Synthesis Of Esterified Tannic Acids With Surface Activities And Studies On Properties Of The Products

Tannic acid (TA) is an excellent natural product being applied in cosmetics, medicine, food and leather industries. But in some way its utilization has been limited due to its poor lipophilicity. Based on the structural characteristics and chemical properties of tannic acid, esterifying reaction of tannic acid with saturated aliphatics was studied, and properties of the products, such as antioxidation, surface activities and antibacterial action were also investigated.It was found that varying aliphatic groups could be easily introduced to tannic acid through acylation reaction. Taking the preparation of stearoyl tannic acid (C18TA) as an example, the optimum reaction conditions were that n(TA):n(stearoyl chloride)=1:20, m(TA):m(catalyst)=l:0.03. The reaction was conducted in reflux temperature of dioxane (100 ~ 102C) for 4h with protection of nitrogen atmosphere. Similarly, a series of C10TA, C14TA and C18TA was also synthesized by using different reaction molar ratio of reactants.It is shown that C18TA has better antioxidation than BHT. Furthermore, it is proved that tannic acid derivatives with varying aliphatic groups present excellent surface activities. Compared with TA, esterified tannic acids have better wetting and emulsifying abilities. Especially, C10TA has the best surface activity properties among the products.It's indicated that esterified tannic acids can obviously inhibit the growth of bacteria at optimum conditions(0.05~0.1g/100mL). However, it is found that theesterified tannic acids present stronger inhibiting effects on Escheridia coli whilst tannic acid on Aspergillus niger.The structural analyses of IR and UV spectra indicate that products still keep benzopyranyl and phenolic hydroxyl structures whilst phenolic ester groups and aroyls are probably derived. It is also proved that there are less phenolic hydroxyls and more carbonyl groups in products than in TA. It may predicate that phenolic hydroxyls are the main groups for esterifying reaction.The method of improving lipophilicity of tannic acid has been established and properties of the products have also been explored. It is a unique and original method that tannic acid is modified to be a new surface active agent, which may be theoretically and practically significant in its applied fields.