Vibrational study and thermal behavior of dihydrogenotriphosphate trihydrate of 4-aminobenzoic acid and its anhydrous new form fertilizer type NP

Chemical synthesis methods and IR spectrometry studies are reported for an organic triphosphate (NH3C6H4COOH)3H2P3O10.3H2O and its anhydrous new form NH3C6H4COOH)3H2P3O10. The hydrate compound (NH3C6H4COOH)3H2P3O10.3H2O was synthetized by the ion-exchange resin method. The dehydration of (NH3C6H4COOH)3H2P3O10.3H2O leads at 130°C to (NH3C6H4COOH)3H2P3O10 crystallizing in the triclinic system with space group P 1 (Z = 2) [a = 14.566(6) Å, b = 6.866 (1) Å, c = 6.445 (6) Å, α = 112.36 (3) °, β = 94.51 (1) °, γ = 95.94(7) °, and V = 587.98 (1) Å]. Merit’s figures are M (10) = 91.9 and F (10) = 55.6 (0.0032, 56). Its thermal behavior and kinetic study were studied by using thermal analyses TGA and DTA techniques between 25 and 600°C.


Introduction
The P-carboxyphenylamine (4-aminobenzoic acid) considered as a biological molecule, has an anticoagulant and antioxidant properties. It exists naturally in foods; it is produced by essential symbiotic bacteria to metabolize constantly in the human body 1 . The active sites of several biological systems have kind of hydrogen bonding in hybrid compound 2 . Indeed, the crystal structures of 4-carboxyphenylammonium dihydrogen phosphate and 4-carboxyanilinium hydrogen sulphate compounds have been recently studied 3,4 . Furtherer, the p-carboxyphenylammonium dihydrogen-monophosphate monohydrate compound was found to consist of H2PO4anions, water molecules and p-HOOC-C6H4-NH3 + cations 5 . In this structure, anions and cations are linked to each other through strong hydrogen bonds, formed by all H atoms covalently bonded to anions, nitrogen, carboxylic groups and water molecules. A three-dimensional complex network of hydrogen bonds ensures the cohesion of the ionic structure.
The present study reports on the chemical preparation, IR vibrational spectroscopy, thermal dehydration and decomposition by thermal analyses (TGA and DTA) of (NH3C6H4COOH)3H2P3O10.3H2O. The total thermal dehydration of this compound leads to the corresponding anhydrous form, which is a new triphosphate of para carboxyphenylammonium (NH3C6H4COOH)3H2P3O10. The kinetic parameters of dehydration have been studied for the title compound. Indeed, (NH3C6H4COOH)3H2P3O10.3H2O and (NH3C6H4COOH)3H2P3O10 are binary organic fertilizers type NP (nitrogen and phosphorus) second generation and corrosion inhibitors [14][15] . The two triphosphates associated with para carboxyphenylammonium reported in the present work are stable in the normal conditions of temperature and hygrometry.

Synthesis (NH3C6H4COOH)3H2P3O10.3H2O
Single crystals of (NH3C6H4COOH)3H2P3O10.3H2O were prepared by slowly adding dilute cyclotriphosphoric acid, H5P3O10, to an aqueous solution of para carboxyphenylammonium, NH2C6H4COOH according to the following chemical reaction: The so-obtained solution was then slowly evaporated at room temperature until large prisms of (NH3C6H4COOH)3H2P3O10.3H2O were obtained. The triphosphoric acid, H5P3O10, used in this reaction was prepared from an aqueous solution of Na5P3O10 passed through an ion-exchange resin 'Amberlite IR120' 11 . (NH3C6H4COOH)3H2P3O10.3H2O is stable in the normal conditions of temperature and hygrometry. (NH3C6H4COOH)3H2P3O10.3H2O was also obtained using the same method, by the hydrolysis of P3O9 3ion in aqueous solution (NH3C6H4COOH)3H2P3O10.
The product resulting from the total thermal dehydration of (NH3C6H4COOH)3H2P3O10.3H2O, at 130°C, is a new anhydrous triphosphate of para carboxyphenylammonium (NH3C6H4COOH)3H2P3O10. The reaction is the following: (NH3C6H4COOH)3H2P3O10 is stable in the normal conditions of temperature and hygrometry.
With the additional increase in temperature, (NH3C6H4COOH)3H2P3O10 is decomposed by evolving NH3 followed by CO2.

