Preparation Of L-arabinose And One-step Catalytic Isomerization Of L-ribose

Crude L-arabinose was prepared by crystallization using arabic gum as raw material and higher purity of L-arabinose was gained by recrystallization. The influencing factors were studied in detail in the preparation of crude L-arabinose and the conditions of purification of L-arabinose by recrystallization were discussed. The optimal reaction conditions for the preparation of crude L-arabinose by hydrolysis of arabic gum were 1.5% H2SO4 as catalyst, reaction temperature 90℃, hydrolysis time 4h, barium hydroxide for neutralization, methanol as solvent after concentration. After filter and concentration the solution crystallized to give crude L-arabinose with yield of 21.0% and purity of 87.2%. The optimal recrystallization conditions of exact by recrystallization were mass concentration of solution 50% above, pH value 6~7, concentration of ethanol 90% above, crystallization time 4h, mass concentration of crystal seed 20% above, and the highest yield and purity of L-arabinose was 15.6% (theoretical yield was 31.0%) and 97.5% respectively. The products washed and dried out to give L-arabinose with good appearance, melting point of 153.9~156.3℃and optical rotation of (c=2.8, water).The technology of isomerization of L-arabinose with Mo catalyst and separation of L-ribose by synthesis of L-ribose anilide was studied. L-ribose was prepared by one-step isomerization of L-arabinose with Mo catalyst. The condition of One-step Catalytic isomerization of L-ribose from L-arabinose were a solution of L-arabinose (5g), MoO3 (0.5g) and 4-pyridinepropanol (0.05g), reaction temperature 100℃, reaction time 3h. The synthetic conditions of L-ribose anilide were alkaline adsorbent resins (10.0g) and activated carbon (0.50g) used for decolorization and impurity removal, sebsequent treatment of filter and concentration gave a syrup. The syrup thus obtained was dissolved in methanol (1.0mL) and kept in a refrigerator. The resulting crystalline L-arabinose(1.59g) was filtered off and the filtrate was concentrated in vacuo. The resulting syrup was treated with anilide in ethanol and kept in a refrigerator to give L-ribose anilide (0.66g), and the yield was 40%. The L-ribose anilide was treated with formaldehyde, then crystallized from ehanol to give L-ribose (0.38g), and the yield was 13.2%, mp 82~84℃. The structure of L-ribosee was identified by IR spectrum and 1H NMR spectrum.