Claiscn-Schmidt condensation

Mixed aldol condensations in which a ketone reacts with an aromatic aldehyde are known as Claisen-Schmidt condensations  [c.775]

Claisen-Schmidt condensation (Section 18 10) A mixed al dol condensation involving a ketone enolate and an aro matic aldehyde or ketone  [c.1279]

Claisen-Schmidt condensation  [c.225] Catalyzed. Depending on the nature of the hydrocarbon groups attached to the carbonyl, ketones can either undergo self-condensation, or condense with other activated reagents, in the presence of base. Name reactions which describe these conditions include the aldol reaction, the Darzens-Claisen condensation, the Claisen-Schmidt condensation, and the Michael reaction.  [c.487]

Mixed aldol condensations in which a ketone reacts with an aromatic aldehyde are known as Claisen-Schmidt condensations.  [c.775]

Claisen-Schmidt condensation (Section 18.10) A mixed al-dol condensation involving a ketone enolate and an aromatic aldehyde or ketone.  [c.1279]

Claisen-Schmidt reaction. Aromatic aldehydes condense with aliphatic or mixed alkyl-aryl ketones in the presence of aqueous alkali to form ap-unsaturated ketones  [c.709]

Ludwig Claisen was a Ger man chemist who worked during the last two decades of the nineteenth century and the first two decades of the twentieth His name is associated with three reac tions The Claisen-Schmidt reaction was presented in Section 18 10 the Claisen condensation is discussed in this section and the C/a/sen rearrangement will be intro duced in Section 24 13  [c.887]

Claisen-Schmidt reaction (Section 18.10) A mixed aldol condensation in which an aromatic aldehyde reacts with an enolizable aldehyde or ketone.  [c.783]

Ludwig Claisen was a German chemist who worked during the last two decades of the nineteenth century and the first two decades of the twentieth. His name is associated with three reactions. The Claisen-Schmidt reaction was presented in Section 18.10, the Claisen condensation is discussed in this section, and the Claisen rearrangement will be introduced in Section 24.13.  [c.887]

This condensate was washed with dilute caustic soda solution and dried over calcium chloride. The exit gases from this condenser were scrubbed with water and dilute caustic soda solution, dried and passed to a condenser cooled with a mixture of solid carbon dioxide and trichloroethylene which caused the unchanged 1,1,1-trifluoro-2-chloroethane to condense. This second condensate was then combined with the first and the mixture was fractionally distilled.  [c.754]

Phosphorus tribromide. Into a 500 ml. three-necked flask, provided with a mechanical stirrer (sealed with dry carbon tetrachloride), a dropping funnel and a reflux condenser, are placed 28 g. of purified red phosphorus (Section II,50,J), and 200 ml. of carbon tetrachloride (dried over anhydrous calcium chloride). Dry bromine (198 g. 63-5 ml.) is placed in the dropping funnel and added to the vigorously stirred contents of the flask at the rate of about 3 drops per second. A little hydrogen bromide is evolved so that the preparation should be carried out in a fume cupboard. After all the bromine has been added, the mixture is refluxed for 15 minutes by immersing the flask in a water bath at 80-90°. The clear solution is then decanted through a fluted filter paper, and the carbon tetrachloride is distilled off through a short column (e.g., the  [c.189]

A. 2-Methyl-2-butene. Assemble an apparatus consisting of a 500 ml. round-bottomed flask, a Hempel fractionating column (filled, say, with glass rings or with or i" porcelain rings) (1), a Liebig condenser, and a bent adapter fitted by means of a cork into a filter flask as receiver (compare Fig. 77, 76, 1). Fit a thermometer (preferably 0-110° range) to the top of the column. The amylene is a highly volatile and inflammable liquid, and the necessary precautions against fire must be taken (e.g., absence of flames in the vicinity, lead-off tube from the filter flask, etc.). Disconnect the flask. Cautiously add 25 ml. of concentrated sulphuric acid slowly and with constant stirring to 50 ml. of water contained in a small beaker (2). Cool the dilute acid, transfer it to the flask, add 40 ml. of tertiary amyl alcohol and a few fragments of porous porcelain. Reassemble the apparatus completely, making sure that all the corks are secure, and arrange for the flask to be heated on a water bath or steam bath. Heat gently and when distillation commences, regulate the temperature of the bath so that the temperature on the thermometer does not exceed 40-41° (1-2 drops per second). Stop the distillation when the temperature can no longer be maintained below 41°. The product is practically pure, but contains a little water (3). Transfer the distillate to a small conical flask and dry it over 1-5-2 g. of anhydrous magnesium sulphate or calcium chloride. The flask must be well stoppered owing to the volatility of the hydrocarbon. The yield is 15-16 g. Pure 2-methyl-2-butene boils at 38 5°.  [c.239]

