The application of biomass-based carbonaceous solid acids in catalysis is attracting increasing attention in the field of chemistry. In this study, a heterogeneous carbon-based solid acid biocatalyst (CXH-SO3H) with regular spherical structure was synthesized from xylan-type hemicellulose (XH) by a simple two-step method. The catalyst was successfully applied in the synthesis of O- and N-heterocycles with yields of 80–99% and 60–97%, respectively. In view of environment and economy, CXH-SO3H shows the merits of environmental friendliness, easy operation, simple work-up, excellent yields, and the avoidance of use of organic solvents and expensive catalysts. Moreover, the as-synthesized solid acid catalyst could be used for several cycles without significant loss in its catalytic activity. The results of FT-IR, XRD, and SEM showed that no distinct differences in physico-chemical structures of CXH-SO3H were observed. Thus, the eco-friendly CXH-SO3H catalyst is a promising candidate for green synthesis of O- and N-heterocycles from low-cost feed-stocks and has good prospect in partially substituting commercially available solid and liquid acid catalysts and precious metal catalysts.
N,O-Heterocycles play an important role in the characteristic flavor of green tea owing to their strong odors and low odor thresholds. In this study, a rapid and sensitive method was developed to determine seven N,O -heterocycles in green tea by using headspace solid-phase microextraction Arrow (HS-SPME-Arrow) coupled with gas chromatography-triple quadrupole-tandem mass spectrometry. The HS-SPME-Arrow extraction was performed using a Carbon WR SPME Arrow fiber. Good linear ranges (5–1000 ng/mL) were obtained, with correlation coefficients (R 2 ) higher than 0.99 for all target compounds. LODs and LOQs were in the range of 0.44–5.12 and 1.48–17.04 μg/kg, respectively. The recoveries of seven N,O -heterocycles were found to vary from 83.1% to 117.3%, with RSDs being lower than 10%. The dynamic changes of N,O -heterocycles during the drying process revealed that 25- and 40-min-long drying processes were key transition points. Furfural could be used as a key indicator compound for evaluating the extent of the drying. Moreover, furfural and 2-methylfuran revealed a significant positive correlation with proline ( p < 0.05). The possible formation mechanisms of N,O -heterocycles were further elaborated by simulated Maillard reactions . Our results provide a theoretical foundation for the improvement and directional regulation of aroma quality of green tea during manufacturing.
Yancong Li,Jiliang Ma,Zhendong Liu,Dongnv Jin,Gaojie Jiao,Yanzhu Guo,Qiang Wang,Jinghui Zhou,Runcang Sun
A simple and efficient photocatalytic method for the synthesis of dihydropyrimidinones (DHPMs) and their derivatives via porous ultrathin carbon nitride nanosheets (p-CNNs) without solvents was demonstrated. The yields of 3,4-dihydropyrimidin-2(1H)-ones/thiones and their derivatives were up to 97.0%. Furthermore, the yield of 5-ethoxycarbonyl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one in the 10th cycle retained 98.9% of its 1st value. Considering the environmental and economic benefits, this work exhibits various merits including excellent yields, environmental friendliness, inexpensiveness, and avoiding the use of solvents and metal-based photocatalysts. In addition, the excellent performance of the p-CNNs and environmentally benign reaction system have also been checked by the photocatalytic synthesis of 12-phenyl-9,9-dimethyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one and 5-phenyl-1(4-methoxyphenyl)-3[(4-methoxy-phenyl)-aminol]-1H-pyrrol-2(5H)-one. This work paves a new way for carrying out a three-component reaction using metal-free photocatalysts under mild reaction conditions.
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