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Commercial periodic acid is generally available in 95% and 50% sizes. Periodic acid can selectively oxidize compounds having two hydroxyl groups or one hydroxyl group and one amino group on adjacent carbon atoms. Namely: C - C bond breaks.
RCH ( OH ) CH ( OH ) R' + HIO4 → RCHO + R'CHO + HIO3 + H2O
RCH ( OH ) CH ( NH2 ) R' + HIO4 → RCHO + R'CHO + HIO3 + NH3
Oxidation can occur only when two hydroxyl groups or one hydroxyl group and one amino group are on adjacent carbons, so the reaction can be used to check for the presence of adjacent hydroxyl groups (eg , 1,2 -diol) and adjacent hydroxyl groups, amino groups. A compound having a hydroxyl group adjacent to a carbonyl group or adjacent to a carbonyl group and a carbonyl group may also be oxidized, such as:
RCH ( OH ) COR' + HIO4 → RCHO + R'CO2H + HIO3
RCOCOR' + HIO4 + H2O → RCO2H + R'CO2H + HIO3
Oxidation is carried out between pH 3-5 and the reaction with NaIO4 KIO4. The solubility of sodium periodate in water is: 0.07 g?mL-1 , and the addition of a base will form a poorly soluble Na2H3IO6 precipitate. ( Na2H3IO6 solubility in water 0.2% ). If the reactants are insoluble in water, the oxidation reaction should be carried out in ethanol, methanol or acetic acid diluted with water. The oxidant should be in a slight excess, otherwise the resulting oxidation product is a partial oxidation product.
18 . Benzoyl peroxide
Benzoyl peroxide is a dangerous substance that can easily explode. Commercial products are very cheap and generally contain 25% water. In the experiment, a small amount of benzoyl peroxide can be prepared by reacting benzoyl chloride and hydrogen peroxide in the presence of a strong base.
In a fume hood, add 50 mL ( 0.175 mol ) of 12% ( 40 vol) hydrogen peroxide to a 600 mL beaker immersed in an ice bath, while mechanically stirring, 30 mL of 4 mol?L-1 The sodium hydroxide solution and 30g ( 25 mL , 0.214 mol ) of freshly distilled benzoyl chloride (with tearing, attention protection) were placed in two dropping funnels, the funnel neck was immersed in the beaker, and the mixture was dropped while stirring. In the beaker. During the addition process, pay attention to the solution to maintain weakening, the temperature does not exceed 5 ~ 8 °C . After all the addition is completed, stirring is continued for half an hour. At this time, the odor of benzoyl chloride is no longer present, and the flocculent precipitate is filtered, washed with a small amount of cold water, and then air-dried on a filter paper to obtain 12 g of 46% pure benzene peroxide. Formyl. It can be purified by dissolving in a volume of chloroform and adding two volumes of methanol to precipitate. Benzoyl peroxide does not recrystallize in hot chloroform because it produces a very severe explosion. Benzoyl peroxide melts and decomposes at 160 °C . Like all organic peroxides, benzoyl peroxide should be handled carefully after the shield and should be treated with a spoon or a polyethylene spoon.
In order to determine the content of benzoyl peroxide (containing other organic peroxides), the following steps can be used: accurately weigh 0.5 g of benzoyl peroxide and dissolve in a 350 mL Erlenmeyer flask containing 15 mL of chloroform. Cool to -5 °C , add 25 mL of 0.1 mol?L-1 methanol-methanol solution, cool and shake for 5 min . When the solution is -5 °C , stir vigorously, add 100 mL of ice water, 5 mL of 10% sulfuric acid and 2 g of potassium iodide dissolved in 20 mL of 10% sulfuric acid, and then titrate with 0.10 mol?L-1 of standard sodium sulfite. Iodine
1 mL 0.10 mol?L-1 Na2S2O3 → 0.0121 g benzoyl peroxide
19 . hydrogen peroxide
The concentration of commercially available hydrogen peroxide is generally 28% and 70% . There is also a high concentration of hydrogen peroxide, such as a concentration of 86% . Concentrated hydrogen peroxide can explode when in contact with organic or transition metals, so care must be taken.
