Sulphurous Acid Anhydride

Preparation. 1. What forms when sulphur burns in the air  

Put several sodium sulphite crystals into a test tube and add 2-3 drops of a 70% sulphuric acid solution. Write the equation of the reaction and explain the direction of the process on the basis of the law of mass action. 

Assemble an apparatus (see Fig. 53a), replacing the second wash bottle with a dry U-tube (wear eye protection ). Pour a small amount of a 96% sulphuric acid solution into the first wash bottle. Put the U-tube into a bath cooled by a mixture whose temperature should be below —10 °C. Put 5-10 g of copper shavings into a Wurtz flask and pour the calculated amount of a 96 % sulphuric acid solution over them. Heat the reaction flask strongly in a sand bath until the intensive evolution of gas begins, after which remove the burner. Watch the temperature of the cooling mixture. What gathers in the U-tube Write the equation of the reaction. 

Properties. 1. Pour several drops of liquid sulphurous acid anhydride into a 50-ml thick-walled hottle (see Fig. 536). After its evaporation, cover the mouth of the bottle with a stopper provided with a drawn out glass tube. Invert the bottle with the gas, and in this position immerse it into a bath with water. Explain what occurs. Write the equation of the reaction. What equilibria set in when sulphurous acid anhydride is dissolved in water  

What salts form consecutively when sulphur dioxide is passed into a sodium hydroxide solution What products form when these salts are roasted  

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END USES...Sulphur dioxide, sulphurous acid anhydride, is a non-flammable, colourless gas at normal ambient temperature with a characteristic pungent odour. It is supplied as a water white clear liquid-compressed gas with a purity of 99.98 %. Commercial grade containing not more than 0.05 % moisture is suitable for most applications. It has a boiling point of 14 °F(-10 °C). 

The sulphinic acid that forms efficiently destroys the hydroperoxides and is able to repeatedly terminate oxidation chains by reacting with peroxide radicals. At higher temperatures sulphinic acid may also eliminate sulphurous-acid anhydride leading to the formation of sulphuric acid, which also effectively destroys hydroperoxides ... 

COT is prepared by the polymerization of ethyne at moderate temperature and pressure in the presence of nickel salts. The molecule is non-planar and behaves as a typical cyclic olefin, having no aromatic properties. It may be catalytically hydrogenated to cyclo-octene, but with Zn and dil. sulphuric acid gives 1,3,6-cyclooclairiene. It reacts with maleic anhydride to give an adduct, m.p. 166 C, derived from the isomeric structure bicyclo-4,2,0-octa-2,4,7-triene(I) ... 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

As the equation indicates, it is the anhydride of iodic-acid(V), which is re-formed when water is added to the pentoxide. Mixed with concentrated sulphuric acid and silica, it is a quantitative oxidising agent for carbon monoxide at room temperature ... 

Ethyl acetate. Various grades of ethyl acetate are marketed. The anhydrous comjjound, b.p. 76-77°, is of 99 per cent, purity, is inexpensive, and is suitable for most purposes. The 95-98 per cent, grade usually contains some water, ethyl alcohol and acetic acid, and may be ptuified in the following manner. A mixture of 1 litre of the commercial ethyl acetate, 100 ml. of acetic anhydride and 10 drops of concentrated sulphuric acid is refluxed for 4 hours and then fractionated. The distU-late is shaken with 20-30 g. of anhydrous potassium carbonate, filtered and redistilled. The final product has a purity of about 99-7% and boils at 77°/760 mm. 

To obtain maleic acid, evaporate the maleic anhydride with one half of its weight of water on a water bath remove the last traces of water by leaving in a desiccator over concentrated sulphuric acid. The resulting maleic acid has m.p. 143° and is quite pure (1). It may be recrystaUised, if desired, from acetone- light petroleum (b.p. 60-80°) and then melts at 144° (1). 

