19319-26-7Relevant articles and documents
Dehydration of 2-methylbutanal and methyl isopropyl ketone to isoprene using boron and aluminium phosphate catalysts
Hutchings, Graham J.,Hudson, Ian D.,Bethell, Donald,Timms, Don G.
, p. 291 - 299 (1999)
The synthesis of isoprene from the dehydration of 2-methylbutanal is described using boron phosphate, aluminium phosphate, and mixed boron/aluminium phosphates as catalysts. Both boron phosphate and aluminium phosphate deactivate steadily with reaction time due to loss of catalyst activity but the selectivity to isoprene is not significantly affected by catalyst deactivation. Catalyst deactivation is shown to be due to two factors: (i) loss of surface phosphorus and (ii) coke formation. Reactivation of the catalysts at temperatures up to 500°C in an air atmosphere does not successfully restore the catalyst activity, although this procedure does remove all the coke. It is shown that high-temperature calcination (800°C) removes both the surface carbon and restores the surface phosphorus content, and hence this procedure is a necessary prerequisite for the successful reactivation of boron and aluminium phosphate as a catalyst for 2-methylbutanal dehydration. Two samples of aluminium phosphate were studied, prepared from the reaction of phosphoric acid with aluminium chloride or sulfate. The chloride route gives a mixed cristabolite/tridymite AlPO4 and this is shown to be more active than a catalyst containing only the tridymite form of AlPO4 formed from the sulfate route. However, both are less active than BPO4 which can be readily prepared in the cristabolite structure. Mixed B/AlPO4 catalysts (Al:B mol ratio = 1:0.05 and 1:0.1) have also been investigated and these are shown to have a superior catalytic performance when compared with undoped AlPO4. 31P, 27Al, and 11B MAS NMR spectroscopy shows that B and Al are in the same lattice in these mixed phosphate catalysts. Addition of Nb is shown to stabilize the catalytic performance. The BPO4 and AlPO4 catalysts are also shown to be active catalysts for the synthesis of isoprene from methyl isopropyl ketone, which is the major by-product formed from the reaction of 2-methylbutanal. It is suggested that a process for the synthesis of isoprene based on the dehydration of 2-methylbutanal would involve the recycle and conversion of the by-products. The mechanism of the reaction is discussed and it is proposed that 2-methyl-but-2-en-1-ol is an intermediate central to the formation of the two major products of the dehydration reaction: isoprene and methyl isopropyl ketone.
OXIDATION OF ISOPRENE BY MOLECULAR OXYGEN IN THE PRESENCE OF THE TETRAPHENYLPORPHIN COMPLEX OF DIVALENT MANGANESE
Karakozova, E. I.,Solov'eva, A. B.,Karmilova, L. V.
, p. 197 - 198 (1986)
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Regulating Hydrogenation Chemoselectivity of α,β-Unsaturated Aldehydes by Combination of Transfer and Catalytic Hydrogenation
Zhou, Yangyang,Li, Zihao,Liu, Yanbo,Huo, Jia,Chen, Chen,Li, Qiling,Niu, Songyang,Wang, Shuangyin
, p. 1746 - 1750 (2020/02/25)
Two hydrogenation mechanisms, transfer and catalytic hydrogenation, were combined to achieve higher regulation of hydrogenation chemoselectivity of cinnamyl aldehydes. Transfer hydrogenation with ammonia borane exclusively reduced C=O bonds to get cinnamyl alcohol, and Pt-loaded metal–organic layers efficiently hydrogenated C=C bonds to synthesize phenyl propanol with almost 100 % conversion rate. The hydrogenation could be performed under mild conditions without external high-pressure hydrogen and was applicable to various α,β-unsaturated aldehydes.
Asymmetric Aza-Wacker-Type Cyclization of N-Ts Hydrazine-Tethered Tetrasubstituted Olefins: Synthesis of Pyrazolines Bearing One Quaternary or Two Vicinal Stereocenters
Kou, Xuezhen,Shao, Qihang,Ye, Chenghao,Yang, Guoqiang,Zhang, Wanbin
supporting information, p. 7587 - 7597 (2018/06/04)
We have developed an asymmetric aza-Wacker-type cyclization of N-Ts hydrazine-tethered tetrasubstituted olefins, affording optically active pyrazolines bearing chiral tetrasubstituted carbon stereocenters. This reaction is tolerant to a broad range of substrates under mild reaction conditions, giving the desired chiral products with high enantioselectivities. Generation of two vicinal stereocenters on the C=C double bonds was also achieved with high selectivities, a process which has been rarely studied for Wacker-type reactions. A mechanistic study revealed that this aza-Wacker-type cyclization undergoes a syn-aminopalladation process. It was also found that for substrates bearing two linear alkyl substituents on the outer carbon atom of the olefin, both of which are larger than a methyl group, the alkyl substituent that is cis to the intranucleophilic group participates more readily in β-hydride elimination. When one of the two alkyl substituents on the outer carbon atom of the olefin is a methyl group, β-hydride elimination proceeds selectively at the methylene side, thus both diastereomers can be prepared via switching the configuration of the olefin. Furthermore, the product can be converted to a pharmaceutical compound in high yields over three steps.
