C6H14 binary solvent systems

Spectrochimica Acta Part A 60 (2004) 3119–3123

Solvent effect on infrared spectra of methyl methacrylate in CCl4 /C6H14 , CHCl3/C6H14 and C2 H5OH/C6H14 binary solvent systems Jianping Zheng, Qing Liu∗ , Hui Zhang, Danjun Fang Department of Chemistry, Zhejiang University, Hangzhou 310027, People’s Republic of China Received 1 January 2004; accepted 27 February 2004

Abstract Research of methyl methacrylate (MMA) in three kinds of binary solvent systems (CCl4 /C6 H14 , CHCl3 /C6 H14 and C2 H5 OH/C6 H14 ) on the infrared (IR) spectra was reported. Two types of carbonyl stretching vibration bands for MMA in CHCl3 /C6 H14 or C2 H5 OH/C6 H14 mixtures were found with the changing of the mole fraction of CHCl3 (XCHCl3 ) or C2 H5 OH (XC2 H5 OH ). The carbonyl stretching vibration bands at lower frequencies in the above two mixtures were attributed to the formation of hydrogen bonding between MMA and CHCl3 or C2 H5 OH. While in CCl4 /C6 H14 mixtures there was only one type of carbonyl stretching vibration band of MMA. Good linear correlations between the frequencies of C=O or C=C stretching vibration band of MMA and XCCl4 , XCHCl3 or XC2 H5 OH were found, respectively. The solute–solvent interactions in the three different binary solvent systems were discussed in detail. © 2004 Elsevier B.V. All rights reserved. Keywords: Methyl methacrylate; Binary solvent systems; Infrared spectra; Carbonyl stretching vibration band; Hydrogen bonding

1. Introduction The nature and extent of solute–solvent interactions are able to affect various properties of some compounds in different solvent systems. And infrared (IR) spectroscopy study provides an important tool for the qualitative study of such interactions [1–11]. The study of tetraalkylurea in carbon tetrachloride and/or hexane and in chloroform and/or hexane 1% solvent systems with IR was reported [12]. It indicated that the type of intermolecular complexes formed was dependent upon the mol% CCl4 /C6 H14 or mol% CHCl3 /C6 H14 and the steady decrease in the frequency of the carbonyl stretching vibration band (νC=O ) was attributed in part to the bulk dielectric effects of the solvent system. In this paper, IR spectra are employed to investigate the solute–solvent interaction of MMA in three binary solvent systems: CCl4 /C6 H14 , CHCl3 /C6 H14 and C2 H5 OH/C6 H14 . The stretching vibration bands of C=O (νC=O ) and C=C ∗ Corresponding author. Tel.: +86-571-8795-1289; fax: +86-571-8795-1995. E-mail address: [email protected] (Q. Liu).

1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2004.02.024

(νC=C ) for MMA are studied, respectively. It shows that the frequencies of the νC=O is quite sensitive to the solvent. Methyl methacrylate (MMA) has a variety of commercial applications. It is the monomer of poly(methyl methacrylate) (PMMA) that is a kind of thermoplastics used in industry and dentistry [13]. The polymerization behaviour of MMA is influenced by not only the polymerization conditions such as the reaction temperature, time and catalyst, but also the properties of the solvent used in the reaction [14] due to the interaction between the solute and the solvent. In previous work, solvent effect on infrared spectra of MMA in 20 different organic solvents were undertaken to investigate the solute–solvent interactions. The frequencies of νC=O for MMA were correlated with the solvent properties such as the KBM parameter, the solvent acceptor number (AN) and the linear solvation energy relationship (LSER). The results showed that the correlation between KBM and the frequencies of νC=O for MMA was not good while there was a better correlation with LSER than the correlation with AN.

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2. Experiment

Table 1 Infrared data for MMA in CCl4 /C6 H14 binary solvent system

2.1. Spectroscopy

No.

