научная статья по теме ADIABATIC COMPRESSIBILITIES OF SOME SYNTHESIZED DERIVATIVES OF DIHYDROPYRIMIDINES IN N,N-DIMETHYL FORMAMIDE AND DIMETHYL SULFOXIDE AT 298.15 K Химия

Текст научной статьи на тему «ADIABATIC COMPRESSIBILITIES OF SOME SYNTHESIZED DERIVATIVES OF DIHYDROPYRIMIDINES IN N,N-DIMETHYL FORMAMIDE AND DIMETHYL SULFOXIDE AT 298.15 K»

ХИМИЧЕСКАЯ ТЕРМОДИНАМИКА И ТЕРМОХИМИЯ

УДК 536.7

ADIABATIC COMPRESSIBILITIES OF SOME SYNTHESIZED DERIVATIVES OF DIHYDROPYRIMIDINES IN N,N-DIMETHYL FORMAMIDE AND DIMETHYL SULFOXIDE AT 298.15 K © 2010 R. Gajera, R. Bhalodia and S. Baluja

Physical Chemical Laboratory, Department of Chemistry, Saurashtra University, Rajkot (360 005), India

E-mail: shipra_baluja@rediffmail.com Received May 22, 2009

Abstract — Sound velocities of solutions of some derivatives of dihydropyrimidines (DHPMs) in N,N-di-me-thyl formamide (DMF) and dimethyl sulfoxide (DMSO) were measured at 298.15 K over a wide range of concentration. Adiabatic compressibilities, apparent adiabatic molar compressibilities and apparent adiabat-ic molar volumes were also evaluated. Results of sound velocity measurements provide useful information about ion—ion and ion—solvent interactions and are of significant help in understanding the behavior of electrolytes in solutions.

INTRODUCTION

Dihydropyrimidines are an important class of compounds, which is becoming increasingly important due to their therapeutic and pharmacological properties [1]. These compounds have emerged as the integral backbones of several calcium channel blockers, antihypertensive agents, and alpha-la-antagonists [2]. The present study is a part of our systematic investigation of thermodynamic properties of synthesized biologically active dihydropyrimidines in dipolar aprot-ic solvents. In this paper, the concentration dependence of sound velocity and adiabatic compressibility coefficients for solutions of various substituted dihydropyrimidines in N,N-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) at 298.15 K are studied. From these data, the apparent adiabatic molar compressibility and apparent adiabatic molar volumes are also calculated.

Results of ultrasonic measurements provide useful information about ion—ion and ion—solvent interactions and are of significant help in understanding the behavior of solutes in solutions.

gle capillary pyknometer, made of borosil glass having a bulb capacity of 10 ml. The ultrasonic velocity of pure solvents and their solutions were measured by using Single Crystal Variable Path Ultrasonic Interferometer operating at 2 MHz. The accuracy of density and velocity are ±0.0001 g/cm3 and ±0.1 cm/s respectively. All the measurements were carried out at 298.15 K. The uncertainty of temperature is ±0.1 K and that of concentration is 0.0001 mol/dm3.

RESULTS AND DISCUSSION

In both DMF and DMSO solutions, density (p) and ultrasonic velocity (u) increase with concentration for all the compounds. The adiabatic (isentropic) compressibility of solution, ks, is related to density (p) and sound velocity (u) by the Laplace equation

ks = 1/u2p, (1)

which provides the link between thermodynamics and acoustics.

EXPERIMENTAL

The synthesized dihydropyrimidines were recrys-tallized in N,N-dimethyl formamide. All the synthesized compounds characterized by IR, NMR and mass spectra. The structure of these compounds is given in Fig. 1.

The solvents DMF and DMSO used in the present work were of AR grade and were purified according to the standard procedure described in [3].

The computation of ultrasonic and thermodynamic properties requires the measurements of ultrasonic velocity (u) and density (p). The densities of pure solvents and their solutions were measured by using a sin-

R-NH

NH

A

O

Fig. 1. General structure of dihydropyrimidines derivative, where, R = (RVG-1) 4-OCH3C6H4, (RVG-2) 4-CH3C6H4, (RVG-3) 4-ClC6H4, (RVG-4) 4-CH3C6H4, (RVG-5) 2-OCH3C6H4.

