Water As a Reaction Medium for Clean Chemical Processes
Total Page：16
File Type：pdf, Size：1020Kb
Clean Techn Environ Policy (2005) 7: 62–69 DOI 10.1007/s10098-004-0262-y ERRATUM Wu Wei Æ Charlene C. K. Keh Æ Chao-Jun Li Rajender S. Varma Water as a reaction medium for clean chemical processes Published online: 30 November 2004 Ó Springer-Verlag 2004 Abstract Solvent usage is often an integral part of (Anastas and Warner 1998). The studies of green manufacturing process, whether it is chemical or another chemistry have led to the development of cleaner and industrial sector. Thus, this unavoidable choice of a relatively benign chemical processes with many new specific solvent for a desired manufacturing process can technologies being developed each year. Among them, have profound economical, environmental, and societal there is a large proportion of effort that has been de- implications. Some of the impacts are long lasting voted to the use of non-traditional solvent for chemical especially from an environmental perspective, which has synthesis. These unconventional media include sol- been well documented in the scientific literature. The ventless (Cherouvier et al. 2001; Tanaka 2003; Togo pressing need to develop alternative solvents for manu- and Hirai 2003; Varma 1999; Varma 2000a; Varma facturing processes originates, in part, from these 2000b; Varma 2001), water (Chan and Issac 1996; Li implications and constitutes an essential strategy under 1993; Li 1996; Li 2002; Li and Chan 1997; Li and an emerging field of green chemistry. Whereas there Chan 1999), supercritical CO2 (Devetta et al. 1999; have been excellent advances in developing several Ishii and Oi 1998; Jessop and Leitner 1999; Matruda alternative ‘‘clean’’ solvents, it is unlikely that the one et al. 2001; Wei et al. 2002), ionic liquids (Rogers and solvent will be a panacea for various chemical protocols. Seddon 2002; Wasserscheid and Keim 2000), perfluo- This article provides some examples of using water as an rinated solvent (Gladysz and Curran 2002; David et al. alternative solvent for chemical reactions with wide- 2002; Moineau et al. 1999), and some others (Harano ranging possibilities that include direct use of water et al. 2000; Westacott et al. 2001). During these soluble renewable materials, C–C bond forming reac- explorations, a familiar question is frequently asked tions using organometallic reagents, and exploiting the even within the green chemistry community about the use of alternate energy sources such as solar, microwave relative greenness of a medium over others. There is no and ultrasound in accelerating chemical syntheses. clear answer to this question if the context of the discussion is not defined. For example, water is com- monly considered as a benign solvent for its non-tox- icity and abundant natural occurrence, yet in the Within the last decade or so, green chemistry has semiconductor industry, wastewater contaminated with attained the status of a major scientific discipline trace amount of metals is a serious environmental problem (Aoki et al. 2002; Uchida et al. 2002). Thus, it The online version of the original article can be found at http:// is important to recognize that there is no universal best dx.doi.org/10.1007/s10098-003-0242-7 solvent for all chemical processes. Instead, the different W. Wei Æ C. C. K. Keh Æ C.-J. Li choices provide various alternatives for the end-users Department of Chemistry, Tulane University, to select based on their own assessments of overall New Orleans, LA 70118, USA environmental impact. Water is undoubtedly the E-mail: [email protected] cleanest solvent on earth. The use and release of ‘‘clean C.-J. Li water’’ will have the least impact to the environment. Department of Chemistry, McGill University, However, it should be stressed that the release of a 801 Sherbrooke St. West, Montreal, PQ H3A 2K6, Canada large amount of uncleaned (untreated) water has been R. S. Varma (&) a major problem. In this article we will briefly discuss, Clean Processes Branch, National Risk Management Res. Lab, U.S. Environmental Protection Agency, 26 West M.L.K. Drive, with selected examples, some of the main advantages MS 443, Cincinnati, OH 45268, USA of using water as a reaction medium to develop cleaner E-mail: [email protected] chemical processes. 63 (1) Direct utilization of water-soluble compounds and renewable materials The first common advantage of using water as solvent for clean technology is the opportunity to directly utilize water-soluble compounds and renewable materials such as carbohydrates without the necessary derivatizations. However, in order to accomplish this goal, chemical reactions that can tolerate water and reactive functional groups such as hydroxyl, amine, and acids should be developed. Within the past two decades many reactions that are conventionally believed to proceed only in or- ganic solvents have been developed in water. Since the seminal work of Breslow on aqueous Diels–Alder reac- tions (Breslow 1999), there have been profound research activities of developing organic reactions in aqueous media. Among the many significant developments in