Synthesis and Performance of N-( Benzoyl ) Stearic Acid Hydrazide

N-(benzoyl) stearic acid hydrazide was synthesized from benzoyl hydrazine and stearyl chloride which was deprived from stearic acid via acylation. The structure of the compound had been characterized by FT-IR, H NMR, at the same time, the structure of N-(benzoyl) stearic acid hydrazide was optimized by the semiempirical method PM3. The influence of the reaction ratio, reaction time and reaction temperature to the yield of N-(benzoyl) stearic acid hydrazide was investigated by orthogonal experiment, and the optimized reaction condition was molar ratio of benzoyl hydrazine: stearyl chloride 1:1, reaction time 6 h, reaction temperature 70 °C, and the yield was 92.9%. The TGA thermal analysis of N-(benzoyl) stearic acid hydrazide showed that thermal stability of N-(benzoyl) stearic acid hydrazide was affected by heating rate, and the N-(benzoyl) stearic acid hydrazide enhanced the tensile strength, modulus and elongation at break of Poly(L-lactic acid)(PLLA).


Introduction
With the increasing development of science and technology, amides, as a kind of very important organic compound, has a wider application fields.Besides the traditional fields of synthetic intermediates 1,2 , material chemistry 3,4 , amides play an active role in drug discovery 5 , polymer [6][7][8] , etc and obtained a lot of progress.For example, the importance of the amides in polymer has been recently highlighted by Cai and co-workers 6 .In that article, N,N'-bis(benzoyl) suberic acid dihydrazide as heterogeneous nucleation agent can significantly improve the crystallization of poly(L-lactic acid)(PLLA).N,N'-bis(benzoyl) suberic acid dihydrazide leads to the shift of the melt crystallization to higher temperature and becomes much sharper in the melting crystallization process of PLLA.Upon the addition of 0.8% N,N'-bis(benzoyl) suberic acid dihydrazide, the crystallization half-time of PLLA/ N,N'-bis(benzoyl) suberic acid dihydrazide decreases from 26.5 min to 1.4 min at 115 ℃.
Furthermore, Angela and co-workers 8 also reported that ethylene bis-stearamide can serve as a nucleating agent of PLLA for dramatic increasing in crystallization rate and final crystalline content as indicated by isothermal and nonisothermal crystallization measurements.Thus, amide will play more important role in industry and agriculture.
In order to further develop the more amide compounds, and adequately investigate the performance of amide compounds.In this study, N-(benzoyl) stearic acid hydrazide was synthesized from benzoyl hydrazine and stearyl chloride which was deprived from stearic acid via acylation.The influence of the reaction conditions to the yield and thermal stability of product was investigated by orthogonal experiment and TGA respectively.Finally, the effection of N-(benzoyl) stearic acid hydrazide towards PLLA's mechanical properties were further investigated.

Experimental
The materials used in this study were of analytical grade (AR).Benzoyl hydrazine and stearic acid were procured from Chengdu Kelong Chemical Reagents Company respectively (Sichuan Province, China); Thionyl dichloride, N, N-dimethylacetamide and Pyridine were procured from Mianyang Rongshen Chemical Reagents Company (Sichuan Province, China).poly(L-lactic acid)(PLLA) was purchased from Nature Works LLC, USA.

Synthesis procedure of N-(benzoyl) stearic acid hydrazide
N-(benzoyl) stearic acid hydrazide was prepared as shown in Scheme 1: stearic acid and thionyl dichloride of 50 mL was mixed in the presence of N,N-dimethylacetamide as catalyst.Then the mixture was heated up to 80 ℃ and held at 80 ℃ with stirring for 7 h.After cooling to room temperature and evaporation of thionyl dichloride in vacuum, the residue was stearyl chloride.
Benzoic hydrazide and N,N-dimethylacetamide of 50 mL were mixed and the mixture was purged under nitrogen atmosphere.Stearyl chloride was added slowly onto the mixture, followed by adding pyridine of 0.057 mol, then the mixture was heated up to 60～ 80 ℃ and held at 60～ 80 ℃ for period of time with stirring.The reaction mixture was poured onto water of 250 mL and stirred, followed by filtrating.Obtained crude product was washed four times by water of each 250 mL at room temperature, and then washed by methanol of 200 mL at 50 ℃ to eliminate raw materials and by-products, the resulting product was dried in a vacuum at 55 ℃.

Preparation of PLLA/N-(benzoyl) stearic acid hydrazide samples
PLLA was dried overnight at 50 ℃ under vacuum to remove residual water.Blending of PLLA and dried N-benzoyl stearic acid hydrazide was performed on a counter-rotating mixer with a rotation speed of 32 rpm for 5min, then at 64 rpm for 5 min.The processing temperature was set at 185 ℃.Products were hot pressed at 180 ℃ under 20 MPa for 3 min to prepare sheets with a thickness of approximately 0.4 mm.The sheets were then cooled down to room temperature by being compressed at room temperature under 20 MPa for 10 min.

