Misplaced Pages

#908091

60-465: Trichloroethyl chloroformate is used in organic synthesis for the introduction of the trichloroethyl chloroformate (Troc) protecting group for amines , thiols and alcohols . It readily cleaves vs other carbamates and can be used in an overall protecting group strategy. The troc group is traditionally removed via Zn insertion in the presence of acetic acid, resulting in elimination and decarboxylation. 2,2,2-Trichloroethoxycarbonyl ( Troc ) group

120-429: A Grignard reagent , and carboxylation . In the synthesis of Ibuprofen proposed by Kjonass et al ., p -isobutylacetophenone, the starting material, is reduced with sodium borohydride (NaBH 4 ) to form an alcohol functional group . The resulting intermediate is acidified with HCl to create a chlorine group. The chlorine group is then reacted with magnesium turnings to form a Grignard reagent. This Grignard

180-428: A Kuderna-Danish concentrator to efficiently separate a low boiling extraction solvent such as methylene chloride from volatile but higher boiling extract components (e.g., after the extraction of organic contaminants in soil). The Widmer column was developed as a doctoral research project by student Gustav Widmer at ETH Zurich in the early 1920s, combining a Golodetz-type arrangement of concentric tubes and

240-601: A retrosynthetic framework , a type of synthetic design developed by Elias James Corey , for which he won the Nobel Prize in Chemistry in 1990. In this approach, the synthesis is planned backwards from the product, obliging to standard chemical rules. Each step breaks down the parent structure into achievable components, which are shown via the use of graphical schemes with retrosynthetic arrows (drawn as ⇒, which in effect, means "is made from"). Retrosynthesis allows for

300-470: A blown glass ring seal), forming a water jacket, and is fitted with side ports near the ends for cooling fluid inflow and outflow. The ends of the inner tube, that carries the vapor and condensed liquid, are open. Compared to the simple air-cooled tube, the Liebig condenser is more efficient at removing the heat of condensation and at maintaining the inner surface a stable low temperature. The West condenser

360-459: A given compound, and comes in many forms. Examples of common characterization methods include: nuclear magnetic resonance (NMR), mass spectrometry , Fourier-transform infrared spectroscopy (FTIR), and melting point analysis. Each of these techniques allow for a chemist to obtain structural information about a newly synthesized organic compound. Depending on the nature of the product, the characterization method used can vary. Organic synthesis

420-424: A layer of gas with even lower vapor contents right next to the condensing surface, further lowering the boiling point. Therefore, the condenser's design must be such that the gas is well-mixed and/or that all of it is forced to pass very close to the condensation surface. Finally, if the input to the condenser is a mixture of two or more miscible liquids (as is the case in fractional distillation ), one must consider

480-467: A mixture is heated until the more volatile components boil off, the vapors are condensed, and collected in a separate container. In reflux, a reaction involving volatile liquids is carried out at their boiling point, to speed it up; and the vapors that inevitably come off are condensed and returned to the reaction vessel. In Soxhlet extraction, a hot solvent is infused onto some powdered material, such as ground seeds, to leach out some poorly soluble component;

540-505: A much more diverse choice of enantiomerically pure materials. Using techniques developed by Robert B. Woodward paired with advancements in synthetic methodology, chemists have been able synthesize stereochemically selective complex molecules without racemization. Stereocontrol provides the target molecules to be synthesized as pure enantiomers (i.e., without need for resolution). Such techniques are referred to as stereoselective synthesis . Many synthetic procedures are developed from

600-426: A new synthetic route can be developed and tested. For practical, industrial applications additional reaction conditions must be considered to include the safety of both the researchers and the environment, as well as product purity. Organic Synthesis requires many steps to separate and purify products. Depending on the chemical state of the product to be isolated, different techniques are required. For liquid products,

660-416: A racemic mixture. Early examples include stereoselective hydrogenations (e.g., as reported by William Knowles and Ryōji Noyori ) and functional group modifications such as the asymmetric epoxidation by Barry Sharpless ; for these advancements in stereochemical preference, these chemists were awarded the Nobel Prize in Chemistry in 2001. Such preferential stereochemical reactions give chemists

SECTION 10

#1732783447909

720-417: A reaction mixture using filtration techniques. To obtain solid products a vacuum filtration apparatus can be used. Vacuum filtration uses suction to pull liquid through a Büchner funnel equipped with filter paper, which catches the desired solid product. This process removes any unwanted solution in the reaction mixture by pulling it into the filtration flask and leaving the desired product to collect on

