Volume 84, Issue 3

The first Special Topic issue devoted to green chemistry was published in Pure and Applied Chemistry in July 2000 [ Pure Appl. Chem. 72 , 1207-1403 (2000)]. Since then, three collections of works have been published, arising from the recently launched IUPAC series of International Conferences on Green Chemistry: - 1st International Conference on Green Chemistry (ICGC-1), Dresden, Germany, 10-15 September 2006: Pure Appl. Chem. 79 , 1833-2100 (2007) - 2nd International Conference on Green Chemistry (ICGC-2), Moscow, Russia, 14-20 September 2008: Pure Appl. Chem. 81 , 1961-2129 (2009) - 3rd International Conference on Green Chemistry (ICGC-3), Ottawa, Canada, 15-18 August 2010: Pure Appl. Chem. 83 , 1343-1406 (2011) This Special Topic issue forms part of the series on green chemistry, and is an outcome of IUPAC Project No. 2008-016-1-300: “Chlorine-free Synthesis for Green Chemistry” previously announced in Chemistry International , May-June, p. 22 (2011). The IUPAC Subcommittee on Green Chemistry was founded in July 2001 and has selected the following definition for green chemistry [1]: “The invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazardous substances” [2]. Much controversy persists about the appropriate terminology to describe this new field of research. Which term should be selected, “green chemistry” or “sustainable chemistry”? Perhaps consensus can be achieved if different purposes and interests of chemists are reconciled. If we are involved in fundamental research devoted to the discovery of new reaction pathways and reagents, “green” is the best word because it defines these intents, thus the term “green chemistry” would be the best name for this field of research. If we are interested in exploitation of a process or a product that must be profitable, then such chemical manufacture must be sustainable by many criteria (price, competition, profit, environment, etc.), and, accordingly, “sustainable chemistry” is the term that best defines this objective. This Special Topic issue has been designed with the intent to explore the restriction, or preferably prevention, of the use of halogenated compounds, whenever feasible, through the assembly and reporting of already identified information. This intent has been pursued through innovative synthetic pathways using clearly identified production drivers (e.g., energy consumption, environmental impact, economical feasibility, etc.). In past decades, scientific knowledge and feasible technologies were unavailable, but we now have enough expertise to pursue discontinuation of hazardous and toxic reagents. In fact, the replacement of reagents that are toxic, dangerous, and produced by eco-unfriendly processes is still an underdeveloped area of chemistry today. Pietro Tundo Project Co-chair 1. For a short history of green chemistry, see: P. Tundo, F. Aricò. Chem. Int. 29 (5), (2007). 2. P. Anastas, D. Black, J. Breen, T. Collins, S. Memoli, J. Miyamoto, M. Polyakoff, W. Tumas, P. Tundo. Pure Appl. Chem. 72 , 1207 (2000).

Since the Industrial Revolution, chlorine has featured as an iconic molecule in process chemistry even though its production by electrolysis of sodium chloride is very energy-intensive. Owing to its high energy and reactivity, chlorine allows the manufacture of chlorinated derivatives in a very easy way: AlCl 3 , SnCl 4 , TiCl 4 , SiCl 4 , ZnCl 2 , PCl 3 , PCl 5 , POCl 3 , COCl 2 , etc. in turn are pillar intermediates in the production of numerous everyday goods. This kind of chloride chemistry is widely used because the energy is transferred to these intermediates, making further syntheses easy. The environmental and health constraints (toxicity and eco-toxicity, ozone layer depletion) and the growing need for energy (energy efficiency, climate change) force us to take advantage from available knowledge to develop new chemical strategies. Substitution of chlorine in end products in compounds where “chlorine is used in the making” means that we avoid electrolysis as primary energetic source; this makes chemistry “without chlorine” considerably more difficult and illustrates why it has not found favor in the past. The rationale behind this Special Topic issue is to seek useful and industrially relevant examples for alternatives to chlorine in synthesis, so as to facilitate the development of industrially relevant and implementable breakthrough technologies.

