Sulfuryl chloride

Sulfuryl chloride

Sulfuryl chloride is an inorganic compound with the formula SO₂Cl₂. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis.

Sulfuryl chloride is commonly confused with thionyl chloride, SOCl₂. The properties of these two sulfur oxychlorides are quite different: sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions. An alternative IUPAC name is sulfuroyl dichloride.

Sulfur is tetrahedral in SO₂Cl₂, being bound to two oxygen atoms via double bonds and to two chlorine atoms via single bonds. The oxidation state of the sulfur atom is +6, as in H₂SO₄.

Synthesis

SO₂ + Cl₂ à SO₂Cl₂

SO₂Cl₂ is prepared by the reaction of sulfur dioxide and chlorine in the presence of a catalyst, such as activated carbon.  The crude product can be purified by fractional distillation. It is uncommon to prepare SO₂Cl₂ in the laboratory because it is commercially available. Sulfuryl chloride can also be considered a derivative of sulfuric acid.

Reactions

Sulfuryl chloride reacts with water, releasing hydrogen chloride gas and sulfuric acid:

2 H₂O + SO₂Cl₂ à 2 HCl + H₂SO₄

SO₂Cl₂ will also decompose when heated to or above 100 °C, about 30 °C above its boiling point.  Upon standing, SO₂Cl₂ decomposes to sulfur dioxide and chlorine, which gives the older samples a slightly yellowish color.

Uses

Sulfuryl Chloride is the Sulfuric oxychloride where as sulfinyl chloride is the sulfurous oxychloride. Sulfuryl Chloride is a colorless to yellowish liquid with a pungent odor. It boils at 69°C, decomposed by hot water and alkalies; soluble in most organic solvents (benzene, chloroform, carbon tetrachloride and acetic acid). It is not found in nature due to strong hydrolysis. It is explosive also with donor solvents such as alcohols, ethers, DMSO and DMF. It decompose at its boiling point. It has two S-Cl single bonds and two S=O solid bonds. It is prepared by the reaction of sulfur dioxide and chlorine in the presence of activated carbon. It is used as a solvent and as a source of chlorine in chemical reactions. Sulfuryl chloride is useful mainly in preparing pesticides. It is used as a chlorinating (and sulfochlorinating) agent of alcohols, alkyls, aromatics, and epoxides for the target molecules of pharmaceuticals, disinfectants, dyestuffs, rayon, and poison gases. Chlorination in organic synthesis with sulfuryl chloride is more selective than elementary chlorine. It is useful to avoid secondary reactions. Chlorination of alcohols to yield alkyl chloride.

Sulfuryl chloride is often used as a source of Cl₂. Because it is a pourable liquid, it is considered more convenient than Cl₂ to measure, store, and dispense. SO₂Cl₂ is widely used as a reagent in the conversion of C-H → C-Cl adjacent to activating substituents such as carbonyls and sulfoxides. It also chlorinates alkanes, alkenes, alkynes, aromatics, and epoxides. Such reactions occur under free radical conditions using an initiator such as AIBN.

Overall reaction

C₄H₉Cl + SO₂Cl₂+AIBNàC₄H₈Cl₂ + SO₂ + HCl

Below side reaction possible if there is more amount of sulfuryl chloride.

It can also be used to convert disulfides into their corresponding sulfenyl chlorides. SO₂Cl₂ can also convert alcohols to alkyl chlorides. In industry, sulfuryl chloride is most used in producing pesticides.

SO₂Cl₂ can also be used to treat wool to prevent shrinking.

Precautions

SO₂Cl₂ is toxic, corrosive, and acts as a lachrymator. As described above, it can form explosive mixtures with water, as well as donor solvents such as DMSO and DMF.

