Preparation of Sulfuric Acid

In the 1800s, the most important method for producing H2S04 was by the lead chamber process. Today, sulfuric acid is produced by a method known as the contact process. In the contact process, sulfur is burned to give S02 or the required S02 is recovered from coal burning or ore roasting processes. The S02 is then oxidized in the presence of a catalyst to produce SO3 (see Section 15.7.2). Typical catalysts are spongy platinum or sodium vanadate. Next, the SO3 is dissolved in 98% sulfuric acid  

water can be added to produce any desired concentration of sulfuric acid, even 100%  

Earlier in this chapter, we described the preparation of S02 from burning fossil fuels and roasting ores as sources of S02 that are replacing the burning of sulfur. 

In the older lead chamber process, S02, oxygen, steam, NO, and N02 were introduced into lead-lined chambers. The nitrogen oxides catalyze the oxidation of S02, and the reactions that occur can be summarized as follows  

The actual reactions are quite complex, however, and they will not be described further because the process is no longer of commercial importance. 

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Anhydrous sulfuric acid is a dense, viscous liquid which is readily miscible wilh water in all proportions the reaction is extremely exothermic ( 880kJmol at infinite dilution) and can result in explosive spattering of the mixture if the water is added to the acid it is therefore important always to use the reverse order and add the acid to the water, slowly and with stirring. The large-scale preparation of sulfuric acid is a major industr) in most countries and is described in the preceding Panel. 

But by far the greatest use of sulfur is in the preparation of sulfuric, acid (H.S0 ). This acid enters into the (CONTINUED ON PAGE 52)... 

The commercial significance of SO3 for the preparation of sulfuric acid has already been mentioned, and this is the most important aspect of its industrial chemistry. However, substantial amounts of pure SO3 are prepared commercially for use in the manufacture of, for example, chloro- and fluorosulfonic acids, thionyl chloride, and as a sulfonating agent. Pure, hquid SO3 is obtained industrially by distillation from oleum. 

The equations for the preparation of sulfuric acid starting with sulfur are ... 

SO2 Sulfur dioxide Preparation of sulfuric acid food preservative metal refining... 

How can we explain how a catalyst can influence a reaction without being consumed by it Briefly, the catalyst must participate in at least one step of a reaction and be regenerated in a later step. Consider the commercial preparation of sulfuric acid, H2SO4, from sulfur dioxide, SO2. The first step involves the reaction of SO2 with O2 to produce sulfur trioxide, SO3. For this reaction to occur at an economical rate, it requires a catalyst. An early industrial process employed nitric oxide, NO, as the catalyst. 

During the commercial preparation of sulfuric acid, sulfur dioxide reacts with oxygen in an exothermic reaction to produce sulfur trioxide. In this step, sulfur dioxide mixed with oxygen-enriched air passes into a reaction tower at about 420°C, where reaction occurs on a vanadium(V) oxide catalyst. Discuss the conditions used in this reaction in terms of its effect on the yield of sulfur trioxide. Are there any other conditions that you might explore in order to increase the yield of sulfur trioxide ... 

FIGURE 23.7c Preparation of sulfuric acid solutions of any specific gravity from concentrated sulfuric add. From G. W. Vinal, Storage Batteries, Wiley, New York, 1955, p. 129.)... 

The danger is greater with more concentrated preparations of sulfuric acid, but even the normal laboratory "dilute" grade (approximately 1 M, 10%) will char paper by dehydration if left in contact for a sufficient time. Therefore, solutions equal to or stronger than 1.5 M are labeled "CORROSIVE", while solutions greater than 0.5 M but less than 1.5 M are labeled "IRRITANT". Fuming sulfuric acid (oleum) is not recommended for use in schools as it is quite hazardous. 

The combination of sulfuric acid addition to propene followed by hydrolysis of the resulting isopropyl hydrogen sulfate is the major method by which over 10 lb of isopropyl alcohol is prepared each year m the United States... 

As a method for the preparation of alkenes a weakness in the acid catalyzed dehydration of alcohols IS that the initially formed alkene (or mixture of alkenes) sometimes isomenzes under the conditions of its formation Write a stepwise mechanism showing how 2 methyl 1 butene might isomenze to 2 methyl 2 butene in the presence of sulfuric acid... 

