51

SYNTHESIS AND MESOPHASE CHARACTERIZATION OF NOVEL

2,4,6-TRI(P-ACYLOXYPHENYL) PYRIDINE DERIVATIVES AS

DISCOTIC LIQUID CRYSTALS

Since the discovery of liquid crystals in 1888, several thousands of pure

compounds have been found to exhibit thermotropic mesomorphism. The distinctive

feature common to all of them is the rod-like or lath-like shape of the molecule. Brooks

and Taylor1 described the formation of mesophases consisting of plate-like molecules at

relatively high temperature (~450oC) during the carbonization of certain graphitable

substances, such as petroleum and coal tar pitches. However, carbonaceous mesophases

are rather complex materials composed of large molecules of a range of molecular

weights (typically around 2000) and certainly cannot regarded as simple component

liquid crystalline systems. The first observation of thermotropic mesomorphism in pure,

single-component systems of relatively simple plate-like or disc–like molecules were

observed by Chandrasekhar et. al in 1977. The compounds2 investigated were benzene

Hexa-n-alkanoates, which were synthesized according to the procedure of Neifert and

Bartow3. From optical, thermodynamic and X-ray studies, Chandrasekhar et.al4

concluded that hexa-substituted esters of benzene form are entirely new type of liquid

crystals, unlike the classical nematic or smectic types. The structure proposed was

illustrated in Figure-I. The discs are stacked periodically in columns, the different

column constituting a two dimensional arrangement2.

52

Fig. I Schematic representation of the structure of the columnar liquid crystal

The mesophase has transitional periodicity in two dimensions but liquid like

disordered in third ,the mesophase has been subcategorized as canonic5,6, columnar7 and

discotic8, the last often being to describe the molecules as well as mesophases formed by

them.

A number of disc-like mesogens have been invented by various groups working in

the laboratories of Thomson–CSF, college de France centre de Recherché Paul Pascel9

and notably by the Paris and Bordeaux8,10,11 groups. The canonic or columnar of

levelut12,13.

X-ray diffraction studies are used to determine the column order packing and the

distance between the inter-coulnmardiscs14,15,16. In the diffraction pattern, we observe

three features related to different aspects of the structure of columnar phases.

I. Inter columnar distance (a) gives rise to some narrow rings at the lower angles.

In this case the shape of unit cell corresponds to a hexagonal lattice.

II. The diffuse ring corresponding to the disordered paraffinic chains is observed

at angles corresponding to an arrange spacing of 4.5A.

53

III. The presence of an intense and sharp ring at larger angles depends on the inter

core stacking distance(h) with in the column and when we observe the reflection, the

hexagonal columnar phase is ordered(Dho)(Lattice parameters Figure II).

a

Figure- II

The first and best investigated homologues series contain hexa substituted

benzene17or triphenyls18-20 as cores. Recent publications on the synthesis and purification

of discotic triphenylene derivatives with unequal length of attached alkyl chains21,22

encouraged the synthesis of mono and bifunctional disc like monomers.

Some new 9, 10-antraquinone (rufigallol) derivatives have been prepared and

their menomorphic properties have been studied23. The unsymmetrical allyl substituted

tetrahydropyranyloxy-ethers(THP-ethers) exhibited columnar mesomorphism at fairly

low temperature and X-ray studies24 carried out for one of the homologues confirmed the

hexagonal nature of mesophase. The deprotected derivatives of these THF ethers also

form columnar mesophase.

In the following pages the synthesis and characterization of various discotic liquid

crystal compounds was described besides hexa ethers of hexa hydroxy benzenes

54

I. Hexa Esters of Hexa Hydroxy Benzene(I):

Chandrasekhar et.al2 had reported the synthesis of above compounds adopting the

procedure of Neifert and Bartoow3.These compounds were prepared starting from

glyoxal. The synthetic route is as shown in Scheme-I. The phase transition temperature

and heat of transition of hexa esters of hexa hydroxy benzene(I) were given in Table-I.

Scheme-I

CHO

CHO

O2

Na2SO3

OH

OH

ONaHO

OHNaO

HCl

O

O

OHHO

OHHO

HCl/SnCl2

OH

OHHO

OHHO

OH

RCOCl/Py

OCOR

OCORROCO

OCORROCO

OCOR

(I)

55

Table – I

Transition temperature and heat of transition of hexaesters of hexa hydroxy

benzene(I):

