Green Chemistry (v.13, #3)

Front cover (457-457).

Inside front cover (458-458).

Contents (459-470).

Processing of metals and metal oxides using ionic liquids by Andrew P. Abbott; Gero Frisch; Jennifer Hartley; Karl S. Ryder (471-481).
Hydrometallurgy lies at the heart of many industrial processes and is the source of a large volume of aqueous waste. Treating dilute streams of acidic and basic by-products is both energy and chemical intensive, and is one of the largest sources of metal-based emissions into the environment. Over the past decade, numerous studies have been made into the use of ionic liquids for metal dissolution, extraction and recovery. This article critically reviews the potential efficacy of these methods and signposts the areas where further research is needed.

Viable methodologies for the synthesis of high-quality nanostructures by Jonathan M. Patete; Xiaohui Peng; Christopher Koenigsmann; Yan Xu; Barbara Karn; Stanislaus S. Wong (482-519).
The development of environmentally benign methods for the synthesis of nanomaterials has become increasingly relevant as chemists look to shape a more sustainable future. In this critical review, we present current work towards developing alternative methods for synthesizing a wide range of high-quality nanomaterials with predictable and controllable size, shape, composition, morphology and crystallinity. In particular, we focus on the inherent advantages of utilizing porous membrane templates, ultrasonic and microwave irradiation, alternative solvent systems, as well as biologically-inspired reagents as reasonably cost-effective, environmentally responsible methods to generate metal, metal oxide, fluoride, sulfide, selenide and phosphate nanomaterials.

Converting carbohydrates to bulk chemicals and fine chemicals over heterogeneous catalysts by Maria J. Climent; Avelino Corma; Sara Iborra (520-540).
In this Critical Review, we discuss how carbohydrates can be transformed into a variety of chemicals through heterogeneous catalysis. We focus particularly on oxidation, reduction and dehydration of hexoses, as well as one-pot reactions of di- and polysaccharides. Most of the reactions involve heterogeneous catalysts, although some interesting homogeneously catalyzed processes are also included.

Tert-butyl nitrite easily releasing alkoxyl radical and NO in combination with compressed CO2 under metal free condition was applied to efficiently and selectively initiate aerobic cleavage of benzylic CC bonds. Notably, compressed CO2 in this study not only provides a safe reaction environment but also tunes the selectivity.

CuO/SiO2: a simple and efficient solid acid catalyst for epoxide ring opening by Federica Zaccheria; Federica Santoro; Rinaldo Psaro; Nicoletta Ravasio (545-548).
A cheap, non toxic, easy to prepare and easy to use supported CuO material has shown to be a very effective catalyst for the alcoholysis of epoxides giving β-alkoxyalcohols in very good yield without generating any waste. The catalyst is heterogeneous in nature and can be reused without any reactivation treatment.

The direct alkynylation of isatins catalyzed by NHC–Ag complexes via the activation of alkyne C–H bond on water was developed for the efficient synthesis of 3-hydroxy-3-ethynylindolin-2-ones under an air atmosphere. A remarkable rate-enhancement by water in the aqueous heterogeneous system was observed.

Oxidation of 5-hydroxymethylfurfural to maleic anhydride with molecular oxygen by Zhongtian Du; Jiping Ma; Feng Wang; Junxia Liu; Jie Xu (554-557).
5-Hydroxymethylfurfural (HMF) was converted to maleic anhydride in 52% yield via selective oxidation with molecular oxygen using VO(acac)2 as catalyst in liquid phase.

A new bio-inspired system composed of a vitamin B12 derivative and Rose Bengal, catalyzed the dehalogenations of various toxic alkyl halides such as 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) via a noble-metal-free and visible-light-driven process. This system also catalyzed radical-involved organic reactions such as the 1,2-migration of acyl group via a tin-free process.

Cu2O acting as a robust catalyst in CuAAC reactions: water is the required medium by Kai Wang; Xihe Bi; Shuangxi Xing; Peiqiu Liao; Zhongxue Fang; Xianyu Meng; Qian Zhang; Qun Liu; Yu Ji (562-565).
Cu2O as the catalyst in water was found to be quite robust for the azide-alkyne cycloaddition (AAC) reaction, which was verified by a wide variety of applicable azides and alkynes. Water was proved to play an essential role because of a significant rate acceleration compared with reactions using organic solvents and conducted under neat conditions. The high catalytic performance of Cu2O/H2O system was further argued by decreasing the catalyst loading to ppm levels.