Comparative catalytic liquid-phase benzylation of aromatic compouds (e.g., benzene and ethylbenzene) to diphenylmethane (DPM) derivatives with benzyl alcohol (BnOH) was investigated over various catalysts like zeolite (HSZ 600 mordenite, CBV 20A mordenite, H-beta zeolites with Si/Al ratios of 10.8 and 35.8, respectively) and nano-structured inorganic fluorides (MgF 2 ) at 80–120 °C under atmospheric pressure. The reactions were carried out in batch reactors using two methodologies: (i) by introducing both the solution of substrate and BnOH at the beginning of the reaction, and (ii) by drop-wise addition of BnOH (1–2 drops/min for 4 h) to the reaction mixture. The analysis of the reaction products indicated that the conversion and product distribution depend on the experimental method and the nature of the catalyst. The reaction rate was found to correlate to the nucleophilicity of the substrates and their ability to delocalize the positive charge in the Wheland intermediate by inductive and resonance effects.

The use of novel general halogen-free methodology for the synthesis of phosphines, phosphine chalcogenides, and phosphinic acids from elemental phosphorus and alkenes and alkynes in the superbase suspensions is described.

Catalytic syntheses of cyclohexyl carbamates via alcoholysis of dicyclohexyl urea (DCU), which can be synthesized from CO 2 and amines, were first investigated with low-molecular-weight alcohols, i.e., methanol, ethanol, butan-1-ol. TiO 2 /SiO 2 catalyst was prepared by wet impregnation method using tetrabutyl titanate as titanium source. The catalyst was characterized by inductively coupled plasma/atomic emission spectroscopy (ICP/AES), N 2 adsorption, X-ray diffraction (XRD), field emission/scanning electron microscopy (FE/SEM), transmission electron microscopy TEM), and NH 3 /temperature-programmed desorption (TPD) in detail. TiO 2 /SiO 2 with 5 wt % loadings and calcination at 600 °C exhibited better catalytic activity, and excellent yields of >95 % with 98 % selectivities for desired carbamates were achieved. Accordingly, the strong acidity was considered to be responsible for its superior activity. Moreover, the catalytic activity can essentially be preserved during the recycling tests. The scope was also expanded to synthesize other alkyl or aryl carbamates via alcoholysis of the corresponding disubstituted ureas, and 94 % yields with 96 % selectivities can be achieved. It provided a good candidate for the organic carbamates syntheses via a phosgene/halogen-free and effective route.

1,3-Diphenylurea (DPU) has been proposed as a synthetic intermediate for phosgene-free synthesis of methyl N -phenylcarbamate and phenyl isocyanate, which are easily obtained from the urea by reaction with methanol. Such an alternative route to synthesis of carbamates and isocyanates necessitates an improved phosgene-free synthesis of the corresponding urea. In this work, it is reported that Pd(II)-diphosphine catalyzed reductive carbonylation of nitrobenzene in acetic acid (AcOH)-methanol proceeds in high yield and selectivity as a one-step synthesis of DPU. We have found that the catalytic activity and selectivity of this process depends on solvent composition and on the bite angle of the diphosphine ligands. Under optimum reaction conditions, yields in excess of 90 molar % and near-quantitative selectivity can be achieved.

Iodinated contrast agents, such as iopamidol, are worldwide employed for performing a number of X-ray diagnostic procedures. Every year, thousands of tons of iodinated contrast agents are manufactured for the market with chemical processes that usually employ thionyl chloride. In this paper, we describe two new green approaches to iopamidol that avoid or reduce the use of this noxious reagent.

Laser electrodispersion (LED) of metals is a promising technique for the preparation of heterogeneous catalysts as an alternative to wet impregnation of supports with the corresponding salt solutions. The LED technique can be used to deposit highly active chloride- and nitrate-free metal nanoparticles onto carbon or oxide supports. We report preparation and properties of new Ni-, Pd-, and Au-containing alumina-supported catalysts with low metal loadings (10 –3 –10 –4 % mass) and their comparison with the previously studied carbon (Sibunit) supported systems. The catalysts demonstrate high stability and extremely high specific catalytic activity (by 2–3 orders of magnitude higher than for traditional catalysts) in the gas-phase hydrodechlorination (HDC) of chlorobenzene (CB).