COMPOUND MESOREGION Enthalpy(∆H)

mj/mg

Crystal Mesophase Isotropic

Benzene

hexa -n-pentanoate

Benzene

hexa-n-hexanoate

Benzene

hexa-n-heptanoate

Benzene

hexa-n- octanoate

Benzene

hexa-n-nonanoate

Benzene

hexa-n-decanoate

-

-

-

-

-

-

-

-

-

-

-

68.3

On cooling

80.2

On cooling

79.4

On cooling

-

On cooling

-

106

86

83.23

86.2

83.6

83.6

87.5

79.6

74.6

83.5

6.9

4.78

4.77

6.97

4.68

9.69

3.79

16.28

3. 38

18.24

56

II.Hexa-n-alkoxy triphenelenes(II) and hexa-n-alkanoates of triphenelenes (III):

Tri phenelene derivatives are among the most extensively studied discotic liquid

crystals, and they are known to form an ordered hexagonal(Dho) mesophase which is ideal

for one dimensional energy25 and electron transport26. Traditionally tri phenelene hexa

ethers and hexa esters were synthesized via the route outlined in Scheme-II27,28. Veratrole

(1,2- dimethoxybenzene) is oxidatively trimerised25 to hexa methoxy tri phenelene using

chloranil in 70% sulphuric acid. Hexa methoxy tri phenelene is demethelated typically

with BBr3 and alkylated/acylated to give the discogen (II),(III) .the phase transition and

heat of transition of hexa-n-alkoxy tri phenelenes(II) and hexa -n-alkanoates of tri

phenelenes(III) were detailed in Table-II and Table.III.

57

Scheme-II

OMe

MeO

OMe

OMe

MeO

OMe

OH

HO

OH

OH

OH

HO

RBr/DMF

RCOCl/Py

OR

RO

OR

OR

OR

RO

OCOR

ROCO

OCOR

OCOR

OCOR

ROCO

OMe

OMe

1.chloranil2.con H2SO4

1.Demethylation2.BBr3/HI

(III) (II)

58

Table - II

Transition temperature and heat of transition of hexa-n-alkoxy tri phenelenes(II):

Structre -II

R=1

MESOREGION Enthalpy(∆H)

mj/mg

Crystal Mesophase Isotropic

CH3

C 2H5

C 3H7

C 4H9

C 5H11

C 6H13

C 7H15

C 8H17

C 9H19

C 10H21

C 13H27

317

247

117

88.6

69

68

68.6

66.8

57

58

-

-

-

-

14.6

122

97

93

85.6

77.6

69

49

-

-

-

-

-

-

-

-

-

-

-

-

-

4.03

5.52

7.80

8.68

14.4

19.92

17

17

-

59

Table-III

Transition temperature and heat of transition of hexa-n-alkanoates of tri

phenelenes(III):

Structre -II

R=1

MESOREGION Enthalpy

(∆H) mj/mg

Crystal Mesophase Isotropic

C 2H5

C 3H7

C 4H9

C 5H11

C 6H13

C 7H15

C 8H17

C 9H19

C 10H21

C11H23

C12H25

C 13H27

296

230

193

134

108

64

62

75

67

80

83

86.5

-

-

-

-

-

-

-

-

56

93

99.2

96

-

-

-

146

120

130

125

125.5

108

111

99.2

96

-

4.78

4.67

5.9

3.46

4.72

6.11

11.3

12.0

12.5

17

-

60

III. Hexa alkoxy truxene(IV) as discotic liquid crystals:

3,4-di hydroxy dihydro cinnamic acid is the starting compound , used by Destrade

et.al24 in the synthesis of hexa alkoxy truxenes21,22. The synthetic route as shown in

Scheme-III. The required alkyl chains were attached to the 3,4-dihydroxy dihydro

cinnamic acid and cyclization of corresponding acid was performed in PPA leading to

the formation of indanone, which afforded the corresponding truxene upon trimerisation.

The phase transition temperatures and heat of transitions of hexa alkoxy truxenes (IV)

were given in Table-IV

61

Scheme -III

HO

HOCOOH

RBr/DMF

RO

ROCOOH

PPA

RO

RO

O

Trimerisation

ORRO

OR

OR

RO

RO

(IV)

62

Table-IV

Transition temperature and heat of enthalpy(∆H) of Hexa alkoxy truxene(IV):

Structre -II

R=1

MESOREGION Enthalpy

(∆H) mj/mg

Crystal Mesophase Isotropic

C 5H11

C 6H13

C 7H15

C 8H17

C 9H19

C 10H21

C11H23

C12H25

C 13H27

75

70

66

58

61

56

67

50

60

79

-

86

67

67

64

73

59

75

-

-

-

-

-

-

-

-

-

11.3,4.2

15.4,17.5

10.4,19.1,

17.5,8.2

15.3,8.6

21.6,11.0

21.0

12.0

29.0,17.5

IV. 2,2,6,61- tetra aryl bi pyran -4-ylidenes (V) as discotic liquid crystals:

Fugnitto et.al29 has synthesized the above compounds which allows either four or

two fold symmetry. 2,21,6,61-tetra aryl bipyran -4-ylides30,31(V); may be synthesized in

two steps starting from methyl-p-alkyl-phenyl ketone. The intermediate perchlorate was

obtained in 70-90% yield. The synthetic route is as shown Scheme-IV. The phase

transition temperature of 2,21,6,61-tetra aryl bipyran -4-ylides were given in Table-V