In a 2-1. three-necked flask, fitted with a dropping funnel, a stopcock, and a long condenser, is placed 556 g. (2 moles) (Note i) of methyl isothiourea sulfate (Org. Syn. 12, 52). From the end of the condenser the gas is led into a safety trap, consisting of an empty gas-washing bottle, which in turn is cormected to a second wash bottle containing 100 cc. of dilute sulfuric acid (i volume of concentrated sulfuric acid to 2 volumes of water). The gas is then passed through a tower (height about 30 cm.) containing calcium chloride into an empty 2-I. flask, which acts as a trap, and finally into a 2-I. flask containing the absorption mixture. This consists of 80.5 g. (3 5 gram atoms) of clean sodium dissolved in 1500 cc. of absolute alcohol. The exit tube from the absorption mixture is attached to an empty r-1. flask and this is cormected with a i-l. flask containing 500 cc. of a saturated solution of lead acetate (Note 2). The exit tube from the latter leads to a suction pump. A very slow current of air is drawn through the apparatus while 800 cc. of cold 5 N  [c.54]

During this time, a second system is assembled, consisting of a 500-ml. three-necked flask fitted with a mechanical stirrer, a reflux condenser topped with a calcium chloride-filled drying tube attached to a xylene-filled bubbler, and a pressure-equalizing dropping funnel through which a slow stream of nitrogen is passed into the flask. In the flask are placed 200 ml. of sodium-dried xylene and 11.5 g. (0.5 gram atom) of sodium. The mixture is heated to boiling, and the sodium is finely dispersed by  [c.31]

The mechanism of the Claisen condensation of ethyl acetate is presented in Figure 21.1. The first two steps of the mechanism are analogous to those of aldol addition (Section 18.9). An enolate ion is generated in step 1, which undergoes nucleophilic addition to the carbonyl group of a second ester molecule in step 2. The species formed in this step is a tetrahedral intermediate of the same type that we encountered in our discussion of nucleophilic acyl substitution of esters. It dissociates by expelling an ethoxide ion, as shown in step 3, which restores the carbonyl group to give the p-keto ester. Steps 1 to 3 show two different types of ester reactivity one molecule of the ester gives rise to an enolate the second molecule acts as an acylating agent.  [c.887]

The isocitrate lyase reaction (Figure 20.29) produces succinate, a four-carbon product of the cycle, as well as glyoxylate, which can then combine with a second molecule of acetyl-CoA. Isocitrate lyase catalyzes an aldol cleavage and is similar to the reaction mediated by aldolase in glycolysis. The malate synthase reaction (Figure 20.30), a Claisen condensation of acetyl-CoA with the aldehyde of glyoxylate to yield malate, is quite similar to the citrate synthase reaction. Compared with the TCA cycle, the glyoxylate cycle (a) contains only five steps (as opposed to eight), (b) lacks the COg-liberating reactions, (c) consumes two molecules of acetyl-CoA per cycle, and (d) produces four-carbon units (oxaloacetate) as opposed to one-carbon units.  [c.670]

Two possible mechanisms exist for the Friedlander reaction. The first involves initial imine formation followed by intramolecular Claisen condensation, while the second reverses the order of the steps. Evidence for both mechanisms has been found, both  [c.411]

The above are examples of the Claisen - Schmidt reaction. The formation of p-nitrostyrenes by reaction of nitroalkanes with aromatic aldehydes in the presence of aqueous alkali may be included under the Claisen- hmidt condensation  [c.709]

