In this work, comprehensive studies of 2,4-dinitroanisole(2,4DNAN) were carried out using powder thermorentgenography of the internal standard. The time of the complete polymorphic transition in the solid phase β→a ...In this work, comprehensive studies of 2,4-dinitroanisole(2,4DNAN) were carried out using powder thermorentgenography of the internal standard. The time of the complete polymorphic transition in the solid phase β→a in 2,4DNAN under various combinations of conditions has been determined. It has been established that, regardless of the season of manufacture of the substance, when it is stored for 8-9months, with a change in ambient temperature from minus 30℃ to plus 30℃, a complete polymorphic transition β→a occurs. When stored in conditions below minus 5℃, polymorphic transition does not occur. When stored in conditions above plus 30℃ in a closed container, polymorphic transition occurs within 3 weeks. The polymorphic transition is accompanied by a decrease in density by 1.3%-1.5% and an increase in melting temperature by 10-12℃, depending on the degree of purity of the starting substance. The activation energy of the molecular rearrangement was 68-70 k J/mol(16.5 ± 3 kcal/mol). The mechanism of polymorphic transition has been evaluated, which is presumably based on internal homodiffusion and energy transfer to the surface of the mass of powder particles and the product. The average activation energy of the polymorphic transition process was 110 ± 6.2 k J/mol(26.2 kcal/mol). In an open container, reactions proceed by a homogeneous mechanism, and in a closed container by a heterogeneous mechanism involving the gas phase.展开更多
The selective hydrogenation of dimethyl toluene-2,4-dicarbamate(TDC)to methyl cyclohexyl-2,4-dicarbamate(also called hydrogenated TDC,HTDC)is an essential process for non-phosgene synthesis of methylcyclohexane-2,4-di...The selective hydrogenation of dimethyl toluene-2,4-dicarbamate(TDC)to methyl cyclohexyl-2,4-dicarbamate(also called hydrogenated TDC,HTDC)is an essential process for non-phosgene synthesis of methylcyclohexane-2,4-diisocyanate.Herein,we prepared a series of supported Rh-based catalysts by the excessive impregnation method and investigated their catalytic performance for the selective hydrogenation of TDC.The emphasis was put on the influence of support properties on the catalytic performance.Among the prepared catalysts,Rh/g-Al_(2)O_(3)performed the best:a HTDC yield of 88.4%was achieved with a 100%conversion of TDC under the conditions of 100℃,3 MPa and 1 h.Furthermore,Rh/γ-Al_(2)O_(3)could be repetitively used for 4 times without a significant loss of its catalytic activity.TEM,XRD,N_(2)adsorption-desorption,H_(2)-TPR,NH_(3)/CO_(2)-TPD,XPS and ICP characterizations were employed to distinguish the properties of the prepared catalysts and the results were correlated with their catalytic performance.It is indicated that the yield of HTDC shows a positive relevance with the percentage of moderate-to-strong acid sites and the content of Rh^(n+)(n≥3)in the catalysts.High values of the percentage and the content can promote a strong interaction between Rh nanoparticles and the supports,facilitating both the transfer of electrons from Rh to the support and the formation of Rh^(n+)species.This is conducive to activating the benzene ring of TDC and thereby improving the yield of HTDC.展开更多
基金supported by the Ministry of Science and Higher Education of the Russian Federation(Agreement with Zelinsky Institute of Organic Chemistry RAS Grant No.075-15-2020-803).
文摘In this work, comprehensive studies of 2,4-dinitroanisole(2,4DNAN) were carried out using powder thermorentgenography of the internal standard. The time of the complete polymorphic transition in the solid phase β→a in 2,4DNAN under various combinations of conditions has been determined. It has been established that, regardless of the season of manufacture of the substance, when it is stored for 8-9months, with a change in ambient temperature from minus 30℃ to plus 30℃, a complete polymorphic transition β→a occurs. When stored in conditions below minus 5℃, polymorphic transition does not occur. When stored in conditions above plus 30℃ in a closed container, polymorphic transition occurs within 3 weeks. The polymorphic transition is accompanied by a decrease in density by 1.3%-1.5% and an increase in melting temperature by 10-12℃, depending on the degree of purity of the starting substance. The activation energy of the molecular rearrangement was 68-70 k J/mol(16.5 ± 3 kcal/mol). The mechanism of polymorphic transition has been evaluated, which is presumably based on internal homodiffusion and energy transfer to the surface of the mass of powder particles and the product. The average activation energy of the polymorphic transition process was 110 ± 6.2 k J/mol(26.2 kcal/mol). In an open container, reactions proceed by a homogeneous mechanism, and in a closed container by a heterogeneous mechanism involving the gas phase.
基金financially supported by National Natural Science Foundation of China(U21A20306,21978066)Hebei Province Fig.7.Reaction mechanism of selective hydrogenation of TDC over Rh-based catalysts.Graduate Innovation Funding Project(CXZZBS2023033).
文摘The selective hydrogenation of dimethyl toluene-2,4-dicarbamate(TDC)to methyl cyclohexyl-2,4-dicarbamate(also called hydrogenated TDC,HTDC)is an essential process for non-phosgene synthesis of methylcyclohexane-2,4-diisocyanate.Herein,we prepared a series of supported Rh-based catalysts by the excessive impregnation method and investigated their catalytic performance for the selective hydrogenation of TDC.The emphasis was put on the influence of support properties on the catalytic performance.Among the prepared catalysts,Rh/g-Al_(2)O_(3)performed the best:a HTDC yield of 88.4%was achieved with a 100%conversion of TDC under the conditions of 100℃,3 MPa and 1 h.Furthermore,Rh/γ-Al_(2)O_(3)could be repetitively used for 4 times without a significant loss of its catalytic activity.TEM,XRD,N_(2)adsorption-desorption,H_(2)-TPR,NH_(3)/CO_(2)-TPD,XPS and ICP characterizations were employed to distinguish the properties of the prepared catalysts and the results were correlated with their catalytic performance.It is indicated that the yield of HTDC shows a positive relevance with the percentage of moderate-to-strong acid sites and the content of Rh^(n+)(n≥3)in the catalysts.High values of the percentage and the content can promote a strong interaction between Rh nanoparticles and the supports,facilitating both the transfer of electrons from Rh to the support and the formation of Rh^(n+)species.This is conducive to activating the benzene ring of TDC and thereby improving the yield of HTDC.
