 nm, from 0.8 to 5.6 mg% at 305 nm.

Determination of pirroxan in a substance

Factorial weighed of the substance (approximately 0.018 g) was dissolved in water or 95% ethanol in a volumetric flask of 100 ml. 5 ml of solution was transferred into a volumetric flask of 50 ml, adjusted to the mark with used solvent, thoroughly mixed and the absorbance of the solution was measured at 231, 276, 306 nm (water) or 230, 275, 305 nm (95% ethanol). The results of determination of pirroxan in the substance are shown in table 2.

The method of determining the pirroxan in tablets.

Artificial tablet mass was prepared for analysis according to officinal quality control procedures. The average weight of the tablet is 0.1 g with the content of the drug 0.015g.

About 0.12 g of synthetic tablet weight (factor weighed) was placed into a volumetric flask of 100 ml was added 70 – 80 ml of 95% ethanol and heated in boiling water bath for 3 minutes. The solution was cooled, adjusted to the mark with 95% ethanol and filtered. The first portion of the filtrate was discarded, and the subsequent of 5 ml were taken and transferred into a volumetric flask of 50 ml, the solvent was adjusted to the mark and thoroughly mixed. Absorbance was measured at 230, 275 and 305 nm.

The method of determining 1% solution of pirroxan for injection

1% solution of pirroxan in water for injection was prepared for analysis in accordance with it`s officinal quality control procedure. 2 ml of 1% solution was placed into a volumetric flask of 100 ml and adjusted to the mark. 5 ml of the resulting solution was transferred into a volumetric flask of 50 ml, the solvent was adjusted to the mark and mixed. The absorbance of the solution determined at 231, 276 and 306 nm.

Determination results of pirroxan tablets and a 1% solution for injections are given in table 2.

Table 2

The results of quantitative determination of pirroxan in a substance and medicine (tablets and a 1% solution for injections)

Medicine	Solvent	Wavelength, nm	Metrological characteristic
Pirroxan (substance)	Water	231 276 306	99, 68 ±1,27 99,69 ± 1,57 99,93 ± 1,47
	95% ethanol	230 275 305	100,01 ± 0,61 100,33 ± 0,96 100,12 ± 1,01
Pirroxan (tablets) 0,015/ 0,10	95% ethanol	230 275 305	99,97 ± 1,32 99, 75 ± 0,87 99,83 ± 1,35
1% solution of pirroxan for injection	Water	231 276 306	99,44 ± 1,20 99, 60 ± 0,62 100,07 ± 1,32

Conclusions

1. Three absorption bands with _max of 230 – 232, 274 – 278 and 300 – 320 nm are observed on the spectral curves of solutions of pirroxan; The first band is characterized as β-band, the second band is a typical absorption band of benzene type ¹L_b, and the third band is the result of p-π- conjugation with the carbonyl group of the drug 1,4-benzodioxane cycle.

2. In most cases π→π *-transitions of the benzene ring of pirroxan are characterized with a bathochromic shift of the maxima in the transition from low- to more polar solvents.

3. Spectrophotometric method of quantitative determination substances of pirroxan in medicine (tablets and a 1% solution for injections) is characterized with high selectivity and accuracy. In all cases, the error determination does not exceed ± 1,57%.

Literature

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