Table 1. Sound velocities, densities, adiabatic compressibilities, apparent molar adiabatic compressibilities, apparent molar volume and solvation number of pyrimidines in DMF at T = 298.15 K

с, M u х 10 5, cm s 1 р, g cm 3 ks х 10 n, cm2 dyn 1 Фк х 10-8 Фу Sn

RVG-1

0.00 1.4516 0.9453 5.02 - - -

0.01 1.4552 0.9494 4.97 -4.70 -353.43 2.46

0.02 1.4580 0.9506 4.94 -2.88 -202.52 3.20

0.04 1.4604 0.9531 4.91 -1.45 -129.18 4.57

0.06 1.4656 0.9555 4.87 -1.26 -103.33 4.70

0.08 1.4676 0.9577 4.84 -0.87 -74.31 5.42

0.10 1.4688 0.9584 4.83 -0.42 -46.42 6.40

RVG-2

0.01 1.4640 0.9485 4.91 -9.80 -259.01 1.04

0.02 1.4648 0.9498 4.90 -4.84 -157.33 1.86

0.04 1.4660 0.9516 4.88 -2.08 -83.52 3.25

0.06 1.4668 0.9536 4.87 -1.14 -60.67 4.39

0.08 1.4676 0.9554 4.85 -0.65 -45.35 5.36

0.10 1.4680 0.9571 4.84 -0.32 -34.11 6.30

RVG-3

0.01 1.4548 0.9488 4.97 -3.77 -290.39 2.88

0.02 1.4568 0.9491 4.96 -1.61 -115.00 4.25

0.04 1.4584 0.9520 4.94 -0.80 -93.36 5.77

0.06 1.4604 0.9527 4.92 -0.17 -44.04 7.21

0.08 1.4612 0.9543 4.91 0.12 -29.74 8.51

0.10 1.4628 0.9565 4.88 0.19 -26.30 8.96

RVG-4

0.01 1.4536 0.947 4.99 -1.15 -101.02 4.63

0.02 1.4556 0.9474 4.98 -0.46 -31.06 5.49

0.04 1.4572 0.9478 4.97 0.40 16.39 8.27

0.06 1.4588 0.9484 4.95 0.65 30.41 9.84

0.08 1.4604 0.9489 4.94 0.79 40.02 10.97

0.10 1.4624 0.9505 4.91 0.74 35.17 10.82

RVG-5

0.01 1.4536 0.9494 4.98 -3.61 -353.43 3.23

0.02 1.4548 0.9517 4.96 -2.37 -256.60 4.12

0.04 1.4568 0.953 4.94 -0.81 -119.63 6.07

0.06 1.4580 0.9555 4.92 -0.41 -92.97 7.17

0.08 1.4592 0.9577 4.90 -0.17 -74.31 8.02

0.10 1.4612 0.9597 4.88 -0.05 -59.92 8.39

Tables 1 and 2 show the density, velocity and isen-tropic compressibility of studied compounds in both the solvents. Figure 2 shows the variation of sound velocity (u) of pyrimidines in DMF and DMSO at

298.15 K. It is observed that velocity increases with increasing concentration of pyrimidines in both the solvents while the adiabatic compressibility decreases with increasing concentration as shown in Fig. 3. The

ADIABATIC COMPRESSIBILITIES OF SOME SYNTHESIZED DERIVATIVES

867

Table 2. Sound velocities, densities, adiabatic compressibilities, apparent molar adiabatic compressibilities, apparent molar volume and solvation number of pyrimidines in DMSO at T = 298.15 K

