Luca Bernazzani

Furfural from corn stover hemicelluloses. A mineral acid-free approach

Furfural was obtained from corn stover hemicelluloses by a microwave-assisted, green and heterogeneously catalyzed two-step cascade process as follows: first step, hydrothermal fractionation of corn stover hemicelluloses, and second step, hydrolysis/dehydration of soluble hemicellulosic sugars over niobium phosphate to yield furfural at moderate temperatures (<200 °C), with both steps being performed in water. Furfural yields of up to 23 mol% with respect to the starting raw biomass were reached.

Predicting Physical−Chemical Properties of Compounds from Molecular Structures by Recursive Neural Networks

In this paper, we report on the potential of a recently developed neural network for structures applied to the prediction of physical chemical properties of compounds. The proposed recursive neural network (RecNN) model is able to directly take as input a structured representation of the molecule and to model a direct and adaptive relationship between the molecular structure and target property. Therefore, it combines in a learning system the flexibility and general advantages of a neural network model with the representational power of a structured domain. As a result, a completely new approach to quantitative structure-activity relationship/quantitative structure-property relationship (QSPR/QSAR) analysis is obtained. An original representation of the molecular structures has been developed accounting for both the occurrence of specific atoms/groups and the topological relationships among them. Gibbs free energy of solvation in water, Delta(solv)G degrees , has been chosen as a benchmark for the model. The different approaches proposed in the literature for the prediction of this property have been reconsidered from a general perspective. The advantages of RecNN as a suitable tool for the automatization of fundamental parts of the QSPR/QSAR analysis have been highlighted. The RecNN model has been applied to the analysis of the Delta(solv)G degrees in water of 138 monofunctional acyclic organic compounds and tested on an external data set of 33 compounds. As a result of the statistical analysis, we obtained, for the predictive accuracy estimated on the test set, correlation coefficient R = 0.9985, standard deviation S = 0.68 kJ mol(-1), and mean absolute error MAE = 0.46 kJ mol(-1). The inherent ability of RecNN to abstract chemical knowledge through the adaptive learning process has been investigated by principal components analysis of the internal representations computed by the network. It has been found that the model recognizes the chemical compounds on the basis of a nontrivial combination of their chemical structure and target property.

Thermodynamic study of the partitioning of organic compounds between water and octan-1-ol. Effects of water as cosolvent in the organic phase

The effect of water, as cosolvent, in changing the affinity of octan-1-ol towards organic solutes according to their chemical nature, has been examined by determining the thermodynamic functions of solvation, ΔsolvX°(j)(X=G, H, S), in anhydrous (j= oct) and in water-saturated octan-1-ol (j= oct*) of organic compounds of the RY type (R = hydrocarbon frame, Y = H, O, CO, NH2, NH, N). From these data and the analogous thermodynamic functions of hydration, ΔsolvX°(W), the thermodynamic functions, ΔtrX°(j→j*), for the three ideal or practical processes of transfer (namely, w→oct, w→oct*, oct→oct*) have been calculated.The ΔtrX°(j→j*) functions have been correlated with the structure of the solutes by using their intrinsic volume as a unique structural parameter. The coefficients of the linear equations obtained give information about the contributions to the envisaged thermodynamic function, connected with the formation of a cavity containing the solute and to the solute–solvent interactions. In the case of the ΔtrG°(j→j*) functions, the LSERs (linear solvation energy relationships) have also been used for correlating the thermodynamic functions to the structural features of the solutes.

Isothermal vapour/liquid equilibria of binary mixtures with dibutyl ether at 298.15 K

A head-space gas chromatographic technique has been used to determine vapour/liquid equilibria at 298.15 K of binary mixtures of di-n-butyl ether plus an organic compound (hexane, octane, diethyl ether, tetrahydrofuran, propylamine, butylamine, propanone, cyclopentanone, methanol, butan-1-ol, acetonitrile). Excess molar Gibbs energies, GE, for the systems investigated have been obtained by a least-squares treatment of equilibrium data. Mixtures with hexane, octane and diethyl ether revealed an almost ideal behaviour. Other systems showed positive deviations, which increase with the polarity of the second component. Dibutyl ether + butanol and + cyclopentanone revealed the formation of azeotropic compositions. The Kirkwood–Buff integrals over the entire composition range have been calculated from the composition dependence of GE, and briefly discussed.

Interactions between inorganic pigments and rabbit skin glue in reference paint reconstructions

The thermal degradation of rabbit skin glue, a collagen-based proteinaceous material used as a paint binder in paintings, was investigated in this paper. Paint reconstructions of the glue on its own or mixed with azurite (Cu3(CO3)2(OH)2), calcium carbonate (CaCO3), hematite (Fe2O3·nH2O) and red lead (Pb3O4) were analysed using a thermoanalytical approach. This method enabled us to investigate the interactions between the glue and pigments before and after artificial indoor light ageing. The study was carried out using differential scanning calorimetry, thermogravimetry and thermogravimetry/FTIR analysis already successfully employed to characterize the paint binders. The results highlighted that all the inorganic pigments interact with rabbit skin glue, thus decreasing the thermal stability of the binder. Light ageing further decreased the thermal stability of pigmented paint replicas, suggesting a moderate increase in the rate of the degradation.

