Pyridines manufacture

Raw Material and Energy Aspects to Pyridine Manufacture. The majority of pyridine and pyridine derivatives are based on raw materials like aldehydes or ketones. These are petroleum-derived starting materials and their manufacture entails cracking and distillation of alkanes and alkenes, and oxidation of alkanes, alkenes, or alcohols. Ammonia is usually the source of the nitrogen atom in pyridine compounds. Gas-phase synthesis of pyridines requires high temperatures (350—550°C) and is therefore somewhat energy intensive. 

Few data, especially recent data, are available on occupational exposure levels of pyridine. In 1978, the United States P Tidine Task Force of the Interagency Testing Committee reported that in United States workplaces where pyridine was manufactm-ed or used as a chemical intermediate or as a solvent, workers were exposed to 8-h time-weighted average (TWA) pyridine concentrations ranging from 0.008 to 1.0 ppm [0.026 to 3.24 mg/m ]. Technicians working in quality control and research and development laboratories of one of the pyridine manufacturers were exposed to TWA concentrations (measiu ed over 6-h periods) of no more than 0.09 ppm [0.29 mg/m ] (Santodonato etal, 1985). 

Commercially, pyridine is manufactured from ethyne and ammonia. It is used as a solvent, particularly in the plastics industry, in the manufacture of nicotinic acid, various drugs and rubber chemicals. 

Acid-cataly2ed hydroxylation of naphthalene with 90% hydrogen peroxide gives either 1-naphthol or 2-naphthiol at a 98% yield, depending on the acidity of the system and the solvent used. In anhydrous hydrogen fluoride or 70% HF—30% pyridine solution at — 10 to + 20°C, 1-naphthol is the product formed in > 98% selectivity. In contrast, 2-naphthol is obtained in hydroxylation in super acid (HF—BF, HF—SbF, HF—TaF, FSO H—SbF ) solution at — 60 to — 78°C in > 98% selectivity (57). Of the three commercial methods of manufacture, the pressure hydrolysis of 1-naphthaleneamine with aqueous sulfuric acid at 180°C has been abandoned, at least in the United States. The caustic fusion of sodium 1-naphthalenesulfonate with 50 wt % aqueous sodium hydroxide at ca 290°C followed by the neutralization gives 1-naphthalenol in a ca 90% yield. 

Analytical and Test Methods. The acid number of terephthahc acid discussed above is a titration of a sample dissolved in pyridine, using a sodium or potassium hydroxide titrant. However, specifications on certain impurities are so strict that this test caimot, as a practical matter, be failed. Its use has been discontinued by some manufacturers. 

In Europe, where an abundant supply of anthracene has usually been available, the preferred method for the manufacture of anthraquinone has been, and stiU is, the catalytic oxidation of anthracene. The main problem has been that of obtaining anthracene, C H q, practically free of such contaminants as carbazole and phenanthrene. Many processes have been developed for the purification of anthracene. Generally these foUow the scheme of taking the cmde anthracene oil, redistilling, and recrystaUizing it from a variety of solvents, such as pyridine (22). The purest anthracene may be obtained by azeotropic distillation with ethylene glycol (23). 

N -Heterocyclic Sulfanilamides. The parent sulfanilamide is manufactured by the reaction of A/-acetylsulfanilyl chloride with excess concentrated aqueous ammonia, and hydrolysis of the product. Most heterocycHc amines are less reactive, and the condensation with the sulfonyl chloride is usually done in anhydrous media in the presence of an acid-binding agent. Use of anhydrous conditions avoids hydrolytic destmction of the sulfonyl chloride. The solvent and acid-binding functions are commonly filled by pyridine, or by mixtures of pyridine and acetone. Tertiary amines, such as triethylamine, may be substituted for pyridine. The majority of A/ -heterocycHc sulfanilamides are made by simple condensation with A/-acetylsulfanilyl chloride and hydrolysis. 

Important commercial alkylpyridine compounds are a-picoline (2), Ppicoline (3), y-picoline (4), 2,6-lutidine (5), 3,5-lutidine (6), 5-ethyl-2-methylpyridine (7), and 2,4,6-coUidine (8). In general, the alkylpyridines serve as precursors of many other substituted pyridines used in commerce. These further substituted pyridine compounds derived from alkylpyridines are in turn often used as intermediates in the manufacture of commercially usehil final products. 

As is the case with most specialty organic compounds, pyridine sales are generally not pubHcized, and industrial processes for their manufacture are either retained as trade secrets or patented (see Patents and trade secrets). Up to about 1950, most pyridines were isolated from coal-tar fractions however, after 1950 synthetic manufacture began to take an ever-increasing share of products sold. By 1988, over 95% of all pyridines were produced by synthetic methods. 

