Organic synthesis of the monomer of poly(p-phenylenevinylene) was performed starting by the 2,5-dimethylphenol compound. An iodine atom was added to one end of the aromatic ring and then the iodine atom was substituted by a cyano group. Opposite to the cyano group was added a chain of six carbon atoms and the end of the carbon chain has an added bromine atom. The characterizations of the obtained compounds were made by FTIR, GC-MS, 1H, and 13C NMR and showed that almost all of the proposed monomers were obtained in their totality.
One of the ways used to change the electronic properties of conjugated polymers is to add side chain substituents, donors, and/or electron acceptors in the polymer chain, as it is known that when substituted benzenes undergo electrophilic attack, the substituent groups already present in the ring affect the rate of reaction and the attack site. The substituent groups can be divided into two classes according to their influence on the reactivity of the ring [
Those which make ring more reactive than benzene are activator groups, and those which make the ring less reactive than benzene are called deactivator groups. The activating groups on the aromatic ring influence electrophilic reactions in order to guide the attack electrophiles in a position
Two effects are responsible for the orientations of the aromatic electrophilic substitutions: inductive effect and the resonance effect. The resonance effect, that is, the effect realized by hydroxyl present in the 2,5-dimethylphenol, is found by substituents which have one or more pairs of nonbonding electrons and refers to the ability to increase or decrease the stability of intermediate ion by resonance [
Resonance structures of
By carefully choosing the deactivator or activating group or altering the side chain functionalities, one should be able to fabricate polymeric films to be applied as an active layer of electrochemical sensors, for example, humidity sensors [
In this paper we propose the synthesis of a derivative monomer PPV that has in its structure a cyano group and
In this organic synthesis, Scheme
Synthesis of 4-iodo-2,5-dimethylphenol.
The mixture was stirred with the aid of magnetic stirring and after the addition of all the solution from the funnel, the mixture was left under stirring for another two hours at a temperature between 0 and 2°C [
In the synthesis of Scheme
Synthesis of 4-hydroxy-2,5-dimethylbenzonitrile.
The system has been mounted in which a flask inputs received the dropping funnel; the other was connected to a condenser and the third way is closed. With the aid of magnetic stirrer and heater it started heating. With the beginning of reflux the entire solution was dripped slowly in the dropping funnel. After complete addition, the solution was refluxed continuously for another 6 hours [
After this stage, the solution was cooled down to obtain better crystals and then filtered. For purification the product was performed chemically active with an extraction solvent, where it is first dissolved in chloroform and we transferred the entire contents to a separating funnel, which underwent five washes with 5% sodium hydroxide. When obtaining an aqueous extract it was adjusted to pH 7.0 with drops of concentrated hydrochloric acid to obtain a precipitate which is filtered and dried in a vacuum desiccator [
The synthesis of Scheme
Synthesis of 4-[(6-hydroxyhexyl)oxy]-2,5-dimetilbenzonitrile.
The reaction proceeded with stirring and reflux for 22 hours. After complete reaction the product was extracted with 30 mL of chloroform. This organic phase was washed with a sodium hydroxide solution of 10% and boiling water successively. Dry the resulting organic layer with anhydrous magnesium sulphate for 24 hours, and then we filtered and carried out a fractionated distillation of the solvent under reduced pressure, b.p. about 40°C/400 mmHg, to give 4-[(6-hydroxyhexyl)oxy]-2,5-dimethylbenzonitrile, a light brown oil [
For this synthesis, Scheme
Synthesis of 4-[(6-bromohexyl)oxy]-2,5-dimetilbenzonitrile.
The system was allowed to warm to 30°C for 2 hours and formed two phases. We moved the cooled reaction mixture to a separatory funnel, separated the organic phase, washed it with 20 mL 10% hydrochloric acid, 20 mL of distilled water, and 10 mL of an aqueous solution of 5% sodium hydroxide, and finally we washed it again with 20 mL of distilled water. The dry organic phase was extracted with anhydrous magnesium sulphate during a time of 24 hours.
With filtration of the dried product directly to a 25 mL flask and held fractional distillation under reduced pressure, b.p. about 40°C/400 mmHg, the yield was approximately 85%.
In addition to the techniques FTIR and NMR this reaction was characterized by GC-MS to verify the change of the hydroxyl group by bromine.
The solid obtained was dissolved in appropriated solvent at room temperature. An appropriate solution volume was injected into the chromatographer with a microsyringe. GC-MS was performed in a Shimadzu gas chromatograph coupled with a mass selective detector model QP2000A.
A 60 m long and 0.25 mm diameter SE-30 GC capillary column coated with poly(dimethyl siloxane) was used and the appropriate solution was injected at 80°C. Column temperature was programmed to remain at 40°C for 6 min and then raised to 150°C at a heating rate of 10°C min−1. Helium was used as a carrier gas at a flow rate of 30 mL min−1.
In the reaction described for obtaining 4-iodo-2,5-dimethylphenol, it is necessary basic medium to occur, NaOH, because the presence of the base has the function to remove a proton from the hydroxyl group present in the compound 2,5-dimethyl-phenol, thereby forming an activating group
To precipitate the crystals, the pH was adjusted to 7 for the product to acquire the characteristic of the organic salt and thus lose the water solubility. We carried out measurement of the melting point and this was 90°C, while the theoretical melting point of this compound is between 94 and 95°C. Compared to the melting point of 2,5-dimethylphenol, 75°C, it appears that the increase in temperature recorded is consistent, given that the addition of an iodine atom increases the molecular weight of the compound thereby increasing its melting point.
The compound was characterized by infrared spectroscopy, FTIR, and nuclear magnetic resonance 1H NMR, and such characterizations are shown in Figures
FTIR spectrum of 4-iodo-2,5-dimethylphenol.
