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Communication

Synthesis and Characterization of Amide-Based Cyclotriphosphazene Derivatives with Alkoxy Terminal Groups

by
Khairunnisa Abdul Rahim
and
Zuhair Jamain
*
Organic Synthesis and Advanced Materials (OSAM) Research Group, Faculty of Science and Technology, Universiti Malaysia Sabah, Jalan UMS, Kota Kinabalu 88400, Malaysia
*
Author to whom correspondence should be addressed.
Molbank 2025, 2025(3), M2039; https://doi.org/10.3390/M2039
Submission received: 30 May 2025 / Revised: 12 July 2025 / Accepted: 17 July 2025 / Published: 21 July 2025
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Abstract

A series of new amide-based cyclotriphosphazene molecules consisting of different terminal groups (heptyl, decyl, and tetradecyl) at the periphery was successfully synthesized and characterized. The reaction began with the alkylation of methyl-4-hydroxybenzoate with 1-bromoheptane, 1-bromodecane, and 1-bromotetradecane, which was followed by reduction with potassium hydroxide to form a series of benzoic acid intermediates (1a–c). These intermediates underwent a reaction with thionyl chloride, followed by a reaction with 4-nitroaniline and triethylamine, to form para-substituted amides (2a–c). Further reduction of intermediates 2a–c with sodium sulfide hydrate produced the anilines 3a–c. Another reaction of hexachlorocyclotriphosphazene (HCCP) with methyl-4-hydroxybenzoate yielded intermediate 4, which was then reduced with sodium hydroxide to form intermediate 5. Finally, chlorination of intermediate 5 with thionyl chloride, followed by a reaction with the aniline derivatives (3a–c), formed the hexasubstituted cyclotriphosphazene compounds 6a–c, with two amide linkages. The structures of these compounds were confirmed using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and CHN elemental analysis.

1. Introduction

Cyclotriphosphazenes contain six-membered ring structures formed by alternating phosphorus and nitrogen atoms. The alternating P and N atoms, with two substituents attached to each phosphorus atom of the cyclotriphosphazene, create a hexasubstituted cyclotriphosphazene. Hexasubstituted cyclotriphosphazenes, or hexachlorocyclotriphosphazene (HCCP), exhibit excellent thermal properties, including fire retardancy and self-extinguishing capabilities [1,2]. In addition, HCCP is known as a versatile core compound for synthesis, often undergoing nucleophilic substitution due to the high reactivity between the P–Cl bonds, leading to the formation hexasubstituted cyclotriphosphazene derivatives [3,4,5].
HCCP compounds have long been considered as fire retardants with a wide range of thermal and chemical stability [6,7,8,9]. Researchers found that the nitrogen and phosphorus atoms in cyclotriphosphazene contribute to its thermal, fire retardant and self-extinguishing properties [10,11]. The incorporation of hexasubstituted cyclotriphosphazenes into the polymer matrix improves its thermal properties [12,13,14], which are valuable for industrial applications such as fire retardants [15], coatings and adhesives [16], and liquid crystals [17]. Examples of these compounds are illustrated in Figure 1.
Amides are known for their thermal stability and ability to form hydrogen bonds and serve as linking units in compounds to enhance the fire retardant properties [17]. The linking unit is attached between the ring systems to lengthen the molecules and modify their polarizability and flexibility [18]. Moreover, linking units are structural units that connect the cores of molecular structures and maintain the compatibility and linearity of the molecular structure effectively [19]. The linking groups, such as amide linking units or Schiff bases, can combine with phenyl rings to improve the polarizability of molecules [20,21]. The presence of an amide linking unit increases the rigidity of the molecular structure due to the partial double bond character of the C–N bond [22,23,24]. Amide linkages have excellent thermochemical performance, including a high thermal degradation temperature [25].
Hence, this study aims to synthesize a new type of hexasubstituted cyclotriphosphazene with several types of terminal groups. These compounds are important for use in advanced technologies such as high-performance polymers in automotive components, protective coatings and applications in energy storage devices. The newly synthesized amide-based cyclotriphosphazene compounds are quite useful because they are expected to act as additives and also to enhance the fire retardant properties when incorporated into polymer materials.

2. Results and Discussion

2.1. Synthesis Flow

Benzoic acid derivatives 1a–c were synthesized using the alkylation reactions of methyl-4-hydroxybenzoate with different alkyl bromides (heptyl, decyl, and tetradecyl), as shown in Scheme 1 [26]. Next, the reaction of 1a–c with thionyl chloride, followed by the reaction with 4-nitroaniline and triethylamine, formed para-substituted amides 2a–c [27]. Subsequently, reduction of intermediates 2a–c with sodium sulfide hydrate formed anilines 3a–c (Scheme 2) [28]. The reaction of cyclotriphosphazene with methyl-4-hydroxybenzoate yielded hexasubstituted derivate 4, which was then reduced with sodium hydroxide to form intermediate 5 [29]. The final step involved chlorination with the thionyl chloride of benzoic acid derivative 5 and the reaction of the benzoyl chloride intermediates with aniline derivatives 3a–c to form the hexasubstituted cyclotriphosphazene compounds 6a–c (Scheme 3) [17]. All the compact data for these compounds have been summarized in Section 3.3, along with the NMR spectrum for all the compounds in the Supplementary Materials Section.