780-509: A separate piece of equipment, or may be only a part of a condenser of another type. Cold fingers are also used to condense vapors produced by sublimation in which case the result is a solid that adheres to the finger and must be scraped off, or as a cold-trap , where the liquid or solid condensate is not intended to return to the source of the vapor (often used to protect vacuum pumps and/or prevent venting of harmful gasses). The Friedrichs condenser (sometimes incorrectly spelled Friedrich's )

840-401: A separate piece of equipment. Straight tube condensers are no longer widely used in research laboratories, but may be used in special applications and simple school demonstrations. The still head is another ancient type of air-cooled condenser. It consists of a roughly globular vessel with an opening at the bottom, through which the vapor is introduced. The vapor condenses on the inner wall of

900-423: A spiral coil running the length of the condenser through which coolant flows, and this coolant coil is jacketed by the vapor–condensate path. A Dimroth condenser , also known as a spiral condenser , named after Otto Dimroth , is somewhat similar to the coil condenser; it has an internal double spiral through which coolant flows such that the coolant inlet and outlet are both at the top. The vapors travel through

960-442: A very common separation technique is liquid–liquid extraction and for solid products, filtration (gravity or vacuum) can be used. Liquid–liquid extraction uses the density and polarity of the product and solvents to perform a separation. Based on the concept of "like-dissolves-like", non-polar compounds are more soluble in non-polar solvents, and polar compounds are more soluble in polar solvents. By using this concept,

1020-437: Is a wide glass tube divided into sections (usually 3 to 6) by horizontal glass partitions or constrictions. Each partition has a hole, into which seats a hollow glass bead with an inverted "teardrop" shape. Vigreux-like glass "fingers" limit the vertical motion of each bead. These floating glass stoppers act as check valves, closing and opening with vapor flow, and enhancing vapor-condensate mixing. A Snyder column can be used with

1080-467: Is an important chemical process that is integral to many scientific fields. Examples of fields beyond chemistry that require organic synthesis include the medical industry, pharmaceutical industry, and many more. Organic processes allow for the industrial-scale creation of pharmaceutical products. An example of such a synthesis is Ibuprofen . Ibuprofen can be synthesized from a series of reactions including: reduction , acidification , formation of

1140-549: Is carboxylated and the resulting product is worked up to synthesize ibuprofen. This synthetic route is just one of many medically and industrially relevant reactions that have been created, and continued to be used. Condenser (laboratory) In chemistry , a condenser is laboratory apparatus used to condense vapors  – that is, turn them into liquids – by cooling them down. Condensers are routinely used in laboratory operations such as distillation , reflux , and extraction . In distillation,

1200-498: Is circulated, to provide a more effective cooling. Laboratory condensers are usually made of glass for chemical resistance, for ease of cleaning, and to allow visual monitoring of the operation; specifically, borosilicate glass to resist thermal shock and uneven heating by the condensing vapor. Some condensers for dedicated operations (like water distillation ) may be made of metal. In professional laboratories, condensers usually have ground glass joints for airtight connection to

1260-430: Is essentially the same as of that surface. Therefore, the primary consideration in the design or choice of a condenser is to ensure that its inner surface is below the liquid's boiling point. As the vapor condenses, it releases the corresponding heat of vaporization , that tends to raise the temperature of the condenser's inner surface. Therefore, a condenser must be able to remove that heat energy quickly enough to keep

SECTION 20

#1732783447909

1320-438: Is important to understand the chemical reactions , reagents , and conditions required in each step to guarantee successful product formation. When determining optimal reaction conditions for a given synthesis, the goal is to produce an adequate yield of pure product with as few steps as possible. When deciding conditions for a reaction, the literature can offer examples of previous reaction conditions that can be repeated, or

1380-410: Is largely used as a protecting group for amines in organic synthesis . Organic synthesis A total synthesis refers to the complete chemical synthesis of molecules from simple, natural precursors . Total synthesis is accomplished either via a linear or convergent approach. In a linear synthesis —often adequate for simple structures—several steps are performed sequentially until

1440-412: Is most favorable to use but the drawback of this condenser is that as the vapors get condensed, it tends to move them up in the tube to evaporate which will also lead to the flooding of solution mixture. It may also be called Inland Revenue condenser due to the application for which it was developed. A coil condenser is essentially a Graham condenser with an inverted coolant–vapor configuration. It has

