Volume 79, Issue 11

IUPAC's initiatives and publications have been closely identified with green chemistry over the past several years. However, a significant milestone was reached in a project on Synthetic Pathways and Processes in Green Chemistry, chaired by Prof. Pietro Tundo (University of Venice), as a first IUPAC undertaking devoted exclusively to the theme of green chemistry. This culminated in publication of a Special Topic issue of Pure and Applied Chemistry [ Pure Appl. Chem. 72 (7), (2000); <http://www.iupac.org/publications/pac/2000/7207>], which attracted an exceptionally high level of readership interest and has hitherto accumulated a record number of nearly 900 citations. Indeed, one of the papers published in that collection, Ionic Liquids: Green Solvents of the Future, by M. J. Earle and K. R. Seddon (The Queen's University of Belfast) [ Pure Appl. Chem. 72 (7), 1391 (2000)], boasts no fewer than 349 citations (recorded on 30 April 2007)! Shortly thereafter, Prof. M. Kidwai and his colleagues at the University of Delhi launched an IUPAC-sponsored International Symposium on Green Chemistry in January 2001 [ Pure Appl. Chem. 73 (1), (2001); <http://www.iupac.org/publications/pac/2001/7301>], and have since organized a sequel in 2006 [ Pure Appl. Chem. 78 (11), (2006); <http://www.iupac.org/publications/pac/2006/7811>]. The record of that first event focused strongly on insights into green catalysis and methodology, and also has the distinction of heading the citation record for PAC event collections in 2001. Later in 2001, the Conference on Green Chemistry: Toward Environmentally Benign Processes and Products was held in Boulder, Colorado, under the guidance of Drs. D. L. Hjeresen and P. T. Anastas [ Pure Appl. Chem. 73 (8), (2001); <http://www.iupac.org/publications/pac/2001/7308>]. This was the 14th of the CHEMRAWN series, an acronym for CHEM istry R esearch A pplied to W orld N eeds, that is most aptly served by this important collection of works, dealing with a range of policy, educational, and research and development issues around the title topic. Although the foregoing publication projects are explicitly identified with green chemistry, the theme features repeatedly in numerous papers arising from other IUPAC-sponsored events in recent years, or underpins other disciplinary themes, for example, in the Special Topic collection devoted to Electrochemistry and Interfacial Chemistry for the Environment [ Pure Appl. Chem. 73 (12), (2001); <http://www.iupac.org/publications/pac/2001/7312>]. This trend is destined to continue, and is perhaps symptomatic of growing social responsibility in current research and development. Furthermore, it demonstrates that IUPAC has an ongoing role to play in fostering activities that fulfil its commitment to shaping and serving the chemical sciences in the interests of societal upliftment and progress. It is thus fitting that the Union should now take the initiative to regularize its role in promoting green chemistry, through a series of biennial conferences. It is equally appropriate to highlight the published record of the 1st International Conference on Green-Sustainable Chemistry as a Special Topic feature of PAC, in recognition of the topicality of this authoritative and representative collection of papers. James R. Bull Scientific Editor

