Sulphonation of aromatic hydrocarbons

SULPHONATION OF AROMATIC HYDROCARBONS Aromatic hydrocarbons may be mono-sulphonated by heating with a slight excess of concentrated sulphuric acid for benzene, oleum (7-8 per cent. SOj) gives somewhat better results. The reaction is usually complete when all the hydrocarbon has dissolved. Examples are  

Because of the great solubility of sulphonic acids in water and the consequent difficulty in crystallisation, the free sulphonic adds are not usually isolated but are converted directly into the sodium salts. The simplest procedure is partly to neutralise the reaction mixture (say, with solid sodium bicarbonate) and then to pour it into water and add excess of sodium chloride. An equilibrium is set up, for example  

The high sodium ion concentration results in facile crystallisation of the sodium salt. This process of salting out with common salt may be used for recrystallisation, but sodium benzenesulphonate (and salts of other acids of comparable molecular weight) is so very soluble in water that the solution must be almost saturated with sodium chloride and consequently the product is likely to be contaminated with it. In such a case a pure product may be obtained by crystallisation from, or Soxhlet extraction with, absolute alcohol the sul-phonate is slightly soluble but the inorganic salts are almost insoluble. Very small amounts of sulphones are formed as by-products, but since these are insoluble in water, they separate when the reaction mixture is poured into water  

The sulphonation of toluene at 100-120° results in the formation of p-toluene-sulphonic acid as the chief product, accompanied by small amounts of the ortho and meta isomers these are easily removed by crystallisation in the presence of sodium chloride. Sulphonation of naphthalene at about 160° 3uelds largely the p-sulphonic acid at lower temperatures (0-60°) the a-siil-phonic acid is produced almost exclusively. 

Sulphonation is a reversible reaction and, in general, an excess of sulphuric acid is employed, for example  

however, the water formed is removed as formed (compare the preparation of di-n-butyl ether. Section 111,57), the sulphuric acid may react completely and the method may be employed for the preparation of the free sulphonic acid. 

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Di-(l-naphthylmethyl)sulphone forms an excimer but does not react to give an intramolecular cycloaddition product like the corresponding ether but rather fragments to give sulphur dioxide and (l-naphthyl)methyl radicals (Amiri and Mellor, 1978). I-Naphthylacetyl chloride has a very low quantum yield of fluorescence and this is possibly due to exciplex formation between the acyl group and the naphthalene nucleus (Tamaki, 1979). Irradiation leads to decarbonylation. It is known that acyl chlorides quench the fluorescence of aromatic hydrocarbons and that this process leads to acylation of the aromatic hydrocarbon (Tamaki, 1978a). The decarboxylation of anhydrides of phenylacetic acids [171] has been interpreted as shown in (53), involving... 

In liquid-liquid systems, a chemical reaction is encountered for three distinct purposes. Firstly, the reaction may be a part of the process, such as nitration and sulphonation of aromatic substances, alkylation, hydrolysis of esters, oximation of cyclohexanone, extraction of metals and pyrometallurgical operations involving melts and molten slag. Secondly, a chemical reaction is deliberately introduced for separation purposes (e.g. removal of dissolved acidic solutes from a variety of hydrocarbons). Finally, the yield and the rate of formation of many single phase reactions are affected and often can be favourably increased by the deliberately controlled addition to the reaction system of an immiscible extractive phase, whose major purpose is to extract the product from the reactive phase. Such operations are sometimes referred to as "extractive reactions" and have been discussed previously in some detail (14-17). 

A further difference between aliphatic and aromatic hydrocarbons is that only the latter are capable of direct sulphonation. Thus benzene when heated with concentrated sulphuric acid gives benzenesulphonic acid, a reaction which proceeds more readily, however, if chlorosulphonic acid is used instead of sulphuric acid an excess of chlorosulphonic acid however may convert the sul phonic acid into the sulphonyl chloride (c/. p. 181). 

