Preparative routes

Some important routes are described below. Examples are chosen to illustrate both the generality of the method and important classes of complexes. 

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This chapter is an attempt to present the important results of studies of the synthesis, reactivity, and physicochemical properties of this series of compounds. The subject was surveyed by Bulka (3) in 1963 and by Klayman and Gunther (4) in 1973. Unlike the oxazoles and thiazoles. there are few convenient preparative routes to the selenazoles. Furthermore, the selenium intermediates are difficult to synthesize and are often extremely toxic selenoamides tend to decompose rapidly depositing metallic selenium. This inconvenience can be alleviated by choice of suitable reaction conditions. Finally, the use of selenium compounds in preparative reactions is often complicated by the fragility of the cycle and the deposition of metallic selenium. 

The protonation of the nitrogen atom of thiazole induces a large increase in reactivity of the 2-position (193, 194). This is in contrast to the pyridine series, where the reactivity of both positions adjacent to the nitrogen atom are enhanced (194). The phenylation of conjugate acid of 5-alkylthiazoles may then be considered as a preparative route to alkyl-thiazoles. The results (isomer percent and overall reactivity) are indicated in Tables III-31 (196) and 01-32 (196). 

Iron(II) bromide [7789-46-0] FeBr2, can be prepared by reaction of iron and bromine ia a flow system at 200°C and purified by sublimation ia oitrogea or uader vacuum. Other preparative routes iaclude the reactioa of Fe202 with HBr ia a flow system at 200—350°C, reactioa of iroa with HBr ia methanol, and dehydration of hydrated forms. FeBr2 crystallizes ia a layered lattice of the Cdfy type and has a magnetic moment of... 

Other preparative routes iaclude hydrogenation of succinonitdle in the presence of methylamine and hydrogenation of solutions of maleic or succinic acid and methylamine (82,83). Properties are Hsted in Table 3. l-Meth5i-2-pyrrohdinone is completely miscible with water, lower alcohols, lower ketones, ether, ethyl acetate, chloroform, and benzene. It is moderately soluble in aUphatic hydrocarbons and dissolves many organic and inorganic compounds. 

Preparative routes to aziridines and 1-azirines are derived from cycloelimination processes in which one, and sometimes two, bonds are formed directly to the nitrogen atom (Scheme 1). For aziridines these include the two intramolecular cyclization pathways involving either nucleophilic displacement by the amine nitrogen (or nitrenium anion) on the /3-carbon (route a) or nucleophilic displacement by a /3-carbanionic centre on the amine nitrogen... 

Although by no means a preparative route to either 1- or 2-azirines, the elimination of nitrogen (by flash vacuum pyrolysis at 400 °C) from the regioisomeric 4,5-disubstituted IH-1,2,3-triazoles (376) leads to similarly regioisomeric 1-azirines (377) <73JCS(P1)550). 

The first step in the biosynthesis of eicosanoids from arachidonic acid is generally a lipoxygenation reaction. The resulting hydroperoxides (HPETE s) can undergo reduction to the corresponding alcohols (HETE s). Preparative routes to the 5-, 11-, and 15-HETE s and HPETE s have been developed as oudine below. 

As a preparative route to A -3-ketones, the anhydrous reaction in benzene at room temperature gives 40-55 % of product after chromatography and is inferior to a stepwise conversion (via A -3-ketone). The principal side reaction (which also occurs in the acid catalyzed reaction of A -3-ketones with two moles of DDQ) appears to be addition of the hydroquinone ... 

Oxidative reactions frequently represent a convenient preparative route to synthetic intermediates and end products This chapter includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes and ketones, carboxylic acids, nitrogen compounds, and organophosphorus, -sulfur, -selenium, -iodine, and -boron compounds... 

Trifluoromethyl-substituted diazonium betaines [176]. Synthetic routes to trifluoromethyl-substituted diazo alkanes, such as 2,2,2-trifluorodiazoethane [ 177, 7 78, 179] and alkyl 3,3,3-trifluoro-2-diazopropionates [24], have been developed Rhodium-catalyzed decomposition of 3,3,3-tnfluoro-2-diazopropionates offers a simple preparative route to highly reactive carbene complexes, which have an enormous synthetic potential [24] [3-1-2] Cycloaddition reactions were observed on reaction with nitnles to give 5-alkoxy-4-tnfluoromethyloxazoles [750] (equation 41)... 

A simple preparative route to the previously unknown lH-3-pyrazolines via azomethine imines was developed. Olefins of the type R cH=CHR react with hexafiuoroacetone azine to give azomethine mines, which undergo a sequence of prototropic shifts to form 17/-3-pyrazolines [196, 202], On heating, the latter are transformed into 3-trifluoromethylpyrazoles [196, 206] and, on treatment with bases, into 1,2,5,6-tetrahydropynmidines [206] (equation 45)... 

