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Boiling point 149 ~ 156 °C , density d = 0.9487 , refractive index n 20D = 1. 4305 , colorless liquid, soluble in most organic solvents and water, is an excellent organic solvent. Commercially available DMF contains small amounts of impurities such as water, amines and formaldehyde. Some decomposition occurs during atmospheric distillation to produce dimethylamine and carbon monoxide. If acid or alkali is present, the decomposition is accelerated. After adding solid potassium hydroxide or sodium hydroxide, it is partially decomposed after being left at room temperature for several hours. Therefore, it is preferred to dry it with calcium sulfate, magnesium sulfate, cerium oxide, silica gel or molecular sieve, and then distillate under reduced pressure to collect a fraction of 76 ° C / 4.79 kPa ( 36 mmHg ). If the water content is high, one tenth of the volume of benzene may be added, and water and benzene are distilled off under normal pressure and below 80 ° C , and then dried with magnesium sulfate or cerium oxide, and then distilled under reduced pressure.
10 . Dimethyl sulfoxide
The boiling point of 189 ° C , the melting point of 18.5 ° C , the density d = 1.100 , the refractive index n 20D = 1.4783 . Dimethyl sulfoxide is miscible with water and can be dried by long-term placement with molecular sieves. Then, it was distilled under reduced pressure, and a fraction of 76 ° C / 1.6 kPa was collected . The temperature during distillation should not exceed 90 °C , otherwise disproportionation will occur to form dimethyl sulfone and dimethyl sulfide. It may also be dried by using calcium oxide, cerium oxide or anhydrous barium sulfate, and then distilled under reduced pressure. When dimethyl sulfoxide is mixed with certain substances, it may explode, such as sodium hydride, periodic acid or magnesium perchlorate.
11 . carbon dioxide
Carbon dioxide can be prepared using calcium carbonate and dilute hydrochloric acid ( 1 : 1 ) in a Kaipu generator. The acid mist is removed by passing the gas through a gas cylinder containing sodium bicarbonate. If drying is required, the gas is passed to another two scrubbers containing concentrated sulfuric acid.
A large amount of carbon dioxide can be used in commercial cylinder gas, and the gas can be dried by two gas cylinders filled with concentrated sulfuric acid, and a small amount of air is present in the carbon dioxide gas.
In order to achieve certain experimental purposes (such as Grignard reaction), solid carbon dioxide (dry ice) can be used. Note that solid carbon dioxide cannot be taken directly by hand without protection, otherwise it will be frostbitten. If you want to use dry ice powder, wrap large chunks of dry ice in a cloth and mash. The carbon dioxide gas can be stably supplied when the dry ice is volatilized, and the appropriate size of dry ice can be placed in the flask, and the generated gas is connected to the reactor through a concentrated sulfuric acid gas cylinder and a safety bottle.
12 . manganese dioxide
The main use of manganese dioxide in organic synthesis is the selective oxidation of allyl and benzyl containing 1o and 2o alcohols to the corresponding carbonyl compounds. The activity of manganese dioxide varies with the preparation method, and is highly active. Manganese dioxide can be obtained by oxidizing divalent manganese ions with an excess of permanganate under basic conditions:
Dissolve 223 g ( 1 mol ) of manganese sulfate tetrahydrate in 300 mL of water to form a solution ( a ), prepare 240 mL of 40% aqueous solution of sodium hydroxide ( b ), and then dissolve 190 g ( 1.2 mol ) in 1200 mL of water. Potassium permanganate was stirred with heating, and ( a ) and ( b ) were simultaneously added thereto over 1 hour, and finally a pure manganese dioxide brown precipitate was separated. The manganese dioxide is very fine, centrifuged, and thoroughly washed with water until the solution is colorless and dried at 100 to 120 °C . It is also possible to extend the filtration time as much as possible to remove most of the water, and then distill the remaining water with 150 mL of benzene and 25 g of filter cake. The manganese dioxide reactivity obtained by the precipitation method is sufficient for the direct oxidation reaction. To evaluate the reactivity of a manganese dioxide sample, dissolve 0.25 g of pure phenylpropanol in 50 mL of dry petroleum ether ( bp 30 ~ 60 °C ), and add 2 g of MnO2 sample previously dried with P2O5 . The solution was shaken at room temperature for 2 hours. Filtration, evaporation of the solvent, the product 2, in methanol 4 - dinitrophenyl hydrazine salt treatment. The obtained cinnamaldehyde 2,4 -dinitrophenylhydrazine was collected and recrystallized from ethyl acetate. The yield of the highly active manganese dioxide-derived derivative should exceed 0.35 g ( 60% ) and the melting point was 255 °C .
13 . Dioxane
The boiling point is 104.5 °C and the density is d = 1.0336 . It is miscible with water, colorless, flammable, and can form an azeotrope with water (content is 81.6 %, boiling point 87.8 °C ). It usually contains a small amount of diacetal acetal and water. It can be refluxed with 10 % concentrated hydrochloric acid for 3 hours. Nitrogen gas was slowly introduced to remove the generated acetaldehyde. After cooling, the granular potassium hydroxide was added until it was no longer dissolved, the aqueous layer was separated, and dried with granular potassium hydroxide for one day. Filtration, addition of sodium metal reflux for several hours, distillation. The long-lasting dioxane may contain peroxide, which should be removed and then treated.
14 . N,N- dicyclohexylcarbodiimide ( DCC ; C6H11N=C=NC6H11 )
The melting point of 33 ~ 35 °C , is a waxy low melting point solid, the agent is highly corrosive to the skin, can cause allergies, must be careful when using. High quality DCC (purity 99% ) can be purchased, and the reagent bottle can be liquefied in a small amount of hot water for weighing.
