摘要
1.前言 硝基苯在pd、Rh和Ru配合物催化剂作用下,在乙醇介质中可以直接还原羰基化为苯氨基甲酸乙酯。在最佳的反应条件下,硝基苯转化率和苯氨基甲酸乙酯选择性可达到或接近100％。但是,由于相对于底物的贵金属催化剂用量较大,且均相配合物催化剂难于回收再生使用,阻碍了羰基化法在工业上的应用。 本文在原有工作的基础上,对PdCl_2-邻菲咯啉(phen)催化剂体系加以改进。发现添加Ce(SO_4)_2和V_2O_5作为助催化剂,能明显提高Pd(Ⅱ)-phen催化剂的活性;在[ArNO_2]/[Pd]摩尔比值高达7000的条件下,硝基苯的转化率可达100％。
Phenylurethane and its derivatives are useful intermediates in the synthesis of polyurethane resins (such as TDI and MDI) and are also applied as pesticides. It was known that Pd(Ⅱ) complexes with phen-anthroline (phen ) derivatives showed high activity and selectivity in the reductive earbonylation of nitrobenzene to phenylurethane. In the present work, we find that the catalytic efficiency of Pd (Ⅱ)-phen catalysts can be significantly improved when Ce(SO4)2 and V2O5 were used as promoters.V2O5 has been suggested to be an effective promoter for the palladium-catalyzed reductive carbonylation of PhNO2. In this paper, we also show that Ce(SO4)2 plays an important role in the Pd (Ⅱ) -phen catalyst system.
A catalyst prepared by mixing PdCl2, Ce(SO4)2, V2O5 and phen gave 100% conversion with 97.2% selectivity for phenylurethane at a very high substrate to Pd ratio ( [PhNO2]/[Pd] = 7000 ). Decreasing the amount of noble metal catalyst used is of particular importance, in view of the industrial application. This is, to our knowledge the first example of catalytic system which contains rare earth sulfate as an efficient co-catalyst used for the reductive carbonylation of nitrobenzene.
We speculate that the cerium compound in a high oxidation state might prevent the reduction of Pd (Ⅱ) to inactive Pd black. In the presence of a low oxidation state it might accelerate the deoxygenation of nitrobenzene.
The influences of catalyst and promoter concentration, reaction temperature and CO pressure on the activity and selectivity of Pd (Ⅱ) -phen catalysts were also studied.
出处
《分子催化》
EI
CAS
CSCD
1991年第4期372-376,共5页
Journal of Molecular Catalysis(China)