This Special Topic issue on green chemistry pursues the same objectives as the Special Topic issue published in July 2000 and can be considered as its continuation. The articles have been selected (with great difficulty) from the massive and valuable scientific contributions on green chemistry by numerous professors and researchers during the 1st International IUPAC Conference on Green-Sustainable Chemistry held 10-15 September 2006 (for more details on the conference, see Chemistry International , Vol. 29, No. 3, 2007). The wide selection of topics was chosen with the intent to attract industrial researchers and representatives, colleagues from universities, as well as politicians and students who are interested in green and sustainable chemistry. The week-long conference was divided into five topics, each of which included several subtopics. This special issue covers the following topics discussed during the conference: benign syntheses routes (heterogeneous catalysis, new reagents, and catalysis for degradation of pollutants); benign process technology (microwave technology, photochemistry, new regulation devices); use of renewable sources (starch, cellulose, sugar, new detergents, biomass technology); and future green energy sources (hydrogen technology, fuel cell technology, biodiesel). All the articles reported in this issue point out a general need for novel green processes which comes from a new paradigm in process and product evaluation that must include environmental and health issues (see Chemistry International , Vol. 29, No. 5, 2007). In order to reach this objective, one priority should be to push for more basic research on chemical reactions related to green chemistry, where our knowledge is far from completion. In recent times, in fact, the difference between sustainable chemistry and green chemistry is becoming more evident. Sustainable chemistry envisages an industrial involvement and promotion with the aim of achieving fewer pollutant processes and more valuable products, maintaining, at the same time, profits. Whereas green chemistry is more innovative because it is not necessarily connected to profits, it involves fundamental aspects and does not aim automatically at an industrial process. There is a great need to create a new type of chemistry focused on a new production system and utilization of chemical derivatives, in order to prepare the younger generation to reach a greener future. Following this scenario, this special issue has been planned with the aim of extending the knowledge on green chemistry, not disregarding, however, the industrial interest. Nowadays, globalization (induced by many factors such as industrial development) pushes the chemistry community to adopt ethical issues. In this respect, green chemistry can achieve, better than sustainable chemistry, the approval of society by teaching students to be confident in science and at the same time by convincing people that it is possible to achieve technological development respecting and taking care of the environment in which we live. In order to realize these objectives, it is important that education and fundamental research are strictly connected, so that democracy and development can also grow and progress side by side. In my personal experience I think that the young generation is very interested and passionate about green chemistry. An example is dott. Fabio Aricò (postdoctorate fellow in my group) who helped me through the organization of the IUPAC conference and the preparation of this special issue with enthusiasm and passion. Pietro Tundo Conference Chairman

Three acid zeolites (H-BEA, H-FAU, and H-MWW) were used as catalysts for acetylation in batch reactors with acetic anhydride of five aromatic compounds (benzenic and naphthalenic derivatives). The substrate reactivity is mainly governed by electronic factors (the nature of the substituents and degree of ring activation), but steric effects also play a relevant role when the reaction takes place in a narrow micropore system. In general, H-FAU was the most active catalyst, whereas with H-BEA remarkable steric constraints were observed. H-MWW showed good stability toward deactivation and an interesting activity of the sites located on the external surface.

New industrially important catalytic processes for application in the fine chemicals industry (e.g., synthesis of vitamins and key-intermediates) are presented. Protocols with indium catalysts provide the advantages of high selectivity and low catalyst loading for Friedel-Crafts-type alkylation, Wagner-Meerwein rearrangement, and acylation reactions. The transformations discussed could be carried out in a continuous manner.

After giving some general considerations about the specific properties of nanoparticles below 20 nm, procedures for size stabilization, and the importance of developing green alcohol oxidation reactions, catalytic data are presented showing that gold nanoparticles (3-7 nm) supported on nanoparticulated ceria (4 nm) are far more chemoselective than related palladium catalysts for the aerobic oxidation of allylic alcohols. Using palladium catalysts, in addition to minor oxidation of the alcohol functional group, we have also observed polymerization, 1-2 hydrogen shift, and hydrogenation. In contrast, ceria-supported gold nanoparticles exhibit a remarkable chemoselectivity (in many cases, almost complete) to the alcohol oxidation.