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis Bucherer reaction Cannizzaro reaction Claisen aldoi condensation Claisen condensation Claisen-Schmidt reaction. Clemmensen reduction Darzens glycidic ester condensation Diazoamino-aminoazo rearrangement Dieckmann reaction Diels-Alder reaction Doebner reaction Erlenmeyer azlactone synthesis Fischer indole synthesis Fischer-Speior esterification Friedel-Crafts reaction  [c.1210]

AldolRea.ctlons, In the same way, hydroxybenzaldehydes react readily with aldehydes and ketones to form a,P-unsaturated carbonyl compounds in the Claisen-Schmidt or crossed-aldol condensation (60).  [c.506]

A. Purification train. Oxygen from a cylinder (A) fitted with a reducmg valve (5) is led to a pressure release tube (C). This is a T-tube, the long arm of which dips into a test tube of mercury. The height of the mercury column should be about 2 to 3 cm. The release tube is connected through a stopcock (1) to a 40-cm. condenser jacket (D). This is filled with 4-mesh anhydrous calcium chloride held in place by plugs of glass wool at the ends. A second condenser jacket ( ) is filled about halfway with 4-mesh soda lime, then a 4- to 6-in. layer of anhydrous calcium chloride, and the remainder of the tube is packed with glass wool. The ends of the condensers are closed with rubber stoppers. Part F is a flowmeter, the U-tube of which should be about 20 cm. long. The bore of the capillary should be about 0.5 mm. in diameter. The flowmeter tube is filled about half full  [c.63]

Mix 40 g. (51 ml.) of isopropyl alcohol with 460 g. (310 ml.) of constant boiling point hydrobromic acid in a 500 ml. distilling flask, attach a double surface (or long Liebig) condenser and distil slowly (1-2 drops per second) until about half of the liquid has passed over. Separate the lower alkyl bromide layer (70 g.), and redistil the aqueous layer when a further 7 g. of the crude bromide will be obtained (1). Shake the crude bromide in a separatory funnel successively with an equal volume of concentrated hydrochloric acid (2), water, 5 per cent, sodium bicarbonate solution, and water, and dry with anhydrous calcium chloride. Distil from a 100 ml. flask the isopropyl bromide passes over constantly at 59°. The yield is 66 g.  [c.277]

Mix 30 g. (38 ml.) of iaopropyl alcohol with 450 g. (265 ml.) of constant boiling point hydriodic acid (57 per cent.) (Section 11,49,2) in a 500 ml. distilling flask, attach a condenser for downward distillation, and distil slowly (1-2 drops per second) from an air bath (compare Fig. II, 5, 3). When about half the liquid has passed over, stop the distillation. Separate the lower layer of crude iodide (80 g.). Redistil the aqueous layer and thus recover a further 5 g. of iodide from the flrst quarter of the distillate (1). Wash the combined iodides with an equal volume of concentrated hydrochloric acid, then, successively, with water, 5 per cent, sodium carbonate solution, and water. Dry with anhydrous calcium chloride and distil. The isopropyl iodide distils constantly at 89°.  [c.285]

The experimental conditions for conducting the above reaction in the presence of dimethylformamide as a solvent are as follows. In a 250 ml. three-necked flask, equipped with a reflux condenser and a tantalum wire Hershberg-type stirrer, place 20 g. of o-chloronitrobenzene and 100 ml. of diinethylform-amide (dried over anhydrous calcium sulphate). Heat the solution to reflux and add 20 g. of activated copper bronze in one portion. Heat under reflux for 4 hours, add another 20 g. portion of copper powder, and continue refluxing for a second 4-hour period. Allow to cool, pour the reaction mixture into 2 litres of water, and filter with suction. Extract the solids with three 200 ml. portions of boiling ethanol alternatively, use 300 ml. of ethanol in a Soxhlet apparatus. Isolate the 2 2- dinitrodiphenyl from the alcoholic extracts as described above the 3ueld of product, m.p. 124-125°, is 11 - 5 g.  [c.528]