Structure of N-(benzoyl) stearic acid hydrazide
The FT-IR spectra of N-(benzoyl) stearic acid hydrazide is shown in Figure 1.As showen in the spectra, the peak at 3400 cm -1 contributes to the absorption of N-H stretching vibration; the absorption peaks at 2917.6 cm -1 , 2849 cm -1 and 716.7 cm -1 contribute to CH 2 symmetrical stretching vibration, asymmetrical stretching vibration and rocking vibration respectively.Owing to conjugated effect, C=O of benzoic hydrazide moves to lower vibrational frequency.That's to say, the absorption peak at 1638.1 cm -1 contributes to C=O stretching vibration, and the absorption peak at 1666.7 cm -1 contributes to C=O of amide.Then the absorption peaks at 1602.2 cm -1 , 1572.7 cm -1 , 1500 cm -1 , and 1469.2 cm -1 prove the existence of benzene.The 1 H NMR patterns of N-(benzoyl) stearic acid hydrazide is depicted in Figure 2. The single peak at δ H =10.27 and 9.82 are proton resonance peak of N-H of N-(benzoyl) stearic acid hydrazide, the multiple peaks at δ H =7.47-7.88 are proton resonance peaks of benzene, the triplet peaks at δ H =2.15-2.18are CH 2 which is near amide proton resonance peak.As for the multiple peaks at δ H =1.24-1.56,they belong to other CH 2 proton resonance peaks, the triplet peaks at δ H =0.84-0.86 are CH 3 proton resonance peaks.NMR analysis further confirms that N-(benzoyl) stearic acid hydrazide was synthesized.In order to further investigate the structure of N-(benzoyl) stearic acid hydrazide, the optimized geometric structure of N-(benzoyl) stearic acid hydrazide was carried out by the theoretical calculation which were performed by the program VAMP using the semiempirical method PM3.The optimized geometry structure of N-(benzoyl) stearic acid hydrazide is shown in Figure 3 and the HOMO and LUMO of phthalimide is -9.852 eV and -0.309 eV, respectively.

Synthesis conditions of N-(benzoyl) stearic acid hydrazide
The influence of the reaction ratio, reaction time and reaction temperature to the yield of product was investigated by orthogonal experiment.Factors and levels of orthogonal experiment are listed in Table 1 and the results are listed in Table 2.As seen in Table 2.It is clear that reaction time is more important to yield than other factors.The reason is that the high reactivity of stearyl chloride can result in shorter reaction time, which lower the side effects greatly.And the optimized reaction condition are as follows: molar ratio of benzoyl hydrazine: stearyl chloride 1:1, reaction time 6 h, reaction temperature 70 ℃, and the yield is 92.9 %.

Thermal decomposition of N-(benzoyl) stearic acid hydrazide
Thermal stability is very important for application of N-(benzoyl) stearic acid hydrazide, thus, the thermal stability of N-(benzoyl) stearic acid hydrazide was investigated by TGA.
Figure 4 shows the TGA curves of N-(benzoyl) stearic acid hydrazide with a heating ramp of 2.5, 5, 10, 20, 30 ℃/min from room temperature to 500 ℃ under nitrogen flow.As seen in Figure 4, N-(benzoyl) stearic acid hydrazide begins to decomposition above 185 ℃, which suggests that N-(benzoyl) stearic acid hydrazide has good thermal stability in daily application.After that, N-(benzoyl) stearic acid hydrazide decomposes fast and completely in one stage above 200 ℃ at all heating rates.Furthermore, with the increasing of heating rate, the decomposition temperature increases and heating decomposition degree decreases.Rapid heating rate makes the decomposition of N-(benzoyl) stearic acid hydrazide not achieve at set temperature, at the same time, the temperature has get into the following set temperature, resulting in decomposition achieving at higher temperature.

Conclusion
N-(benzoyl) stearic acid hydrazide was synthesized from benzoyl hydrazine and stearyl chloride which was deprived from stearic acid via acylation.The optimum reaction conditions were determined by orthogonal experiment as follows: molar ratio of benzoyl hydrazine to stearyl chloride 1:1, reaction time 6 h, reaction temperature 70 ℃ and the yield was 92.9 %.TGA results indicated good thermal stability of N-(benzoyl) stearic acid hydrazide, and thermal stability was affected by heating rate.Besides, the N-(benzoyl) stearic acid hydrazide enhanced tensile strength, modulus and elongation at break of PLLA.

Figure 5 .
Figure 5.The mechanical properties of PLLA with different N-(benzoyl) stearic acid hydrazide contents.

Table 1 .
Factors and levels of orthogonal experiment.

Table 2 .
Results of orthogonal experiment.