XCCl4

νC=O (cm−1 )

νC=C (cm−1 )

1 2 3 4 5 6 7 8 9 10 11

0.000 0.131 0.253 0.367 0.474 0.575 0.670 0.760 0.844 0.924 1.000

1731.24 1730.74 1730.37 1729.81 1729.37 1728.90 1728.18 1727.64 1727.07 1726.57 1726.00

1640.85 1640.73 1640.66 1640.54 1640.47 1640.35 1640.24 1640.14 1640.05 1639.96 1639.82

Infrared spectra were recorded on a Nicolet Nexus 670 FTIR spectrometer with a Ge/KBr beamsplittor and a DTGS detector. For all spectra 40 scans recorded at 1 cm−1 resolution were averaged and 1.0 mm pathlength NaCl cells was used. The spectra of pure solvents were recorded under the same conditions and were stored in the computer. 2.2. Preparation of solutions All solvents used were of analytical purity. The binary solvent system was prepared by volume using micro syringes. The volume fractions of CCl4 , CHCl3 and C2 H5 OH in the cosolvents were 0.0, 0.2, 0.4, . . . , 1.0, respectively. The concentrations of the solution ranged from 1.0 × 10−5 to 5.0 × 10−5 mol l−1 .

1726.00 cm−1 with the increase of XCCl4 and there is a good linear correlation between νC=O and XCCl4 : νC=O = −5.28XCCl4 + 1731.60, R2 = 0.98, SD = 0.24 cm−1

(1)

The wavenumber displacement of νC=O for MMA in CCl4 /C6 H14 mixture solvents can be explained in terms of the dipole-induced dipole interaction between the C=O group of MMA and the CCl4 . MMA is a molecule possessing a permanent dipole moment µ, which can induce a dipole moment in a neighbouring non-polar molecule. Thus, the attraction exists between the two partners. The bigger the induced dipole moment will be the larger the polarizability of the non-polar molecule experiencing the induction of the permanent dipole is. Because the polarizability of CCl4 is more than the one of C6 H14 , the dipole-induced dipole force between the C=O group of MMA and the solvents increases when CCl4 is gradually added to the solution of MMA in C6 H14 . As a result, the frequencies of νC=O are shifted to lower wavenumbers (νC=O = 5.24 cm−1 ) as XCCl4 increases.

3. Results and discussion In the three different binary solvent systems, the C=O stretching vibration band of MMA appears in the region of 1731.30–1712.21 cm−1 . The C=C stretching vibration band of MMA appears in the region of 1640.94–1638.80 cm−1 . Two remarkable bands of the νC=O for MMA are observed in CHCl3 /C6 H14 or C2 H5 OH/C6 H14 mixtures. It means that two species of νC=O for MMA coexist in the two systems, respectively. 3.1. In CCl4 /C6 H14 binary solvent system The wavenumbers of νC=O and νC=C for MMA measured in CCl4 /C6 H14 binary solvent system are listed in Table 1. There is only one C=O absorption band in the system. Fig. 1 shows the plots of νC=O and νC=C for MMA versus the mole fraction of CCl4 (XCCl4 ) in CCl4 /C6 H14 mixtures. In Fig. 1a, the νC=O of MMA shifts from 1731.24 to

νC=C = −1.01XCCl4 + 1640.90, R2 = 0.98, SD = 0.04 cm−1

(2)

1733 1732

1641

-1

1730

cm

cm

-1

1731

c= c

1728

1640

U

U

c= o

1729

1727 1726 1639

0.0

(a)

0.2

0.4

0.6

0.8

1.8

mole fraction of CCl4 ( XCCl4)

0.0

(b)

0.2

0.4

0.6

0.8

mole fraction of CCl4 (XCCl4 )

Fig. 1. Plots of νC=O and νC=C for MMA vs. the mole fraction of CCl4 in CCl4 /C6 H14 mixtures.

1.0

J. Zheng et al. / Spectrochimica Acta Part A 60 (2004) 3119–3123 Table 2 Infrared data for MMA in CHCl3 /C6 H14 binary solvent system No.