63

Scheme-IV

O

R

1)CH(OEt)3

2)HClO4O

R R

ZnCN,MeCN

O O

RR

RRV

R=CnH2n+1n=5,9,12

Table-V

Phase transition temperature of 2,21 ,6,61-tetra aryl bipyran -4-ylides(V)

STRUCTRE CRYSTAL1 CRYSTAL2 MESOPHASE LIQUID

5 x 135 x x 228 x

9 x 53.5(2.0) 171.5(5.0) x

12 x 40(6.8) x 96(3.8) x 147 (6.7) x

64

For many years, L.C polymers with the mesogen in the main chain or in the side

chain group have been investigated intensively, for their scientific and technical

potential32,33,34. Parallel to the research on L.C polymers with rod-like moiety, disc-like

mesogens have been developed in the field of low molecular weight L.C׳s. The synthesis

of polymers carrying disc likes mesogens either as a side group or within the polymer

side chain may be possible. The spacer concept35-38 for L. C polymers with rod-like

mesogens, the fixation of disc like mesogens should at least retain the formation of

discotic phases. Columnar phases are the analogue to smectic phases while the nematic

disc like phase(Nd) correspond to classic nematic phase.

In our laboratory, we have a programme of synthesizing various liquid crystals

and characterize them using a polarizing microscope and record their

textures.Cycloswientol39, Friedelon esters40,41, 1-phenyl naphthalene's, dihydro flavones,

tri terpinoid and steroid fatty acid esters42, were synthesized and characterized for their

liquid crystalline properties and data was published.

65

PRESENT WORK

Earlier reports from our research lab found that esterified flavones 43-46 (flavanoid

esters) and 1-phenyl naphthalene exhibited the properties of discotic liquid crystal

materials. These systems may be possess quasi planarity with a rigid aromatic core which

is a necessitate for L.C behavior. These compounds exhibit mesophase region at

relatively low temperature than other classes of discotic liquid crystal compounds. Tri

phenelene compounds are the most extensively studied discotic liquid crystals which are

known to form ordered hexagonal (Dho) mesophase which is ideal for one-dimensional

energy47and electron transport48.

With the view to study and characterize novel crystals, it is to proposed to

synthesize novel liquid crystals and further characterize their liquid crystal properties.

2,4,6-tri(p-acyloxy phenyl) pyridine׳s are expected to be potential for this study. Hence in

this present investigation, we report synthesis of 2, 4, 6-tri (p-acyloxy Phenyl) pyridine׳s

and the structure was confirmed by spectral data. All the newly synthesized compounds

exhibited liquid crystalline properties. The mesomorphic properties of long chain

substituted hetero aromatic compounds were examined by polarizing microscope

equipped with hot stage and also by differential scanning calorimeter (DSC data). The

observed textures were photographed and the respective thermo grams were recorded at

the rate of heating 100c/min.

Synthesis: To a mixture of p-hydroxy acetophenone (I) (4mmol) and p-hydroxy

benzaldehyde(II) (2mmol), and (NH4)2CO3 (4mmol)was refluxed in water for 6 hours at

1500C under sealed conditions(seal tube). After the completion of reaction the reaction

mixture is cooled to room temperature and poured in crushed ice, yellow colour 2,4,6-

tri(p-hydroxy Phenyl)pyridine49-51(III) yield (93-98%) is obtained as a crystalline solid

(Scheme-V) which is further purified by column chromatography and the purity was

checked by TLC and HPLC, mp : >3000C above

66

Scheme-V

CH3O

OH

+

HO

OH

I.(NH4)2CO3

2.water,150 o c3.seal tube N

OH

HO OHIII

I II

N

OCOR

OCORROCO

1.RCOCl

IV

2.DMAP

3.CH2Cl2

RCOCl, V= CH3(CH2)9COCl

VI= CH3(CH2)10COCl

VII= CH3(CH2)14COCl

VIII= CH3(CH2)16COCl

67

The structure of compound (III) was confirmed by its IR, 1H NMR, 13C NMR,, mass

spectral technique.

IR(Vmax, KBr ):3472 ,1600,1583,1472,1440,1204,1162,1125,925,763,677 (Fig.3)

1H NMR (DMSO/ TMS,90 MHZ ) :6.84-6.94(6H,d), 7.76-8.15(8H,m), 9.80(1H,brs)

(Fig.4 )

13 C NMR(DMSO/ TMS,22.5 MHz):113.5, 115.5,115.9, 128.3, 128.7, 130.3, 144.9, 149,

156.3, 158.2 (Fig.5)

Mass ion(m/z) :370.1[M+] (Fig.6).