Selenium dioxide

Selenium dioxide (SeO₂)

Selenium dioxide (SeO₂) is an important reagent in organic syntheses, as it is both an oxidant and weakly acidic.  Selenium dioxide is the chemical compound with the formula SeO₂. This colorless solid is one of the most frequently encountered compounds of selenium.  The solid sublimes readily. The vapor has an odor resembling horseradish sauce and can burn the nose and throat on inhalation.  SeO₂ is considered an acidic oxide: it dissolves in water to form selenous (selenious) acid. Often the terms selenous acid and selenium dioxide are used interchangeably. It reacts with base to form selenite salts containing the SeO2−3 anion. For example, reaction with sodium hydroxide produces sodium selenite:

SeO₂ + 2 NaOH → Na₂SeO₃ + H2O

Uses in Organic synthesis:

SeO₂ is an important reagent in organic synthesis. Oxidation of paraldehyde (acetaldehyde trimer) with SeO₂ gives glyoxal and the oxidation of cyclohexanone gives cyclohexane-1,2-dione. The selenium starting material is reduced to selenium, and precipitates as a red amorphous solid which can easily be filtered off. This type of reaction is called a Riley oxidation. It is also renowned as a reagent for "allylic" oxidation, a reaction that entails the conversion

R₂C=CR'-CHR"₂ + [O] → R₂C=CR'-C(OH)R"₂

(where R, R', R" are alkyl or aryl).

Mechanism of oxidation

Procedures:

A 500-ml three-necked, round-bottomed flask is fitted with a mechanical stirrer, a thermometer, a dropping funnel, and a reflux condenser. A solution of 0.74 g. (0.0067 mole) of selenium dioxide in 150 ml. of tert-butyl alcohol is introduced into the flask, followed by 68 g. (0.50 mole) of β-pinene. The resulting mixture is warmed to 40 °C with a hot water bath before 35 ml. (0.62 mole) of 50% aqueous hydrogen peroxide is added drop wise over 90 minutes, during which time the mixture is maintained at 40–50 °C by occasional immersion in a cold water bath. After stirring for an additional 2 hours, the reaction mixture is diluted with 50 ml. of benzene, washed with three 50-ml. portions of saturated aqueous ammonium sulfate, and dried over sodium sulfate. A small amount of hydroquinone is added, and the solvents are removed on a rotary evaporator. trans-Pinocarveol is isolated by simple distillation under reduced pressure, yielding 37–42 g. (49–55%), b.p. 60–70° (1 mm.).

Procedure was taken from Organic Syntheses, Coll. Vol. 6, p.946 (1988); Vol. 56, p.25 (1977).

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1,2-Cyclohexanedione. A 3-l. round-bottomed flask, fitted with stirrer and dropping funnel, is placed in a water bath containing a coppercoil through which cooling water may be circulated. In the 3-l. flask is placed 1708 g. (17.4 moles, 1.8 l) of cyclohexanone. Tap water is circulated through the cooling coil, and a solution containing 387 g. (3 moles) of selenious acid (H₂SeO₃), 500 ml. of 1,4-dioxane, and 100 ml. of water is added drop wise and with stirring to the cyclohexanone over a period of 3 hours. The reaction mixture immediately turns yellow, and red amorphous selenium gradually appears. Stirring is continued for 5 additional hours at water-bath temperatures and then for 6 more hours at room temperature. Removal of the bulky, amorphous selenium is accomplished with the aid of a 6-in. Buchner funnel. The selenium is returned to the reaction flask and extracted with 300 ml. of boiling 95% ethanol for 1 hour. The solution, obtained by decantation from the compact gray selenium, is combined with the above filtrate in a 4-l. distilling flask. Distillation under reduced pressure gives two fractions. The lower-boiling fraction (25–60°/16 mm.) consists mainly of ethanol, water, dioxane, and cyclohexanone; the higher-boiling one (60–90°/16 mm.) contains cyclohexanone and 1,2-cyclohexanedione with traces of water and dioxane. The yield of crude product is approximately 322 g.

Procedure was taken from Organic Syntheses, Coll. Vol. 4, p.229 (1963); Vol. 32, p.35 (1952).

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Microwave-assisted selenium dioxide mediated selective oxidation of 1-tetralones to 1,2-naphthoquinones

This is a microwave reaction reported in Tetrahedron Letters Volume 50, Issue 1, 7 January 2009, Pages 39-40

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Tips: 

1. Since only catalytic quantities of selenium dioxide are required, the danger of handling large quantities of this material is avoided.
2. Formation of selenium and organoselenides commonly arise in oxidations using molar quantities of selenium dioxide, are not encountered.
3. If too much selenous acid is added at once, or the cooling discontinued, the solution will heat up and the reaction will become extremely vigorous with subsequent decrease in yield.
4. Selenium compounds are exceedingly toxic