Data Collection and Reduction
Thermal behavior. Coupled TGA-DTA thermal analyses were performed using the multimodule 92 Setaram Analyzer operating from room temperature up to 1400°C, in a platinum crucible, at various heating rates from 1 to 15°C/min. Infrared spectrometry. The infrared spectra of the powdered samples of (NH3C6H4COOH)3H2P3O10.3H2O and (NH3C6H4COOH)3H2P3O10 were recorded in the range 4000-400 cm -1 with a Perkin-Elmer IR 983G spectrophotometer, using samples dispersed in spectroscopically pure KBr pellets.

Vibrations analysis of H2P3O10 3-
The anion dihydrogenotriphosphate (H2P3O10) 3− supposed to be of symmetry group C1, has 39 internal vibration modes [Γint =3 9A' (IR, Ra)]. According to this hypothesis, the anionic modes of (H2P3O10) 3− free are all active in Raman and Infrared thus should appear in the form of simple bands.
In the structure of (NH3C6H4COOH)3H2P3O10.3H2O,), space group _ 1 P (Group of factors Ci) 16 , (H2P3O10) 3− The anions have a C1 site symmetry. This implies that all anionic internal modes (Table 1) generally remain infrared and Raman assets in the crystal site group. Theoretically, the presence of two units per unit of formula (Z = 2) doubles the number of cationic and anionic modes with Ag and Au symmetry in the group of factors C i . In the crystal being centrosymmetric (Ci group factor), only Au insensitive augs are active in infrared. All modes of vibration are theoretically active in infrared and Raman. These anionic modes correspond mainly to the vibrations of the PO4 3and P-O-P.

Vibrations analysis of 4-carboxyphenyl ammonium
The free 4-carboxyphenyl ammonium cation is assumed to be of Cs symmetry point group, and then has 48 internal vibrational modes described as Γint = 32A' (IR, Ra) + 16 A' (IR, Ra). According to this assumption, the cationic modes are all Raman and Infrared active and should appear as single bands. In the structure of (NH3C6H4COOH)3H2P3O10.3H2O compound, of P1 space group (C i factor group) 16 , 4-carboxyphenyl ammonium cations have C1 site symmetry. This implies that all cationic internal modes ( Table 2) usually remain infrared and Raman actives in the site group of the crystal. The presence of two motifs per formula unit (Z = 2) doubles theoretically the number of cationic modes having Ag and Au symmetry in the factor group C i . It is concluded that all vibrational modes are theoretically Infrared and Raman active. Due to the centro symmetry of the crystal, only the ungerade modes Au are Infrared active for the cations. The mainly crucial cationic vibration bands correspond principally to the vibrations of amino NH3 + , carboxyl groups and benzene ring. It is to note that the distribution of the internal vibrations modes for benzene group by developing the normal coordinate analysis has been carried out 17 . In its free state, the NH3 + cation has C3v symmetry with a pyramidal geometry; the corresponding normal vibrational modes are described as non-degenerative modes [ν1(A1), ν1(A1)], and doubly degenerated [ν3(E) and ν4(E)], which all active as well as in Raman and Infrared. In the 4-carboxyphenyl ammonium cation of Cs symmetry, all NH3 + modes become nondegenerative, with A' and A" symmetry as indicated above, and usually remain Infrared and Raman active. The COOH has 9 internal vibrations modes given by 3m-3, where m is the number of atoms in the group. These modes correspond to O-H stretching, C-O stretching, C=O Stretching, in-plane-rocking, in-plane bending of C-O, in-plane bending of C=O, in-plane-bending of OH, out-of-plane wagging, and out-of-plane torsion.