Water-prompted synthesis of alkyl nitrile derivatives via Knoevenagel condensation and Michael addition reaction by Ebrahim Soleimani; Mohammad Mehdi Khodaei; Nasim Batooie; Mostafa Baghbanzadeh (566-569).
A straightforward and efficient method for the synthesis of nitriles or β-cyanocarbonyls via Knoevenagel condensation and Michael addition reaction of a barbituric acid, aldehyde and sodium cyanide in water without using any catalyst or activation at 70 °C is reported.

An effective medium of H2O and low-pressure CO2 for the selective hydrogenation of aromatic nitro compounds to anilines by Xiangchun Meng; Haiyang Cheng; Shin-ichiro Fujita; Yancun Yu; Fengyu Zhao; Masahiko Arai (570-572).
Chemoselective hydrogenation of water-insoluble aromatic nitro compounds can be achieved over Ni catalysts in a H2O–compressed CO2 system at 35–50 °C without using any environmentally harmful solvent. The effective CO2 pressure is much lower than the critical pressure of CO2. The hydrogenation of nitro group should be the rate-determining step.

Green glycosylation promoted by reusable biomass carbonaceous solid acid: an easy access to β-stereoselective terpene galactosides by Bala Kishan Gorityala; Jimei Ma; Kalyan Kumar Pasunooti; Shuting Cai; Xue-Wei Liu (573-577).
An efficient green protocol has been developed for the atom economic glycosylation of unprotected, unactivated glycosyl donors and glycosylation of glycosyl trichloroacetimidates with the aid of reusable eco-friendly biomass carbonaceous solid acid as catalyst.

A metal-free decarboxylative cyclization from natural α-amino acids to construct pyridine derivatives by Qiang Wang; Changfeng Wan; Yang Gu; Jintang Zhang; Lingfeng Gao; Zhiyong Wang (578-581).
A metal-free decarboxylative cyclization from natural α-amino acids was developed and applied in the preparation of pyridine derivatives. By virtue of this method, a series of pyridines containing the moiety of natural α-amino acids can be synthesized efficiently from the corresponding natural α-amino acids.

An environmentally benign approach for the synthesis of bifunctional sulfonamide-amide compounds via isocyanide-based multicomponent reactions by Ahmad Shaabani; Afshin Sarvary; Sabrieh Ghasemi; Ali Hossein Rezayan; Rahim Ghadari; Seik Weng Ng (582-585).
Three-component reaction of the zwitterion generated from dialkyl acetylenedicarboxylate and an alkyl or aryl isocyanide with an alkyl or aryl sulfonamide is described. The reaction afforded the corresponding special type of ketenimine sulfonamide derivatives in water without using any activation and modification. The products could be easily hydrolyzed to the corresponding sulfonamide-butanamide derivatives at 80 °C in good yields without using a catalyst.

An efficient and recyclable mesoporous silica-grafted bifunctional acid–base organocatalyst for the Michael addition of ketones to β-nitrostyrenes has been synthesized by click chemistry, affording the products with excellent diastereoselectivity. A remarkable enhancement in the reaction rates could be observed with respect to the corresponding monofunctional organocatalyst.

CuCl-catalyzed green oxidative homocoupling of terminal alkynes produces symmetrical 1,4-disubstituted 1,3-diynes in good to excellent yields, using air as an environmentally friendly oxidant and the occurrence of water as exclusive byproduct in the whole process, and eliminating the need for ligands, bases, oxidants and expensive palladium catalysts.

Solvent- and catalyst-free synthesis of 2,3-dihydro-1H-benzo[d]imidazoles by Da-Peng Li; Guang-Liang Zhang; Li-Tao An; Jian-Ping Zou; Wei Zhang (594-597).
Reactions of acyclic ketones and o-phenylenediamines under solvent- and catalyst-free conditions have been developed for the preparation of dihydrobenzimidazoles. This method can also be used for the synthesis of other heterocyclic compounds such as dihydrobenzothiazoles and perimidines.