JVJV-Diethylhydrazine. Fit a 1-litre three-necked flask with a double surface reflux condenser, a mercury-sealed stirrer and a dropping funnel, and insert calcium chloride guard tubes into the openings of the reflux condenser and dropping funnel. The apparatus must be dry. Place 10-0 g. of finely powdered lithium aluminium hydride and 500 ml. of sodium-dried ether in the flask, stir for 10 minutes, and add a solution of 23 -5 g. of diethyl nitrosamine (Section 111,124) in 135 ml. of anhydrous ether at the rate of 2-3 drops per second. After about 20 minutes, the ether refluxes gently and a white sohd separates henceforth adjust the rate of addition to maintain the reaction under control. After the addition of the nitrosamine is complete (about 1 hour), continue the vigorous stirring for 10 minutes, and then add an excess of ethyl acetate to decompose the residual hthium aluminium hydride. Now introduce 50 ml. of ION sodium hydroxide solution, stir for 10 minutes, filter with suction, and wash the residue with two 50 ml. portions of ether. Dry the combined filtrate and washings first over potassium hydroxide pellets and then over anhydrous calcium sulphate, distil through an efficient fractionating column (e.g.. a 10 vacuum-jacketed Widmer column) and collect the oa-diethylhydrazine at 98-99 5°. The yield is 10 g.  [c.880]

Cholestenone. Place a mixture of 20 g. of purified cholesterol (m.p. 149°-150° dried to constant weight at 80-100°), 150 ml. of A.R. acetone and 200 ml. of sodium-dried benzene in a dry 1-litre round-bottomed flask fitted with a reflux condenser and calcium chloride guard tube. Introduce a boiling tube (Fig. 1,3, 1) to prevent bumping. Heat the mixture to boiling in an oil bath at 75-85°, add a solution of 16 g. of aluminium tert.-butoxide in 100 ml. of anhydrous benzene in one portion to the boihng solution. The mixture becomes cloudy and develops a yellow colour in 10 to 15 minutes. Continue gentle boiling at a bath temperature of 75-85° for 8 hours. Treat the cold mixture with 40 ml. of water, then with 100 ml. of 10 per cent, sulphuric acid, shake vigorously and transfer to a 1-Utre separatory funnel. Dilute the mixture with 300 ml. of water, shake for 5 minutes (filter, if necessary), then run off the yellow aqueous layer into a second separatory funnel and extract the latter with 25 ml. of benzene. Wash the combined benzene extracts thoroughly with water, dry with anhydrous magnesium sulphate and remove the solvent (steam bath final traces at 60° under vacuum of water pump). The yellow oily residue solidifies when it is cooled in an ice-salt bath and scratched with a glass rod keep a small portion for seeding in the subsequent crys-taUisation. Dissolve the solid in a warm mixture of 14 ml. of acetone and 20 ml. of methanol, allow the solution to cool very slowly and seed, if necessary. When the bulk of the solid has crystallised, keep the mixture at 0° for 24 hours, filter with suction, wash with 20 ml. of ice-cold methanol, and dry in a vacuum desiccator. The yield of almost colourless cholestenone, m.p. 79-80°, is 17 g.  [c.888]

The mechanism of the Claisen condensation of ethyl acetate is presented m Fig ure 21 1 The first two steps of the mechanism are analogous to those of aldol addition (Section 18 9) An enolate ion is generated m step 1 which undergoes nucleophilic addi tion to the carbonyl group of a second ester molecule m step 2 The species formed m this step IS a tetrahedral intermediate of the same type that we encountered m our dis cussion of nucleophilic acyl substitution of esters It dissociates by expelling an ethox ide ion as shown m step 3 which restores the carbonyl group to give the p keto ester Steps 1 to 3 show two different types of ester reactivity one molecule of the ester gives rise to an enolate the second molecule acts as an acylatmg agent  [c.887]

Produced- W terSoftening. In secondary-oil recovery projects involving steam injection to heat oil remaining in strata and to make it more fluid, the steam condenses and the water becomes contaminated with calcium, magnesium, and other salts (see Petroleum). This water is cycled back to steam generators after it is separated from the oil. However, severe scaling results if the water is not softened before the generator. Softening is a challenge because NaCl concentrations are usuaHy in the several thousand mg/L range, or higher. The greater the Na" concentration with respect to Ca " and Mg ", the lower the degree of softening and the lower the operating capacity. At the lower total salt concentrations, two columns of strong acid resins are used in series. The second column acts as a poHsher and is regenerated with an NaCl solution in an upflow situation. At higher total salt concentrations, a weak acid resin, which has greater selectivity for divalent cations, is used in place of the strong acid resin. At very high total salt concentrations, a chelate resin is used in place of the weak acid resin.  [c.386]