1500-431: Is not exclusive, since several types can be used in both modes. The simplest type of condenser is a straight tube , cooled only by the surrounding air. The tube is held in a vertical or oblique position, and the vapor is fed through the upper end. The heat of condensation is carried away by convection . The neck of the retort is a classical example of a straight tube condenser. However, this kind of condenser may also be

1560-401: Is variant of the Liebig type, with a more slender design, with cone and socket. The fused-on narrower coolant jacket may render more efficient cooling with respect to coolant consumption. The Allihn-condenser or bulb condenser is named after Felix Richard Allihn (1854–1915). The Allihn-condenser consists of a long glass tube with a water jacket . A series of bulbs on the tube increases

1620-551: The French glass blower Henri Vigreux  [ fr ] (1869–1951) who invented it in 1904, consists of a wide glass tube with multiple internal glass "fingers" that point downwards. Each "finger" is created by melting a small section of the wall and pushing the soft glass inwards. The vapor that enters from the lower opening condenses on the fingers and drips down from them. It is usually air-cooled, but may have an outer glass jacket for forced fluid cooling. The Snyder column

1680-426: The partial pressure of its vapor must be considered when obtaining its condensation temperature. For example, if the gas entering the condenser is a mixture of 25% ethanol vapor and 75% carbon dioxide (by moles) at 100 kPa (typical atmospheric pressure), the condensation surface must be kept below 48 °C, the boiling point of ethanol at 25 kPa. Moreover, if the gas is not pure vapor, condensation will create

1740-499: The Dufton-type rod-with-spiral core. It consists of four concentric glass tubes and a central glass rod, with a thinner glass rod coiled around it to increase the surface area. The two outer tubes (#3 and #4) form an insulating dead air chamber (shaded). Vapor rises from a boiling flask into space (1), proceeds up through the space between tubes #2 and #3, then down the space between tubes #1 and #2, and finally up between tube #1 and

1800-405: The central rod. Arriving at space (3), vapor is then directed via a distillation head (glass branching adapter) to cooling and collection. A so-called modified Widmer column design was reported as being in wide use, but undocumented, by L. P. Kyrides in 1940. A packed column is a condenser used in fractional distillation . Its main component is a tube filled with small objects to increase

1860-421: The condensation takes place. The Liebig condenser is the simplest design with circulating coolant, easy to build and inexpensive. It is named after Justus von Liebig, who perfected an earlier design by Weigel and Göttling and popularized it. It consists of two concentric straight glass tubes, the inner one being longer and protruding at both extremities. The ends of the outer tube are sealed (usually by

2,2,2-Trichloroethoxycarbonyl chloride - Misplaced Pages Continue

1920-420: The cooling fluid. The flow may be open, from a tap to a sink, and driven only by the water pressure in the tap. Alternatively, a closed system may be used, in which the water is drawn by a pump from a tank, possibly refrigerated , and returned to it. Water-cooled condensers are suitable for liquids with boiling points well above 0 °C, and can easily condense vapours with boiling points much higher than that of

1980-573: The cooling surface, so that the condenser can be shorter than an equivalent Liebig condenser. According to Alan Gall, archivist of the Institute of Science and Technology, Sheffield, England, the 1981 catalog of Adolf Gallenkamp & Co. of London (makers of scientific apparatus) states that the Davies condenser was invented by James Davies, a director of the Gallenkamp company. In 1904, Gallenkamp

2040-401: The design of condenser systems becomes a precise engineering science. In order for a substance to condense from a pure vapor, the pressure of the latter must be higher than the vapor pressure of the adjacent liquid; that is, the liquid must be below its boiling point at that pressure. In most designs, the liquid is only a thin film on the inner surface of the condenser, so its temperature

2100-458: The desired product. Robert Burns Woodward , who received the 1965 Nobel Prize for Chemistry for several total syntheses including his synthesis of strychnine , is regarded as the grandfather of modern organic synthesis. Some latter-day examples of syntheses include Wender's , Holton's , Nicolaou's , and Danishefsky's total syntheses of the anti-cancer drug paclitaxel (trade name Taxol). Before beginning any organic synthesis, it

2160-457: The filter paper. Liquid products can also be separated from solids by using gravity filtration . In this separatory method, filter paper is folded into a funnel and placed on top of a reaction flask. The reaction mixture is then poured through the filter paper , at a rate such that the total volume of liquid in the funnel does not exceed the volume of the funnel. This method allows for the product to be separated from other reaction components by

