Direct Deoxydehydration of Cyclic Trans-Diol Substrates: An Experimental and Computational Study of the Reaction Mechanism of vanadium(V)-Based Catalysis

<p>The deoxydehydration of carbohydrates represents a key target to leverage renewable biomass resources chemically. Using a vanadium(V)-based catalyst, we demonstrate that it is possible to directly deoxydehydrate <i>trans</i>-cyclic diol substrates. Accompanying mechanistic characterisation of this process by density functional calculations points to an energetically tractable route for deoxydehydration of cyclic <i>trans</i>-diol substrates involving stepwise cleavage of the diol C-O bonds <i>via</i> the triplet state; experimentally, this is supported by light dependence of the reaction. Calculations also indicate that cyclic <i>cis</i>-diols and a linear diol substrate can additionally proceed by a concerted singlet DODH mechanism. This work potentially opens a new and cost-effective way to efficiently convert carbohydrates of <i>trans</i>-diol stereochemistry into alkenes. </p>

Direct Deoxydehydration of Cyclic Trans-Diol Substrates: An Experimental and Computational Study of the Reaction Mechanism of vanadium(V)-Based Catalysis

<p>The deoxydehydration of carbohydrates represents a key target to leverage renewable biomass resources chemically. Using a vanadium(V)-based catalyst, we demonstrate that it is possible to directly deoxydehydrate <i>trans</i>-cyclic diol substrates. Accompanying mechanistic characterisation of this process by density functional calculations points to an energetically tractable route for deoxydehydration of cyclic <i>trans</i>-diol substrates involving stepwise cleavage of the diol C-O bonds <i>via</i> the triplet state; experimentally, this is supported by light dependence of the reaction. Calculations also indicate that cyclic <i>cis</i>-diols and a linear diol substrate can additionally proceed by a concerted singlet DODH mechanism. This work potentially opens a new and cost-effective way to efficiently convert carbohydrates of <i>trans</i>-diol stereochemistry into alkenes. </p>

Isoprene and monoterpene emissions in south-east Australia: comparison of a multi-layer canopy model with MEGAN and with atmospheric observations

One of the key challenges in atmospheric chemistry is to reduce the uncertainty of biogenic volatile organic compound (BVOC) emission estimates from vegetation to the atmosphere. In Australia, eucalypt trees are a primary source of biogenic emissions, but their contribution to Australian air sheds is poorly quantified. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) has performed poorly against Australian isoprene and monoterpene observations. Finding reasons for the MEGAN discrepancies and strengthening our understanding of biogenic emissions in this region is our focus. We compare MEGAN to the locally produced Australian Biogenic Canopy and Grass Emissions Model (ABCGEM), to identify the uncertainties associated with the emission estimates and the data requirements necessary to improve isoprene and monoterpene emissions estimates for the application of MEGAN in Australia. Previously unpublished, ABCGEM is applied as an online biogenic emissions inventory to model BVOCs in the air shed overlaying Sydney, Australia. The two models use the same meteorological inputs and chemical mechanism, but independent inputs of leaf area index (LAI), plant functional type (PFT) and emission factors. We find that LAI, a proxy for leaf biomass, has a small role in spatial, temporal and inter-model biogenic emission variability, particularly in urban areas for ABCGEM. After removing LAI as the source of the differences, we found large differences in the emission activity function for monoterpenes. In MEGAN monoterpenes are partially light dependent, reducing their dependence on temperature. In ABCGEM monoterpenes are not light dependent, meaning they continue to be emitted at high rates during hot summer days, and at night. When the light dependence of monoterpenes is switched off in MEGAN, night-time emissions increase by 90–100 % improving the comparison with observations, suggesting the possibility that monoterpenes emitted from Australian vegetation may not be as light dependent as vegetation globally. Targeted measurements of emissions from in situ Australian vegetation, particularly of the light dependence issue are critical to improving MEGAN for one of the world's major biogenic emitting regions.