1-Bromobutane, reaction with potassium

The small effect on reaction rates of the addition of crown ethers to the lower alcohols was also observed in the reaction of potassium acetate with 1-bromobutane in ethanol (Hirao et al., 1978a,b). The displacement of fluorine in either o-nitro- or p-nitro-fluorobenzene by a methoxy group, by reaction with potassium methoxide in methanol was hardly influenced by the presence of dicyclohexyl-18-crown-6 (Del Cima et al., 1973). Mariani et al. (1978), too,... 

Crown ether-catalysed reaction of 1-bromobutane (0.05 or 0.1 M) with potassium phenoxide (0.02 M) in dioxan at 25°C ... 

Reaction of 1-Bromobutane with Potassium Acetate at Solvent Reflux... 

Write structural formulas for all the alkenes that can be formed in the reaction of 2-bromobutane with potassium ethoxide. 

Mixtures of Products in the E2 The E2 reaction requires abstraction of a proton on a carbon atom next to the carbon bearing the halogen. If there are two or more possibilities, mixtures of products may result. In most cases, Zaitsev s rule predicts which of the possible products will be the major product the most substituted alkene. For example, the E2 reaction of 2-bromobutane with potassium hydroxide gives a mixture of two products, but-l-ene (a monosubstituted alkene) and but-2-ene (a disubsti-tuted alkene). As predicted by Zaitsev s rule, the disubstituted isomer but-2-ene is the major product. 

Equation 8.28 shows only the anionic nucleophile explicitly, since the counterion does not appear to take part in the reaction. Nevertheless, the counterion affects the solubility of a nucleophilic salt, which therefore can influence the polarity of the solvent needed for the reaction. An alternative to the use of a more polar solvent to dissolve a salt for nucleophilic substitution is to use crown ether additives. Crown ethers are cyclic polyethers that can coordinate with cations and therefore increase their solubility in organic solvents. The nomenclature provides the total number of atoms and the number of oxygen atoms in the ring. Compoimd 51 is 12-crown-4, and 52 is 18-crown-6 (Figure 8.32). Coordination of a crown ether with a cation helps to dissolve the salt in a less polar solvent and leaves the anion relatively unsolvated. The activation energy for substitution therefore does not include a large term for desolvation of the nucleophilic anion, and the reactions are fast. For example, adding dicyclohexano-18-crown-6 (53) to a solution of 1-bromobutane in dioxane was found to increase its reactivity with potassium phenoxide by a factor of 1.5 x 10. Moreover, Liotta and Harris were able to use KF solubilized with 18-crown-6 (52) to carry out Sn2 reactions on 1-bromooctane in benzene. ... 

Outline a complete mechanistic sequence for the reaction of 2-bromobutane with potassium 2-methyl-2-propoxide in 2-methyl-2-propanol solvent to form the three alkenes generated in the reaction (1-butene, fra s-2-butene, and cis-2-butene). Include a clear drawing of the anti-periplanar transition state for the formation of each alkene. 

Substrate selectivity effects were investigated with polystyrene-supported polyethylene glycol) catalysts 51 (n = 3,61% RS) and 56 (Z = phenyl, n = 30, 8 % RS) under solid/solid/liquid conditions 180). The difference in rates of reaction of 1-bromobutane and 1-bromooctane with solid potassium phenoxide was a factor of about 3 (51 was more active). Measurements of the distribution of both bromides between... 

Numerous examples of solid/solid/liquid phase transfer catalysis are now known to be useful synthetically but have not been investigated mechanistically. Poly(ethylene glycol) immobilized on alumina and silica gel is active for reaction of solid potassium acetate with 1-bromobutane 184). Some of the best synthetic results with polymer supports are shown in Table 15. Often use of other solid salts or other catalysts gave poorer yields. It would be valuable to know for the design of future syntheses how these reactions depend on the partial solubility of the inorganic salts in the organic solvents and on the presence of trace amounts of water. 

Figure IS. Percent of 1-butene formed in reactions of 0 1 M 2-bromobutane with 0 5 M potassium t-butoxide in t-butyl alcohol in the presence of added dimethyl sulfoxide at 50 0° (Bartsch etal., 1973a).

Only two examples will be mentioned here in more detail. The Sn2 alkylation reaction of ambident potassium 2-naphtholate (2-naphthol -I- KOH) with 1-bromobutane in [BMIM]+PF6 at room temperature proceeds at a similar rate as observed in dipolar aprotic solvents such as DMF or DMSO, to regioselectively afford 1-butyl 2-naphthyl ether in 98 cmol/mol isolated yield (0/C alkylation ratio > 99 1) [899]. In contrast to the reaction in dipolar aprotic solvents, which are difficult to remove from the product, the ether product can be simply extracted into an organic solvent such as toluene, leaving the ionic liquid behind. The by-product (potassium bromide) of the reaction can be extracted with water, and the ionic liquid can be used again. 

Replacement of an hydroxyl group in resorcinol, most probably through tautomerism and imine formation, has been effected by heating it in an autoclave with 1-aminobutane and a small amount of phosphoric acid at 200°C under pressure (13 bar) for 8 hours. Only the monobutylamino substitution product was obtained but by phase transfer catalysis on the reaction product, with a benzyttrimethylammonium salt, (formed in situ from a surfactant and potassium iodide), sodium hydroxide solution and 1-bromobutane for 20 hours at 60-80°C, 3-dibutylaminphenol was produced in 64% yield (ref. 106). 

It has been found [117] that polyethylene glycol (PEG) produces a strong catalytic effect during the reaction of butyl bromide with KI. The yield of the butyl iodide product increases linearly with an increase in the length of the PEG chains. A similar acceleration of the reaction between solid potassium phenolate and 1-bromobutane is observed in toluene in the presence of oligoethylene glycols [178]. The synthesis of 8 esters based on alcohols and phenols in two-phase system liquid-liquid catalyzed by PEG is discussed [178a]. 

The effects of the organic solvents on the reaction rate are given in Table 13.3.9. The rates of the reactions of the tetra-n-butylammonium and potassium salts of phenoxide with 1 -chlorobutane and 1 -bromobutane in pure solvents and solvent mixtures varying in dielectric constant from 2.2 to 39 were obtained by Uglestad et al. ... 

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