Certain trifluoromethyl-substituted 1,2,4,5 tetrazines [260, 26i] and 1,2,4 triazines [i06] can be used as cyclic hetero-1,3-dienes and provide efficient preparative routes to partially fluorinated heterocycles (equations 55 and 56)... 

A mixture of nitromethane and hexafluorobenzene, when thermolyzed at 550 °C, yields pentafluorotoluene and pentafluorophenol as major products- The formation of nitrosyl and mtryl fluondes is probably a dnving force in this transfor-madon [705] A potential general preparative route to various perfluorovmyl amines is pyrolytic decarboxylation of potassium salts of perfluoro-2-(dialky-... 

Most of the following methods represent less general preparative routes to enamines. In some examples the enamines produced can be obtained via methods already described in preceding sections, while in other examples the enamines produced are uniquely synthesized. In an attempt to present these miscellaneous preparations in other than a random order, they have been divided into reactions involving alkylations (A) and others (B). 

The most effective preparative routes to hydrazine are still based on the process introduced by F. Raschig in 1907 this involves the reaction of ammonia with an alkaline solution of sodium hypochlorite in the presence of gelatin or glue. The overall reaction can be written as... 

Most preparative routes to HN3 and its derivatives involve the use of NaN3 since this is reasonably stable and commercially available. NaN3 can be made by adding powdered NaN03 to fused NaNH2 at 175° or by passing N2O into the same molten amide at 190° ... 

Consistent with this NNO can be made from NH4N03, and N NO from NH4 N03. Alternative preparative routes (Fig. 11.9) are the reduction of aqueous nitrous acid with either hydroxylamine or hydrogen azide ... 

Reaction with concentrated acids provides a preparative route to nitrosyl salts such as N0[HS04], N0[HSe04], N0[C104], and NO[Bp4], e.g. ... 

The most general preparative route to phosphides (Faraday s method) is to heat the metal with the appropriate amount of red P at high temperature in an inert atmosphere or an evacuated sealed tube ... 

Organic derivatives fall into 4 classes RP0(0H)2, HP0(0R)2, R P0(0R)2 and the phosphite esters R(OR)3 this latter class has no purely inorganic analogues, though it is, of course, closely related to PCI3. Some preparative routes have already been indicated. Reactions with alcohols depend on conditions ... 

MfiSiz I " (M = Nb,Ta). The original papers, should be consulted for preparative routes and structural details. A review is also available. 

Metal sulfides can be prepared in the laboratory or on an industrial scale by a number of reactions pure products are rarely obtained without considerable refinement and nonstoichiometric phases abound (p. 679). The more important preparative routes include ... 

Cations containing 4 S atoms include S4N3+, S4N4 + and S4N5+, as well as the unique radical cation S4N4+. The structures are in Fig. 15.40 and typical preparative routes... 

There is also a bewildering variety of structural motifs in polytelluride-ligand complexes as the brief selection in Fig. 16.10 indicates the original papers should be consulted for preparative routes and other details. Thus, dissolution of the alloy K2Hg2Te3 in ethylenedi-amine, followed by treatment with a methano-lic solution of [NBu JBr, yields the dark brown... 

A detailed discussion of individual halides is given under the chemistry of each particular element. This section deals with more general aspects of the halides as a class of compound and will consider, in turn, general preparative routes, structure and bonding. For reasons outlined on p. 805, fluorides tend to differ from the other halides either in their method of synthesis, their structure or their bond-type. For example, the fluoride ion is the smallest and least polarizable of all anions and fluorides frequently adopt 3D ionic structures typical of oxides. By contrast, chlorides, bromides and iodides are larger and more polarizable and frequently adopt mutually similar layer-lattices or chain structures (cf. sulfides). Numerous examples of this dichotomy can be found in other chapters and in several general references.Because of this it is convenient to discuss fluorides as a group first, and then the other halides. 

A similar set of preparative routes is available as were outlined above for the fluorides, though the range of applicability of each method and the products obtained sometimes vary from halogen to halogen. When hydrolysis is not a problem... 

During the past 20 y numerous other highly coloured halogen cations have been characterized by Raman spectroscopy. X-ray crystallography, and other techniques, as summarized in Table 17.18. Typical preparative routes involve direct oxidation of the halogen (a) in the absence of solvent, (b) in a solvent which is itself the oxidant (e.g. AsFs) or (c) in a non-reactive solvent (e.g. SO2). Some examples are listed below ... 

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