Even with a high concentration of hydrogen peroxide (greater than 50% ), it can be treated with certain safety precautions. First, it is best to wear protective goggles and rubber or plastic gloves, because high concentrations of the solution will burn the textile and must be worn with a rubber or plastic apron. All operations involving this solution should be carried out in a fume hood and the reaction unit should be installed in a plastic tray filled with water to prevent hydrogen peroxide from escaping.
Inhalation of high concentrations of hydrogen peroxide vapor can cause pain in the nose and throat, which can cause ulceration of the cornea. Splashes of hydrogen peroxide on the skin should be washed immediately with tap water. Water should be prepared prior to operation to flush spilled and leaked hydrogen peroxide.
The concentration of the hydrogen peroxide solution can be roughly determined according to the oxygen content. Under standard conditions, 1 mL of 30% hydrogen peroxide solution can be completely decomposed by heating to obtain 100 mL of oxygen. The aqueous hydrogen peroxide solution is treated with acidic potassium iodide to release iodine, which is then titrated with standard sodium thiosulfate. This method also measures the concentration of aqueous hydrogen peroxide solution.
20 . Phosgene (carbonyl chloride)
There is a commercially available phosgene in a cylinder or a phosgene toluene solution ( 12.5% ) contained in an ampoule. Due to the high toxicity of phosgene, all operations should be carried out in a fume hood. The excess phosgene must be 20% hydrogen. The sodium oxide solution is absorbed. Phosgene is generally not prepared the laboratory, but a small amount of the phosgene can be prepared by the following steps: the experimental apparatus shown in Figure 1, a small round-bottomed flask was equipped with a reflux condenser, a reflux condenser An upper end of a "T" The joint is connected to a drop funnel, the " T " joint is connected to a series of scrubbers, A and C are used as safety bottles, and the toluene contained in B absorbs phosgene. The 20% aqueous sodium hydroxide solution contained in D absorbs HCl and traces of phosgene. The round bottom flask was filled with concentrated sulfuric acid, and then 2% diatomaceous earth of concentrated sulfuric acid (dried by burning) was added. Carbon tetrachloride was placed in a dropping funnel, oil bath of concentrated sulfuric acid was heated to 120 ~ 130 ℃, carbon tetrachloride was slowly added dropwise, the generated light is absorbed by the gas in toluene (B), hydrogen chloride remain in D in.
3 CCl4 + 2 H2SO4 → 3 COCl2 + 4 HCl + S2O5Cl2
Figure 1 Preparation of phosgene device
21 . Potassium
Care must be taken when handling potassium. Cut metal potassium in a mortar containing petroleum ether. Do not use fragile beakers or petri dishes. The outer oxide layer was cut and the crumb was placed in another mortar containing petroleum ether. The freshly cut potassium was clamped to the filter paper with tweezers, quickly blotted dry, and then added to a known quality petroleum ether-containing beaker and weighed. The weighed potassium is added to the reaction. Potassium crumb should not be placed for a long time and should be disintegrated immediately. The mortar containing potassium crumb can be transferred to a fume hood, and a small amount of t-butanol (not methanol or ethanol) can be added in batches with a pipette. The acceleration makes the reaction not very intense. Prepare a heat shield that can be covered with a baffle if the solution catches fire. Potassium chips stuck to the knife and in the mortar should also be carefully treated with t-butanol in a fume hood.
22 . formaldehyde
The commercial formalin is an aqueous solution containing 37 to 40% formaldehyde ( 0.37 to 0.40 g per milliliter of formaldehyde), and 12% methanol is added as a stabilizer. When dry gaseous formaldehyde is required, it can be obtained by depolymerization of paraformaldehyde at 180 to 200 °C .
23 . Metal hydride
Metal hydrides are widely used and simple to handle, and are often selected as reducing agents for many organic functional groups. The following metal hydride deuterated products are commercially available which can introduce a deuterium atom at a known position in the organic compound, and thus such compounds are very useful in estimating the reaction pathway and reaction mechanism.