This reagent is often used as a dehydrating agent and is removed as a dicyclohexylurea after the reaction. The recovered dicyclohexylurea ( mp 234 °C ) can be recrystallized from ethanol and then converted to DCC by reaction with p-toluenesulfonyl chloride, phosphorus oxychloride or phosphorus pentoxide in a pyridine solution: 17.1 g ( 47 mL) with stirring , 0.11 mol ) of phosphorus oxychloride was added dropwise to a solution of 22.5 g ( 0.1 mol ) of dicyclohexylurea in 50 mL of pyridine, and then heated to 60 to 90 ° C for 1.5 hours, and the reaction product was poured on crushed ice. It was extracted with petroleum ether ( bp 60 to 80 ° C ), and the extract was dried over anhydrous sodium sulfate, and the solvent was evaporated on a rotary evaporator, and the remaining oil was distilled under reduced pressure. The yield of the diimide is about 14 g ( 68% ), bp 157 to 159 ° C / 2.0 kPa ( 131 ° C / 0.5 kPa ).
15 . Potassium fluoride
Anhydrous potassium fluoride can be prepared by the following steps: crystals of potassium fluoride are finely ground, heated to 180 to 210 ° C with a heating mantle , and stored in a desiccator. Potassium fluoride was dried for three hours before use and then ground in a heated mortar ( 50 °C ).
16 . Chromium oxidant
Cr ( VI ) is widely used as an oxidant in organic chemistry. Chromium oxide is a deliquescent red crystal that is easily soluble in water and sulfuric acid. It is a strong oxidant and must be handled with care. It is usually used in its acetic acid or acetic anhydride solution. Adding chromium oxide to ice-cold acetic anhydride can be formulated into a solution of chromium oxide in acetic anhydride. It is important not to add an acid anhydride to the chromium oxide. Adding the acid anhydride to a large amount of chromium oxide causes explosive decomposition. In the reaction of oxidizing a simple primary alcohol to an aldehyde, a secondary alcohol to a ketone, and an alkylborane to a ketone, an aqueous solution of sodium dichromate in sulfuric acid may also be used as the oxidizing agent. Since the aldehyde formed by the oxidation of the primary alcohol is continuously oxidized to a carboxylic acid, the acid chromate is generally not used to oxidize the primary alcohol to form an aldehyde. Cr ( VI ) can be selectively oxidized in an inert medium. Currently, Cr ( VI ) pyridine complexes (dichromate pyridinium and chlorochromate pyridinium salts) are widely used in primary alcohols and acid-sensitive group alcohols. Selective oxidation.
The step of oxidizing the primary alcohol and the secondary alcohol with dichromate pyridinium salt is: adding 6 g ( 60 mmol ) of chromium trioxide to 150 mL of dichloromethane containing 9.49 g ( 12 mmol ) of pyridine under magnetic stirring. Then, the flask was stoppered with a drying tube containing a desiccant, the solution was dark purple, stirred for 15 min , and a part of an alcohol solution ( 10 mmol ) dissolved in a small amount of dichloromethane was added at the end of stirring, and a black precipitate was observed immediately. The solution temperature was kept at room temperature and stirring was continued for 15 min . At this time, the solution and the residue were separated, and the residue was washed with 200 mL of diethyl ether. The organic layer was washed with three portions of 100 mL of 5% aqueous NaOH three times, 100 mL of 5% aqueous HCl wash, washed once in 100 mL of 5% aqueous NaHCO3, saturated aqueous NaCl wash Add 100 mL, and then dried over magnesium sulfate Finally, the layered methylene chloride was concentrated, and the residue was extracted with diethyl ether. The insoluble chromium salt was filtered, washed with dilute alkali and saturated brine, dried over magnesium sulfate, and evaporated to give a crude product of aldehyde and ketone. . The alcohol which can be oxidized by such a procedure is 2 -octanol ( 97% yield of carbonyl compound), 1 -octanol ( 90% ), benzyl alcohol ( 89% ), borneol ( 89% ), cinnamyl alcohol ( 96 ). % ).
Pyridinium chlorochromate is formed by the action of chromium trioxide and pyridine in the presence of hydrochloric acid. It has a weak acidity and easily reacts with a basic group, and it can replace the oxidic acid dichromate pyridinium salt. The pyridinium chlorochromate can be prepared by the following method: 100 g ( 1 mol ) of chromium oxide ( VI ) is rapidly added to 184 mL of 6 mol?L-1 HCl ( 1.1 mol ) during stirring, and the solution is cooled after 5 min. At 0 °C , carefully add 79.1 g ( 1 mol ) of pyridine (at least 10 min ) and re-cool to 0 °C to give an orange-yellow solid. The solid was placed in a fritted glass funnel and dried in vacuo for 1 hour. 188.8 g ( 84% ). It is not easy to measure whether the solid is completely dry with a moisture analyzer, so it needs to be left at room temperature for a while. The pyridinium chlorochromate can oxidize 1 -heptanol to heptaldehyde.
The pyridinium chlorochromate adsorbed on alumina in some reactions is more effective. At 40 °C , 6 g of chromium trioxide was dissolved in 11 mL of hydrochloric acid ( 6 mol?L-1 ), 4.75 g of pyridine was added within 10 min , and the solution was cooled to below 10 °C until an orange-yellow solid formed, and then heated to 40. °C , the solid was dissolved, 50 g of alumina was added under stirring, the temperature was kept at 40 ° C , and the solvent was evaporated to give an orange solid, which was dried in vacuo for 2 hr. The reagent can be stored in a vacuum desiccator for several weeks in the dark, and its activity is unchanged.
Properties and preparation of commonly used reagents (continued)
9 . N,N -dimethylformamide ( DMF ) Â