Compound(III) on reaction with long chain fatty acid chloride (RCOCl, R=

undecyl, lauryl, stearyl, palmityl)in DMAP and dichloromethane at reflux temperature

yielded 2,4,6-tris(P-acyloxyphenyl)pyridine derivatives(V,VI,VII,VIII). The synthetic

route is shown in Scheme-V. All the esters were purified by column chromatography with

n-Hexane : ethyl acetate (9:1) as eulent. These products were recrystallized from

methanol and purity of these above esters were checked by TLC and HPLC (99%).

68

69

70

71

72

Synthesis of 2,4,6-tri(p-palmitoyloxy Phenyl) pyridine (VII): 2,4,6-tri(p-hydroxy

phenyl) pyridine(III) and palmitoyl chloride (prepared by action of SOCl2 in palmtic acid

and palmitoyl chloride thus prepared was distilled at reduced pressure) were refluxed in

the presence of DMAP in DCM for 5-6 hrs, After usual workup, it yields a crude ester.

Purification of the crude ester over a column of silica gel eulating with n-hexane : ethyl

acetate(9:1)afforded 2,4,6-tri(p-palmitoyloxy phenyl)pyridine(VII). Purity of this

compound was checked TLC and HPLC. HPLC data (flow rate, retention time and

percentage of purity)of compound(VII) shown below, the HPLC chromatogram was

presented in (Fig.7a).

Purity of Compound(VII)(HPLC):

Mobile phase : Acetonitrile

Flow rate : 1ml / min.

Retention time : 3.88 min

% of purity : 98.26%

The structure of compound(VII) was confirmed by IR, 1H NMR, 13C NMR and

Mass spectral data. The IR spectrum of compound(VII) were recorded and represented

in Fig.7

IR(Vmax KBr ): 2959,2918,2840, 1757,1702,1588,1513,1409,11117,931,719 ) (Fig.7)

The 1H NMR spectrum and 13CNMR spectrum of compound(VII) were recorded and

represented in Fig.8&9;

1H NMR (DMSO+CDCl3/TMS,400 MHz): 0.8-0.9(methyl, s), 1.2-1.5(-CH2-,s), 2.1-

2.3(-COCH2- t), 7.0-7.1(aromatic protons ), 7.9-8.1(aromatic protons ) (Fig.8).

13 CNMR(DMSO+CDCl3/TMS,100MHZ): 12.4,20.8,23.1,27.3,27.4, 27.6,27.7, 30, 32.4

73

,114.5, 115,115.8,128.8,151.9,159.4,173.4 (Fig.9). Mass spectrum of compound(VII)

was recorded and presented in (Fig.10) .

Mass ion(m/z) :1069(M+) (Fig.10).

Based on the above spectral data the compound (VII) was confirmed as 2,4,6-

tri(P-palmitoyloxy phenyl) pyridine. The thermographic liquid crystal behavior of the

compound (VII) was evaluated by differential scanning calorimeter (DSC) and polarizing

microscope.

74

75

76

77

78

79

Differential Scanning Calorimeter Study:

The Differential Scanning Calorimetric data was recorded on DSC Q2000 V

24.9 Built 121 instrument at I.I.T Hyderabad, India and Aurabindo Labs, Hyderabad.

Compound (VII) 10mg, dried completely was placed in a aluminum sample pan

and sealed. The compound was studied for differential scanning calorimetric data at a

heating rate 100c/min up to 2500C and on cooling also. The DSC thermogram for

Compound (VII) was recorded on cooling from isotropic to mesophase. compound(VII)

exhibited mesophase between the temperature 41.460C-54.00C and enthalpy(∆H)

60.22j/g. . The phase transition temperature and the enthalpy (∆H) were recorded and

presented in Fig.11

In order to further confirm the mesophase, compound (VII) was studied

using polarizing microscope on slow cooling from isotropic liquid state, texture53(a

texture typical that of a hexagonal columnar mesophase) was observed during the

mesophase. The observed texture was presented in Fig.12.

Similarly compounds (V, VI, VIII) were synthesized and characterized by

spectroscopic data and the spectral data was recorded in Table-VI. HPLC purity and

retention times were recorded in Table-VII. Spectrums of compounds ( VI, VIII) were

presented Fig.13(a,b,c,d) ,Fig.14(a,b,c,d) respectively.

The DSC thermogram for Compound (V) was recorded on cooling from isotropic

to mesophase. compound(V) exhibited mesophase between the temperature 53.330c-

68.00c and enthalpy(∆H) 26.10j/g. . The phase transition temperature and the enthalpy

(∆H) were recorded and presented in Fig.15.