The driving force for moving the magnesium vapor to the condenser is the volume change of the magnesium vapor going from a vapor to a Hquid or sohd state. A small amount of argon [7440-37-1] is purged to the reaction vessel through the feed system to minimise the condensation of magnesium metal on the colder parts of the feed system. The process operates on a 16—24 hour cycle, with the cycle spHt in two halves. The end of the first half is used to tap slag and refill the feed system with dolime. The end of the second half is used to replenish all feed materials, tap slag, and remove the filled magnesium cmcible. Thus in every cycle, the condenser assembly shown in Figure 8 is removed and a clean, empty unit is attached to the reduction vessel for continued operation on the next cycle. The slag is removed from the furnace using an oxygen [7782-44-7] lance to penetrate a clay plug or a carbonaceous plug. The calcium aluminosiUcate slag is a cementaceous product and can be used as a cement or liming agent.  [c.321]

The crude chlorinated mixture is steam-distilled in the special apparatus to obtain thiocarbonyl perchloride and to decompose the sulfur chloride. In flask A is placed 1200 cc. of water which is heated to boiling by means of the ring burner. Steam is passed in through tubes B and C. The chlorinated mixture is placed in the separatory funnel H and the connecting tubes are filled with the liquid which is allowed to pass into A at about 5 drops per second (Note 8). Sulfur begins to separate in the column and in the condensers. The steam distillation requires about five hours and gives 10-12 1. of distillate consisting of water, sulfur and a heavy red oil. The water is decanted and the rest of the mixture is filtered by suction through glass wool. The oil is separated and dried over about 10 g. of calcium chloride.  [c.88]

One hundred sixty grains (1.70 moles) of a good grade of phenol and 80 g. (1.43 moles) of potassium hydroxide are placed in a 2-1. flask, and the mixture is heated to 130-140° until all of the alkali has dissolved. The potassium phenoxide is cooled to 100-110°, and 0.5 g. of copper catalyst (Note i) and 78.8 g. (0.5 mole) of -nitrochlorobenzene are added. The flask is then fitted with a mechanical stirrer, thermometer, and a reflux condenser. The stirrer is started, and the contents of the flask are warmed with a Bunsen burner to 150-160°, at which temperature a spontaneous reaction begins with ebullition and the separation of potassium chloride. The flame should be removed during this stage of the reaction. Boiling nearly ceases within five to seven minutes and another 78.8 g. (0.5 mole) of -nitrochlorobenxene is added. The mixture is again heated as before until a second spontaneous reaction begins. This also proceeds for about five minutes without the application of heat. When boiling due to the exothermic reaction has ceased, heat is applied and a temperature of 150-160° is maintained for an additional thirty minutes. The dark-colored melt is then poured into 1.5 1. of ice water containing 50 g. of sodium hydroxide and stirred well for the removal of excess phenol. The crude -nitrodiphenyl ether separates as a dark brown crystalline mass which is allowed to settle. The product is filtered on a Buchner funnel, washed with 2 1. of water, and pressed as free from water as possible. After drying in the air it is distilled from a 500-cc. Claisen flask. The small fraction boiling up to i7o°/8 mm., which contains  [c.66]

In a i-l. three-necked, round-bottomed flask fitted with a reflux condenser, a mechanical stirrer, and a dropping funnel (Note i) are placed 25 g. (o.i mole) of the azlactonc of a-ben-zoylaminocinnamic acid (Notes 2, 3), 20 g. (0.64 gram atom) of red phosphorus, and 135 g. (125 cc.) of acetic anhydride. During a period of about one hour 195 g. (125 cc., 0.76 mole) of 50 per cent hydriodic acid (sp. gr. 1.56) is added with stirring (Note 4). The mixture is refluxed for three to four hours and, after cooling, is filtered with suction. The unreacted phosphorus is washed on the filter with two 5-cc. portions of glacial acetic acid, and discarded. The filtrate and washings are evaporated to dryness under reduced pressure, in a 500-cc. Claisen flask heated in a water bath. A 250-cc. distilling flask cooled in ice is used as a receiver, and the distillate is reserved for a second reduction (Note 5).  [c.80]

