Lignosulfonate with low polydispersity index of 1.178-1.210 was isolated by gel column chromatography of Sephacryl S-100 eluted with 0.2 mol/L of NaNO_3 aqueous solution,whereas nearly monodisperse ligosulfonate fraction with polydispersity of 1.0(57 can be obtained after chromatographic separation twice.This method provides an available approach to investigate the structure and characteristics of lignosulfonate.
Xin Ping OuyangPan ZhangChun Mei TanYong Hong DengDong Jie YangXue Qing Qiu
The effects of oxidant dosage,oxidation temperature and time on the degradation of soda lignin by hydrogen peroxide with and without the presence of microwave irradiation were investigated.It is found that the oxidative degradation of lignin includes the cleavage of ether bond inβ-O-4 structure,the partial destruction of aromatic ring,and the re-condensation of the degraded lignin.Compared to the conventionally heated oxidation of lignin,the microwave irradiation efficiently facilitates the degradation of the lignin with high molecular weight and the re-condensation of that with low molecular weight at a low oxidant dosage,low oxidation temperature,or a short oxidation time,which leads to the formation of the degraded lignin with narrower molecular weight distribution and lower molecular weight.Additionally,the lignin degraded in the presence of microwave irradiation has the characteristics of higher content of phenolic hydroxyl group,lower content of methoxyl group,and lower degree of condensation,which enhances the reactivity of lignin.Therefore,the oxidative degradation of lignin assisted by microwave irradiation may be a new pretreatment approach for efficiently utilizing the soda lignin.
A trimeric lignin model compound composed of a-O-4 and b-O-4 linkages was prepared by the microwave-assisted synthesis,which consisted of three steps:(a)the synthesis of 3-methoxy-4-benzyloxyacetophenone(2)from acetovanillone(1),(b)the bromination of compound 2 to produce 3-methoxy-4-benzyloxy-a-bromoacetophenone(3),and(c)followed by a nucleophilic substitution of compound(3)to obtain 3-methoxy-4-benzyloxy-a-(3-methoxy-4-(1-propenyl)phenol)-acetophenone(4).The target product was characterized by MS,1H NMR and13C NMR spectroscopy.It was found that the trimeric compound synthesized can be used as a preferable lignin model compound because it contains guaiacyl structural unit(3-methoxy-4-hydroxy phenyl propane)linked by a-O-4 and b-O-4linkages.In addition,under the conditions of microwave irradiation,the reaction time of each step is signifcantly reduced,and the selectivity of target product is greatly improved.The yields of each step and the overall sequence are 95.31%,87.3%,90.6%and 75.4%(95.31%87.3%90.6%),respectively.