80

In order to further confirm the mesophase, compound (V) was studied using

polarizing microscope on slow cooling from isotropic liquid state, texture was observed

during the mesophase. The observed texture was presented in Fig.16.

The DSC thermogram for Compound (VI) was recorded on cooling from isotropic to

mesophase. compound(VI) exhibited mesophase between the temperature 41.980c-52-00c

and enthalpy(∆H) 123.10j/g. . The phase transition temperature and the enthalpy (∆H)

were recorded and presented in Fig.17.

In order to further confirm the mesophase, compound (VI) was studied

using polarizing microscope on slow cooling from isotropic liquid state, texture was

observed during the mesophase. The observed texture was presented in Fig.18.

The DSC thermogram for Compound (VIII) was recorded on cooling from

isotropic to mesophase. compound(VIII) exhibited two mesophses, one mesophase

was in between the temperature 56.00c-71.00c and enthalpy(∆H) 149.3j/g and the second

mesophase was in between 138.350c-161.00c and enthalpy(∆H) 12.7j/g. The phase

transition temperature and the enthalpy (∆H) were recorded and presented in Fig.19.

In order to further confirm the mesophase, compound (VIII) was studied using

polarizing microscope on slow cooling from isotropic liquid state, a road like texture was

observed during the mesophase. The observed texture was presented in Fig.20. DSC

thermographic data i.e. phase transition temperature and enthalpy(∆H) were recorded for

the above esters (V, VI,VII, VIII) in Table-VIII.

81

Table-VI Spectral data of 2,4,6-tri(P-acyloxy phenyl)pyridine derivatives(V-VIII):

Compound IR spectral data (cm-1)

1HNMR spectral data(δ ppm) 13CNMR spectral data(δ ppm)

Mass ion (m/z)

V

VI

VII

VIII

2954,2916,2849,1754

,1700,1605,1593,147

2,1247,1166,1145,92

4,763

2954,2918,2845,1754

,1702,1676,1598,151

5,1293,1215,936,

832

2959,2918,2840,1757

,1702,1588,1513,140

9,1117,931,719

2954,2918,2818,1759

,1702,1603,1547,150

5,1420,1200,1164,

926,838,724

0.8-0.9(9H,s),1.2-1.5(48H ,m)

,2.2-2.3(6H,s) 7.1-7. 2 (6H, d),

7.5-7.8 (6H,aromatic)

0.8-0.9(9H,s),1.2-1.6 (54H,

m),2.2-2.3(6H,s), 7.0-7.1

(6H,d),7.6-7.9(8H, aromatic).

0.8-0.9(9H,S),1.3-1. 6 ( 78 H

,S),2.1-2.2(6H,s)7.0-7.1

(6H,d),7.9-8.1(8H, aromatic)

0.8-0.9(9H,s),1.2-1.8 (90H ,

S),2.5 -2.7(6H,s),

7.2-8.2(14H,aromatic)

13.95,22.4,24.6,28.8,2

9.03,29.09,29.4,31.6,3

4.1,116.4,121.7,122.2,

127.9,128.0,136.5,151

.4,156.2,171.9

13.8,22.3,24.6,28.8,28

.9,29.1,29.2,31.5,33.9,

115.3,115.7,116.2,128.

4,128.8,153.2,159.3,1

75.3

12.4,20.8,23.1,27.3,27

.4,27.6,27.7,30,32.4,1

14.5,115,115.8,128.8,1

51.9,159.4,173.4

13.4,21.9,24.1,28.5,28

.7,28.9,31.1,33.6,111,1

21.2,121.7,127.4,127.

5,135.4,148,150,155,1

71.4

1069

82

Table-VII

Retention time and Percentage of purity of 2,4,6-tri(P-acyloxy phenyl)pyridine

esters(V-VIII):

S. No. Compound Retention Time(min)

Percentage (%) Purity

I

2

3

4

V

VI

VII

VIII

3.434

3.56

3.388

3.536

98.5

98.7

98.26

98.2

HPLC experimental conditions:

Mobile phase : acetonitrile

Column : silica column

Flow rate : 1ml/min

Detector : UV(254nm)

Injected quantity : 10µl

83

Table-VIII

DSC Thermographic data of compounds V to VIII ( DSC Q2000 V24.9 Build 121) :

Compound Temperature in 0C

crystal(K)-

mesophase(S1)

Enthalpy(∆H)

K-S1 j/mg

Temperature in 0C

S1—Isotropic

Enthalpy(∆H)

S1-I j/mg

V

VI

VII

VIII

53.330c-68.00c

41.980c-52-00c

41.460c-54.00c

56.00c-71.00c

26.10j/g

123.10j/g

60.22j/g

149.3j/g

_

_

_

138.350c-161.00c

_

_

_

12.7j/g

84

85

86

87

88

89

90

91

92

93

94

95

96

Characterization of the discotic mesophase:

After a through study of the thermograms and the textures we extended our

studies to confirm the columnar phase of the above new synthesized liquid crystals by X-

ray diffraction study.