In general, however, the diacetyl derivatives are unstable in the presence of water, undergoing hydrolysis to the mono-acetyl compound, so that when they (or a mixture of mono- and di-acetyl derivatives) are crystallised from an aqueous solvent, e.g., dilute alcohol, only the mono-acetyl derivative is obtained. A further disadvantage of the use of acetic anhydride in the absence of a solvent is that all the impm-ities in the amine are generally present in the reaction product. Heavily substituted amines, t.g., 2 4 6-tribromoaniline, react extremely slowly with acetic anhydride, but in the presence of a few drops of concentrated sulphuric acid as catalyst acetylation occurs rapidly, for example ... 

Certain ortho substituted derivatives of aromatic amines are difficult to acetylate under the above conditions owing to steric hindrance. The process is facilitated by the addition of a few drops of concentrated sulphuric acid (compare Section IV,47), which acts as a catalyst, and the use of a large excess of acetic anhydride. 

I) Hydroquinone dIacetate may be prepared as follows. Add I drop of concentrated sulphuric acid to a mixture of 55 g. of hydroquinone and 103 g. (05-5 ml.) of A.R. acetic anhydride in a 500 ml. conical flask. Stir the mixture gently by hand it warms up rapidly and the hydroquinone dissolves. After 5 minutes, pour the clear solution on to 400 ml. of crushed ice. Alter with suction and wash with 500 ml. of water. Recrystallise the solid from 50 cent, ethanol by weight (ca. 400 ml. are required). The yield of pure hydroquinone diacetate, m.p. 122°, is 89 g. 

Place in a dry test-tube 0 -5 g. of the compound and an equal bulk of pure phthahc anhydride, mix well together, and add 1 drop of concentrated sulphuric acid. Stand the tube for 3-4 minutes in a smah beaker of concentrated sulphuric acid or oil previously heated to 160°, Remove from the bath, allow to cool, add 4 ml. of 5 per cent, sodium hydroxide solution and stir until the fused mass has dissolved. Dilute with an equal... 

By oxidation of the methyl derivative of an aromatic hydrocarbon with a solution of chromic anhydride in acetic anhydride and acetic acid. The aldehyde formed is immediately converted into the (/m-diacetate, which is stable to oxidation. The diacetate is collected and hydrolysed with sulphuric acid, for example ... 

Equip a I litre three-necked flask with a mechanical stirrer and a thermometer, and immerse the flask in a bath of ice and salt. Place 306 g. (283 ml.) of acetic anhydride, 300 g. (285 ml.) of glacial acetic acid and 25 g. of p-nitrotoluene in the flask, and add slowly, with stirring, 42 5 ml. of concentrated sulphuric acid. When the temperature has fallen to 5°, introduce 50 g. of A.R. chromic anhydride in small portions at such a rate that the temperature does not rise above 10° continue the stirring for 10 minutes after all the chromium trioxide has been added. Pour the contents of the flask into a 3 litre beaker two-thirds filled with crushed ice and almost fill the beaker with cold water. Filter the solid at the pump and wash it with cold water until the washings are colourless. Suspend the product in 250 ml. of cold 2 per cent, sodium carbonate solution and stir mechanically for 10-15 minutes filter (1), wash with cold water, and finally with 10 ml. of alcohol. Dry in a vacuum desiccator the yield of crude p-nitrobenzal diacetate is 26 g. (2),... 

The S3mthesis of antbraquinone is instructive. Phthalic anhydride condenses with benzene in the presence of aluminium chloride (shghtly more than two equivalents, see 1 above) to 3deld o-benzoylbenzoic acid, and the latter is heated with concentrated sulphuric acid ... 

Thiele acetylation. Quinones, when treated with acetic anhydride in the presence of perchloric acid or of concentrated sulphuric acid, undergo simultaneous r uctive acetylation and substitution to yield triacetoxy derivatives, e.g., benzoquinone gives 1 2 4-triacetoxybenzene. 

Add 0-1 ml. of concentrated sulphuric acid or of 72 per cent, perchloric acid cautiously to a cold solution of 0 01 mol (or 1 0 g.) of the quinone in 3-5 ml. of acetic anhydride. Do not permit the temperature to rise above 50°. AUow to stand for 15-30 minutes and pour into 15 ml, of water. Collect the precipitated sohd and recrystaUise it from alcohol. 

Phenol condenses with phthahc anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkah is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a h3q)othetical unstable Intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows ... 

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