CHAPTER II SYNTHESIS AND CHARACTERIZATION BY IR, PMR, …shodhganga.inflibnet.ac.in/bitstream/10603/18252/8/08_chapter2.pdf · 12 CHAPTER II SYNTHESIS AND CHARACTERIZATION BY IR,

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CHAPTER II

SYNTHESIS AND CHARACTERIZATION BY IR, PMR, 13C

NMR, MASS, UV STUDIES OF BENZOINS AND ITS

DERIVATIVES

2.1. INTRODUCTION

All the substituted benzoins and its derivatives were synthesized using

procedure reported in the literature [1]. All the reagents used for synthesizing the

title compound were of AR grade and the solvents used were commercial products

of the highest available purity. The products were purified by column

chromatography or by PTLC using silica gel [60-120 mesh S.D fine]. Solvents were

purified by the procedures given in ‘Vogel’. High boiling liquids were purified by

distillation under reduced pressure and solid substances by recrystallisation using

suitable solvents [2].

The qualitative analysis on the synthesized compounds has been carried

out using Mass spectrometer to confirm the molecular weight and molecular formula

of the compound. Infrared spectroscopy is used to identify the functional groups of

the synthesized compounds. KBr pellet technique was employed. NMR

spectroscopy is used to determine the molecular structure based on the chemical

environment of the magnetic nuclei like 1H, 13C, 31P etc., even at low concentrations.

This is one of the most powerful non-destructive techniques in elucidating the

molecular structure of the biological and chemical compounds. The optical

absorption range has been carried out to know the suitability of synthesized single

crystals for optical applications.

2.2. SYNTHESIS OF 4 -METHOXY BENZOIN [4MB]

The 4MB was synthesized by benzoin condensation using 4 g of KCN

dissolved in 75 cc of water in a one litre flask. 6.8 g [0.05 mole] of p-anisaldehyde,

13

7 g [0.05 mole] of benzaldeyde and 75 cc of 95% ethanol was added into the flask.

The mixture formed a solution at the boiling temperature and was refluxed for one

and half hours. Steam was then passed through the solution until all the alcohol and

nearly all the unreacted aldehyde were removed. The condensed water was decanted

from the product and latter set aside for crystallization. The product was then

pressed as free as possible from oily material on a suction funnel and washed with

cold alcohol. About 8.1 g [yield: 65%] of crude product was obtained. The crude

mixture was dissolved in alcohol and allowed to crystallize slowly. The 4MB

crystallized out as lumps of long needle. Melting point of the compound was found

to be 110˚C. The yield of pure 4-methoxy benzoin amounted to 50% of the expected

product [Scheme 2.1].

Scheme.2.1 Schematic representation of synthesis of 4MB

Synthesized compound was purified by the successive recrystallization

process. In order to improve the purity of the synthesized compound, the basic

material was purified thoroughly. The purification of 4MB was done by repeated

crystallization and the purity of the material was monitored by TLC and measuring

its melting point in each time.

2.2.1 Mass spectral analysis of 4MB

The results of mass spectral analysis [Table 2.1] confirm the molecular

weight [Fig.2.1] and molecular formula of the compound.

14

Figure 2.1. Mass spectra of 4MB

Table 2.1. Mass spectral fragmentation peaks for 4MB

Peaks Fragmentation 242.45 M+ 229.34 M+-CH3

205.7377 M+-OCH3 133.8113 [C6 H4- CO -OCH3]+ 106.0817 [-C6H5-CO+] 91.0843 Tropylium cation

2.2.2. FTIR Spectral Analysis of 4MB

The FTIR spectrum of the 4MB crystal was recorded in the frequency

region of 4000 cm-1- 400 cm-1. The FTIR spectrum of the 4MB shows the presence

of secondary alcoholic group with broad band around 3369 cm-1 attributed to the

–OH stretching modes. The bands around 3086 cm−1 in FTIR are assigned to the

aromatic C–H stretching modes. The aliphatic –CH stretching vibration is assigned

to the band at 2922 cm−1. The symmetric stretching mode of the carbonyl group

appears at 1715 cm−1 with very strong intensity in the FTIR spectrum. The aromatic

15

C = C symmetric stretching vibrations appear at1589 cm−1.The in-plane deformation

of C–OH appears around 1300-1294 cm−1 as a medium band in the FTIR. The –OH

out of plane deformation is observed as strong bands around 1000 cm−1 in concern

spectrum. The band at 1102 cm−1 in is assigned to the benzene ring deformation.