Nowadays available by clean industrial processes, dimethyl carbonate (DMC) possesses properties of nontoxicity and biodegradability which make it a true green reagent/solvent to devise syntheses that prevent pollution at the source. In particular, the versatile reactivity of DMC allows both methylation and carboxymethylation protocols that can replace conventional and highly noxious reagents such as methyl halides (and dimethyl sulfate, DMS) and phosgene. In the field of DMC-mediated methylations, representative examples are the reactions of DMC with CH 2 -active compounds and primary aromatic amines. In the presence of organic/inorganic bases or zeolites (faujasites) catalysts, these processes proceed with unprecedented selectivity (up to 99 %, at complete conversion) toward the corresponding mono- C- and mono- N- methyl derivatives, a result hitherto not possible with conventional alkylation reagents. In the case of ambident amines (e.g., aminophenols, aminobenzyl alcohols, aminobenzoic acids, and aminobenzamides), the unique combination of DMC and zeolites allows not only a very high mono- N -methyl selectivity, but also a complete chemoselectivity toward the amino group. The other nucleophilic functionalities (OH, CO 2 H, CH 2 OH, CONH 2 ) are fully preserved from alkylation and/or transesterification reactions, usually observed over basic catalysts.

Adducts of dimethylamine and carbon dioxide form a "distillable ionic liquid" (DIMCARB) that may used as both a reaction medium and catalyst in the direct, atom-economical synthesis of useful synthetic building blocks, such as mono-condensed α,β-unsaturated ketones. The utilization of such building blocks in the synthesis of two new classes of versatile macrocycles, by a sequence of condensation reactions (H 2 O by-product), is described. Investigation into the mechanism of action of DIMCARB catalysis and observation of an aniline impurity arising from a competing reaction sequence led to development of a new multicomponent reaction for the direct preparation of 2- or 4-substituted anilines. Some of the macrocycles and anilines are, respectively, supramolecular host compounds and ligands for the preparation of metal complexes.

Direct, efficient, organic solvent- and catalyst-free synthesis of a series of polyphosphates was accomplished. The reaction involved a gas-liquid interfacial polycondensation between arylphosphoric dichlorides and bisphenol A. The polyphosphates were characterized by IR, 1 H NMR, 31 P NMR, inherent viscosity, thermal analysis, and molar mass. Yields in the range 70-90 % and inherent viscosities in the range 0.30-0.40 dl/g were obtained. The thermal stability of the polyphosphates was investigated by using thermogravimetry.

This paper deals with the catalytic properties of different supported heteropolyacids (HPAs), both molybdenum- and tungsten-based, in the oxidative desulfurization process of diesel. We are jointly developing a new oxidative desulfurization process, aimed at reducing the sulfur content in diesel to less than 10 ppm (parts per million) using in situ produced peroxides. In this new process, high-molecular-weight organosulfur compounds, such as 4,6-dimethyl-dibenzothiophene (DMDBT), difficult to be eliminated by conventional hydrodesulfurization, are oxidized to the corresponding sulfones and subsequently removed by adsorption. Molybdenum-based HPAs, with Keggin structure, proved to be the most active and selective catalysts for oxidizing DMDBT with on-stream lifetimes exceeding 1500 h time on stream (t.o.s.).

We establish the full potential energy diagram for the direct NO decomposition reaction over stepped transition-metal surfaces by combining a database of adsorption energies on stepped metal surfaces with known Brønsted-Evans-Polanyi (BEP) relations for the activation barriers of dissociation of diatomic molecules over stepped transition- and noble-metal surfaces. The potential energy diagram directly points to why Pd and Pt are the best direct NO decomposition catalysts among the 3d, 4d, and 5d metals. We analyze the NO decomposition reaction in terms of a Sabatier-Gibbs-type analysis, and we demonstrate that this type of analysis yields results that to within a surprisingly small margin of error are directly proportional to the measured direct NO decomposition over Ru, Rh, Pt, Pd, Ag, and Au. We suggest that Pd, which is a better catalyst than Pt under the employed reaction conditions, is a better catalyst only because it binds O slightly weaker compared to N than the other metals in the study.

The utilization and decomposition of chlorinated wastes without formation of dioxins are challenges of great environmental importance. In this work, the catalytic reductive methods of chlorinated organics processing are described, focusing on catalyst development. Pd-containing catalysts are improved by modification of supports [use of ultra dispersed diamond (UDD) or double oxides] or by dilution of Pd by not-noble metals (Fe, Ni, Cu). Both ways are effective for the processing of 1,3,5-trichlorobenzene (TCB) as a model of polychlorinated organics. The reasons for improvement of catalysts are discussed. The best catalysts were effectively used for hydrodechlorination (HDC) of hexachlorobenzene (HCB).