2.2. FTIR Spectral Discussion

FTIR spectroscopy was used in this study to identify the functional groups in the compounds by measuring the infrared light absorption. According to the FTIR spectra of compounds 6a–c (Figure 2), the characteristic N–H stretching of hexasubstituted cyclotriphosphazene with amide linkages was observed at 3350 cm−1. However, the FTIR spectra did not show this peak clearly, which might be due to the complexity of the compound hindering the appearance of this peak [30]. Compounds 6a–c showed bands at 2931 and 2897 cm−1 for the symmetrical and unsymmetrical Csp3–H stretching, respectively. The absorption band at 1658 cm−1 is attributed to C=O stretching. Other peaks, such as C=C and C–O, were observed at 1600 and 1250 cm−1, respectively. The structure of the cyclotriphosphazene in the compounds was characterized by the peaks at 1175 and 969 cm−1 for P=N stretching and P–O–C stretching, respectively.

2.3. NMR Spectral Discussion

Compound 6a was chosen as the representative structure of the final compound among the homologues. The complete atomic numbering of its structure is depicted in Figure 3.
The 1H NMR spectrum of compound 6a (Figure 4) showed two singlet signals at 10.05 (H-11) and 10.14 (H-6) ppm, indicating the presence of two amide linkages (-CO-N–H) in the molecule, which confirms the successful formation of the second amide linkage unit. H-11 experienced a more downfield shift due to its proximity to the cyclotriphosphazene ring system. Six aromatic protons appeared as doublets in the range of 6.58–8.32 ppm and were assigned to the para-substituted aromatic protons. H-3 was assigned to 8.32 ppm due to its proximity to the electronegative carbonyl group and the cyclotriphosphazene ring [31]. The signals at around 7.92 and 7.95 ppm almost overlapped and appeared as two attached doublets due to their similar chemical environment, showing only a slight difference in the chemical shift [32]. Referring to the chemical structure of the compound, H-2 was assigned to 7.95 ppm as it was close to the cyclotriphosphazene ring, while the peak at 7.92 ppm was assigned to H-14. H-15 was assigned to 7.07 ppm, while H-8 and H-9 experienced less deshielding and resonated at 6.58 and 7.00 ppm, respectively. The oxymethylene proton was observed at 4.03 ppm (H-17), and the heptyl chains were observed in the upfield region at 1.30–1.84 ppm (H-18–H-22). A triplet in the most upfield region (0.89 ppm) was assigned to H-23.
The assignment of all the proton correlations was further confirmed via the COSY (1H–1H) NMR experiment. The COSY (1H–1H) NMR spectrum showed the correlation between the protons and their neighboring protons. Based on Figure 5 showing the COSY (1H–1H) NMR spectrum, H-6 and H-11 were not correlated with the other protons, confirming the presence of the amide linking units. Next, the aromatic protons can be seen to be correlated between H-2 and H-3, H-8 and H-9, and H-14 and H-15, respectively. These protons were assigned to the para-substituted positions in compound 6a. Lastly, the heptyl protons showed correlations between them accordingly.
The 13C NMR spectrum (Figure 6a) reveals the total carbon content of compound 6a, showing that it contains 21 carbons in the side arms. These include two carbonyl carbons, six aromatic carbons, six quaternary carbons, six methylene carbons, and one methyl carbon. The DEPT experiment was conducted to differentiate between the various types of carbons. DEPT 135 (Figure 6c) shows methylene (CH2) carbons as negative signals, while the methine (CH) and methyl (CH3) carbons appear as positive signals. Meanwhile, DEPT 90 (Figure 6b) reveals the presence of aromatic or methine (CH) carbons in the spectrum of compound 6a.
The aromatic carbons appear at 114.95 (C-9), 116.24 (C-8), 123.09 (C-15), 124.69 (C-14), 125.64 (C-2), and 129.11 (C-3) ppm. The signals of the six quaternary carbons were assigned to 145.01 (C-13), 146.80 (C-4), 148.10 (C-10), 155.96 (C-7), 162.95 (C-16), 163.01 (C-1), 165.06 (C-12), and 166.00 (C-5) ppm. The disappearance of these carbon signals in both DEPT spectra confirms that they are indeed quaternary carbons. Based on Figure 6a, C-5 is located at 166.00 ppm, which is in the more downfield region of the spectrum. The signal for C-5 is further downfield than that of C-12 due to the electronegativity of cyclotriphosphazene, which results in a lower electron density around the carbon, causing a greater deshielding effect on the former carbon [33]
Furthermore, the methylene carbons resonate at 68.57 (C-17), 31.78 (C-18), 29.16 (C-19), 29.05 (C-20), 25.98 (C-21), and 22.62 (C-22) ppm. These methylene carbons (C-15–C-20) show signals in the negative region of the DEPT 135 spectrum. However, the signal at 14.10 ppm disappears in DEPT 90 but appears in the positive region of the DEPT 135 spectrum, which confirms that this carbon signal belongs to the methyl carbon (C-23).
The protonated carbons of compound 6a were confirmed via the HSQC NMR experiment (Figure 7). The aromatic correlations were observed at H-2 and C-2 at 125.64 ppm; H-3 and C-3 at 129.11 ppm; H-8 and C-8 at 116.24 ppm; H-9 and C-9 at 114.95 ppm; H-14 and C-14 at 124.69 ppm; and H-15 and C-15 at 123.09 ppm. The oxymethylene proton of H-17 was observed at 4.03 ppm and was correlated with C-17 at 68.57 ppm. Moreover, the connectivity of the methylene protons of H-18–H-22 was observed with the corresponding carbons of C-18–C-22 in the HSQC spectrum. A triplet signal at 0.89 ppm (H-23) for the methyl proton showed the connectivity with its methyl carbon at 14.10 ppm. Table 1 summarizes the COSY (1H–1H) and HSQC (1H–13C) spectral data of compound 6a.
The 31P NMR spectrum (Figure 8) of cyclotriphosphazene shows chemically equivalent phosphorus atoms in compound 6a, corresponding to a singlet signal at 9.11 ppm. Jamain et al. (2020) reported that the pure HCCP region is observed in the downfield region at 20.00 ppm [22]. The 31P NMR spectrum appears in the most upfield region (9.11 ppm), indicating that all the phosphorus atoms have been substituted with the same side arms. As the hexasubstituted cyclotriphosphazene undergoes more shielding, the peak for the hexasubstituted cyclotriphosphazene ring shifts to the upfield region [17].