1H NMR spectrum of 4-iodo-2,5-dimethylphenol.
In Table
Major bands found in the FTIR spectrum of 4-iodo-2,5-dimethylphenol.
Chemical bond | Stretch | Absorption band (cm−1) |
---|---|---|
O-H | Axial deformation | 3340 |
C-H Csp3 methyl | Axial deformation | 2914–2857 |
C=C aromatic ring | Axial deformation | 1543, 1406 and 1250 |
C-O | Axial deformation | 1134 |
C-I | Vibration | 602 |
The characterization by 1H NMR to ascertain main reason is that the connection of the ring formed with iodine is carried out in carbon position to the radical present in the phenol ring.
The 1H NMR spectrum of Figure
The result showed that the product obtained was really the 4-iodo-2,5-dimethylphenol. The yield of synthesis was about 70%. One possible alternative for increasing the yield of this reaction was dripped sodium hypochlorite more slowly to the reaction mixture or to control the temperature so that it does not exceed 2°C [
The inclusion of the cyanide group,
The theoretical melting point of this compound is 110°C. The melting point of the compound is consistent when comparing it with the 2,5-dimethylphenol, 75°C, and the 4-iodo-2,5-dimethylphenol, 90°C, since the addition of a CN group increases the number of hydrogen bonds by increasing the intermolecular force system which causes the melting point to be also higher. To verify the formation of CN-C coupling was performed and FTIR spectroscopy, obtaining the spectrum of Figure
FTIR spectrum of 4-hydroxy-2,5-dimethylbenzonitrile.
The assignment of the bands observed in this spectrum can follow the same system used in the allocation of spectrum bands of 4-hydroxy-2,5-dimethylbenzonitrile. However one must consider the disappearance of the band at 602 cm−1 shown in Figure
In Table
Major bands found in the FTIR spectrum of 4-hydroxy-2,5-dimethylbenzonitrile.
Chemical bond | Stretch | Absorption band (cm−1) |
---|---|---|
O-H | Axial deformation | 3332 |
C-H Csp3 methyl | Axial deformation | 2922–2857 |
CN | Axial deformation | 2224 |
C=C aromatic ring | Axial deformation | 1543, 1406 and 1250 |
C-O | Axial deformation | 1134 |
The 1H NMR spectrum in Figure
1H NMR spectrum of 4-hydroxy-2,5-dimethylbenzonitrile.
In the spectrum of Figure
Peaks found in the 1H NMR showed the chemical shifts expected for the hydrogen atoms present in the molecule 4-hydroxy-2,5-dimethylbenzonitrile. With the results obtained by the characterizations, we confirmed the formation of the expected product in this organic synthesis.
This reaction aims to form a compound containing six carbon atoms between the aromatic ring and an OH grouping at end of chain. This structure is interesting to act as a strong flexible drive to the proton conduction function in the compound after the polymerization [
According to the spectrum shown in Figure
FTIR spectrum of 4-[(6-hydroxyhexyl)oxy]-2,5-dimethylbenzonitrile.
The values of the bands of each connection are shown in Table
Major bands found in the spectrum FTIR of 4-[(6-hydroxyhexyl)oxy]-2,5-dimethylbenzonitrile.
Chemical bond | Stretch | Absorption band (cm−1) |
---|---|---|
O-H | Axial deformation | 3400 |
C-H Csp3 methyl | Axial deformation | 2940 |
C-H Csp3 (-CH2-) | Axial deformation (asymmetric and symmetric) | 2853 |
CN | Axial deformation | 2220 |
C=C aromatic ring | Axial deformation | 1600, 1500 |
C-O (alkyl-aryl-ether) | Axial deformation (asymmetric and symmetric) | 1250 |
C-O alcohol | Axial deformation | 1080 |
1H NMR Spectrum of 4-[(6-hydroxyhexyl)oxy]-2,5-dimethylbenzonitrile.
The spectrum of Figure
It can be said then that the aromatic ring is connected to not only the methyl group in positions 2 and 5 because of the signs in 2.47 and 2.15 ppm, but also the cyano group and the side chain composed of 6 carbon atoms attached to the aromatic ring and a hydroxyl group at the end of carbon chain.
According to Figure
FTIR spectrum of 4-[(6-bromohexyl)oxy]-2,5-dimethylbenzonitrile.
It is also possible to see that there was a decrease of the band at 3470 cm−1 when compared to the spectrum of Figure
1H NMR spectrum of 4-[(6-bromohexyl)oxy]-2,5-dimethylbenzonitrile.
Figure
In Figure
13C NMR spectrum of 4-[(6-bromohexyl)oxy]-2,5-dimethylbenzonitrile.
The chemical shifts of the signal expected for the carbon-bromine bond are at 33.80 ppm, whereas carbon-hydroxyl bond happens at 62.70 ppm. There is a chemical shift signal at 32.79 ppm and a small signal at 33.60 ppm. These values could be evidence that the compound 4-[(6-bromohexyl)oxy]-2,5-dimethylbenzonitrile was obtained but in the same spectrum there is a signal at 62.93 ppm. These values lead us to believe that the compound was obtained but is present in a mixture with the 4-[(6-hydroxyhexyl)oxy]-2,5-dimethylbenzonitrile compound.
In Figure
Mass spectra of 4-[(6-bromohexyl)oxy]-2,5-dimethylbenzonitrile.
Due to large extension of the target molecule an enormous fragment was waited in chromatogram. Peak with
In this work organic synthesis of the monomers precursors of class of the
The authors declare that there is no conflict of interests regarding the publication of this paper.