300
M. Hong
ideal biomass resource because of its wide availability at a low cost. In 2020, Hong
and Wang established a versatile bio-refinery platform to a high-quality gasolinelike biofuel and a heat- and solvent-resistant acrylic bioplastic (T g = 263.7 °C,
T d = 364.0 °C) via LP-mediated selective dimerization and polymerization of
lignocellulose-based β-angelica lactone (β-AL, Scheme 8.12a) [61]. Because of inert
cyclic double bond of β-AL compared to its analogues (reactivity: β-AL < MC <
MMA < γ MMBL) as well as the acidity of γ -H of β-AL which is susceptible to form
the dimer or oligomer via chain transfer to monomer, β-AL has remained an unexploited bio-based monomer for polymerization. In this study, when RAl(BHT) 2 (R
= Me, Et,
i Bu)/I
i Pr CLA was utilized as the catalyst, the first successful polymerization of β-AL can be achieved. A noticeable increase of activity and PβAL M n were
observed with enhancing the steric hindrance of LA, and increasing LA/I
i Pr ratio
from 2/1 to 4/1 was also proved to be an effective way to enhance M n of PβAL. With a
[β-AL] 0 :[
i BuAl(BHT) 2 ] 0 :[I
i Pr] 0 ratio of 300:4:1, quantitative β-AL conversion was
accomplished within 5 min (TOF = 3600 h
−1 ), affording exclusively PβAL with
relatively high M n up to 26.0 kg/mol (Ð = 1.61). Unlike the commonly observed
nucleophilic initiation pathway in LPP, this polymerization is initiated via basic
pathway via the formation of [I
i Pr-H]
+ –enolaluminate ion pair active species through
the deprotonation of γ -H of MeAl(BHT) 2 -activated β-AL by I
i Pr (Scheme 8.12b).
The catalytic cycle of RAl(BHT) 2 /I
i Pr CLA-mediated polymerization is proposed to
consist of basic initiation-conjugate addition-MeAl(BHT) 2 release-chain transfer to
monomer fundamental steps (Scheme 8.12b). The keys to successful polymerization
by RAl(BHT) 2 (R = Me, Et,
i Bu)/I
i Pr CLA have mainly relied on (1) the balanced
Lewis acidity of RAl(BHT) 2 which is sufficient for monomer activation but the lowest
possible to suppress the LA-activated chain transfer to monomer; (2) the utilization of
strongly Lewis basic I
i Pr to shut down chain transfer to [I
i Pr-H]
+ . Intriguingly, when
switching from I
i Pr to weakly basic Et 3 N to construct FLP with MeAl(BHT) 2 , the
resultant product shifted from exclusive polymer to the dimer without any detectable
PβAL formation. It is noteworthy that MeAl(BHT) 2 /Et 3 N is highly active toward the
selective dimerization of β-AL (TOF: 200–1000 h
−1 ). Even though 4000 equiv. of
β-AL were employed, quantitative β-AL conversion can be accomplished within
810 min. The exquisite selectivity of MeAl(BHT) 2 /Et 3 N FLP toward dimerization has the relationship with the unique H-shuttling chain transfer to [Et 3 N-H]
+
[Scheme 8.12c (top)], besides chain transfer to monomer [Scheme 8.12c (bottom)].
Most remarkably, the obtained dimer can further act as a practical precursor for
hydrodeoxygenation to generate gasoline-like alkanes. Upon treatment with Pt/C +
TaOPO 4 metal-acidic solid catalyst at 300 °C under 200 psi H 2 for 3 h, high-quality
biofuel in the gasoline volatility range was yielded with high alkane selectivity of
87% (C8: 72.6%, C9: 14.4%).
M. Hong
ideal biomass resource because of its wide availability at a low cost. In 2020, Hong
and Wang established a versatile bio-refinery platform to a high-quality gasolinelike biofuel and a heat- and solvent-resistant acrylic bioplastic (T g = 263.7 °C,
T d = 364.0 °C) via LP-mediated selective dimerization and polymerization of
lignocellulose-based β-angelica lactone (β-AL, Scheme 8.12a) [61]. Because of inert
cyclic double bond of β-AL compared to its analogues (reactivity: β-AL < MC <
MMA < γ MMBL) as well as the acidity of γ -H of β-AL which is susceptible to form
the dimer or oligomer via chain transfer to monomer, β-AL has remained an unexploited bio-based monomer for polymerization. In this study, when RAl(BHT) 2 (R
= Me, Et,
i Bu)/I
i Pr CLA was utilized as the catalyst, the first successful polymerization of β-AL can be achieved. A noticeable increase of activity and PβAL M n were
observed with enhancing the steric hindrance of LA, and increasing LA/I
i Pr ratio
from 2/1 to 4/1 was also proved to be an effective way to enhance M n of PβAL. With a
[β-AL] 0 :[
i BuAl(BHT) 2 ] 0 :[I
i Pr] 0 ratio of 300:4:1, quantitative β-AL conversion was
accomplished within 5 min (TOF = 3600 h
−1 ), affording exclusively PβAL with
relatively high M n up to 26.0 kg/mol (Ð = 1.61). Unlike the commonly observed
nucleophilic initiation pathway in LPP, this polymerization is initiated via basic
pathway via the formation of [I
i Pr-H]
+ –enolaluminate ion pair active species through
the deprotonation of γ -H of MeAl(BHT) 2 -activated β-AL by I
i Pr (Scheme 8.12b).
The catalytic cycle of RAl(BHT) 2 /I
i Pr CLA-mediated polymerization is proposed to
consist of basic initiation-conjugate addition-MeAl(BHT) 2 release-chain transfer to
monomer fundamental steps (Scheme 8.12b). The keys to successful polymerization
by RAl(BHT) 2 (R = Me, Et,
i Bu)/I
i Pr CLA have mainly relied on (1) the balanced
Lewis acidity of RAl(BHT) 2 which is sufficient for monomer activation but the lowest
possible to suppress the LA-activated chain transfer to monomer; (2) the utilization of
strongly Lewis basic I
i Pr to shut down chain transfer to [I
i Pr-H]
+ . Intriguingly, when
switching from I
i Pr to weakly basic Et 3 N to construct FLP with MeAl(BHT) 2 , the
resultant product shifted from exclusive polymer to the dimer without any detectable
PβAL formation. It is noteworthy that MeAl(BHT) 2 /Et 3 N is highly active toward the
selective dimerization of β-AL (TOF: 200–1000 h
−1 ). Even though 4000 equiv. of
β-AL were employed, quantitative β-AL conversion can be accomplished within
810 min. The exquisite selectivity of MeAl(BHT) 2 /Et 3 N FLP toward dimerization has the relationship with the unique H-shuttling chain transfer to [Et 3 N-H]
+
[Scheme 8.12c (top)], besides chain transfer to monomer [Scheme 8.12c (bottom)].
Most remarkably, the obtained dimer can further act as a practical precursor for
hydrodeoxygenation to generate gasoline-like alkanes. Upon treatment with Pt/C +
TaOPO 4 metal-acidic solid catalyst at 300 °C under 200 psi H 2 for 3 h, high-quality
biofuel in the gasoline volatility range was yielded with high alkane selectivity of
87% (C8: 72.6%, C9: 14.4%).