Sulfur, dehydration with

Ma.nufa.cture. Nitroguanidine may be made by several methods. In all the processes guanidine nitrate is the iatermediate which is then dehydrated with sulfuric acid. When used ia propellants, the average particle size of nitroguanidine has to be carefully controlled. 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Sulfur reacts with alkanes to either dehydrate (eq. 1), oxidize, forming carbon disulfide and hydrogen sulfide (eq. 2), or cyclize, forming thiophenes (eq. 3). The products of alkane sulfurization depend on the temperature, the time at the temperature, and the stmcture of the hydrocarbon (1). 

The butanols undergo the typical reactions of the simple lower chain aUphatic alcohols. For example, passing the alcohols over various dehydration catalysts at elevated temperatures yields the corresponding butenes. The ease of dehydration increases from primary to tertiary alcohol /-butyl alcohol undergoes dehydration with dilute sulfuric acid at low temperatures in the Hquid phase whereas the other butanols require substantially more stringent conditions. 

The Knorr quinoline synthesis refers to the formation of a-hydroxyquinolines 4 from P-ketoesters 2 and aryl amines 1. The reaction usually requires heating well above 100°C. However, some cases do exist when the cyclization takes place in the presence of a catalytic amount of mineral acid at temperatures as low as -10 °C. The intermediate anilide 3 undergoes cyclization by dehydration with concentrated sulfuric acid. The reaction is conceptually close to the Doebner-Miller and Gould-Jacobs reactions. ... 

B) Preparation of Diphenyl-(N-Methyl-4-Plperidylidene)Methane The carbinol can be dehydrated with 60% sulfuric acid. In general, to one part of the carbinol there is added... 

Jansson et al. [189] used the conventional approach of blending the solid particles with solvent after which an aliquot was taken to determine the volatile compounds (e.g., phenols and chlorobenzenes). A second fraction was taken after the lipid removal for determination of compounds sensitive to concentrated sulfuric acid. The bulk lipids were removed by oxidative dehydration with Si02 /H2S04 and further cleaned-up with GPC. The chloroparaffins were isolated at this stage. Separation on silica isolated the OCPs, and the organochlorines and organobromines were finally fractionated on active charcoal. 

PENTOSAN. A complex carbohydrate (hemicellulose) present with the cellulose in many woody plant tissues, particularly cereal straws and brans, characterized by hydrolysis to give five-carbon-atom sugars (pentoses). Thus the pentosan xylan yields the sugar xylose (HOH,C CHOH CHOH CHOH CHO) that is dehydrated with sulfuric acid to yield furfural (C5H4O2). 

Attempted dehydration using an acid catalyst or iodine failed, giving mainly acetophenone. When acetic anhydride is employed instead of trlfluoroacetlc anhydride, the reaction proceeds very slowly. Dehydration with excess methanesulfonyl chloride and triethylamine gives the product in high yield however, the distilled product has a strong odor of sulfur compound. 

B) Preparation of diphenyl-(N-Methyl-4-Piperidylidene)methane the carbinol can be dehydrated with 60% sulfuric acid. In general, to one part of the carbinol there is added 10 parts of 60% sulfuric acid. The mixture after heating for 6 hours is poured onto cracked ice, the solution made alkaline with dilute sodium hydroxide and the oily basic layer extracted with ether. The ether extracts after washing with water are dried over sodium sulfate, and... 

Carboxylic acids can also be activated by converting them to their anhydrides. For this purpose they are dehydrated with concentrated sulfuric acid, phosphorus pentoxide, or 0.5 equivalents of SOCl2 (1 equivalent of SOCl2 reacts with carboxylic acids to form acid chlorides rather than anhydrides). However, carboxylic anhydrides cannot transfer more than 50% of the original carboxylic acid to a nucleophile. The other 50% is released—depending on the pH value—either as the carboxylic acid or as a carboxylate ion and is therefore lost. Consequently, in laboratory chemistry, the conversion of carboxylic acids into anhydrides is not as relevant as carboxylic acid activation. Nonetheless, acetic anhydride is an important acetylat-ing agent because it is commercially available and inexpensive. 

A variety of conditions have been employed to convert o-quinone dioximes into benzofurazans, including dehydration with acetic anhydride, thionyl chloride, sulfuric acid, and phenyl isocyanate, and steam distillation in the presence of alkali. Alternatively, cyclization may be achieved by boiling with aqueous alkali or thermolysis of the corresponding dioxime diacetates or dibenzoates. 

Conditions for the ring closure of readily available 3-(2-hydroxy-2-phenylethyl)-2-iminotetrahydro-l,3-thiazole (263) (82S511) to (262), the racemate of the anthelmintic tetramisole, involve (a) dehydration with concentrated sulfuric acid or (b) reaction with thionyl chloride, phosphorus oxychloride or phosphorus pentachloride in the presence of base followed by dehydrochlorination (66JMC545,68JOC1350). 

Many N-unsubstituted pyrazoles 80 can be obtained from A-allyl-A-nitrosamides 79 (Scheme 46) <1990H(30)789>. Cyclocondensation of -alkoxyvinyl trifluoromethyl ketones 81 with thiosemicarbazide under mild conditions affords 4,5-dihydro-l//-pyrazole-l-thiocarboxamides 82, which can be easily dehydrated with concomitant thiocarboxamide group hydrolysis in concentrated sulfuric acid to give N-unsubstituted pyrazoles 83 (Scheme 47) <1998JFC(92)23>. 

The clean, cool, partially dried gas leaves the top of the condenser and passes through electrostatic mist precipitation to final dehydration with strong sulfuric acid, Chapter 6. 

Dehydration with Strong Sulfuric Acid (Tables 6.3-6.5)... 

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