The band at 719 cm-1 is established the presence of disubstituted benzene ring. The

characteristic vibrational frequencies of the functional groups present in 4MB have

been compared to its parent molecule benzoin [Table 2.2]. Study of the spectrum of

the solid benzoin [Fig.2.2] differs from the spectrum of the same compound in

solution. In solution of different concentration it was observed that the intensity of

the carbonyl group absorption decreases and ultimately disappears in very high

dilution, while the intensity of –OH absorption increases. This clearly shows the

existence of equilibrium between a keto form and the enol form [Scheme 2.2].

'Ar

O

'C C

O

Ar

H

H

Enol form ( in solition) Keto form ( in solid)

C C

O

Ar Ar

OH H

Scheme 2.2. Keto-enol tautomerism exhibited by benzoin compound

Figure 2.2. IR spectra of 4MB in solid KBr

16

Table 2.2 Vibrational assignments of the 4MB

FTIR for 4MB [wave number cm-1] Band assignments

3369 cm-1 -OH stretching

3086 cm-1 Aromatic C-H stretching

2922 cm−1[w] Aliphatic C-H stretching

1715 cm-1[vs] Sym C=O stretching

1589 cm-1[vs] Aromatic sym C=C stretching

1300- 1294 cm−1[m] C-OH in plane deformation

1000 cm-1[s] -OH out of plane deformation

1102 cm−1 Presence of Benzene ring deformation

719 cm-1 Disubstituted benzene ring deformation

w:weak; vw:very weak, m:medium, s:strong, vs:very strong.

2.2.3. FT NMR Spectral Analysis of 4MB

The 1H NMR and 13C NMR spectra of the title compound are presented in

Fig.2.3 [a] and 2.3 [b] respectively. The chemical shifts are tabulated with the

assignments in Table 2.3. In the PMR spectrum of two signals appear in the range

of 2.9 and 3 ppm indicating the presence of a C–H and a –OH protons. A singlet at

3.8 ppm indicates the presence of methoxy group. Signals in the range of 6.8 to

7.48 ppm indicate the presence of aromatic protons. A multiplet around 8.01ppm

indicates the ene-diol –OH protons. In the 13C NMR the aliphatic carbon atoms

appear around 58 ppm, the aromatic carbon atoms appear in the range of 128 to

132 ppm. The signal at 167 ppm indicates the carbonyl carbon and that at 197 ppm

indicates the ene-diol carbon atom.

17

Figure 2.3. [a] 1H NMR of 4MB in acetone d6

Figure 2.3. [b] 13C NMR of 4MB in acetoned6

18

Table 2.3. The chemical shift in 1H NMR and 13C NMR spectrum of 4MB

Spectrum Signal [ppm] Group identification

2.9-3[d] C-H of –OH proton 1H NMR 3.8 [singlet] Methoxy group of 4MB

6.9 to 7.5 [multiplet] Aromatic protons

8.01 ppm enediol of –OH protons 13C NMR 58 ppm Aliphatic carbon atoms

128 to 138 ppm Aromatic carbon atoms

167 ppm Carbonyl carbon of 4MB

197 ppm Ene-diol carbon atom

2.2.4. UV-Visible Spectral Analysis of 4MB

From the absorbance spectrum, it was found that there is almost no

absorbance in the entire visible region. This indicates the crystal of 4MB is a

potential material for optical device fabrication [3]. Strong absorption band is

observed in UV-VIS region in the range of 320-400 nm with fine structure [Fig.2.4].

Another strong absorption appears between 210-300 nm. The former can be

attributed to the absorption due to benzene rings and the latter to the carbonyl group.

The crystal is transparent in the entire visible region which is key factor for this

compound as it is be exploited for NLO applications in the room temperature [4].