Lithium aluminum hydride ( LiALH4 ) is a strong reducing agent that rapidly reduces many functional groups. A typical example is the reduction of an ester to an alcohol. This reagent is usually sealed in a plastic bag in a powder form and placed in a metal can. It can also be dissolved in diethyl ether, dimethyl ether, tetrahydrofuran or toluene in the form of a solution. Lithium aluminum hydride reacts violently with water, releasing hydrogen, and must also avoid contact with traces of water vapor, since the heat generated can ignite lithium aluminum hydride. Therefore, special care must be taken when handling this reagent. The remaining powder reagents should be safely destroyed by placing a container behind the safety barrier with petroleum ether ( bp 60 to 80 °C ). The lithium aluminum hydride powder was suspended therein, and ethyl acetate was added dropwise with careful stirring until the obvious reaction was stopped, and then the mixture was allowed to stand overnight, and the above procedure was repeated with ethanol and then with water. Finally, the water layer is poured into the sewer and the organic layer is recovered.
The reduction of lithium aluminum hydride is usually carried out in an ether solvent such as strictly dried diethyl ether or tetrahydrofuran, and the solubility in the two solvents is 25 to 30 g/kg and 13 g/kg, respectively . These solutions often contain a large amount of insoluble matter, which may be caused by the reaction of hydride and water vapor during the operation, but these components are less than 1% and will not affect the next reduction reaction.
Sodium borohydride ( NaBH4 ) is a mild reducing agent relative to lithium aluminum hydride. In carbonyl compounds, it generally only reduces aldehydes and ketones, and sodium borohydride is more selective than lithium aluminum hydride. It can be obtained as solid NaBH4 or in ethylene glycol dimethyl ether or glycerol trimethyl ether. The solution. Unlike lithium aluminum hydride, sodium borohydride is insoluble in ether (but soluble in dioxane) and, when used as a reducing agent, is generally soluble in water or ethanol solution.
24 . Phosphate
Commercially available phosphoric acid is 85% , d = 1.75 ; 1.57 g per milliliter of phosphoric acid, equivalent to 65% P2O5 . It is also possible to obtain 100% phosphoric acid (anhydrous phosphoric acid, equivalent to 72% P2O5 ), and 100% phosphoric acid can be prepared by mixing 90% phosphoric acid with P2O5 in a mass ratio of 4 : 1 .
Polyphosphoric acid (approximate formula 2P2O5.3H2O ) contains 82 to 84% phosphoric acid, which is a viscous liquid. When taken, it can be heated by a steam bath to form a flowing liquid. It can also be prepared by dissolving P2O5 in 88-90 % phosphoric acid (mass ratio of 1.8 : 1 ), which is equivalent to 87% of P2O5 .
25 . Hydrogen sulfide
Hydrogen sulphide is toxic and should be reacted and prepared in a well-ventilated fume hood. It is usually prepared by using ferrous sulfide and dilute hydrochloric acid ( 1 : 3 ) in a Kepp generator. It is washed with water to remove a small amount of acid gas. Iron contains a small amount of elemental iron, so the hydrogen sulfide produced contains a small amount of hydrogen. There is also a high purity cylinder gas with a purity of 99.6% .
26 . Dialkyl sulfate
Dimethyl sulfate is a liquid with a boiling point of 188.5 ° C and almost no odor. Both gaseous and liquid dimethyl sulfate are highly toxic and should be used in fume hoods and rubber gloves. Inhalation of gaseous dimethyl sulfate can cause dizziness and even poisoning, and liquid dimethyl sulfate can penetrate the skin and cause poisoning. If liquid dimethyl sulfate is accidentally spilled on your hands, immediately rinse it with concentrated ammonia water, decompose it before it penetrates the skin, and then gently wipe it with a cotton pad soaked in ammonia.
