Sulphurous Anhydride

Neighbouring-group participation by a 5a-acetoxy-group in the substitution of a 3fi-OR group is paralleled by Sa-acetylthio-groups. The crystalline 3a,5a-cyclic onium perchlorate (31) was generated by reaction of the 3j9-hydroxy-compound (29) with acetic anhydride-sulphuric acid [via the 3/1-acetyl sulphate (30)], followed by the addition of perchloric acid. Hydrolysis of the onium salt gave the 3a-acetoxy-5a-thiol (32). 

Chloromercurithiophene or mercury 2 2 -dithienyl is treated with arsenious chloride and the product warmed on the water-bath. The filtrate from this mixture is treated with aqueous sodium hydroxide, then with hydrogen peroxide. Addition of barium chloride then helps to remove any inorganic arsenic which has not crystallised out as sodium arsenate. The whole is filtered, the filtrate freed from barium and sulphuric acid and evaporated down after the addition of concentrated hydrochloric acid. The residue is dissolved in alcohol, boiled with charcoal, and treated with sodium hydroxide. The sodium salt of the arsinic acid crystallises out in transparent, colourless, non-deliquescent, rhombic plates, which are very soluble in water. The free acid forms tufts of needles, M.pt. 185 5° C., fairly soluble in water or alcohol. At 106° to 108° C. it is converted into the corresponding anhydride. Sulphurous acid in the presence of a trace of hydriodic acid reduces it to thienyl-2-arsenoxide, whilst with sodium hydrosulphite it yields 2 2 -arsenothiophe-ne,... 

Sulphurous acid I71B, 3664-S-6-8, 4066 H2SO3 Sulphurous anhydride. Sulphurous anhydride See sulphurous acid. 

Sulphurous acid and its anhydride sulphur dioxide bear the same relation to each other as was found to exist between carbonic acid and its anhydride, carbon dioxide. No change in valence occurs in the formation of sulphurous acid from sulphur dioxide, so the acid is capable of undergoing the same sort of reactions of oxidation and reduction as its anhydride does. 

Composition.—Water containing 9 2 per cent, by weight of sulphurous anhydride (sulphurous acid gas, SO2). ... 

An abbreviated synthesis of penta-O-acetyl-a-D-altropyranose, and hence altrose, involves treatment of methyl 2,3-anhydro-4,6-0-benzylidene-o -D-allo-pyranoside with acetic anhydride-sulphuric acid mixtures. The peracetate was obtained in 64% yield. ... 

Cinnamaldehyde-acetic anhydride-sulphuric acid for steroid-sapogenins. 

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),... 

A further example is given below illustrating the use of a dibasic anhydride (succinic anhydride) the succinoylation reaction is a valuable one since it leads to aroyl carboxylic acids and ultimately to polynuclear hydrocarbons. This general scheme of synthesis of substituted hydrocarbons through the use of succinic anhydride is sometimes called the Haworth reaction. Thus a-tetralone (see below) may be reduced by the Clemmensen method to tetralin (tetrahydronaphthalene) and the latter converted into naphthalene either catal3d.ically or by means of sulphur or selenium (compare Section, VI,33). 

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. 

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