3. Materials and Methods

3.1. Chemicals

The chemicals and solvents used in this research were 1-bromoheptane, 1-bromodecane, 1-bromotetradecane, 4-nitroaniline, acetone, ethanol, hexachlorocyclotriphosphazene, methyl-4-hydroxybenzoate, N,N-dimethylformamide (DMF), n-hexane, ethyl acetate, thionyl chloride, methanol, potassium carbonate, potassium iodide, potassium hydroxide, sodium hydroxide, sodium sulfide hydrate, hydrochloric acid, dichloromethane (DCM), tetrahydrofuran (THF) and triethylamine. All the chemicals and solvents were used in this study as received, without any further purification, and they were purchased from Merck, QREC, Sigma-Aldrich, Acros Organics, Fluka and BDH Laboratory.

3.2. Instrumentation

The synthesized compounds were analyzed using FTIR (Bruker ALPHA II, Bruker, Ettlingen, Germany) to identify the functional groups in the range of 500–4000 cm−1. NMR (Bruker 500 MHz Ultrashield, Bruker Corporation, Karlsruhe, Germany) was used to determine their structures by studying the 1H, 13C, and 31P nuclei, with CDCl3 and DMSO-d6 used as solvents. Around 20 mg of each sample was dissolved in a deuterated solvent and placed in an NMR tube. CHN analysis was conducted to check the purity of the compounds by comparing the measured carbon, hydrogen, and nitrogen content with the theoretical values.

3.3. Synthesis Method

3.3.1. Synthesis of 4-(Alkoxy)benzoic Acid (1a-c)

Intermediate 1a is used as a representative method of discussion. Methyl-4-hydroxybenzoate (0.1 mol) was dissolved in DMF (20 mL), while 1-bromoheptane (0.1 mol) was dissolved in DMF (20 mL), separately. The solutions were mixed, and under stirring, K2CO3 (0.15 mol) and KI (0.01 mol) were added to the mixture and subjected to reflux for twelve hours. The reaction progress was monitored using a thin layer of chromatograph (TLC). Upon completion, the mixture was poured into cold water (300 mL) and the resulting precipitate was filtered off and dried overnight.
The precipitate was then dissolved in EtOH (250 mL) containing KOH (0.20 mol) and the reaction was refluxed for three hours. The progress of the reaction was continuously monitored using TLC. The mixture was then poured into water (300 mL). Next, 1N HCl was added until the pH = 4–5. Stirring was continued until a precipitate formed. The precipitate was collected, filtered, washed with water and dried overnight under a vacuum to afford a white powder. Using the same method, the procedure was repeated for intermediates 1b–c.
4-(Heptyloxy)benzoic Acid (1a)
Yield: 20.42 g (86%), mp: 97–98 °C, white powder. FTIR (cm−1): 3391 (O–H str.), 2931 and 2850 (Csp3–H str.), 1669 (C=O str.), 1606 (C=C str.), 1254 (C–O str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 7.78 (d, J = 5.0 Hz, 2H), 6.73 (d, J = 10.0 Hz, 2H), 3.97 (t, J = 7.5 Hz, 2H), 1.68–1.74 (m, 2H), 1.40–1.46 (m, 2H), 1.31–1.38 (m, 6H), 0.89 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 168.78, 158.91, 135.20, 130.31, 112.80, 67.73, 31.09, 28.83, 28.27, 25.44, 21.82, 13.60. CHN elemental analysis: calculated for C14H20O3: C: 71.16%, H: 8.53; found: C: 71.10%, H: 8.48%.
4-(Decyloxy)benzoic Acid (1b)
Yield: 6.11 g (73%), mp: 94–95 °C white powder. FTIR (cm−1): 3405 (O–H str.), 2920 and 2851 (Csp3–H str.), 1671 (C=O str.), 1605 (C=C str.), 1246 (C–O str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 7.78 (d, J = 10.0 Hz, 2H), 6.73 (d, J = 10.0 Hz, 2H), 3.96 (t, J = 7.5 Hz, 2H), 1.68–1.73 (m, 2H), 1.40–1.46 (m, 2H), 1.29–1.36 (m, 12H), 0.87 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 168.78, 159.00, 134.78, 130.36, 112.83, 67.73, 31.13, 28.82, 28.79, 28.77, 28.62, 28.47, 25.45, 21.85, 13.60. CHN elemental analysis: calculated for C17H26O3: C: 73.34%, H:9.41; found: C: 73.14%, H: 9.35%.
4-(Tetradecyloxy)benzoic Acid (1c)
Yield: 7.78 g (78%), mp: 102–103 °C, white powder. FTIR (cm−1): 3391 (O–H str.), 2920 and 2851 (Csp3–H str.), 1638 (C=O str.), 1600 (C=C str.), 1247 (C–O str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 7.80 (d, J = 5.0 Hz, 2H), 6.74 (d, J = 10.0 Hz, 2H), 3.97 (t, J = 5.0 Hz, 2H), 1.68–1.74 (m, 2H), 1.40–1.46 (m, 2H), 1.25–1.36 (m, 20H), 0.87 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 169.18, 159.26, 134.27, 130.42, 113.02, 67.91, 31.11, 28.82, 28.81, 28.81, 28.80, 28.79, 28.77, 28.76, 28.59, 28.44, 25.44, 21.80, 13.49. CHN elemental analysis: calculated for C17H26O3: C: 75.41%, H:10.25%; found: C: 75.35%, H: 10.21%.

