Converting Thiophene in Simulated Coking Crude Benzene to N,N-Dimethyl-2-thiophenecarboxamide by Dimethylcarbamyl Chloride Under Mild Conditions

Since the content of thiophene in coking crude benzene is high, it is necessary to remove it from coking crude benzene for efficient utilization. In this study, an important intermediate, N,N-dimethyl-2-thiophenecar-boxamide, was synthesized from thiophene and dimethylcarbamyl chloride. The influences of the dosages of dimethylcarbamyl chloride and ZnCl₂ catalyst, reaction temperature and time on the removal rate were further explored based on the reaction kinetics. The structure of the target product was characterized by means of MS, ¹H NMR and ¹³C NMR. The removal rate of thiophene was 98.14% after the reaction for 2 h and thiophene was almost removed after the reaction for 3 h under the optimal reaction conditionsa molar ratio of n(thiophene):n(dimethylcarbamyl chloride):n(ZnCl₂)=1:12:10, 300 r/min, 318 K and 101.325 kPa]. The acylation of thiophene with dimethylcarbamyl chloride was approximately in accord with the first order kinetic equation at 303-323 K. The activation energy was 53.9850 kJ/mol and the pre-exponential factor was 1.4521×10⁹ h^-1.