Photocatalytic water splitting is a challenging reaction because it is an ultimate solution to energy and environmental issues. Recently, many new powdered photocatalysts for water splitting have been developed. For example, a NiO (0.2 wt %)/NaTaO 3 :La (2 %) photocatalyst with a 4.1-eV band gap showed high activity for water splitting into H 2 and O 2 with an apparent quantum yield of 56 % at 270 nm. Overall water splitting under visible light irradiation has been achieved by construction of a Z-scheme photocatalysis system employing visible-light-driven photocatalysts, Ru/SrTiO 3 :Rh and BiVO 4 for H 2 and O 2 evolution, and an Fe 3+ /Fe 2+ redox couple as an electron relay. Moreover, highly efficient sulfide photocatalysts for solar hydrogen production in the presence of electron donors were developed by making solid solutions of ZnS with AgInS 2 and CuInS 2 of narrow band gap semiconductors. Thus, the database of powdered photocatalysts for water splitting has become plentiful.

A series of photochemical reactions are assessed under the environmental aspect by using Eissen and Metzger's EATOS (environmental assessment tool for organic syntheses) method and are compared with strictly analogous thermal processes. These include C-C bond-forming reactions (arylation and alkylation) and selective oxidation and reduction reactions. In most cases, the photochemical method is experimentally simpler and less expensive than the thermal alternative. A disadvantage is that photochemical reactions are carried out in rather dilute solution, and this factor gives by far the main contribution to the assessment. However, if the solvent is recovered, the photochemical reaction is more environment-friendly.

Three photochemical reactions were investigated under solar irradiation conditions with moderately concentrated sunlight: the photoacylation of naphthoquinone with butyraldehyde and the dye-sensitized photooxygenations of citronellol and 1,5-dihydroxynaphthalene, respectively. All reactions were easily performed on multigram-to-kilogram scales using cheap and commercially available starting materials, and yielded important key intermediates for industrial applications.

Photochemically induced electron transfer considerably enriches the redox chemistry of organic molecules. This primary step has been used to produce α-amino alkyl radicals that can be added to various double bonds. The addition to olefinic and carbonyl bonds is discussed. Homogeneous and heterogeneous photocatalysis methods with various electron-transfer sensitizers are described.

A microreaction system for organic photoreactions was developed, and the processes of diastereo-differentiating photosensitized reaction, photocatalytic oxidation and reduction of organic compounds, and amine N-alkylation were examined in microspace. These model reactions proceeded very rapidly with considerably large photonic efficiencies because of some distinct properties of microreactors for photoreactions, such as higher spatial illumination homogeneity and better light penetration through the entire reactor depth, and large surface-to-volume ratio in comparison with large-scale batch reactors. These results suggest feasibility of microreaction systems on organic photoreactions.

The principles of green chemistry include a statement as to the necessity for real-time analysis for prevention of pollution. Methodologies need to be developed for real-time, in-process monitoring and control prior to the formation of hazardous substances. These should be carried out by (chemical) sensors. Monitoring also allows optimizing the efficient use of reagents and permits determination of the composition of waste and effluents. In this paper, new monitoring strategies are surveyed and some of the recent advances which have been achieved with respect to novel devices in terms of miniaturization and reliability are indicated. Emphasis is given to continuous and online flow and injection methodologies and the requirements for successful sensors. Particular attention is given to the future potential of electrochemical flow and batch injection sensors which can often be used without external sample pretreatment. Electrochemical sensors using carbon film-based electrodes, including their application in room-temperature ionic liquids (RTILs) for which electrochemical methodologies are directly suited are also described.