с, M u х 10 5, cm s 1 p, g cm 3 ks х 10 n, cm2 dyn 1 Фк х 10-8 Фу Sn

RVG-1

0.00 1.4824 1.0959 4.15 - - -

0.01 1.4856 1.0971 4.13 -1.18 -22.58 2.84

0.02 1.4868 1.0982 4.12 -0.59 -17.01 3.84

0.04 1.4916 1.0989 4.09 -0.33 21.39 4.12

0.06 1.4936 1.0998 4.07 -0.01 32.45 5.06

0.08 1.4964 1.1004 4.05 0.11 42.36 5.53

0.10 1.4976 1.1012 4.04 0.26 47.26 6.33

RVG-2

0.01 1.4844 1.0971 4.13 -0.95 -22.67 3.72

0.02 1.4872 1.0987 4.11 -0.28 -39.93 3.15

0.04 1.4904 1.0992 4.09 -0.13 14.19 4.16

0.06 1.4932 1.1005 4.07 0.04 21.28 4.63

0.08 1.4948 1.1017 4.06 0.19 26.83 5.31

0.10 1.4964 1.1023 4.05 -0.58 36.32 5.95

RVG-3

0.01 1.4832 1.0965 4.14 0.62 32.15 5.78

0.02 1.4852 1.0973 4.13 0.20 24.03 6.22

0.04 1.4860 1.0994 4.12 0.35 10.10 7.87

0.06 1.4876 1.1009 4.10 0.40 15.89 8.28

0.08 1.4904 1.101 4.08 0.48 35.71 8.36

0.10 1.4924 1.1026 4.07 0.46 34.72 8.31

RVG-4

0.01 1.4836 1.0974 4.14 -0.36 -50.00 4.72

0.02 1.4860 1.0982 4.12 -0.43 -17.19 4.08

0.04 1.4916 1.0992 4.08 -0.45 14.19 3.73

0.06 1.4908 1.0996 4.09 0.20 34.94 5.90

0.08 1.4928 1.101 4.07 0.24 34.80 6.24

0.10 1.4956 1.1027 4.05 0.20 32.68 6.13

RVG-5

0.01 1.4860 1.0969 4.12 -1.26 -4.35 2.66

0.02 1.4876 1.0985 4.11 -0.92 -30.66 3.29

0.04 1.4888 1.0996 4.10 -0.08 5.46 5.18

0.06 1.4904 1.1003 4.09 0.21 24.85 6.36

0.08 1.4920 1.1017 4.07 0.29 27.55 6.94

0.10 1.4964 1.1026 4.05 0.22 34.49 6.40

decrease in adiabatic compressibility is attributed to the fact that the dihydropyrimidines (DHPM) molecules in dilute solutions are considerably ionized and these ions are surrounded by a layer of solvent molecules firmly

bound and oriented toward the ions. The orientation of solvent molecules around the ions is attributed to the influence of the electrostatic field of the ions, which lowers the compressibility of the DHPMs solutions [4].

u x 10 5, cm s 1

(a)

1.4651- □

1.455

1.496

1.488

1.480

О л

X о

(b)

§

0.02

л Ъ

□ О

л х о

в

8

О □

8 А

0.06

ft

О

01П2А3Х4°5

О □

х

0.10 с, M

ks x 10 n, cm2 dyn 1

5.00

4.90

4.14

4.10

4.06

(a)

X

Я X

2 X

О 2 X

□ О S

□ □

1 □ 2 а 3 X 4 о 5 9

(b)

О д x

л 8

0.02

0.06

X 6

□ О

л 8

5

х 6

□ О

$

0.10 с, M

Fig. 2. Variation of sound velocity (u) of DHPMs against concentration in (a) DMF and (b) DMSO; (1) RVG-1, (2) RVG-2, (3) RVG-3, (4) RVG-4, (5) RVG-5.

Fig. 3. Variation of isentropic compressibility (ks) of DHPMs against concentration in (a) DMF and (b) DMSO; (I)-(5) see Fig. 2.

The results of adiabatic compressibility have also been explained in terms of Bachem's equation [5]

ks = ks1 + Ac + Bc3/2,

(2)

where A and B are constants, с is the molar concentration of DHPMs, and ks and ks1 are the adiabatic com-

pressibilities of the solution and solvent respectively. The constants A and B have been determined from the intercept and slope of the plots of (ks — ks1)/c vs. c1/2 and are recorded in Table 3. It is observed that for all the compounds in both the solvents, A values are negative whereas B values are positive. The negative A

Table 3. Bachem's, Gucker's and Masson's constants of Pyrimidines in DMF and DMSO at 298.15 K

Compounds -A x 1011, dyn-1 cm-3 mol-1 B x 1011, dyn-1 cm-1/2 mol-3/2 10s, dyn 1 mol 1 Sk x 108, dyn-1 cm-3/2 mol-3/2 -ф^, cm3 mol 1 Sv, cm3 mol 1

DMF

RVG-1 4.629 8.7972 3.3025 8.8136 252.31 1804.3

RVG-2 4.8972 10.098 39784 11.617 113.15 817.66

RVG-3 3.7944 8.242 3.0021 10.745 134 1205.1

RVG-4 2.7633 6.2117 2.0558 10.839 6.4976 590.72

RVG-5 3.6667 7.7383 2.0841 6.5901 155.94 988.95

DMSO

RVG-1 2.742 5.6196 1.3065 5.0384 25.027 819.51

RVG-2 1.8766 2.5988 0.9653 3.5489 0.5184 359.72

RVG-3 1.3760 2.4847 0.0474 1.8949 7.6917 419.02

RVG-4 1.3568 1.3155 0.6134 2.9043 57.559 1632.2

RVG-5 2.8254 7.1072 2.1338 9.1884 10.126 450.73

ADIABATIC COMPRESSIBILITIES OF SOME SYNTHESIZED DERIVATIVES

869

and positive B suggests solute—solvent interactions in the system.

Further, the apparent molar compressibility (Ok) were calculated by the following equation [6]

Ok = [(poks - pKsl)(1000/cpo)] + [ks1M2/p

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