The absorption of UV and visible light involves promotion of the electron in the

n and orbital from the ground state to higher states. Very good optical absorbance

with the lower cut-off wavelength of 240 nm may be attributed to → * or

n→ * transitions. The absence of strong absorption in the region between

400 nm to 1000 nm in UV–Vis spectrum shows that the 4MB crystals are useful for

the SHG application.

19

Figure 2.4. UV spectra of 4MB

2.3. SYNTHESIS AND PURIFICATION OF 2-CHLORO-4′METHOXY

BENZOIN [2C4MB]

2C4MB compound was synthesized by benzoin condensation using 4 g of

KCN dissolved in 75 cc of water in a one litre flask. About 6.8 g [0.05 mole] of

4-methoxy benzaldeyde, 7 g [0.05 mole] of 2-chloro benzaldeyde and 75 cc of 95 %

ethanol was added into the flask. The mixture was formed a solution at the boiling

temperature and was refluxed for one and half hour. Steam was then passed through

the solution until all the alcohol and nearly all the unreacted aldehyde were

removed. The condensed water was decanted from the product and latter set aside

for crystallisation. The product was then pressed as free as possible from oily

material on a suction funnel and washed with cold alcohol. By this way about 14 g

[yield was 60 %] of crude product was obtained. The crude mixture was dissolved in

hot alcohol and allowed to crystallise slowly [Scheme 2.3]. The 2-chloro-4′-methoxy

benzoin crystallizing out as colourless, hexagonal crystals suitable for X-ray

diffraction study was obtained [5]. Melting point of the compound was found to be

84˚C. The yield of pure 2-chloro-4′methoxy benzoin is amounted to 60-70 % [6].

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CH

OH

C

O

Cl

OCH3

Cl

CHO OCH3OHC alc.KCN

4-methoxy benzaldehyde

2-chloro-4'methoxy benzoin

+

2-chloro benzaldehyde

Scheme 2.3. Schematic representation of 2C4MB

2.3.1. Mass spectral analysis of 2C4MB

Molecular weight and molecular formula of the compound has been

confirmed using mass spectroscopy. The various fragmentations are listed in the

Table 2.4. The molecular weight of the compound was determined by the FAB mass

spectrometer which shows a weak signal [molecular ion peak] [Fig.2.5] at m/z 277,

which confirms the assigned molecular mass of the 2C4MB. The fragments record,

intense signals at m/z 261.97, 246,166, 133, 103, 91 indicating the loss of methyl

group, methoxy, -C6H4Cl, MeO-C6H4CO, -C6H5CO and Tropylium cation

respectively.

Figure 2.5. Mass spectra of 2C4MB

21

Table 2.4. Mass spectral fragmentation peaks for 2C4MB

Peaks Fragmentation 277.092 M+

261.9 M+-CH3 246 M+-OCH3 166 M+-C6H4Cl 133 MeO-C6H4CO 103 [-C6H5-CO+] 91 Tropylium cation

2.3.2. FTIR spectral analysis of 2C4MB

The infrared spectrum of 2C4MB in solid KBr is shown in [Fig 2.6]. The

strong band at 1666 cm-1 corresponds to C=O stretching and shows sharp band at

3475 cm-1 corresponding to a -OH stretching frequency, indicating the presence of

intramolecular hydrogen bonding [7] and absorption at 3060 cm-1 corresponds to

aromatic C-H stretching. Absorption at 1569 cm-1 and at 1602 cm-1correspond to

aromatic C = C stretching frequency. The two weak absorptions at 979 cm-1 can be

assigned to C-H deformation of disubstituted benzene. [Table 2.5]

Figure 2.6. IR spectra of 2C4MB in solid KBr

22

Table 2.5. Vibrational assignments of the 2C4MB

FTIR for 2C4MB [wavenumber]

]]cm-1]

Band assignments





1569,1602 cm-1[vs] Aromatic sym C=C stretching

1268 cm−1[m] C-OH in plane deformation


1087 cm−1 and 1030 cm−1 Presence of Benzene ring

deformation w:weak; vw:very weak, m:medium, s:strong, vs:very strong.