A two-step ball milling method synthesizes and purifies α,β-unsaturated esters by William C. Shearouse; Chelsea M. Korte; James Mack (598-601).
Over the last decade, solvent-free methods have been gaining interest as replacements for traditional organic chemistry techniques. While solvent-free methods are well known for many processes, a simple, solvent-free purification procedure that supplements them does not exist. We report the solvent-free synthesis of α,β-unsaturated esters using a solvent-free Horner–Wadsworth–Emmons (HWE) reaction using high-speed ball milling (HSBM). We were able to perform the HWE reaction on a variety of aldehydes, and isolate their respective a,b-unsaturated esters in high yields, purities, and diastereoselectivities.

Rapid and efficient selective hydrogenation of a range of α,β-unsaturated carbonyl compounds to their corresponding allylic alcohols was achieved in neat water using gold supported on a mesostructured CeO2 matrix. Both the activity and chemoselectivity for the reduction of carbonyl compounds improved significantly on going from organic solvents to water for the reaction media. Results in the intermolecular competitive hydrogenation showed that the intrinsic higher rate for the Au-catalyzed aldehyde reduction in water was responsible for the high activity and chemoselectivity observed.

Pentaalkylmethylguanidinium methylcarbonates 6 can easily be prepared from pentaalkylguanidines 5 and dimethyl carbonate (DMC) in a sustainable solvent-free synthesis. Most of the title compounds are room temperature ionic liquids (RTILs) which provide convenient access to halide-free guanidinium-based ILs (GILs) 7via acid–base reactions and subsequent decarboxylation, similar to industrially important imidazolium methylcarbonates 1.

Tertiary amine solvents having switchable hydrophilicity by Philip G. Jessop; Lisa Kozycz; Zahra Ghoshouni Rahami; Dylan Schoenmakers; Alaina R. Boyd; Dominik Wechsler; Amy M. Holland (619-623).
Several tertiary amines serve as switchable-hydrophilicity solvents, meaning that they are hydrophobic solvents having very low miscibility with water when under air but hydrophilic solvents having complete miscibility with water when under an atmosphere of CO2. Unlike the only previously reported switchable-hydrophilicity solvent, these amines are easily prepared and, in some cases, commercially available. The effect of temperature, gas flow rates, choice of amine and additives on the switching process is described. These solvents can be applied to the recycling of polystyrene foam.

The use of l-lysine decarboxylase as a means to separate amino acids by electrodialysis by Yinglai Teng; Elinor L. Scott; Albert N. T. van Zeeland; Johan P. M. Sanders (624-630).
Amino acids (AA's) are interesting materials as feedstocks for the chemical industry as they contain chemical functionalities similar to conventional petrochemicals. This offers the possibility to circumvent process steps, energy and reagents. AA's can be obtained by the hydrolysis of potentially inexpensive voluminous protein streams derived from biofuel production. However, isolation of the preferred AA is required in order to carry out further transformation into the desired product. Theoretically separation may be achieved using electrodialysis. To increase efficiency, specific modification to a product of industrial interest and removes charged groups of AA's with similar isoelectric points is required. Here, the reaction of l-lysine decarboxylase (LDC) was studied as a means to specifically convert l-lysine (Lys) to 1,5-pentanediamine (PDA) in the presence of l-arginine (Arg) to produce products with different charge thus allowing isolation of products by electrodialysis. Immobilization of LDC in calcium alginate enhanced the operational stability and conversion in mixtures of amino acids was highly specific. At 30 °C the presence of Arg had little effect on the activity of the enzyme although inhibition by the product PDA could be observed. Volumetric productivity was calculated and raw material and transformation costs were estimated for a potential process using a mixture of Arg and Lys.

Double metal cyanide catalysts bearing lactate esters as eco-friendly complexing agents for the synthesis of highly pure polyols by Ji Hwan Yoon; In Kyu Lee; Hye Yoon Choi; Eun Ji Choi; Ju Ho Yoon; Sang Eun Shim; Il Kim (631-639).
A green way of synthesizing double metal cyanide (DMC) catalysts for the ring opening polymerization of propylene oxide has been developed by using environmentally friendly and nontoxic lactate esters as complexing agents (CAs). The total amount of CA consumed in the catalyst preparation procedure can also be greatly reduced by combining with co-complexing agents bearing polyether backbones. The DMC catalysts produce highly pure polymers in high activity, enough to avoid labor, energy, and time-consuming catalyst removal procedures.

