SYNTHESIS AND CHARACTERIZATION OF NEW AROMATIC HYDROXY ACID COMPOUNDS

Four novel aromatic hydroxy acid (HA) compounds N-(4-hydroxyphenyl)-4’-trimellitimide, N-(3-hydroxyphenyl)-4’-trimellitimide, N-(5-hydroxynaphthyl)-4’-trimellitimide and N-{4’-[2-(4-hydroxyphenyl) isopropyl phenyl]}-4’’-trimellitimide are synthesized through nucleophilic substitution reaction of trimelitic dianhydrides with the corresponding aminophenol/aminonaphthol using polar aprotic solvents. The hydroxy acid compounds are characterized by FT-IR and H-NMR spectroscopy.


INTRODUCTION
Bifunctional molecule has properties of two different types of functional groups.Some common functional groups are -COOH (carboxylic acids), -CHO (aldehyde), -CONH 2 (amide), -CN (nitrile), -OH (alcohol), -NH 2 (amino), -X (halo), etc.The functional groups determine the chemical and biological behavior of the compounds.Many of bifunctional molecules are used to produce medicine, catalysts and also used in condensation polymerization to synthesize polyester, polyamide, etc. [1][2][3].Biological molecules such as proteins are made up of bifunctional amino acids.Bifunctional molecules having -COOH and -NH 2 are used to synthesize polyamides by self polycondenzation reaction [4,5] and the molecules having active -NO 2 and -OH group are used to make polyether by nucleophilic displacement reaction [6,7].Bifunctional molecules having the combination of -COOH and -F, -CHO and -F, -CONH 2 and -F, -CN and -F, -COOH and -NO 2 , -CHO and -NO 2 , -CONH 2 and -NO 2, -COOH and -Cl, -CHO and -Cl, -CONH 2 and -Cl, etc. are used to synthesize numerous organic compounds that are used to prepare medicines, polymers, etc. [8,9].Among the bifunctional molecules, hydroxy acids (HAs) represent a class of compounds which have been widely used in a number of cosmetic, therapeutic formulations and polymer synthesis.Salicylic acid, a most important hydroxy acid is used as a starting material for synthesizing drugs etc.Even though the hydroxy acids are commercially important, the available compounds are less, particularly aromatic hydroxy acids are very limited.This prompted me to synthesize stable imide containing hydroxy acid.In this research work four novel imide containing hydroxy acid compounds are synthesized through two step process and the structures are characterized by spectroscopic analysis.

Materials and instruments
1 H-NMR spectra were recorded in DMSO-d 6 solution using Bruker 300 MHz instrument and FT-IR spectra were obtained on spectrum one (Perkin Elmer, USA).Aniline, bisphenol-A, 4aminophenol, 3-aminophenol, 5-amino-1-naphthol and trimellitic anhydride were purchased from Sigma-Aldrich Chemicals India and they were used without further purification.N-methyl pyrolidone (NMP) was distilled under reduced pressure before using.All the reagents used were analytical grade.The compound 2-(4-aminophenyl)-2-(4'-hydroxyphenyl) propane was prepared in the laboratory starting from bisphenol-A and aniline as per the procedure reported in our previous publications [10][11][12].

Structural characterization of hydroxy acid compounds by FT-IR spectroscopy
The hydroxy acid compounds were prepared by the nucleophilic substitution reaction of trimelitic dianhydrides with the corresponding aminophenol/aminonaphthol under nitrogen atmosphere using NMP as solvent in a two step process.In the first step intermediate amic acid was prepared through the nucleophilic attack of the amino group on the carbonyl carbon of the anhydride group.In the second step, the imidization was accompanied through nucleophilic attack of the amide nitrogen on the acid carbonyl carbon with the elimination of water.The complete cyclisation of the intermediate amic acid was achieved by toluene-water azeotropic distillation (Scheme 1).The FT-IR spectrum of the monomer IIIa (Figure 1) showed a characteristic absorption band for the imide ring at 1779 cm -1 (imides C=O symmetrical stretching), 1724 cm -1 (imides C=O asymmetrical stretching), 728 cm -1 (imide ring deformation).The stretching of -COOH group merged with penolic -OH stretching and showed a broad and strong absorption band at 3600-2500 cm -1 .The C-H (sp 2 ) absorption band (at 3330 cm -1 ) merged into the absorption band of -COOH and -OH group.The FT-IR spectrum of the compound IIIa confirmed the formation of imide ring between the trimellitic anhydride and 4aminophenol.Similarly the FT-IR spectral data of the hydroxy acid compounds IIIb, IIIc and IIId (Figure 2) supported the proposed structures.

Structural characterization of hydroxyl acid compounds by
The 1 H-NMR spectrum of N-3.The phenolic proton appeared as a singlet at 9.81 δ ppm.The two aromatic protons the hydroxyl group appeared as a doublet at to the hydroxyl group appeared as a doublet at and ortho to the carboxylic group and flanked between by imide carbonyl and carboxyl group appeared as a doublet at 8.06 proton flanked by imide carbon protons designated in

CONCLUSION
We have successfully synthesised four imide containing hydroxyl acid (HA) compounds through two step process with high yield.The structures of the compounds are confirmed by FT-IR and 1 H-NMR spectroscopy analysis.These compounds can be used as a starting material for synthesize of new organic compounds and also can be used to synthesise polyesters, polyether, polyamides, etc.Thus, these HAs are considered to be more useful compounds for further applications.

Figure range 8 .
41-8.03 δ ppm because of the electron withdrawing peaks at 2.5 δ ppm and at 3.4 δ ppm are due to DMSO and water in DMSO.Similarly the NMR spectrum of the hydroxyl acid compounds (Figure6) supported the proposed structures.

Figure 4 . 1 H
Figure ortho to δ ppm and the two aromatic protons meta δ ppm.The two aromatic proton meta to the carboxylic group and flanked between by imide carbonyl and carboxyl group respectively.The aromatic δ ppm.The "d", "e" and "f" appeared in the farthest downfield in the and imide groups.The 5 δ ppm and at 3.4 δ ppm are due to DMSO and water in DMSO.Similarly the 1 H-5) and IIId