3.3.2. Synthesis of 4-(Substituted)-N-(4-nitrophenyl)benzamide (2a-c)

Intermediate 2a is used as a representative method of discussion. A solution of intermediate 1a (0.03 mol) in DCM (40 mL) and thionyl chloride (0.03 mol) in DCM (40 mL) were mixed in a 150 mL round-bottom flask to form an acid chloride. The mixture was stirred at room temperature for two hours to form a clear solution. A solution of 4-nitroaniline (0.03 mol) in THF (20 mL) was added dropwise to the mixture and a white precipitate began to form. Triethylamine, Et3N (0.015 mol), was added dropwise to the mixture, which was stirred for eight hours. All the reaction’s progress was monitored by TLC. The precipitate formed was filtered and the filtrate was collected. After it was dried, the product formed was recrystallized from methanol. The same method was used to synthesize 2b–c.
4-(Heptyloxy)-N-(4-nitrophenyl)benzamide (2a)
Yield: 7.56 g (71%), mp: 93–94 °C, yellow powder. FTIR (cm−1): 3357 (N–H str.), 2932 and 2851 (Csp3–H str.), 1660 (C=O str.), 1604 (C=C str.), 1246 (C–O str.), 1168 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 10.61 (s, 1H), 8.23 (d, J = 5.0 Hz, 2H), 8.03 (d, J = 5.0 Hz, 2H), 7.95 (d, J = 10.0 Hz, 2H), 7.04 (d, J = 10.0 Hz, 2H), 4.03 (t, J = 7.5 Hz, 2H), 1.68–1.74 (m, 2H) 1.37–1.43 (m, 2H), 1.23–1.34 (m, 6H), 0.85 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 166.15, 162.59, 146.09, 143.42, 130.26, 126.95, 124.78, 120.56, 115.03, 68.82, 31.51, 29.08, 28.66, 25.81, 22.22, 13.94. CHN elemental analysis: calculated for C20H24O4: C: 67.40%, H: 6.79%, N: 7.86%; found: C: 67.33%, H: 6.72%, N: 7.80%.
4-(Decyloxy)-N-(4-nitrophenyl)benzamide (2b)
Yield: 7.45 g (62%), mp: 86–87° C, yellow powder, FTIR (cm−1): 3376 (N–H str.), 2915 and 2849 (Csp3–H str.), 1670 (C=O str.), 1604 (C=C str.), 1250 (C–O str.), 1167 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 10.33 (s, 1H), 8.19 (d, J = 10.0 Hz, 2H), 7.99 (d, J = 5.0 Hz, 2H), 7.95 (d, J = 5.0 Hz, 2H), 7.03 (d, J = 10.0 Hz, 2H), 4.07 (t, J = 7.5 Hz, 2H), 1.70–1.76 (m, 2H), 1.39–1.45 (m, 2H), 1.26–1.34 (m, 12H), 0.85 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 166.18, 162.51, 146.05, 143.24, 130.29, 126.72, 124.89, 120.51, 114.93, 68.66, 31.59, 29.24, 29.20, 29.02, 28.99, 28.92, 25.80, 22.32, 14.06. CHN elemental analysis: calculated for C23H30N2O4: C: 69.32%, H: 7.59%, N: 7.03%; found: C: 69.12%, H: 7.59%, N: 6.99%.
4-(Tetradecyloxy)-N-(4-nitrophenyl)benzamide (2c)
Yield: 12.58 g (92%), mp: 103–104° C, dark brown powder, FTIR (cm−1): 3342 (N–H str.), 2915 and 2849 (Csp3–H str.), 1652 (C=O str.), 1602 (C=C str.), 1251 (C–O str.), 1168 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 10.25 (s, 1H), 8.17 (d, J = 5.0 Hz, 2H), 7.95 (d, J = 5.0 Hz, 2H), 7.92 (d, J = 10.0 Hz, 2H), 7.00 (d, J = 5.0 Hz, 2H), 4.05 (t, J = 5.0 Hz, 2H), 1.68–1.74 (m, 2H), 1.37–1.43 (m, 2H), 1.23–1.34 (m, 20H), 0.82 (t, J = 5.0 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 166.31, 162.53, 145.91, 143.33, 130.25, 126.66, 124.86, 120.61, 114.98, 68.70, 31.55, 29.25, 29.23, 29.22, 29.19, 29.18, 29.16, 29.15, 28.94, 28.89, 25.75, 22.28, 14.00. CHN elemental analysis: calculated for C27H38N2O4: C: 71.33%, H: 8.43%, N: 6.16%; found: C: 71.28%, H: 8.40%, N: 6.11%.