Selective photocatalytic reductions of nitrobenzene derivatives using PbBiO2X and blue light by Stefan Füldner; Patrick Pohla; Hanna Bartling; Stephan Dankesreiter; Roland Stadler; Michael Gruber; Arno Pfitzner; Burkhard König (640-643).
Blue light irradiation of heterogeneous photocatalysts PbBiO2X (X = Cl, Br) in the presence of triethanolamine as an electron donor leads to hydrogen evolution, and the selective, clean and complete reduction of nitrobenzene derivatives to their corresponding anilines.

N-Heterocyclic carbene functionalized MCM-41 as an efficient catalyst for chemical fixation of carbon dioxide by Hui Zhou; Yi-Ming Wang; Wen-Zhen Zhang; Jing-Ping Qu; Xiao-Bing Lu (644-650).
N-Heterocyclic carbene (NHC) functionalized MCM-41 was synthesized by reacting 1,3-bis-(4-allyl-2,6-diisopropylphenyl) imidazolium chloride with MCM-41 using 3-mercaptopropyltrimethoxysilane as silane coupling agent, and its CO2 adduct (designated as MCM-41-IPr-CO2) was further synthesized by the reaction with CO2. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to investigate the reversible CO2 capture-release ability of MCM-41-NHC. MCM-41-IPr-CO2 adduct proved to be an efficient heterogeneous catalyst for the cycloaddition of CO2 to epoxides or aziridines with excellent regioselectivity under mild conditions. Moreover, the catalyst could be recovered easily through a simple filtration process and reused multiple times without obvious loss in activity, owing to CO2 as protective group for effectively stabilizing the NHC anchored on MCM-41.

A facile method for one-step synthesis of size-controlled gold nanoparticles (AuNPs) supported on collagen fiber (CF) at room temperature was proposed. Epigallocatechin-3-gallate (EGCG), a typical plant polyphenol, was grafted onto CF surface to serve as reducing/stabilizing agent, so that the AuNPs were generated on CF surface without introduction of extra chemical reagents or physical treatments. The prepared AuNPs were fully characterized, and the results showed that the dispersed AuNPs were successfully produced and the mean particle size of AuNPs could be effectively controlled in range of 18 to 5 nm simply by varying the grafting degree of EGCG on CF surface. These stabilized AuNPs were found to be active heterogeneous catalysts for the reduction of 4-nitrophenol to 4-aminophenol in aqueous phase. The catalytic behaviors of AuNPs depended on the particle size and the grafting degree of EGCG. A distinct advantage of these catalysts is that they can be easily recovered and reused at least twenty times, because of the high stability of the AuNPs supported by EGCG-grafted CF.

Simple green synthesis of polyborosiloxanes as environmentally-safe, non-halogenated flame retardant polymers by Ravi Mosurkal; Romy Kirby; Wayne S. Muller; Jason W. Soares; Jayant Kumar (659-665).
A novel class of boron-containing siloxane copolymers (polyborosiloxanes) was synthesized by simple environmentally friendly methods. A boron containing monomer, specifically phenylboronic acid (PBA), and imide forming monomers, specifically aromatic dianhydrides 4,4′-oxydiphthalicanhydride (Oxy) and 1,1,4,4-tetracarboxylicphenyldianhydride (DAH), were employed to make terpolymers with propylamino-terminated polydimethylsiloxane (A12-PDMS). The terpolymer synthesis was carried out using various PBA : Oxy and PBA : DAH compositions ranging from 0 : 1 to 1 : 0 mole ratios. The thermal and flame retardant properties of the novel polymers were investigated. Intermediate ratios of both PBA : Oxy and PBA : DAH resulted in optimal thermal stability and flame retardancy. These novel terpolymers are promising candidates as environmentally-safe, non-halogenated alternatives to traditional flame retardant polymers.

