Haloalkanes preparation

Physical Properties of Haloalkanes Preparation of Haloalkanes by Halogenation of Alkanes Mechanism of Halogenation of Alkanes Allylic Halogenation Radical Autoxidation Radical Addition of HBr to Alkenes... 

Although the first ionic liquid expressly categorized as being task-specific featured the incorporation of the function within the cation core, subsequent research has focused on the incorporation of functionality into a branch appended to the cation [11]. In this fashion, a number of task-specific ionic liquids built up from 1-methyl- and 1-butylimidazole have been prepared, produced by means of the reaction between these imidazoles and haloalkanes also incorporating a desired functional group (Scheme 2.3-1). Bazureau has used this approach to prepare imida-... 

Alkylation of the anion 2 with iodomethane or other haloalkanes provides alkyldicarbonyl(t/5-cyclopentadienyl)iron complexes such as 53,0 (see also Houben-Weyl, Vol. 13/9a, p 209). Migratory insertion of carbon monoxide occurs on treatment with phosphanes or phosphites9 -11 (see also Houben-Weyl, Vol. d3/9a, p257) to provide chiral iron-acyl complexes such as 6. This is the most commonly used preparation of racemic chiral iron-acyl complexes. 

Bromoethane (Ethyl bromide) [74-96-4] EtBr FPA H98, 1981 HCS 1980, 472 Preparative hazard See Bromine Ethanol, etc. See other HALOALKANES C2H5Br... 

Methyl trifluorovinyl ether, b.p. 10.5- 12.5°C, prepared from tetrafluoroethylene and sodium methoxide [1], has considerable explosive potential. On ignition, it decomposes more violently than acetylene and should be treated with extreme caution [2], Other trifluorovinyl ethers are similarly available from higher alkoxides [1], and although not tested for instability, should be handled carefully. Presence of fluoro-haloalkanes boiling lower than the ether stabilises the latter against spark-initiated decomposition in both fluid phases [3],... 

A previous method [1] of preparing 3,3-dimethylbutyne by dehydrochlorination of the title compound in a sodium hydroxide melt is difficult to control and hazardous on the large scale. Use of potassium ferf-butoxide as base in DMSO is a high-yielding, safe and convenient alternative method of preparation of the alkyne [2], See Dimethyl sulfoxide Metal alkoxides See other HALOALKANES... 

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32... 

In situ reaction of the resultant phosphine, converted to its conjugate base, with several types of electrophiles has been investigated for organophosphorus syntheses. While early reports of the use of white phosphorus in basic solution with haloalkanes did not in themselves provide procedures for the efficient preparation of organophosphorus compounds, they pointed the way for the development of more useful techniques. 

The haloalkane (10 mmol), TBA-Br (79 mg, 0.3 mmol) in PhH (50 ml) and freshly prepared l-alkylthioethaniminium halide (10 mmol), obtained by refluxing thioacetamide... 

As an alternative to the oxidation of sulphides and sulphoxides (see Chapter 10), sulphones can be prepared by the nucleophilic substitution reaction of the sulphinite anion on haloalkanes. In the absence of a phase-transfer catalyst, the reaction times are generally long and the yields are low, and undesirable O-alkylation of the sulphinite anion competes with S-alkylation. The stoichiometric reaction of the preformed tetra-n-butylammonium salt of 4-toluenesulphinic acid with haloalkanes produces 4-tolyl sulphones in high yield [1], but it has been demonstrated that equally good... 

Using a soliddiquid two-phase system of the sodium arenesulphinite in 1,2-dimethoxyethane, or in the complete absence of a solvent, permits the use of less reactive haloalkanes [3,4], This is a particularly good method for the preparation of sulphones where the sulphinic acid salts are readily available and, in addition to the synthesis of the tolyl sulphones listed in Table 4.28, it has been used to prepare phenyl sulphones [3]. Phenyl sulphones have also been prepared in good yield using a polymer supported catalyst [5] (Table 4.29). As the system is not poisoned by iodide ions, reactive iodoalkanes can be used and there is the additional advantages in the ease of isolation of the product and the re-use of the catalyst. 

A range of alkylating agents have been used for the preparation of 1 -alkylpyrroles (Table 5.30). However, in contrast with the corresponding reaction of the indoles, no alkylation of the ring carbon atoms occurs with saturated haloalkanes, but there is... 

Although aliphatic azides can be prepared under liquidrliquid phase-transfer catalytic conditions [3-5], they are best obtained directly by the reaction of a haloalkane with sodium azide in the absence of a solvent [e.g. 6, 7]. Iodides and bromides react more readily than chlorides cyclohexyl halides tend to produce cyclohexene as a by-product. Acetonitrile and dichloromethane are the most frequently used solvents, but it should be noted that prolonged contact (>2 weeks) of the azide ion with dichloromethane can produce highly explosive products [8, 9] dibromomethane produces the explosive bisazidomethane in 60% yield after 16 days [8]. 