3.3.3. Synthesis of N-(4-aminophenyl)-4-(substituted)benzamide, 3a-c

Intermediate 3a is used as a representative method of discussion. A solution of intermediate 2a (0.01 mol) in EtOH (40 mL) and a solution of sodium sulfide hydrate (Na2S.9H2O, 0.01 mol) in a mixture of EtOH (20 mL) and water (20 mL) were mixed in a 250 mL round-bottom flask. The mixture was refluxed for 12 h. The reaction’s progress was monitored by TLC. The precipitate formed was filtered, washed with cold ethanol, and dried overnight. The same method was used to synthesize 3b–c.
N-(4-aminophenyl)-4-(heptyloxy)benzamide (3a)
Yield: 0.43 g (87%), mp: 157–158 °C, white powder, FTIR (cm−1): 3338 (N–H str.), 3427 (N–H2 str.), 2915 and 2848 (Csp3–H str.), 1655 (C=O str.), 1606 (aromatic C=C str.), 1255 (C–O str.), 1177 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 9.69 (s, 1H), 7.89 (d, J = 10.0 Hz, 2H), 7.34 (d, J = 10.0 Hz, 2H), 7.00 (d, J = 5.0 Hz, 2H), 6.53 (d, J = 10.0 Hz, 2H), 4.87 (s, 2H), 4.02 (t, J = 7.5 Hz, 2H), 1.69–1.75 (m, 2H), 1.38–1.44 (m, 2H), 1.26–1.35 (m, 6H), 0.86 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 164.64, 161.46, 145.46, 129.72, 128.75, 127.64, 122.74, 114.38, 114.17, 68.15, 31.68, 29.05, 28.87, 25.90, 22.50, 14.40. CHN elemental analysis: calculated for C20H26N2O2: C: 73.59%, H: 8.03%, N: 8.58%; found: C: 73.51%, H: 7.98%, N: 8.50%.
N-(4-aminophenyl)-4-(decyloxy)benzamide (3b)
Yield: 3.10 g (67%), mp: 154–155 °C, white powder, FTIR (cm−1): 3372 (N–H str.), 3422 (N–H2 str.), 2917 and 2850 (Csp3–H str.), 1654 (C=O str.), 1606 (aromatic C=C str.), 1255 (C–O str.), 1175 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 9.68 (s, 1H), 7.89 (d, J = 10.0 Hz, 2H), 7.34 (d, J = 10.0 Hz, 2H), 7.00 (d, J = 10.0 Hz, 2H), 6.53 (d, J = 10.0 Hz, 2H), 4.87 (s, 2H), 4.03 (t, J = 7.5 Hz, 2H), 1.69–1.75 (m, 2H), 1.38–1.44 (m, 2H), 1.25–1.32 (m, 12H), 0.86 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 164.57, 161.45, 145.48, 129.72, 128.77, 127.69, 122.73, 114.38, 114.14, 68.15, 31.75, 29.45, 29.40, 29.21, 29.14, 29.05, 25.93, 22.55, 14.42. CHN elemental analysis: calculated for C23H32N2O2: C: 74.96%, H: 8.75%, N: 7.60%; found: C: 74.65%, H: 8.75%, N: 7.57%.
N-(4-aminophenyl)-4-(tetradecyloxy)benzamide (3c)
Yield: 0.49 g (83%), mp: 152–153 °C, white powder, FTIR (cm−1): 3344 (N–H str.), 3422 (N–H2 str.), 2915 and 2848 (Csp3–H str.), 1655 (C=O str.), 1606 (C=C str.), 1254 (C–O str.), 1176 (C–N str.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 9.31 (s, 1H), 7.88 (d, J = 10.0 Hz, 2H), 7.34 (d, J = 10.0 Hz, 2H), 6.98 (d, J = 10.0 Hz, 2H), 6.59 (d, J = 10.0 Hz, 2H), 4.06 (t, J = 7.5 Hz, 2H), 1.73–1.77 (m, 2H), 1.42–1.46 (m, 2H), 1.28–1.41 (m, 20H), 0.87 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 164.93, 161.69, 145.25, 131.67, 129.63, 129.39, 122.94, 114.74, 114.60, 68.64, 31.62, 29.34, 29.33, 29.30, 29.27, 29.26, 29.24, 29.12, 29.06, 28.95, 25.86, 22.31, 14.02. CHN elemental analysis: calculated for C27H40N2O2: C: 76.37%, H: 9.50%, N: 6.60%; found: C: 76.33%, H: 9.45%, N: 6.54%.

