Fibrous sulfur

Fibrous sulfur ip-Sulfur Fibrous sulfur Crystalline catena-S Space group not known... 

Cellulose Acetate. Almost all cellulose acetate, with the exception of fibrous triacetate, is prepared by a solution process employing sulfuric... 

Perchloric acid is a weU-known acetylation catalyst, especially in the fibrous method of preparing cellulose triacetate. Unlike sulfuric acid, perchloric acid does not combine with cellulose (78), ie, it does not form esters, and therefore virtually complete acetylation (DS 3.0, 44.8% acetyl) occurs. However, the extremely corrosive nature of perchloric acid and explosive nature of its salts have precluded its use industrially as an acetylation catalyst. 

Solution Process. With the exception of fibrous triacetate, practically all cellulose acetate is manufactured by a solution process using sulfuric acid catalyst with acetic anhydride in an acetic acid solvent. An excellent description of this process is given (85). In the process (Fig. 8), cellulose (ca 400 kg) is treated with ca 1200 kg acetic anhydride in 1600 kg acetic acid solvent and 28—40 kg sulfuric acid (7—10% based on cellulose) as catalyst. During the exothermic reaction, the temperature is controlled at 40—45°C to minimize cellulose degradation. After the reaction solution becomes clear and fiber-free and the desired viscosity has been achieved, sufficient aqueous acetic acid (60—70% acid) is added to destroy the excess anhydride and provide 10—15% free water for hydrolysis. At this point, the sulfuric acid catalyst may be partially neutralized with calcium, magnesium, or sodium salts for better control of product molecular weight. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Attacks rubber and most fibrous materials. May cause ignition of organic materials such as wood. Some acids, such as sulfuric acid, may result in explosion Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Figure 15.9 The structure of right-handed and left-handed Sot helices in fibrous sulfur (see...

First attempts to model the vibrational spectrum of polymeric sulfur have been reported by Dultz et al. who assumed a planar zig-zag chain structure [172]. The calculated vibrational DOS was in qualitative agreement with the observed Raman spectrum of fibrous sulfur. However, some details of the spectrum like the relative intensities of the modes as well as the size of the gap between stretching and bending vibrations could not be reproduced exactly by this simplified model [172]. 

Sulfur trioxide Rubbery form of SO3 precipitates from solution of SO3 in SOa 0 -U- X Low melting fibrous form melts at 31.5°C... 

Hydroxylamine is a powerful reducant, particularly when anhydrous, and if exposed to air on a fibrous extended surface (filter paper) it rapidly heats by aerobic oxidation. It explodes in contact with air above 70°C [1]. Barium peroxide will ignite aqueous hydroxylamine, while the solid ignites in dry contact with barium oxide, barium peroxide, lead dioxide and potassium permanganate, but with chlorates, bromates and perchlorates only when moistened with sulfuric acid. Contact of the anhydrous base with potassium dichromate or sodium dichromate is violently explosive, but less so with ammonium dichromate or chromium trioxide. Ignition occurs in gaseous chlorine, and vigorous oxidation occurs with hypochlorites. 

The bond data are very similar to those of fibrous sulfur, and the values are intermediate between those of Sg and Sg, and similar to those of Sig. The lattice constants are... 

As mentioned, freshly drawn fibrous sulfur is a mixture, containing Sg and possibly other rings. Geller prepared a substance with an identical X-ray pattern by applying a pressure of 27 kbar (57). 

Fibrous sulfur is probably rarely pure. Impurities can influence the structure in many ways. As long as only mixtures are available, further, apparently contradictory reports on similar structures are to be expected. We discuss some of these forms in Section III. 

Fibrous sulfur, described in Section II, is prepared by quenching liquid sulfur. Aten and Erametsa s 7r-sulfur is obtained from the melt at... 

Fibrous glass Poly(sulfur nitride) Poly(boron nitride) Silicon carbide... 

Fia. 4-7.—The helix with seven atoms in two turns, proposed as the repeating unit in the chains of fibrous sulfur. 

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