Sulphonation with 20 oleum

Continuous sulphonation with oleum is a four-stage process (see figure 2). 

the dilution product is allowed to separate into two phases and the lower, aqueous acid layer is removed as spent acid . 

Much of the colour produced during sulphonation is contained in the spent acid. The upper layer in the separator, which contains around 90% alkylbenzene sulphonic acid (the remainder being primarily dissolved sulphuric acid) is also removed from the separator and neutralised with sodium hydroxide solution or with sodium carbonate solution to yield the active paste. When sodium hydroxide is used a considerable amount of heat must be removed. This is done in the third loop reactor of this process, the neutralisation heat exchanger (also known as the neutraliser). If sodium carbonate solution is used, the neutralisation is much less exothermic and no heat exchanger is needed at this stage. 

The active paste has a typical composition of 40 - 50% AD, 5-9% sodium sulphate and less than 1% unsulphonated organic material (free oil). Pastes from oleum sulphonation do not require bleaching. 

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For the other feedstocks, sulphonation with 20% oleum (or sulphuric acid) results in products of unacceptable quality and/or low degrees of conversion. 

Sulphur is considerably cheaper as a starting material from which to raise SO3 than liquid SO3, 65% oleum and 20% oleum. It is also more economical than the three liquid options in transport, handling and storage. Most important of all is the problem of spent acids, resulting from sulphonation with 20% oleum (a dark, 80% strength sulphuric acid, difficult to recycle in the chemical industry) or 65% oleum (a dark, concentrated sulphuric acid, in most countries returnable to producers only at very low prices, sometimes not even compensating for transport costs). 

Spent acid" constitutes the sulphuric acid by-product resulting from sulphonation with 20% oleum or SO3 stripped from 65% oleum ... 

After sulphonation is complete, water is added to the acid products to achieve separation of the alkylbenzene sulphonic acid from sulphuric acid. The "spent acid" represents the lower (high gravity) phase and consists of 78% sulphuric acid, hi y coloured material and about 0.1 - 0.2% sulphonic acids. The separation is based on the principle that many sulphonic acids are relatively insoluble in sulphuric acid of intermediate strength (i.e. about 50 -80%) obtained by suitable dilution of the reaction mixture of sulphonic acid and sulphuric acid after sulphonation with 20% oleum or 100% sulphuric acid. This 70 - 80% sulphuric acid is unlike normal sulphuric acid especially with respect to colour, organic matter and viscosity. It has generally a dark brown/black colour and a strong odour of SO2. 

Chemistry of sulphonation with 20% oleum, mass balances and heat... 

Electrophilic substitution at the anthraquinone ring system is difficult due to deactivation (electron withdrawal) by the carbonyl groups. Although the 1-position in anthraquinone is rather more susceptible to electrophilic attack than is the 2-position, as indicated by jt-electron localisation energies [4], direct sulphonation with oleum produces the 2-sulphonic acid (6.3). The severity of the reaction conditions ensures that the thermodynamically favoured 2-isomer, which is not subject to steric hindrance from an adjacent carbonyl group, is formed. However, the more synthetically useful 1-isomer (6.7) can be obtained by sulphonation of anthraquinone in the presence of a mercury(II) salt (Scheme 6.4). It appears that mercuration first takes place at the 1-position followed by displacement. Some disulphonation occurs, leading to the formation of the 2,6- and 2,7- or the 1,5- and 1,8-disulphonic acids, respectively. Separation of the various compounds can be achieved without too much difficulty. Sulphonation of anthraquinone derivatives is also of some importance. 

Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol. 

The chief advantage in the use of this acid is its selective property, whereby certain sulphonic acids are formed, which could not be formed by direct sulphonation with sulphuric acid or oleum, or which might be formed only in presence of other isomers, the separation of which might be difficult. For example, naphthalene sulphonated with oleum at the ordinary temperature gives a mixture of 1 5- and 1 6-disulphonic acids, while chlorosulphonic acid yields only the 1 5-acid. Similarly, with toluene, chiefly the ortho acid is formed. With excess of chlorosulphonic acid a sulphonyl chloride is formed, except in the case of phenols or naphthols, which give the free sulphonic acid. 

Fig. (4). Synthesis of alizarin based oil sulphonation with oleum and alkali fusion [20]...

Continuous sulphonation with oleum - a four-stage process Viscosity of sulphur... 

Anthraquinone can be brominated, chlorinated directly to the tetrachloro (I, 4, 5, 8-) stage, nitrated easily in the 1-position, but gives the 1,5-and 1,8-dinitro-derivalives on prolonged nitration the nitro groups in these compounds are easily displaced by neutral solutions of alkali sulphites yielding the corresponding sulphonic acids. Sulphonation with 20-30 % oleum gives the 2- 2,6- and 2,7-derivatives in the presence of Hg the 1- 1,5- and 1,8- derivatives are formed. 

There are certain formal analogies here to m- attack on nitrobenzene (cf. p. 152), but pyridine is very much more difficult to substitute than the former. Thus nitration, chlorination, bromination and Friedel-Crafts reactions cannot really be made to take place usefully, and sulphonation only occurs on heating with oleum for 24 hours at 230°, with an Hg2 catalyst. This difficulty of attack is due partly to the fact that pyridine has an available electron pair on nitrogen, and can thus protonate (66), or interact with an electrophile (67) ... 