Infrared Spectra of hydrate and anhydrous compounds
The infrared spectra of (NH3C6H4COOH)3H2P3O10.3H2O and (NH3C6H4COOH)3H2P3O10 compounds, recorded the range 4000-400 cm -1 , are given in Figures 1a and 1b. These compounds consist of NH3 + groups, COOH; para-substituted benzene ring, H2P3O10, and 3H2O in the case of hydrate compound. * NH3 + vibrations: Generally, the antisymmetric and symmetric stretching modes of the NH3 + group appear in the spectral region of 3200-2800 cm -1 spectral region; whereas the antisymmetric and symmetric deformations appear in the 1660-1610 cm -1 and 1550-1480 cm -1 regions, respectively. In the Infrared spectrum of the anhydrous compound, the νas (NH3 + ) stretching is observed as a medium band at 3230 cm -1 . The νs (NH3 + ) stretching modes give a weak and broad band at 2880 cm -1 in the case of the anhydrous compound and a medium band at 2887 cm -1 for the hydrated compound. The remaining bands corresponding to wagging w(NH3 + ), twisting t((NH3 + ) and rooking ρ (NH3 + ) bending vibrations are assigned as indicated in Table 3.
* Para substituted benzene ring vibrations: The C-H stretching modes of benzene ring are generally expected in the 3115-3005 cm -1 20, 21 . The β(C-H) "in-plane" and δ(C-H) "out-plane" bending vibrations are located in the range 1250-1000 cm -1 and 900-690 cm -1 , respectively 21,22 . For the studied compounds, the β(C-H) and δ(C-H) of the benzene ring are observed in the expected ranges, as indicated in Table  3. The C=C and C-C benzene ring stretching modes occur in the 1650-1430 cm -1 and 1400-1300 cm -1 , regions respectively 20, 21 . For the two compounds, these modes are assigned to the corresponding bands as illustrated in Table 3. Finally, the C-N stretching and the ring breathing modes were identified for the studied compounds and given in Table 3.
* H2P3O10 3vibrations: The assignment of bands due to the fundamental modes, valence and bending, of P3O10 5anions are presented in Table 3 for both triphosphates. The frequencies of the P3O10 5anion are assigned based on the characteristic vibrations of the P-O-P bridge, PO2 and PO3 groups. Since the P-O bond in the PO2 and PO3 group is weaker than that in the P-O-P Bridge, the vibrational frequencies of PO2 and PO3 are expected to be higher than those for P-O-P. The bands due to the symmetric and antisymmetric stretching frequencies of PO2 and PO3 in P3O10 5are generally observed in the region 1190-1010 cm -1 22, 23 . The bands observed in the domain 970-840 cm -1 are attributed to the antisymmetric and symmetric POP stretching modes. The bands due to δ(OPO), δ (PO2), δ (PO3) and δ (POP) are also identified in Table 3, which contains the IR frequencies and the vibrational modes corresponding to Rb3H2P3O10.1,5H2O, paracarboxyphenylammonium NH2C6H4COOH, compared with those of (NH3C6H4COOH)3H2P3O10.3H2O and (NH3C6H4COOH)3H2P3O10. The IR frequencies of the P3O10 5anions observed in the two triphosphates associated to para carboxyphenylammonium, (NH3C6H4COOH)3H2P3O10.3H2O and (NH3C6H4COOH)3H2P3O10, are the same as those observed in the triphosphate associated to rubidium Rb3H2P3O10.1,5H2O 22   1673  1698  1632  1602  1614  1600  1580  1578  1561  1532  1550  1539  1510  1516  1441  1431  1468  1420 1403 1424