X-ray Diffraction Study:

X-ray diffraction studies of different arms on a 1,3,5-benzene core, are reported

by Matthias Lehmann. et. al52. In their investigations, the x-ray diffraction pattern of the

1,3,5-benzene core mesogen, a set of three reflections were observed in the small angle

region with reciprocal spacing's in the ratio 1: √3 : 2. These peaks are assigned to the

(10),(11),(20) reflections of a hexagonal columnar mesophase, confirming the discotic

liquid crystal phase. In the wide-angle region, X-ray diffraction data displays an

amorphous halo reflecting, the mean distance between the aliphatic side chains is 4.2A0.

The d- spacing values are theoretically calculated by using Brag׳s formula.

Brag׳s equation → nλ = 2dsinθ

In our investigations the X-ray diffraction pattern of the 2,4,6-tri(p-palmityoloxy

phenyl)pyridine(VII), the existence of the mesophase as a hexagonal columnar( Colh)

phase was confirmed by XRD. XRD data was recorded at Advanced Analytical

Laboratory, Instrument facility, Andhra University, Visakhapatnam. The diffraction

pattern for compound(VII) was recorded at room temperature to confirm the columnar

phase of compound(VII). XRD pattern of compound(VII) was presented in Fig.21, in

which 2θ profile on x-axis versus one dimensional intensity on Y-axis was recorded. In

the small angle region, three sharp peaks were observed, the observed peaks are in

97

ascending order of diffraction angle. The d -spacing values of first three intensive peaks

of were 17.9A0, 10.01A0 and 8.6A0 respectively. The d- spacing of the first reflection

(lowest angle and highest intensity) to the other two, was in the ratio 1:1/√3:1/2. These

values correspond to that expected from a two dimensional hexagonal lattice. In the wide

angle region, there were two diffused peaks; a broad one at 19.80 and another sharp peak

at higher angles. The broad peak with a d-spacing of 4.4 A0was due to the liquid-like

packing of the aliphatic chains. The relatively narrow peak, which was separated from the

broader one, corresponds to a spacing of 3.56 A0 and was due to core-to-core(intra

columnar) separation. All the features confirm the hexagonal columnar (Colh)phase, in

which the disc-like molecules stack one on top of another to form columns, and the

columns in turn, are arranged in a two-dimensional hexagonal lattice.

98

Fig.21. X-ray Diffraction pattern of 2,4,6-tri(p-palmitoyloxy Phenyl) pyridine (VII).

Peak List

Pos.[°2Th.] Height [cts] FWHMLeft[°2Th.] d-spacing [Å] Rel. Int. [%] TipWidth Matched by 4.987400 763.083000 0.076800 17.93098 100.00 8.866070 14.720810 0.028800 10.01550 1.52 10.159880 31.508320 0.115200 8.61215 3.11 19.889860 55.171270 0.076800 4.44379 6.59 25.116130 87.652540 0.038400 3.56125 11.43

Based on the above XRD data it is observed and confirmed that compound(VII) exhibits discotic

heagonal columnar mesophase.

99

RESULTS AND DISCUSSION

From the literature survey we examined that liquid crystal properties of 2,4,6-

tri(p-acyloxy phenyl) pyridine derivatives which are not reported earlier by any research

group. Hence we synthesized 2,4,6-tri(p-acyloxy phenyl)pyridine esters. 2,4,6-tri(p-

acyloxy phenyl) pyridine esters Scheme-V and the structure was confirmed by IR, IH

NMR,13CNMR and its mass spectral data. The newly synthesized compounds were

examined for liquid crystal properties. During the course of our studies on thermotropic

liquid crystals of hetero aromatic compounds, it is observed that 2,4,6-tri(p-stearoyloxy

phenyl)pyridine display mesophase on wide range of temperature.

Observation of data from Table.(VIII) Viz., the meshophase region and the heat

of transition, it is very clear that these esters exhibit mesophase from or above 410-720c,

except in case of compound(VIII), which show a second liquid crystal phase 138.350-

161.650c. In case of compound (VIII) viz,. the stearate ester, it is interesting to note that

the compound required more heat of transition(∆H)(149.3j/g)for the phase during 56.00-

71.60c, but the heat of transition decreases to lower value i. e (12.7 j/g)during the second

mesophase (138.50-161.610c). Another important thing is all the synthesized novel

2,4,6-tri(p-acyloxy phenyl)pyridine(V,VI,VII,VIII) exhibited first mesophase at lower

temperature. All the compounds are potential for further study to explore room

temperature liquid crystals, which are aimed for industrial applications.

