Synthesis from Sources

Methane and carbon monoxide are presently the two primary raw materials of practical importance in Ci hydrocarbon chemistry. According to the present industrial practice, natural gas (methane) or coal can be converted to a mixture of carbon monoxide and hydrogen called synthesis gas  

The two approaches, however, are interconvertible, since methane itself is obtained from synthesis gas in the methanation reaction. Both methane and carbon monoxide, in turn, can be converted to hydrocarbons. 

Hydrocarbons can be produced from synthesis gas through the Fischer-Tropsch synthesis. Because of poor economics the process was, however, practiced on large scale only under extreme conditions (wartime Germany, South Africa under trade boycott). 

Although it is a desirable goal, methods of the direct coupling of methane to C2 and subsequently to higher hydrocarbons have not yet achieved practical application. Exceptions are the acetylene-based technologies. 

According to another important and promising technology, hydrocarbons are produced from methanol, which, in turn, is synthesized from synthesis gas. Called the methanol-to-gasoline process, it was practiced on a commercial scale and its practical feasibility was demonstrated. Alternative routes to eliminate the costly step of synthesis gas production may use direct methane conversion through intermediate monosubstituted methane derivatives. An economic evaluation of different methane transformation processes can be found in a 1993 review.1 

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M.p. 190-192 C. The enolic form of 3-oxo-L-gulofuranolactone. It can be prepared by synthesis from glucose, or extracted from plant sources such as rose hips, blackcurrants or citrus fruits. Easily oxidized. It is essential for the formation of collagen and intercellular material, bone and teeth, and for the healing of wounds. It is used in the treatment of scurvy. Man is one of the few mammals unable to manufacture ascorbic acid in his liver. Used as a photographic developing agent in alkaline solution. 

Many valuable chemicals can be recovered from the volatile fractions produced in coke ovens. Eor many years coal tar was the primary source for chemicals such as naphthalene [91-20-3] anthracene [120-12-7] and other aromatic and heterocycHc hydrocarbons. The routes to production of important coal-tar derivatives are shown in Eigure 1. Much of the production of these chemicals, especially tar bases such as the pyridines and picolines, is based on synthesis from petroleum feedstocks. Nevertheless, a number of important materials continue to be derived from coal tar. 

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

There are three general processes that ate used, as of ca 1996, woddwide for steroid production (/) direct isolation from natural sources, (2) partial synthesis from steroid raw materials that have been isolated from plants and animals, and (J) total synthesis from nonsteroidal starting materials (120). 

The earliest method for manufacturiag carbon disulfide involved synthesis from the elements by reaction of sulfur and carbon as hardwood charcoal in externally heated retorts. Safety concerns, short Hves of the retorts, and low production capacities led to the development of an electric furnace process, also based on reaction of sulfur and charcoal. The commercial use of hydrocarbons as the source of carbon was developed in the 1950s, and it was still the predominate process worldwide in 1991. That route, using methane and sulfur as the feedstock, provides high capacity in an economical, continuous unit. Retort and electric furnace processes are stiU used in locations where methane is unavailable or where small plants are economically viable, for example in certain parts of Africa, China, India, Russia, Eastern Europe, South America, and the Middle East. Other technologies for synthesis of carbon disulfide have been advocated, but none has reached commercial significance. 

Thermal chlorination of methane was first put on an industrial scale by Hoechst in Germany in 1923. At that time, high pressure methanol synthesis from hydrogen and carbon monoxide provided a new source of methanol for production of methyl chloride by reaction with hydrogen chloride. Prior to 1914 attempts were made to estabHsh an industrial process for methanol by hydrolysis of methyl chloride obtained by chlorinating methane. 

Most of the production of hydrocarbons by Fischer Tropsch method uses synthesis gas produced from sources that yield a relatively low... 

Sophorolipid is a glycolipid, ie it is composed of carbohydrate and lipid. It therefore contains moieties of widely different oxidation levels and its synthesis from single demand carbon sources has a high ATP demand. However, the demand for ATP is reduced if a mixture of glucose and C-18 alkane is used. If glucose and fatty add is used the ATP demand is reduced further and relatively high spedfic production rates can be achieved. 