the field are the Diels–Alder (including hetero-Diels–Alder) and sigmatropic rearrangements (Chandrasekhar et al. 2002; Grieco 1991; Libineau et al. 1992; Loh et al. 1996; Otto and Engberts 1999; Otto et al. 1998; Otto et al. 1996; Wipf and Ribs 2001), the catalytic hydrogenations and hydroformylations, the metal-mediated carbon– carbon bond formations, the water-tolerant Lewis acid catalysis (Heeres et al. 2001; Haumann et al. 2002; Ko- bayashi and Manabe 2002; Gu et al. 2001; Li 2002; Li et al. 2002a; Li et al. 2002b; Lindstoem 2002; Munoz- Moniz et al. 2003; Paganelli et al. 2000; Shimizu et al. 2000; Shirakawa 2001; Tin et al. 1999) including solid acids (Okuhara 2002), transition-metal catalyzed car- bon–carbon bond formations (Li et al. 1998; Li et al. 2002a; Li et al. 2002b; Zhang et al. 2000), radical reac- Scheme 1 Synthesis of sialic acid in water tions (Poonkodi and Anbalagan 2001), and various asymmetric carbon–carbon bond formations in water (Manabe and Kobayashi 2002). High temperature water and the catalyst can be recycled readily. Through this has also shown to be a promising medium for new strategy, it is possible to recycle the aqueous catalyst chemistry (Shaw et al. 1991). These reactions provided solution for an extended period of time without the need the possibility of directly modifying water-soluble and either to discharge it or to regenerate it. renewable materials in water without the necessary A second key to develop clean catalysis in water is to protection–deprotection sequences that are commonly develop reactions with high atom efficiency. This is associated with conventional chemistry, thus reducing important as low atom efficiency will lead to the accu- the overall synthetic steps. An example is the higher mulation of unwanted materials in the solution, which carbon-sugar synthesis from carbohydrate by Chan will eventually require the change and discharge of the (Chan and Li 1992) and Whitesides (Gao et al. 1994) catalyst solution. Examples of successfully developed (Scheme 1). catalytic reactions include catalytic hydrogenations, hydroformylations, Wacker’s oxidation, and some polymerization reactions. (2) Catalyst recycling and product isolation via phase Hydrogenation, together with hydrocyanation, hy- separation drosilylation, and hydrostannation, are useful transition metal-catalyzed reactions in organic synthesis (Augus- Another potential opportunity of clean chemical syn- tine 1965; Freifelder 1971; Freifelder 1978; Rylander thesis in water is the development of catalytic processes 1979; Rylander 1985). The first successful catalytic that can simplify catalyst recycling and product isola- hydrogenation in aqueous solution was reported in 1975 tion. While designing ideal catalytic processes for clean by using a catalyst having water-soluble phosphine li- synthesis in water, a key is to develop catalysts that are gands (Joo and Beck 1975). Since then, both hydroge- soluble in water. Ideally, the reactant and the product nation of C–C unsaturated bonds and C–O double should have no or very little water solubility. As a result, bonds in aqueous medium have been extensively studied. the product can be isolated by simple phase separations For example, Joo and Benyei have shown that by using 64 RuCl2(TPPMS)2 and sodium formate as hydrogen do- nor, a variety of aromatic and a,b-unsaturated alde- (3) The combination of electrochemistry–solar hydes were transformed to the corresponding saturated chemistry in water alcohols in aqueous solution (Benyei and Joo 1990; Joo and Benyei 1989). Many excellent asymmetric hydroge- Additional examples of developing clean chemical syn- nation processes have also been developed (Toth et al. thesis in water is the development of electrochemical 1990). A highly regio- and stereoselective hydrosilylation oxidations and reductions as well as solar-cell-based of terminal alkyne has been developed (Wu and Li chemical technologies. As an example, the production of 2003). adiponitrile is an important industrial process involving The hydroformylation process is one of the most the electro-hydrodimerization (EHD) of acrylonitrile. successful applications of aqueous medium catalysis in Adiponitrile is used as an important precursor for hex- industrial manufacture. A series of patents in 1982 de- amethylenediamine and adipic acid, the monomers re- scribed the reaction process (Cornils et al. 1982), the quired for the manufacture of nylon-66 polymer (Danly recovery of rhodium catalyst (Gaertner et al. 1984a), and King 1991). A high-yield adiponitrile synthesis and the preparation of water-soluble sulfonated phos- (Baizer 1980) was realized via an electrochemical process phane ligands (Gaertner et al. 1984b). The best known by using a concentrated solution of certain quaternary hydroformylation is Ruhrchemie/Rhoˆ ne-Poulenc’s pro- ammonium salts (QAS) together with lead or mercury cathodes (Scheme 4). cess (Bexten et al. 1986) that uses HRh(CO)(tppts)3 as catalyst (Scheme 2). The product is separated from the catalyst solution by a simple phase separation, and the catalyst solution is recharged to the reactor for further reaction.