This paper describes synthesis, characterization, and catalase activity of a water-soluble diMn(III) complex of a sulphonato-substituted Schiff-base ligand. DiMn(III) complex is highly efficient to disproportionate hydrogen peroxide in basic aqueous solutions or in DMF.
Three major steps have been used to synthesize diMn(III) complex. First, sodium 3- methylsalicylaldehyde-5-sulfonate is prepared from commercially available 3- methylsalicylaldehyde. Sulfonated salicylaldehyde is then reacted with 1,5-diaminopentan-3-ol to form sodium salt of 1,5-bis(3-methyl-5-sulphonatosalicylidenamino)pentan-3-ol (Schiff-base ligand). Finally the diMn(III) complex is prepared by reacting the Schiff-base ligand with Mn(OAc)3.2H2O.
In particular, this article was referred to synthesize sodium 3-methylsalicylaldehyde-5-sulfonate. To begin the synthesis, a mixture of 3-methylsalicylaldehyde (30.66 mmol) and aniline (44.84 mmol) was refluxed in ethanol for 2 h. However, 98 % yield of N-phenyl-3-methylsalicyldimine was not observed as it explained in the article. So the reaction time was increased to 6 h and it resulted 97 % yield of the protected compound. N-phenyl-3-methylsalicyldimine (30 mmol) was then treated with concentrated sulfuric acid (150 mmol) and the mixture was stirred at 90 °C for 2 h. Yellow N-phenyl-3-methylsalicyldimine-5-sulfonic acid was formed in 47 % yield when the reaction mixture was slowly added on to ice after 2 h of reaction time. Next, N-phenyl-3- methylsalicyldimine-5-sulfonic acid was hydrolyzed by boiling in a saturated Na2CO3 solution for 2 h. After treating with glacial acetic acid it afforded 3-methylsalicylaldehyde-5-sulfonate in 64 % yield.
In summary, reproducibility of the reactions described in the article has been good. However, extension of the reaction time from 2 h to 6 h is recommended at the very first step of the synthesis for better yields.