3.3.4. Synthesis of Hexa(oxy-4-benzoate)cyclotriphosphazene, 4

In a 250 mL round-bottom flask, a mixture of methyl-4-hydroxybenzoate (0.07 mol), HCCP (0.01 mol) and K2CO3 (0.1 mol) was mixed in acetone (150 mL). The mixture was refluxed for four days using a reflux condenser, and all the reaction’s progress was monitored using TLC. Upon completion, the mixture was poured into cold water (250 mL). The resulting precipitate was filtered, washed with water and dried overnight to obtain a dry white powder.
Yield: 9.37g (90%), mp: 152–154 °C, white powder. FTIR (cm−1): 1721 (C=O str.), 1603 (C=C str.), 1270 (benzene C–O str.), 1181 (P=N str.), 956 (C–H bend.), 881 (C–Cl bend.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 7.78 (d, J = 10.0 Hz, 2H), 7.05 (d, J = 5.0 Hz, 2H), 3.87 (s, 3H). 13C NMR (125 MHz, DMSO-d6) δ, ppm: 165.13, 152.85, 131.08, 126.91, 120.62, 52.23. 31P-NMR (202 MHz, DMSO-d6) δ, ppm: 7.99 (s, 1P). CHN elemental analysis: calculated for C48H42N3O18P3: C: 55.34%, H:4.06%, N: 4.03%; found: C: 55.28%, H: 4.02%, N: 3.99%.

3.3.5. Synthesis of Hexa(oxy-4-carboxy)cyclotriphosphazene, 5

Intermediate 4 (8.17 mmol) and NaOH (0.12 mol) in EtOH (150 mL) were mixed in a round-bottom flask (250 mL). The mixture was then refluxed for five hours using a reflux condenser, with the reaction’s progress monitored by TLC. Upon completion, the mixture was poured into cold water (250 mL). A clear solution was observed, which was then acidified with HCl until a precipitate formed. The precipitate was filtered using filter paper and washed with water. The precipitate was dried completely to yield a white solid.
Yield: 7.12 g (91%), mp: >300 °C, white powder. FTIR (cm−1): 3004 (O–H str.), 1698 (C=O str.), 1603 (C=C str.), 1274 (benzene C–O str.), 1182 (P=N str.), 1158 (C–O str.), 944 (C–H bend.). 1H NMR (500 MHz, DMSO-d6) δ, ppm: 7.83 (d, J = 10.0 Hz, 2H), 6.99 (d, J = 5.0 Hz, 2H), one exchangeable proton could not be observed. 13C NMR (125 MHz, DMSO-d6) δ, ppm: 166.25, 152.72, 131.22, 128.24, 120.49. 31P NMR (202 MHz, DMSO-d6) δ, ppm: 8.04 (s, 1P). CHN elemental analysis: calculated for C42H30N3O18P3: C: 52.68%, H: 3.16%, N: 4.39%; found: C: 52.63%, H: 3.12%, N: 4.33%.

