Synthesis and spectral studies of some N -[( E )-phenylmethylidene]benzenesulfonamides

A series of some N -[( E )-phenylmethylidene]benzenesulfonamide derivatives have been synthesised using solid SiO 2 -H 3 PO 4 catalyst under solvent free conditions in microwave irradiation. The synthesised E -N-benzene sulfonilimines purities have been verified by their physical constants and spectroscopic data. The spectral frequencies are correlated with Hammett substituent constants, F and R parameters using linear regression analysis. From the results of statistical analysis the effect of substituents on the group frequencies will be discussed.

Organic Chemists and researcher have paid more attention to green synthesis, due to the operational simplicity, lesser times, high yields, easy handling procedure and less hazardous to reaction and environment. The spectroscopic data is useful for analysis ground state molecular equilibration and configuration of organic molecules [58][59][60][61]. Also these findings were carried out via spectral correlations. The spectral group frequencies were correlated various substituent constants and F and R parameters gave the effects of the substituents on the group frequency of the corresponding molecule.
This type of study was studied only in ketones, esters, imines, acyl halides, pyrazolines, unsaturated aldehydes and acids [62][63][64][65][66]. With a view to above, there is no report available in the literature for solvent free synthesis and the study of effects of substituent on the group frequencies of some E-N-benzene sulfonilimines by SiO 2 -H 3 PO 4 catalyzed condensation of aldehydes and sulphonamides. Therefore the authors have taken efforts to synthesis of some E-N-benzene sulfonilimines and studied the spectral correlations on the specified group frequencies using Hammett correlation equation.

1. Materials and Methods
All chemicals used were purchased from Sigma-Aldrich and E-Merck chemical companies. Infrared spectra (KBr, 4000-400 cm -1 )were recorded on AVATAR-300 Fourier transform spectrophotometer. The NMR spectra of all E-N-benzene sulfonilimines were recorded in INSTRUM AV300 NMR spectrometer operating at 500 MHz for 1 H and 125. 46 MHz for 13 C spectra in DMSO solvent using TMS as internal standard. Mass spectra were recorded on a SIMADZU GC-MS2010 Spectrometer using Electron Impact (EI) techniques.

Synthesis of SiO 2 -H 3 PO 4 catalyst
The SiO 2 -H 3 PO 4 catalyst was prepared by procedure published in literature [55].

3. Synthesis of E-N-benzene sulfonilimines
To an appropriate mixture of substituted benzaldehydes (2 mmol), benzene sulphonamide (2 mmol) and 0.5 g of SiO 2 -H 3 PO 4 were taken in 50 mL glass beaker and covered with lid. This mixture was subjected to microwave heating for 5-8 minutes at 650 W (Samsung GW73BD microwave oven, 100-750 W, 230 V A/C, 2450 MHz). The completion of the reaction was monitored by thin layer chromatography. After completion of reaction, dichloromethane (20 mL) was added, followed by simple filtration.

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The pure product was obtained by the evaporation of dichloromethane and recrystallization with ethanol. The yields of the E-N-benzene sulfonilimines are more than 90 %. The purities of these E-N-benzene sulfonilimines were persuade by their physical constants, IR, 1 H, 13 C NMR and Mass spectral data. Analytical and mass spectral data are presented in Table 1.   [33] 290[M + ]

1. Spectral linearity
In the present study the Hammett spectral linearity of these synthesised E-N-benzene sulfonilimines has been studied by evaluating the substituent effects [61][62][63][64][65][66] on the group frequencies. The assigned spectroscopic data of all E-N-benzene sulfonilimines such as absorption infrared carbonyl stretches of νC=N, νS=O, (cm -1 ), NMR chemical shifts δ(ppm) of CH, C=N have been assigned and these data are correlated with various substituent constants.

