Oxidation of benzoin catalyzed by oxovanadium (IV) schiff base complexes

BACKGROUND: The oxidative transformation of benzoin to benzil has been accomplished by the use of a wide variety of reagents or catalysts and different reaction procedures. The conventional oxidizing agents yielded mainly benzaldehyde or/and benzoic acid and only a trace amount of benzil. The limits of practical utilization of these reagents involves the use of stoichiometric amounts of corrosive acids or toxic metallic reagents, which in turn produce undesirable waste materials and required high reaction temperatures. In recent years, vanadium complexes have attracted much attention for their potential utility as catalysts for various types of reactions. RESULTS: Active and selective catalytic systems of new unsymmetrical oxovanadium(IV) Schiff base complexes for the oxidation of benzoin is reported. The Schiff base ligands are derived between 2-aminoethanol and 2-hydroxy-1- naphthaldehyde (H2L1) or 3-ethoxy salicylaldehyde (H2L3); and 2-aminophenol and 3-ethoxysalicylaldehyde (H2L2) or 2-hydroxy-1-naphthaldehyde (H2L4). The unsymmetrical Schiff bases behave as tridentate dibasic ONO donor ligands. Reaction of these Schiff base ligands with oxovanadyl sulphate afforded the mononuclear oxovanadium(IV) complexes (VIVOLx.H2O), which are characterized by various physico-chemical techniques. The catalytic oxidation activities of these complexes for benzoin were evaluated using H2O2 as an oxidant. The best reaction conditions are obtained by considering the effect of solvent, reaction time and temperature. Under the optimized reaction conditions, VOL4 catalyst showed high conversion (>99%) with excellent selectivity to benzil (~100%) in a shorter reaction time compared to the other catalysts considered. CONCLUSION: Four tridentate ONO type Schiff base ligands were synthesized. Complexation of these ligands with vanadyl(IV) sulphate leads to the formation of new oxovanadium(IV) complexes of type VIVOL.H2O. Elemental analyses and spectral data of the free ligands and their oxovanadium(IV) complexes were found to be in good agreement with their structures, indicating high purity of all the compounds. Oxovanadium complexes were screened for the oxidation of benzoin to benzil using H2O2 as oxidant. The effect of time, solvent and temperature were optimized to obtain maximum yield. The catalytic activity results demonstrate that these catalytic systems are both highly active and selective for the oxidation of benzoin under mild reaction conditions.Web of Scienc

Unmarked? Criminal Record Clearing and Employment Outcomes

An estimated one in three American adults has a criminal record. While some records are for serious offenses, most are for arrests or relatively lowlevel misdemeanors. In an era of heightened security concerns, easily available data, and increased criminal background checks, these records act as a substantial barrier to gainful employment and other opportunities. Harvard sociologist Devah Pager describes people with criminal records as “marked” with a negative job credential. In response to this problem, lawyers have launched unmarking programs to help people take advantage of legal record clearing remedies. We studied a random sample of participants in one such program to analyze the impact of the record clearing intervention on employment outcomes. Using methods to control for selection bias and the effects of changes in the economy in our data, we found evidence that: (1) the record clearing intervention boosted participants’ employment rates and average real earnings, and (2) people sought record clearing remedies after a period of suppressed earnings. More research needs to be done to understand the durability of the positive impact and its effects in different local settings and labor markets, but these findings suggest that the record clearing intervention makes a meaningful difference in employment outcomes for people with criminal records. The findings also suggest the importance of early intervention to increase employment opportunities for people with criminal records. Such interventions might include more legal services, but they might also include record clearing by operation of law or another mechanism that does not put the onus of unmarking on the person with a criminal record