3.3.6. Synthesis of hexakis((4-substituted-phenyl)benzamide)cyclotriphosphazene, 6a–c

Intermediate 3a (0.07 mol) and thionyl chloride (0.03 mol) were mixed in DCM (40 mL) in a round-bottom flask (250 mL). The mixture was stirred at room temperature for two hours, forming an acid chloride (in situ reaction) by replacing the carboxyl function of intermediate 5. The acid chloride solution of intermediate 5 (0.01 mol) further reacted with intermediate 3a without isolation in THF (20 mL), which was added dropwise to the mixture. A white precipitate began to form. Next, triethylamine, Et3N (0.02 mol), was added to the mixture, which was stirred for another 24 h. The reaction progress made was monitored using TLC. The precipitate formed was filtered and the filtrate was collected and dried. Once completely dried, the product formed was recrystallized from methanol. The same method has been used to synthesize compounds 6b–f.
Hexakis-((4-heptyl-phenyl)benzamide)cyclotriphosphazene (6a)
Yield: 1.29 g (90%), mp: 131–133 °C, white powder. FTIR (cm−1): 3357 (N–H str.), 2931 and 2897 (Csp3–H str.), 1658 (C=O str.), 1602 (aromatic C=C str.), 1278 (C–O str.), 1169 (C–N str.), 1175 (P=N stretching), 969 (P–O–C bend.). 1H NMR (500 MHz, CDCl3) δ, ppm: 10.14 (s, 1H), 10.05 (s, 2H), 8.32 (d, J = 10.0 Hz, 2H), 7.95 (d, J = 10.0 Hz, 2H), 7.93 (d, J = 5.0 Hz, 2H), 7.07 (d, J = 10.0 Hz, 2H), 7.00 (d, J = 10.0 Hz, 2H), 6.58 (d, J = 10.0 Hz, 2H), 4.03 (t, J = 7.5 Hz, 2H), 1.78–1.84 (m, 2H), 1.43–1.49 (m, 2H), 1.30–1.39 (m, 6H), 0.89 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ, ppm: 166.00, 165.06, 163.01, 162.95, 155.96, 148.10, 146.80, 145.01, 129.11, 125.64, 124.69, 123.09, 116.214, 114.95, 68.57, 31.78, 29.16, 29.05, 25.98, 22.62, 14.10. 31P NMR (202 MHz, CDCl3) δ, ppm: 9.11 (s, 1P). CHN elemental analysis: calculated for C162H174N15O24P3: C: 69.29, H: 6.25%, N: 7.48%; found: C: 69.22%, H: 6.20%, N: 7.41%.
Hexakis-((4-decyl-phenyl)benzamide)cyclotriphosphazene (6b)
Yield: 1.35 g (88%), mp: 135–137 °C, white powder. FTIR (cm−1): 3392 (N–H str.), 2916 and 2850 (Csp3–H str.), 1673 (C=O str.), 1605 (aromatic C=C str.), 1255 (C–O str.), 1164 (P=N str.), 951 (P–O–C bend.). 1H NMR (500 MHz, CDCl3) δ, ppm: 10.11 (s, 1H), 10.01 (s, 1H), 8.32 (d, J = 10 Hz, 2H), 7.95 (d, J = 10 Hz, 2H), 7.93 (d, J = 5 Hz, 2H), 7.05 (d, J = 10 Hz, 2H), 7.00 (d, J = 10 Hz, 2H), 6.57 (d, J = 10 Hz, 2H), 4.03 (t, J = 7.5 Hz, 2H), 1.78–1.84 (m, 2H), 1.43–1.49 (m, 2H), 1.27–1.35 (m, 12H), 0.88 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ, ppm: 166.01, 165.04, 163.01, 162.00, 155.95, 148.10, 146.80, 145.01, 129.12, 125.65, 124.69, 123.08, 116.24, 114.95, 68.57, 31.92, 29.58, 29.57, 29.39, 29.34, 29.16, 26.01, 22.70, 14.14. 31P NMR (202 MHz, CDCl3) δ, ppm: 9.15 (s, 1P). CHN elemental analysis: calculated for C180H210N15O24P3: C: 70.64%, H: 6.92%, N: 6.86%; found: C: 70.58%, H: 6.88%, N: 6.82%.
Hexakis-((4-tetradecyl)phenyl)benzamide)cyclotriphosphazene (6c)
Yield: 1.34 g (79%), mp: 107–109 °C, white powder. FTIR (cm−1): 3342 (N–H str.), 2915 and 2848 (Csp3–H str.), 1659 (C=O str.), 1605 (aromatic C=C str.), 1282 (C–O str.), 1171 (P=N str.), 940 (P–O–C bend.). 1H NMR (500 MHz, CDCl3) δ, ppm: 10.11 (s, 1H), 10.00 (s, 1H), 8.32 (d, J = 10.0 Hz, 2H), 7.95 (d, J = 10.0 Hz, 2H), 7.93 (d, J = 5.0 Hz, 2H), 7.07 (d, J = 10.0 Hz, 2H), 7.00 (d, J = 10.0 Hz, 2H), 6.58 (d, J = 10.0 Hz, 2H), 4.04 (t, J = 7.5 Hz, 2H), 1.78–1.84 (m, 2H), 1.43–1.49 (m, 2H), 1.25–1.36 (m, 20H), 0.87 (t, J = 7.5 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ, ppm: 166.01, 165.10, 163.00, 161.95, 156.14, 148.20, 146.82, 145.01, 129.01, 125.64, 124.69, 123.09, 116.23, 114.94, 68.57, 31.95, 29.71, 29.70, 29.69, 29.68, 29.67, 29.62, 29.58, 29.38, 29.16, 26.01, 22.71, 14.14. 31P NMR (202 MHz, CDCl3) δ, ppm: 9.13 (s, 1P). CHN elemental analysis: calculated for C204H258N15O24P3: C: 72.12%, H: 7.65%, N: 6.18; found: C: 72.07%, H: 7.60%, N: 6.11%.

4. Conclusions

A series of new amide-based cyclotriphosphazene molecules consisting of different terminal groups (heptyl, decyl, tetradecyl, hydroxyl, chlorine, and nitro) at the periphery, 6a–f, was synthesized and characterized. The FTIR analysis showed that all the peaks corresponding to certain chemical bonds and groups were present, which preliminarily characterized each intermediate and final compound (6a–c). Next, 1H, 13C, and 31P NMR spectroscopy experiments were conducted, providing better structural information on the molecules, and the assignment of carbon and hydrogen was confirmed using 2D NMR. Furthermore, CHN elemental analysis was conducted for all the compounds (1a–c, 2a–c, 3a–c, 4, 5, and 6a–c) to assess the purity of each compound. The CHN elemental analysis showed that the percentage errors was less than 2%, indicating that the compounds were successfully synthesized with high purity.

Supplementary Materials

Figure S1. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 1a; Figure S2. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 1b; Figure S3. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 1c; Figure S4. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 2a; Figure S5. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 2b; Figure S6. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 2c; Figure S7. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 3a; Figure S8. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 3b; Figure S9. (a) 1H NMR (500 MHz, DMSO-d6) and (b) 13C (125 MHz, DMSO-d6) NMR spectra of intermediate 3c; Figure S10. (a) 1H NMR (500 MHz, DMSO-d6), (b) 13C (125 MHz, DMSO-d6) and (c) 31P (500 MHz, DMSO-d6) NMR spectra of intermediate 4; Figure S11. (a) 1H NMR (500 MHz, DMSO-d6), (b) 13C (125 MHz, DMSO-d6) and (c) 31P (500 MHz, DMSO-d6) NMR spectra of intermediate 5; Figure S12. (a) 1H NMR (500 MHz, CDCl3), (b) 13C (125 MHz, CDCl3) and (c) 31P (500 MHz, CDCl3) NMR spectra of compound 6a; Figure S13. (a) 1H NMR (500 MHz, CDCl3), (b) 13C (125 MHz, CDCl3) and (c) 31P (500 MHz, CDCl3) NMR spectra of compound 6b; Figure S14. (a) 1H NMR (500 MHz, CDCl3), (b) 13C (125 MHz, CDCl3) and (c) 31P (500 MHz, CDCl3) NMR spectra of compound 6c.

