Synthesis and Study the Mesomorphic Behaviour of New N-acetyl and Their Diazetine : Mono and Twin

Synthesis ,characterization of new mono and twin compounds containing heterocyclic four member ring as, 1,3diazetine by four steps. The first step; includes preparation of 2amino thiazole derivatives [I]a-c via ring closure reaction between acetophenone derivatives with thiourea in I2, while the second step includes condensation reaction between 2-amino thaizole derivatives[I]a-c and p-methoxy benzaldehyde to produce Schiff bases[II]a-c. The third step includes neculophilic attach from imine group toacetyl chloride to give Nacetyl cross bonding[III]a-c.Finally ; the fourth step is completed by the reaction of Nacetyl derivatives with sodium azide (NaN3) to yield new 1,3-diazetines. The synthesized compounds were characterized byNMR and IR spectroscopy. The study of liquid crystalline behaviour was carried out using optical polarising microscopy (OPM) and some of them by differential scanning calorimetry (DSC). All compounds were synthesized which showed liquid crystalline properties on heating.


Introduction
The chemistry of heterocyclic is one of the most complicated branches of organic chemistry [1].Heterocyclic compounds have a wide applications, but very interested in medicinal chemistry and industrial application area [2].Thiazole is one member of the heterocyclic compound containing both nitrogen and sulfur atoms as a part of aromatic five membered ring.Many workers were interested in thiazoles liquid crystalline compounds containing imine linkage [3][4][5][6][7] studied a correlation.Murzaet.al., [8] have synthesized new liquid crystalline azomethines containing thiazole ring and studied a correlation between the geometric parameters and liquid crystalline properties.On the other hand, Tomma [9] reported the synthesis and study of the liquid crystalline properties of some N-Acetyl derivatives, the study explains enatiotropic mesomorphic behaviour with high transition temperature of the synthesized compounds.A diazetine is a four membered ring with two nitrogen atoms.According to the nitrogen atompositions, the diazetines are existed in two isomeric forms: 1,2 -diazetine and 1,3-diazetine [10].A diazetine compounds have played a good role as an intermediate in the synthesis of pharmacological active heterocyclic compounds [11].The addition of alkyl or aryl isocyanates to double bond of N-alkyl andNaryl carbodiimides to yield 4-arylimino-1,3-diazetidine-2-one derivatives was mentioned by Ulrich et al. [12].While Lazim [13] synthesized the diazetine from the addition reaction of sodium azide (NaN3) to N-acyl group.Mormanna and Brahm synthesized and studied mesomorphic properties of 4-isocyanatophenyl 4-methoxybenzoate and the corresponding diazetidinedione [14].In addition, by intramolecular cyclization of N-aryl thiourea derivatives, Pansuriya prepared new series of 1,3-diazetines [15].The literatures survey reveals that no evidence for synthesis and study of the liquid crystalline properties of 1,3-diazetines, therefore we decided synthesis, characterization and study of the liquid crystalline properties of new derivatives for new 1,3-diazetines and their N-acetyl.

Experimental
Chemicals: Chemicals were supplied from Merck, GCC and Aldrich Chemicals Co. and used as received.

Techniques:
The FTIR spectra were recorded on a Shimadzu (Ir prestige-21) by using potassi um bromide discs,.NMR spectra were carried out by company : Ultra Shield 300 MHz, Bruke r, Switzerland, at University of Al-Albayt , Jordan, and were reported in ppm(δ), DMSO was used as a solvent with an internal standard (TMS).Uncorrected melting points were determined on Hot-Stage, Gallen Kamp melting point apparatus,DSC thermographs were carr ied out on a STA PT-1000 Linseis instrument, Ramp rate : 5 ºC/min on heating and cooling, POM was determined using a microscope model PW-BK 5000 PR equipped with a hot-stage system of HS-400 (KER 3100-08S).Thin layer chromatography (TLC) was carried outusing aluminum sheets.Synthesis: The new compounds were synthesized according to two routes, scheme (1).

Synthesis of 1,3-diazetine derivatives[IV]a-c.
Sodium azide(0.65g, 0.01 mol) was added to a stirring solution of N-acyl derivatives (0.01mol) in (10 mL) dimethyl formamide(DMF) to synthesize compound [IV]a while (1.3g ,0.02 mol) was added for synthesized compounds [IV]b,c.After the addition, the mixture was heated for 12 hrs.at (55-60) ºC in water bath with stirring.Afterword cooling the reaction mixture to room temperature and filtered the precipitate, washed with cold water and recrystalized from DMF\ethanol.

Results and Discussion
The routes of synthetic for synthesized mono [I-IV] a and twin [I-IV]b,c compounds are outlined in Scheme (1).All of the synthesized compounds gave satisfactory analysis for the proposed structures, which were conformed on the basis of their Fourier transform Infrared(FT-IR) and 1 H , 13 C nuclear magnetic resonance (NMR).The di-ketone compounds A and B were prepared based on the methods mentioned in the reference [16].The first step in Scheme ( 1 Liquid Crystalline Behaviour.

) is the synthesis of compound [I]a-c by the reaction of mixture between [A]or[B]or[C] with iodine and thiourea in fusion according to the
optical polarizing microscopy (OPM) and differential scanning calorimetry (DSC) (of some of them) were used for the study of the mesomorphic properties of all synthesized compounds [I-IV]a-c.The chemical structures of mono and twin mesogenic compounds were shown in scheme1.All the synthesized compounds were containing thaizole ring besides to phenyl as a rigid core and strong donating terminal alkoxy groups (OCH3) see Figure (7), also the mono-mesogenic compounds [I-IV] a containing Br therefore the later compounds showed different properties than the twin -compounds.The type of transitions and the thermal data of the synthesized compounds were listed in table (1).All compounds[II-IV] a-c exhibited mesomorphic behaviour on heating, while the thaizole compounds [I]a-c did not show any liquid crystalline properties only transition from crystal to isotropic.
Table The mesomorphic behavior of mono-mesogenic compounds[II-IV]a these compounds were similar in terminal group and central core ,but there was a strong difference between them in the linkage group, so in the cohesive forces compound [I]aand did not contain linkage group, the compound [II]a contains imine linkage C=N (planer sp2 hybrid) that conjugate with thaizole see Fig.