2220-530: The force of gravity, instead of a vacuum. Most complex natural products are chiral, and the bioactivity of chiral molecules varies with the enantiomer . Some total syntheses target racemic mixtures, which are mixtures of both possible enantiomers . A single enantiomer can then be selected via enantiomeric resolution .   As chemistry has developed methods of stereoselective catalysis and kinetic resolution have been introduced whereby reactions can be directed, producing only one enantiomer rather than

2280-412: The form of a vertical tube that is cooled from the inside, that is to be immersed in the vapor while supported at the upper end only. This may be either flow-cooled, with both coolant ports at the top, or open-topped where liquid or solid coolant is simply placed inside. The vapor is meant to condense on the rod and drip down from the free end, and eventually reach the collecting vessel. A cold finger may be

2340-493: The glass against gravity. This flow of water cools any escaping substrate and condenses it back into the reaction flask to continue reacting and ensure that all product is contained. The use of reflux condensers is an important technique within organic syntheses and is utilized in reflux steps, as well as recrystallization steps. When being used for refluxing a solution, reflux condensers are fitted and closely observed. Reflux occurs when condensation can be seen dripping back into

2400-399: The jacket from bottom to top. Dimroth condensers are more effective than conventional coil condensers. They are often found in rotary evaporators which may use a more elaborate arrangement with several spirals. There also exists a version of Dimroth condenser with an external jacket, like in a Davies condenser, to further increase the cooling surface. A cold finger is a cooling device in

2460-524: The late 18th century. Several designs that are still in common use were developed and became popular in the 19th century, when chemistry became a widely practiced scientific discipline. Designing and maintaining systems and processes using condensers requires that the heat of the entering vapor never overwhelm the ability of the chosen condenser and cooling mechanism; as well, the thermal gradients and material flows established are critical aspects, and as processes scale from laboratory to pilot plant and beyond,

2,2,2-Trichloroethoxycarbonyl chloride - Misplaced Pages Continue

2520-523: The layers, the product-containing layer can be isolated and the other layer can be removed. Many reactions require heat to increase reaction speed. However, in many situations increased heat can cause the solvent to boil uncontrollably which negatively affects the reaction, and can potentially reduce product yield. To address this issue, reflux condensers can be fitted to reaction glassware. Reflux condensers are specially calibrated pieces of glassware that possess two inlets for water to run in and out through

2580-425: The molecule is complete; the chemical compounds made in each step are called synthetic intermediates . Most often, each step in a synthesis is a separate reaction taking place to modify the starting materials. For more complex molecules, a convergent synthetic approach may be better suited. This type of reaction scheme involves the individual preparations of several key intermediates, which are then combined to form

2640-442: The reaction flask from the reflux condenser; 1 drop every second or few seconds. For recrystallization , the product-containing solution is equipped with a condenser and brought to reflux again. Reflux is complete when the product-containing solution is clear. Once clear, the reaction is taken off heat and allowed to cool which will cause the product to re-precipitate, yielding a purer product. Solid products can be separated from

2700-543: The reaction to produce a higher yield . Previously, this type of reaction was reserved for large-scale industrial chemistry but has recently transitioned to bench-scale chemistry to improve the efficiency of reactions on a smaller scale. Currently integrating automated synthesis into their work is SRI International , a nonprofit research institute. Recently SRI International has developed Autosyn, an automated multi-step chemical synthesizer that can synthesize many FDA -approved small molecule drugs. This synthesizer demonstrates

2760-407: The relative solubility of compounds can be exploited by adding immiscible solvents into the same flask and separating the product into the solvent with the most similar polarity. Solvent miscibility is of major importance as it allows for the formation of two layers in the flask, one layer containing the side reaction material and one containing the product. As a result of the differing densities of

2820-455: The solvent is then automatically distilled out of the resulting solution, condensed, and infused again. Many different types of condensers have been developed for different applications and processing volumes. The simplest and oldest condenser is just a long tube through which the vapors are directed, with the outside air providing the cooling. More commonly, a condenser has a separate tube or outer chamber through which water (or some other fluid)

2880-722: The surface area and the number of theoretical plates . The tube can be the inner conduit of some other type, such as Liebig or Allhin. These columns can achieve theoretical plate counts of 1–2 per 5 cm of packed length. A large variety of packing materials and object shapes has been used, including beads, rings, or helices (such as Fenske rings Raschig or Lessing rings) of glass, porcelain , aluminum , copper , nickel , or stainless steel ; nichrome and inconel wires (akin to Podbielniak columns ), stainless steel gauze ( Dixon rings ), etc. Specific combinations are known as Hempel , Todd , and Stedman columns. Condensers with forced-circulation cooling usually employ water as

