Hexan alkyl halides from

Organolithium compounds are sometimes prepared in hydrocarbon solvents such as pentane and hexane, but nonnally diethyl ether is used. It is especially important that the solvent be anhydrous. Even trace amounts of water or alcohols react with lithium to form insoluble lithium hydroxide or lithium alkoxides that coat the surface of the metal and prevent it from reacting with the alkyl halide. Furthennore, organolithium reagents are strong bases and react rapidly with even weak proton sources to fonn hydrocarbons. We shall discuss this property of organolithium reagents in Section 14.5. 

General Method for Forming Derivatives with Reagent III. To make the derivatives. 111 was dissolved in 5 mL dimethylformamide, and the alkyl halide was added to the salt solution. The mixture was allowed to stand at room temperature for 24 h, and the dimethylformamide was removed under reduced pressure. The residue was dissolved in water, and the derivative was extracted with 25 mL of chloroform. The derivative was then precipitated from the chloroform with ether-hexane. ... 

When isobutene is polymerised in an inert solvent such as w-hexane by a metal halide with water as co-catalyst, the same end-groups are formed [9, 10] However, with other solvents, especially alkyl halides, transfer reactions may also introduce end-groups derived from the solvent [11, 12], for example ... 

A solution of 1 equiv of (S)- or (/ )-2-methoxymetliyl-1-[(2,2-dimethyl-l,3-dioxan-5-ylidene)amino]pyrro-lidine in THF (4 mL/mmol) is cooled to — 78 °C. 1.1 Equiv of tert-butyllithium in hexane (1.7 M) are added dropwise and the mixture is stirred for 2 h at — 78 °C. The solution of the metalated hydrazone is cooled to — 100 CC, 1.2 equiv of the alkyl halide (neat or as a solution in anhyd THF) are added dropwise, and the mixture is stirred for 1 h at —100 °C and then warmed slowly to r.t. (about 15 h). Finally, diethyl ether (30 mL/mmol) is added and the mixture is washed with pH 7 buffer (3 mL/mmol) and two 3-mL portions of brine, dried over MgSO and evaporated under reduced pressure. The Crude product is heated to 50 C for a short time if necessary (about 15 min for isomerization from the Z- to the L-isotiler monitored by TLC) and purified by silica gel column chromatography (diethyl ether/ pentane, 1 1 -2 5 Rf - > RfZ-iso-mer) to give a colorless or pale yellow product. See Table 2 for physical data. 

Ketones of great structural variety may therefore be prepared by careful selection of the starting /7-keto ester (cf. Section 5.14.3, p. 736) and the alkyl halides. The standard procedure is illustrated for the preparation of hexan-2-one from ethyl acetoacetate (Expt 5.95), and it may be suitably adapted to the preparation of most alkyl (straight-chain and branched-chain) methyl ketones. 

The carbon-halogen bond is slightly polar. Overall, however, an alkyl halide is not much more polar than an alkane, so the physical properties of an alkyl halide are not very different from those of an alkane of similar molecular weight. For example, the boiling point of 1-chlorobutane (MW = 92.5 g/mol) is 78°C, whereas that of hexane (MW = 86 g/mol) is 69°C. In general, alkyl halides are insoluble in water. Because of the presence of the more massive halogen atom, the alkyl halide may be more dense than water. For example, when dichloromethane, a common laboratory solvent, and water are mixed, two layers are formed, with dichloromethane as the lower layer. 

Lithium aminoborohydrides are obtained by the reaction of -BuLi with amine-boranes [FF2, FH5, NT2]. They can be generated in situ as THF solutions or as solids when formed in diethylether or hexane (n-BuLi must then be used in sub-stoichiometric amounts). They are stable under dry air and are slowly decomposed by water [NT2] or methanol so that workup of the reactions mixtures can be carried out with 3M HCl. They reduce alkyl halides (Section 2.1), epoxides (Section 2.3), aldehydes, and ketones (Section 3.2.1) (in the latter case with an interesting stereoselectivity [HFl]), and esters to primary alcohols (Section 3.2.5). a,(3-Unsaturated aldehydes, ketones, and esters are reduced to allyl alcohols (Section 3.2.9) [FF2, FS2]. Depending on the bulkiness of the amines associated with the reagent and to the substrate, tertiary amides give amines or alcohols (Section 3.2.8) [FFl, FF2]. Amines are also formed from imines (Section 3.3.1) [FB1 ] and from azides (Section 5.2) [AFl]. However, carboxylic acids remain untouched. 

A number of light promoted reductions are of interest from the synthetic perspective. The irradiation with a xenon laser of a DMF solution of electrogenerated nickel(I) salen, water and a primary alkyl halide such as 1-bromo-hexane, followed by a brief exposure to air, results in the formation a product mixture containing a significant amount of aldehyde (Scheme 11). A more... 

Aikyl fluorides by exchange from alkyl halides or methanesulfonates. The resin used for the reaction is the F form of Amberlyst-A26 (Rohm and Haas), a macroreticular anion-exchange resin containing ammonium groups. When this material and primary alkyl halides or sulfonates are refluxed in a solvent (pentane, hexane, ether), alkyl fluorides are formed, usually in satisfactory yields. Alkenes accompany fluorides in the reaction of secondary substrates. This reaction has been conducted previously under phase-transfer catalysis (5, 322). ... 

A 1.6 M soln. of n-butyllithium in n-hexane added with acetone-Dry Ice cooling below -60° under Ng to a stirred suspension of 4-(2-thienyl)-l,2,3-thiadiazole (prepared from methyl 2-thienyl ketone) in anhydrous tetrahydrofuran, stirring continued 10 min. at - 60°, ethyl iodide added in one portion, and allowed to warm to 0° -> l-ethylthio-2-(2-thienyl)ethyne (Y 81%) refluxed 4hrs. with methanol and aq. 3 N H2SO4, the resulting ester mixture hydrolyzed with methanolic 3 N NaOH 2-thienylacetic acid (Y 88%). F. e., also reactions with dimethyl sulfate and acid halides instead of alkyl halides, s. R. Raap and R. G. Micetidi, Can. J. Chem. 46, 1057 (1968). 

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