2.3.3. FT NMR Spectral Studies of 2C4MB

The signals observed in the 1H NMR and 13C NMR spectra of the benzoin

under study [Figs. 2.7[a] and 2.7[b] are presented in Table 2.6. The spectra exhibit a

multiplet at 6.9-7.5 ppm for the hydrogens of the aromatic rings. The signal at

7.9 ppm represent the enolic -OH, while the signal at 3.8 ppm is due to the hydrogen

of the methoxy group.

13C NMR data for the title compound in MeOD shows that the signals for

the aromatic carbon atoms appear as a cluster at 113.59, 127.13, 127.23, 129.05,

129.56, 130.69, 133.02, 137.32 ppm, hydrogen bonded carbonyl carbon, at 164.18

ppm, [C-OH]. Signal at 196 ppm indicates the existence of ene-diol formation.

23

Figure.2.7. [a] 1H NMR spectra of 2C4MB

Figure 2.7. [b] 13C NMR of 2C4MB in MeOD

24

Table 2.6. The chemical shift in 1H NMR and 13C NMR spectrum of 2C4MB

Spectrum Signal [ppm] Group identification 1H NMR 3.8 [singlet] Methoxy group of 2C4MB

6.9 to 7.5[multiplet] Aromatic protons

7.9 ppm ene-diol of –OH protons 13C NMR 54 and 72 ppm Aliphatic carbon atoms


164 ppm Carbonyl carbon of 2C4MB

196 ppm ene-diol carbon atom

2.3.4. UV-Visible Analysis of 2C4MB

The optical absorption spectrum of the grown crystals in ethanol was

recorded from 200 nm to 800 nm and the absorption spectrum is shown in Fig. 2.8.

From the absorption spectrum, it is found that there is a very low absorbance in the

entire visible region. The absorption of UV and visible light involves the promotion

of the electron in π → π * or n → π * transitions from the ground state to higher

energy states. A very weak absorption between 250 nm and 290 nm can be attributed

to π → π* transitions. The absorption around 300 nm indicates n → π* strong

vibrational fine structure. The absence of strong absorption in the region from

400 nm to 1000 nm in UV-Visible spectrum shows that the 2C4MB crystals are

useful for SHG applications. This indicates that the crystals of 2C4MB are potential

material for optical device fabrication.

25

Figure.2.8. UV spectra of 2C4MB

2.4. SYNTHESIS AND PURIFICATION BENZOIN [BEN]

3L round-bottomed flask fitted with a reflux condenser. About 60 cc. of

95 % alcohol are placed in. 50 cc. of water, 50 g. [47.6 cc., 0.47 moles] of pure

benzaldehyde and 5 g. of potassium cyanide [96–98 %] added into the flask. The

mixture is then heated and kept boiling for one and half an hour. In the course of

about twenty minutes, crystals begin to separate from the hot solution. At the end of

the thirty minutes, the solution is cooled, filtered with suction, and washed with a

little water. 45 – 46 g [90-92 % of theoretical amount] yield of a dry crude benzoin,

which is light yellow, was obtained. To get completely pure benzoin, the crude

substance is recrystallized from 95 % alcohol. About 9 g of crude material dissolved

in 70 cc. of boiling alcohol; as slow evaporation, 8.3 g. of colourless pure benzoin

which melts at 135˚C was obtained [Scheme 2.4].

Scheme 2.4. Schematic representation of benzoin

CHO 2 alc.KCN CH

OH

C

O

Benz a ldehy de Be nz oin

26

2.4.1. Mass spectral analysis of BEN

The results of mass spectral analysis [Table 2.7] confirm the molecular

weight [Fig.2.9] and molecular formula of the compound.