The mechanism of aromatic sulphonation is complex and may vary, e.g. with the concentration of water or oleum in the acid, the temperature, and the hydrocarbon. One active agent is SO3, and one simplified route may be ... 

Paraffin and Aromatic Hydi ocarbon may be separated by the action of fuming sulphuric acid, 4iich forms the sulphonic and with the aromatic hydrocarbon. The product is poured into water. The sulphonic acid dissolves readily in water, whereas the paiaffin is insoluble. 

Since N02 and S03H are substituents of the second order, a second substituent enters in the m-position. Oleum containing a high percentage of sulphur trioxide finally converts benzene into benzene tri-sulphonic acid. Chlorosulphonic acid condenses with aromatic hydrocarbons, giving aryl sulphochlorides. 

The range of organic compounds which have been subject to the Simons process is wide and includes aliphatic and aromatic hydrocarbons, halocarbons, ethers, aliphatic and aromatic amines, heterocyclics, thiols, alkyl sulphonic and carboxylic acids, and their derivatives, among others. 

The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

From its general behaviour it is clear that chlorosulphonic acid is closely related to sulphuric acid. Like the latter acid, but with more vigour, it attacks aromatic hydrocarbons with formation of organic sidphonic acids of the structure R.SOa.OH and sulphones of the structure Rx... 

Reaction LXX. Oxidation of certain Hydrocarbons. (B., 14, 1944 A. Spl., 1869, 300 E.P., 1948 (1869).)—This reaction is confined in the aliphatic series almost exclusively to the replacement by hydroxyl of the hydrogen attached to tertiary carbon atoms. A powerful oxidising agent, e.g., chromic acid in glacial acetic acid, is necessary. In the aromatic series the reaction is somewhat more easy to accomplish when the sodium salt of anthraquinone-jS-monosulphonic acid, for example, is fused under pressure with caustic soda and a little potassium chlorate, replacement of both a hydrogen atom and the sulphonic acid group by hydroxyl occurs, and alizarin ( /f-dihydroxyanthraquinone) is obtained. 

Reaction LXXV. Fusion of Aromatic Sulphonic Acids with Caustic Alkalis. (Z. Ch (1876), 3, 299 J. pr., [2], 17, 394 20, 300.)—This method is of technical importance as it is employed to prepare phenols and naphthols from the parent hydrocarbons. These phenols and naphthols are much used as intermediates in the dye industry. The method cannot easily be applied to determine structure, owing to rearrangement liable to occur at the elevated temperatures. Caustic potash is more convenient than soda, since it generally yields a more easily fusible mixture. 

Reaction CXLVI. Action of Concentrated Sulphuric Acid on Hydrocarbons or Substituted Hydrocarbons.—When cone, sulphuric acid acts on an aromatic hydrocarbon or substituted hydrocarbon, one or more of the H atoms in the nucleus is replaced by the sulphonic group (S02.0H). 

The compounds formed are termed sulphones they are also formed by the action of cone, and fuming sulphuric acid on hydrocarbons (see p. 313), and by heating aromatic sulphonic acids with an aromatic hydrocarbon in presence of a dehydrating agent, such as P205. 

The preparation of phenols by the hydrolysis of diazonium salts with hot aqueous acid, and by a recent milder procedure suitable for diazonium salts having additional acid-sensitive groups, is discussed in Section 6.7.1, p. 922, and illustrated in Expt 6.69. Although these methods enable an aromatic hydrocarbon system to be converted in good yield into a phenol via the corresponding nitro and amino derivatives, the shorter route involving the alkaline fusion of the sulphonic acid discussed above may often be preferred. 

For characterisation, aromatic hydrocarbons can be sulphonated, chloro-sulphonated, carboxybenzoylated and nitrated. Polynuclear aromatic hydrocarbons, and many of their derivatives, yield crystalline adducts with picric acid, styphnic acid, 1,3,5-trinitrobenzene and 2,4,7-trinitrofluorenone. 

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