We are also carried out X-ray diffraction studies to 2,4,6-tri(p-palmityoloxy phenyl)-

pyridine(VII) for detection of columnar mesophase. The X-ray diffraction of

compound(VII) shows, the d- spacing of the three sharp peaks were in the ratio

1:1/√3:1/2. These values correspond to that expected from a two dimensional hexagonal

100

lattice. The d -spacing values of first three intensive peaks of were 17.9A0, 10.01A0 and

8.6A0 respectively. In the wide angle region there were two diffused peaks; a broad one at

19.80 and another relatively narrow peak at higher angles. The broad peak with a d-

spacing of 4.4 A0was due to the liquid-like packing of the aliphatic chains. The relatively

narrow peak, which was separated from the broader one, corresponds to a spacing of 3.56

A0 and was due to core-to-core(intra columnar) separation. All the features the hexagonal

columnar (Colh) phase, in which the disc-like molecules stack one on top of another to

form columns, and the columns in turn are arranged in a two-dimensional hexagonal

lattice.

101

EXPERIMENTAL

Synthesis of 2,4,6-tri(p-Hydroxy phenyl)pyridine(III): To the mixture of p-hydroxy

acetophenone (4mmol),p-hydroxy benzaldehyde(2mmol) and ammonium carbonate (4

mmol) was refluxed in water for 6 hours at 1500C under sealed conditions (seal tube).

After the completion of reaction the reaction mixture is cooled to room temperature and

poured in crushed ice yellow colour 2,4,6-tri(p-hydroxy phenyl)pyridine49-51(III) (93-

98%) is obtained as a crystalline solid. which is further purified by column

chromatography and the purity was checked by TLC and HPLC, mp. 300 above

mp :300 (above)

Yeild :93-98%

IR (γmax, KBr) Cm-1 :3472, 1600, 1583, 1472, 1440, 1204, 1162, 1120, 925, 763, 677

(Fig.3)

1H NMR (DMSO+CDCl3/ TMS, 90MHz):6.84-6.94(6H,d),7.76-8.15(8H,m),9.80(1H,s)

(Fig.4)

13C NMR( DMSO+CDCl3/ TMS, 22.5MHz):113.5, 115.5, 115.9, 128.3, 128.7, 130.3,

144.9, 149, 156.3, 158.2(Fig.5)

Mass ion (m/z) : 370.1(M+)(Fig.6)

Preparation of acid chloride: Long chain fatty acid (0.1mol undecanoic acid .palmtic

acid, stearic acid lauric acid) were reacted with freshly distilled SOCl2(0.3mol). The

contents were refluxed for 3 hours. Excess of SOCl2was destroyed by adding formic acid

to flask till no smell of socl2 observed. The crude acid chloride were distilled at reduced

pressure and used immediately for esterification.

102

Synthesis of 2,4,6-tri(p-acyloxy phenyl)pyridine(IV): 2,4,6-tri(P-hydroxy phenyl)

pyridine (1mol), acid chloride (3mol palmtioyl, undecoyl, stearoyl, lauryl),DCM (20ml)

contains catalytic amount of DMAP were refluxed for 3-5 hours. The reaction mixture

was monitored on TLC, till no starting compound was observed. The contents of the flask

were poured in crushed ice and 0.5 ml of con.H2SO4is added. This was extracted with

EtOAC(20ml) for five times and distillation. The crude product was chromatographed

over a small column of silica gel with n-hexane and EtOAC (9:1) as eulent. Further the

product as recrystallized from methanol or mixture of methanol and chloroform which

yielded white crystalline flakes. These compounds were set for spectroscopic and DSC

thermo graphic data to confirm the structure and liquid crystalline properties.

103

Synthesis of 2,4,6-tri(p-undecoyloxy phenyl)pyridine(V): To the above general

procedure was adopted to prepare 2,4,6-tri(p-undecoyloxy phenyl)pyridine as follows.

2,4,6-tri(p-hydroxy phenyl) pyridine(1mmol), undecanoyl chloride (3mmol), and

DCM(20ml) contains catalytically amount of DMAP were refluxed for 3-5 hours, and

resulting ester obtained was crystallized from methanol and the purity checked by TLC

and HPLC. The spectral data was given below.

HPLC:

Mobile phase : Acetonitrile

Flow rate : 1ml / min.

Retention time : 3.434 min

% of purity : 98.5%

IR(γmax,KBr)Cm1:2954, 2916, 2849, 1754, 1700, 1605, 1593, 1472, 1247, 1166, 1145,

924, 763.

1H NMR (DMSO + CDCl3/ TMS, 400MHz): 00.8-0.9(9H,s),1.2-1.5(48H ,m) ,2.2-

2.3(6H,s) 7.1-7.12 (6H, d), 7.5-7.8 (8H, aromatic).