Figure 2.9. Mass spectra of BEN

Table 2.7. Mass spectral fragmentation peaks for BEN

Peaks Fragmentation

212 M+

106 [-C6H5-CO+]

91.0 Tropylium cation

2.4.2. FTIR Spectral Analysis of BEN

The FTIR spectrum of the BEN shows the presence of secondary

alcoholic group with broad band around 3415 cm-1 attributed to the O–H stretching

modes. The bands around 3059 cm-1 in FTIR are assigned to the aromatic

27

C–H stretching modes. The aliphatic -CH stretching vibration is assigned to the

band at 2932 cm-1 in FTIR with weak intensity. The symmetric stretching mode of

the carbonyl group appears at 1678 cm-1 with very strong intensity in the FTIR

spectrum. The aromatic C=C symmetric stretching vibrations appear at 1595 cm-1 as

a very strong intensity in FTIR. The in-plane deformation of C–OH appears around

1262 - 1206 cm−1 as a medium band in the FTIR. The -OH out of plane deformation

is observed as strong bands around 1000 cm−1 in FTIR. The band at 1082 cm−1 and

1068 cm−1 in FTIR is assigned to the benzene ring deformation. [Table 2.8] The

band at 754 cm−1 in FTIR established the presence of disubstituted benzene ring

[Fig.2.10].

Figure 2.10. IR spectra of BEN in solid KBr

28

Table 2.8. Vibrational assignments of the BEN

FTIR for BEN [wavenumber] cm-1] Band assignments


3059 cm-1, 3028 cm-1 Aromatic C-H stretching



1595 cm-1[vs] Aromatic sym C=C stretching

1262- 1206 cm−1[m] C-OH in plane deformation


754 cm-1 Disubstituted benzene ring deformation


2.4.3. FT NMR Spectral Analysis of BEN

In the present investigation, 1H and 13C NMR spectra of the grown

compound have been recorded in acetone-d6 as a solvent. The 1H NMR and 13C NMR spectra of BEN are presented in Fig. 2.11 [a] and 2.11 [b] respectively.

The chemical shifts are tabulated with the assignments in Table 2.9. In the PMR

spectrum a signal appearing in the range of 3.9 ppm indicates the presence of a C-H

of the –CHOH group and a –OH proton appears a broad signal centered at 3.3 ppm.

Signals in the range of 6.2 to 7.6 ppm indicate the presence of aromatic protons. A

multiplet around 8.02 ppm indicates the ene-diol –OH protons. In the 13C NMR

aromatic carbon atoms appear in the range of 128 to 133 ppm. The signal at

197 ppm indicates the ene-diol carbon atom. [Table 2.9]

29

Figure 2.11. [a] 1HNMR of BEN in acetone d6

Figure 2.11. [b] 13C NMR of BEN

30

Table 2.9. The chemical shift in 1H NMR and 13C NMR spectrum of BEN

Spectrum Signal [ppm] Group identification 1H NMR 3.3 ppm -CHOH proton

6.2 to 7.6 ppm [multiplet] Aromatic protons

8.02 ppm Ene-diol of –OH protons 13C NMR 76 ppm Aliphatic carbon atoms



2.4.4. UV-Visible Spectral Analysis of BEN

UV-Visible absorption spectrum has been recorded in the range

200-400 nm. There is almost no absorbance in the entire visible region. Strong

absorption band is observed in UV-VIS region in the range of 200-225 nm with fine

structure and another strong absorption between 250-300 nm. The former can be

attributed to the absorption due to benzene rings and the latter to the carbonyl group

[Fig.2.12]. The crystal is transparent in the entire visible region. The absence of

strong absorption in the region between 300 to 400 nm in UV–Vis spectrum shows

that the benzoin crystals are useful for the SHG application.

Figure 2.12. UV spectra of BEN

31

2.5. SYNTHESIS AND PURIFICATION OF 2-SEMICARBAZONO-1-

HYDROXY, 1-[2-CHLOROPHENYL]-2-[4'-METHOXYPHENYL]

ETHANE [2C4MBS]

The starting material for the 2C4MBS was 2-Chloro-4′-methoxy benzoin

[2C4MB], prepared by benzoin condensation using 4 g of KCN dissolved in 75 cc of

water in a one litre flask. To this was added 6.8 g [0.05 moles] of anisaldehyde, 7 g

[0.05 moles] of 2-Chloro benzaldeyde and 75 cc of 95 % ethanol. On refluxing for

about half an hour, crude mixture was obtained. The crude mixture was dissolved in

hot alcohol and allowed to crystallise slowly. The 2C4MB crystallized out as

colourless, hexagonal crystals. The structure was confirmed by IR, NMR,

Mass spectra and single XRD analysis. [Scheme 2.5.a]