XCHCl3

νC=O (cm−1 )

1 2 3 4 5 6 7 8 9 10 11 12 13

0.000 0.152 0.222 0.288 0.410 0.519 0.618 0.708 0.791 0.829 0.866 0.936 1.000

1731.30 1730.54 1729.86

Band A

νC=C (cm−1 ) Band B 1640.94 1640.47 1640.36 1640.30 1640.19 1640.00 1639.62 1639.55 1639.31 1639.27 1639.15 1639.12 1638.81

1723.11 1722.81 1722.39 1721.92 1721.52 1721.09 1720.72 1720.29 1720.06 1719.31 1719.02 1718.83

The correlation result between νC=C and XCCl4 is shown in Eq. (2). Comparing to Eq. (1), the slope of Eq. (2) is smaller. The value of νC=C is only 1.03 cm−1 (Fig. 1b). It is suggested that the red-shift of C=C group for MMA is caused by the weak bulk dielectric solvent effect of CCl4 /C6 H14 mixture solvents. The dielectric constant (ε) of C6 H14 is 1.88 and the one of CCl4 is 2.23. With the increase of XCCl4 , the bulk dielectric solvent effect of the binary solvent system slightly enhances. So, the wavenumbers of νC=C for MMA are shifted slowly to lower frequencies. 3.2. In CHCl3 /C6 H14 binary solvent system The frequencies of νC=O and νC=C for MMA measured in the mixture solvents of CHCl3 /C6 H14 are listed in Table 2. The dependence of the νC=O for MMA on the mole fraction of CHCl3 (XCHCl3 ) in CHCl3 /C6 H14 mixtures is illustrated in Fig. 2. In pure C6 H14 solvent, MMA exhibits one well-resolved C=O stretching vibration band (band A) at about 1731.30 cm−1 . It belongs to the free monomeric state

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of C=O group for MMA since C6 H14 is an inert solvent and there is no remarkable interaction in such a dilute C6 H14 solution. When CHCl3 is added to a solution of MMA in C6 H14 , band A shifts gradually to lower wavenumbers and a new absorption band of C=O group (band B) appears at about 1723.11 cm−1 when XCHCl3 is 0.152. Because CHCl3 is a polar solvent, such as a Lewis acid, which can donate a proton to form a hydrogen bonding with the oxygen atom of the C=O group, the red-shift of the C=O stretching vibration band will take place. The band B can be assigned to the hydrogen bonding species between the C=O group of MMA and CHCl3 . With the increase of XCHCl3 , band A rapidly becomes less intense and disappears when XCHCl3 is more than 0.222. While band B is shifted to lower wavenumbers until the solvent is pure CHCl3 , it means that most C=O groups of MMA form hydrogen bond with CHCl3 , and the free monomeric C=O group cannot exist in the binary solvents as the concentration of CHCl3 increases. Fig. 3 shows the plot of νC=C for MMA versus the mole fraction of CHCl3 in CHCl3 /C6 H14 binary solvent system. The correlation is shown as: νC=C = −1.96XCHCl3 + 1640.88, R2 = 0.98, SD = 0.08 cm−1

Similar to the shifting character of νC=C in CCl4 /C6 H14 mixtures, the νC=C of MMA in CHCl3 /C6 H14 binary solvents is also shifted slowly to lower wavenumbers by the weak bulk dielectric effect with the concentration of CHCl3 in cosolvents increases. (νC=C = 2.13 cm−1 ). 3.3. In C2 H5 OH/C6 H14 binary solvent system Table 3 lists the wavenumbers of νC=O and νC=C for MMA measured in the mixtures of C2 H5 OH/C6 H14 . There are two kinds of νC=O for MMA coexisting in the

1 7 3 4 .0 1 7 3 2 .5

band A

1 7 3 1 .0 1 7 2 9 .5

U

c =o

cm

-1

1 7 2 8 .0 1 7 2 6 .5 1 7 2 5 .0 1 7 2 3 .5

band B

1 7 2 2 .0 1 7 2 0 .5 1 7 1 9 .0 0 .0

0 .2

(3)

0 .4

0 .6

0 .8

1 .0

m o le fra c tio n o f C H C l 3 ( X C H C l3 ) Fig. 2. A plot of νC=O for MMA vs. the mole fraction of CHCl3 in CHCl3 /C6 H14 mixtures.