Study of the thermal behavior of (NH4)3P3O9
To facilitate the thermal behavior study of (NH3C6H4COOH)3H2P3O10.3H2O, we firstly studied the decomposition of (NH4)3P3O9, which was prepared by the method of ion-exchange resin 9 , and characterized crystallographically by M. Bagieu-Beucher in 1976 23 . It crystallizes in the monoclinic system with space group P21/n (Z = 4) (C2h 5 ), and parameters: a = 11,515 Å, b = 12,206 Å, c = 7.699 Å, β = 101.63 °. The structure of (NH4)3P3O9 was resolved using that of its isotype K3P3O9 23 . In this structure, the P3O9 cycle does not have proper symmetry. Its C1 symmetry is approximately C3v, where k + cations or NH4 + occupy three separate sites.
Indeed, we have prepared (NH4)3P3O9 by the exchange resin method and controlled its purity by X-ray diffraction, and then we examine the thermal behavior, between 25 and 1400°C (sample mass: 23 mg) using the coupled TG-DTA analyses with a heating rate of 1°C/min. TGA, DTA and DTG curves ( Figures 2 and 3) show two distinct steps. The first step between 180°C and 450°C corresponds to a loss in brutal mass 17.5%. This loss is the equivalent of three ammonia molecules per formula unit. The DTG curve indicates two distinct peaks, the first at 180 °C and the second at 295°C. However, the elimination of the first molecule of NH3 does not seem to be accompanied by a thermal effect. For the other two molecules of NH3, the DTA curve indicates a peak, endothermic top temperature to 290°C, which is of asymmetrical profile. This confirms the existence of more than one type of site occupied by NH4 + in the structure of (NH4)3P3O9. Moreover, explains the succeeding departure of 3 molecules of NH3 because of distinct bond energies. At 450°C, after the departure of 3 ammonia molecules per formula unit and a thermal residue, 240 g/mol, destroyed (NH4)3P3O9 and leads to H3P3O9. The reaction scheme is the following:  The second stage, between 450°C and 650°C, corresponds to a weight loss of 64.5%, the equivalent of 2/3 of the weight of thermal residue H3P3O9. This loss is accompanied by an intense and endothermic DTA peak at 586°C due to the decomposition of the acid H3P3O9 amorphous entity which releases H2O and P2O5 with a top speed at 560°C on the DTG curve. At 650°C, the reaction scheme is the following:

Study of the thermal behavior of (NH3C6H4COOH) 3H2P3O10.3H2O
The study of the thermal behavior of tetra (4-carboxyphenyl ammonium) dihydrogenotriphosphate trihydrate (NH3C6H4COOH)3H2P3O10.3H2O, was performed by linear increase in temperature from 25 to 600°C using the TGA coupled on thermodifferential of powder samples of about 20 mg, at different heating rates: v = 1, 3, 6, 10 and 15°C/min under atmospheric pressure.

Thermogravimetric analysis
The TGA thermograms of (NH3C6H4COOH)3H2P3O10.3H2O, realized at different heating rates (Figure 4), have all the same look and show five separate mass loss steps. Careful examination of the thermograms, carried out at low speed, indicates that the first step is not on that initially the water whereas the other four steps are related to entities from the decomposition of the organic matrix and the mineral matrix.
The TGA-DTA thermogram realized at a heating rate of 3°C / min ( Figure 5) shows 5 mass loss steps: -The first stage begins at 110°C and ends at 126°C. It appears to involve a single process of evolving water (mass loss calculated 7.47%, observed 7.5%). The DTG thermogram has a maximum loss of water at 118°C. Between 126 and 168°C, in the TGA thermogram, there is no variation of mass.
-The second step starts at 168°C and ends at 188°C. It corresponds to a mass loss, relatively fast, about 7.01%. It is attributed to the loss of three molecules of ammonia for which the loss mass is theoretically calculated of 7.05%. The maximum loss is observed on the DTG thermogram at 179°C. -The third stage, between 188 and 260°C, corresponding to a mass loss of 18.22%, is assigned to 3 moles of CO2 per formula unit (mass loss calculated 18.2%). Two loss maxima are reported on the DTG curve, during the third step, the first peak well pronounced at 197°C and a second peak doubtful to 214°C. -The fourth step starts at 260 and ends at 310°C. It corresponds to a weight loss of 13.4% and could be attributed to the loss of gas from the decomposition of the residual heat. The maximum rate of loss is observed on the DTG thermogram at 280°C.
-The fifth stage, between 310 and 530°C, corresponding to a mass loss of 20.9%. This loss could be attributed to the combustion of the organic matrix.  -The sixth stage, between 530 and 600°C, corresponding to a weight loss of 17%, is accompanied by a DTG peak at 567°C corresponding to the maximum speed of water H2O and pentaoxide phosphorus P2O5 release from the decomposition of the mineral matrix.