CH

OH

C

O

Cl

OCH3

Cl

CHO OCH3OHC alc.KCN

4-methoxy benzaldehyde

2-chloro-4'methoxy benzoin

+

2-chloro benzaldehyde

Scheme 2.5 a. Schematic representation of 2-chloro-4′-methoxy benzoin

Semicarbazide hydrochloride, anhydrous sodium acetate and 2C4MB in

5 ml ethanol were mixed in the mole ratio 2:4:1, respectively. The prepared solution

was found to be turbid. Hence, ethanol was added and stirred well, and the solution

was gently warmed till a clear solution was obtained [8]. The product obtained was

washed with hexane and purified by repeated recrystallization using ethanol. Single

crystal of 2C4MBS was obtained by slow evaporation technique. The melting point

of the compound was found to be 76.5±1˚C [Scheme 2.5.b].

32

+ NH2 H2N NH C

O

. HCl

CH3COONa

OCH3

Cl

CH

OH

C

O

OCH3

Cl

CH

OH

C

NNHCNH2

O

2-chloro-4'methoxy benzoin Semicarbazide hydrochloride

2-Semicarbazono-1-hydroxy, 1-[2-chlorophenyl]-2-[4'-methoxyphenyl] ethane

Scheme 2.5. b. Schematic representation of 2C4MBS

2.5.1. Mass spectral analysis of 2C4MBS

Mass spectral data and elemental analysis were in good agreement with

the assigned formula [Fig.213 and Table 2.10]

Figure.2.13. Mass spectra of 2C4MBS

33

Table 2.10. Mass spectral fragmentation peaks for 2C4MS

Peaks Fragmentation

326.75 M+

308.59 M+-CH3

273.92 M+-CONH

192.02 [OCH3C6 H4- +HC=NNHCONH2]

149 OCH3C6H4C=N-NH

133.83 OCH3C6H4C=N

106.0817 [-C6H5-CO+]

2.5.2. FTIR Spectral Analysis of 2C4MBS

In the FTIR spectrum of 2C4MBS the O–H and –NH stretching modes

merge and found between 3572-3450 cm-1. The bands around 2840 cm-1 are assigned

to the aromatic C–H stretching modes. The aliphatic -CH stretching vibration is

assigned to the band at 2315 cm-1 and 2055 cm-1 in FTIR with weak intensity. The

symmetric stretching mode of the carbonyl group and C=N appears as broad band

around at1667 cm-1 with very strong intensity. The aromatic C = C symmetric

stretching vibrations appear at 1604 cm-1 as a very strong intensity. The inplane

deformation of C–OH appears around 1297- 1250 cm−1 as a medium band in

spectrum. The OH out of plane deformation is observed as strong band around

1000cm-1 in FTIR .The band at 1086 cm-1 and 1052 cm-1 is assigned to the benzene

ring deformation. The band at 729 cm-1 is establishes the presence of disubstituted

benzene ring [Fig.2.14 and Table 2.11].

34

Figure 2.14. IR spectra of 2C4MBS in KBr

Table 2.11. Vibrational assignments of the 2C4MBS

FTIR for 2C4MBS [wavenumber cm-1]

Band assignments

3540 cm-1-3455 cm-1 -OH and –NH stretching

2840cm-1 Aromatic C-H stretching

2315cm−1, 2055cm−1[w] Aliphatic C-H stretching

1667cm-1[vs] Sym C=O,C=N stretching

1604cm-1[vs] Aromatic sym C=C stretching

1297- 1250cm−1[m] C-OH in plane deformation

1086cm−1 and 1052cm−1 Presence of Benzene ring deformation

758cm-1 Disubstituted benzene ring deformation


35

2.5.3. FT NMR Spectral Analysis of 2C4MBS

The signals observed in the 1H NMR and 13C NMR spectra of the

2C4MBS studied and the data [Figs. 2.15[a] and 2.15[b] were presented in

Table 2.12. The spectra exhibit a multiplet at 6.8-7.8 ppm for the hydrogens of the

aromatic rings. The -CHOH hydrogen leads to a singlet of intensity equivalent to

one hydrogen at 3.3 ppm. The signals at 3.8 ppm due to the hydrogens of the -OCH3

and signal at 6.3 ppm for –CONH2 groups. The spectra show a singlet with an

integration equivalent to one hydrogen at 5.9 ppm corresponding to the hydrogen of

the N–NH group. In the 13C NMR aromatic carbon atoms appear in the range of

127 to 137 ppm. The signal at 197 ppm indicates the ene-diol carbon atom. [Table

2.12]