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J. Zheng et al. / Spectrochimica Acta Part A 60 (2004) 3119–3123

1641.0

1640.0 1639.5

U

C=C

cm

-1

1640.5

1639.0 1638.5 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

mole fraction of CHCl3 ( XCHCl3) Fig. 3. A plot of νC=C for MMA vs. the mole fraction of CHCl3 in CHCl3 /C6 H14 solution.

binary solvents or pure C2 H5 OH solvent except for in pure C6 H14 solvent (Fig. 4). The higher wavenumber band in the region of 1731.30–1727.48 cm−1 (band A) is more intense than the lower wavenumber band in the region of 1717.51–1712.21 cm−1 (band B) all along the whole course. Fig. 5 shows a plot of νC=O versus the mole fraction of C2 H5 OH (XC2 H5 OH ) in C2 H5 OH/C6 H14 mixtures. Both band A and band B shift from high wavenumber to lower one as XC2 H5 OH increases. The corrections between νC=O of the two bands and XC2 H5 OH are shown in Eqs. (4) and (5), respectively. Because the hydroxyl group of C2 H5 OH is not only a hydrogen bonding acceptor, but also a hydrogen bonding donor, the C2 H5 OH molecules can self-associate to become a big molecule. So, there are two types of alcohol molecules in the C2 H5 OH/C6 H14 mixtures, one of them is the associated C2 H5 OH molecule, and the other is the non-associated.

Table 3 Infrared data for MMA in C2 H5 OH/C6 H14 binary solvent system No.

XCHCl3

νC=C (cm−1 ) Band A

Band B

1 2 3 4 5 6 7 8 9 10 11

0.000 0.199 0.359 0.490 0.599 0.691 0.771 0.839 0.900 0.950 1.000

1731.30 1730.79 1730.52 1730.33 1729.90 1729.51 1729.10 1728.67 1728.24 1727.85 1727.48

1717.51 1716.33 1715.68 1714.65 1714.37 1713.68 1713.43 1713.06 1712.51 1712.21

0.34

band A

0.30

0.22 0.18 0.14

Absorbance

0.26

band B

0.10 0.06

0.02

1800

1700

1600

Wavenumbers (cm-1) Fig. 4. The IR spectrum of νC=O for MMA in C2 H5 OH/C6 H14 mixtures (XC2 H5 OH = 0.691).

νC=C (cm−1 )

1640.94 1640.56 1640.33 1640.20 1640.15 1640.04 1639.93 1639.83 1639.68 1639.54 1639.43

J. Zheng et al. / Spectrochimica Acta Part A 60 (2004) 3119–3123

It is also due to the weak bulk dielectric effect of the solvent system. The correction between νC=C and XC2 H5 OH is shown in Eq. (6):

1732 1730 1728

band A

-1

1726

νC=C = −1.36XC2 H5 OH + 1640.90,

cm

1724

R2 = 0.97, SD = 0.08 cm−1

1722

c =o

3123

1720

(6)

U

1718

band B

1716

4. Conclusions

1714 1712 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

mole fraction of C2H5O H ( X C 2 H 5 O H ) Fig. 5. A plot of νC=O for MMA vs. the mole fraction of C2 H5 OH in C2 H5 OH/C6 H14 mixtures.

When C2 H5 OH is added to the solution of MMA in C6 H14 , the non-associated C2 H5 OH can donate a proton to form a hydrogen bonding with the oxygen atom of the C=O group for MMA owing to C2 H5 OH being a protic solvent. The corresponding band (band B) appears at lower wavenumbers. However, it is difficult to produce the hydrogen bonding between the associated C2 H5 OH molecules and the C=O group because of the steric hindrance of the associated alcohols. The interaction between the C=O group of MMA and associated alcohols can be explained by dipole–dipole force, which corresponds to band A at higher wavenumbers. Moreover, for its own weak steric hindrance, the majority of C2 H5 OH molecules can associate by themselves in the mixture solvents. So, band A is more intense than band B.

