Selective Activation of C=C Bond in Sustainable Phenolic Compounds from Lignin via Photooxidation: Experiment and Density Functional Theory Calculations.

Selective Activation of C=C Bond in Sustainable Phenolic Compounds from Lignin via Photooxidation: Experiment and Density Functional Theory Calculations.

Photochemistry and photobiology (2015-08-14)

Morgan Zielinski Goldberg, Luke A Burke, Alexander Samokhvalov

ABSTRACT

Lignocellulosic biomass can be converted to high-value phenolic compounds, such as food additives, antioxidants, fragrances and fine chemicals. We investigated photochemical and heterogeneous photocatalytic oxidation of two isomeric phenolic compounds from lignin, isoeugenol and eugenol, in several nonprotic solvents, for the first time by experiment and the density functional theory (DFT) calculations. Photooxidation was conducted under ambient conditions using air, near-UV light and commercial P25 TiO2 photocatalyst, and the products were determined by TLC, UV-Vis absorption spectroscopy, HPLC-UV and HPLC-MS. Photochemical and photocatalytic oxidation of isoeugenol proceeds via the mild oxidative "dimerization" to produce the lignan dehydrodiisoeugenol (DHDIE), while photooxidation of eugenol does not proceed. The DFT calculations suggest a radical stepwise mechanism for the oxidative "dimerization" of isoeugenol to DHDIE as was calculated for the first time.

MATERIALS

Product Number

Brand

Product Description

D4551

Sigma-Aldrich

N,N-Dimethylformamide, for molecular biology, ≥99%

224227

Sigma-Aldrich

Titanium(IV) oxide, rutile, powder, <5 μm, ≥99.9% trace metals basis

204730

Sigma-Aldrich

Titanium(IV) oxide, rutile, 99.995% trace metals basis

204757

Sigma-Aldrich

Titanium(IV) oxide, rutile, ≥99.98% trace metals basis

227056

Sigma-Aldrich

N,N-Dimethylformamide, anhydrous, 99.8%

D158550

Sigma-Aldrich

N,N-Dimethylformamide, ReagentPlus^®, ≥99%

319937

Sigma-Aldrich

N,N-Dimethylformamide, ACS reagent, ≥99.8%

33120

Sigma-Aldrich

N,N-Dimethylformamide, puriss. p.a., ACS reagent, reag. Ph. Eur., ≥99.8% (GC)

494488

Sigma-Aldrich

N,N-Dimethylformamide, biotech. grade, ≥99.9%

700347

Sigma-Aldrich

Titanium(IV) oxide, mixture of rutile and anatase, nanoparticles, <150 nm particle size (volume distribution, DLS), dispersion, 40 wt. % in H₂O, 99.5% trace metals basis

634662

Sigma-Aldrich

Titanium(IV) oxide, mixture of rutile and anatase, nanopowder, <100 nm particle size (BET), 99.5% trace metals basis

637262

Sigma-Aldrich

Titanium(IV) oxide, rutile, nanopowder, <100 nm particle size, 99.5% trace metals basis

635057

Sigma-Aldrich

Titanium(IV) oxide, rutile, <001>, (single crystal substrate), ≥99.9% trace metals basis, L × W × thickness 10 mm × 10 mm × 0.5 mm

14021

Sigma-Aldrich

Titanium(IV) oxide, ReagentPlus^®, ≥99%