2940-428: The surface area upon which the vapor constituents may condense. Ideally suited for laboratory-scale refluxing ; indeed, the term reflux condenser often means this type specifically. A Davies condenser , also known as a double surface condenser, is similar to the Liebig condenser, but with three concentric glass tubes instead of two. The coolant circulates in both the outer jacket and the central tube. This increases

3000-435: The temperature low enough, at the maximum rate of condensation that is expected to occur. This concern can be addressed by increasing the area of the condensation surface, by making the wall thinner, and/or by providing a sufficiently effective heat sink (such as circulating water) on the other side of it. The condenser must also be dimensioned so that the condensed liquid can flow out at the maximum rate (mass over time) that

3060-431: The vapor input at the top and the liquid output at the bottom. The countercurrent condensers are intended to return the liquid toward the source of the vapor, as required in reflux and fractional distillation. They are usually mounted vertically, above the source of the vapor, that enters them from the bottom. In both cases, the condensed liquid is allowed to flow back to the source by its own weight. The classification

SECTION 50

#1732783447909

3120-413: The vapor is expected to enter it. Care must also be taken to prevent the boiling liquid to enter the condenser as splattering from explosive boiling , or droplets created as bubbles pop. Additional considerations apply if the gas inside the condenser is not pure vapor of the desired liquid, but a mixture with gases that have a much lower boiling point (as may occur in dry distillation , for example). Then

3180-457: The vapor pressure and the percentage of the gas for each component, which depends on the composition of the liquid as well as its temperature; and all these parameters typically vary along the condenser. Most condensers can be divided in two broad classes. The concurrent condensers receive the vapor through one port and deliver the liquid through another port, as required in simple distillation. They are usually mounted vertically or tilted, with

3240-435: The vapor source and the liquid receptacle; however, flexible tubing of an appropriate material is often used instead. The condenser may also be fused to a boiling flask as a single glassware item, as in the old retort and in devices for microscale distillation . The water-cooled condenser, which was popularized by Justus von Liebig , was invented by Weigel , Poisonnier , and Gadolin , and perfected by Göttling , all in

3300-421: The versatility of substrates and the capacity to potentially expand the type of research conducted on novel drug molecules without human intervention. Automated chemistry and the automated synthesizers used demonstrate a potential direction for synthetic chemistry in the future. Necessary to organic synthesis is characterization . Characterization refers to the measurement of chemical and physical properties of

3360-524: The vessel, and drips along it, collecting at the bottom of the head and then draining through a tube to a collecting vessel below. A raised lip around the input opening prevents the liquid from spilling through it. As in the tube condenser, the heat of condensation is carried away by natural convection. Any vapor that does not condense in the head may still condense in the neck. Still head type condensers are now rarely used in laboratories, and are usually topped by some other type of reflux condenser where most of

3420-506: The visualization of desired synthetic designs. A recent development within organic synthesis is automated synthesis . To conduct organic synthesis without human involvement, researchers are adapting existing synthetic methods and techniques to create entirely automated synthetic processes using organic synthesis software . This type of synthesis is advantageous as synthetic automation can increase yield with continual "flowing" reactions. In flow chemistry , substrates are continually fed into

3480-434: The water. Other cooling fluids may be used instead of water. Air with forced circulation can be effective enough for situations with high boiling point and low condensation rate. Conversely, low-temperature coolants , such as acetone cooled by dry ice or chilled water with antifreeze additives, can be used for liquids with low boiling point (like dimethyl ether , b.p. −23.6 °C). Open-topped cold fingers can use

3540-420: Was invented by Fritz Walter Paul Friedrichs , who published a design for this type of condenser in 1912. It consists of a large water-cooled finger tightly fitted inside a wide cylindrical housing. The finger has a helical ridge along its length, so as to leave a narrow helical path for the vapor. This arrangement forces the vapor to spend a long time in contact with the finger. The Vigreux column , named after

3600-412: Was offering "Davies' Condensers" for sale:. In 1920, Gallenkamp listed "J. Davies" as a director of the company. A Graham or Grahams condenser has a coolant-jacketed spiral coil running the length of the condenser serving as the vapor–condensate path. This is not to be confused with the coil condenser. The coiled condenser tubes inside will provide more surface area for cooling and for this reason it

#908091