Scandium trifluoromethanesulfonate Sc

The above acid-catalyzed polycondensations were carried out at more than 100 °C, whereas Takasu et al. reported room temperature polyesterification with scandium trifluoromethanesulfonate [Sc(OTf)3] or scandium trifluo-romethanesulfoimide [Sc(NTf2)3] [27,28]. Thus, the direct polycondensation of methylsuccinic acid and 1,4-butanediol proceeded in bulk under reduced pressure (0.3-30 mmHg) using 1.4 mol % of Sc(OTf)3 at 35 °C for 96 h to afford poly(butylene methylsuccinate) with Mn of 12400 (Scheme 5). When HfCl4-(THF)2 was used in this room temperature polymerization instead of Sc(OTf)3, only low molecular weight polyester (Mn = 1100) was afforded. The scandium catalysts did not promote transesterification ethanol selectively reacted with acetic acid even in the presence of equimolar methyl acetate. 

The element scandium (Sc) is in group 3 (above La and Y), and its radius is appreciably smaller than those of any other rare earth elements. Scandium is uncommon probably because of the lack of rich sources and difficulties of separation. Its chemical behavior is known to be intermediate between that of aluminum and lanthanides [1]. Use of scandium in organic synthesis was rather limited before scandium trifluoromethanesulfonate (Sc(OTf)3) was first introduces as a promising Lewis add in 1993 [2],... 

Takasu et al. [24] reported that scandium trifluoromethanesulfonate [Sc(OTQ3] and scandium trifluoromethanesulfonimide [Sc(NTf2)s] are effective for one-step dehydration polycondensation of L-lactic acid. Bulk polycondensation of L-lactic acid was carried out at 130-170°C to give PLLA with Mn of 5.1 xlO -7.3xl0 (yield 32%-60%). However, the solution polycondensation was... 

Kobayashi, S. Hachiya, L Araki, M. Ishitani, H., Scandium trifluoromethanesulfonate (Sc(OTf)3). A novel reusable catalyst in the Diels-Alder reaction. Tetrahedron Lett, 1993, 34,3755-8. 

Interestingly, salts other than tin(ll) bis-(2-ethylhexanoate) such as scandium and tin trifluoromethanesulfonate [41 3], zinc octoate [44, 45], and aluminum acetyl acetonate [45] were reported to mediate the ROP of lactones. As far as scandium trifluoromethanesulfonate is concerned, the main advantage is the increase of its Lewis acidity enabling the polymerization to be carried out at low temperatures with acceptable kinetics. Later, faster kinetics were obtained by extending the process to scandium trifluoromethanesulfonimide [Sc(NTf2)3] and scandium nonafluorobutanesulfonimide [Sc(NNf2)3] and to other rare earth metal catalysts (metal=Tm, Sm, Nd) [46]. 

Scandium(lll) trifluoromethanesulfonate [Sc(OTf)3] was purchased from Aldrich Chemical Company, Inc., (99% purity) and used without additional purification. 

Other RE(OTf)3 were also examined as catalysts in the reaction of 1 with acetic anhydride (Table 2). Catalytic amounts of all the RE(OTf)3 listed effectively mediated the acylation of 1. Among these, scandium trifluoromethanesulfonate (scandium triflate, Sc(OTf)3)[6] or Yb(OTf)3 was superior to other RE(OTf)3 and afforded the acylation product 2 quantitatively. When, on the other hand, lanthanum trifluoromethanesulfonate (lanthanum triflate, La(OTf)3) was used, the yield of 2 was relatively low. The yields shown in Table 2 may reflect the catalytic activity of respective RE(OTf)3. 

Scandium-based Lewis acid catalysts, especially its trifluoromethanesulfonate (Sc(OTf)3), are versatile catalysts that can accelerate a variety of organic reactions even in water as an environmentally benign solvent [48]. Various kinds of polymer-immobilization techniques have been developed as shown below. 

Scandium(III) trifluoromethanesulfonate (Sc(OTf)3) is extensively used in organic synthesis to catalyze a wide variety of carbon-carbon bond-forming reactions in aqueous media. The polymer microencapsulated triflate ME catalysts are recoverable and reusable, often reduce metal leaching, and have activity similar to that of their homogeneous counterparts [128]. 

The rare-earth salts of trifluoromethanesulfonic acid (triflic acid) are popular reagents for lanthanide-mediated organic reactions. Especially scandium(III) triflate, Sc(CF3S03)3, and ytterbium(lll) triflate, Yb(CF3S03)3, are often used as mild Lewis acids for reactions in water (Kobayashi et al., 2002). It is therefore surprising that only very few studies of cerium(IV)-mediated reactions describe the use of cerium(IV) triflate, Ce(CF3 803)4 or Ce(OTf)4, as a reagent. This salt was first reported by Kreh et al. (1987), who prepared a solution of cerium(lV) in aqueous triflic acid by electrochemical oxidation of a cerium(III) triflate solution. They illustrated the use of this reagent for oxidation of alkylaromatic and polycyclic aromatic compounds. Imamoto et al. (1990) prepared cerium(IV) triflate by reaction... 

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