Figure 2.15. [a] 1HNMR of 2C4MBS in acetone d6

36

Figure 2.15.[b] 13C NMR of 2C4MBS in MeOD

Table 2.12. The chemical shift in 1H NMR and 13C NMR spectrum of 2C4MBS.

Spectrum Signal [ppm] Group identification 1H NMR 3.3 ppm -CHOH

3.8 ppm [singlet] Methoxy group of 2C4MB

6.8 to 7.8 ppm[multiplet] Aromatic protons

6.3 ppm -CONH2 protons

5.9 ppm [singlet] -NNH proton 13C NMR 54 and 72 ppm Aliphatic carbon atoms


164 ppm Carbonyl carbon of 2C4MB


37

2.5.4. UV-Visible Analysis of 2C4MBS

The optical absorption spectrum of a good quality grown crystal was

recorded in the wavelength range 200–400 nm using ethanol as a solvent. The

obtained absorption spectrum is shown in Fig.2.16, where the lower cut off region is

obtained at 230 nm. The UV spectra show the presence of a wide transparency

window lying above 400 nm.

Figure 2.16. UV spectra of 2C4MBS in acetonitrile

2.6. SYNTHESIS AND PURIFICATION OF 2-2′DICHLOROHYDRO

BENZOIN [22′CD]

The starting material, for the synthesis of 22′CD is 2,2′dichlorobenzoin

which was synthesized by benzoin condensation. About 4 g of KCN dissolved in

75 cc of water in a one litre flask. 14 g of 2-chloro benzaldeyde and 75 cc of 95 %

ethanol were added into the flask. The mixture formed into a solution at the boiling

temperature and was refluxed for one and half hour. Steam was then passed through

the solution until all the alcohol and nearly all the unreacted aldehyde were

removed. The condensed water was decanted from the product and latter set aside

for crystallisation. The product was then pressed as free as possible from oily

material on a suction funnel and washed with cold alcohol. In this way about 14 g

38

[yield was 60%] of crude product was obtained. It is noteworthy that this product is

exceptionally easily oxidized to 2, 2′dichlorobenzil when comes into contact with

air [9]1.5 g of 2, 2′- dichlorobenzil was diluted in 15 mL of absolute ethanol, and

taken in Erlenmeyer flask. It was gently warmed with swirling. 300 mg of sodium

borohydride was added in small portions over 3-4 minutes. Flask was swirled or

stirred continuously for another 15 minutes. 30 mL of water was added cautiously

and flask was cooled in a ice bath, and constantly stirred. Concentrated HCl was

added in drop wise, and stirred until foaming ceases. To this 10 mL of water was

added and stirred continuously for 10-15 minutes. The precipitate was collected

using suction funnel. The precipitate was washed with 25 mL of cold water and

allowed to dry in air. The crude product was recrystallised from acetone-petroleum

ether by vapour diffusion method [Scheme 2.6].

Cl

lC

O

C

OH

CH air (O) C

O

Cl

Cl

C

O

2-2'dichlorobenzoin 2-2'dichlorobenzil

O

C

Cl

lC

O

CNaBH4

CH

O

Cl

Cl

CH

OH

H

2-2'dichlorobenzil 2-2'dichlorohydrobenzoin

Scheme 2.6. Schematic representation of 2,2′dichloro hydrobenzoin

CH

OH

C

O

Cl

ClCl

C HO2 alc KC N

2 Ch lo ro benz aldehy d e2-2 ' dichlorob enz oin

39

2.6.1. Mass spectral analysis of 22′CD

Mass spectral data and elemental analysis were in good agreement with

the assigned formula [Fig.2.17 and Table 2.13]