Author Contributions

Conceptualization, Z.J.; methodology, Z.J.; software, K.A.R. and Z.J.; validation, K.A.R. and Z.J.; formal analysis, K.A.R.; investigation, K.A.R. and Z.J.; resources, Z.J.; data curation, K.A.R. and Z.J.; writing—original draft preparation, K.A.R. and Z.J.; writing—review and editing, K.A.R. and Z.J.; visualization, K.A.R. and Z.J.; supervision, Z.J.; project administration, Z.J.; funding acquisition, Z.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Universiti Malaysia Sabah (UMS) under grant numbers SPB0004-2020 and GKP2407. The APC was funded by the correspondence.

Data Availability Statement

The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author.

Acknowledgments

The authors gratefully acknowledged the lab facility support from Universiti Malaysia Sabah (UMS) and Universiti Sains Malaysia (USM).

Conflicts of Interest

The authors declare no conflicts of interest.

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Molbank 2025 m2039 g001
Figure 1. Chemical structures of compounds with fire retardant [15], coating and adhesive [16], and liquid crystal [17] applications.
Figure 1. Chemical structures of compounds with fire retardant [15], coating and adhesive [16], and liquid crystal [17] applications.
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Scheme 1. Alkylation reaction of intermediates 1a–c.
Scheme 1. Alkylation reaction of intermediates 1a–c.
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Scheme 2. Formation of intermediates 2a–c and 3a–c.
Scheme 2. Formation of intermediates 2a–c and 3a–c.
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Scheme 3. Formation of intermediates 4–5 and compounds 6a–c.
Scheme 3. Formation of intermediates 4–5 and compounds 6a–c.
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Figure 2. FTIR spectra overlay of compounds 6a–c.
Figure 2. FTIR spectra overlay of compounds 6a–c.
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Figure 3. Structure of compound 6a with the complete set of atomic numbering.
Figure 3. Structure of compound 6a with the complete set of atomic numbering.
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Figure 4. 1H NMR spectrum (500 MHz, CDCl3) of compound 6a.
Figure 4. 1H NMR spectrum (500 MHz, CDCl3) of compound 6a.
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Figure 5. COSY (1H–1H) NMR spectrum of compound 6a.
Figure 5. COSY (1H–1H) NMR spectrum of compound 6a.
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Figure 6. (a) 13C NMR, (b) DEPT 90, and (c) DEPT 135 spectra (125 MHz, CDCl3) of compound 6a.
Figure 6. (a) 13C NMR, (b) DEPT 90, and (c) DEPT 135 spectra (125 MHz, CDCl3) of compound 6a.
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Figure 7. HSQC (1H–13C) NMR spectrum of compound 6a.
Figure 7. HSQC (1H–13C) NMR spectrum of compound 6a.
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Figure 8. 31P NMR spectrum (202 MHz, CDCl3) of compound 6a.
Figure 8. 31P NMR spectrum (202 MHz, CDCl3) of compound 6a.
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Table 1. 1H, COSY, and HSQC NMR data of compound 6a.
Table 1. 1H, COSY, and HSQC NMR data of compound 6a.
Proton1H [δ (ppm), Multiplicity, Coupling Constant (Hz)]COSY (1H–1H) CorrelationHSQC (1H–13C) Correlation
(δ, ppm)
H-610.05 (s)--
H-1110.14 (s)--
H-27.95 (d, J = 5.0 Hz, 2H)H-3C-2 (125.64)
H-38.32 (d, J = 10.0 Hz, 2H)H-2C-3 (129.11)
H-87.00 (d, J = 10.0 Hz, 2H)H-9C-7 (116.24)
H-96.58 (d, J = 5.0 Hz, 2H)H-8C-8 (114.95)
H-147.93 (d, J = 5.0 Hz, 2H)H-15C-14 (124.69)
H-157.07 (d, J = 10.0 Hz, 2H)H-14C-15 (123.09)
H-174.03 (t, J = 7.5 Hz, 2H)H-18C-17 (68.57)
H-181.78–1.84 (m, 2H)H-17, H-1–H-9C-18 (31.78)
H-19–H-221.30–1.49 (m, 2H)H-18–H-23C-19 (29.16)
C-20 (29.05)
C-21 (25.98)
C-22 (22.62)
H-230.89 (t, J = 7.5 Hz, 3H)H-22C-23 (14.10)
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Abdul Rahim, K.; Jamain, Z. Synthesis and Characterization of Amide-Based Cyclotriphosphazene Derivatives with Alkoxy Terminal Groups. Molbank 2025, 2025, M2039. https://doi.org/10.3390/M2039

AMA Style

Abdul Rahim K, Jamain Z. Synthesis and Characterization of Amide-Based Cyclotriphosphazene Derivatives with Alkoxy Terminal Groups. Molbank. 2025; 2025(3):M2039. https://doi.org/10.3390/M2039

Chicago/Turabian Style

Abdul Rahim, Khairunnisa, and Zuhair Jamain. 2025. "Synthesis and Characterization of Amide-Based Cyclotriphosphazene Derivatives with Alkoxy Terminal Groups" Molbank 2025, no. 3: M2039. https://doi.org/10.3390/M2039

APA Style

Abdul Rahim, K., & Jamain, Z. (2025). Synthesis and Characterization of Amide-Based Cyclotriphosphazene Derivatives with Alkoxy Terminal Groups. Molbank, 2025(3), M2039. https://doi.org/10.3390/M2039

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