Solvent substitution

In addition, iu May 1988 an iucident at Shell s Norco plant (54) limited production. These outages hastened many customers to switch over to other solvent substitutes. The price of MEKia October 1994 was about 0.88/kg. Supply fluctuations caused the price to range from 0.55 to 1.10 /kg siace the early 1980s. 

These regulations are based in part on the amount of solvents in relation to the amount of soHds. Most wood stains are low soHds materials which rely on their transparency and their abiHty to penetrate and dry fast. Those characteristics themselves put great emphasis on the type of solvents that are used to formulate stains. The low soHds content of wood stains limits the scope of solvent substitution or reformulation. 

Timberlake, D. L., and R. Govind (1994). Expert System for Solvent Substitution. Preprints of Papers Presented at the ZOSth ACS National Meeting, August 21-25,1994, Washington, DC, 215-217. Center for Great Lakes Studies, University of Wis-consin-Milwaukee, Milwaukee, WL Division of Environmental Chemistry, American Chemical Society. 

Joback, K. G. (1994). Solvent Substitution for Pollution Prevention. Pollution Prevention Via Process and Product Modifications, ed. M. El-Halwagi, and D. P. Petrides, 98-103. AIChE Symposium Series 303. New York American Institute of Chemical Engineers. 

A very different neutrally charged complex for alkane activation has been reported recently and is shown in Scheme 34(A). The compound is a hydridoplatinum(II) complex bearing an anionic ligand based on the familiar nacnac-type, but with a pendant olefin moiety (97).This complex is extremely soluble in arenes and alkanes and activates C-H bonds in both types of hydrocarbons. This is indicated by deuterium incorporation from deuterated hydrocarbon into the substituents on the arene of the ligand and into the Pt hydride position (A A-d27, Scheme 34). The open site needed for hydrocarbon coordination at Pt(II) is created by olefin insertion instead of anion or solvent substitution (97). 

The strength of a solvent bond influences the rate of solvent substitution in a given compound. Kinetic measurements by means of the T-jump relaxation technique have illustrated that for the reactions of the solutions of SbCl5 with triphenylchloromethane in different solvents a relationship exists between the rate constant and the donicity of the solvent used. 

Fig. 18. Rate constants kn and enthalpy of hydration for the solvent substitution reactions in water for various metal ions...

For this reason, SCCO2 was investigated as solvent substitute in the hydroformylation process. 

US Environmental Protection Agency (EPA) Integrated Solvent Substitution Data System. Online. Available HTTP (accessed ... 

Spent solvents constitute a major source of pollution in the chemical and pharmaceutical industries. Much of this pollution can be prevented by solvent substitution using solvents that are more environmentally compatible or possess higher performance. This can lead to a reduction in the amount used. However, identifying replacement solvents is often a difficult process performed in an ad hoc manner. 

In the material that follows we describe high solvent use areas. It will be these areas where green solvent research and solvent substitution will have the greatest impact... 

The solvation dynamics following charge-transfer electronic excitation of diatomic solutes immersed in a methanol-water mixture provides a direct window on the molecular changes occurring upon solvent substitution. The solvation response of the mixtures is separated into methanol and water contributions in order to elucidate the role played by each molecular species on the solvation dynamics. Significandy different responses for the two solutes are found and related to the fact that the solute with the smaller site diameters is a much better hydrogen (H)-bond acceptor than the larger diameter solute (Skaf and Ladanyi, 1996). 

As computers become more pervasive and increasingly powerful, specialized programs and databases are being developed to assist in a wide variety of research efforts. This is true in the search for solvent alternatives, and in this section we review the application of computers to solvent substitution studies and cover computer-aided molecular design of new solvents, methods developed for the prediction of physical properties, methods for predicting less precise chemical characteristics such as toxicity and carcinogenicity, and computer-aided design of alternative synthetic pathways. 

Constraints on the selection of a solvent are diverse. Enviromnental, safety, health, reactivity, stability, and regulatory considerations must be considered (Zakrzewski, 1991). These should be added to the model. For many applications, conventional organic solvents are highly desirable because of familiarity, low cost, ease of handling, and ease of disposal. To satisfy the needs of these applications a large variety of new, alternative solvents are being offered. Because there are no exact drop-in replacements, a systematic evaluation of solvent substitutes must be performed. 

At the core of many of these algorithms for solvent substitution is a method for predicting the properties of proposed molecules, given only the molecular structure. Much work has been done in this area alone, and several programs have been developed to guide this process. Some of these programs are listed in table 9.1. Additionally, process simulation software such as Aspen Plus contain several different approaches for the prediction of properties from molecular structure. 

Process simulation is a key tool in computer-assisted solvent substitution. More complicated than the prediction of physical and chemical properties is the prediction of more loosely defined molecular characteristics such as toxicity. These properties are not traditionally included in process simulation software, so special attention must be paid to their prediction. 

A complicated problem is that of solvent substitution for organic reaction optimization. The solvent is important in organic synthesis, and several solvent polarity scales have been developed to attempt to quantify this, specifically work by Reichardt (Rei-chardt, 1988). 

Table 9.2. Solvent substitution resources on the World Wide Web.

A single repository for pollution prevention, compUance assurance, and enforcement information databases has the database umbrella architecture for solvent alternatives solvent substitution data systems Integrated Solvent Substitution Data System (ISSDS) Hazardous Solvent Substitution Data System on-line product information, material safety data sheets... 

SMART (Solvent Measurement, Assessment, and Revamping Tool) is a software program that allows assessment of solvents used for batch processing based on both empirical data and property estimation methods (Modi et al., 1996). This system includes a new conjugation based method for the estimation of reaction rates in solution, which is based on the concept that the absolute reaction rate coefficient can be obtained from a function dependent on the change in molecular charge distribution between reactants and activated complex (Sherman et al., 1998). Table 9.2 provides a list of solvent substitution resources available on the World Wide Web. 

Copeland, A. E. (1990) In Solvent Substitution, Annual International Workshop, Department of Energy, Phoenix, AZ, pp. 115-117. 

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