The current main concern of global sustainable development pushes toward the substitution of corrosive and highly waste-producing chlorine-containing conventional catalysts (such as the strongly acidic AlCl 3 –HCl mixture, still widely used in the production of chemicals) by environmentally friendly systems. The outstanding benefits in terms of environmental sustainability as well as of economic advantage related to the use of acid and micro- and/or mesoporous molecular sieves are here depicted, analyzing some selected examples in the field of oil refining, petrochemicals, and fine chemicals production: namely, n -C 5 –C 6 alkane isomerization, isobutane/butene (I/B) alkylation, benzene ethylation, aromatic acylation, and Fries rearrangement. In the large-scale processes of refining and petrochemistry, the shift toward this kind of green and efficient solid catalysts is an established reality. In contrast, in fine chemicals synthesis, most of the novelties are still at a lab-scale level, and additional hurdles, related to the large differences between the national legislations about environmental protection, strongly limit this substitution.

A convenient chlorine-free procedure for the direct esterification of cinnamic acids with phenols is described. The method does not require stoichiometric activation of the carboxyl group with thionyl chloride or condensing reagents. The methodology is very simple, environmentally friendly, and high-yielding for both electron-releasing and -withdrawing substituted phenols. The Keggin heteropoly acids H 3 PMo 12 O 40 and H 4 SiMo 12 O 40 were employed as catalyst in simple bulk form. The effects of temperature, reaction time, and amount of the catalyst used on the ester yield were checked. Suitable conditions for the reaction include a 1:1 molar ratio of reactants and a 1 mmol % of catalyst to reactant ratio. Seventeen aryl cinnamates were obtained, yields ranged from 80 to 91 % for most of the esters. The catalyst was shown to be reusable for at least four times without any appreciable loss of its activity.

A new room-temperature ionic liquid (RTIL) consisting of a polyoxometalate (POM) anion and tri-block copolymer (P123)-functionalized imidazolium cation was synthesized and utilized as a halogen-free catalyst for esterification. The catalytic system was a homogeneous solution at the beginning of the reaction, but an emulsion formed during the course of the reaction, and a progressive phase separation of the catalyst occurred at 0 °C over the course of 3 h. Dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier transform/infrared spectroscopy (FT/IR) have been used to characterize the properties of the IL during the reaction. The new IL catalyst was found to be highly efficient in the esterification of various alcohols and can be recycled at least seven times.

Chlorine-free is not only one of the new concepts of green chemistry, but also a problematical task for chemical processes in industrial utility. During the past several decades, we devoted ourselves to the study of chlorine-free organic synthesis. Herein, we describe an efficient chlorine-free copper-catalyzed oxidative approach providing 1,3,4-oxadiazoles in good yields from readily available starting materials. This transformation requires only a green and inexpensive reagent to afford the structurally useful motifs, and has a broad functional groups tolerance.

Direct epoxidation of propylene to propylene oxide (PO) with H 2 and O 2 has been performed on bifunctional catalysts, Au nanoparticles supported on novel Ti-MWW titanosilicate (Au/Ti-MWW). In comparison to conventional Au/TS-1 catalysts, Au/Ti-MWW exhibited a similar phenomenon with respect to PO formation, that is, the PO selectivity increased with increasing Si/Ti ratio of titanosilicate. However, at optimized Ti contents corresponding to Si/Ti ratio >140, the PO selectivity of Au/Ti-MWW catalysts was lower than 60 % in comparison to ca. 90 % achieved on Au/TS-1. A large number of boron species and defect-site-related hydroxyl groups contained in Ti-MWW were assumed to retard the desorption of PO from the channels or crystallite surface of zeolite, which favors side reactions such as over-oxidation and decomposition of PO. Poststructural rearrangement was then carried out on Ti-MWW with piperidine (PI) solution to improve effectively its hydrophobicity, leading to defect-less Re-Ti-MWW. This enhanced significantly the PO selectivity of Au/Re-Ti-MWW thus prepared, which reached as high as 92 % at Si/Ti ratio of 135. Au/Re-Ti-MWW(135) then gave the highest PO formation rate of 22.0 g PO kg –1 h –1 .