The source of long-chain fatty acids is either dietary lipid or de novo synthesis from acetyi-CoA derived from carbohydrate. Fatty acids may be oxidized to acetyl-CoA (P-oxidation) or esterifred with glycerol, forming triacylglycerol (fat) as the body s main fuel reserve. 

The increase in the price of oil and natural gas motivates the chemical industry to develop processes that use alternative raw materials and to develop efficient and economical processes for liquid fuels synthesis from coal and natural gas. An innovative promising approach for producing gasoline from methane is presented in [5]. Other important tasks are development of efficient methods for producing liquid fuels from unconventional sources such as oil shale, tar sands, and deep-sea methane hydrates. 

The above account of selectivity of inorganic plus organic chemistry in synthesis is given rather extensively to stress three points. All the four (Mg, Fe, Co and Ni) porphyrin products came from one source, the synthesis of uroporphyrin. The basis of selection is very different from that in primitive centres which use thermodynamic stability constant selectivity based on different donor atoms for different metal ions. Here, all ion complexes have the same donor atoms, nitrogen, the most constrained being the coordination of Mg2+ by five nitrogens exactly as is seen for Fe in haemoglobin. Hence, there also has to be a new control feedback to ensure that the appropriate quantities of each metal cofactor is produced in a balanced way, that is synthesis from uroporphyrin has to be divided based upon... 

Kojic acid, 5-hydroxy-2-(hydroxymethyl)-4//-pyran-4-one1 (II), is produced from carbohydrate sources in an aerobic process by a variety of microorganisms. The acid was discovered in 1907, its structure was established in 1924, and its chemical synthesis from D-glucose was achieved in 1930. Since then, a considerable amount of study has been devoted to the biosynthesis of kojic acid, and numerous publications have dealt with its chemical and biological properties. After nearly half a century, kojic acid remains a scientists curiosity, without industrial importance. It con-... 

Tetrabromobenzene used from sources other than Lancaster Synthesis contained trace amounts of an impurity that carried through the entire reaction scheme. This impurity gave a proton resonance at 1.58 ppm in the starting... 

The synthesis of chalcogenides such as those of the rare earth elements has traditionally been performed through the reaction of rare earth metals or oxides with a molten or vaporous chalcogen source in a high-temperature environment. Soft synthetic methods utilizing lower temperature conditions, such as hydrothermal or flux syntheses, can allow access also to thermodynamically metastable phases. Flux syntheses of R chalcogenides via an alkali poly-chalcogenide flux have been shown to be extremely versatile for the preparation of many new structures, some of which cannot be obtained by direct synthesis from the elements. 

At that time, as now, the enantiomers of many chiral amines were obtained as natural products or by synthesis from naturally occurring amines, a-amino acids and alkaloids, while others were only prepared by introduction of an amino group by appropriate reactions into substances from the chiral pool carbohydrates, hydroxy acids, terpenes and alkaloids. In this connection, a recent review10 outlines the preparation of chiral aziridines from enantiomerically pure starting materials from natural or synthetic sources and the use of these aziridines in stereoselective transformations. Another report11 gives the use of the enantiomers of the a-amino acid esters for the asymmetric synthesis of nitrogen heterocyclic compounds. 

The ease of the Strecker synthesis from aldehydes makes a-aminonitriles an attractive and important route to a-amino acids. Fortunately, the microbial world offers a number of enzymes for carrying out the necessary conversions, some of them highly stereoselective. Nitrilases catalyze a direct conversion of nitrile into carboxylic acid (Equation (11)), whereas nitrile hydratases catalyze formation of the amide, which can then be hydrolyzed to the carboxylic acid in a second step (Equation (12)). In a recent survey, with a view to bioremediation and synthesis, Brady et al have surveyed the ability of a wide range of bacteria and yeasts to grow on diverse nitriles and amides as sole nitrogen source. This provides a rich source of information on enzymes for future application. 

Although the use of an epoxide hydrolase was already claimed for the industrial synthesis of L- and meso-tartaric acid in 1969 [51], it was only recently that applications to asymmetric synthesis appeared in the hterature. This fact can be attributed to the limited availabihty of these biocatalysts from sources such as mammals or plants. Since the production of large amounts of crude enzyme is now feasible, preparative-scale applications are within reach of the synthetic chemist. For instance, fermentation of Nocardia EHl on a 701-scale afforded > 700 g of lyophilized cells [100]). 

