1999 Progress Report: Photochemical Alternatives for Pollution PreventionEPA Grant Number: R825330
Title: Photochemical Alternatives for Pollution Prevention
Investigators: Kraus, George
Current Investigators: Kraus, George , Tanko, James
Institution: Iowa State University
Current Institution: Iowa State University , Virginia Polytechnic Institute and State University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $400,000
RFA: Technology for a Sustainable Environment (1996) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Objective:The objectives of this project are to: (1) extend the photochemically mediated acylation and alkylation reactions; (2) use photochemistry to produce acyl radicals that will decarbonylate to alkyl radicals; (3) evaluate supercritical solvents for our photochemically mediated additions of aldehydes to quinones (with Dr. James Tanko, VPI); and (4) understand the factors that influence the scale-up of the reaction.
We have made good progress on our objectives. One manuscript has been published entitled "A Photochemical Alternative to Certain Friedel Crafts Reactions." Manuscripts describing our efforts toward Objectives 1 and 3 are in preparation.
A goal of Objective 1 is the creation of photochemically based annulation procedures. The following regioselective additions have been achieved.
These results show that the acyl radicals react regioselectively with the acyl quinones. This result is in contrast to earlier published work that proposed a meta relationship for the acyl groups. The structure for the product where R = R' = Ph was determined by x-ray diffraction.
We recently prepared the aldehyde shown below and are irradiating it in the presence of benzoquinone and benzophenone. Preliminary results indicate that the isoflavone structure has been formed. Isoflavones constitute a large group of natural products, many of which exhibit useful biological activity.
A goal of Objective 3 is to evaluate supercritical solvents for our photochemically mediated additions of aldehydes to quinones. Results from Dr. Tanko's laboratory follow.
To determine whether the benzophenone-mediated additions of aldehydes to benzoquinone is a free radical process, in addition to the photochemical route, Dr. Tanko's group carried out several reactions in benzene between benzaldehyde and benzoquinone using free radical initiators, such as t-butyl peroxide and benzoyl peroxide (Table 1). In addition to probing the mechanism of the reaction, they were hoping to decrease reaction times significantly. However, the yield never exceeded 1 percent (60-99 percent unreacted benzoquinone). Consequently, this reaction does not appear to be a chain process, and the mechanism of this reaction likely involves hydrogen abstraction from the aldehyde by the excited state quinone, followed by in-cage radical-radical coupling.
Table 1. The reaction between 1,4-benzoquinone and benzaldehyde in benzene of the free in the presence radicals initiators
|Temperature; ?C||Acylhydroquinone yield, %|
The reaction time was 8 hours.
Dr. Tanko's group has built the 6 mL high pressure reactor with two sapphire windows, which allowed them to check solubility of chemicals in SC-CO2 by visual observations. They have observed that most of 1,4-benzoquinone at the pressures of 1,200 psi and 2,500 psi is soluble in this solvent. Benzophenone and benzaldehyde were fully soluble in SC-CO2 at these pressures. The goal is to check if it is possible to use alcohols as cosolvents. They have performed several experiments in benzene with addition of several alcohols between benzaldehyde and benzoquinone. The results are summarized in the Table 2.
From these experiments, they have learned that only when t-buthanol was used as a cosolvent for benzene it was possible to obtain similar product yields as in benzene: 56 percent in benzene and 46 percent in benzene+5 percent t-buthanol. Other cosolvents, such as methanol, ethanol, and isopropanol, gave no more than 19 percent of product yield. Finally, the reactions were performed in SC-CO2 using 17 mL high pressure reactor and 150 Watts Xenon lamp with Pyrex glass filter. The results are introduced in Table 3.
Table 2. The reaction of benzaldehyde (0.1M) and benzozoquinone (0.015M) in presence of benzophenone (0.015M) in benzene
|Solvent||Acylhydroquinone yield, %||Hydroquinone yield, %||Benzoquinone unreacted, %|
|Benzene+ 5% isoPrOH||13||40||0|
|Benzene+ 5% MeOH||19||46||0|
Time of irradiation: 3 days.
Table 3. The reaction between benzoquinone (0.015M) and benzaldehyde (0.1M) in presence of benzophenone (0.015M) in SC-CO2
|Solvent||Pressure, psi||Reaction time, days||Product Yield, %||Hydroquinone yield, %|
|SC-CO2 + 5% t-BuOH||4672||3||49||6|
|SC-CO2 + 5% t-BuOH||4548||2||44||6|
Temperature: 50 C.
Dr. Tanko's group was able to obtain the desired product with 44 percent of yield performing the reaction in SC-CO2 at the pressure 6,055 psi for 2 days. Similar results were obtained in the presence of tert-butyl alcohol as a cosolvent.
Future Activities:Continue efforts to meet all of our objectives.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 9 publications||3 publications in selected types||All 2 journal articles|
||Kraus GA, Khwang K, Lu Y. Photoalkylation of quinones with ethers. Journal of Photochemistry and Photobiology A: Chemistry 1999;129(1-2):49-50.||