Dehydration. Moisture can be leadily removed from liquids by adding a solid hygroscopic substance which does not act chemically upon the liquid. The common dehydrating agents aie calcium chloride, potassium carbonate, sodium sulphate (anhydrous), quicklime, c. Alkalis cannot of course be used for dehydrating organic acids, nor can calcium chloride be employed in conjunction with alcohols or organic bases, with which it combines. In the present instance it can be used. A few small pieces of the granulated or fused calcium chloride are added to the liquid. The flask is corked and left to stand for some hours until the liquid becomes clear. It is then distilled. A thermometer is inserted into the neck of the flask with the bulb just below the side tube. The flask is attached to a condenser and heated gently on the water-bath, so that the liquid distils at a moderate speed (2—3 drops a second). The temperature is noted and the portion boiling at 35—43° collected in a separate flask. This consists of ethyl bromide which may contain a little ether. Yield 75—80 grams.  [c.56]

The final step in the /3-oxidation cycle is the cleavage of the /3-ketoacyI-CoA. This reaction, catalyzed by thiolase (also known as j8-ketothiolase), involves the attack of a cysteine thiolate from the enzyme on the /3-carbonyI carbon, followed by cleavage to give the etiolate of acetyl-CoA and an enzyme-thioester intermediate (Figure 24.17). Subsequent attack by the thiol group of a second CoA and departure of the cysteine thiolate yields a new (shorter) acyl-CoA. If the reaction in Figure 24.17 is read in reverse, it is easy to see that it is a Claisen condensation—an attack of the etiolate anion of acetyl-CoA on a thioester. Despite the formation of a second thioester, this reaction has a very favorable A).q, and it drives the three previous reactions of /3-oxidation.  [c.788]

Ketone body synthesis occurs only in the mitochondrial matrix. The reactions responsible for the formation of ketone bodies are shown in Figure 24.28. The first reaction—the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA—is catalyzed by thiolase, which is also known as acetoacetyl-CoA thiolase or acetyl-CoA acetyltransferase. This is the same enzyme that carries out the thiolase reaction in /3-oxidation, but here it runs in reverse. The second reaction adds another molecule of acetyl-CoA to give (i-hydroxy-(i-methyl-glutaryl-CoA, commonly abbreviated HMG-CoA. These two mitochondrial matrix reactions are analogous to the first two steps in cholesterol biosynthesis, a cytosolic process, as we shall see in Chapter 25. HMG-CoA is converted to acetoacetate and acetyl-CoA by the action of HMG-CoA lyase in a mixed aldol-Claisen ester cleavage reaction. This reaction is mechanistically similar to the reverse of the citrate synthase reaction in the TCA cycle. A membrane-bound enzyme, /3-hydroxybutyrate dehydrogenase, then can reduce acetoacetate to /3-hydroxybutyrate.  [c.798]

The cholesterol biosynthetic pathway begins in the cytosol with the synthesis of mevalonate from acetyl-CoA (Figure 25.31). The first step is the /3-ketothi-olase-catalyzed Claisen condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA. In the next reaction, acetyl-CoA and acetoacetyl-CoA join to form 3-hydroxy-3-methylglutaryl-CoA, which is abbreviated HMG-CoA. The reaction—a second Claisen condensation—is catalyzed by HMG-CoA synthase. The third step in the pathway is the rate-limiting step in cholesterol biosynthesis. Here, HMG-CoA undergoes two NADPH-dependent reductions to produce 3R-mevalonate (Figure 25.32). The reaction is catalyzed by HMG-CoA reductase, a 97-kD glycoprotein that traverses the endoplasmic reticulum membrane with its active site facing the cytosol. As the rate-limiting step, HMG-CoA reductase is the principal site of regulation in cholesterol synthesis.  [c.833]

See pages that mention the term Claiscn-Schmidt condensation : [c.485]    [c.566]    [c.970]   
Organic syntheses Aconitic Acid (1937) -- [ c.12 , c.22 ]