Differential thermal analysis
DTA thermograms made at different speeds and coupled with the thermogravimetric analysis are shown in Figure 6. The analysis of the thermogram corresponding to the heating rate 3°C/min (Figure 7) allows to highlight the following points: The first phase, between 110 and 126°C, accompanied by an endothermic peak at 118°C, which coincides with the maximum reported loss on the derivative curve at 118°C. This peak corresponds to the loss of 3 water molecules according to the following reaction scheme: An exothermic peak was observed at 147°C only for the weak heating rates for 1 and 3°C/min after the total removal of water. It corresponds to the crystallization of the corresponding anhydrous (NH3C6H4COOH)3H2P3O10. This wellcrystallized phase was characterized by its IR spectrum (Figure 1).
-The second stage, between 168 and 188°C, is accompanied by two endothermic peaks at 174 and 180°C. The last peak at 180°C coincides with the maximum loss at 179°C. These two endothermic effects are attributed to the loss of three molecules of ammonia. The presence of two endothermic peaks may be interpreted based on structural data of (NH3C6H4COOH)3H2P3O10.3H2O, which indicates the presence of three types of nitrogen atoms. The first endothermic peak at 174°C, can be attributed to the departure of two moles of ammonia NH3 (1) and NH3 (3), the two nitrogen atoms having thermal agitation factors very close 2,7 , and the second at 180 ° C, the last remaining ammonia molecule NH3 (2) (having a nitrogen atom of thermal agitation factor low 12 ). The reaction scheme is as follows: -The third stage, between 188 and 260°C, corresponding to the departure of 3 moles of CO2, is accompanied by an endothermic peak at 197°C which coincides with the maximum loss rep orted on the DTG curve peak at 197°C. It is worth noticing that this third stage can be subdivided into two distinct stages. The first one is made between 188 and 210°C, the second between 210 and 260°C. In this case, the endothermic peak observed at 197°C would be the CO2 group the more weakly bonded to the organic chain The endothermic peak observed at 197 ° C is related to the CO2 group, more weakly bonded to the organic chain (CO2 (7)), and it corresponds to the liberation of 6.06%, the CO2 removed between (1/3) 188 and 210°C (18.02%). The second stage from 12.1% per formula unit; (2/3) of CO2 corresponding to groups (CO2 (14)) and (CO2 (21)). Indeed, the structure of the compound shows that the C6-C7 distance is relatively longer, 1.498Å longer, longer than 1.498Å. The reaction scheme in this step is as follows: The thermal residue obtained at the end of the third stage (C6H5)3H2P3O10 after loss successively of 3 H2O, (2NH3, 1NH3) and 3 CO2 per formula unit undergoes thermal degradation of organic matrices and mineral. The ATD Thermogram brings up an exothermic peak at around 300°C, which could be attributed to an atomic reorganization. Indeed, the temperature of the start of the exothermic effect coincides with the onset temperature of the 4th stage and the exothermic peak observed at 300°C corresponds to the temperature of the end of this step.
-The fifth stage, between 310 and 530°C, make appear an exothermic peak at the top temperature of 432°C, which may be due to the burning of the residue of the organic matrix. Ozawa and KAS methods are selected in studying the kinetics of thermal dehydration of the title compound. So, water loss kinetic parameters were evaluated from the curves ln(v/T²m) = f(1/Tm) and ln(v) = f(1/Tm) (Figures 8 and 9), where (v) is the heating rate and Tm the sample temperature at the thermal effect maximum. The characteristic temperatures at maximum dehydration rates, Tm in °C, at different heating rates from the DTA curves of (NH3C6H4COOH)3H2P3O10.3H2O are gathered in Table 4.  (Figure 8), equals to : -Ea/R allows the apparent activation energy to be calculated (Table 4). With reference to the Ozawa method, the slope of the resulting straight line on the curve: ln(v) = f(1/Tm) (Figure 9), equals to -1.0516E/R, also allows the apparent activation energy to be calculated by this second way ( Table 4). The equations used for the two methods are the following: for KAS 27 (1) for Ozawa 27 (2) The pre-exponential factor or Arrhenius constant (A) and the related thermodynamic functions can be calculated by using the activated complex theory (transition state) of Eyring 29-31. The following general equation can be written 31 : Where e is the Neper number (e = 2.7183), χ is the transition factor, which is unity for the monomolecular reaction, kB is the Boltzmann constant ( kB = 1.3806 × 10-23 J K-1), h is Plank's constant ( h = 6.6261 × 10-34 J s), Tm is the peak temperature of the DTA curve, R is the gas constant ( R = 8.314 J K -1 mol -1 ) and S* is the entropy change of transition state complex or entropy of activation. Thus, the entropy of activation may be calculated as follows: The enthalpy change of transition state complex or heat of activation (H*) and Gibbs free energy of activation (G*) of decomposition were calculated according to Eqs. (5) and (6), respectively: Where, E* is the activation energy Ea of both KAS 25 and Ozawa 26 methods. The values of the activation energy are gathered in (Table 5). Thermodynamic functions were calculated from Eqs. (4), (5) and (6) and summarized in (Table 6). The negative values of S* from two methods for the dehydration step reveals that the activated state is less disordered compared to the initial state. These ΔS* values suggest a large number of degrees of freedom due to rotation which may be interpreted as a « slow » stage [30][31][32][33] in this step. The positive values of ΔG* at all studied methods are because, the dehydration processes are not spontaneous. The positivity of ΔG* is controlled by a small activation entropy and a large positive activation enthalpy according to the Eq. 6. The endothermic peaks in DTA data agree well with the positive sign of the activation enthalpy (ΔH*). The estimated thermodynamic functions ΔS* and ΔG* (equation 6, Table 6) from two methods are approximatively the same due to the same preexponential factor of about 10 12 . While ΔH* (equation 5, Table 6) exhibits, in all the cases, an independent behavior on the pre-exponential factor as seen from exhibiting nearly the same value.