1. 1. IR spectral study
The assigned C=N and S=O frequencies (cm -1 ) of synthesised E-N-benzene sulfonilimines of present study are tabulated in Table 2. These data have been correlated with Hammett substituent constants [55][56][57][58][59][60][61][62][63][64][65][66] and Swain-Lupton constants [67] and are presented in Table 3. In this correlation the structure parameter Hammett equation employed is as shown in the following equation: Where ν is the carbonyl frequencies of substituted system and ν 0 is the corresponding quantity of unsubstitued system; σ is a Hammett substituent constant, which in principle is characteristics of the substituent and ρ is a reaction constant which is depend upon the nature of the reaction. The results of single parameter statistical analysis of νC=N stretches with Hammett σ and σ + substituent constants gave satisfactory correlations. The Hammett σ I , σ R and R parameters were satisfactorily correlated with νC=N stretches excluding H, 2-Cl, 2-F and 4-CH 3 substituents. If these substituents were included in the correlation, the correlations were reduced significantly. The field effect components of the substituents were fail in correlation. All correlations gave positive ρ values. This may mean that the normal substituent effect operates in all E-N-benzene sulfonilimines. The failure in correlation is due the conjugation between the substituent and the C=N group in all E-N-benzene sulfonilimines as shown in Figure 1.
The correlation of νC=S stretches with Hammett σ, σ + and σ I substituent constants gave satisfactory r values [σ (r = 0.906), σ + (r = 0.906) and σ I (r = 0.903)] excluding H, 3-Br and 4-CH 3 substituents. If these substituents were included in the correlation, the correlations were reduced significantly. The resonance and field effect components of the substituents were fail in correlations. While seeking the ρ values, all correlation gave positive ρ values

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and it is evident for the normal substituent effects operates in all systems. The failure in correlation is due the conjugation between the substituent and the C=N group in all E-Nbenzene sulfonilimines as shown in Figure 1. In view of the inability of some of the  constants to produce individually satisfactory correlations, it was thought that worthwhile to seek multiple correlations involving either  I and  R constants or Swain-Lupton's [67]

1. 2. 1 H NMR spectral study
Deuterated dimethylsulphoxie was used for recording the 1 H NMR spectra of synthesized E-N-benzene sulfonilimines employing tetramethylsilane (TMS) as internal standard. The CH protons signals of the E-N-benzene sulfonilimines were obtained as a singlet and assigned from their spectra. The assigned CH proton chemical shifts δ(ppm) of all E-N-benzene sulfonilimines were presented in Table 2.
International Letters of Chemistry, Physics and Astronomy Vol. 13 Table 3. Results of statistical analysis of infrared absorptions (ν, cm -1 ) and NMR chemical shifts (δ, ppm) of E-N-benzene sulfonilimines with Hammett σ, σ + , σ I , σ R and F and R parameters. In nuclear magnetic resonance spectra, the proton or the 13 C chemical shifts (δ) depends on the electronic environment of the nuclei concerned. The assigned vinyl proton chemical shifts (ppm) have been correlated with reactivity parameters using Hammett equation in the form of where δ 0 is the chemical shift of unsubstitued ketones.
Application of Swain-Lupton's [67] treatment to the relative chemical shifts (δ,ppm) of CH with F and R values is successful with resonance, inductive effect generates the multi regression equations 7-8.
The C=N chemical shifts (ppm) gave satisfactory correlation with Hammett substituent constants excluding 3-Br, 2-F and 4-CH 3 substituents. All correlations produced positive ρ values. This means that the normal substituent effect operates in all correlations. The F and R parameters were fail in correlation. This is due to reasons stated earlier with the resonance conjugative structure shown in Figure 1.

CONCLUSIONS
We have synthesised more than 90 % yield of some E-N-benzene sulfonilimines using a solid SiO 2 -H 3 PO 4 acid catalyst by solvent free condensation of benzene solfonyl chloride and substituted benzaldehydes under microwave irradiation. The effects of substituent on the group frequencies (ν, cm -1 ) such as C=N, S=O and the chemical shifts (δ, ppm) of CH and C=N all the E-N-benzene sulfonilimines have been studied.