Large amounts of waste may result from the neutralization of homogeneous acid catalysts following reaction. Here we present examples of in situ acid formation and self-neutralization, thus eliminating waste and offering advantages for product recovery. The formation of a-terpineol (2) from b-pinene (1) is a reaction of commercial significance that is typically run with strong acid. We demonstrate that the reaction can be performed under more environmentally benign conditions using the in situ acid formation capabilities of two different green technologies: CO 2 expanded liquids and reactions in hot water (200 °C). This work presents an example of the application of these methods to a reaction that has commercial significance and adds to our knowledge about the benefits and effects of co-solvents. The relative rates and product distributions achieved in each system are presented and discussed.

Acids are the most common industrial catalysts but have the disadvantage of requiring post-reaction neutralization and salt disposal. We show the catalytic use of self-neutralizing acids. Carbon dioxide interacts with water and amines to form carbonic acid and carbamates. A similar interaction occurs with alcohols to form alkylcarbonic acids. All three solvent systems provide in situ acid formation for catalysis which can be easily neutralized by removal of carbon dioxide. However, water has poor organic solubility and amines form salts so only alkylcarbonic acids combine good organic solubility with simple neutralization via depressurization. The use of in situ acid also completely eliminates the solid salt wastes associated with many acid processes. To elucidate how to implement these systems in place of a standard acid system we compare the reaction rates of several alkylcarbonic acids with diazodiphenylmethane (DDM). We report also the effect of CO 2 pressure on reaction rate of DDM as well as measure the dielectric constant of these systems. Finally, a Hammett plot is used to identify the dominant step in alkylcarbonic acid catalysis.

Development of ionic liquids for specific tasks is currently being pursued by many researchers as numerous cation/anion combinations are theoretically possible. However, only a small fraction of these combinations melt below 100 °C. Recently, large melting point depressions of several ionic solids with compressed carbon dioxide have been reported. This investigation details the melting point depression of a large number of ionic organic compounds (ionic liquids) with gaseous, liquid, and supercritical CO2. Large and previously unreported depressions were observed for some of the ionic solids. This methodology greatly expands the numbers of compounds and functional groups that can be employed in an ionic liquid/compressed gas system for various applications. Thermodynamic analysis indicates that even small amounts of CO2 can lead to substantial melting point depression, due to its very low melting temperature and negative deviations to Raoult's law.

Despite widespread use, homogeneous acid catalysis has the drawback of requiring downstream neutralization, resulting in salt waste. Methylcarbonic acid is a self-neutralizing acid that forms in situ in methanol/CO 2 systems at mild pressures (10-47 bar) and then decomposes by depressurization. In the work presented here, methylcarbonic acid catalyzes the diazotization of aniline, which is either coupled with N,N-dimethyl aniline to form methyl yellow or reacted with iodide to form iodobenzene. The syntheses of methyl yellow and iodobenzene represent a class of industrially important reactions.

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