13CNMRDMSO+CDCl3/TMS,100MHz):13.9, 22.4, 24.6, 28.8, 29.03, 29.09, 29.4, 31.6,

34.1, 116.4, 121.7, 122.2, 127.9, 128.0, 136.5, 151.4, 156.2, 171.9.

104

Synthesis of 2,4,6-tri(p-lauroyloxy phenyl)pyridine(VI): To the above general

procedure was adopted to prepare 2,4,6-tri(p-lauroyloxy phenyl)pyridine as

follows.2,4,6-tri(p-hydroxy phenyl) pyridine(1mmol), lauroyl chloride (3mmol), and

DCM(20ml) contains catalytically amount of DMAP were refluxed for 3-5 hours, and

resulting ester obtained was crystallized from methanol and the purity checked by TLC

and HPLC. The spectral data was given below.

HPLC: (Fig.13a)

Mobile phase : Acetonitrile

Flow rate : 1ml / min.

Retention time : 3.56 min

% of purity : 98.7%

IR( v max, KBr ) cm-1 : 2954, 2918, 2845, 1749, 1702, 1626, 1598, 1515, 1293, 1215,

936, 832 (Fig.13b).

1H NMR (DMSO+CDCl3/ TMS, 400MHz ): 0.8-0.9(9H,s),1.2-1.6 (54H, m),2.2-

2.3(6H,s), 7.0-7.1 (6H,d),7.6-7.9(8H, aromatic). (Fig.13c).

13CNMRDMSO+CDCl3/TMS,100MHz):13.8, 22.3, 24.6, 28.8, 28.9, 29.1, 29.2, 31.5,

33.9, 115.3 , 115.7, 116.2, 128.4, 128.8, 153.2, 159.3, 175.3. (Fig.13d).

105

Synthesis of 2,4,6-tri(p-palmitoyloxy phenyl) pyridine(VII): Adopting to the above

general procedure was adopted to prepare 2,4,6-tri(p-palmitoyloxy phenyl)pyridine as

follows.2,4,6-tri(p-hydroxy phenyl)pyridine(1mmol),palmitoyl chloride (3mmol), and

DCM(20ml) contains catalytically amount of DMAP were refluxed for 3-5 hours, and

resulting ester obtained was crystallized from MeOH-CHCl3 and the purity checked by

TLC and HPLC. The spectral data was given below.

HPLC:(Fig.7a)

Mobile phase : Acetonitrile

Flow rate :1ml / min.

Retention time :3.388 min

% of purity : 98.26%

IR (γmax,KBr)Cm-1 :2959, 2918, 2840, 1757, 1702, 1588, 1513, 1409, 11117 , 931, 719

(Fig.7).

1HNMR(DMSO+CDCl3/TMS,400MHz): 0.8-0.9(9H,S),1.3-1. 6 ( 78 H ,S),2.1-

2.2(6H,s)7.0-7.1 (6H,d),7.9-8.1(8H, aromatic) (Fig.8).

13CNMRDMSO+CDCl3/TMS,100MHz):12.4, 20.8, 23.1, 27.3, 27.4, 27.6, 27.7, 30,

32.4, 114.5 , 115, 115.8, 128.8, 151.9, 159.4, 173.4 (Fig.9)

Mass ion(m/z):1069[M+](Fig.10).

106

Synthesis of 2,4,6-tri(P-stearoyloxy phenyl) pyridine(VIII): To the above general

procedure was adopted to prepare 2,4,6-tri(p-stearoyloxy phenyl)pyridine as follows.

2,4,6-tri(p-hydroxy phenyl) pyridine(1mmol), stearoyl chloride (3mmol), and

DCM(20ml) contains catalytically amount of DMAP were refluxed for 3-5 hours, and

resulting ester obtained was crystallized from methanol-chloroform and the purity

checked by TLC and HPLC. The spectral data was given below.

HPLC: 98.2( Fig.14a)

Mobile phase : Acetonitrile

Flow rate : 1ml / min.

Retention time : 3.536 min

% of purity : 98.2%

IR(γmax,KBr)Cm1:2954, 2918, 2818, 1759, 1702, 1603, 1547, 1505, 1420, 1200, 1164,

926, 838, 724( Fig.14b).

1H NMR (DMSO+CDCl3/ TMS, 400MHz ): 0.8-0.9(9H,s),1.2-1.8 (90H , S),2.5 -

2.7(6H,s),7.2-7.4(6H,aromatic), 7.7-8.2(8H, aromatic). ( Fig.14c).

13C NMR DMSO+CDCl3/ TMS, 100MHz) :13.4, 21.9, 24.1, 28.5, 28.7, 28.9, 31.1, 33.6,

111, 121.2, 121.7, 127.4, 127.5, 135.4, 148, 150, 155, 171.4(14d).

107

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