In the infrared spectra study of MMA in CCl4 /C6 H14 , CHCl3 /C6 H14 and C2 H5 OH/C6 H14 binary solvent systems, three kinds of solvent-solute interactions were observed. They were the dipole-induced dipole interaction, the hydrogen bonding and the bulk dielectric solvent effect. In CCl4 /C6 H14 binary solvents, the wavenumber displacement of νC=O for MMA would be explained in terms of the dipole-induced dipole interaction between the C=O group and the CCl4 . In CHCl3 /C6 H14 mixture solvents, there were two kinds of νC=O for MMA. Band A belonged to the free monomeric state of C=O group for MMA and the lower wavenumber band (band B) could be assigned to the hydrogen bonding species between the C=O group and CHCl3 . In C2 H5 OH/C6 H14 cosolvents, band A and band B were corresponded to the C=O of MMA interacting with the associated alcohols and non-associated alcohols, respectively. On the other hand, the dipole–dipole force between the solvents and MMA made the νC=O red-shift in the latter two binary solvents. It is similar that the νC=C of MMA was shifted slowly to lower wavenumbers by weak bulk dielectric solvent effect.

νC=O (A) = −3.75XC2 H5 OH + 1731.74, R2 = 0.93, SD = 0.36 cm−1

(4)

νC=O (B) = −6.47XC2 H5 OH + 1718.74, R2 = 0.99, SD = 0.13 cm−1

(5)

The plot of νC=C for MMA versus XC2 H5 OH is shown in Fig. 6. The value of red-shift of νC=C (νC=C ) is 1.51 cm−1 . 1641.0 1640.8 1640.6 1640.4

U

c =c

cm

-1

1640.2 1640.0 1639.8 1639.6 1639.4 1639.2 1639.0 0 .0

0 .2

0 .4

0 .6

0 .8

1 .0

mole fraction of C2H5OH (XC2H5OH) Fig. 6. A plot of νC=C for MMA vs. the mole fraction of C2 H5 OH in C2 H5 OH/C6 H14 mixtures.

Acknowledgements The Analysis and Measurement Foundation of Zhejiang Province, P.R. China supported this work. References [1] U. Mayer, Pure Appl. Chem. 51 (1979) 1697. [2] J.B.F. Engberts, A. Perjéssy, M.J. Blandamer, J. Chem. Soc., Faraday Trans. 89 (1993) 4199. [3] R.A. Nyquist, R. Streck, Vib. Spectrosc. 8 (1994) 71. [4] A. Perjéssy, J.B.F.N. Engberts, Monatshefte für Chemie 126 (1995) 871. [5] R.A. Nyquist, C.L. Putzig, T.D. Clark, Vib. Spectrosc. 12 (1996) 81. [6] R.A. Nyquist, R. Streck, G. Jeschek, J. Mol. Struct. 377 (1996) 113. [7] I. Bratu, R. Grecu, R. Constantinescu, T. Iliescu, Spectrochim. Acta Part A 54 (1998) 501. [8] D.J. Fang, J.P. Zheng, Univ. Sci. 3 (2002) 559. [9] D.J. Fang, J.P. Zheng, J. Mol. Struct. 608 (2002) 253. [10] D.J. Fang, J.P. Zheng, Spectrochim. Acta Part A 59 (2003) 471. [11] D.J. Fang, J.P. Zheng, Spectrochim. Acta Part A 60 (2004) 397. [12] R.A. Nyquist, D.A. Luoma, Appl. Spectrosc. 45 (1991) 1497. [13] U. Kedjarune, P. Leggat, Occu. Health Ind. Trans. 89 (2000) 4199. [14] W.Q. Hu, J.Q. Sun, Z.D. Pan, Z.L. Wu, Xu, J. Zhejiang Univ. Sci. 1 (2000) 157.