CO 2 is very attractive as a typical renewable feedstock for manufacturing commodity chemicals, fuel, and materials since it is an abundant, nontoxic, nonflammable, and easily available C1 resource. The development of greener chemical methodologies for replacing the utility of hazardous and environmentally undesirable phosgene largely relies on ingenious activation and incorporation of CO 2 into valuable compounds, which is of paramount importance from a standpoint of green chemistry and sustainable development. Great efforts have been devoted to constructing C–C, C–O, and C–N bond on the basis of CO 2 activation through molecular catalysis owing to its kinetic and thermodynamic stability. The aim of this article is to demonstrate the versatile use of CO 2 in organic synthesis as the alternative carbonyl source of phosgene, with the main focus on utilization of CO 2 as phosgene replacement for the synthesis of value-added compounds such as cyclic carbonates, oxa-zolidinones, ureas, isocyanates, and polymers, affording greener pathways for future chemical processes .

Dimethyl carbonate (DMC) is considered as an environmentally benign chemical due to negligible ecotoxicity, low bioaccumulation, and low persistence. However, the traditional process of DMC synthesis via phosgene and methanol is limited in industry owing to the toxic raw material involved. Thus, environmentally friendly phosgene-free processes for DMC production have been proposed and developed in the past decades. Until now, the alternatives appear to be the oxidative carbonylation of methanol, the transesterification of propylene or ethylene carbonate (PC or EC), the methanolysis of urea, and the direct synthesis of DMC from CO 2 with methanol. In this review, we present some recent developments of these phosgene-free approaches and their prospects for industrialization.

This article provides an overview on recent progress in the green synthesis of cyclic carbonates (CCs) from carbon dioxide (CO 2 ) catalyzed by chlorine-free catalysts. Special emphasis is placed on the synthetic routes and catalyst structures that govern the reactivity and selectivity.

Polyurethanes and polycarbonates are widely used in a variety of applications including engineering, optical devices, and high-performance adhesives and coatings, etc., and are expected to find use also in the biomedical field owing to their biocompatibility and low toxicity. However, these polymers are currently produced using hazardous phosgene and isocyanates, which are derived from the reaction between an amine and phosgene. Extensive safety procedures are required to prevent exposure to phosgene and isocyanate because of its high toxicity. Therefore, the demand for the production of isocyanate-free polymers has now emerged. Among the alternative greener routes that have been proposed, a popular way is the ring-opening polymerization (ROP) of cyclic carbonate in bulk or solution, usually using metallic catalyst, metal-free initiator, or biocatalyst. This review presents the recent developments in the preparation and application of cyclic carbonates as monomers for ROP, with emphasis on phosgene- and isocyanate-free polymerization to produce aliphatic polycarbonates and polyurethanes and their copolymers.

Ordered periodic mesoporous benzene-silicas (Ph-PMOs) functionalized with organotin were synthesized by co-condensing (MeO) 2 ClSi(CH 2 ) 3 SnCl 3 , tetraethyl orthosilicate (TEOS), and 1,4-bis(triethoxysilyl)-benzene in a Pluronic 123 acid solution. The diffraction lines for (100), (110), and (200) facets observed in their X-ray diffraction (XRD) patterns and parallel channels in their transmission electron microscopy (TEM) images show that the samples have highly ordered hexagonal array structure. The presence of bands characteristic for phenyl groups, tetrahedral and octahedral Sn species, and Q n and T n species in their Fourier transform/infrared (FT/IR), diffuse reflectance UV–vis, and NMR spectra gives convincing evidence for the incorporation of phenyl groups and (MeO) 2 ClSi(CH 2 ) 3 SnCl 3 into the framework or silica wall. The organotin-functionalized Ph-PMOs exhibit much higher catalytic activity than organotin-functionalized mesoporous silica lacking phenyl groups in the framework, for direct synthesis of dimethyl carbonate (DMC) from methanol and CO 2 , although both have high catalytic stability. This may be attributed to its enhanced surface hydro-phobicity and the presence of a large number of hexa-coordinated Sn species and tiny Sn oxide clusters in the former sample. The DMC yield obtained over the prepared organotin-functionalized Ph-PMOs increases monotonically with increasing CO 2 pressure. The material also exhibits high catalytic stability upon reusage.