Microwave-assisted extraction of lactones from Ligusticum chuanxiong Hort. using protic ionic liquids by Chi Yansheng; Zhang Zhida; Li Changping; Liu Qingshan; Yan Peifang; Urs Welz-Biermann (666-670).
Traditional Chinese medicine is still the main source for medical treatment in China. Extraction processes are usually adopted to separate bioactive ingredients from local plants. However, volatile traditional organic solvents are commonly used in the extraction process, which would lead to solvent loss and environment pollution. In this work, in order to improve the extraction process and develop a greener process, a microwave-assisted extraction (MAE) method was investigated to extract senkyunolide I, senkyunolide H and Z-ligustilide from Ligusticum chuanxiong Hort. Two ionic liquids, N,N-dimethyl-N-(2-hydroxyethoxyethyl)ammonium propionate (DMHEEAP) and N,N-dimethyl(cyanoethyl)ammonium propionate (DMCEAP), were employed as extractants. Important factors such as system temperature, extraction time, solid-to-solvent ratio and particle size were studied. The results show the system temperature was main factor which affects the microwave assisted extraction process. The extraction equilibrium could be reached in a short period of time. The extraction efficiency was not affected by the phase ratio within a certain solid/solvent ratio range. The particle size of Ligusticum chuanxiong powder had no remarkable effect on extraction efficiency. The back-extraction of protic ionic liquids using n-hexane was realized, and the concentration of senkyunolide I and senkyunolide H hardly decreased, but the concentration of Z-ligustilide decreased by 39.7%. The extraction mechanism of the investigated microwave assisted ionic liquid extraction was the same as traditional organic solvent extraction.

In situ spectroscopic investigation of the cobalt-catalyzed oxidation of lignin model compounds in ionic liquids by Joseph Zakzeski; Pieter C. A. Bruijnincx; Bert M. Weckhuysen (671-680).
The cobalt-catalyzed oxidation of lignin and lignin model compounds using molecular oxygen in ionic liquids proceeds readily under mild conditions, but mechanistic insight and evidence for the species involved in the catalytic cycle is lacking. In this study, a spectroscopic investigation of the complexes involved during this process was conducted using in situ ATR-IR, Raman, and UV-Vis spectroscopy. A plausible mechanism was proposed that explains the role of the ionic liquid and the other reaction conditions necessary to achieve high catalytic activity. Direct spectroscopic evidence for the species involved in the catalytic cycle was obtained. In addition, substrate consumption and product formation during the oxidation of several lignin model compounds, such as veratryl alcohol, cinnamyl alcohol, and a model compound with a β-O-4 linkage, was directly monitored. The reaction proceeds via the coordination of alcohol-containing substrates to the Co followed by formation of a Co-superoxo species. The presence of hydroxide is necessary for coordination of the alcohol to occur. Hydrogen peroxide that forms as a reaction by-product underwent rapid disproportionation to yield water and molecular oxygen. Involvement of the various intermediates was further confirmed by 18O2 labeling studies. The properties of the ionic liquid greatly influence the catalytic activity both by stabilizing reactive intermediates and by favoring the coordination of the substrate to the cobalt over the direct oxidation of the cobalt without substrate.

Trihexyl(tetradecyl)phosphonium ionic liquids (ILs) are found to support the formation of Pd(0) nanoparticles without the addition of reducing agents such as NaBH4. The resulting particles are highly crystalline and have been characterized by a range of techniques including TEM and XRD. Their sizes are in the range 7 ± 2 nm. The particle formation process is highly dependent on the anion of the IL with no nanoparticles observed when the chloride derivative was used. Particle shape could be controlled through varying the anion of the IL and the Pd(ii) precursor used. Palladium chloride reagents gave truncated octahedron shaped particles in trihexyl(tetradecyl)phosphonium dodecylbenzenesulfonate, whereas palladium acetate under the same conditions afforded a mixture of shapes including triangular plates. We propose that the presence of chloride anions in the reaction mixtures led to oxidative etching of the particles and that this process can be reduced in the presence of certain anion partners in the IL including bis(2,4,4-trimethylpentyl)phosphinate. Two possible reduction mechanisms based on reactions of the phosphonium cation are suggested for the formation of the Pd(0) species. The resulting nanoparticles are effective in catalyzing the Suzuki reaction of 4-bromotoluene and benzene boronic acid.

