| Salicylaldehyde(OHB) is an important fine chemical product, which is widely used in the synthesis of pesticide, medicine, spice, pigment and so on. In this paper, esterification-oxidation process was used to synthesize OHB with phenol, boric acid, paraformaldehyde(PF) as raw materials, which including six steps, namely dehydration, esterification, hydroxymethylation, saponification, oxidation and acidification. The advantages of this approach lie in its cheap raw materials, less pollution to the environment over others.In the step of esterification, dehydration of boric acid and then esterifying with phenol were carried out in order to increase conversion of esterification. Effect of reaction temperature, consumption of boric acid, kinds and consumption of dehydrolating agent on the yield of esterification was studied. The experimental results showed that high conversion of 98% of esterification was obtained.In the step of hydroxymethylation, gaseous formaldehyde, which was decomposed by paraformaldehyde, was conducted into the reactor. Orthogonal test was designed to investigate the factors of water content in material of PF, reaction temperature, reaction time and consumption of PF on the hydroxymethylation. The results show that water content in material of PF and the reaction temperature have significant influences on the yield of OHB, others seem to have less effect.The catalyst of 5% Pd/C was used in oxidation step, and the effect of the amount of catalyst, reaction temperature and reaction time on the yield of OHB were studied. The optimal conditions were selected.Attentions were also made in saponification step and acidification step. Steam distillation followed by saturated NaHSO3 operation was adopted in the separation step. GC analysis of final products was conducted and showed that the purity of the products was above 96% and the yield of OHB was 60.5% , which was close to the international literature value of 67%, but higher than the domestic literature value of 51%.
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