The toxicity of diethyl sulfate is weaker than that of dimethyl sulfate, but the same precautions should be taken during use and handling. All operations should be carried out with rubber gloves in a fume hood. If diethyl sulfate is black, it should be washed in ice separator with a separatory funnel and then washed with sodium bicarbonate until it is not acidic. Finally, it is dried with calcium oxide and fractionated to collect a fraction of 93 ° C / 1.7 kPa .
27 . Chlorine gas
Chlorine is a highly irritating irritating gas that must be handled and used in a well ventilated fume hood. For the use of large amounts of chlorine, commercially available cylinder chlorine can be used. The gas can be dried by two gas cylinders filled with concentrated sulfuric acid and then passed through a glass wool-filled gas cylinder to remove the acid mist. A small amount of chlorine can be obtained by the reaction of potassium permanganate and concentrated hydrochloric acid in the apparatus shown in Figure 2. The amount of potassium permanganate (about 0.9 g of KMnO4 for 1 g of Cl2 ) was calculated based on the mass of chlorine required and added to a round bottom flask. A slight excess of concentrated hydrochloric acid was placed in a constant pressure dropping funnel ( 1 g of KMnO 4 required 6.2 mL of concentrated hydrochloric acid) and then the constant pressure funnel was stoppered and the piston was fitted with a rubber band. The chlorine is passed through a water-filled gas cylinder to remove HCl , and then dried by another gas cylinder containing concentrated sulfuric acid, preferably a safety bottle is placed between the reactor and the drying device. Hydrochloric acid should be slowly added dropwise to the permanganate crystals and the flask was continually shaken. When the acid is added in half, the volatilization rate of the gas is gradually lowered. At this time, the flask should be slightly heated, and after the acid is added, the mixture is heated to a slight boiling to completely evaporate the chlorine.
Figure 2 chlorine gas preparation device
28 . Chloroform
Chloroform has a boiling point of 61.2 °C and a density of d = 1.4916 . It is insoluble in water and easily decomposes into Cl2 , HCl , CO2 and phosgene (very toxic) in sunlight. It should be stored in a brown bottle. The chloroform supplied on the market is 1% more . Ethanol to eliminate phosgene, ethanol in chloroform can be tested by iodoform, free hydrogen chloride can be used to test the alcohol solution of AgNO3 .
Purification of chloroform: first remove the ethanol with concentrated sulfuric acid, then dry with anhydrous calcium chloride, and finally carry out distillation. Chloroform will explode in the presence of sodium metal and cannot be dried with sodium metal.
29 . Chlorosulfonic acid ( ClSO3H )
Care must be taken when handling chlorosulfonic acid, which is highly corrosive to skin and clothing and reacts violently with water. If impure reagent, distillation can be performed in all-glass apparatus, the fraction boiling at 148 ~ 150 ℃ / 100kPa, the fraction moistureproof measure to deal with.
30 . Stannous chloride
Anhydrous stannous chloride is easily soluble in acetone and 1 -pentanol, soluble in anhydrous methanol and absolute ethanol; insoluble in benzene, toluene, xylene and chloroform. As long as there is a trace amount of water, it immediately hydrolyzes to form a milky precipitate.
The crystalline stannous chloride ( SnCl2?2H2O ) is heated in an oil bath at 195 to 200 °C for 1 hour, and the melt is cooled to become a powder. It can be stored in a desiccator or a stoppered bottle. The obtained product is in many experiments. Can meet the requirements.
Use the following procedure to obtain a better anhydrous stannous chloride: Add 102 g ( 89.5 mL , 1 mol ) of freshly distilled acetic anhydride to a 400 mL beaker, 123 g of analytically pure SnCl2?2H2O ( 0.5 mol ) The crystals are immediately dehydrated, exothermic, and the acetic anhydride boils. After 1 hour, anhydrous stannous chloride was filtered through a Buchner funnel or a fritted glass funnel, washed with two portions of 30 mL of anhydrous ether to remove acetic anhydride, and then dried overnight in a desiccator. Can be stored in a desiccator or in a stoppered bottle.
Properties and Preparation and Purification of Commonly Used Reagents (Continued 2)
17 . Periodic acid