3 research outputs found
Solvothermal Alcoholysis Routes for Recycling Polylactide Waste as Lactic Acid Esters
In
this work, we investigated the possible use of polylactide (PLA),
a biodegradable polymer obtained from renewable biofeedstock, to produce
a range of industrially useful lactic acid esters. We describe a simple
and convenient solvothermal alcoholysis method for large-scale recycling
of PLA resins or residues from disposable packaging in the presence
of the appropriate alcohol under catalyst-free or catalytic conditions.
This process proceeds easily both without and with a catalyst. The
results show that the best catalytic activities involve magnesium
and calcium alkoxides synthesized in situ from organometallic or metallic
precursors and an alcohol. We determined the crystal structure of
the chiral mononuclear postcatalyst [Ca(LAc)<sub>2</sub>(EL)<sub>2</sub>] (<b>1</b>; LAc = lactic acid anion, EL = ethyl lactate),
obtained directly from the reactor. Particular emphasis is placed
on the operating conditions and high activity of the catalyst used.
Key factors that affect the catalytic activity and reaction mechanism
are also highlighted
Synthesis and Structural Characterization of Magnesium Drug Complexes: Efficient Initiators for Forming Polylactide–Drug Conjugates
Five novel magnesium alkoxides supported
by drug chelating agents <i>pridinolum</i> (PriOH = 1,1-diphenyl-3-(1-piperidinyl)-1-propanol)
and <i>venlafaxinum</i> (VenlOH = (<i>RS</i>)-1-[2-dimethylamino-1-(4-methoxyphenyl)-ethyl]cyclohexanol)
were successfully synthesized and characterized. Direct reaction of
PriOH and VenlOH with MgBu<sub>2</sub> (1:1) in toluene gives the
dimeric compounds [Mg(μ,η<sup>2</sup>-OPri)<sup><i>n</i></sup>Bu]<sub>2</sub> (<b>1</b>) and [Mg(μ,η<sup>2</sup>-VenlO)<sup><i>n</i></sup>Bu]<sub>2</sub> (<b>2</b>), respectively. Furthermore, the crystallization of an equimolar
mixture of <b>1</b> and <b>2</b> in toluene yields heteroleptic
magnesium complex [Mg(μ,η<sup>2</sup>-OVenl)(η<sup>1</sup>-OPri)]<sub>2</sub> (<b>3</b>). Moreover, reactions
of <b>1</b> and <b>2</b> with 2 molar equivs of the corresponding
drug–ligands give the homoleptic magnesium bis-alkoxides [Mg(μ,η<sup>2</sup>-OPri)(η<sup>1</sup>-OPri)]<sub>2</sub> (<b>4</b>) and [Mg(μ,η<sup>2</sup>-OVenl)(η<sup>1</sup>-OVenl)]<sub>2</sub> (<b>5</b>). The treatment of compound <b>1</b> with 2 equivs of VenlOH or <b>2</b> with 2 equivs of PriOH
leads to the formation of <b>3</b>. Complexes <b>1</b>–<b>5</b> were characterized by elemental analysis,
nuclear magnetic resonance, and single crystal X-ray diffraction (for <b>1</b>–<b>4</b>). It was found that complexes <b>1</b>–<b>5</b> are efficient initiators of the ring-opening
polymerization of l-LA, yielding PLA-OPri and PLA-OVenl conjugates,
respectively. Moreover, the ring-opening polymerization of l-LA initiated by <b>3</b> led to the simultaneous generation
of a blend of poly-l-lactide conjugates with end-capped VenlO
and PriO groups
Molecular Routes to Group IV Magnesium and Calcium Nanocrystalline Ceramics
The effect of alkaline-earth-metal
alkoxides on the protonolysis of Cp<sub>2</sub>M′Cl<sub>2</sub> (M′ = Ti, Zr, Hf; Cp = cyclopentadiene) was investigated.
This approach enabled the design of compounds with well-defined molecular
structures to generate high-purity binary metal oxides. Single-source
molecular precursors with structures of [M<sub>2</sub>M′<sub>2</sub>(μ<sub>3</sub>-OEt)<sub>2</sub>(μ-OEt)<sub>4</sub>(OEt)<sub>6</sub>(EtOH)<sub>4</sub>] with M = Mg and M′ =
Ti (<b>1</b>), Zr (<b>2</b>), and Hf (<b>3</b>),
[Ca<sub>6</sub>Ti<sub>4</sub>(μ<sub>6</sub>-O)<sub>2</sub>(μ<sub>4</sub>-O)<sub>2</sub>(μ<sub>3</sub>-OEt)<sub>12</sub>(OEt)<sub>12</sub>(EtOH)<sub>6</sub>Cl<sub>4</sub>] (<b>4</b>), and [M<sub>2</sub>M′<sub>2</sub>(μ<sub>4</sub>-O)(μ-OEt)<sub>5</sub>(OEt)<sub>4</sub>(EtOH)<sub>4</sub>Cl]<sub><i>n</i></sub> with M = Ca and M′ = Zr (<b>5</b>) and Hf (<b>6</b>) were prepared via elimination of the cyclopentadienyl ring
from Cp<sub>2</sub>M′Cl<sub>2</sub> as CpH in the presence
of M(OEt)<sub>2</sub> and ethanol (EtOH) as a source of protons. Meanwhile,
similar reactions involving the initial substitution of Cl ligands
by OEt groups in Cp<sub>2</sub>M′Cl<sub>2</sub> (M′
= Ti, Zr, Hf) resulted in the formation of [M<sub>2</sub>M′<sub>2</sub>(μ<sub>3</sub>-OEt)<sub>2</sub>(μ-OEt)<sub>4</sub>(OEt)<sub>6</sub>(EtOH)<sub>4</sub>] with M = Ca and M′ =
Ti (<b>7</b>), Zr (<b>8</b>), and Hf (<b>9</b>).
The precursors were characterized by elemental analysis, NMR spectroscopy,
and single-crystal X-ray structural analysis. Magnesium compounds <b>1</b>–<b>3</b> decomposed at 750–850 °C
to give MgTiO<sub>3</sub> along with small amounts of Mg<sub>2</sub>TiO<sub>4</sub>, Mg<sub>2</sub>Zr<sub>5</sub>O<sub>12</sub>, or Mg<sub>2</sub>Hf<sub>5</sub>O<sub>12</sub> binary metal oxides. The thermolysis
of calcium compounds <b>4</b> and <b>7</b>–<b>9</b> led to highly pure CaTiO<sub>3</sub>, CaZrO<sub>3</sub>,
or CaHfO<sub>3</sub> perovskite-like oxide particles with diameters
of 20–30 nm