Study On The Reaction Kinetics Of The Photochemical Synthesis Of Hydroxycobalamin And Its Key Process Parameters

Vitamin B₁₂ and its derivatives,known as cobalamins（Cbls）,play an important role in human health.Their names depend on the different functional groups connected to theβposition of the cobalaline ring structure.Among them,hydroxycobalamin(B_12b)is a long-acting vitamin B₁₂ with fast absorption and high utilization rate.The photochemical method is more in line with the concept of green chemistry than the traditional chemical synthesis route.Vitamin B₁₂ is photosensitive.The photochemical preparation of hydroxy-cobalamin at different wavelengths follows first-order reaction kinetics.The performance is optimal at 450nm,for which the kinetic equation is ln C=-0.417t+4.6832.In addition,the effects of different light sources,initial concentration,light intensity and optical path length on the reaction were also investigated.The results showed that the reaction rate under white parallel light source was faster than that under a 450 nm monochrome light source.The reaction rate decreased with the increase of initial concentration.For the 450 nm monochromatic light source,with the increase of light intensity and the decrease of illumination distance,the reaction rate constant k increases,while the change in optical path length has no obvious effect on the reaction kinetics when using the white parallel light source.As measured by the electrochemical workstation,k is inversely proportional to C₀ under the white parallel light source because the light energy obtained per unit B₁₂ molar concentration is small,and the optical path length does not affect the current response value.Under the450 nm monochromatic light source,the relationship between the fitted rate constant and the key process parameters is:k=109.53I_x/I₀（6-d）e^-.0005C0e^（-Ea/RT）,1（≤d≤）5.Under the white parallel light source,for light intensity I_x=I₀=1A,1≤d≤5,there is:k=187.16e^-.0006C0e^（-Ea/RT）.Cyanocobalamin(B₁₂)and methylcobalamin were selected as different raw materials to study the activation energy of photochemical preparation of hydroxycobalamin.The results showed that the activation energy Ea of preparing hydroxycobalamin from cyanocobalamin was 11.6 k J.mol^-1,and the Ea of preparing hydroxycobalamin from methylcobalamin was 5.41 k J.mol^-1.Both k increased slightly with the increase of temperature,which also indicated that the reaction was controlled by actinology.B₁₂ does not react when there is no light,and produces B_12b under light.After exposure to light,B₁₂ and the product B_12b exhibit a dynamic equilibrium,and separation needs to be carried out in time as the next step.In this paper,the kinetics of preparing hydroxycobalamin by photochemical method was studied,and the reaction process parameters were explored.The product has high purity and the process emits no pollutants.This provides a theoretical basis for the optimization of the synthesis of hydroxycobalamin at an industrial scale,and will potentially promote the competitiveness of China’s vitamin B₁₂ products in the international market.