Cholesterol can be derived from two sources—food or endogenous synthesis from ace-tyl-CoA. A substantial percentage of endogenous cholesterol synthesis takes place in the liver. Some cholesterol is required for the synthesis of bile acids (see p. 314). In addition, it serves as a building block for cell membranes (see p. 216), or can be esterified with fatty acids and stored in lipid droplets. The rest is released together into the blood in the form of lipoprotein complexes (VLDLs) and supplies other tissues. The liver also contributes to the cholesterol metabolism by taking up from the blood and breaking down lipoproteins that contain cholesterol and cholesterol esters (HDLs, IDLs, LDLs see p.278). 

The successful application of compound 16 to the synthesis of sialic acid glycosides points to the need for a more direct and efficient route to such systems. Partial synthesis from carbohydrate sources would be a promising alternative to total synthesis. This goal and the goal of extending the scope of the exchange reaction to include secondary sugar alcohol substrates, are now important objectives of our laboratory. 

Eundamental research on DME synthesis from renewable sources is ongoing. In Sweden, for example, Chemrec developed a process for producing DME through... 

Hotrienol was found for the first time in Ho leaf oil as the S enantiomer [7], but has been found since then in many natural sources for instance, the R enantiomer was found in black tea and in green tea. The product can be used in many flavours, such as eldertlower, grape, berry and honey flavours. It can be prepared from linalool obtained from citrus oils or Chinese Ho oils, but most linalool is obtained by synthesis from isoprene from petrochemical sources. 

Mammalian cells (and some bacteria) lack the enzymes required for folate synthesis from PABA and depend on exogenous sources of folate therefore, they are not susceptible to sulfonamides. Sulfonamide resistance may occur as a result of mutations that (1) cause overproduction of PABA, (2) cause production of a folic acid-synthesizing enzyme that has low affinity for sulfonamides, or (3) impair permeability to the sulfonamide. Dihydropteroate synthase with low sulfonamide affinity is often encoded on a plasmid that is transmissible and can disseminate rapidly and widely. Sulfonamide-resistant dihydropteroate synthase mutants also can emerge under selective pressure. 

Homocysteine (Hey) metabolism is closely linked to that of the essential amino acid methionine and thus plays a central role in several vital biological processes. Methionine itself is needed for protein synthesis and donates methyl groups for the synthesis of a broad range of vital methylated compounds. It is also a main source of sulphur and acts as the precursor for several other sulphur-containing amino acids such as cystathionine, cysteine and taurine. In addition, it donates the carbon skeleton for polyamine synthesis [1,2]. Hey is also important in the metabolism of folate and in the breakdown of choline. Hey levels are determined by its synthesis from methionine, which involves several enzymes, its remethylation to methionine and its breakdown by trans-sulphuration. 

Prior to this time, other ventures had already been operating to produce commercial quantities of aliphatic chemicals from petroleum sources. Truly commercial production of ethylene glycol had been achieved by 1925 (10) using natural gas fractions as a starting material, and even earlier (about 1920) there had been the manufacture of isopropyl alcohol from cracking plant propylene (20), which may be termed the pioneer operation on a successful, continuing basis in the sphere of aliphatic synthesis from petroleum. 

An interesting case of interproduct competition is that of the four original lacquer solvents—ethyl alcohol, butyl alcohol, ethyl acetate, and butyl acetate. These were once produced mainly by fermentation processes, but today all are also produced by synthesis from petroleum hydrocarbons. Moreover, in the past 30 years solvents have been developed from petroleum sources which are competing successfully with these materials even though the new compounds are not identical in all properties isopropyl alcohol competes with ethyl alcohol methyl isobutyl carbinol and n-propyl alcohol can replace butyl alcohol methyl ethyl ketone to a large extent supplants ethyl acetate and methyl isobutyl ketone can be substituted for butyl acetate. Thus, petroleum aliphatic chemicals have served both by displacement of source and replacement of end product to supplement and to compete with the fermentation solvents. 

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