Natural rubber empirical formula

If natural rubber is treated with a proton donor such as sulfuric acid or starmic chloride, the produet is eyeUzed rubber (empirical formula of —CsHg—), having the following moleeular strueture ... 

If natural rubber is treated with proton donors a product is formed which has the same empirical formula. (CjHjj), and is soluble in hydrocarbon solvents but which has a higher density, is inelastic and whose unsaturation is only 51% that of natural rubber. It is believed that intramolecular ring formation occurs to give products containing the segments shown in Figure 30.5. Known as cyclised rubber it may be prepared by treating rubber, on a mill, in solvent or in a latex with materials such as sulphuric acid or stannic chloride. 

Treatment of natural rubber with chlorine gives a product, chlorinated rubber, with a maximum chlorine content of 65% corresponding to the empirical formula C10H11CI7. Such a compound corresponds neither to a hypothetical simple addition to the double bond (Figure 30.6 (I)) nor to a product with a-methylenic substitution in addition (II). 

Crude rubber is primarily hydrocarbon in nature. In 1826 English chemist Michael Earaday (1791-1867) analyzed natural rubber and found it to have the empirical (simplest) formula C5H8, along with 2 to 4 percent protein and 1 to 4 percent acetone-soluble materials (resins, fatty acids, and sterols). In 1860 English chemist Charles Hanson Greville Williams (1829-1910) confirmed Earaday s analysis and in 1862 distilled natural rubber to obtain the pure monomer, which he named isoprene. He determined isoprene s vapor density and molecular formula, and he showed that it polymerizes to a rubbery product—an observation that led to the notion that rubber is a linear polymer of isoprene, proposed in 1910 by English chemist Samuel Shrowder Pickles (1878-1962). 

The product after the first stage contains 35% chlorine, and is rubbery. The second stage product that contains 57% chlorine has no unsaturated groups. Further chlorination results in the final product containing 65.5% chlorine, with the empirical formula -CjgHjjCl -. The final product of chlorination of natural rubber is a pale cream or off-white thermoplastic powder, which is inflammable and highly resistant to chemical attack. 

Natural rubber, a product of the Hevea brasiliensis tree, is a hydrocarbon with the empirical formula GgHg. When rubber is decomposed in the absence of oxygen, the monomer isoprene is obtained... 

Although the minor constituents of rubber have some effect on the bulk properties, it is clearly the rubber hydrocarbon which determines the major features. Accordingly, the elucidation of the structure of rubber hydrocarbon has received the attention of many workers over the past 100 years or so. In 1826, Faraday established the empirical formula of rubber hydrocarbon as CsHs and in 1860 Williams obtained isoprene (I) by dry distillation of rubber. In 1879, Bouchardat converted isoprene to a rubber-like material by treatment with hydrochloric acid and concluded that isoprene was the mother substance of natural rubber. In 1888, Gladstone and Hibbert showed that rubber was unsaturated under normal conditions, 2 atoms of bromine were added for each CsHg unit. 

Of all the materials provided by nature for man to use as a material of construction, natural rubber is unique. The characteristic of high reversible extensibility fascinates the enquiring mind. As the years have passed since its introduction to the Eastern Hemisphere by Columbus and his fellow explorers the roll of famous men who have studied the material has steadily lengthened. These include Priestley, who coined the word rubber Faraday, who determined its empirical formula Weizmann, who in later years became the first president of Israel, and the Nobel Chemistry Prizewinners Staudinger, Flory, Ziegler and Natta. 

Whilst Faraday had shown in 1826 that rubber was a hydrocarbon of empirical formula CsHg few further important developments occurred until the closing years of the 19th century when the structure of natural rubber began to be progressively revealed, a process which only became substantially complete about 1930 and which is considered in the next chapter. 

The empirical formula for the natural rubber (NR) molecule appears to have been first determined by Faraday who reported his findings in 1826. He concluded that carbon and hydrogen were the only elements present and his results correspond to the formula CsHg. Whilst this result was obtained using a product which contained associated non-rubbery materials subsequent studies with highly purified materials have confirmed Faraday s conclusion. 

Many years later Weber indicated that the natural rubber molecule was unsaturated since it reacted with bromine to give a material of empirical formula C5H8Br2. This clearly implied an addition reaction to a double bond. This was borne out by the more accurate and reliable iodine chloride method of Kemp in 1927 and the refractive index technique of Macallum and Whitby in 1924. 

The empirical formula of halogenated natural rubber is C5H8CI3.5. This strongly suggests that the chlorination reaction involves more than one isoprene unit and, since the products are soluble, cyclization rather than cross-linking is indicated. 

Synonyms Alkanesulfonic acids, sodium salts Sodium alkane sulfonate Uses Antistat used in plastic and rubber compounds solubilizer, welling agent, hydrotrope in shampoos, all purpose cleaners Regulatory Canada DSL Trade Names Avitone A Sodium allyloxy hydroxypropyl sulfonate Synonyms Sodium 1-allyloxy-2-hydroxypropyl sulfonate Ionic Nature Anionic Empirical CgH -NaOsS Formula CH,=CHCH20CH2CH0HCH2S03Na Properties M.w. 218... 

Empirical Ci6H3o04Zn Formula [CH3(CH2)3C2HsCHCOO]2Zn Properties Lt. straw-colored vise, liq. sol. in hydrocarbon soivs. insol. in water m.w. 351.79 dens. 0.90 kg/l Precaution Combustible Uses Activator for natural and syn. rubbers drier for paints, in food-contact coatings stabilizer for foam processing catalyst in food-pkg. adhesives inktransfer preventive in food-contact paper/paperboard Regulatory FDA 21CFR 175.105, 175.300, 176.130, 176.170... 

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