Addition of Sulfuric Acid to Alkenes

Acids Other than hydrogen halides also add to the carbon-carbon bond of alkenes. Concentrated sulfuric acid, for example, reacts with certain alkenes to form alkyl hydrogen sulfates. 

Notice in the following example that a proton adds to the carbon that has the greater number of hydrogens, and the hydrogen sulfate anion ( OSO2OH) adds to the carbon that has the fewer hydrogens. 

Markovnikov s rule is obeyed because the mechanism of sulfuric acid addition to alkenes is analogous to that described earlier for the electrophilic addition of hydrogen halides. 

Alkyl hydrogen sulfates can be converted to alcohols by heating them with water. This is called hydrolysis, because a bond is cleaved by reaction with water. It is the oxygen-sulfur bond that is broken when an alkyl hydrogen sulfate undergoes hydrolysis. 

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 in the United States. 

The mechanism is similar to that for the addition of HX. In the first step of this reaction the alkene donates a pair of electrons to a proton from snlfnric acid to form a carbocation in the second step the carbocation reacts with a hydrogen sulfate ion to form an alkyl hydrogen snlfate  

The addition of sulfuric acid is also regioselective, and it follows Maikovnikov s rule. Propene, for example, reacts to yield isopropyl hydrogen sulfate rather than propyl hydrogen sulfate  

In one industrial synthesis of ethanol, ethene is first dissolved in 95% sulfuric acid. In a second step water is added and the mixture is heated. Outline the reactions involved. 

---

Addition of Sulfuric Acid to Alkenes 239 Ethylene and Propene The Most Important... 

The overall result of the addition of sulfuric acid to an alkene followed by... 

Boron trifluoride-triethylamine effects a ring-opening elimination of 4,4-difluoro-3-trifluoromethyl-l,2-oxathietane 2,2-dioxide to give fluorosulfonyl-trifluoromethylketene. Eliminations occur from intermediate 3-sultones, obtained by addition of sulfur trioxide to alkenes, to give alkenesulfonic acids. ... 

In another vein, addition of sulfuric acid to an alkene in the presence of a nitrile (R-C=N) or hydrogen cyanide (HC N), either of which can react with the carbo-cation as a nucleophile, apparently leads to nitrilium ions. These ions, on hydrolysis, produce amides. As amides can be hydrolyzed in acid or basic medium to amines and carboxylic acids, the overall process (the Ritter reaction) of carbocation... 

There are actually three reactions called by the name Schmidt reaction, involving the addition of hydrazoic acid to carboxylic acids, aldehydes and ketones, and alcohols and alkenes. The most common is the reaction with carboxylic acids, illustrated above.Sulfuric acid is the most common catalyst, but Lewis acids have also been used. Good results are obtained for aliphatic R, especially for long chains. When R is aryl, the yields are variable, being best for sterically hindered compounds like mesi-toic acid. This method has the advantage over 18-13 and 18-14 that it is just one laboratory step from the acid to the amine, but conditions are more drastic. Under the acid conditions employed, the isocyanate is virtually never isolated. 

Detergents have been manufactured from long-chain alkenes and sulfuric acid, especially those obtained from shale oil or cracking of petroleum wax. These are sulfated with 90—98 wt % acid at 10—15°C for a 5-min contact time and at an acid—alkene molar ratio of 2 1 (82). Dialkyl sulfate initially forms when 96 wt % acid is added to 1-dodecene at 0°C, but it is subsequently converted to the hydrogen sulfate in 80% yield upon the further addition of sulfuric acid. The yield can be increased to 90% by using 98 wt % sulfuric acid and pentane as the solvent at -15°C (83). 

The chemistry of alkyl and alkenyl azides has been well summarized in several recent reviews.233-237 The azides can be prepared via numerous methods, of which the addition of hydrazoic acid to C—C multiple bonds is one. With the exception of cyclopropenes,238 most alkenes are unreactive towards hydrazoic acid itself. However, the addition can be catalyzed by acids (phosphoric acid,239 sulfuric acid260 or trifluoroacetic acid261) or Lewis acids (aluminum trichloride, boron trifluoride or titanium tetrachloride).262... 

Early work on the electrophilic addition of hydrogen peroxide to alkenes was performed in the presence of an acid catalyst, usually sulfuric acid364 or p-toluenesulfonic acid.363 The reaction proceeds via Markovnikov-directed protonation of the double bond (Scheme 3). Subsequent nucleophilic attack of hydrogen peroxide on the carbocation, followed by loss of a proton, furnishes the alkyl hydroperoxide.366... 

Addition of sulfuric acid (Section 6.8) Alkenes react with sulfuric acid to form alkyl hydrogen sulfates. A proton and a hydrogen sulfate ion add to the double bond in accordance with Markovnikov s rule. Alkenes that yield tertiary carbocations on protonation tend to polymerize in concentrated sulfuric acid (Section 6.21). 

This method is also used with alcohols of the stmcture Cl(CH2) OH (114). HaloaLkyl chlorosulfates are likewise obtained from the reaction of halogenated alkanes with sulfur trioxide or from the chlorination of cycHc sulfites (115,116). Chlorosilanes form chlorosulfate esters when treated with sulfur trioxide or chlorosulfuric acid (117). Another approach to halosulfates is based on the addition of chlorosulfuric or fluorosulfuric acid to alkenes in nonpolar solvents (118). 

---