Sulfur trioxide 117 Water molecule

Sulfur oxides (SO,) are compounds of sulfur and oxygen molecules. Sulfur dioxide (SO2) is the predominant form found in the lower atmosphere. It is a colorless gas that can be detected by taste and smell in the range of 1, (X)0 to 3,000 uglm. At concentrations of 10,000 uglm , it has a pungent, unpleasant odor. Sulfur dioxide dissolves readily in water present in the atmosphere to form sulfurous acid (H SOj). About 30% of the sulfur dioxide in the atmosphere is converted to sulfate aerosol (acid aerosol), which is removed through wet or dry deposition processes. Sulfur trioxide (SO3), another oxide of sulfur, is either emitted directly into the atmosphere or produced from sulfur dioxide and is readily converted to sulfuric acid (H2SO4). 

Anhydride. A chemical compound derived from an acid by elimination of the atoms that make up water. Example SO3, sulfur trioxide, is the anhydride of sulfuric acid, H2SO4. Anhydrides are a class of organic compounds derived from the combination of two carboxylic acids (R-COOH) by. elimination of a molecule of water. For example, acetic acid (CH3COOH) minus water gives acetic anhydride. 

Hydrated nickel sulfate on heating at 103°C loses all of its water molecules. At 848°C, the anhydrous sulfate decomposes to nickel oxide and sulfur trioxide ... 

Gas phase molecular aggregates that contain acid molecules have been produced with free jet expansion techniques and detected by using electron impact ionization mass spectrometry. The clusters of aqueous nitric acid paralleled many properties of the condensed phase. Multiple nitric acid molecules were found in the clusters that were sufficiently dilute. The acid molecule was absent in the ionized clusters involving HC1 and only water was evident. Experiments also demonstrated the reactivity of ammonia with aqueous nitric acid and sulfur dioxide clusters and of sulfur trioxide with water clusters. The natural occurrence of acid cluster negative ions offers a means to probe the gas phase acid loading of the atmosphere through laboratory and field studies of the ion chemistry. 

PROP Chemical compounds derived from acids by elimination of a molecule of water. Thus, sulfur trioxide (SO3) is the anhydride of sulfuric acid (H2SO4) carbon dioxide (CO2) is the anhydride of carbonic acid (H2CO3) phthaUc acid (C6H4(C02H)2) minus water gives phthalic anhydride (C6H4(C02)0). This term should not be confused with anhydrous, meaning without water. 

Sulfur trioxide (SO3) is an industrially important compound key to the production of sulfuric acid. It tends to polymeric forms both in the solid and liquid states. As a gas, the molecules have a planar triangular structure in which the sulfur atom has a high affinity for electrons. This explains its action as a strong Lewis acid towards bases that it does not oxidize. It can thus crystallize complexes with pyridine or trimethy-lamine. It has a very strong affinity for water and hence rapidly associates with water in the environment. 

The sulfur trioxide reacts very rapidly with water to form a H20-S03 complex that reacts with a further water to form the aquated sulfuric acid molecule. It is also likely that SO3 reacts with water in aerosols. Although there are possibilities that SO3 could react with ammonia to form sulfamic acid, most of the trioxide will be converted to sulfuric acid (Findlayson-Pitts and Pitts, 2000). 

Sulfenes (1) are the inner anhydrides of sulfonic acids, derived formally by the removal of one molecule of water from one molecule of the acid. They occur chiefly as short-lived intermediates in a number of valuable synthetic reactions it is probably fair to state that they are, surprisingly, both more frequently used and less well-known than their analogues such as sulfur trioxide or ketenes. This suggests that, although a number of aspects of sulfene chemistry have been presented in reviews1-4, there is a place for an up-to-date source whereby chemists may become better acquainted with the chemistry of sulfenes we hope that this chapter will fill the need for the present. 

Note that as the water molecule attaches to sulfur trioxide, a proton shift occurs to form suifuric acid. 

The sulfonation of benzene by concentrated sulfuric acid is another reaction that involves the reaction of benzene with an electrophilic species. When benzene reacts with sulfuric acid, it attacks the electrophilic sulfur atom, as shown in the illustration, to give arenium ion intermediate 43. This intermediate loses a proton via the El reaction, but it also loses a molecule of water to give benzenesulfonic acid (44). (See Chapter 16, Section 16.9, for an introduction to sulfonic acids.) Concentrated sulfuric acid reacts with the water byproduct, which effectively removes this product from the reaction, and drive the reaction toward 44. In other words, concentrated sulfuric acid acts as a drying agent. If fuming sulfuric acid (which is simply concentrated sulfuric acid saturated with sulfur trioxide, SO3) is used rather than sulfuric acid, the reaction proceeds faster to give 44 and with fewer problems. This latter reaction depends on the fact that the sulfur atom in SO3 is more electrophilic than the sulfur atom in sulfuric acid. 

For compounds containing two non-metal atoms, the actual number of atoms of the element or the oxidation number is stated, for example carbon monoxide, CO, where mon- means one, and carbon dioxide, CO2, where di- means two. Sulfur dioxide is SO, but could also be named sulfur(iv) oxide, where iv (4) is the oxidation number of sulfur. Sulfur trioxide, SO3, where tri-means three, could also be named sulfur(vi) oxide. There are a small number of simple molecules that do not follow these rules. For example, water, H2O, ammonia, NH3 and methane, CH4. 

Figure 9.5 The ionic formulations of the sulfur trioxide and water molecules... 

Antimony trioxide is obtained by direct reaction of the element with oxygen. In the vapor and in the solid below 570°C it consists of P406 type molecules the high-temperature solid form is polymeric. It is insoluble in water or dilute nitric and sulfuric acids, but soluble in hydrochloric and certain organic acids. It dissolves in... 

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