Manufacturing methods must suit the scale of manufacture. By the late 1980s, some 6,000 t of pyridine (1) were consumed in the United States, and nearly 20,000 t worldwide. 

Commercial Manufacture of Pyridine. There are two vapor-phase processes used in the industry for the synthesis of pyridines. The first process (eq. 21) uti1i2es formaldehyde and acetaldehyde as a co-feed with ammonia, and the principal products are pyridine (1) and 3-picoline (3). The second process produces only alkylated pyridines as products. 

Commercial Manufacture of Specific Pyridine Bases. Condensation of paraldehyde with ammonia at 230°C and autogenous pressure (eq. 22) is used to manufacture 5-ethyl-2-methylpyridine (7). This is one of the few Hquid-phase processes used in the industry to make relatively simple aLkylpyridines, and one of the few processes known to make a single alkylpyridine product selectively. 

By-Products. Almost all commercial manufacture of pyridine compounds involves the concomitant manufacture of various side products. Liquid- and vapor-phase synthesis of pyridines from ammonia and aldehydes or ketones produces pyridine or an alkylated pyridine as a primary product, as well as isomeric aLkylpyridines and higher substituted aLkylpyridines, along with their isomers. Furthermore, self-condensation of aldehydes and ketones can produce substituted ben2enes. Condensation of ammonia with the aldehydes can produce certain alkyl or unsaturated nitrile side products. Lasdy, self-condensation of the aldehydes and ketones, perhaps with reduction, can lead to alkanes and alkenes. 

Although the volume of commercial pyridine compounds is relatively large, economic aspects resemble those of specialty markets more than those of commodities. Commercial transactions occur withHtde pubHcity, trade secrets are carefully guarded, and patents proliferate, thus obscuring the industrial processes used for their manufacture. 

Pyridine A Oxides. Analgesic and antiinflammatory dmgs niflumic acid [4394-00-7] (68) and pranoprofen [52549-17-4] (69) are manufactured from nicotinic acid N-oxide [2398-81 -4]. The antiulcer dmg omeprazole (66) is produced from 2,3,5-trimethylpyridine N-oxide [74409-42-0]. Zinc pyrithione, the zinc salt of pyrithione (45), is a fungicide derived from 2-chloropyridine N-oxide (45). 

Low DS starch acetates ate manufactured by treatment of native starch with acetic acid or acetic anhydride, either alone or in pyridine or aqueous alkaline solution. Dimethyl sulfoxide may be used as a cosolvent with acetic anhydride to make low DS starch acetates ketene or vinyl acetate have also been employed. Commercially, acetic anhydride-aqueous alkaU is employed at pH 7—11 and room temperature to give a DS of 0.5. High DS starch acetates ate prepared by the methods previously detailed for low DS acetates, but with longer reaction time. 

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

Sources of Raw Materials. Coal tar results from the pyrolysis of coal (qv) and is obtained chiefly as a by-product in the manufacture of coke for the steel industry (see Coal, carbonization). Products recovered from the fractional distillation of coal tar have been the traditional organic raw material for the dye industry. Among the most important are ben2ene (qv), toluene (qv), xylene naphthalene (qv), anthracene, acenaphthene, pyrene, pyridine (qv), carba2ole, phenol (qv), and cresol (see also Alkylphenols Anthraquinone Xylenes and ethylbenzenes). 

The fact that the binder used in the layer can affect the reagent is shown in the monograph on 4-(4-Nitrobenzyl)pyridine reagent. It is not possible to employ this reagent on Nano-SIL C 18-100 UV254 plates (Macherey-Nagel) because the whole surface of the layer is colored bluish-violet. The corresponding water-wettable layers produced by the same manufacturer do not present any difficulties. 

Innovatory boronated carbons (manufactured in the Institute of Chemistry and Technology of Petroleum and Coal, Wroclaw University of Technology, Poland) were obtained by co-pyrolysis of coal-tar pitch with a pyridine-borane complex. In the first stage of pyrolysis (520°C) the so-called semi-coke is obtained. Further carbonization at 2500°C leads to obtaining boron-doped carbonaceous material (sample labeled 25B2). 

As early as 1907, A.V. Braun and J. Tscherniak first obtained phthalocyanine from phthalimide and acetic anhydride [5]. The prepared blue substance, however, was not investigated further. In 1927, de Diesbach and von der Weid, in an attempt to synthesize phthalonitrile from o-dibromobenzene and copper cyanide in pyridine at 200°C, obtained a blue copper complex. The substance was found to be exceptionally fast to acid, alkali, and high temperature [6], Approximately one year later, in trying to manufacture phthalimide from phthalic anhydride and ammo-... 

Pyridine, C5H5N, is used to manufacture medications and vitamins. Calculate the base dissociation constant for pyridine if a 0.125 mol/L aqueous solution has a pH of 9.10. 

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