The development of biorefineries represents the key for access to an integrated production of food, feed, chemicals, materials, goods, and fuels of the future [1]. Biorefineries combine the necessary technologies of the biogenic raw materials with those of intermediates and final products. The main focus is directed on the precursor carbohydrates, lignins, oils, and proteins, and the combination between biotechnological and chemical conversion of substances. Currently, the lignocellulosic feedstock (LCF) biorefinery, green biorefinery, whole-crop biorefinery, and the so-called two-platform concept are favored in research, development, and industrial implementation.

In concepts for new products, performance, product safety, and product economy criteria are equally important. They are taken into account already when the raw materials base for a new industrial product development is defined. Here, renewable resources gain-again after the earlier "green trend" in the 1980s-increasing attention as an alternative raw materials source compared to fossil feedstock. The industrial use of carbohydrates, proteins, and vegetable oils aligns perfectly with the principles of Responsible Care and is an important part of green chemistry and sustainability in general. Since the 1950s, oleochemistry has grown to a major research and technology area in several institutions and industries. A large variety of products based on fats and oils have been developed since then for different uses, such as specialties for polymer applications, biodegradable mineral oil replacements for lubricants, and surfactants and emulsifiers for the home and personal-care industries. However, at present it seems that the use of renewable resources, especially vegetable oils, has to compete more and more with the increasing demand for bioenergy, which could cause an unbalanced supply and demand in the future or even a threat for the increasing demand for food in certain areas of the world.

In this review, attention is focused on the use of group 3 metal complexes for the ring-opening polymerization (ROP) of lactide to give polylactides (PLAs). Synthesis of PLAs has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. ROP of lactide, a cyclic diester of lactic acid, provides PLA. This review includes our recent research results and implications in developing new amino-bis(phenolate) group 3 initiators for the synthesis of polyesters.

Arjunolic acid, a triterpenoid, renewably resourced from Terminalia arjuna sawdust, has the potential of being used as a structural molecular framework in supramolecular chemistry and nanoscience. The nanosized chiral triterpenoid on derivatization could immobilize varieties of organic solvents at low concentrations. The low-molecular-mass organic compounds self-assembled in organic media to form fibrous network structures having fibers of nano- to micrometer diameters. A dual-component supramolecular gelation has been demonstrated, exhibiting interesting thermochromic property. An arjunolic acid-derived crown ether showed efficient binding to monovalent cations, including a primary ammonium ion paving the way for chiral recognition of amino acids.

We extracted polysaccharides (PS) from Aphanothece sacrum using a hot alkaline solution which degraded other biopolymers such as proteins and nucleotides. The spectroscopy and elemental analyses indicated the PS contain carboxyls and sulfate groups. The degree of sulfation was estimated as about 10 mol %. 1 H NMR studies demonstrated that the PS of A. sacrum had a dimethylated fucose unit. The combination of sulfate group and fucose in the prokaryotic PS was first evidenced by the direct spectroscopic studies. The PS showed efficient gelation behavior, binding to metal ions abundant in soil, and the swelling volume of the gel was approximately 250 times the dry volume. These results imply that PS of A. sacrum , which has been mass cultivated in Japan for a long time, may have potential as an environmentally benign water absorbent.

A large variety of C,C-bond forming reactions and functional group interconversions can be achieved by electron transfer. For the conversion of renewable feedstocks, electrolysis has been applied to coupling of radicals generated by anodic decarboxylation of fatty acids and carboxylic acids of carbohydrates. Furthermore, a derivative of L-gulonic acid is converted nearly quantitatively into L-xylonolacton. Trimethyl aconitate from trimethyl citronate is dimerized stereoselectively at the cathode in 72 % yield to a cyclic hexamethyl ester by an inter- and intramolecular Michael addition. Two acetoxy groups are added anodically to methyl conjuenate (obtained from methyl linoleate) to form methyl ( E )-9,12-diacetoxy-10-octenoate and methyl ( E )-10,13-diacetoxy-11-octenoate in 85 % yield. The primary hydroxy groups in mono- and disaccharides can be oxidized to carboxylic acid groups in good yield and high selectivity by anodic oxidation with 2,2,6,6-tetramethylpiperidine- N -oxyl (TEMPO) as mediator. The results demonstrate that electrolysis is in good accordance with many of the 12 principles of green chemistry.