Conclusion
The structural and thermal study of 4-carboxyphenyl dihydrogenotriphosphate ammonium trihydrate (NH3C6H4COOH)3H2P3O10.3H2O developed by IR spectrometry vibration and TGA-DTA analyses coupled brings up the following results: The reaction of phosphoric acid with aminobenzoic acid leads, due to the hydrolysis of P3O9 3ion in aqueous solution or by using H5P3O10, to a triphosphate with a formula (C7H8NO2)3H2P3O10.3H2O. The structural resolution shows the existence of ion channels H2P3O10 3linked together by hydrogen bonds. Organic cations, water molecules and phosphates chains are linked together by hydrogen bonds. A detailed vibrational study is reported for (NH3C6H4COOH)3H2P3O10.3H2O with all of its entities NH3, C6H4COOH, H2P3O10 and H2O. The thermal analysis showed that the compound is stable between 25 and 90°C and has confirmed the number of water molecules per formula unit. This loss of water takes place in one step and leads to the crystallization of the anhydrous phase, (C7H8NO2)3H2P3O10, which was characterized by its X-ray powder diffraction pattern and IR spectrum. This phase (C7H8NO2)3H2P3O10 was found stable in a small temperature range, 150-160°C. We have shown that by raising the temperature, the anhydrous phase loses successively 3H2O ((2) NH3, (1) NH3) and 3CO2 per formula unit. For each of these entities released, the apparent activation energy was measured. These energies are respectively 73,4 kJ/mol for 1 NH3 and 92,29 kJ/mol for 3CO2. Between 260 and 300°C, the residual mass, (C6H5)3H2P3O10 undergoes a weight loss corresponding to a molar loss of 70 g/mol. This weight loss is accompanied by an atomic rearrangement which results on the DSC thermogram with a peak at 300°C. Beyond 300°C, there is degradation of the organic matrix and / or the mineral matrix. An exothermic peak at the top temperature at 432°C could be the combustion of the residue of the organic matrix.