The purity of a pharmaceutical preparation of sulfanilamide, C6H4N2O2S, can be determined by oxidizing the sulfur to SO2 and bubbling the SO2 through H2O2 to produce H2SO4. The acid is then titrated with a standard solution of NaOH to the bromothymol blue end point, where both of sulfuric acid s acidic protons have been neutralized. Calculate the purity of the preparation, given that a 0.5136-g sample required 48.13 mL of 0.1251 M NaOH. 

Furfural was first isolated in the eady nineteenth century. Dobereiner is credited with the discovery. He obtained a small amount of a yellow "oil" (too Htde to characterize) as a by-product in the preparation of formic acid (8). Other chemists found that the same "oil" having a charactedstic aroma could be obtained by boiling finely divided vegetable materials such as oats, com, sawdust, bran, etc, with aqueous sulfuric acid or other acids (9,10). The oil was present in the Hquid resulting from condensation of the vapors produced during heating. The empirical formula was determined by Stenhouse... 

Magnesium sulfate heptahydrate may be prepared by neutralization of sulfuric acid with magnesium carbonate or oxide, or it can be obtained directly from natural sources. It occurs abundantly as a double salt and can also be obtained from the magnesium salts that occur in brines used for the extraction of bromine (qv). The brine is treated with calcium hydroxide to precipitate magnesium hydroxide. Sulfur dioxide and air are passed through the suspension to yield magnesium sulfate (see Chemicals frombrine). Magnesium sulfate is a saline cathartic. 

MAA and MMA may also be prepared via the ammoxidation of isobutylene to give meth acrylonitrile as the key intermediate. A mixture of isobutjiene, ammonia, and air are passed over a complex mixed metal oxide catalyst at elevated temperatures to give a 70—80% yield of methacrylonitrile. Suitable catalysts often include mixtures of molybdenum, bismuth, iron, and antimony, in addition to a noble metal (131—133). The meth acrylonitrile formed may then be hydrolyzed to methacrjiamide by treatment with one equivalent of sulfuric acid. The methacrjiamide can be esterified to MMA or hydrolyzed to MAA under conditions similar to those employed in the ACH process. The relatively modest yields obtainable in the ammoxidation reaction and the generation of a considerable acid waste stream combine to make this process economically less desirable than the ACH or C-4 oxidation to methacrolein processes. 

Nitric acid is a strong monobasic acid, a powerful oxidising agent, and nitrates many organic compounds. Until the end of the nineteenth century, it was made by heating a metallic nitrate salt with less volatile concentrated sulfuric acid. Removal of the volatile nitric acid permits the reaction to go to completion. This method is still used for laboratory preparation of the acid. 

The reaction proceeds quantitatively and the hydroiodic acid can be removed by repeated distillation at 5.3 kPa (40 mm Hg), leaving pure H2PO2 as the product. Phosphinic acid may also be prepared by the treatment of barium hypophosphite [14871-79-5] with a stoichiometric quantity of sulfuric acid to precipitate barium sulfate. 

Synthetic Iron Oxides. Iron oxide pigments have been prepared synthetically since the end of the seventeenth century. The first synthetic red iron oxide was obtained as a by-product of the production of sulfuric acid from iron sulfate containing slate. Later, iron oxide pigments were produced direcdy by the thermal decomposition of iron sulfates. In the 1990s, about 70% of all iron oxide pigments consumed are prepared synthetically. 

Synthesis. Hydroxyhydroquiaone is not produced on a large scale, but many uses for it are being developed. The most convenient preparation of hydroxyhydroquiaone is the reaction of -benzoquiaone with acetic anhydride ia the preseace of sulfuric acid or phosphoric acid. The resultant triacetate (29) can be hydrolyzed to hydroxyhydroquiaone (86). 

Electrolytic reductions generally caimot compete economically with chemical reductions of nitro compounds to amines, but they have been appHed in some specific reactions, such as the preparation of aminophenols (qv) from aromatic nitro compounds. For example, in the presence of sulfuric acid, cathodic reduction of aromatic nitro compounds with a free para-position leads to -aminophenol [123-30-8] hy rearrangement of the intermediate N-phenyl-hydroxylamine [100-65-2] (61). 

