Sunday, May 07, 2006

Wittig Reaction (Thomas Dursch)


In the near future, perfection of Organic Light Emitting Diode (OLED) technology will create an alternative to LCD screens, revolutionizing the display market. Problems associated with the emission of blue light in OLEDs currently inhibit their mass production. According to Wikipedia.com, organic compounds that emit blue light have a lifespan of only 1,000 hours, whereas, the red and green emitting compounds have a lifespan of roughly 500,000 hours. Improvements upon the longevity of blue emitters will open a new door to display technology.

According to the article “Reliability and Degradation of Small Molecule-Based
Organic Light-Emitting Devices” in the IEEE Journal of Quantum Electronics, the cause of this limited lifespan is an undesirable reaction between oxygen molecules and the organic emitting layer. Due to the permeability of the glass substrate, oxygen molecules are able to diffuse into the organic emitting layer. During the operation of an OLED, singlet oxygen is formed due to the energy transfer from the excited organic molecules to oxygen molecules. The singlet oxygen molecules, known as radicals, then attack the structure of the organic compound eventually destroying the organic layer.

Currently, my freshman design group is working on a solution to lengthen the lifespan of the blue emitting compound. Since it is very difficult to find a blue emitting compound that does not react with oxygen at all, we decided to find a compound that reacts with oxygen, but extremely slowly. Our group is currently investigating a class of compounds known as the triarylamines, specifically, a triphenylamine-based conjugated polymer known as MPa (chosen due to MPa’s high thermal stability, low tg, and high quantum yield of nearly 64 %). In order to create MPa we must use the Wittig Reaction. According to Organic-chemistry.org, the Wittig Reaction allows the preparation of an alkene by the reaction of an aldehyde or ketone with the ylide generated from a phosphonium salt. MPa is created by a reaction of an aldehyde group found on PFT with benzyltriphenylphosphonium bromide and THF under N2. For a detailed description of the reaction please refer to “Macromolecules” by the Tokyo Institute of Technology.


Friday, May 05, 2006

Esterification Reaction of Phenylacetic acids



Esterification reactions are condensation reactions between alcohols and carboxylic acids in the presence of an acid catalyst to form esters. According to a Wikipedia article, esterification is commonly used in substances such as lotions or perfumes, as they tend to give off various scents and flavors. Phenylacetic acids are found in plants, as a type of hormone known as auxin, which is generally used in the plants’ fruits. Phenylacetic acids tend to possess a honey-like odor in smaller concentrations and may be used in perfumes. Esterification reactions of carboxylic acids create esters that are excellent solvents and can then be used in soaps and lotions (“Intro to General, Organic, and Biological Chemistry,” Solomon).
In an experimental setting, an esterification reaction, as shown above, was tested using a catalyst, cerium (IV) ammonium nitrate (CAN), and simple primary and secondary alcohols in order to increase the efficiency of basic esterification reactions. A link to this experiment can be found here.
The synthesis of aspirin, also known as acetylsalicylic acid, also uses an esterification reaction. For more information on the uses of aspirin, please see the class blog.

Monday, May 01, 2006

Aspirin - Acetylsalicylic Acid (Thomas Dursch)



Since the time of Hippocrates, there have been written records of pain relief treatments, including powder obtained from the insides of willow trees. According to From a Miracle Drug written by Sophie Jourdier for the Royal Society of Chemistry, “It was not long before the active ingredient in willow bark was isolated; in 1828, Johann Buchner, professor of pharmaceuticals at the University of Munich, isolated a tiny amount of bitter tasting yellow crystals, which he called salicin”.



According to Wikipedia, an online encyclopedia, salicin undergoes a “Kolbe-Schmitt reaction and the final product is an aromatic hydroxyl acid known as salicylic acid”. Minimally, what happens in a Kolbe-Schmitt reaction is a sodium phenolate is heated with carbon dioxide, then the final product is treated with sulfuric acid, eventually producing salicylic acid. Today, scientists recognize salicylic acid as being harmful when ingested. Instead of using salicylic acid, the commonly used pain reliever is acetylsalicylic acid, now known as aspirin. The newly discovered acetylsalicylic acid is what is known as an “acetyl ester” formed through a process known as esterification. According to Wikipedia, for this esterification, “a carboxylic acid reacts with the phenol group of salicylic acid to produce the acetyl ester”. Simply, an ester can be thought of as a product of a condensation reaction of an acid usually an organic acid and an alcohol or phenol.



Aspirin helps cure headaches, reduce fevers, and reduce swelling to minor injuries, and since the time of its discovery, has risen to one of the leading over-the-counter drugs. According to Paul May at the University of Bristol School of Chemistry, “each year, more than 40 million pounds of aspirin is produced in the United States alone, a rate that translates to about 300 tablets per year for every man, woman and child”.



To further supplement this information and for a complete reaction/experiment, please refer to the following link.