Sulfonation of naphthalene

Sulfonation. Sulfonation of naphthalene with sulfuric acid produces mono-, di-, tri-, and tetranaphthalenesulfonic acids (see Naphthalene derivatives), ah of the naphthalenesulfonic acids form salts with most bases. Naphthalenesulfonic acids are important starting materials in the manufacture of organic dyes (15) (see Azo dyes). They also are intermediates used in reactions, eg, caustic fusion to yield naphthols, nitration to yield nitronaphthalenesulfonic acids, etc. 

Generally, the sulfonation of naphthalene leads to a mixture of products. Naphthalene sulfonation at less than ca 100°C is kineticaHy controlled and produces predominandy 1-naphthalenesulfonic acid (4). Sulfonation of naphthalene at above ca 150°C provides thermodynamic control of the reaction and 2-naphthalenesulfonic acid as the main product. Reaction conditions for the sulfonation of naphthalene to yield desired products are given in Figure 1 alternative paths are possible. A Hst of naphthalenesulfonic acids and some of their properties is given in Table 1. 

Naphthalenesulfonic Acid. The sulfonation of naphthalene with excess 96 wt % sulfuric acid at < 80°C gives > 85 wt % 1-naphthalenesulfonic acid (a-acid) the balance is mainly the 2-isomer (P-acid). An older German commercial process is based on the reaction of naphthalene with 96 wt % sulfuric acid at 20—50°C (13). The product can be used unpurifted to make dyestuff intermediates by nitration or can be sulfonated further. The sodium salt of 1-naphthalenesulfonic acid is required, for example, for the conversion of 1-naphthalenol (1-naphthol) by caustic fusion. In this case, the excess sulfuric acid first is separated by the addition of lime and is filtered to remove the insoluble calcium sulfate the filtrate is treated with sodium carbonate to precipitate calcium carbonate and leave the sodium l-naphthalenesulfonate/7J(9-/4-J7 in solution. The dry salt then is recovered, typically, by spray-drying the solution. 

The older methods have been replaced by methods which require less, if any, excess sulfuric acid. For example, sulfonation of naphthalene can be carried out in tetrachloroethane solution with the stoichiometric amount of sulfur trioxide at no greater than 30°C, followed by separation of the precipitated l-naphthalenesulfonic acid the filtrate can be reused as the solvent for the next batch (14). The purification of 1-naphthalenesulfonic acid by extraction or washing the cake with 2,6-dimethyl-4-heptanone (diisobutyl ketone) or a C-1—4 alcohol has been described (15,16). The selective insoluble salt formation of 1-naphthalenesulfonic acid in the sulfonation mixture with 2,3-dimethyl aniline has been patented (17). 

Sulfonation can be conducted with naphthalene—92 wt % H2SO4 in a 1 1.1 mole ratio with staged acid addition at 160°C over 2.5 h to give a 93% yield of the desired product (20). Continuous mono sulfonation of naphthalene with 96 wt % sulfuric acid in a cascade reactor at ca 160°C gives... 

Stuerga et al. [74] showed that, in the sulfonation of naphthalene, the ratio of the products, naphthalene-1- and 2-sulfonic acids, depends on the MW power applied. Higher powers, which cause higher heating rates, increase the proportion of the thermodynamically more stable product, naphthalene 2-sulfonic acid, in the product mixture. 

Sulfonation. Sulfonation of naphthalene with sulfuric acid produces mono-, di-, tri-, and leLranaplitlialenesulfoiiic acids. Naplitlialeiiesulfonic acids are important starting materials in the manufacture of organic dyes. They arc also intermediates used m reactions. 

Stuerga, D., Gonon, K. and Lallemant, M., Microwave heating as a new way to induce selectivity between competitive reactions - application to isomeric ratio control in sulfonation of naphthalene, Tetrahedron, 1993, 49, 6229. 

Fig. 5.19. Kinetically controlled sulfonation of naphthalene (thermodynamically controlled sulfonation of naphthalene Figure 5.8).

Fig. 13.57. Examples of products obtained from the sulfonation of naphthalene.

Technical Observations. The sulfonation of naphthalene is carried out in huge cast iron kettles holding 1000 to 3000 liters. Heating is done either directly with generator gas or by means of a steam jacket (double wall) (Figure 31) which must withstand at least 6 atmospheres in order that the required temperature of 174° can be attained. 

The sulfonation of naphthalene by concentrated sulfuric acid at 80 °C gives naphthalene-1-sulfonic acid. At 160 °C, naphthalene-2-sulfonic acid predominates (Scheme 12.6). The 1-isomer is the more readily formed and is stable at the reaction temperature of 80 °C. However, at 160 °C, not only is naphthalene-1-sulfonic acid desulfonated, but also there is sufficient energy to convert naphthalene into the 2-sulfonic acid, which is stable even at the higher temperature. The 2-substituted isomer is more... 

Figure 12.1 Energy profile for the sulfonation of naphthalene. AG = energy of activation for 1-substitution AG = energy of activation for 2-substitution AG ...

Sulfonation of naphthalene at 40° gives chiefly the a-sulfonic acid above 160° the beta isomer is formed. The mono-, di-, and poly-... 

Sulfonation of naphthalene at 80 yields chiefly 1-naphthalenesulfonic acid sulfonation at 160° or higher yields chiefly 2-naphthalenesulfonic acid. When 1-naphthalenesulfonic acid is heated in sulfuric acid at 160°, it is largely converted into the 2-isomer. These facts become understandable when we recall that sulfonation is readily reversible (Sec. 11.12). 

An example of the interesting sensitivity of sulfonation processes to temperature changes is the well-known sulfonation of naphthalene. At temperatures below 80°, -naphthalenesulfonic acid is formed. At 160 to 165°, the /1-isomer is produced either by direct sulfonation or by heating the a-isomcr with sulfuric acid ... 

Derivation Sulfonation of naphthalene at high temperature and separation from 2,6-isomer. 

PROBLEM 12.20 Sulfonation of naphthalene is reversible at elevated temperature. A different isomer of naphthalenesulfonic acid is the major product at 160°C than is the case at 0°C. Which isomer is the product of kinetic control Which one is formed under conditions of thermodynamic control Can you think of a reason why one isomer is more stable than the other Hint Build space-filling models of both isomers.)... 

Sulfonation of naphthalene does not always lead to substitution at the 1-position. If the reaction is carried out under conditions which cause it to be irreversible (80 °C), substitution occurs at the 1-position. 

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