Reaction of / fZ-amyl alcohol with urea in the presence of sulfuric acid gives a monoalkylated urea (61,62). Monoalkyl ureas are used to prepare uracil derivatives which are useful as herbicides, fungicides, and plant growth regulators (61). 

Sulfamic acid [5329-14-6] (amidosulfuric acid), HSO2NH2, molecular weight 97.09, is a monobasic, inorganic, dry acid and the monoamide of sulfuric acid. Sulfamic acid is produced and sold in the form of water-soluble crystals. This acid was known and prepared in laboratories for nearly a hundred years before it became a commercially available product. The first preparation of this acid occurred around 1836 (1). Later work resulted in identification and preparation of sulfamic acid in its pure form (2). In 1936, a practical process which became the basis for commercial preparation was developed (3,4). This process, involving the reaction of urea with sulfur trioxide and sulfuric acid, continues to be the main method for production of sulfamic acid. 

Later, a completely different and more convenient synthesis of riboflavin and analogues was developed (34). It consists of the nitrosative cyclization of 6-(A/-D-ribityl-3,4-xyhdino)uracil (18), obtained from the condensation of A/-D-ribityl-3,4-xyhdine (11) and 6-chlorouracil (19), with excess sodium nitrite in acetic acid, or the cyclization of (18) with potassium nitrate in acetic in the presence of sulfuric acid, to give riboflavin-5-oxide (20) in high yield. Reduction with sodium dithionite gives (1). In another synthesis, 5-nitro-6-(A/-D-ribityl-3,4-xyhdino) uracil (21), prepared in situ from the condensation of 6-chloro-5-nitrouracil (22) with A/-D-ribityl-3,4-xyhdine (11), was hydrogenated over palladium on charcoal in acetic acid. The filtrate included 5-amino-6-(A/-D-ribityl-3,4-xyhdino)uracil (23) and was maintained at room temperature to precipitate (1) by autoxidation (35). These two pathways are suitable for the preparation of riboflavin analogues possessing several substituents (Fig. 4). 

Arsenic trifluoride (arsenic(III) fluoride), AsF, can be prepared by reaction of arsenic trioxide with a mixture of sulfuric acid and calcium fluoride or even better with fluorosulfonic acid. Chlorine reacts with ice-cold arsenic trifluoride to produce a hygroscopic soHd compound, arsenic dichloride trifluoride [14933-43-8] ASCI2F35 consisting of AsQ. and AsF ions (21). Arsenic trifluoride forms a stable adduct, 2AsF2 SSO, with sulfur trioxide and reacts with nitrosyl fluoride to give nitrosonium hexafluoroarsenate(V) [18535-07-4] [NO][AsFg]. 

Commercial manufacture of methyl bromide is generally based on the reaction of hydrogen bromide with methanol. For laboratory preparation, the addition of sulfuric acid to sodium bromide and methanol has been used (80). Another method involves the treatment of bromine with a reducing agent, such as phosphoms or sulfur dioxide, to generate hydrogen bromide (81). 

Cellulose acetate [9004-35-7], prepared by reaction of cellulose with acetic anhydride, acetic acid, and sulfuric acid, is spun into acetate rayon fibers by dissolving it in acetone and spinning the solution into a column of warm air that evaporates the acetone. Cellulose acetate is also shaped into a variety of plastic products, and its solutions are used as coating dopes. Cellulose acetate butyrate [9004-36-8], made from cellulose, acetic anhydride, and butyric anhydride in the presence of sulfuric acid, is a shock-resistant plastic. 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

Other mixed esters, eg, cellulose acetate valerate [55962-79-3] cellulose propionate valerate [67351-41-17, and cellulose butyrate valerate [53568-56-2] have been prepared by the conventional anhydride sulfuric acid methods (25). Cellulose acetate isobutyrate [67351-38-6] (44) and cellulose propionate isobutyrate [67351-40-0] (45) have been prepared with a 2inc chloride catalyst. Large amounts of catalyst and anhydride are required to provide a soluble product, and special methods of delayed anhydride addition are necessary to produce mixed esters containing the acetate moiety. Mixtures of sulfuric acid and perchloric acid are claimed to be effective catalysts for the preparation of cellulose acetate propionate in dichi oromethane solution at relatively low temperatures (46) however, such acid mixtures are considered too corrosive for large-scale productions. 

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