Benzylic halides produce isonitriles (80-90%) with tetramethylammonium cyanoargentate, prepared from tetramethylammonium chloride and silver cyanide [20]. The reaction fails with simple haloalkanes. 

The polymer-supported hydridoiron tetracarbonyl (33 mmol) is prepared by the addition ofFe(CO)5(6.46g, 33 mmol) to KOH (5.6 g, 0.1 mol) in aqueous EtOH (1 1 v/v, 100 ml) under N2. The mixture is heated with stirring under reflux for 2 h and Amberlyst A-26 resin (24 g) is then added and the mixture is stirred for a further 15 min. The resin is collected, washed with degassed H20 (to neutrality), MeOH and Et20, dried at room temperature under a flow of N2, and used immediately. The haloalkane (11 mmol) in THF (50 ml) is added to the resin and the mixture is stirred under reflux for ca. 4 h. When GLC analysis shows the reaction to be complete, the resin is removed by filtration, and the filtrate evaporated under reduced pressure to give the aliphatic aldehyde. 

During the hydrogenolysis of primary haloalkanes, diborane is produced and it provides a viable route for its preparation in non-ethereal solvents (see Section 11.5) [5]. 

The polymer supported HFe(CO)4 ion (33 mmol), prepared according to procedure 8.4.3, is stirred with the haloalkane (ll mmol) in THF (50 ml) for 4 h at room temperature. The resin is separated by filtration and the solvent is evaporated under reduced pressure to yield the alkane. 

Optically pure alcohols are converted via their mesylates into the corresponding chiral haloalkanes with the opposite configuration (>70% with an optical purity 90%) by a liquiddiquid phase-transfer catalysed SN2 reaction (2.1.5) with the appropriate potassium halide [7]. The preparation of chiral fluorides normally requires more vigorous conditions (160°C, 14 h in an autoclave). By-products of the reaction are the alcohol and alkene. 

Ethers can be prepared by refluxing a haloalkane with an alkoxide (see p. 56). For example, ethoxyethane is made by heating chloroethane with a solution of potassium ethoxide in ethanol. 

Ruthenium vinylidene species can be transformed into small carbocyclic rings via carbocyclization reactions. Ruthenium vinylidene complex 2, generated from the electrophilic reaction of alkyne complex 1 with haloalkanes, was deprotonated with "BU4NOH to give the unprecedented neutral cyclopropenyl complex 3 (Scheme 6.2) [5]. Gimeno and Bassetti prepared ruthenium vinylidene species 4a and 4b bearing a pendent vinyl group when these complexes were heated in chloroform for a brief period, cyclobutylidene products 5a and Sb formed via a [2 + 2] cycloaddition between the vinylidene Ca=Cp bond and olefin (Scheme 6.3) [6]. 

S)-2-Amino-3-methylbutanol [(S)-valinol] derived oxazolidinones, i.e., (S)-3-acyl-4-iso-propyl-2-oxazolidinones 1, have been used extensively for the preparation of a-alkylated acids, aldehydes and alcohols. The enolates are formed by deprotonation with lithium diisopropyl-amide or sodium hexamethyldisilazanide at low temperature in tetrahydrofuran. Subsequent addition of a haloalkane gives alkylation, which occurs from the Si-face2. The diastereoselectivities are usually good (>90 10), and the products are usually purified by flash chromatography and/or recrystallization (see Table 10). Additional examples of alkylation of 1 have been published5 l0 12- 20 22-29 39.44.-47,49.57.70-78... 

Furthermore, the halofluorination method can also be modified to prepare vicinal difluorides by a one-pot two-step reaction. Halofluorination followed by nucleophilic halogen-fluorine exchange is carried out simply by adding silver(I) fluoride to a solution of the initially formed a-fluoro-/J-haloalkanes, effecting the exchange in situ202 203 (Table 12). 

The development of new methods, both physical and preparative, has stimulated a renewed interest in the photochemistry of small polyatomic halogen compounds. In this review our aim is to present a critical account of the results of recent studies in this field, with particular emphasis on haloalkanes and halocarbonyl compounds. The account is restricted to studies made in the gas phase. 

Open-chain (acyclic) dialkylhalonium ions of the type R2X+ (X = Cl, Br, I) were unknown until the 1960s, as were alkylarylhalonium ions (ArRX+). Realization of their possible role as intermediates in alkylation reactions of haloalkanes and -arenes has followed their preparation and study.333... 

Halonium ions are an important class of onium ions.43 The dialkylchloro, bromo, and iodohalonium ions can be prepared and even isolated as stable salts (i.e., 46), as shown by Olah et al. by reacting an excess of haloalkane with strong Lewis acid halides in solvents of low nucleophilic-ity (eq 14). In superacid solution, dialkylhalonium ions show enhanced alkylating reactivity.44 It is considered that this enhanced reactivity is due to further protolytic (or electrophilic) activation involving the non-bonded... 

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