Impact of ionic liquids on extreme microbial biotypes from soil by Francisco J. Deive; Ana Rodríguez; Adélia Varela; Cátia Rodrígues; Maria C. Leitão; Jos A. M. P. Houbraken; Ana B. Pereiro; María A. Longo; M. Ángeles Sanromán; Robert A. Samson; Luís Paulo N. Rebelo; Cristina Silva Pereira (687-696).
This work aims at identifying, amongst extreme soil biotypes at locations of high salinity and high hydrocarbon load, microbial strains able to survive short or long-term exposure to the presence of selected ionic liquids. We have evaluated the impact of ionic liquids on the diversity of the soil microbiota to identify which microbial strains have higher survival rates towards ionic liquids, and consequently those which might possibly play a major role in their biotic fate. To the best of our knowledge, this is the first study of this kind. Soils, from a region in Portugal (Aveiro) were sampled and the bacterial and fungal strains able to survive after exposure to high concentrations of selected ionic liquids were isolated and further characterised. We have mainly focused on two types of cations: imidazolium – the most commonly used; and cholinium – generally perceived as benign. The surviving microbial strains were isolated and taxonomically identified, and the ionic liquid degradation was analysed during their cultivation. The continuing exposure of the microbial strains to petroleum hydrocarbons is likely to be the basis for their acquired resistance to some imidazolium salts; also, the higher capacity of fungi – compared to bacteria – to grow, even during their exposure to these liquid salts, became evident in this study.

Esterification of glycerol with acetic acid using double SO3H-functionalized ionic liquids as recoverable catalysts by Xiumei Liu; Huiyuan Ma; Yue Wu; Chang Wang; Miao Yang; Peifang Yan; Urs Welz-Biermann (697-701).
Esterification of glycerol with acetic acid was studied using a series of Brønsted acidic ionic liquids as catalysts. The results indicate that double SO3H-functionalized ionic liquids show high catalytic activity and fair reusability even at very low catalyst loadings, while the conventional non-functionalized ionic liquids show poor activity. The Brønsted acidity–catalytic activity relationships were also investigated and the results showed that the sequence of the catalytic activity observed in the transformation was in good agreement with the Brønsted acidity order determined by the Hammett method.

The heteropoly phosphotungstic acid, H3PW12O40 (HPW), was successfully immobilized on the surface of MCF, SBA-15 and MCM-41 by means of chemical bonding to aminosilane groups. The as-obtained materials were characterized by N2 sorption, TEM, XRD, FT-IR, 13C-, 29Si-, 31P-MAS NMR and XPS. Characterization results suggest that the surface area decreased after grafting amino groups to silica. The as-prepared HPW-NH2-MCF is highly efficient in the O-heterocyclization of cycloocta-1,5-diene (COD) to 2,6-dihydroxy-9-oxabicyclo[3.3.1] nonane (1) and 2-hydroxy-9-oxabicyclo [3.3.1] nonane-6-one (2) with a COD conversion of 100% and (1 + 2) selectivity up to 98%. It is worth mentioning that this material could be reused six times without any significant loss of activity and selectivity. The good stability can be attributed to the strong interaction between the amino groups on the surface of MCF and HPW anions.

Efficient biodegradation of common ionic liquids by Sphingomonas paucimobilis bacterium by Concepcion Abrusci; Jose Palomar; Jesus L. Pablos; Francisco Rodriguez; Fernando Catalina (709-717).
The biodegradation of ionic liquids (ILs) was evaluated by an indirect impedance technique, through which carbon dioxide production was measured during bioassay time. The biodegradation study was focused on finding a microorganism able to efficiently degrade common IL compounds. For the first time, a bacteria strain of Sphingomonas paucimobilis was employed in biodegradability tests of ILs, carried out for 37 commercial imidazolium-, pyridinium-, pyrrolidinium-, ammonium- and phosphonium-based ILs, including in the sample 12 different anions and 14 different cations. Remarkably, more than half of ILs studied (54% of the sample) exhibited a biodegradation percentage ≥60% after a 28-day incubation period with S. paucimobilis at 45 °C; therefore, they behave as easily biodegradable compounds from the indirect impedance test. In summary, current results suggested the possibility of biotreatment for the rapid and ultimate mineralisation of widely used ILs, such as BmimNTf2, BmimPF6, etc., which were noted as recalcitrant to biodegradation in previous standard tests with other microorganisms.

Microwave-promoted efficient synthesis of dihydroquinazolines by Rupam Sarma; Dipak Prajapati (718-722).
A solvent- and catalyst-free synthesis of dihydroquinazolines is described. 2,4-Disubstituted-1,2-dihydroquinazolines can be readily obtained from 2-aminobenzophenone and aldehydes under microwave irradiation using urea as an environmentally benign source of ammonia, with a small amount of the corresponding quinazolines as the minor product. The reaction is simple, clean and excellent yields are obtained within minutes.

Back cover (723-724).