Construction Of Thiourea Catalyst For Catalytic Schiff Base Synthesis Reaction

Thiourea catalyst has been widely used in various types of organic reactions as hydrogen bond type catalyst. It havs special functional groups in its activations including carbonyl substrate(C=O), carbon nitrogen double bond(C=N) and nitrogen oxygen double bond(N=O) groups. In recent years, more and more researchers put their focus on the Schiff base due to its pharmacological activity and physiological activity. However, there still exist some problems in the process of Schiff base synthesis, such as low yields, long reaction time, and so on. Therefore, the study on the synthetic method of the high performance thiourea catalyst and its application in the synthesis of Schiff base is far-reaching significance.Firstly, N,N-diphenyl thiourea catalysts have been synthesized using aniline and carbon disulfide as raw materials, which aimed to be applied in the synthesis of Schiff base. Then, four kinds of Schiff base compounds have been synthesised using phenylmethylketone(4-methoxyphenylmethylketone) and hydrazine compounds as materials, including phenyl methyl ketone-2-hydroxybenzoyl hydrazone, phenyl methyl ketone-4-hydroxybenzoyl hydrazone, 4-methoxy-phenyl methyl ketone-2--hydroxybenzoyl hydrazone and 4-methoxy-phenyl methyl ketone-4-hydroxybenzoyl hydrazone. Finally, the structure of the compounds were characterized by elemental analysis, IR, 1H NMR, SEM and thermal gravimetric analysis. The reaction conditions of synthesis Schiff base using N,N-diphenyl thiourea as catalyst was also explored. The results shown that under reflux conditions, the yield of phenyl methyl ketone-2-hydroxybenzoyl hydrazone under optimum conditions was up to 89.4% when the amount of N,N-diphenyl thiourea catalyst was 1.60 g(7 mmol) during reacting about 6 hours. At the same time, the yield of phenyl methyl ketone-4-hydroxybenzoyl hydrazone was up to 52.4% while the amount of N,N-diphenlthiourea catalyst was 0.80 g(3.5 mmol) during reacting time about 6 hours. Similarly, the yield of 4-methoxy-phenyl methyl ketone-2-hydroxybenzoyl hydrazone was up to 88.8% while the amount of N,N-diphenlthiourea catalyst was 1.03 g(4.5 mmol) while reacting 6 hours and the yield of 4-methoxy-phenylmethyl ketone-4-hydroxybenzoyl hydrazone was up to 47.7% while using about 1.03 g(4.5 mmol) N,N-diphenlthiourea catalyst and reacting 6 hours.The new thiourea catalysts named as N,N-(2-benzimidazolyl)-diphenylthiourea, N,N-(3-benzimidazolyl)-diphenylthiourea and N,N-(4-benzimidazolyl)-diphenlthiou--rea have been synthesized using o-nitrotoluene(m-nitrotoluene, p-nitrotoluene), o-phenylenediamine and carbon disulfide as raw materials, which aimed to be applied in the synthesis of Schiff base. Then, two kinds of Schiff base compounds have been synthetised using phenylmethylketone(4-methoxyphenylmethylketone) and 4-hy--droxybenzoyl hydrazineas materials, including phenyl methyl ketone-4-hydroxy benzoyl hydrazone, and 4-methoxy-phenyl methyl ketone-4-hydroxybenzoyl hydraz--one. The structure of the compounds were characterized by elemental analysis, IR, and thermal gravimetric analysis. The reaction conditions of synthesis of Schiff base using the new thiourea catalysts as catalyst were also explored. The results shown that under reflux conditions, the yield of phenyl methyl ketone-4-hydroxybenzoyl hydrazone under optimum conditions was up to 74.8% when the amount of N,N-(2-benzimida-zolyl)-diphenylthiourea catalyst was 1.15 g(2.5 mmol)during reacting about 6 hours; the yield of 4-methoxy-phenyl methyl ketone-4-hydroxyben--zoyl hydrazone was up to 73.6% while the amount of N,N-(2-benzimidazolyl)di--phenylthiourea catalyst was 1.38 g(3 mmol) during reacting about 6 hours. At the same time, the yield of phenyl methyl ketone-4-hydroxybenzoyl hydrazone under optimum conditions was up to 67.6% when the amount of N,N-(3-benzimidazolyl)-diphenylthiourea catalyst was 0.69 g(1.5 mmol) during reacting time about 6 hours; the yield of 4-methoxy-phenyl methyl ketone-4-hydroxybenzoyl hydrazone was up to 69.8% while the amount of N,N-(3-benzimidazolyl)-diphenylthiourea catalyst was 0.92 g(2 mmol) during reacting time about 6 hours. Similarly, the yield of phenyl methyl ketone-4-hydroxybenzoyl hydrazone was up to 63.3% while the amount of N,N-(4-benzimidazolyl)-diphenylthiourea catalyst was 1.38 g(3 mmol) while reacting 6 hours and the yield of 4-methoxy-phenylmethyl ketone-4-hydroxybenzoyl hydrazone was up to 62.3% while using about 1.15 g(2.5 mmol) N,N-(4-benzimi--dazolyl)diphenylthiourea catalyst and reacting 6 hours.