Synthesis of unsymmetrical organic carbonates by transesterification of various alcohols with diethyl carbonate (DEC) is an interesting topic in green chemistry. In this work, we synthesized a kind of zirconium phosphonate functionalized with pendent N -SO 3 H group by the reaction of ZrOCl 2 ·8H 2 O with N , N -bis(phosphonomethyl)-sulfamic acid, which was formed from sulfamic acid through a Mannich-type reaction. The functionalized zirconium phosphonate was characterized by Fourier transform/infrared (FT/IR), N 2 adsorption and desorption, scanning electron microscopy (SEM), and powder X-ray diffraction (XRD) techniques, and was used as the heterogeneous catalyst for the synthesis of unsymmetrical organic carbonates by transesterification of various alcohols with DEC. It was demonstrated that the catalyst is very active and selective for the reactions, and very high yields of the desired products could be obtained. In addition, the catalyst could be easily recovered and the decrease in catalytic activity and selectivity was minor after three-fold usage. The mechanism for the transesterification reactions is discussed.

Aliphatic amines react sluggishly with dimethyl carbonate (DMC) to give a mixture of N-methylation and carbamoylation. Nanoparticulated ceria as catalyst increases, in general, conversion and selectivity toward carbamoylation. This increase in catalytic activity and selectivity toward carbamoylation is even increased by deposition of Au nanoparticles on ceria. However, in contrast to aromatic amines for which a complete selectivity toward carbamoylation using ceria-supported Au nanoparticles can be achieved, the catalytic carbamoylation of aliphatic amines by ceria-supported Au nanoparticles occurs only with moderate selectivity.

The synthesis of N -phenylcarbamate from aniline and dimethyl carbonate (DMC) in the presence of homogeneous, supported heterogeneous, and heterogeneous catalysts was investigated in batch conditions. First, a selection of homogeneous catalysts was studied and their reactivity in the same reaction conditions was compared to zinc acetate, a catalyst extensively used for this reaction. Then the best homogeneous catalysts were supported on silica or alumina, and the resulting heterogeneous supported catalysts were tested for the carbamoylation of aniline. Finally, several heterogeneous catalysts were investigated. Zinc carbonate basic was shown to be the best catalyst, giving quantitative conversion and selectivity for the N -phenylcarbamate. Its catalytic activity was fully investigated taking into account substrate concentration, amount of catalysts, and temperature influence. Zinc carbonate was also shown to be recyclable, once it was recovered from the reaction mixture and calcinated.

A number of six-membered cyclic carbamates (oxazinanones) were synthesized from the reaction of a primary amine or hydrazine with a dicarbonate derivative of 1,3-diols in a one-pot reaction, in good yield, short time span, and in the absence of a solvent. The reaction proceeds in two steps: an intermolecular reaction to give a linear intermediate and an intramolecular cyclization to yield the cyclic carbamate. This is the first example of a carbonate reacting selectively and sequentially, firstly at the carbonyl center to form a linear carbamate and then as a leaving group to yield a cyclic carbamate.

Conventionally, ionic liquids with anions generated from simple organic acids are prepared following a metathetic procedure from a halide salt, usually a chloride. Here, we describe an efficient means of generating hydroxide solutions of the cations of interest, allowing many ionic liquids to be produced by simple acid–base reactions, completely avoiding the use of halides.

Ionic liquids (ILs) are desirable for use in a large number of applications because of their unique properties; however, compositions comprising only a single IL are expensive to synthesize and difficult to purify, and the widely used chloride-based ILs can be toxic and corrosive. Therefore, there is a need for new IL compositions that minimize common disadvantages encountered with single IL composition and synthetic methods which avoid halide intermediates. In this study, IL mixtures, which are chloride-free, were synthesized by a one-pot process, and the mixtures were used to dissolve biopolymers. The synthesized IL mixtures show high capability to dissolve the two exemplary biopolymers, cellulose and chitin.

Glycerol carbonate is a key multifunctional compound used as solvent, additive, and building block in alternative chlorine-free processes. Here, we report the synthesis of glycerol carbonate from renewable materials (glycerol and dimethyl carbonate, DMC) using basic ionic liquids (ILs) as catalysts. After process optimization, it has been possible to isolate pure glycerol carbonate in quantitative yield using a three-fold excess of DMC and ca. 15 % of IL. The IL could be reused at least four times without any significant reduction in the conversion yield.