The yellow crust is then finely ground and extracted with 95% alcohol. This dissolves the toluidine, thiotoluidine, and the dehydrothiotoluidine, leaving the insoluble primuline base (p. 389). The extract is evaporated to dryness and heated to 250°, which removes the toluidine and part of the thiotoluidine. The mixture is then sulphonated with 25% oleum and poured on to ice, filtered, and well washed with water until the washings give only a faint acid reaction. The toluidine and thiotoluidine sulphonic acids pass into solution. The residue is dissolved in 50 gms. of 20% ammonia solution and 800 c.cs. water, and heated to 80°, other 100 c.cs. of water being then added. The solution is filtered hot, if necessary, and the ammonium salt of dehydrothiotoluidine sulphonic acid separates out in the course of 2 days. Primuline can be obtained from the mother liquor by saturating with common salt at the boiling point. 

Sulphonation with sulphuric acid or oleum is initially rapid and exothermic. The rate of reaction is highly dependent on the concentration of the sulphuric acid, so the reaction slows significantly as the sulphonating agent is consumed and further diluted by the water which is a by-product of the reaction. Processes based on sulphuric acid use large excesses, resulting in high levels of waste acid or residual sulphate in the neutralised product. An alternative is to remove the water from the reaction mixture, usually by two-phase distillation, with excess substrate as a carrier. 

Chemistry and general properties. The product is prepared by reacting a fatty acid, typically oleic acid (a 08 1 acid), with oleum, or preferably sulphur trioxide. If a saturated fatty acid is used, the product is an a-sulphofatty acid, R(S03H)C00H and the reaction mechanism is thought to be similar to that previously suggested for the sulphonation of methyl esters. With the use of an unsaturated acid, such as oleic, the picture becomes more complex. The reaction chemistry is not fully understood, but the product is a mixture of y-hydroxy sulpho fatty acid and o -sulphonated oleic acid. 

Sulphophenyl-a-naphthylmethylarsine oxide, (CgHi.SOjH) (CioH-) CH3)AsO, results when the preceding oxide is treated with oleum (20 per cent. SO 3) and the whole poured into water. The precipitate formed is dissolved in ammonium hydroxide, the solution boiled with charcoal and filtered into hot acetic acid. The sulphonic acid separates on cooling in fine white crj stals, M.pt. 249 C. ... 

Nucleophilic substitution by a hydroxyl ion displaces a hydride ion. Alizarin plants were subsequently built in Germany and England [17-19]. The procedure developed by Koch (B.A.S.F.) is based on the sulphonation of the anthraquinone with oleum followed by alkali fusion under addition of an oxidising agent (Fig. (4)) [20]. 

In the detergent industry sulphonation processes with sulphuric acid, oleum and SO3-complexes are essentially of historical significance, and are not any longer used in developed countries. In the production of white oils, however, sulphonation with concentrated sulphuric acid and oleum is still used. The sulphuric acid treatment of selected petroleum fractions lead to petroleum sulphonates the sodium or ammonium salts of which are used in tertiary oil recovery, metallurgy, froth flotation and concrete industry, while the magnesium, calcium and barium salts are used as dopes in fuels and lubricants. The sulphonation with chlorosulphonic acid continue to remain useful in batch processes, typically on a relatively small scale ... 

Sulphonation of saturated fatty acids (or esters) can be effected with oleum, stabilized sulphur trioxide, dilute vaporized sulphur dioxide or chlorosulphonic acid. Trichloromethane, tetrachloromethane, tetra-chloroethene and liquid sulphur dioxide have been used as reaction solvent. 

The treatment of this collected oleum is described in section 7.3.1. A small amount of oleum mist is formed which has to be removed before the sulphonation stage. Oleum reacts rapidly with organics, leading to poor colour/charring of organic feedstock and by-product formation (e.g. dioxane). Moreover oleum droplets or crystals can cause maldistribution of organic feedstock in the top of the reactor. The installation of a high-efficiency demister is therefore recommended. 

Pyrroles containing electron-attracting substituents have been sulphonated with sulphuric acid or oleum, and also chlorosulphonated 3 . 

The sulphonic acids are usually prepared by the action of sulphuric acid upon a compound. The concentration of the acid and the temperature of reaction are varied according to the reactivity of the compound. Often oleum is used or even chiorosulphonic acid. Alternatively sulphur trioxide complexed to pyridine or dioxan can be used with reactive substrates. Aminosulphonic acids such as sulphanilic and naphthionic acids are most conveniently prepared by heating the sulphate of the amine at ISO C. 

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 ... 

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 ... 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

The situation that was described in the previous accident happened again and even twice, with o-nitrotoluene and p-nitrotoluene during their sulphonation. Oleum containing 24% sulphur trioxide had been added to o-nitrotoiuene at 32 C. The reaction went out of control and caused the 2 I reactor to break and a very large volume of carbonised compound to be ejected (this was probably due to the decomposition of the sulphonic acid formed) ... 

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