Course Description: Topics may include recent developments in organic synthesis, organometallics, heterocyclics, phase transfer catalysis, and physical organic chemistry. May be repeated under different topics. Number of Credit Hours: 3 semester hours - 3 hours lecture Course
Course Description: Topics may include recent developments in organic synthesis, organometallics, heterocyclics, phase transfer catalysis, and physical organic chemistry. May be repeated under different topics. Number of Credit Hours: 3 semester hours - 3 hours lecture
The lab of synthetic chemist László Kürti made elusive chiral biaryl compounds in a single-flask process that does not require the use of transition metals.
These biaryls are called organocatalysts because they catalyze chemical reactions without metal ions. They eliminate the need for transition metals and simplify chemical processes to synthesize new molecules. Transition metals are conductive metals that include titanium, iron, nickel, silver, copper, palladium and gold and are commonly used in catalysis.
HOUSTON - (Nov. 24, 2015) - Rice University scientists using an efficient metal-free process have synthesized dozens of small-molecule catalysts, tools that promise to speed the making of novel chemicals, including drugs.
After a reaction is completed, the solution often times does not only contain the desired product, but also undesired byproducts of the reaction, unreacted starting material(s) and the catalyst (if it was used). These compounds have to be removed in the process of isolating the pure product. A standard method used for this task is an extraction or often also referred to as . Strictly speaking, the two operations are targeting different parts in the mixture: while the extraction removes the target compound from an impure matrix, the washing removes impurities from the target compound i.e., water by extraction with saturated sodium chloride solution. Washing is also used as a step in the recrystallization procedure to remove the impurity containing mother liquor adhering to the crystal surface.
Many liquid-liquid extractions are based on acid-base chemistry. The liquids involved have to be immiscible in order to form two layers upon contact. Since most of the extractions are performed using aqueous solutions (i.e., 5 % NaOH, 5 % HCl), the miscibility of the solvent with water is a crucial point as well as the compatibility of the reagent with the compounds and the solvent of the solution to be extracted. Solvents like dichloromethane (=methylene chloride in older literature), chloroform, diethyl ether, or ethyl ester will form two layers in contact with aqueous solutions if they are used in sufficient quantities. Ethanol, methanol, tetrahydrofuran (THF) and acetone are usually not suitable for extraction because they are completely miscible with most aqueous solutions. However, in some cases it is possible to accomplish a phase separation by the addition of large amounts of a salt (“salting out”). Commonly used solvents like ethyl acetate (8.1 %), diethyl ether (6.9 %), dichloromethane (1.3 %) and chloroform (0.8 %) dissolved up to 10 % in water. Water also dissolves in organic solvents: ethyl acetate (3 %), diethyl ether (1.4 %), dichloromethane (0.25 %) and chloroform (0.056 %). Oxygen containing solvents are usually more soluble in water (and vice versa) because of their ability to act as hydrogen bond donor and hydrogen bond acceptor. The higher water solubility lowers the solubility of weakly polar or non-polar compounds in these solvents i.e., wet Jacobsen ligand in ethyl acetate. Other solvents such as alcohols increase the solubility of water in organic layers significantly because they are miscible with both phases and act as a mediator. This often leads to the formation of emulsions.
The most important point to keep in mind throughout the entire extraction process is which layer contains the product. For an organic compound, it is relatively safe to assume that it will dissolve better in the organic layer than in most aqueous solutions unless it has been converted to an ionic specie, which makes it more water-soluble. If a carboxylic acid (i.e., benzoic acid) was deprotonated using a base or an amine (i.e., lidocaine) was protonated using an acid, it would become more water-soluble because the resulting specie carries a charge. Chlorinated solvents (i.e., dichloromethane, chloroform) exhibit a higher density than water, while ethers, hydrocarbons and many esters possess a lower density than water (see solvent table), thus form the top layer . One rule that should always be followed when performing a work-up process:
Never dispose of any layer away until you are absolutely sure (=100 %) that you will never need it again. The only time that you can really be sure about it is if you isolated the final product in a reasonable yield, and it has been identified as the correct compound by melting point, infrared spectrum, etc. Keep in mind that it is always easier to recover the product from a different layer in a beaker than from the waste container or the sink. In this context it would be wise to label all layers properly in order to be able to identify them correctly later if necessary.
In order to separate compounds from each other, they are often chemically modified to make them more ionic i.e., convert a carboxylic acid into a carboxylate by adding a base. Standard solutions that are used for extraction are: 5 % hydrochloric acid, 5 % sodium hydroxide solution, saturated sodium bicarbonate solution (~6 %) and water. All of these solutions help to modify the (organic) compound and make it more water-soluble and therefore remove it from the organic layer. More concentrated solutions are rarely used for extraction because of the increased evolution of heat during the extraction, and potential side reactions with the solvent.
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After separation of the organic and the aqueous layer, the amine can be recovered by addition of a strong base like NaOH or KOH to the acidic extract i.e., lidocaine synthesis. Note that amides are usually not basic enough to undergo the same protonation (pKa of conjugate acid: ~ -0.5).
Most neutral compounds cannot be converted into salts without changing their chemical nature. Many of these neutral compounds tend to react in undesired ways i.e., esters undergo hydrolysis upon contact with strong bases or strong acids. One has to keep this in mind as well when other compounds are removed. For instance, epoxides hydrolyze to form diols catalyzed by acids and bases. Ketones and aldehydes undergo condensation reactions catalyzed by both, acids and bases. Esters also hydrolyze to form carboxylic acids (or their salts) and the corresponding alcohol. In order to separate these compounds from each other, chromatographic techniques are often used, where the compounds are separated based on their different polarities (see Chromatography chapter).
Based on the discussion above the following overall separation scheme can be outlined. Which sequence is the most efficient highly depends on the target molecule. There is obviously no reason to go through the entire procedure if the compound sought after can be isolated in the first step already. Note that many of these steps are interchangeable in simple separation problems.
An illustration details the single-step, single-flask process by which Rice University scientists have simplified the rapid synthesis of small-molecule catalysts. The catalysts promise to speed the process of making novel chemicals, including drugs. (Credit: Illustration by László Kürti/Rice University)
- One semester hour, three hours lab per week. Study of syntheses and reactions of inorganic chemistry. Prerequisites: CHE 134, 134L. Corequisite: CHE 241. Required lab fee. (F)
Course Description: Practical work in an industrial setting for a minimum of eight weeks under the joint guidance of a practicing chemist and SFA faculty member. May be repeated for credit if content differs.
Number of Credit Hours: 3 semester hours
Course Prerequisites and Corequisites: Prerequisite: Permission of the department chair and instructor. Pass-Fail grading.
Program Learning Outcomes:
3. The student will perform qualitative/quantitative chemical analyses/syntheses using modern instrumentation.
4. The student will articulate scientific information through oral communication.
5. The student will articulate scientific information through written communication.
6. The student will demonstrate ability to integrate knowledge content, laboratory skill, critical thinking and problem solving, and communication skills via participation in research projects.
General Education Core Curriculum Objectives: There are no specific general education core curriculum objectives in this course. This course is not a general education core curriculum course.
Course Objective: The student should demonstrate the practicing chemist's role in an industrial plant setting.
Student Learning Outcomes: Upon completion of this course, students will be able to:
• work independently, responsibly, and efficiently to solve problems occurring in an industrial plant setting.
• demonstrate clear oral and written communication skills. (PLO 4, 5)
• demonstrate an ability to find and use applicable procedures and chemical methods. (PLO 3)