Free energy and enthalpy changes for the process of transfer from gas and from dilute aqueous solutions of some alkanes and monofunctional saturated organic compounds

Standard free energies, ΔsolvG°(oct), and enthalpies, ΔsolvH°(oct), of solvation in octan-1-ol of some alkanes (heptane, octane), ketones (propan-2-one, butan-2-one, hexan-2-one, heptan-4-one), ethers (dipropyl ether, dibutyl ether, tetrahydropyran), alkanols (butan-1-ol, butan-2-ol, 2-methylpropan-2-ol) and amines (pyrrolidine, N-methylpyrrolidine, and piperidine) with open-chain and cyclic structure have been determined at 298.15 K. The ΔsolvG°(oct) values were obtained from measurements of partial vapour pressures of dilute solutions and the ΔsolvH°(oct) values, by adding the heats of solution, determined by calorimetry, to known values of enthalpy of vaporization.These data are compared with the standard free energies and enthalpies of solvation in water, and the standard thermodynamic functions for the ideal transfer process of the solutes from pure water to pure octan-1-ol, δtrX°(w–oct)(X=G, H) are calculated.For the examined solutes, hydrocarbons and monofunctional saturated organic compounds, the thermodynamic functions of solvation in octanol and in water are closely correlated to the position of the functional group in the molecular skeleton. The values of the enthalpy of transfer from water to octan-1-ol are also related more to the topologic characteristics of the solute molecules than to their size or to the nature of their functional group. In contrast, the size of the molecules, as well as the presence of a functional group, are important with regard to ΔtrG°(w–oct). An increase of 1 cm3 mol–1 in the intrinsic volumes corresponds to an increase in the value of the partition coefficients of ca. 15%. The substitution of a part of the hydrocarbon surface with a polar surface produces a very large increase in the values of the partition coefficients.The values of the enthalpy of transfer from water to octan-1-ol are always positive, in contrast to the standard free energies of transfer. The entropic term operates by always favouring the transfer towards the alcoholic phase.The potential ability of anhydrous octanol to extract organic solutes of various molecular structure from water-saturated octanol and from hexadecane is also evaluated and discussed.

Thermodynamic study of organic compounds in di-n-butyl ether. Enthalpy and Gibbs energy of solvation

The Gibbs energies and enthalpies of solvation of some hydrocarbons (n-hexane, n-octane, cyclohexane), alcohols (methanol, propan-1-ol, butan-1-ol, butan-2-ol), ethers (diethyl ether, tetrahydrofuran), ketones (propanone, pentan-3-one, cyclopentanone), amines (n-propylamine, n-butylamine), and acetonitrile in di-n-butyl ether have been determined at 298.15 K from vapour–liquid equilibrium measurements and from limiting enthalpies of solution. The data obtained have been compared with the corresponding values of the solvation functions in octan-1-ol and hexadecane. The phenomenology has been discussed in terms of a simple group additivity scheme. The interaction effects of polar and non-polar groups with the solvents have been deduced from the above group contributions combined with the cavity terms estimated through the scaled particle theory. The linear solvation energy relationships (LSER) have also been used for correlating the thermodynamic solvation function to the structural features of the solutes. All the approaches consistently highlight that the hydrophobic groups exhibit interactions with the solvent of nearly the same strength in the three media, while clearly different interactions are shown by polar groups.

Analog calorimetry and UNIQUAC group contributions approaches to the miscibility of pvc with eva copolymers

The miscibility of blends of poly(vinyl-chloride) (PVC) with poly(ethylene-co-vinyl acetate) (EVA) was investigated through analog calorimetry and a group contribution procedure based on the UNIQUAC model. The group contribution parameters quantifying the pair interactions between the structural features of the above polymers were calculated from experimental excess enthalpies of a series of binary mixtures of chlorocompounds, esters and hydrocarbons. Enthalpy data were also collected for the ternary mixtures (2-chloropropane+ethyl acetate+n-heptane) and (2-chlorobutane + methyl acetate+n-heptane), chosen as possible models for the studied macromolecular mixtures. The miscibility window of the PVC-EVA blends is fairly predicted by the group contribution method. It is also acceptably predicted by the enthalpic behaviour of the first ternary set, but only when the latter is calculated with binary data. A slightly narrower miscibility range is predicted by the binary interaction model. The results of these procedures are compared and the higher reliability of the group contribution procedure is emphasized in terms of its capability to reproduce the exact structure of the macromolecules and the non-univocal choice of the model molecules involved in the analog calorimetry approach.

Effect of water as cosolvent in the organic phase on the partitioning of nonelectrolytes between aqueous solution and octan-1-ol☆

Enthalpies of solution at infinite dilution of propanone, tetrahydrofuran, n-propylamine, and tri-n-butylamine in water-octan-1-ol mixtures, ΔsolnH° (oct-w), with water content ranging from zero to saturation have been determined. The observed trends of ΔsolnH° (oct-w) vs. the mole fraction of water are discussed and compared with the trend of the apparent molar volume of water in octan-1-ol. The connection between structural organization of water in the solvent medium and enthalpies of solution are pointed out and discussed. An attempt is also made to evaluate the observed phenomenology in terms of a preferential solvation model.

Thermodynamics of the solvation of non-electrolytes in C8 monofunctional organic solvents

Abstract Some results are reported concerning the enthalpies of solvation (ΔsolvH0) of some hydrocarbons (hexane, cyclohexane), ethers (tetrahydrofuran), ketones (cyclopentanone, pentan-3-one), alcohols (butan-1-ol, butan-2-ol), and water in octan-2-ol and hexylacetate. The ΔsolvH0 values were calculated by combining the calorimetric heats of solution here determined with the known enthalpies of vaporisation. In the investigated solvents, the enthalpies of solvation become less negative going from alcohols to ketones to ethers and to hydrocarbons. As regards alcohols and ketones, the ΔsolvH0 values are more differentiated in octan-2-ol than in hexylacetate. This reflects the different nature of the two solvents, amphiprotic the former and hydrogen bond acceptor the latter. The results are interpreted in terms of specific solute–solvent interactions.