Sulfur-containing odorants materials

Natural gas, liquefied petroleum gas (LPG), and carbon materials serving as the raw materials for cheap technical hydrogen usually contain marked amounts of sulfur compounds. In addition, sulfur-containing odorants (tetrahydrothiophene or ethylmercaptan) often are purposely added to the gas distribution network so that gas leaks may be detected in a timely manner, because natural gas is usually odorless. 

Another area in which sulfur compounds have long found use is in the area of agricultural chemicals. Many of these materials had been produced by the manufacturer of the agricultural chemicals, but difficulties in containing odor and the use of hydrogen sulfide in heavily populated areas again pushed toward specialization by several companies. A Hst of agricultural chemicals, and the thiol that is used or has been used in production, follows ... 

Odor. Pure sulfur is free of odor odor indicates impurities. While whole wood exudes a very pleasant odor, a large number of useful sulfur modifiers unfortunately exude an unpleasant odor. Often, modified sulfur contains some decomposition products which impart to the final material a faint but insiduous odor to which many people are quite sensitive. Likewise, commercial wood products exude an unpleasant odor from excess formaldehyde which remains unreacted and is released over several months. 

Hydrogen sulfide is a colorless, flammable gas with important chemical and toxicological properties. It is the product of a number of natural processes, including the decay of sulfur-containing material. Its noxious odor of rotten eggs permits its detection at extremely low concentration (0.02 ppm). Because the olfactory sense is dulled by its action, however, higher concentrations may be tolerated, and the lethal concentration of 100 ppm may be exceeded. Aqueous solutions of the gas were used traditionally as a source of sulfide for the precipitation of metals, but because of the toxicity of H2S, this role has been taken over by other sulfur-containing compounds such as thioacetamide. 

In addition to resin acids, rosin contains neutral materials and oxidized impurities. Tall oil rosin contains about 1-5% fatty acid and small amounts of sulfur compounds and phenolics. In tall oil pitch, which is the bottom fraction in the tall oil distillation process, besides residual amounts of rosin and fatty acids, a substantial amount of unsaponifiable matters has been identified and recovered as B-sitosterol (30). Gum rosin contains large amounts of neutrals that contribute to the typical odor and reduce its tendency to crystallize. The amount of neutral materials present in a rosin largely depends upon the location where the raw material originates and its processing conditions. 

For some produets, elemental sulfur or sulfur-containing benzothiazole compounds are added to flie eompound as a euring agent. Sulfur reacts to form C-S-C bonds. This is an inexpensive reaetion seheme and it is useful for production of rubber compounds across a very wide hardness range. Residual sulfur eompounds lead to odors and acid products that are not well suited to applieations where elean materials are desired. Thiazole compounds provide better handling and more eontrollable erosslinking proeesses, with low residual odor and extraetables. 

Because calcium sulfide contained in the black ash had a highly unpleasant odor, methods were developed to remove the odor by recovering the sulfur, therein providing at least part of the raw-material for the sulfuric acid required in the first part of the process. Thus, the Leblanc prtKcss demonstrated, at the very beginning, the typical ability of the chemical industry to develop new processes and new products, and often in so doing to turn a liability into an asset. 

Sulfur compounds such as furfuryl mercaptans have a rotten odor but in small amounts are coffee-like.15 Furfuryl mercaptan itself has an odor threshold of 0.005 ppb in water but at 10 ppb in water it imparts a distinctly stale odor.19 The particular precursors of furfuryl mercaptan seem to be the coffee cell wall material which contains both arabinogalactan as a pentose sugar source and protein such as glutathione.84 Other sulfur compounds such as kahweofuran and methyldithiofurans impart a meaty odor if their concentrations are high enough.19... 

The majority of these materials are organic sulfur compounds that may also contain an odor intensifier. These chemicals are generally volatile liquids at room temperature with odors that are detectable at very low levels. Under normal battlefield conditions, these materials do not pose a serious danger to the life of an exposed individual and do not produce any permanent injury. Since approximately 0.2% of the population is unable to detect odors (anosmic), compositions may contain multiple malodorant components. 

The fat refining and bleaching operation is carried out to remove impurities that would cause color and odor in the finished soap. The wastewater from this source has a high soap concentration, treatment chemicals, fatty impurities, emulsified fats, and sulfuric acid solutions of fatty acids. Where steam is used for heating, the condensate may contain low-molecular-weight fatty acids, which are highly odorous, partially soluble materials. 

Of the few known terpene compounds that contain heteroatoms such as nitrogen or sulfur, the thiol 8-mercapto-p-menthan-3-one described below has qualitatively important applications as a fragrance and flavor substance. The second thiol, -p-menthene-8-thiol, is described because its odor threshold value is far lower than that of most other fragrance and flavor materials. 

Odor is a sensation associated with smell, which can be hard to quantify. The same quantities of different materials cause different odor intensities. The unit of odor intensity (W) is based on the odor of tertiary butyl mercaptan or TBM (W = 1.0). Using that reference, H2S, for example, has an odor intensity of W = 0.08, or 8% of TBM. Most odorant substances contain sulfur. Table 3.31 lists a number of odorant substances and their relative odor intensities (W). 

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