The structure–activity relationship and reaction mechanism for selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) in toluene were studied on vanadium oxide domains on TiO 2 , Al 2 O 3 , Nb 2 O 5 , ZrO 2 , and MgO and with a wide range of VO x surface densities. The structures of these catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy (UV–vis DRS), and Raman spectroscopy, and their reducibility was probed by H 2 -temperature programmed reduction. The structures of the VO x domains evolved from monovanadate to polyvanadate structures with increasing the VO x surface densities, and finally to crystalline V 2 O 5 clusters at surface densities above one-monolayer capacity. Within one-monolayer capacity, higher VO x surface densities and more reducible supports led to higher reducibility and reactivity of the VO x domains. The support surfaces covered with polyvanadates and V 2 O 5 clusters and the supports with acidity favored the formation of DFF. The correlation between the reducibility and reactivity, together with the kinetic studies, suggests that the HMF oxidation to DFF proceeds via the redox mechanism involving the V 5+ /V 4+ redox cycles and the reoxidation of V 4+ to V 5+ by O 2 as the rate-determining step. These results may provide guidance for the design of more efficient catalysts for the HMF oxidation to synthesize DFF.

Hydrogenation of methyl laurate was conducted over a Cu/ZnO/Al 2 O 3 catalyst, using methanol as the solvent and hydrogen source, to give lauryl alcohol. In this process, the solvent underwent partial decomposition in contact with the catalyst to generate hydrogen, which served as the hydrogenation agent. The effect of different factors on the reaction was examined, to optimize production of lauryl alcohol with high conversion efficiency and selectivity. Use of methanol as the solvent not only favored the reaction, but also suppressed a side reaction involving transesterification between methyl laurate and lauryl alcohol. Under optimal reaction conditions, 91.8 % conversion of methyl laurate and 88.8 % yield of lauryl alcohol could be achieved .

Poly(ethylene terephthalate) (PET) is widely used for beverage bottles, electrical and electronic instruments, household wares, and so on. As a consequence of dramatically increasing consumption, recycling of post-consumer PET products has become an important environmental opportunity for sustainable usage in society. In this paper, we investigated the use of chlorine-free metallic acetate ionic liquids (ILs) as catalysts for the degradation of PET because of their lower toxicity, corrosivity, and cost. 1,3-Diethylimidazolium triaceticzincate ([deim][Zn(OAc) 3 ]) behaved as the best in this group. The synthesized ILs and the major product, characterized by a variety of techniques and factors affecting glycolysis, were examined. Under optimum conditions, conversion of PET reached 98.05 %, and the selectivity of the bis(hydroxyethyl) terephthalate (BHET) monomer was 70.94 %. A probable mechanism for the glycolysis of PET catalyzed by [deim][Zn(OAc) 3 ] was given. In our opinion, catalysis accounted for the synergic effect of the cation and anion of the IL.

In light of the biological importance of carbohydrates and their role when present in antibiotic agents, the design and synthesis of carbohydrate-based antibiotics has occupied a prominent place in drug discovery. This review focuses on synthetic carbohydrate antimicrobial agents, giving special emphasis to novel structures easily accessible from readily available carbohydrate precursors.

Organometallic complexes of halogen metallic salts have been used as catalysts in different organic reactions, mainly the oxidation of organic compounds. Their use has not only allowed the reduction of the amounts of catalyst (since they can be reused) but also a lower generation of byproducts and wastes. The different reaction media developed through the research were analyzed by several green parameters, and the best results were obtained with complexes that have cyclodextrins as organic ligands. The proposed methodology is an alternative to use of molecular halogen as oxidant or catalyst when halogens are significant chemoselective reactants.

Synthesis plans for the following important industrial commodity chemicals using phosgene and phosgene-free chemistries have been analyzed and compared by green metrics to determine the most material-efficient routes so far developed (number of plans given in parentheses): dimethyl carbonate (DMC) (31), diphenyl carbonate (DPC) (40), diphenylurea (DPU) (23), methyl carbamate (MC) (8), methyl chloroformate (MCF) (6), methyl N -phenylcarbamate (MNPC) (25), methyl phenyl carbonate (MPC) (32), phenyl isocyanate (PI) (19), phenyl chloroformate (PCF) (10), and urea (13). Implications of these results are discussed.