Figure.2.17. Mass spectra of 22′CD

Table 2.13. Mass spectral fragmentation peaks for 22′CD

Peaks Fragmentation

282.96 M+

247.2 M+-Cl

177.5 M+-CONH

164.4 [C6 H4Cl- OC-CO-]+

140.4 [C6 H4Cl- CH(OH)]+

40

2.6.2. FTIR Spectral Analysis of 22′CD

In FTIR spectrum of the 22′CD the –OH stretching modes found at

3332 cm-1. The bands around 3000 cm-1 in FTIR are assigned to the aromatic C–H

stretching modes. The aliphatic -CH stretching vibration is assigned to the band at

2925 cm-1 in FTIR with weak intensity [Table 2.14]. The aromatic C=C symmetric

stretching vibrations appear at 1439 cm-1 as a strong intensity. The –OH out of plane

deformation is observed as strong band around 1007 cm-1. The band at 741 cm-1 in

FTIR indicates presence of disubstituted benzene ring [Fig.2.18].

Figure 2.18. IR spectra of 22′CD in KBr

Table 2.14. Vibrational assignments of the 22′CD

FTIR for 22′CD [wavenumber cm-1] Band assignments 3332 cm-1[vs] -OH stretching


2925cm−1[w] Aliphatic C-H stretching

1439 cm−1[s] Aromatic sym C=C stretching

1007 cm−1 -OH out of plane deformation

741 cm-1 Disubstituted benzene ring deformation w:weak; vw:very weak, m:medium, s:strong, vs:very strong.

41

2.6.3. FT NMR Spectral Analysis of 22′CD

The 1H NMR and 13C NMR spectral signals of the 22′CD were observed

Figs. 2.19[a] and 2.19[b].The corresponding datum are presented in Table 2.15. The

spectra exhibit a multiplet at 6.8-7.5 ppm for the hydrogens of the aromatic rings

hydrogen. The -CHOH hydrogen leads to a broad singlet of intensity equivalent to

two hydrogens at 3 ppm. The spectra shows doublet with an integration equivalent

to two hydrogen at 5.8-5.9 ppm corresponding to the hydrogen of the –CH-CH

group [the signal appears as a doublet of doublet in expanded spectra].

In the 13C NMR aliphatic carbon appear in the range of 60-80 ppm,

aromatic carbon atoms appear in the range of 127 to 137 ppm. [Table 2.15]

Figure 2.19. [a] 1HNMR of 22′CD in acetone d6

42

Figure 2.19. [b] 13C NMR of 22′CD

Table 2.15. The chemical shift in 1H NMR and 13C NMR spectrum of 22′CD

Spectrum Signal [ppm] Group identification 1H NMR 2.0 ppm -CHOH

5.8-5.9 ppm CH-CH

6.8 to 7.5 ppm [multiplet] Aromatic protons 13C NMR 60 and 80 ppm Aliphatic carbon atoms


43

References

[1] a. J S Buck and W S Ide Org. Reactions 4 269 1948

b. Organic Syntheses, Coll. 1 94 1941

[2] A I Vogel Textbook of Practical Organic Chemistry 5th edn. [London : Longman][1989]

[3] N Vijayan, R Ramesh Babu, R Gopalakrishnan, P Ramasamy and W T A Harrison J. Cryst. Growth 262 490 2004

[4] N Vijayan, R Ramesh Babu, M Gunasekaran, R Gopalakrishnan,R Kumarasen, P Ramasamy and C W Lan J. Cryst. Growth 249 309 2003

[5] Organic Syntheses coll.1 33 1921

[6] Buck and Ide. J.Am.Chem.Soc. 51, 1592. 1929

[7] I suryanarayana, B Subrahmanyam, N V Subba Rao Proc. Indian Acad.Sci. 82A 55 1975

[8] B S Furniss, A J Hannaford, P W G Smith and A R Tatachell Vogel′s Text Book of Practical Organic Chemistry 5th edn. [English Language Book Society] [1996]

[9] E. Robert, Lutz, S. Robert and Murphey J. Am. Chem. Soc.71 478 1949

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