Acylation of different amino derivatives (ethanol amine, diethanol amine, N -aminoethylpiperazine) was carried out under green conditions with oleic acid or tail oil fatty acids. The experiments were carried out using as heterogeneous catalysts mesoporous Al-Meso and UL-ZSM-5 with Si/Al ratios between 100 and 20, in the range of the temperatures 80-180 °C without any solvent or in octane or water. The efficiency of the catalysts for the acylation of the investigated substrates appeared to be directly dependent on the Si/Al ratio and the size of the pores. The selectivity toward esters or amides was firstly controlled by temperature, and then by the Si/Al ratios. Additionally, both the conversion and selectivity were controlled by the solvent in which the reaction was carried out. The use of water led mostly to a mixture of esters and amides.

The demand for transportation fuels - gasoline (for cars), diesel (for trucks and cars), and kerosene (for aircraft) - is predicted to increase. The fastest growth will be observed for kerosene, in competition with diesel, inducing constraints on diesel. At the same time, all of these fuels are derived mainly from oil (more than 95 %), thus generating growing, uncontrolled CO 2 emissions. Therefore, production of diesel derived from biomass (the so-called biodiesel) appears as a major objective. In this paper, we describe the existing industrial processes, discuss the possible improvements, and present the new routes (the "second-generation" processes) under development that will allow biodiesel to gain a significant percentage of the diesel (and maybe of middle distillates) pool.

Poly(ether sulfone)s from 4,4'-difluorodiphenylsulfone (DFDPhS), 4,4'-bis-trimethylsiloxy-diphenylsulfone, and 2,5-bis-trimethylsiloxy-biphenyl were obtained by melt polycondensation with high molecular weights (η inh > 0.4 dl/g). The nonsulfonated samples showed a single glass-transition temperature ( T g ) in the range from 180 to 230 °C depending on the monomer composition in the polymer backbone. The T g of sulfonated samples could not be detected by differential scanning calorimetry (DSC). Membranes with a theoretical ion-exchange capacity (IEC) ranging from 0 to 2.08 mmol/g should be obtained, assuming only a sulfonation of the pendant phenyl ring. However, the sulfonation with concentrated sulfuric acid always led to the introduction of two sulfonic acid groups into the phenylhydroquinone (PhHQ) moieties in the polymer backbone; one at the desired position at the pendant phenyl ring and one at the phenyl ring in the polymer backbone. Membranes prepared from N -methyl-2-pyrrolidone (NMP) solutions of nonsulfonated and sulfonated samples were transparent and soft to slightly brittle. The water uptake at room temperature increased with increasing IEC from 4 to 50 % (IEC ~ 1.50 mmol/g). On further increase of the IEC, a strong water uptake until dissolution was observed. Methanol diffusion coefficients for samples with an IEC up to 1.10 mmol/g were one order of magnitude lower than that reported for Nafion ® .

Using a photo-assisted deposition (PAD) method, nanosized Pd metal can be highly dispersed on Ti-containing silicalite zeolite (TS-1) under UV-light irradiation (PAD-Pd/TS-1). The nanosized Pd metal was deposited directly on the photo-excited tetrahedrally coordinated titanium oxide species (tetra-Ti-oxide) of TS-1 zeolite. Under the flow of H 2 and O 2 in water solvent, the efficient formation of H 2 O 2 could be observed by the PAD-Pd/TS-1 catalyst under mild reaction conditions (ambient temperature and atmospheric pressure). Furthermore, the presence of phenol in this reaction system led to the formation of the products from the partial oxidation of phenol with the formed H 2 O 2 .